uu.seUppsala universitets publikasjoner
Endre søk
Begrens søket
123 1 - 50 of 104
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Afifi, Hala
    et al.
    King’s College London, Institute of Pharmaceutical Science, U.K..
    Karlsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Heenan, Richard K
    ISIS-CCLRC, Rutherford Appleton Laboratory, U.K..
    Dreiss, Cécile A
    King’s College London, Institute of Pharmaceutical Science, U.K..
    Solubilization of Oils or Addition of Monoglycerides Drives the Formation of Wormlike Micelles with an Elliptical Cross-Section in Cholesterol-Based Surfactants: A Study by Rheology, SANS, and Cryo-TEM2011Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 12, s. 7480-7492Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the formation of wormlike micelles (WLM) in poly(oxyethylene) cholesteryl ether (ChEO(10)) aqueous solutions by the addition of lipophilic monoglycerides at room temperature (monolaurin (ML), monocaprin (MC), and monocaprylin (MCL)) bearing 12-, 10-, and 8-carbon alkyl chains, respectively. A combination of rheology, small-angle neutron scattering (SANS), and cryo-TEM was used to study their viscoelastic properties and structure. With the successive addition of cosurfactant, a significant increase in viscosity and a clear solidlike behavior is obtained, suggesting the formation of a viscoelastic network of wormlike micelles. Only for MCL is typical Maxwellian behavior obtained. The onset of micellar growth, as detected by the occurrence of solidlike behavior and a significant increase in viscosity, is obtained for 0.30 (1 wt %), 0.34 (1 wt %), and 0.60 (1.5 wt %) cosurfactant/ChEO(10) molar ratios with ML, MC, and MCL, respectively. With ML and MC, extremely long relaxation times (exceeding 20 s) compared to those of MCL are obtained, and zero-shear viscosity values are more than 1 order of magnitude higher than with MCL. These results show that cosurfactants with longer alkyl chain lengths (ML and MC) induce the formation of longer wormlike micelles and do so at lower concentrations. SANS measurements on dilute solutions confirm that the viscoelastic behavior correlates with an increase in contour length and reveals an elliptical cross-section with an axial ratio of around 2. Cryo-TEM images provide visual evidence of the wormlike micelles and confirm the elliptical shape of the cross-section. The addition of small amounts of aliphatic oils (ethyl butyrate, EB, and ethyl caprylate, EC) and cyclic oils (peppermint, PP, and tea tree, TT, oils) to ChEO(10) solutions induces wormlike micelle formation at a lower cosurfactant concentration or even in its absence (for PP, TT, and EC) because of their probable localization in the palisade layer. The viscosity peak and height of the plateau modulus occur at increasing monoglyceride concentration following the order PP ≈ TT > EC > EB > no oil.

  • 2.
    Agmo Hernández, Víctor
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Karlsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Intrinsic Heterogeneity in Liposome Suspensions Caused by the Dynamic Spontaneous Formation of Hydrophobic Active Sites in Lipid Membranes2011Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 8, s. 4873-4883Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The spontaneous, dynamic formation of hydrophobic active sites in lipid bilayer membranes is studied and characterized. It is shown that the rates of formation and consumption of these active sites control at least two important properties of liposomes: their affinity for hydrophobic surfaces and the rate by which they spontaneously release encapsulated molecules. The adhesion and spreading of liposomes onto hydrophobic polystyrene nanoparticles and the spontaneous leakage of an encapsulated fluorescent dye were monitored for different liposome compositions employing Cryo-TEM, DLS, and fluorescence measurements. It was observed that an apparently homogeneous, monodisperse liposome suspension behaves as if composed by two different populations: a fast leaking population that presents affinity for the hydrophobic substrate employed, and a slow leaking population that does not attach immediately to it. The results reported here suggest that the proportion of liposomes in each population changes over time until a dynamic equilibrium is reached. It is shown that this phenomenom can lead to irreproducibility in, for example, spontaneous leakage experiments, as extruded liposomes leak much faster just after preparation than 24 h afterward. Our findings account for discrepancies in several experimental results reported in the literature. To our knowledge, this is the first systematic study addressing the issue of an existing intrinsic heterogeneity of liposome suspensions.

  • 3.
    Agthe, Michael
    et al.
    Stockholm Univ, Arrhenius Lab, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden..
    Wetterskog, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Bergström, Lennart
    Stockholm Univ, Arrhenius Lab, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden..
    Following the Assembly of Iron Oxide Nanocubes by Video Microscopy and Quartz Crystal Microbalance with Dissipation Monitoring2017Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, nr 1, s. 303-310Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the growth of ordered arrays by evaporation-induced self-assembly of iron oxide nanocubes with edge lengths of 6.8 and 10.1 nm using video microscopy (VM) and quartz crystal microbalance with dissipation monitoring (QCM-D). Ex situ electron diffraction of the ordered arrays demonstrates that the crystal axes of the nanocubes are coaligned and confirms that the ordered arrays are mesocrystals. Time-resolved video microscopy shows that growth of the highly ordered arrays at slow solvent evaporation is controlled by particle diffusion and can be described by a simple growth model. The growth of each mesocrystal depends only on the number of nanoparticles within the accessible region irrespective of the relative time of formation. The mass of the dried mesocrystals estimated from the analysis of the bandwidth-shift-to-frequency-shift ratio correlates well with the total mass of the oleate-coated nanoparticles in the deposited dispersion drop.

  • 4. Alison, Lauriane
    et al.
    Demirörs, Ahmet F
    Tervoort, Elena
    Teleki, Alexandra
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci. Nutritional R&D Center Formulation and Application, DSM Nutritional Products Ltd., P.O. Box 2676, 4002 Basel, Switzerland.
    Vermant, Jan
    Studart, Andre R
    Emulsions Stabilized by Chitosan-Modified Silica Nanoparticles: pH Control of Structure-Property Relations2018Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, nr 21, s. 6147-6160Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In food-grade emulsions, particles with an appropriate surface modification can be used to replace surfactants and potentially enhance the stability of emulsions. During the life cycle of products based on such emulsions, they can be exposed to a broad range of pH conditions and hence it is crucial to understand how pH changes affect stability of emulsions stabilized by particles. Here, we report on a comprehensive study of the stability, microstructure, and macroscopic behavior of pH-controlled oil-in-water emulsions containing silica nanoparticles modified with chitosan, a food-grade polycation. We found that the modified colloidal particles used as stabilizers behave differently depending on the pH, resulting in unique emulsion structures at multiple length scales. Our findings are rationalized in terms of the different emulsion stabilization mechanisms involved, which are determined by the pH-dependent charges and interactions between the colloidal building blocks of the system. At pH 4, the silica particles are partially hydrophobized through chitosan modification, favoring their adsorption at the oil-water interface and the formation of Pickering emulsions. At pH 5.5, the particles become attractive and the emulsion is stabilized by a network of agglomerated particles formed between the droplets. Finally, chitosan aggregates form at pH 9 and these act as the emulsion stabilizers under alkaline conditions. These insights have important implications for the processing and use of particle-stabilized emulsions. On one hand, changes in pH can lead to undesired macroscopic phase separation or coalescence of oil droplets. On the other hand, the pH effect on emulsion behavior can be harnessed in industrial processing, either to tune their flow response by altering the pH between processing stages or to produce pH-responsive emulsions that enhance the functionality of the emulsified end products.

  • 5.
    Alison, Lauriane
    et al.
    Swiss Fed Inst Technol, Dept Mat, Complex Mat, CH-8093 Zurich, Switzerland..
    Ruhs, Patrick A.
    Swiss Fed Inst Technol, Dept Mat, Complex Mat, CH-8093 Zurich, Switzerland..
    Tervoort, Elena
    Swiss Fed Inst Technol, Dept Mat, Complex Mat, CH-8093 Zurich, Switzerland..
    Teleki, Alexandra
    DSM Nutr Prod Ltd, Nutr R&D Ctr Formulat & Applicat, POB 2676, CH-4002 Basel, Switzerland..
    Zanini, Michele
    Swiss Fed Inst Technol, Interfaces Soft Matter & Assembly, Dept Mat, Complex Mat, CH-8093 Zurich, Switzerland..
    Isa, Lucio
    Swiss Fed Inst Technol, Interfaces Soft Matter & Assembly, Dept Mat, Complex Mat, CH-8093 Zurich, Switzerland..
    Studart, Andre R.
    Swiss Fed Inst Technol, Dept Mat, Complex Mat, CH-8093 Zurich, Switzerland..
    Pickering and Network Stabilization of Biocompatible Emulsions Using Chitosan-Modified Silica Nanoparticles2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 50, s. 13446-13457Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Edible solid particles constitute an attractive alternative to surfactants as stabilizers of food-grade emulsions for products requiring a long-term shelf life. Here, we report on a new approach to stabilize edible emulsions using silica nanoparticles modified by noncovalently bound chitosan oligomers. Electrostatic modification with chitosan increases the hydrophobicity of the silica nanoparticles and favors their adsorption at the oil water interface. The interfacial adsorption of the chitosan-modified silica particles enables the preparation of oil-in-water emulsions with small droplet sizes of a few micrometers through high-pressure homogenization. This approach enables the stabilization of food-grade emulsions for more than 3 months. The emulsion structure and stability can be effectively tuned by controlling the extent of chitosan adsorption on the silica particles. Bulk and interfacial rheology are used to highlight the two stabilization mechanisms involved. Low chitosan concentration (1 wt % with respect to silica) leads to the formation of a viscoelastic film of particles adsorbed at the oil water interface, enabling Pickering stabilization of the emulsion. By contrast, a network of agglomerated particles formed around the droplets is the predominant stabilization mechanism of the emulsions at higher chitosan content (5 wt % with respect to silica). These two pathways against droplet coalescence and coarsening open up different possibilities to engineer the long-term stabilization of emulsions for food applications.

