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Mamedov, Fikret, Ph.D., Dr.Sci.ORCID iD iconorcid.org/0000-0002-6218-3039
Publications (10 of 90) Show all publications
Ahmadova, N. & Mamedov, F. (2018). Formation of tyrosine radicals in photosystem II under far-red illumination. Photosynthesis Research, 136(1), 93-106
Open this publication in new window or tab >>Formation of tyrosine radicals in photosystem II under far-red illumination
2018 (English)In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 136, no 1, p. 93-106Article in journal (Refereed) Published
Abstract [en]

Photosystem II (PS II) contains two redox-active tyrosine residues on the donor side at symmetrical positions to the primary donor, P680. TyrZ, part of the water-oxidizing complex, is a preferential fast electron donor while TyrD is a slow auxiliary donor to P680 +. We used PS II membranes from spinach which were depleted of the water oxidation complex (Mn-depleted PS II) to study electron donation from both tyrosines by time-resolved EPR spectroscopy under visible and far-red continuous light and laser flash illumination. Our results show that under both illumination regimes, oxidation of TyrD occurs via equilibrium with TyrZ at pH 4.7 and 6.3. At pH 8.5 direct TyrD oxidation by P680 + occurs in the majority of the PS II centers. Under continuous far-red light illumination these reactions were less effective but still possible. Different photochemical steps were considered to explain the far-red light-induced electron donation from tyrosines and localization of the primary electron hole (P680 +) on the ChlD1 in Mn-depleted PS II after the far-red light-induced charge separation at room temperature is suggested.

Keywords
Photosystem II, Tyrosine Z and D, electron transfer
National Category
Biochemistry and Molecular Biology
Research subject
Chemistry with specialization in Biophysics
Identifiers
urn:nbn:se:uu:diva-320914 (URN)10.1007/s11120-017-0442-3 (DOI)000427394300007 ()28924898 (PubMedID)
Funder
Swedish Research Council
Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2018-05-16Bibliographically approved
Norrbo, I., Curutchet, A., Kuusisto, A., Makela, J., Laukkanen, P., Paturi, P., . . . Lastusaari, M. (2018). Solar UV index and UV dose determination with photochromic hackmanites: from the assessment of the fundamental properties to the device. Materials Horizons, 5(3), 569-576
Open this publication in new window or tab >>Solar UV index and UV dose determination with photochromic hackmanites: from the assessment of the fundamental properties to the device
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2018 (English)In: Materials Horizons, ISSN 2051-6347, E-ISSN 2051-6355, Vol. 5, no 3, p. 569-576Article in journal (Refereed) Published
Abstract [en]

Extended exposure to sunlight or artificial UV sources is a major cause of serious skin and eye diseases such as cancer. There is thus a great need for convenient materials for the easy monitoring of UV doses. While organic photochromic molecules are tunable for responses under different wavelengths of UV radiation, they suffer from rather poor durability because the color changes involve drastic changes in molecular structure. Inorganic materials, on the other hand, are durable, but they have lacked tunability. Here, by combining computational and empirical data, we confirm the mechanism of coloration in the hackmanites, nature-based materials, and introduce a new technique called thermotenebrescence. With knowledge of the mechanism, we show that we can control and thus tune the energy of electronic states of synthetic hackmanites (Na,M)(8)Al6Si6O24(Cl,S)(2) so that their body color is sensitive to the solar UV index as well as UVA, UVB or UVC radiation levels. Finally, we demonstrate that it is possible to use images taken with an inexpensive cell phone to quantify the radiation dose or UV index. The hackmanite materials thus show great potential for use in portable healthcare both in everyday life and in laboratories.

National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-355466 (URN)10.1039/c8mh00308d (DOI)000431741300026 ()
Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-07-04Bibliographically approved
Pavlou, A., Jacques, J., Ahmadova, N., Mamedov, F. & Styring, S. (2018). The wavelength of the incident light determines the primary charge separation pathway in Photosystem II. Scientific Reports, 8, Article ID 2837.
Open this publication in new window or tab >>The wavelength of the incident light determines the primary charge separation pathway in Photosystem II
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2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 2837Article in journal (Refereed) Published
Abstract [en]

