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Publications (10 of 23) Show all publications
Svensson, P., Schwob, L., Grånäs, O., Unger, I., Björneholm, O., Timneanu, N., . . . Berholts, M. (2024). Heavy element incorporation in nitroimidazole radiosensitizers: molecular-level insights into fragmentation dynamics. Physical Chemistry, Chemical Physics - PCCP, 26(2), 770-779
Open this publication in new window or tab >>Heavy element incorporation in nitroimidazole radiosensitizers: molecular-level insights into fragmentation dynamics
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2024 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 26, no 2, p. 770-779Article in journal (Refereed) Published
Abstract [en]

The present study investigates the photofragmentation behavior of iodine-enhanced nitroimidazole-based radiosensitizer model compounds in their protonated form using near-edge X-ray absorption mass spectrometry and quantum mechanical calculations. These molecules possess dual functionality: improved photoabsorption capabilities and the ability to generate species that are relevant to cancer sensitization upon photofragmentation. Four samples were investigated by scanning the generated fragments in the energy regions around C 1s, N 1s, O 1s, and I 3d-edges with a particular focus on NO2+ production. The experimental summed ion yield spectra are explained using the theoretical near-edge X-ray absorption fine structure spectrum based on density functional theory. Born-Oppenheimer-based molecular dynamics simulations were performed to investigate the fragmentation processes.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2024
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-522697 (URN)10.1039/d3cp03800a (DOI)001090175100001 ()37888897 (PubMedID)
Funder
Swedish Research Council, 2019-03935Swedish Research Council, 2017-05128Swedish Research Council, 2018-00740Swedish Foundation for Strategic ResearchSwedish National Infrastructure for Computing (SNIC), 2022/1-36Swedish National Infrastructure for Computing (SNIC), 2022/22-597
Available from: 2024-02-08 Created: 2024-02-08 Last updated: 2024-02-08Bibliographically approved
Ponzi, A., Rosa, M., Kladnik, G., Unger, I., Ciavardini, A., Di Nardi, L., . . . Lanzilotto, V. (2023). Inequivalent Solvation Effects on the N 1s Levels of Self-Associated Melamine Molecules in Aqueous Solution. Journal of Physical Chemistry B, 127(13), 3016-3025
Open this publication in new window or tab >>Inequivalent Solvation Effects on the N 1s Levels of Self-Associated Melamine Molecules in Aqueous Solution
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2023 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 127, no 13, p. 3016-3025Article in journal (Refereed) Published
Abstract [en]

This work shows how the N 1s photoemission (PE) spectrum of self-associated melamine molecules in aqueous solution has been successfully rationalized using an integrated computational approach encompassing classical metadynamics simulations and quantum calculations based on density functional theory (DFT). The first approach allowed us to describe interacting melamine molecules in explicit waters and to identify dimeric configurations based on π–π and/or H-bonding interactions. Then, N 1s binding energies (BEs) and PE spectra were computed at the DFT level for all structures both in the gas phase and in an implicit solvent. While pure π-stacked dimers show gas-phase PE spectra almost identical to that of the monomer, those of the H-bonded dimers are sensibly affected by NH···NH or NH···NC interactions. Interestingly, the solvation suppresses all of the non-equivalences due to the H-bonds yielding similar PE spectra for all dimers, matching very well our measurements.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023
National Category
Theoretical Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-500651 (URN)10.1021/acs.jpcb.3c00327 (DOI)000959712000001 ()36972466 (PubMedID)
Funder
EU, Horizon 2020, 730872
Available from: 2023-04-21 Created: 2023-04-21 Last updated: 2023-04-21Bibliographically approved
Leroux, J., Kotobi, A., Hirsch, K., Lau, T., Ortiz-Mahecha, C., Maksimov, D., . . . Bari, S. (2023). Mapping the electronic transitions of protonation sites in peptides using soft X-ray action spectroscopy. Physical Chemistry, Chemical Physics - PCCP, 25(37), 25603-25618
Open this publication in new window or tab >>Mapping the electronic transitions of protonation sites in peptides using soft X-ray action spectroscopy
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2023 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, no 37, p. 25603-25618Article in journal (Refereed) Published
Abstract [en]