  • 6.
    Almgren, Mats
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi.
    Borné, Johanna
    Feitosa, Eloi
    Khan, Ali
    Lindman, Björn
    Dispersed lipid liquid crystalline phases stabilized by a hydrophobically modified cellulose2007Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, nr 5, s. 2768-2777Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aqueous dispersions of monoolein (MO) with a commercial hydrophobically modified ethyl hydroxyethyl cellulose ether (HMEHEC) have been investigated with respect to the morphologies of the liquid crystalline nanoparticles. Only very low proportions of HMEHEC are accepted in the cubic and lamellar phases of the monoolein−water system. Due to the broad variation of composition and size of the commercial polymer, no other single-phase regions were found in the quasi-ternary system. Interactions of MO with different fractions of the HMEHEC sample induced the formation of lamellar and reversed hexagonal phases, identified from SAXD, polarization microscopy, and cryogenic TEM examinations. In excess water (more than 90 wt %) coarse dispersions are formed more or less spontaneously, containing particles of cubic phase from a size visible by the naked eye to small particles observed by cryoTEM. At high polymer/MO ratios, vesicles were frequently observed, often oligo-lamellar with inter-lamellar connections. After homogenization of the coarse dispersions in a microfluidizer, the large particles disappeared, apparently replaced by smaller cubic particles, often with vesicular attachments on the surfaces, and by vesicles or vesicular particles with a disordered interior. At the largest polymer contents no proper cubic particles were found directly after homogenization but mainly single-walled defected vesicles with a peculiar edgy appearance. During storage for 2 weeks, the dispersed particles changed toward more well-shaped cubic particles, even in dispersions with the highest polymer contents. In some of the samples with low polymer/MO ratio, dispersed particles of the reversed hexagonal type were found. A few of the homogenized samples were freeze-dried and rehydrated. Particles of essentially the same types, but with a less well-developed cubic character, were found after this treatment.

  • 7.
    Almgren, Mats
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi.
    Garamus, Vasil M
    Nordstierna, Lars
    Luc-Blin, Jean
    Stébé, Marie-José
    Nonideal mixed micelles of fluorinated and hydrogenous surfactants in aqueous solution: NMR and SANS studies of anionic and nonionic systems.2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 8, s. 5355-5363Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Contrast variation SANS and (19)F chemical shifts were measured for three mixed equimolar micelle systems: sodium perfluorooctanoate (SPFO) and sodiumdecylsulfate (SDeS) in 200 mM NaCl, lithium perfluorononanate (LiPFN) and lithium dodecylsulfate (LiDS) in 200 mM LiCl, and a nonionic system C(8)F(17)C(2)H(4)(OC(2)H(4))(9) and C(12)H(25)(OC(2)H(4))(8) in water, all at 25 degrees C. The chemical shift measurements allow the calculation of the average fraction of nearest neighbors of each kind around the reporter group (the trifluoromethyl group). A preference for like neighbors were found in all systems, smallest in the SDeS/SPFO system and largest in the nonionic system, but in all cases substantially smaller than expected at critical conditions. From the SANS measurements the width of the micelle composition distribution was obtained. For the ionic systems similar values were obtained, showing a broadening compared to ideal mixtures, but not broad enough for demixing or clearly bimodal distributions. In the nonionic system the width was estimated as sigma = 0.18 and 0.22 using two different evaluation methods. These values suggest that the system is close to critical conditions. The lower value refers to a direct modeling of the system, assuming an ellipsoidal shape and a Gaussian composition distribution. The modeling showed the nonionic mixed micelles to be prolate ellipsoids with axial ratio 2.2 and an aggregation number larger than 100, whereas the two ionic systems fitted best to oblate shapes (axial ratios 0.8 and 0.65 for SDeS/SPFO and LiDS/LiPFN, respectively) and aggregation numbers of 60 for both.

  • 8.
    Andersson, Martin
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi I.
    Råsmark, Per Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Elvingson, Christer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi I.
    Hansson, Per
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Single microgel particle studies demonstrate the influence of hydrophobic interactions between charged micelles and oppositely charged polyions.2005Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, nr 9, s. 3773-3781Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The binding of two cationic surfactants, dodecyltrimethylammonium bromide (DoTAB) and N-(1,1,2,2-tetrahydroperfluorodecanyl)pyridinium bromide (HFDePB), to covalently cross-linked sodium poly(styrenesulfonate) (PSS) microgels has been investigated by means of micromanipulator-assisted time-resolved light microscopy on single gels. It is demonstrated that repeated measurements on the same microgel under conditions of controlled liquid flow give highly reproducible results. The two surfactants are found to behave very differently with respect to degree of swelling, surfactant distribution in the gels, both during shrinking and at equilibrium, and kinetics of volume changes induced by them. The main difference is attributed to the presence of a hydrophobic interaction between PSS and the DoTAB micelles, absent in the case of HFDePB. Kinetic shrinking curves are recorded and analyzed using a model for steady-state transport of surfactant between the solution and the gels. Aggregation numbers for DoTAB in PSS solutions obtained from fluorescence quenching measurements are presented. A strong dependence on the surfactant-to-polyion concentration ratio is observed. Relations between surfactant binding isotherms, phase diagrams for linear polyelectrolyte/surfactant/water systems, and the binding to gels are discussed.

  • 9.
    Atluri, Rambabu
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Garcia-Bennett, Alfonso.E
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Sakamoto, Yasuhiro
    Co-Structure Directing Agent Induced Phase Transformation of Mesoporous Materials2009Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, nr 5, s. 3189-3195Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The synthesis of cubic Pmn mesocaged solid templated by cetyltrimethyl ammonium bromide (C16TMABr) surfactant by direct cocondensation of (3-aminopropyl)triethoxysilanes (APES) under strong alkaline conditions is reported. The novel route gives direct incorporation of amino functional groups on the porous silica wall, and the structural formation has been followed by means of in situ SAXS studies performed at a synchrotron beam line. Data shows that a molar ratio of C16TMABr/APES = 0.6 favors the formation of 3D cubic mesocaged solid with Pmn symmetry which transforms to a cylindrical mesoporous phase with p6mm symmetry at higher molar ratios. Further structural evaluation has been performed by means electron crystallography (EC). Reconstructed 3D models based on EC show the presence of spherical cages (A-cages, 45 Å) and ellipsoidal cages (B-cages, 48 × 43 Å) whereby every cage in the unit cell is connected to 14 nearest cages with a window size of 18 Å. Finally, a mechanism is proposed, denoted S+NoI, in which penetration of the neutral aminopropyl moiety within the micellar corona is responsible for the formation of the Pmn phase, accounting for the formation of the hexagonal phase at higher molar ratios and higher temperatures. In comparison to other mesocaged materials with the same symmetry this structure possesses a more open porous network which will help assess its potential in a variety of applications discussed herein.

  • 10. Atluri, Rambabu
    et al.
    Iqbal, Muhammad Naeem
    Bacsik, Zoltan
    Hedin, Niklas
    Villaescusa, Luis Angel
    Garcia-Bennett, Alfonso E
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Self-assembly mechanism of folate-templated mesoporous silica.2013Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, nr 38, s. 12003-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method to form ordered mesoporous silica based on the use of folate supramolecular templates has been developed. Evidence based on in situ small-angle X-ray scattering (SAXS), electron microscopy, infrared spectroscopy, and in situ conductivity measurements are used to investigate the organic-inorganic interactions and synthesis mechanism. The behavior of folate molecules in solution differs distinctively from that of surfactants commonly used for the preparation of ordered mesoporous silica phases, notably with the absence of a critical micellar concentration. In situ SAXS studies reveal fluctuations in X-ray scattering intensities consistent with the condensation of the silica precursor surrounding the folate template and the growth of the silica mesostructure in the initial stages. High-angle X-ray diffraction shows that the folate template is well-ordered within the pores even after a few minutes of synthesis. Direct structural data for the self-assembly of folates into chiral tetramers within the pores of mesoporous silica provide evidence for the in register stacking of folate tetramers, resulting in a chiral surface of rotated tetramers, with a rotation angle of 30°. Additionally, the self-assembled folates within pores were capable of adsorbing a considerable amount of CO2 gas through the cavity space of the tetramers. The study demonstrates the validity of using a naturally occurring template to produce relevant and functional mesoporous materials.

  • 11.
    Bacsik, Zoltan
    et al.
    Department of Materials and Environmental Chemistry , Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University.
    Ahlsten, Nanna
    Department of Organic Chemistry, Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University.
    Ziadi, Asraa
    Department of Organic Chemistry, Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University.
    Zhao, Guoying
    Department of Materials and Environmental Chemistry , Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University.
    Garcia-Bennett, Alfonso E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Martin-Matute, Belen
    Department of Organic Chemistry, Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University.
    Hedin, Niklas
    Department of Materials and Environmental Chemistry , Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University.
    Mechanisms and Kinetics for Sorption of CO(2) on Bicontinuous Mesoporous Silica Modified with n-Propylamine2011Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 17, s. 11118-11128Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.

  • 12.
    Bacsik, Zoltán
    et al.
    Stockholm University.
    Atluri, Rambabu
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Garcia-Bennett, Alfonso E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Hedin, Niklas
    Stockholm University.
    Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 12, s. 10013-10024Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Adsorption-mediated CO2 separation can reduce the costs of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO2 sorption and high CO2-over-N2 selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO2 adsorption in such materials, we studied mesocaged (cubic, Pm3n symmetry) silica adsorbents with tethered propylamines using Fourier transform infrared (FTIR) spectroscopy and volumetric uptake experiments. The degree of heterogeneity in these coatings was varied by either co-synthesizing or post-synthetically introducing the propylamine modification. In situ FTIR spectroscopy revealed the presence of both physisorbed and chemisorbed CO2 in the materials. We present the first direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO2-over-N2 selectivity in amine-rich sorbents. Samples with homogenous coatings showed typical CO2 adsorption trends and large quantities of IR-observable physisorbed CO2. The uptake of CO2 in mesocaged materials with heterogeneous propylamine coatings was higher at high temperatures than at low temperatures. At higher temperatures and low pressures, the post-synthetically modified materials adsorbed more CO2 than did the extracted ones, even though the surface area after modification was clearly reduced and the coverage of primary amine groups was lower. The principal mode of CO2 uptake in post-synthetically modified mesoporous silica was chemisorption. The chemisorbed moieties were present mainly as carbamate–ammonium ion pairs, resulting from the quantitative transformation of primary amine groups during CO2 adsorption as established by NIR spectroscopy. The heterogeneity in the coatings promoted the formation of these ion pairs. The average propylamine–propylamine distance must be small to allow the formation of carbamate–propylammonium ion pairs.