Charge separation is a key component of the reactions cascade of photosynthesis, by which solar energy is converted to chemical energy. From this photochemical reaction, two radicals of opposite charge are formed, a highly reducing anion and a highly oxidising cation. We have previously proposed that the cation after far-red light excitation is located on a component different from P-D1, which is the location of the primary electron hole after visible light excitation. Here, we attempt to provide further insight into the location of the primary charge separation upon far-red light excitation of PS II, using the EPR signal of the spin polarized P-3(680) as a probe. We demonstrate that, under far-red light illumination, the spin polarized P-3(680) is not formed, despite the primary charge separation still occurring at these conditions. We propose that this is because under far-red light excitation, the primary electron hole is localized on Chl(D1), rather than on P-D1. The fact that identical samples have demonstrated charge separation upon both far-red and visible light excitation supports our hypothesis that two pathways for primary charge separation exist in parallel in PS II reaction centres. These pathways are excited and activated dependent of the wavelength applied.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-348115 (URN)10.1038/s41598-018-21101-w (DOI)000424743500053 ()29434283 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy Agency
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-04-11Bibliographically approved
Yang, L., Huang, X., Mamedov, F., Zhang, P., Gogoll, A., Strömme, M. & Sjödin, M. (2017). Conducting redox polymers with non-activated charge transport properties. Physical Chemistry, Chemical Physics - PCCP, 19(36), 25052-25058
Open this publication in new window or tab >>Conducting redox polymers with non-activated charge transport properties
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2017 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 36, p. 25052-25058Article in journal (Refereed) Published
Abstract [en]

Non-activated charge transport has been demonstrated in terephthalate-functionalized conducting redox polymers. The transition from a temperature-activated conduction mechanism to a residual scattering mechanism was dependent on the doping level. The latter mechanism is associated with apparent negative activation barriers to charge transport and is generally found in polymer materials with a high degree of order. Crystallographic data, however, suggested a low degree of order in this polymer, indicating the existence of interconnected crystal domains in the predominantly amorphous polymer matrix through which the charge was transported. We have thus shown that the addition of bulky pendant groups to conducting polymers does not prevent efficient charge transport via the residual scattering mechanism with low barriers to charge transport.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-304625 (URN)10.1039/c7cp03939e (DOI)000411606200067 ()28879367 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Stiftelsen Olle Engkvist ByggmästareEU, Horizon 2020, 64431Swedish Energy Agency
Available from: 2016-10-06 Created: 2016-10-06 Last updated: 2018-06-04Bibliographically approved
Norrbo, I., Carvalho, J. M., Laukkanen, P., Mäkelä, J., Mamedov, F., Peurla, M., . . . Lastusaari, M. (2017). Lanthanide and Heavy Metal Free Long White Persistent Luminescence from Ti Doped Li-Hackmanite: A Versatile, Low-Cost Material. Advanced Functional Materials, 27(17), Article ID 1606547.
Open this publication in new window or tab >>Lanthanide and Heavy Metal Free Long White Persistent Luminescence from Ti Doped Li-Hackmanite: A Versatile, Low-Cost Material
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2017 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 27, no 17, article id 1606547Article in journal (Refereed) Published
Abstract [en]

Persistent luminescence (PeL) materials are used in everyday glow-in-the-dark applications and they show high potential for, e.g., medical imaging, night-vision surveillance, and enhancement of solar cells. However, the best performing materials contain rare earths and/or other heavy metal and expensive elements such as Ga and Ge, increasing the production costs. Here, (Li,Na)(8)Al6Si6O24(Cl,S)(2):Ti, a heavy-metal-and rare-earth-free low-cost material is presented. It can give white PeL that stays 7 h above the 0.3 mcd m(-2) limit and is observable for more than 100 h with a spectrometer. This is a record-long duration for white PeL and visible PeL without rare earths. The material has great potential to be applied in white light emitting devices (LEDs) combined with self-sustained night vision using only a single phosphor. The material also exhibits PeL in aqueous suspensions and is capable of showing easily detectable photoluminescence even in nanomolar concentrations, indicating potential for use as a diagnostic marker. Because it is excitable with sunlight, this material is expected to additionally be well-suited for outdoor applications.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-322524 (URN)10.1002/adfm.201606547 (DOI)000400449200007 ()
Funder
Swedish Energy AgencyKnut and Alice Wallenberg Foundation
Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-05-23Bibliographically approved
Huang, H., Karlsson, C., Mamedov, F., Strömme, M., Gogoll, A. & Sjödin, M. (2017). Polaron Disproportionation Charge Transport in a Conducting Redox Polymer. The Journal of Physical Chemistry C, 121(24), 13078-13083
Open this publication in new window or tab >>Polaron Disproportionation Charge Transport in a Conducting Redox Polymer
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2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 24, p. 13078-13083Article in journal (Refereed) Published
Abstract [en]