Near-edge X-ray absorption mass spectrometry (NEXAMS) around the nitrogen and oxygen K-edges was employed on gas-phase peptides to probe the electronic transitions related to their protonation sites, namely at basic side chains, the N-terminus and the amide oxygen. The experimental results are supported by replica exchange molecular dynamics and density-functional theory and restricted open-shell configuration with single calculations to attribute the transitions responsible for the experimentally observed resonances. We studied five tailor-made glycine-based pentapeptides, where we identified the signature of the protonation site of N-terminal proline, histidine, lysine and arginine, at 406 eV, corresponding to N 1s & RARR; & sigma;*(NHx+) (x = 2 or 3) transitions, depending on the peptides. We compared the spectra of pentaglycine and triglycine to evaluate the sensitivity of NEXAMS to protomers. Separate resonances have been identified to distinguish two protomers in triglycine, the protonation site at the N-terminus at 406 eV and the protonation site at the amide oxygen characterized by a transition at 403.1 eV.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2023
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-515037 (URN)10.1039/d3cp02524a (DOI)001067846000001 ()37721108 (PubMedID)
Available from: 2023-10-25 Created: 2023-10-25 Last updated: 2024-03-14Bibliographically approved
Gopakumar, G., Muchova, E., Unger, I., Malerz, S., Trinter, F., Öhrwall, G., . . . Björneholm, O. (2022). Probing Aqueous Ions with Non-local Auger Relaxation. Physical Chemistry, Chemical Physics - PCCP, 24(15), 8661-8671
Open this publication in new window or tab >>Probing Aqueous Ions with Non-local Auger Relaxation
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2022 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, no 15, p. 8661-8671Article in journal (Refereed) Published
Abstract [en]

The decay of core holes is often regarded as a local process, but in some systems, it involves the autoionization of neighbouring atoms or molecules. Here, we explore such non-local autoionization (Intermolecular Coulombic Decay, ICD) of surrounding molecules upon 1s ionization of aqueous-phase Na+, Mg2+ and Al3+ ions. The three ions are isoelectronic but differ in the strength of the ion-water interactions which is manifested in experimental Auger electron spectra by varying intensities. While for strongly interacting Mg2+ and Al3+ the non-local decay is observed, for weakly bound Na+ no signal was measured. Combined with theoretical simulations we provide a microscopic understanding of the non-local decay processes. We assigned the ICD to decay processes ending with two-hole states delocalized between the central ion and neighbouring water. The ICD process is also shown to be highly selective with respect to water molecular orbitals. The ICD lifetime was estimated to be around 40 fs for Mg and 20 fs for Al. Auger spectroscopy thus represents a novel tool for exploring molecules in the liquid phase, providing simultaneously structural and electronic information.   

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2022
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-451685 (URN)10.1039/D2CP00227B (DOI)000776170500001 ()35356960 (PubMedID)
Funder
EU, European Research Council, 883759Swedish Research Council, VR 2017-04162
Available from: 2021-08-29 Created: 2021-08-29 Last updated: 2022-09-26Bibliographically approved
Patanen, M., Unger, I., Saak, C.-M., Gopakumar, G., Lexelius, R., Björneholm, O., . . . Zieger, P. (2022). Surface composition of size-selected sea salt particles under the influence of organic acids studied in situ using synchrotron radiation X-ray photoelectron spectroscopy. Environmental Science: Atmospheres, 2(5), 1032-1040
Open this publication in new window or tab >>Surface composition of size-selected sea salt particles under the influence of organic acids studied in situ using synchrotron radiation X-ray photoelectron spectroscopy
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2022 (English)In: Environmental Science: Atmospheres, E-ISSN 2634-3606, Vol. 2, no 5, p. 1032-1040Article in journal (Refereed) Published
Abstract [en]

Sea spray aerosols play a key role in the climate system by scattering solar radiation and by serving as cloud condensation nuclei. Despite their importance, the impact of sea spray aerosols on global climate remains highly uncertain. One of the key knowledge gaps in our understanding of sea spray aerosol is the chemical composition of the particle surface, important for various atmospheric chemical processes, as a function of size and bulk composition. Here, we have applied X-ray photoelectron spectroscopy (XPS) to determine the surface composition of both pure inorganic sea salt aerosols and sea salt aerosols spiked with an amino acid (phenylalanine) and a straight chain fatty acid (octanoic acid). Importantly, the use of a differential mobility analyser allowed size-selection of 150, 250 and 350 nm monodisperse aerosol particles for comparison to polydisperse aerosol particles. We observed enrichment of magnesium at the particle surfaces relative to chloride in all aerosols tested, across all particle sizes. Interestingly, the magnitude of this enrichment was dependent on the type of organic present in the solution as well as the particle size. Our results suggest that the observed enrichment in magnesium is an inorganic effect which can be either enhanced or diminished by the addition of organic substances.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2022
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-494394 (URN)10.1039/d2ea00035k (DOI)000841141700001 ()
Funder
Swedish Research Council, 2016-05100Swedish Research Council, 2018-05045Swedish Research Council, 2017-04162
Available from: 2023-01-18 Created: 2023-01-18 Last updated: 2023-01-18Bibliographically approved
Gopakumar, G., Unger, I., Saak, C.-M., Öhrwall, G., Naves de Brito, A., Costa Rizuti da Rocha, T., . . . Björneholm, O. (2022). The Surface Composition of Amino Acid - Halide Salt Solutions is pH-Dependent. Environmental Science: Atmospheres (3)
Open this publication in new window or tab >>The Surface Composition of Amino Acid - Halide Salt Solutions is pH-Dependent
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2022 (English)In: Environmental Science: Atmospheres, no 3Article in journal (Refereed) Published
Abstract [en]