  • 13. Bastiat, Guillaume
    et al.
    Oliger, Patrick
    Karlsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi.
    Lafleur, Michel
    Development of Non-Phospholipid Liposomes Containing a High Cholesterol Concentration2007Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, nr 14, s. 7695-7699Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a novel formulation of non-phospholipid liposomes formed from cholesterol and palmitic acid. Despite the fact that these two lipidic species do not form individually fluid bilayers, we show that once mixed together, fluid bilayers can be obtained and, moreover, these can be extruded using classical extrusion processes to form liposomes. The chem. anal. indicates that these liposomes contain 70 mol % cholesterol, a content that is considerably higher that the satn. limit generally reported for phospholipid bilayers. These cholesterol-rich liposomes, formed with mols. that have low toxicity in vivo, display an improved impermeability relative to that of traditional phospholipid liposomes. In addn., because of the presence of palmitic acid, the stability of the liposomes is pH-dependent, and it is possible to trigger the release of encapsulated materials by pH stimuli.

  • 14.
    Bejhed Stjernberg, Rebecca
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Tian, Bo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Eriksson, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Brucas, Rimantas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Oscarsson, Sven
    Stockholm Univ, Arrhenius Lab, Dept Organ Chem, SE-10691 Stockholm, Sweden..
    Strömberg, Mattias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Svedlindh, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Gunnarsson, Klas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Magnetophoretic Transport Line System for Rapid On-Chip Attomole Protein Detection2015Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, nr 37, s. 10296-10302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A lab-on-a-chip traveling wave magnetophoresis approach for sensitive and rapid protein detection is reported. In this method, a chip-based magnetic microarray comprising lines of micrometer-sized thin film magnetic elements was used to control the movement of magnetic beads (MBs). The MBs and the chip were functionalized, forming a sandwich-type assay. The MBs were transported across a detection area, and the presence of target molecules resulted in the immobilization of MBs within this area. Target quantification was accomplished by MB counting in the detection area using an optical microscope. In order to demonstrate the versatility of the microarray, biotinylated antiavidin was selected as the target protein. In this case, avidin-functionalized MBs and an avidin-functionalized detection area were used. With a total assay time of 1 to 1.5 h (depending on the labeling approach used), a limit of detection in the attomole range was achieved. Compared to on-chip surface plasmon resonance biodetection systems, our method has a larger dynamic range and is about a factor of 500 times more sensitive. Furthermore, our MB transportation system can operate in any chip-based biosensor platform, thereby significantly improving traditional biosensors.

  • 15.
    Bello, Gianluca
    et al.
    Institute of Pharmaceutical Science, King’s College London, London, United Kingdom.
    Eriksson, Jonny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Terry, Ann E.
    Rutherford Appleton Laboratory, Harwell, Oxford, United Kingdom.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Lawrence, M. Jayne
    Institute of Pharmaceutical Science, King’s College London, London, United Kingdom.
    Barlow, David J.
    Institute of Pharmaceutical Science, King’s College London, London, United Kingdom.
    Harvey, Richard D
    Institute of Pharmaceutical Science, King’s College London, London, United Kingdom.
    Characterization of the aggregates formed by various bacterial lipopolysaccharides in solution and upon interaction with antimicrobial peptides2015Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, nr 2, s. 741-751Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The biophysical analysis of the aggregates formed by different chemotypes of bacterial lipopolysaccharides (LPS) before and after challenge by two different anti-endotoxic antimicrobial peptides (LL37 and bovine lactoferricin), was performed in order to determine their effect on the morphology of LPS aggregates. Small-angle neutron scattering (SANS) and cryogenic transmission electron microscopy (cryoTEM) were used to examine the structures formed by both smooth and rough LPS chemotypes and the effect of the peptides, by visualization of the aggregates and analysis of the scattering data by means of both mathematical approximations and defined models. The data showed that the structure of LPS determines the morphology of the aggregates and inuences the binding activity of both peptides. The morphologies of the worm-like micellar aggregates formed by the smooth LPS were relatively unaltered by the presence of the peptides due to their pre-existing high degree of positive curvature being little affected by their association with either peptide. On the other hand the aggregates formed by the rough LPS chemotypes, showed marked morphological changes from lamellar structures to ordered micellar networks, induced by the increase in positive curvature engendered upon association with the peptides. The combined use of cryoTEM and SANS proved to be a very useful tool for studying the aggregation properties of LPS in solution at biologically relevant concentrations.

  • 16.
    Bergstrand, Nill
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Aggregate structure in dilute aqueous dispersions of phospholipids, fatty acids and lysophospholipids2001Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, nr 11, s. 3245-3253Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cryo-transmission electron microscopy (cryo-TEM) was employed to investigate the aggregate structure in dilute aqueous dispersions of egg-phosphatidylcholine (EPC), oleic acid (OA), and the lysophospholipid monooleoylphosphatidylcholine (MOPC). At physiological pH and salt concentration, a relatively monodisperse population of unilamellar liposomes was detected in mixtures containing equimolar concentrations of the three components. Threadlike micelles constituted the dominant aggregate structure in samples containing high concentrations of MOPC. Excess fatty acid forced, on the other hand, the system toward structures with net negative curvature. In the absence of phospholipid, cryo-TEM revealed bilayer fragments in coexistence with threadlike micelles in mixtures containing the same molar amount of MOPC and OA. External addition of MOPC to preformed EPC liposomes gave rise to a concentration dependent evolution of intermediate structures, including open liposomes and bilayer fragments. The structural rearrangements were found to be slow and permitted visualization of a number of interesting transition structures. In addition to the structural studies, static and time-resolved fluorescence measurements were employed to determine some fundamental parameters for MOPC micelles. The results indicate a critical micelle concentration of close to 5 μM and an aggregation number of approximately 142.

  • 17.
    Bergström, L. Magnus
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Bending elasticity of charged surfactant layers: the effect of mixing2006Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, nr 16, s. 6796-6813Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Expressions have been derived from which the spontaneous curvature (H-0), bending rigidity (k(c)), and saddle-splay constant ((k) over bar (c)) of mixed monolayers and bilayers may be calculated from molecular and solution properties as well as experimentally available quantities such as the macroscopic hydrophobic-hydrophilic interfacial tension. Three different cases of binary surfactant mixtures have been treated in detail: (i) mixtures of an ionic and a nonionic surfactant, (ii) mixtures of two oppositely charged surfactants, and (iii) mixtures of two ionic surfactants with identical headgroups but different tail volumes. It is demonstrated that k(c)H(0), k(c), and (k) over bar (c) for mixtures of surfactants with flexible tails may be subdivided into one contribution that is due to bending properties of an infinitely thin surface as calculated from the Poisson-Boltzmann mean field theory and one contribution appearing as a result of the surfactant film having a finite thickness with the surface of charge located somewhat outside the hydrophobic-hydrophilic interface. As a matter of fact, the picture becomes completely different as finite layer thickness effects are taken into account, and as a result, the spontaneous curvature is extensively lowered whereas the bending rigidity is raised. Furthermore, an additional contribution to k(c) is present for surfactant mixtures but is absent for k(c)H(0) and (k) over bar (c). This contribution appears as a consequence of the minimization of the free energy with respect to the composition of a surfactant layer that is open in the thermodynamic sense and must always be negative (i.e., k(c) is generally found to be brought down by the process of mixing two or more surfactants). The magnitude of the reduction of kc increases with increasing asymmetry between two surfactants with respect to headgroup charge number and tail volume. As a consequence, the bending rigidity assumes the lowest values for layers formed in mixtures of two oppositely charged surfactants, and k(c) is further reduced in anionic/cationic surfactant mixtures where the surfactant in excess has the smaller tail volume. Likewise, the reduction of kc is enhanced in mixtures of an ionic and a nonionic surfactant where the ionic surfactant has the smaller tail. The effective bilayer bending constant (k(bi)) is also found to be reduced by mixing, and as a result, k(bi) is seen to go through a minimum at some intermediate composition. The reduction of k(bi) is expected to be most pronounced in mixtures of two oppositely charged surfactants where the surfactant in excess has the smaller tail in agreement with experimental observations.

  • 18.
    Bergström, L. Magnus
    et al.
    Department of Chemistry, Surface, and Corrosion Science, School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
    Skoglund, Sara
    Department of Chemistry, Surface, and Corrosion Science, School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Eriksson, Jonny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Grillo, Isabelle
    Institut Laue Langevin, DS/LSS, 6 rue Jules Horowitz, BP156, 38042 Grenoble Cedex 9, France.
    Self-Assembly in Mixtures of an Anionic and a Cationic Surfactant: A Comparison between Small-Angle Neutron Scattering and Cryo-Transmission Electron Microscopy2013Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, nr 38, s. 11834-11848Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The self-assembly in SOS-rich mixtures of the anionic surfactant sodium octyl sulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been investigated with the complementary techniques small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). Both techniques confirm the simultaneous presence of open and closed bilayer structures in highly diluted samples as well as the existence of small globular and large elongated micelles at higher concentrations. However, the two techniques sometimes differ with respect to which type of aggregates is present in a particular sample. In particular, globular or wormlike micelles are sometimes observed with cryo-TEM in the vicinity of the micelle-to-bilayer transition, although only bilayers are present according to SANS and the samples appear bluish to the eye. A similar discrepancy has previously been reported but could not be satisfactorily rationalized. On the basis of our comparison between in situ (SANS) and ex situ (cryo-TEM) experimental techniques, we suggest that this discrepancy appears mainly as a result of the non-negligible amount of surfactant adsorbed at interfaces of the thin sample film created during the cryo-TEM specimen preparation. Moreover, from our detailed SANS data analysis, we are able to observe the unusually high amount of free surfactant monomers present in SOS-rich mixtures of SOS and CTAB, and the experimental results give excellent agreement with model calculations based on the Poisson?Boltzmann mean field theory. Our careful comparison between model calculations and experiments has enabled us to rationalize the dramatic microstructural transformations frequently observed upon simply diluting mixtures of an anionic and a cationic surfactant.