Herein we report a mechanistic study of the charge transport in poly-3-((2,5-hydroquinone)vinyl)-1H-pyrrole by conductance measurements at various temperatures performed in situ during doping of the polypyrrole backbone in contact with an aqueous electrolyte. Charge transport was found to occur by electron hopping with associated electron transfer activation energies in the range of 0.08-0.2 eV. In situ electron paramagnetic resonance experiments indicated polarons as the dominant charge carriers and the charge transport was found to follow a second-order dependence with respect to the number of accumulated charges. Based on the findings, we present a polaron comproportionation/disproportionation model for electron conduction in poly-3-((2,5-hydroquinone)vinyl)-1H-pyrrole, thus, providing a complement to existing models for charge propagation in conducting polymers.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
National Category
Physical Chemistry Engineering and Technology Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-329648 (URN)10.1021/acs.jpcc.7b03671 (DOI)000404201900013 ()
Funder
Swedish Foundation for Strategic Research Swedish Research CouncilStiftelsen Olle Engkvist ByggmästareSwedish Energy Agency
Available from: 2017-09-26 Created: 2017-09-26 Last updated: 2017-11-25
Daniel, Q., Huang, P., Fan, T., Wang, Y., Duan, L., Wang, L., . . . Sun, L. (2017). Rearranging from 6-to 7-coordination initiates the catalytic activity: An EPR study on a Ru-bda water oxidation catalyst. Coordination chemistry reviews, 346, 206-215
Open this publication in new window or tab >>Rearranging from 6-to 7-coordination initiates the catalytic activity: An EPR study on a Ru-bda water oxidation catalyst
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2017 (English)In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 346, p. 206-215Article, review/survey (Refereed) Published
Abstract [en]

The coordination of a substrate water molecule on a metal centered catalyst for water oxidation is a crucial step involving the reorganization of the ligand sphere. This process can occur by substituting a coordinated ligand with a water molecule or via a direct coordination of water onto an open site. In 2009, we reported an efficient ruthenium-based molecular catalyst, Ru-bda, for water oxidation. Despite the impressive improvement in catalytic activity of this type of catalyst over the past years, a lack of understanding of the water coordination still remains. Herein, we report our EPR and DFT studies on Ru-bda (triethylammonium 3-pyridine sulfonate)(2) (1) at its Ru-III oxidation state, which is the initial state in the catalytic cycle for the O-O bond formation. Our investigation suggests that at this III-state, there is already a rearrangement in the ligand sphere where the coordination of a water molecule at the 7th position (open site) takes place under acidic conditions (pH = 1.0) to form a rare 7-coordinated Ru-III species.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2017
Keywords
Water oxidation, EPR, Ruthenium, Coordination, DFT
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-332735 (URN)10.1016/j.ccr.2017.02.019 (DOI)000402873900014 ()
Funder
Swedish Energy AgencyKnut and Alice Wallenberg FoundationSwedish Research Council
Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2017-12-07Bibliographically approved
Miranda, H., Immerzeel, P., Gerber, L., Hörnaeus, K., Bergström, S. K., Pattanaik, B., . . . Lindblad, P. (2017). Sll1783, a monooxygenase associated with polysaccharide processing in the unicellular cyanobacterium Synechocystis PCC 6803. Physiologia Plantarum: An International Journal for Plant Biology, 161(2), 182-195
Open this publication in new window or tab >>Sll1783, a monooxygenase associated with polysaccharide processing in the unicellular cyanobacterium Synechocystis PCC 6803
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2017 (English)In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 161, no 2, p. 182-195Article in journal (Refereed) Published
Abstract [en]

Cyanobacteria play a pivotal role as the primary producer in many aquatic ecosystems. The knowledge on the interacting processes of cyanobacteria with its environment - abiotic and biotic factors - is still very limited. Many potential exocytoplasmic proteins in the model unicellular cyanobacterium Synechocystis PCC 6803 have unknown functions and their study is essential to improve our understanding of this photosynthetic organism and its potential for biotechnology use. Here we characterize a deletion mutant of Synechocystis PCC 6803, Δsll1783, a strain that showed a remarkably high light resistance which is related with its lower thylakoid membrane formation. Our results suggests Sll1783 to be involved in a mechanism of polysaccharide degradation and uptake and we hypothesize it might function as a sensor for cell density in cyanobacterial cultures.

National Category
Analytical Chemistry Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:uu:diva-337191 (URN)10.1111/ppl.12582 (DOI)000417402000001 ()28429526 (PubMedID)
Funder
Swedish Energy AgencyKnut and Alice Wallenberg FoundationScience for Life Laboratory - a national resource center for high-throughput molecular bioscienceÅke Wiberg FoundationMagnus Bergvall Foundation
Available from: 2017-12-21 Created: 2017-12-21 Last updated: 2018-03-07Bibliographically approved
Sjöholm, J., Ho*, F., Ahmadova, N., Brinkert, K., Hammarström, L., Mamedov*, F. & Styring, S. (2017). The protonation state around Tyr(D)/Tyr((D)) over dot in photosystem II is reflected in its biphasic oxidation kinetics. Biochimica et Biophysica Acta - Bioenergetics, 1858(2), 147-155
Open this publication in new window or tab >>The protonation state around Tyr(D)/Tyr((D)) over dot in photosystem II is reflected in its biphasic oxidation kinetics
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2017 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1858, no 2, p. 147-155Article in journal (Refereed) Published
Abstract [en]