In atmospheric aerosol particles, the chemical surface composition governs both heterogeneous chemical reactions with gas-phase species and the ability to act as nuclei for cloud droplets. The pH in aerosol droplets is expected to affect these properties, but it is very challenging to measure the pH in individual droplets, precluding the investigation of its influence on the particle's surface composition. In this work, we use photoelectron spectroscopy to explore how the surface composition of aqueous solutions containing inorganic salt and amino acids changes as a function of pH. We observe a change by a factor of 4-5 of the relative distribution of inorganic ions at the surface of a liquid water jet, as a function of solution pH and type of amino acid in the solution. The driving forces for the surface enhancement or depletion are ion pairing and the formation of charged layers close to the aqueous surface. Our findings apply to any aqueous interface at which organic species with charged functional groups are present.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-451683 (URN)10.1039/D1EA00104C (DOI)000870720400010 ()
Available from: 2021-08-29 Created: 2021-08-29 Last updated: 2022-11-10Bibliographically approved
Gopakumar, G., Svensson, P., Grånäs, O., Brena, B., Schwob, L., Unger, I., . . . Lindblad, R. (2022). X-ray Induced Fragmentation of Protonated Cystine. Journal of Physical Chemistry A, 126(9), 1496-1503
Open this publication in new window or tab >>X-ray Induced Fragmentation of Protonated Cystine
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2022 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 126, no 9, p. 1496-1503Article in journal (Refereed) Published
Abstract [en]

We demonstrate site-specific X-ray induced fragmentation across the sulfur L-edge of protonated cystine, the dimer of the amino acid cysteine. Ion yield NEXAFS were performed in the gas phase using electrospray ionization (ESI) in combination with an ion trap. The interpretation of the sulfur Ledge NEXAFS spectrum is supported by Restricted Open-Shell Configuration Interaction (ROCIS) calculations. The fragmentation pathway of triply charged cystine ions was modeled by Molecular Dynamics (MD) simulations. We have deduced a possible pathway of fragmentation upon excitation and ionization of S 2p electrons. The disulfide bridge breaks for resonant excitation at lower photon energies but remains intact upon higher energy resonant excitation and upon ionization of S 2p. The larger fragments initially formed subsequently break into smaller fragments.

Place, publisher, year, edition, pages
American Chemical Society (ACS)American Chemical Society (ACS), 2022
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-470959 (URN)10.1021/acs.jpca.1c10158 (DOI)000768687200004 ()35213156 (PubMedID)
Funder
Swedish Research Council, 2018-00740Swedish Research Council, 637-2014-6929Swedish Research Council, VR 2017-04162EU, Horizon 2020, 847693
Available from: 2022-04-01 Created: 2022-04-01 Last updated: 2024-01-15Bibliographically approved
Kaiser, L., Fehre, K., Novikovskiy, N. M., Stindl, J., Tsitsonis, D., Gopakumar, G., . . . Demekhin, P. V. (2020). Angular emission distribution of O 1s photoelectrons of uniaxially oriented methanol. Journal of Physics B: Atomic, Molecular and Optical Physics, 53(19), Article ID 194002.
Open this publication in new window or tab >>Angular emission distribution of O 1s photoelectrons of uniaxially oriented methanol
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2020 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 53, no 19, article id 194002Article in journal (Refereed) Published
Abstract [en]

The angular distribution of O 1s photoelectrons emitted from uniaxially oriented methanol is studied experimentally and theoretically. We employed circularly polarized photons of an energy ofh nu= 550 eV for our investigations. We measured the three-dimensional photoelectron angular distributions of methanol, with the CH3-OH axis oriented in the polarization plane, by means of cold target recoil ion momentum spectroscopy. The experimental results are interpreted by single active electron calculations performed with the single center method. A comparative theoretical study of the respective molecular-frame angular distributions of O 1s photoelectrons of CO, performed for the same photoelectron kinetic energy and for a set of different internuclear distances, allows for disentangling the role of internuclear distance and the hydrogen atoms of methanol as compared to carbon monoxide.