  • 19.
    Bergström, L. Magnus
    et al.
    School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, KTH Royal Institute of Technology, Sweden.
    Skoglund, Sara
    School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, KTH Royal Institute of Technology, Sweden.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Eriksson, Jonny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Grillo, Isabelle
    Institut Laue Langevin, DS/LSS, 6 rue Jules Horowitz, B.P. 156, 38042 Grenoble Cedex 9, France.
    Spontaneous Transformations between Surfactant Bilayers of Different Topologies Observed in Mixtures of Sodium Octyl Sulfate and Hexadecyltrimethylammonium Bromide2014Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, nr 14, s. 3928-3938Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of adding salt on the self-assembly in sodium octyl sulfate (SOS)-rich mixtures of the anionic surfactant SOS and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) have been investigated with the two complementary techniques, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy. We are able to conclude that addition of a substantial amount of inert salt, NaBr, mainly has three effects on the structural behaviors: (i) the micelles become much larger at the transition from micelles to bilayers, (ii) the fraction of bilayer disks increases at the expense of vesicles, and (iii) bilayer aggregates perforated with holes are formed in the most diluted samples. A novel form factor valid for perforated bilayer vesicles and disks is introduced for the first time and, as a result, we are able to directly observe the presence of perforated bilayers by means of fitting SANS data with an appropriate model. Moreover, we are able to conclude that the morphology of bilayer aggregates changes according to the following sequence of different bilayer topologies, vesicles ? disks ? perforated bilayers, as the electrolyte concentration is increased and surfactant mole fraction in the bilayer aggregates approaches equimolarity. We are able to rationalize this sequence of transitions as a result of a monotonous increase of the bilayer saddle-splay constant (k?cbi) with decreasing influence from electrostatics, in agreement with theoretical predictions as deduced from the Poisson?Boltzmann theory.

  • 20.
    Bodvik, Rasmus
    et al.
    KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, Sweden.
    Karlson, Lief
    Akzo Nobel Functional Chemicals AB, Sweden.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Eriksson, Jonny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Thormann, Esben
    KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, Sweden.
    Claesson, Per Martin
    FRIAS, School of Soft Matter Research, University of Freiburg, Germany AND KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry, Surface and Corrosion Science, Sweden.
    Aggregation of modified celluloses in aqueous solution: transition from methylcellulose to hydroxypropylmethylcellulose solution properties induced by a low molecular weight oxyethylene additive2012Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 38, s. 13562-13569Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Temperature effects on viscosity and aggregation behaviour of aqueous solutions of three different cellulose ethers: methylcellulose (MC), hydroxypropylmethylcellulose (HPMC) and ethyl(hydroxyethyl)cellulose (EHEC), were investigated using viscosity and dynamic light scattering measurements as well as Cryo-TEM. In all cases increasing temperature reduces the solvent quality of water, which induces aggregation. It was found that the aggregation rate followed the order EHEC > HPMC > MC, suggesting that cellulose ethers containing some bulky and partly hydrophilic substituents assemble into large aggregates more readly than methylcellulose. This finding is discussed in terms of the organization of the structures formed by the different cellulose ethers. The temperature-dependent association behavior of cellulose ethers was also investigated in a novel way by adding diethyleneglycolmonobutylether (BDG) to methylcellulose aqueous solutions. When the concentration of BDG was at and above 5 wt%, methylcellulose adopted HPMC-like solution behaviour. In particular, a transition temperature where the viscosity was decreasing, prior to increasing at higher temperatures, appeared and the aggregation rate increased. This observation is rationalized by the ability of the amphiphilic BDG to accumulate at non-polar interfaces, and thus also to associate with hydrophobic regions of methylcellulose. In effect BDG is suggested to act as a physisorbed hydrophilic and bulky substituent inducing similar constraints on aggregation as the chemically attached hydroxypropyl groups in HPMC and oligo(ethyleneoxide) chains in EHEC.

  • 21. Boge, Lucas
    et al.
    Bysell, Helena
    Ringstad, Lovisa
    Wennman, David
    Umerska, Anita
    Cassisa, Viviane
    Eriksson, Jonny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Joly-Guillou, Marie-Laure
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Andersson, Martin
    Lipid-Based Liquid Crystals As Carriers for Antimicrobial Peptides: Phase Behavior and Antimicrobial Effect2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 17, s. 4217-4228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The number of antibiotic-resistant bacteria is increasing worldwide, and the demand for novel antimicrobials is constantly growing. Antimicrobial peptides (AMPs) could be an important part of future treatment strategies of various bacterial infection diseases. However, AMPs have relatively low stability, because of proteolytic and chemical degradation. As a consequence, carrier systems protecting the AMPs are greatly needed, to achieve efficient treatments. In addition, the carrier system also must administrate the peptide in a controlled manner to match the therapeutic dose window. In this work, lyotropic liquid crystalline (LC) structures consisting of cubic glycerol monooleate/water and hexagonal glycerol monooleate/oleic acid/water have been examined as carriers for AMPs. These LC structures have the capability of solubilizing both hydrophilic and hydrophobic substances, as well as being biocompatible and biodegradable. Both bulk gels and discrete dispersed structures (i.e., cubosomes and hexosomes) have been studied. Three AMPs have been investigated with respect to phase stability of the LC structures and antimicrobial effect: AP114, DPK-060, and LL-37. Characterization of the LC structures was performed using small-angle X-ray scattering (SAXS), dynamic light scattering, zeta-potential, and cryogenic transmission electron microscopy (Cryo-TEM) and peptide loading efficacy by ultra performance liquid chromatography. The antimicrobial effect of the LCNPs was investigated in vitro using minimum inhibitory concentration (MIC) and time-kill assay. The most hydrophobic peptide (AP114) was shown to induce an increase in negative curvature of the cubic LC system. The most polar peptide (DPK-060) induced a decrease in negative curvature while LL-37 did not change the LC phase at all. The hexagonal LC phase was not affected by any of the AMPs. Moreover, cubosomes loaded with peptides AP114 and DPK-060 showed preserved antimicrobial activity, whereas particles loaded with peptide LL-37 displayed a loss in its broad-spectrum bactericidal properties. AMP-loaded hexosomes showed a reduction in antimicrobial activity.

  • 22.
    Bracic, Matej
    et al.
    Univ Maribor, Inst Engn & Design Mat, SLO-2000 Maribor, Slovenia..
    Hansson, Per
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Perez, Lourdes
    CSIC, Inst Quim Avanzada Cataluna, Dept Chem & Surfactant Technol, ES-08034 Barcelona, Spain..
    Zemljic, Lidija F.
    Univ Maribor, Inst Engn & Design Mat, SLO-2000 Maribor, Slovenia..
    Kogej, Ksenija
    Univ Ljubljana, Fac Chem & Chem Technol, Dept Chem & Biochem, Ljubljana 1000, Slovenia..
    Interaction of Sodium Hyaluronate with a Biocompatible Cationic Surfactant from Lysine: A Binding Study2015Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, nr 44, s. 12043-12053Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mixtures of natural and biodegradable surfactants and ionic polysaccharides have attracted considerable research interest in recent years because they prosper as antimicrobial materials for medical applications. In the present work, interactions between the lysine-derived biocompatible cationic surfactant N-epsilon-myristoyl-lysine methyl ester, abbreviated as MKM, and the sodium salt of hyaluronic acid (NaHA) are investigated in aqueous media by potentiometric titrations using the surfactant-sensitive electrode and pyrene-based fluorescence spectroscopy. The critical micelle concentration in pure surfactant solutions and the critical association concentration in the presence of NaHA are determined based on their dependence on the added electrolyte (NaCl) concentration. The equilibrium between the protonated (charged) and deprotonated (neutral) forms of MKM is proposed to explain the anomalous binding isotherms observed in the presence of the polyelectrolyte. The explanation is supported by theoretical model calculations of the mixed-micelle equilibrium and the competitive binding of the two MKM forms to the surface of the electrode membrane. It is suggested that the presence of even small amounts of the deprotonated form can strongly influence the measured electrode response. Such ionic-nonionic surfactant mixtures are a special case of mixed surfactant systems where the amount of the nonionic component cannot be varied independently as was the case for some of the earlier studies.

  • 23.
    Bysell, Helena
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Malmsten, Martin
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Interactions between Homopolypeptides and Lightly Cross-Linked Microgels2009Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, nr 1, s. 522-528Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The relative importance of electrostatic and nonelectrostatic interactions in peptide-microgel systems was evaluated by micromanipulator-assisted light microscopy, confocal microscopy, and circular dichroism. For this purpose, the interaction of various homopolypeptides with lightly cross-linked polyelectrolyte gel particles ( approximately 70 mum in diameter) was studied with focus on peptide-induced microgel deswelling and its relation to peptide distribution within the microgel particles. Negatively charged poly-l-glutamic acid (pGlu) and poly-l-aspartic acid (pAsp), as well as uncharged poly-l-proline (pPro) and poly-l-threonine (pThr), were found to not bind to negatively charged poly(acrylic acid) microgels under the conditions investigated, but were instead depleted from the microgel particles. Positively charged poly-l-arginine (pArg), poly-l-histidine (pHis), and poly-l-lysine (pLys), on the other hand, interacted strongly with the oppositely charged microgel particles and caused significant deswelling of these. In parallel, cationic acrylamidopropyltriethylammoniumchloride (APTAC) microgels bound negatively charged polypeptides to a much higher extent than positively charged and uncharged ones. These findings suggest that electrostatic interactions dominate peptide binding and resulting microgel deswelling in these systems. Nevertheless, although the amount of cationic peptide bound to the anionic microgel particles was similar for cationic pLys, pArg, and pHis, peptide-induced gel deswelling differed significantly, as did the change in peptide conformation after microgel binding and the peptide distribution within the microgels. These effects, as well as pH dependent binding and release of titrable pHis, are discussed in terms of the effects of the charge density of, and structural differences between, the cationic homopolypeptides on the interaction with the oppositely charged microgel particles.