The tyrosine residue D2-Tyr160 (Tyr(D)) in photosystem II (PSII) can be oxidized through charge equilibrium with the oxygen evolving complex in PSII. The kinetics of the electron transfer from Tyr(D) has been followed using time resolved EPR spectroscopy after triggering the oxidation of pre-reduced Tyr(D) by a short laser flash. After its oxidation Tyro is observed as a neutral radical (Tyr((D)) over dot) indicating that the oxidation is coupled to a deprotonation event. The redox state of Tyro was reported to be determined by the two water positions identified in the crystal structure of PSII [Saito et al. (2013) Proc. Natl. Acad. Sci. USA 110, 7690]. To assess the mechanism of the proton coupled electron transfer of Tyr(D) the oxidation kinetics has been followed in the presence of deuterated buffers, thereby resolving the kinetic isotope effect (KIE) of Tyro oxidation at different H/D concentrations. Two kinetic phases of Tyro oxidation - the fast phase (msec-sec time range) and the slow phase (tens of seconds time range) were resolved as was previously reported [Vass and Styring (1991) Biochemistry 30, 830]. In the presence of deuterated buffers the kinetics was significantly slower compared to normal buffers. Furthermore, although the kinetics were faster at both high pH and pD values the observed KIE was found to be similar (similar to 2.4) over the whole pL range investigated. We assign the fast and slow oxidation phases to two populations of PSII centers with different water positions, proximal and distal respectively, and discuss possible deprotonation events in the vicinity of Tyro.

Keywords
Photosystem II, Tyrosine D, Electron transfer, Proton transfer, Deuterium isotope effect
National Category
Biochemistry and Molecular Biology Biophysics
Identifiers
urn:nbn:se:uu:diva-316938 (URN)10.1016/j.bbabio.2016.11.002 (DOI)000392776400007 ()27823941 (PubMedID)
Funder
Swedish Research Council, 621-2013-5937Swedish Energy Agency, 11674-5Knut and Alice Wallenberg Foundation, KAW 2011.0067
Available from: 2017-03-09 Created: 2017-03-09 Last updated: 2017-04-30
Ahmadova, N., Ho, F., Styring, S. & Mamedov, F. (2017). Tyrosine D oxidation and redox equilibrium in Photosystem II. Biochimica et Biophysica Acta - Bioenergetics, 1858(6), 407-417
Open this publication in new window or tab >>Tyrosine D oxidation and redox equilibrium in Photosystem II
2017 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1858, no 6, p. 407-417Article in journal (Refereed) Published
Abstract [en]

Tyrosine ID (Tyr(D)) is an auxiliary redox active tyrosine residue in photosystem II (PSII). The mechanism of Tyr(D) oxidation was investigated by EPR spectroscopy, flash-induced fluorescence decay and thermoluminescence measurements in PSII enriched membranes from spinach. PSII membranes were chemically treated with 3 mM ascorbate and 1 mM diaminodurene and subsequent washing, leading to the complete reduction of Tyr(D). Tyr(D) oxidation kinetics and competing recombination reactions were measured after a single saturating flash in the absence and presence of DCMU (inhibitor of the Q(B)-site) in the pH range of 4.7-8.5. Two kinetic phases of Tyro oxidation were observed by the time resolved EPR spectroscopy the fast phase (msec-sec time range) and the pH dependent slow phase (tens of seconds time range). In the presence of DCMU, Tyr(D) oxidation kinetics was monophasic in the entire pH range, i.e. only the fast kinetics was observed. The results obtained from the fluorescence and thermoluminescence analysis show that when forward electron transport is blocked in the presence of DCMU, the S(2)Q((S) over bar) recombination outcompetes the slow phase of Tyr(D) oxidation by the S-2 state. Modelling of the whole complex of these electron transfer events associated with Tyr(D) oxidation fitted very well with our experimental data. Based on these data, structural information and theoretical considerations we confirm our assignment of the fast and slow oxidation kinetics to two populations of PSII centers with different water positions (proximal and distal) in the Tyr(D) vicinity.

Keywords
Photosystem II, Electron transfer, Tyrosine D
National Category
Natural Sciences
Research subject
Biochemistry
Identifiers
urn:nbn:se:uu:diva-320913 (URN)10.1016/j.bbabio.2017.02.011 (DOI)000402349000001 ()28235460 (PubMedID)
Funder
Swedish Research Council, 621-2013-5937Swedish Energy Agency, 11674-5Knut and Alice Wallenberg Foundation, 2011.0067
Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2017-07-06Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6218-3039

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