Place, publisher, year, edition, pages
IOP Publishing, 2020
Keywords
photoionization, methanol, molecular-frame photoelectron angular distributions
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-421310 (URN)10.1088/1361-6455/aba3d3 (DOI)000565727400001 ()
Funder
Swedish Research Council, 2017-04162
Available from: 2020-10-12 Created: 2020-10-12 Last updated: 2020-10-12Bibliographically approved
Unger, I., Saak, C.-M., Salter, M., Zieger, P., Patanen, M. & Björneholm, O. (2020). Influence of Organic Acids on the Surface Composition of Sea Spray Aerosol. Journal of Physical Chemistry A, 124(2), 422-429
Open this publication in new window or tab >>Influence of Organic Acids on the Surface Composition of Sea Spray Aerosol
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2020 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 124, no 2, p. 422-429Article in journal (Refereed) Published
Abstract [en]

Recent studies on sea spray aerosol indicate an enrichment of Ca2+ in small particles, which are often thought to originate from the very surface of a water body when bubbles burst. One model to explain this observation is the formation of ion pairs between Ca2+(aq) and surface-active organic species. In this study, we have used X-ray photoelectron spectroscopy to probe aqueous salt solutions and artificial sea spray aerosol to study whether ion pairing in the liquid environment also affects the surface composition of dry aerosol. Carboxylic acids were added to the sample solutions to mimic some of the organic compounds present in natural seawater. Our results show that the formation of a core-shell structure governs the surface composition of the aerosol. The core-shell structure contrasts previous observations of the dry sea spray aerosol on substrates. As such, this may indicate that substrates can impact the morphology of the dried aerosol.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2020
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-406189 (URN)10.1021/acs.jpca.9b09710 (DOI)000508468500018 ()31833771 (PubMedID)
Funder
Swedish Research Council, 2016-05100Knut and Alice Wallenberg Foundation, 2016.0024
Available from: 2020-03-06 Created: 2020-03-06 Last updated: 2023-10-31Bibliographically approved
Saak, C.-M., Richter, C., Unger, I., Mucke, M., Nicolas, C., Hergenhahn, U., . . . Björneholm, O. (2020). Proton dynamics in molecular solvent clusters as an indicator for hydrogen bond network strength in confined geometries. Physical Chemistry, Chemical Physics - PCCP, 22(6), 3264-3272
Open this publication in new window or tab >>Proton dynamics in molecular solvent clusters as an indicator for hydrogen bond network strength in confined geometries
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2020 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 22, no 6, p. 3264-3272Article in journal (Refereed) Published
Abstract [en]

Hydrogen bonding leads to the formation of strong, extended intermolecular networks in molecular liquids such as water. However, it is less well-known how robust the network is to environments in which surface formation or confinement effects become prominent, such as in clusters or droplets. Such systems provide a useful way to probe the robustness of the network, since the degree of confinement can be tuned by altering the cluster size, changing both the surface-to-volume ratio and the radius of curvature. To explore the formation of hydrogen bond networks in confined geometries, here we present O 1s Auger spectra of small and large clusters of water, methanol, and dimethyl ether, as well as their deuterated equivalents. The Auger spectra of the clusters and the corresponding macroscopic liquids are compared and evaluated for an isotope effect, which is due to proton dynamics within the lifetime of the core hole (proton-transfer-mediated charge-separation, PTM-CS), and can be linked to the formation of a hydrogen bond network in the system. An isotope effect is observed in water and methanol but not for dimethyl ether, which cannot donate a hydrogen bond at its oxygen site. The isotope effect, and therefore the strength of the hydrogen bond network, is more pronounced in water than in methanol. Its value depends on the average size of the cluster, indicating that confinement effects change proton dynamics in the core ionised excited state.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2020
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-408101 (URN)10.1039/c9cp06661f (DOI)000518683800011 ()31998901 (PubMedID)
Funder
Swedish Research Council, VR 2018-00740German Research Foundation (DFG), Forschergruppe FOR1789Academy of FinlandThe Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
Available from: 2020-04-05 Created: 2020-04-05 Last updated: 2020-04-05Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1001-4134

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