  • 24.
    CHAKAROV, DV
    et al.
    Chalmers University of Technology.
    Österlund, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    KASEMO, B
    Chalmers University of Technology.
    WATER-ADSORPTION AND COADSORPTION WITH POTASSIUM ON GRAPHITE(0001)1995Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, nr 4, s. 1201-1214Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water and water coadsorbed with potassium on the basal plane of graphite were studied with thermal desorption spectroscopy (TDS) and high-resolution electron energy loss spectroscopy (HREELS) in the temperature range 85-900 K. Water alone adsorbs nondissociatively on the clean graphite surface at 85 K, forming hydrogen bonded aggregates. Its structure depends both on the coverage and on substrate temperature. With increasing coverage at 85 K(0.5-1.0 monolayer (ML)) the libration mode at similar to 86 meV shows a rapid upward shift, indicating a phase transition from a 2D to a 3D structure. The transition can also be induced by annealing the low coverage structure. Water coadsorption with potassium is nonreactive or reactive, depending on temperature and potassium coverage. The nonreactive coadsorption at T-s = 85 K occurs only below a critical potassium coverage of BK less than or equal to 0.3 ML. It is characterized by substantial symmetry changes of the adsorbed water molecules, compared to the pure water adsorption, and is attributed to formation of hydrated-ion species on the surface. The surface solvation number at the lowest K coverage is three to four H2O molecules per potassium atom. K and H2O react at submonolayer coverages at 120-160 K to form surface KOH, KH, KxOy, and volatile products. The surface species gradually transforms/decomposes at elevated temperatures (200-500 K) to first form potassium-oxygen complexes that then serve as precursors to graphite oxidation to CO2 at similar to 750 K.

  • 25. Cheung, Ocean
    et al.
    Bacsik, Z
    Krokidas, P
    Mace, A
    Hedin, N
    Laaksonen, A
    K+ exchanged zeolite ZK-4 as a highly selective sorbent for CO22014Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827Artikkel i tidsskrift (Fagfellevurdert)
  • 26. Cubitt, R.
    et al.
    Fragneto, G.
    Ghosh, R. E.
    Rennie, Adrian
    Department of Chemistry, King's College London.
    REFILL 2002: Advances in the study of interfaces with neutron reflection2003Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, nr 19, s. 7685-7687Artikkel i tidsskrift (Fagfellevurdert)
  • 27.
    da Silva, Marcelo A.
    et al.
    Institute of Pharmaceutical Science, King’s College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, United Kingdom.
    Weinzaepfel, Evelyne
    Institute of Pharmaceutical Science, King’s College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, United Kingdom.
    Afifi, Hala
    Institute of Pharmaceutical Science, King’s College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, United Kingdom.
    Eriksson, Jonny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Grillo, Isabelle
    Institut Laue-Langevin (ILL), DS/LSS, 6, rue Jules Horowitz, B.P. 156, 38042 Grenoble Cedex, France.
    Valero, Margarita
    Departamento de Química Física, Universidad de Salamanca, 37008 Salamanca, Spain.
    Dreiss, Cécile A.
    Institute of Pharmaceutical Science, King’s College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, United Kingdom.
    Tuning the Viscoelasticity of Nonionic Wormlike Micelles with beta-Cyclodextrin Derivatives: A Highly Discriminative Process2013Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, nr 25, s. 7697-7708Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the influence of five β-cyclodextrin (β-CD) derivatives, namely: randomly methylated β-cyclodextrin (MBCD), heptakis (2,6-di-O-methyl)-β-cyclodextrin (DIMEB), heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB), 2-hydroxyethyl-β-cyclodextrin (HEBCD) and 2-hydroxypropyl-β-cyclodextrin (HPBCD), on the self-assembly of mixtures of nonionic surfactants: polyoxyethylene cholesteryl ether (ChEO10) and monocaprylin (MCL). Mixtures of ChEO10/MCL in water form highly viscoelastic wormlike micelle solutions (WLM) over a range of concentrations; herein, the composition was fixed at 10 wt % ChEO10/3 wt % MCL. The addition of methylated β-CDs (MBCD, DIMEB, TRIMEB) induced a substantial disruption of the solid-like viscoelastic behavior, as shown from a loss of the Maxwell behavior, a large reduction in G′ and G″ in oscillatory frequency-sweep measurements, and a drop of the viscosity. The disruption increased with the degree of substitution, following: MBCD < DIMEB < TRIMEB. Cryo-TEM images confirmed a loss of the WLM networks, revealing short rods and disc-like aggregates, which were corroborated by small-angle neutron scattering (SANS) measurements. Critical aggregation concentrations (CAC), measured by fluorescence spectroscopy, increased in the presence of DIMEB for both ChEO10 and MCL, suggesting the existence of interactions between methylated β-CDs and both surfactants involved in WLM formation. Instead, hydroxyl-β-CDs had a very different effect on the WLM. HPBCD only slightly reduced the solid-like behavior, without suppressing it. Quite remarkably, the addition of HEBCD reinforced the solid-like characteristics and increased the viscosity 10-fold. Cryo-TEM images confirmed the subsistence of WLM in ChEO10/MCL/HEBCD solutions, while SANS data revealed a slight elongation and thickening of the worms, and an increase of associated water molecules. CAC data showed that HPBCD had little effect on either surfactant, while HEBCD strongly affected the CAC of MCL and only slightly affected the ChEO10. For both DIMEB and HEBCD, time-resolved SANS measurements showed that morphology changes underlying these macroscopic changes occur in less than 100 ms.

  • 28.
    Dunér, Gunnar
    et al.
    Department of Chemistry, KTH.
    Anderson, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Myrskog, Annica
    IFM, Linköping University.
    Hedlund, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Aastrup, Teodor
    Attana AB.
    Ramström, Olof
    Department of Chemistry, KTH.
    Surface-Confined Photopolymerization of pH-Responsive Acrylamide/Acrylate Brushes on Polymer Thin Films2008Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, nr 14, s. 7559-7564Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dynamic acrylamide/acrylate polymeric brushes were synthesized at gold-plated quartz crystal surfaces. The crystals were initially coated with polystyrene-type thin films, derivatized with photolabile iniferter groups, and subsequently subjected to photoinitiated polymerization in acrylamide/acrylate monomer feeds. This surface-confined polymerizationmethod enabled direct photocontrol over the polymerization, as followed by increased frequency responses of the crystal oscillations in a quartz crystal microbalance (QCM). The produced polymer layers were also found to be highlysensitive to external acid/base stimuli. Large oscillation frequency shifts were detected when the brushes were exposedto buffer solutions of different pH. The dynamic behavior of the resulting polymeric brushes was evaluated, and theextent of expansion and contraction of the films was monitored by the QCM setup in situ in real time. The resultingresponses were rapid, and the effects were fully reversible. Low pH resulted in full contractions of the films, whereashigher pH yielded maximal expansion in order to minimize repulsion around the charged acrylate centers. The surfacesalso proved to be very robust because the responsiveness was reproducible over many cycles of repeated expansionand contraction. Using ellipsometry, copolymer layers were estimated to be ∼220 nm in a collapsed state and ∼340nm in the expanded state, effectively increasing the thickness of the film by 55%.

  • 29.
    Edwards, Katarina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Silvander, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Karlsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Aggregate Structure in Dilute Aqueous Dispersions of Oleic Acid/Sodium Oleate and Oleic Acid/Sodium Oleate/Egg Phosphatidylcholine1995Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, nr 7, s. 2429-2434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cryo-transmission electron microscopy was used to investigate the aggregate structure in dilute aqueous samples of oleic acid, as a function of pH. At pH 10.7, where the fatty acid is almost completely deprotonated, the micrographs show spherical or cylindrical micelles depending on the concentration. Upon a decrease of the pH to values just above 9, formation of unilamellar vesicles is induced. With decreasing pH the vesicles show an increasing tendency to aggregate. At pH between 8 and 7, large clusters of aggregated vesicles coexist with dispersed nonlamellar, presumably inverted hexagonal structures. Further decrease in pH results in a complete transition into nonlamellar liquid-crystalline structures and finally to the formation of oil droplets. Addition of high concentrations of oleic acid to small unilamellar lecithin vesicles induces, at pH 7.4 and lower, clustering and formation of particles with nonlamellar structure. At high pH, on the other hand, oleic acid acts like a conventional cationic surfactant. With increasing fatty acid: lipid molar ratio both significant vesicle growth and finally lipid solubilization into mixed micelles are observed.

  • 30.
    Eriksson, Kristofer L. E.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Chow, Winnie W. Y.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Puglia, Carla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Bäckvall, Jan-Erling
    Göthelid, Emmanuelle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Oscarsson, Sven
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Performance of a Biomimetic Oxidation Catalyst Immobilized on Silicon Wafers: Comparison with Its Gold Congener2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 21, s. 16349-16354Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the aim of extending the usefulness of an existing biomimetic catalytic system, cobalt porphyrin catalytic units with thiol linkers were heterogenized via chemical grafting to silicon wafers and utilized for the catalytic oxidation of hydroquinone to p-benzoquinone. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the morphology and composition of the heterogeneous catalyst. The results of the catalytic oxidation of hydroquinone obtained with porphyrins grafted on silicon were compared with those obtained earlier with the same catalyst in homogeneous phase and immobilized on gold. It was found that the catalysis could run over 400 h, without showing any sign of deactivation. The measured catalytic activity is at least 10 times higher than that measured under homogeneous conditions, but also 10 times lower than that observed with the catalytic unit immobilized on gold. The reasons of this discrepancy are discussed in term of substrate influence and overlayer organization. The silicon-immobilized catalyst has potential as an advanced functional material with applications in oxidative heterogeneous catalysis of organic reactions, as it combines long-term relatively high activity with low cost.

  • 31. Eriksson, Kristofer
    et al.
    Palmgren, Pål
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Yt- och gränsskiktsvetenskap.
    Nyholm, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Oorganisk kemi.
    Oscarsson, Sven
    Electrochemical Synthesis of Gold and Protein Gradients on Particle Surfaces2012Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 28, s. 10318-10323Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A straightforward, versatile approach to the production of protein gradients on planar and spherical particle surfaces is described. The method is based on the spatially controlled oxidation of thiolated surfaces by Au(III) ions generated via the electrochemical oxidation of a gold electrode in a phosphate-buffered saline solution (10 mM PBS, pH 7.2, 150 mM NaCl). Because the gold electrode is in direct contact with the thiolated surfaces, the released Au(III) ions, which are present as Au(III) chloride complexes, give rise to the formation of a surface gradient of Au(I)-thiolate complexes depending on the local redox potential given by the local Au(III) concentration. As is shown on the basis of the use of X-ray photoelectron spectroscopy and fluorescently labeled proteins, the Au(I)-thiolate complexes can subsequently be functionalized with thiolated proteins, yielding surface density protein gradients on micrometer-sized nonconducting polymer beads as well as linear Au(I)-thiolate gradients on planar silicon surfaces.

  • 32.
    Feiler, Adam A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Ytbioteknik, Centrum för ytbioteknik.
    Stiernstedt, Johanna
    Theander, Katarina
    Jenkins, Paul
    Rutland, Mark W.
    Effect of Capillary Condensation on Friction Force and Adhesion2007Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, nr 2, s. 517-522Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Friction force measurements have been conducted with a colloid probe on mica and silica (both hydrophilic and

    hydrophobized) after long (24 h) exposure to high-humidity air. Adhesion and friction measurements have also been

    performed on cellulose substrates. The long exposure to high humidity led to a large hysteresis between loading and

    unloading in the friction measurements with separation occurring at large negative applied loads. The large hysteresis

    in the friction-load relationship is attributed to a contact area hysteresis of the capillary condensate which built up

    during loading and did not evaporate during the unloading regime. The magnitude of the friction force varied dramatically

    between substrates and was lowest on the mica substrate and highest on the hydrophilic silica substrate, with the

    hydrophobized silica and cellulose being intermediate. The adhesion due to capillary forces on cellulose was small

    compared to that on the other substrates, due to the greater roughness of these surfaces.

  • 33.
    Filippov, Sergey K.
    et al.
    Institute of Macromelecular Chemistry, Academy of Sciences of the Czech Republic.
    Starovoytova, Larisa
    Institute of Macromelecular Chemistry, Academy of Sciences of the Czech Republic.
    Konák, Cestmír
    Institute of Macromelecular Chemistry, Academy of Sciences of the Czech Republic.
    Hrubý, Martin
    Institute of Macromelecular Chemistry, Academy of Sciences of the Czech Republic.
    Macková, Hana
    Karlsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Stepánek, Petr
    Institute of Macromelecular Chemistry, Academy of Sciences of the Czech Republic.
    pH sensitive polymer nanoparticles: effect of hydrophobicity on self-assembly2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 18, s. 14450-14457Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of hydrophobicity on formation, stability, and size of pH-responsive methacryloylated oligopeptide-based polymer nanoparticles has been studied by dynamic light scattering (DLS), transmission electron microscopy (Cryo-TEM), and NMR. Different polyanions/surfactant systems have been studied at constant polymer concentration and within a broad range of surfactant concentrations. The two newly synthesized pH-sensitive hydrophobic polyanions, poly(N(ω)-methacryloyl glycyl-L-leucine) and poly(N(ω)-methacryloyl glycyl-L-phenylalanyl-L-leucinyl-glycine), and three nonionic surfactants (Brij97, Brij98, and Brij700) have been investigated. The surfactants were different in the length of hydrophilic poly(ethylene oxide) (PEO) chain. In surfactant-free solution at basic pH, the polyanions form hydrophobic domains. In the presence of a surfactant, our results prove the complex formation at high pH between the nonionic surfactant and the polyelectrolyte; a pearl-necklace structure is formed. At low pH below critical pH (pH(tr)), reversible nanoscale structures occur in solutions for all systems. The detailed mechanism of the formation of pH-sensitive nanoparticles from polymer-surfactant complex with varying pH is established. Our results suggest that the polymer hydrophobicity is of primary importance in pretransitional behavior of the complex. Once preliminary nanoparticle nuclei are formed, the hydrophobicity of the polymer plays a minor role on further behavior of formed nanostructures. The subsequent transformation of nanoparticles is determined by the surfactant hydrophilicity, the length of hydrophilic tail that prevents further aggregation due to steric repulsions.

  • 34.
    Fornander, Louise H.
    et al.
    Chalmers, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden..
    Frykholm, Karolin
    Chalmers, Dept Biol & Biol Engn, S-41296 Gothenburg, Sweden..
    Fritzsche, Joachim
    Chalmers, Dept Appl Phys, S-41296 Gothenburg, Sweden..
    Araya, Joshua
    Northeastern Univ, Dept Chem & Chem Engn, Boston, MA 02115 USA..
    Nevin, Philp
    Northeastern Univ, Dept Chem & Chem Engn, Boston, MA 02115 USA..
    Werner, Erik
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Cakir, Ali
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Persson, Fredrik
    Uppsala universitet, Science for Life Laboratory, SciLifeLab.
    Garcin, Edwige B.
    Aix Marseille Univ, Canc Res Ctr Marseille, Inst Paoli Calmettes, CNRS,UMR7258,Inserm,U1068, F-13273 Marseille, France..
    Beuning, Penny J.
    Northeastern Univ, Dept Chem & Chem Engn, Boston, MA 02115 USA..
    Mehlig, Bernhard
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Modesti, Mauro
    Aix Marseille Univ, Canc Res Ctr Marseille, Inst Paoli Calmettes, CNRS,UMR7258,Inserm,U1068, F-13273 Marseille, France..
    Westerlund, Fredrik
    Chalmers, Dept Biol & Biol Engn, S-41296 Gothenburg, Sweden..
    Visualizing the Nonhomogeneous Structure of RAD51 Filaments Using Nanofluidic Channels2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 33, s. 8403-8412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    RAD51 is the key component of the homologous recombination pathway in eukaryotic cells and performs its task by forming filaments on DNA. In this study we investigate the physical properties of RAD51 filaments formed on DNA using nanofluidic channels and fluorescence microscopy. Contrary to the bacterial ortholog RecA, RAD51 forms inhomogeneous filaments on long DNA in vitro, consisting of several protein patches. We demonstrate that a permanent "kink" in the filament is formed where two patches meet if the stretch of naked DNA between the patches is short. The kinks are readily seen in the present microscopy approach but would be hard to identify using conventional single DNA molecule techniques where the DNA is more stretched. We also demonstrate that protein patches separated by longer stretches of bare DNA roll up on each other and this is visualized as transiently overlapping filaments. RAD51 filaments can be formed at several different conditions, varying the cation (Mg2+ or Ca2+), the DNA substrate (single-stranded or double-stranded), and the RAD51 concentration during filament nucleation, and we compare the properties of the different filaments formed. The results provide important information regarding the physical properties of RAD51 filaments but also demonstrate that nanofluidic channels are perfectly suited to study protein-DNA complexes.

  • 35.
    Forsberg, Pontus S. H.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Mikrosystemteknik.
    Priest, Craig
    Brinkmann, Martin
    Sedev, Rossen
    Ralston, John
    Contact Line Pinning on Microstructured Surfaces for Liquids in the Wenzel State2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 2, s. 860-865Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The wettability of surfaces microstructured with square pillars was studied, where the static advancing contact angle on the planar surface was 72 degrees. We observed elevated advancing angles (up to 140 degrees) on these structures for droplets in the Wenzel state. No air was trapped in the structured surf ices beneath the liquid, ruling out the well-known Lotus leaf effect. Instead, we show that the apparent hydrophobicity is related to contact line pinning at the pillar edges, giving a strong dependence of wetting hysteresis oil the fraction of the contact line pinned on pillars. Simulating the contact line pinning oil these Surfaces showed similar behavior to our measurements, revealing both strong pinning at the edges of the pillars as well as mechanistic details.

  • 36.
    Garcia-Bennett, Alfonso E.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Brohede, Ulrika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Hodgkins, Robert
    Hedin, Niklas
    Strømme, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    A mechanistic study of the formation of mesoporous structures from in situ AC conductivity measurements2007Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, nr 19, s. 9875-9881Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this work is to study the kinetics of self-assembly in the formation mechanism of anionic templated mesoporous solids (AMS-n) during die first few seconds of the synthesis as well as to demonstrate the use of alternating ion current (AIC) conductivity measurements to follow the self-assembly in complex hybrid systems. The formation of different AMS-n caged-type mesostructures through the delayed addition of the silica source is demonstrated and explained in terms of the interaction between the co-structure-directing agent (CSDA) and the oppositely charged surfactant headgroup regions. Our findings, supported by transmission electron microscopy, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, dynamic light scattering (DLS) measurements, and powder X-ray diffraction suggest that the interaction of the CSDA with the surfactant headgroup occurs within seconds after its addition to the synthesis gel leading to interaction between the polymerizing CSDAs and the oppositely charged micelle and to an increase in the micelle-CSDA aggregate size. Both DLS and AIC measurements agree that this process occurs within the first 1000 s after addition of the CSDA to the synthesis gel at room temperature. In addition to the mechanistic study it was found that the intermediate materials are comprised of a three-layer entity. Time-dependent 29Si MAS NMR studies reveal that an organo-silica layer forms around the micelles prior to a condensed outer inorganic shell of silica.

  • 37. Garcia-Perez, Angela
    et al.
    da Silva, Marcelo A.
    Eriksson, Jonny
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Analytisk kemi.
    Gonzalez-Gaitano, Gustavo
    Valero, Margarita
    Dreiss, Cecile A.
    Remarkable Viscoelasticity in Mixtures of Cyclodextrins and Nonionic Surfactants2014Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, nr 39, s. 11552-11562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the effect of native cyclodextrins (alpha, beta, and gamma) and selected derivatives in modulating the self-assembly of the nonionic surfactant polyoxyethylene cholesteryl ether (ChEO(10)) and its mixtures with triethylene glycol monododecyl ether (C12EO3), which form wormlike micelles. Cyclodextrins (CDs) generally induce micellar breakup through a host-guest interaction with surfactants; instead, we show that a constructive effect, leading to gel formation, is obtained with specific CDs and that the widely invoked host-guest interaction may not be the only key to the association. When added to wormlike micelles of ChEO(10) and C12EO3, native beta-CD, 2-hydroxyethyl-beta-CD (HEBCD), and a sulfated sodium salt of beta-CD (SULFBCD) induce a substantial increase of the viscoelasticity, while methylated CDs rupture the micelles, leading to a loss of the viscosity, and the other CDs studied (native alpha- and gamma- and hydroxypropylated CDs) show a weak interaction. Most remarkably, the addition of HEBCD or SULFBCD to pure ChEO(10) solutions (which are low-viscosity, Newtonian fluids of small, ellipsoidal micelles) induces the formation of transparent gels. The combination of small-angle neutron scattering, dynamic light scattering, and cryo-TEM reveals that both CDs drive the elongation of ChEO(10) aggregates into an entangled network of wormlike micelles. H-1 NMR and fluorescence spectroscopy demonstrate the formation of inclusion complexes between ChEO(10) and methylated CDs, consistent with the demicellization observed. Instead, HEBCD forms a weak complex with ChEO(10), while no complex is detected with SULFBCD. This shows that inclusion complex formation is not the determinant event leading to micellar growth. HEBCD:ChEO(10) complex, which coexists with the aggregated surfactant, could act as a cosurfactant with a different headgroup area. For SULFBCD, intermolecular interactions via the external surface of the CD may be more relevant.

  • 38.
    Gibson, Elizabeth A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Le Pleux, Loic
    Fortage, Jerome
    Pellegrin, Yann
    Blart, Errol
    Odobel, Fabrice
    Hagfeldt, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Boschloo, Gerrit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Fysikalisk kemi.
    Role of the Triiodide/Iodide Redox Couple in Dye Regeneration in p-Type Dye-Sensitized Solar Cells2012Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 15, s. 6485-6493Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of perylene dyes with different optical and electronic properties have been used as photosensitizers in NiO-based p-type dye-sensitized solar cells. A key target is to develop dyes that absorb light in the red to near-infrared region of the solar spectrum in order to match photoanodes optically in tandem devices; however, the photocurrent produced was found to decrease dramatically as the absorption maxima of the dye used was varied from 517 to 565 nm and varied strongly with the electrolyte solvent (acetonitrile, propionitrile, or propylene carbonate). To determine the limitations of the energy properties of the dye molecules and to provide guidelines for future sensitizer design, we have determined the redox potentials of the duodide radical intermediate involved in the charge-transfer reactions in different solvents using photomodulated voltammetry. E degrees(I-3(-)/I-2(center dot-)) (V vs Fe(Cp)(2)(+/0)) = -0.64 for propylene carbonate, -0.82 for acetonitrile, and -0.87 for propionitrile. Inefficient regeneration of the sensitizer appears to be the efficiency-limiting step in the device, and the values presented here will be used to design more efficient dyes, with more cathodic reduction potentials, for photocathodes in tandem dye-sensitized solar cells.

  • 39.
    Grime, John M. A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Khan, Malek O.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Bohinc, Klemen
    Interaction between Charged Surfaces Mediated by Rodlike Counterions: The Influence of Discrete Charge Distribution in the Solution and on the Surfaces2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 9, s. 6343-6349Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interaction between two charged surfaces, with discrete or uniform charge distributions, embedded in a solution of rodlike counterions has been studied. Monte Carlo simulations and density functional theory have been applied to study the concentration profiles of counterions and the force between the charged surfaces. We show that for low surface charge densities the repulsive force between like-charged surfaces is observed regardless of the rod length. Where high surface charge densities are present, attractive forces at surface separations related to the rod length are observed.

  • 40.
    Gustafsson, Simon
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Manukyan, Levon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Mihranyan, Albert
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Nanoteknologi och funktionella material.
    Protein-Nanocellulose Interactions in Paper Filters for Advanced Separation Applications2017Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, nr 19, s. 4729-4736Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Protein-based pharmaceutics are widely explored for healthcare applications, and 6 out of 10 best-selling drugs today are biologicals. The goal of this work was to evaluate the protein nanocellulose interactions in paper filter for advanced separation applications such as virus removal filtration and bioprocessing. The protein recovery was measured for bovine serum albumin (BSA), gamma-globulin, and lysozyme using biuret total protein reagent and polyacrylamide gel electrophoresis (PAGE), and the throughput was characterized in terms of flux values from fixed volume filtrations at various protein concentrations and under worst case experimental conditions. The affinity of cellulose to bind various proteins, such as BSA, lysozyme, gamma-globulin, and human IgG was quantified using a quartz crystal microbalance (QCMB) by developing a new method of fixing the cellulose fibers to the electrode surface without cellulose dissolution-precipitation. It was shown that the. mille-feuille filter exhibits high protein recovery, that is, similar to 99% for both BSA and lysozyme. However, gamma-globulin does not pass through the membrane due to its large size (i.e., >180 kDa). The PAGE data show no substantial change in the amount of dimers and trimers before and after filtration. QCMB analysis suggests a low affinity between the nanocellulose surface and proteins. The nanocellulose-based filter exhibits desirable inertness as a filtering material intended for protein purification.

  • 41.
    Gutfreund, Philipp
    et al.
    Inst Laue Langevin, F-38000 Grenoble, France..
    Maccarini, Marco
    Inst Laue Langevin, F-38000 Grenoble, France.;Univ Grenoble 1, TIMC IMAG, F-38706 Grenoble, France..
    Dennison, Andrew J. C.
    Inst Laue Langevin, F-38000 Grenoble, France.;Tech Univ Berlin, Dept Chem, D-10623 Berlin, Germany.;Univ Sheffield, Dept Phys & Astron, Sheffield S10 2TN, S Yorkshire, England..
    Wolff, Max
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    The Search for Nanobubbles by Using Specular and Off-Specular Neutron Reflectometry2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 35, s. 9091-9096Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We apply specular and off-specular neutron reflection at the hydrophobic silicon/water interface to check for evidence of nanoscopic air bubbles whose presence is claimed after an ad hoc procedure of solvent exchange. Nanobubbles and/or a depletion layer at the hydrophobic/water interface have long been discussed and generated a plethora of controversial scientific results. By combining neutron reflectometry (NR), off-specular reflectometry (OSS), and grazing incidence small angle neutron scattering (GISANS), we studied the interface between hydrophobized silicon and heavy water before and after saturation with nitrogen gas. Our specular reflectometry results can be interpreted by assuming a submolecular sized depletion layer and the off-specular measurements show no change with nitrogen super saturated water. This picture is consistent with the assumption that, following the solvent exchange, no additional nanobubbles are introduced at significant concentrations (if present at all). Furthermore, we discuss the results in terms of the maximum surface coverage of nanobubbles that could be present on the hydrophobic surface compatibly with the sensitivity limit of these techniques.

  • 42.
    Hammarström, Leif
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Velikian, Irena
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Karlsson, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Edwards, Katarina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Fysikalisk-kemiska institutionen.
    Cryo-TEM Evidence: Sonication of Dihexadecyl Phosphate Does Not Produce Closed Bilayers with Smooth Curvature1995Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, nr 2, s. 408-410Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Dihexadecyl phosphate (DHP) is commonly used for formation of model membranes. In this report cryo-transmission electron microscopy (cryo-TEM) pictures are presented. They clearly show that after cooling to room temperature, dispersions of DHP sonicated at 80 degrees C are dominated by open and folded bilayer fragments, rather than by vesicles with smooth curvature. Quantitative results of an earlier kinetic investigation of viologen reduction in DHP were reproduced using these dispersions.

  • 43.
    Hellrup, Joel
    et al.
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci. Nanexa AB, Virdings 32B, S-75450 Uppsala, Sweden.
    Holmboe, Michael
    Department of Chemistry, Umeå University.
    Nartowski, Karol P.
    Univ East Anglia, Sch Pharm, Norwich Res Pk, Norwich NR4 7TJ, Norfolk, England.; Wroclaw Med Univ, Fac Pharm, Dept Drug Form Technol, Ul Borowska 211, PL-50556 Wroclaw, Poland.
    Khimyak, Y.Z
    Univ East Anglia, Sch Pharm, Norwich Res Pk, Norwich NR4 7TJ, Norfolk, England.
    Mahlin, Denny
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Farmaceutiska fakulteten, Institutionen för farmaci.
    Structure and mobility of lactose in lactose/sodium montmorillonite nanocomposites2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 49, s. 13214-13225Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study aims at investigating the molecular level organization and molecular mobility in montmorillonite nanocomposites with the uncharged organic low-molecular-weight compound lactose commonly used in pharmaceutical drug delivery, food technology, and flavoring. Nanocomposites were prepared under slow and fast drying conditions, attained by drying at ambient conditions and by spray-drying, respectively. A detailed structural investigation was performed with modulated differential scanning calorimetry, powder X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, scanning electron microscopy, microcalorimetry, and molecular dynamics simulations. The lactose was intercalated in the sodium montmorillonite interlayer space regardless of the clay content, drying rate, or humidity exposure. Although, the spray-drying resulted in higher proportion of intercalated lactose compared with the drying under ambient conditions, nonintercalated lactose was present at 20 wt % lactose content and above. This indicates limitations in maximum loading capacity of nonionic organic substances into the montmorillonite interlayer space. Furthermore, a fraction of the intercalated lactose in the co-spray-dried nanocomposites diffused out from the clay interlayer space upon humidity exposure. Also, the lactose in the nanocomposites demonstrated higher molecular mobility than that of neat amorphous lactose. This study provides a foundation for understanding functional properties of lactose/Na-MMT nanocomposites, such as loading capacity and physical stability.

  • 44.
    Hellsing, Maja
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Rennie, Adrian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Hughes, Arwel V.
    Adsorption of Aerosol-OT to Sapphire: Lamellar Structures Studied with Neutrons2011Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 8, s. 4669-4678Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of sodium bis 2-ethylhexyl sulfosuccinate, NaAOT, to a sapphire surface from aqueous solution has been studied by neutron reflection at concentrations above the critical micelle concentration (cmc). Complementary measurements of the bulk structure were made with small-angle neutron scattering and grazing incidence small-angle neutron scattering. At a concentration of about 1% wt (10 X cmc), lamellar phase NaAOT was observed both at the surface and in the bulk. The structure seen at the interface for a solution of 2% wt NaAOT is a 35 +/- 2 angstrom thick bilayer adsorbed to the sapphire surface at maximum packing density, followed by an aligned stack of fluctuating bilayers of thickness 51 +/- 2 angstrom and with an area per molecule of 40 +/- 2 angstrom(2). Each bilayer is separated by a water: at 25 degrees C, this layer is 148 +/- 2 angstrom. A simple model for the reflectivity from fluctuating layers is presented, and for 2.0% wt NaAOT the fluctuations were found to have an amplitude of 25 +/- 5 angstrom. The temperature sensitivity of the structure at the surface was investigated in the range 15-30 degrees C. The effect of temperature was pronounced, with the solvent layer becoming thinner and the volume occupied by the NaAOT molecules in a bilayer increasing with temperature. The amplitude of the fluctuations, however, is approximately temperature independent in this range. The adsorption of NaAOT at the sapphire surface resembles that previously found at hydrophilic and hydrophobic silica surfaces. The coexisting bulk lamellar phase has a spacing of layers similar to that observed at the surface. These observations are an indication that the major driving force for adsorption is self-assembly, independent of the chemical nature of the interface.

  • 45.
    Hellsing, Maja S.
    et al.
    RISE Res Inst Sweden, Biosci & Mat, Box 5607, SE-11486 Stockholm, Sweden.
    Rennie, A. R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Rodal, Michael
    Biolin Sci AB, SE-42677 Vastra Frolunda, Sweden.
    Höök, Fredrik
    Chalmers Univ Technol, Dept Appl Phys, SE-41296 Gothenburg, Sweden.
    Charged Polystyrene Nanoparticles Near a SiO2/Water Interface2019Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, nr 1, s. 222-228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Quartz crystal microbalance with dissipation (QCM-D) monitoring is used to investigate the adsorption processes at liquid-solid interfaces and applied increasingly to characterize viscoelastic properties of complex liquids. Here, we contribute new insights into the latter field by using QCM-D to investigate the structure near the interface and the high-frequency viscoelastic properties of charge-stabilized polystyrene particles (radius 37 nm) dispersed in water. The study reveals changes with increasing ionic strength and particle concentration. Replacing water with a dispersion is usually expected to give rise to a decrease in frequency, f. Increases in both f and dissipation, D, were observed on exchanging pure water for particle dispersions at a low ionic strength. The QCM-D data are well-represented by a viscoelastic model, with viscosity increasing from 1.0 to 1.3 mPa s as the particle volume fraction changes from 0.005 to 0.07. This increase, higher than that predicted for noninteracting dispersions, can be explained by the charge repulsion between the particles giving rise to a higher effective volume fraction. It is concluded that the polystyrene particles did not adhere to the solid surface but rather were separated by a layer of pure dispersion medium. The QCM-D response was successfully represented using a viscoelastic Kelvin-Voigt model, from which it was concluded that the thickness of the dispersion medium layer was of the order of the particle-particle bulk separation, in the range of 50-250 nm, and observed to decrease with both particle concentration and addition of salt. Similar anomalous frequency and dissipation responses have been seen previously for systems containing weakly adherent colloidal particles and bacteria and understood in terms of coupled resonators. We demonstrate that surface attachment is not required for such phenomena to occur, but that a viscoelastic liquid separated from the oscillating surface by a thin Newtonian layer gives rise to similar responses.

  • 46.
    Hellsing, Maja S.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi.
    Rennie, Adrian R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialfysik.
    Hughes, Arwel V.
    Effect of Concentration and Addition of Ions on the Adsorption of Aerosol-OT to Sapphire2010Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, nr 18, s. 14567-14573Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aerosol-OT (sodium bis 2-ethylhexyl sulfosuccinate or NaAOT) adsorbs to hydrophilic sapphire solid surfaces The structure of the formed bilayer has been determined over the concentration range 0 2-7 4mM NaAOT It was found that the hydrocarbon tails pack at maximum packing limit at very low concentrations, and that the thickness of the bilayer was concentration-independent The adsorption was found to increase with concentration, with the surfactant molecules packing closer laterally The area per molecule was found to change from 138 +/- 25 to 51 +/- 4 angstrom(2) over the concentration range studied, with the thickness of the layer being constant at 33 2 A Addition of small amounts of salt was found to increase the surface excess, with the bilayer being thinner with a slightly larger area per molecule Addition of different salts of the same valency was found to have a very similiar effect, as had the addition of NaOH and HCl Hence, the effects of adding acid or base should be considered an effect of ionic strength rather than an effect of pH Adsorption of NaAOT to the sapphire surface that carries an opposite charge to the anionic surfactant is similar in many respects to the adsorption reported previously for hydrophilic and hydrophobic silica surfaces This suggests that the adsorption of NaAOT to a sui face is driven primarily by NaAOT self-assembly rather than effects of electrostatic at to the interface

  • 47. Hernandez, Victor Agmo
    et al.
    Scholz, Fritz
    Kinetics of the adhesion of DMPC liposomes on a mercury electrode. Effect of lamellarity, phase composition, size and curvature of liposomes, and presence of the pore forming peptide Mastoparan X2006Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, s. 10723-10731Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Liposomes suspended in aqueous electrolyte solutions can adhere at mercury electrodes. The adhesion is a complex process that starts with the docking and opening and leads to a spreading, finally resulting in the formation of islands of adsorbed lecithin molecules. The adhesion process can be followed by chronoamperometry, and a detailed analysis of the macroscopic and microscopic kinetics can be performed yielding rate constants and activation parameters. By using giant unilamellar liposomes and multilamellar liposomes, the effect of lamellarity and liposome size could be elucidated for liposomes in the liquid crystalline, gel, and superlattice phase states. Below the phase transition temperature, the time constant of opening of the liposomes (i.e., the irreversible binding of the lecithin molecules on the preliminary contact interface liposome vertical bar mercury and the therewith associated disintegration of the liposome membrane on that spot) is shown to be strongly size dependent. The activation energy, however, of that process is size independent with the exception of very small liposomes. That size dependence of time constants is a result of the size dependence of the initial contact area. The time constant and the activation energies of the spreading step exhibit a strong size dependence, which could be shown to be due to the size dependence of rate and activation energy of pore formation. Pore formation is necessary to release the solution included in the liposomes. This understanding was corroborated by addition of the pore inducing peptide Mastoparan X to the liposome suspension. The obtained results show that electrochemical studies of liposome adhesion on mercury electrodes can be used as a biomimetic tool to understand the effect of membrane properties on vesicle fusion.

  • 48. Hernandez, Victor Agmo
    et al.
    Scholz, Fritz
    Reply to the comment on kinetics of the adhesion of DMPC liposomes on a mercury electrode. Effect of lamellarity, phase composition, size and curvature of liposomes, and presence of the pore forming peptide mastoparan X2007Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23Artikkel i tidsskrift (Fagfellevurdert)
  • 49.
    Hinnemo, Malkolm
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Zhao, Jie
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Ahlberg, Patrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Hägglund, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Djurberg, Viktor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Scheicher, Ralph H.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Zhang, Shi-Li
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Zhang, Zhi-Bin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    On Monolayer Formation of Pyrenebutyric Acid on Graphene2017Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, nr 15, s. 3588-3593Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As a two-dimensional material with high charge carrier mobility, graphene may offer ultrahigh sensitivity in biosensing. To realize this, the first step is to functionalize the graphene. This is commonly done by using 1-pyrenebutyric acid (PBA) as a linker for biornolecules. However, the adsorption of PBA on graphene remains poorly understood despite reports of successful biosensors functionalized via this route. Here, the PBA adsorption on graphene is characterized through a combination of Raman spectroscopy, ab initio calculations, and spectroscopic ellipsometry. The PBA molecules are found to form a self-assembled monolayer on graphene, the formation of which is self-limiting and Langmuirian. Intriguingly, in concentrated solutions, the PBA molecules are found to stand up and stack horizontally with their edges contacting the graphene surface. This morphology could facilitate a surface densely populated with carboxylic functional groups. Spectroscopic analyses show that the monolayer saturates at 5.3 PBA molecules per nm(2) and measures similar to 0.7 nm in thickness. The morphology study of this PBA monolayer sheds light on the pi-pi stacking of small-molecule systems on graphene and provides an excellent base for optimizing functionalization procedures.

  • 50.
    Hinnemo, Malkolm
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Zhao, Jie
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Ahlberg, Patrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Hägglund, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Djurberg, Viktor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Scheicher, Ralph
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Zhang, Shi-Li
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Zhang, Zhi-Bin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    On Monolayer Formation of Pyrenebutyric Acid on GrapheneInngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827Artikkel i tidsskrift (Fagfellevurdert)
123 1 - 50 of 104
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf