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  • 1.
    Ahmadova, Nigar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Tyrosine D oxidation and redox equilibrium in Photosystem II2017In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1858, no 6, p. 407-417Article in journal (Refereed)
    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.

  • 2. Allahverdiyeva, Yagut
    et al.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Holmström, Maija
    Nurmi, Markus
    Lundin, Björn
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Spetea, Cornelia
    Aro, Eva-Mari
    Comparison of the electron transport properties of the psbo1 and psbo2 mutants of Arabidopsis thaliana2009In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1787, no 10, p. 1230-1237Article in journal (Refereed)
    Abstract [en]

    Genome sequence of Arabidopsis thaliana (Arabidopsis) revealed two psbO genes (At5g66570 and At3g50820) which encode two distinct PsbO isoforms: PsbO1 and PsbO2, respectively. To get insights into the function of the PsbO1 and PsbO2 isoforms in Arabidopsis we have performed systematic and comprehensive investigations of the whole photosynthetic electron transfer chain in the T-DNA insertion mutant lines, psbO1 and psbo2. The absence of the PsbO1 isoform and presence of only the PsbO2 isoform in the psbo1 mutant results in (i) malfunction of both the donor and acceptor sides of Photosystem (PS) 11 and (ii) high sensitivity of PSII centers to photodamage, thus implying the importance of the PsbO1 isoform for proper structure and function of PSII. The presence of only the PsbO2 isoform in the PSII centers has consequences not only to the function of PSII but also to the PSI/PSII ratio in thylakoids. These results in modification of the whole electron transfer chain with higher rate of cyclic electron transfer around PSI, faster induction of NPQ and a larger size of the PQ-pool compared to WT, being in line with apparently increased chlororespiration in the psbo1 mutant plants. The presence of only the PsbO1 isoform in the psbo2 mutant did not induce any significant differences in the performance of PSII under standard growth conditions as compared to WT. Nevertheless, under high light illumination, it seems that the presence of also the PsbO2 isoform becomes favourable for efficient repair of the PSII complex.

  • 3. Allahverdiyeva, Yagut
    et al.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Suorsa, Marjaana
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Vass, Imre
    Aro, Eva-Mari
    Insights into the function of PsbR protein in Arabidopsis thaliana2007In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1767, no 6, p. 677-685Article in journal (Refereed)
    Abstract [en]

    The functional state of the Photosystem (PS) II complex in Arabidopsis psbR T-DNA insertion mutant was studied. The DeltaPsbR thylakoids showed about 34% less oxygen evolution than WT, which correlates with the amounts of PSII estimated from Y(D)(ox) radical EPR signal. The increased time constant of the slow phase of flash fluorescence (FF)-relaxation and upshift in the peak position of the main TL-bands, both in the presence and in the absence of DCMU, confirmed that the S(2)Q(A)(-) and S(2)Q(B)(-) charge recombinations were stabilized in DeltaPsbR thylakoids. Furthermore, the higher amount of dark oxidized Cyt-b559 and the increased proportion of fluorescence, which did not decay during the 100s time span of the measurement thus indicating higher amount of Y(D)(+)Q(A)(-) recombination, pointed to the donor side modifications in DeltaPsbR. EPR measurements revealed that S(1)-to-S(2)-transition and S(2)-state multiline signal were not affected by mutation. The fast phase of the FF-relaxation in the absence of DCMU was significantly slowed down with concomitant decrease in the relative amplitude of this phase, indicating a modification in Q(A) to Q(B) electron transfer in DeltaPsbR thylakoids. It is concluded that the lack of the PsbR protein modifies both the donor and the acceptor side of the PSII complex.

  • 4. Beckmann, K.
    et al.
    Uchtenhagen, Hannes
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Berggren, Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Anderlund, Magnus F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Thapper, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Messinger, J.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Kurz, P.
    Formation of stoichiometrically O-18-labelled oxygen from the oxidation of O-18-enriched water mediated by a dinuclear manganese complex: a mass spectrometry and EPR study2008In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 1, no 6, p. 668-676Article in journal (Refereed)
    Abstract [en]

    Oxygen formation was detected for the oxidations of various multinuclear manganese complexes by oxone (HSO5-) in aqueous solution. To determine to what extent water was the source of the evolved O-2, (H2O)-O-18 isotope-labelling experiments coupled with membrane inlet mass spectrometry (MIMS) were carried out. We discovered that during the reaction of oxone with [Mn-2(OAc)(2)(bpmp)](+) (1), stoichiometrically labelled oxygen (O-18(2)) was formed. This is the first example of a homogeneous reaction mediated by a synthetic manganese complex where the addition of a strong chemical oxidant yields O-18(2) with labelling percentages matching the theoretically expected values for the case of both O-atoms originating from water. Experiments using lead acetate as an alternative oxidant supported this finding. A detailed investigation of the reaction by EPR spectroscopy, MIMS and Clark-type oxygen detection enabled us to propose potential reaction pathways.

  • 5.
    Berggren, Gustav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Anderlund, Magnus F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Thapper, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    FTIR Study of Manganese Dimers with Carboxylate Donors As Model Complexes for the Water Oxidation Complex in Photosystem II2012In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 4, p. 2332-2337Article in journal (Refereed)
    Abstract [en]

    The carboxylate stretching frequencies of two high-valent, di-mu-oxido bridged, manganese dimers has been studied with IR spectroscopy in three different oxidation states. Both complexes contain one monodentate carboxylate donor to each Mn ion, in one complex, the carboxylate is coordinated perpendicular to the Mn-(mu-O)(2)-Mn plane, and in the other complex, the carboxylate is coordinated in the Mn-(mu-O)(2)-Mn plane. For both complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequen-cies decrease for both the Mn-2(IV,IV) to Mn-2(III,IV) transition and the Mn-2(III,IV) to Mn-2(III,III) transition, with only minor differences observed between the two arrangements of the carboxylate ligand versus the Mn-(mu-O)(2)-Mn plane. The IR spectra also show that both carboxylate ligands are affected for each one electron reduction, i.e., the stretching frequency of the carboxylate coordinated to the Mn ion that is not reduced also shifts. These results are discussed in relation to FTIR studies of changes in carboxylate stretching frequencies in a one electron oxidation step of the water oxidation complex in Photosystem II.

  • 6.
    Berggren, Gustav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Eriksson, Lars
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Anderlund, Magnus F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Thapper, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Synthesis and characterisation of low valent Mn-complexes as models for Mn-catalases2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 45, p. 11035-11044Article in journal (Refereed)
    Abstract [en]

    In this work we report the synthesis of two novel manganese complexes, [L1(3)Mn(6)(II)](ClO4)(6) (1 center dot(ClO4)(6)) and [L2Mn(2)(II)(mu-OAc)(mu-Cl)](ClO4)(2) (2 center dot(ClO4)(2)), where L1(2-) is the 2,2'-(1,3-phenylenebis(methylene))bis-((2-(bis(pyridin-2-ylmethyl)amino)ethyl)azanediyl)diacetic acid anion and L2 is N1,N1'-(1,3-phenylenebis(methylene))bis(N2,N2'-bis(pyridin-2-ylmethyl)ethane-1,2-diamine). The ligands Na(2)L1 and L2 are built on the same backbone, L2 only contains nitrogen donors, while two carboxylate arms have been introduced in Na(2)L1. The two complexes have been characterized by single-crystal X-ray diffraction, magnetic susceptibility, EPR spectroscopy, and electrochemistry. X-Ray crystallography revealed that 1 is a manganese(II) hexamer and 2 is a manganese(II) dimer featuring an unprecedented mono-mu-acetato, mono-mu-chlorido bridging motif. The ability of the complexes to catalyse H2O2 disproportionation, thereby acting as models for manganese catalases, has been investigated and compared to the activity of two other related manganese complexes. The introduction of carboxylate donors in the ligands, leading to increased denticity, resulted in a drop in H2O2 disproportionation activity.

  • 7.
    Berggren, Gustav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Thapper, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Eriksson, Lars
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Anderlund, Magnus F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mechanistic Studies on the Water-Oxidizing Reaction of Homogeneous Manganese-Based Catalysts: Isolation and Characterization of a Suggested Catalytic Intermediate2011In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 50, no 8, p. 3425-3430Article in journal (Refereed)
    Abstract [en]

    The synthesis, isolation, and characterization of two high-valent manganese dimers with isomeric ligands are reported. The complexes are synthesized and crystallized from solutions of low-valent precursors exposed to tert-butyl hydroperoxide. The crystal structures display centrosymmetric complexesconsisting of Mn2 IV,IV(μ-O)2 cores, with one ligand coordinating to each manganese. The ligands coordinate with the diaminoethane backbone, the carboxylate, and one of the two pyridines, while the second pyridine is noncoordinating. The activity of these complexes, under water oxidation conditions, is discussed in light of a proposed mechanism for water oxidation, in which this type of complexes have been suggested as a key intermediate.

  • 8.
    Bergman, Nina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Thapper, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjorn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Bergquist, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Shevchenko, Denys
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Quantitative determination of the Ru(bpy)(3)(2+) cation in photochemical reactions by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry2014In: Analytical Methods, ISSN 1759-9660, E-ISSN 1759-9679, Vol. 6, no 21, p. 8513-8518Article in journal (Refereed)
    Abstract [en]

    The coordination compound of Ru(II) with three 2,2'-bipyridine ligands possesses a potent photosensitization capacity for electron- and energy-transfer processes. In combination with salts of peroxydisulfate acid as sacrificial electron acceptors, Ru(bpy)(3)(2+) is widely used for photocatalytic oxidative transformations in organic synthesis and water splitting. The drawback of this system is that bipyridine degrades under the resulting strongly oxidative conditions, the concentration of Ru(bpy)(3)(2+) diminishes, and the photocatalytic reaction eventually stops. A commonly employed assay for the determination of Ru(bpy)(3)(2+), UV-Vis spectroscopy, has low selectivity and does not distinguish between the intact complex and its decayed forms. Here, we report a matrix assisted laser desorption/ionisation mass spectrometric method for the quantitative analysis of Ru(bpy)(3)(2+) in photochemical reaction mixtures. The developed method was successfully used for the determination of intact Ru(bpy)(3)(2+) during the course of the water photooxidation reaction. The significant difference between the results of MALDI MS and UV-Vis analyses was observed.

  • 9.
    Borgström, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Shaikh, Nizamuddin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Anderlund, Magnus
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Åkerman, Björn
    Magnusson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Light induced manganese oxidation and long-lived charge separation in a Mn2II,II-RuII(bpy)3-acceptor triad2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 49, p. 17504-17515Article in journal (Refereed)
    Abstract [en]

    The photoinduced electron-transfer reactions in a Mn2II,II-RuII-NDI triad (1) ([Mn2(bpmp)(OAc)2]+, bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenolate and OAc = acetate, RuII = tris-bipyridine ruthenium(II), and NDI = naphthalenediimide) have been studied by time-resolved optical and EPR spectroscopy. Complex 1 is the first synthetically linked electron donor-sensitizer-acceptor triad in which a manganese complex plays the role of the donor. EPR spectroscopy was used to directly demonstrate the light induced formation of both products: the oxidized manganese dimer complex (Mn2II,III) and the reduced naphthalenediimide (NDI*-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)3]2+ intermediate states and the NDI*- radical in a wide temperature range. The average lifetime of the NDI*- radical is ca. 600 micros at room temperature, which is at least 2 orders of magnitude longer than that for previously reported triads based on a [Ru(bpy)3]2+ photosensitizer. At 140 K, this intramolecular recombination was dramatically slowed, displaying a lifetime of 0.1-1 s, which is comparable to many of the naturally occurring charge-separated states in photosynthetic reaction centra. It was found that the long recombination lifetime could be explained by an unusually large reorganization energy (lambda approximately 2.0 eV), due to a large inner reorganization of the manganese complex. This makes the recombination reaction strongly activated despite the large driving force (Delta-G degrees = 1.07 eV). Thus, the intrinsic properties of the manganese complex are favorable for creating a long-lived charge separation in the "Marcus normal region" also when the charge separated state energy is high.

  • 10.
    Cardona, Tanai
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Battchikova, Natalia
    Agervald, Åsa
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Zhang, Pengpeng
    Nagel, Erik
    Aro, Eva-Mari
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Lindblad, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Isolation and characterization of thylakoid membranes from the filamentous cyanobacterium Nostoc punctiforme2007In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 131, no 4, p. 622-634Article in journal (Refereed)
    Abstract [en]

    Nostoc punctiforme strain Pasteur Culture Collection (PCC) 73102, a sequenced filamentous cyanobacterium capable of nitrogen fixation, is used as a model organism for characterization of bioenergetic processes during nitrogen fixation in Nostoc. A protocol for isolating thylakoid membranes was developed to examine the biochem. and biophys. aspects of photosynthetic electron transfer. Thylakoids were isolated from filaments of N. punctiforme by pneumatic pressure-drop lysis. The activity of photosynthetic enzymes in the isolated thylakoids was analyzed by measuring oxygen evolution activity, fluorescence spectroscopy and ESR spectroscopy. Electron transfer was found functional in both PSII and PSI. Electron transfer measurements in PSII, using diphenylcarbazide as electron donor and 2,6-dichlorophenolindophenol as electron acceptor, showed that 80% of the PSII centers were active in water oxidn. in the final membrane prepn. Anal. of the membrane protein complexes was made by 2D gel electrophoresis, and identification of representative proteins was made by mass spectrometry. The ATP synthase, several oligomers of PSI, PSII and the NAD(P)H dehydrogenase (NDH)-1L and NDH-1M complexes, were all found in the gels. Some differences were noted compared with previous results from Synechocystis sp. PCC 6803. Two oligomers of PSII were found, monomeric and dimeric forms, but no CP43-less complexes. Both dimeric and monomeric forms of Cyt b6/f could be obsd. In all, 28 different proteins were identified, of which 25 are transmembrane proteins or membrane associated ones.

  • 11.
    Chabera, Pavel
    et al.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Liu, Yizhu
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Prakash, Om
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Thyrhaug, Erling
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    El Nahhas, Amal
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Honarfar, Alireza
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Essen, Sofia
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Fredin, Lisa A.
    Lund Univ, Dept Chem, Div Theoret Chem, Box 124, SE-22100 Lund, Sweden..
    Harlang, Tobias C. B.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden.;Tech Univ Denmark, Dept Phys, DK-2800 Lyngby, Denmark..
    Kjaer, Kasper S.
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden.;Tech Univ Denmark, Dept Phys, DK-2800 Lyngby, Denmark..
    Handrup, Karsten
    Lund Univ, Dept Phys, Div Synchrotron Radiat Res, Box 118, SE-22100 Lund, Sweden..
    Ericson, Fredric
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Tatsuno, Hideyuki
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Morgan, Kelsey
    NIST, Boulder, CO 80305 USA..
    Schnadt, Joachim
    Lund Univ, Dept Phys, Div Synchrotron Radiat Res, Box 118, SE-22100 Lund, Sweden..
    Häggström, Lennart
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Sobkowiak, Adam
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lidin, Sven
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Uhlig, Jens
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Bendix, Jesper
    Univ Copenhagen, Dept Chem, Univ Pk 5, DK-2100 Copenhagen, Denmark..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Sundström, Villy
    Lund Univ, Dept Chem, Div Phys Chem, Box 124, SE-22100 Lund, Sweden..
    Persson, Petter
    Lund Univ, Dept Chem, Div Theoret Chem, Box 124, SE-22100 Lund, Sweden..
    Warnmark, Kenneth
    Lund Univ, Dept Chem, CAS, Box 124, SE-22100 Lund, Sweden..
    A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence2017In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 543, no 7647, p. 695-+Article in journal (Refereed)
    Abstract [en]

    Transition-metal complexes are used as photosensitizers(1), in light-emitting diodes, for biosensing and in photocatalysis(2). A key feature in these applications is excitation from the ground state to a charge-transfer state(3,4); the long charge-transfer-state lifetimes typical for complexes of ruthenium(5) and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron(6) and copper(7) being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs(6,8-10), it remains a formidable scientific challenge(11) to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered(12) photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers(13-15). Here we present the iron complex [Fe(btz)(3)](3+) (where btz is 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)), and show that the superior sigma-donor and pi-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(III) d(5) complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer ((LMCT)-L-2) state that is rarely seen for transition-metal complexes(4,16,17). The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

  • 12.
    Chen, Guiying
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Allahverdiyeva, Yagut
    Aro, Eva-Mari
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Electron paramagnetic resonance study of the electron transfer reactions in photosystem II membrane preparations from Arabidopsis thaliana2011In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1807, no 2, p. 205-215Article in journal (Refereed)
    Abstract [en]

    Arabidopsis thaliana is widely used as a model organism in plant biology as its genome has been sequenced and transformation is known to be efficient. A large number of mutant lines and genomic resources are available for Arabidopsis. All this makes Arabidopsis a useful tool for studies of photosynthetic reactions in higher plants. In this study, photosystem II (PSII) enriched membranes were successfully isolated from thylakoids of Arabidopsis plants and for the first time the electron transfer cofactors in PSII were systematically studied using electron paramagnetic resonance (EPR) spectroscopy. EPR signals from both of the donor and acceptor sides of PSII, as well as from auxiliary electron donors were recorded. From the acceptor side of PSII, EPR signals from Q(A)(-)Fe(2+) and Phe(-)Q(A)(-)Fe(2+) as well as from the free Phe(-) radical were observed. The multiline EPR signals from the S-0- and S-2-states of CaMn4Ox-cluster in the water oxidation complex were characterized. Moreover, split EPR signals, the interaction signals from Y-Z center dot and CaMn4Ox-cluster in the S-0-, S-1-, S-2-, and the S-3-state were induced by illumination of the PSII membranes at 5 K and characterized. In addition, EPR signals from auxiliary donors Y-D center dot, Chl(+) and cytochrome b(559) were observed. In total, we were able to detect about 20 different EPR signals covering all electron transfer components in PSII. Use of this spectroscopic platform opens a possibility to study PSII reactions in the library of mutants available in Arabidopsis.

  • 13.
    Chen, Guiying
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Han, Guangye
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Göransson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Stability of the S(3) and S(2) State Intermediates in Photosystem II Directly Probed by EPR Spectroscopy2012In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 51, no 1, p. 138-148Article in journal (Refereed)
    Abstract [en]

    The stability of the S(3) and S(2) states of the oxygen evolving complex in photosystem II (PSII) was directly probed by EPR spectroscopy in PSII membrane preparations from spinach in the presence of the exogenous electron acceptor PpBQ at 1, 10, and 20 degrees C. The decay of the S(3) state was followed in samples exposed to two flashes by measuring the split S(3) EPR signal induced by near-infrared illumination at 5 K. The decay of the S(2) state was followed in samples exposed to one flash by measuring the S(2) state multiline EPR signal. During the decay of the S(3) state, the S(2) state multiline EPR signal first increased and then decreased in amplitude. This shows that the decay of the S(3) state to the S(1) state occurs via the S(2) state. The decay of the S(3) state was biexponential with a fast kinetic phase with a few seconds decay half-time. This occurred in 10-20% of the PSII centers. The slow kinetic phase ranged from a decay half-time of 700 s (at 1 degrees C) to similar to 100 s (at 20 degrees C) in the remaining 80-90% of the centers. The decay of the S(2) state was also biphasic and showed quite similar kinetics to the decay of the S(3) state. Our experiments show that the auxiliary electron donor Y(D) was oxidized during the entire experiment. Thus, the reduced form of Y(D) does not participate to the fast decay of the S(2) and S(3) states we describe here. Instead, we suggest that the decay of the S(3) and S(2) states reflects electron transfer from the acceptor side of PSII to the donor side of PSII starting in the corresponding S state. It is proposed that this exists in equilibrium with Y(Z) according to S(3)Y(2) double left right arrow S(2)Y(Z)(.) in the case of the S(3) state decay and S(2)Y(Z) double left right arrow S(1)Y(Z)(.) in the case of the S(2) state decay. Two kinetic models are discussed, both developed with the assumption that the slow decay of the S(3) and S(2) states occurs in PSII centers where Y(Z) is also a fast donor to P(680)(+) working in the nanosecond time regime and that the fast decay of the S(3) and S(2) states occurs in centers where Y(Z) reduces P(680)(+) with slower microsecond kinetics. Our measurements also demonstrate that the split S(3) EPR signal can be used as a direct probe to the S(3) state and that it can provide important information about the redox properties of the S(3) state.

  • 14. Cox, Nicholas
    et al.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Pewnim, Naray
    Steffen, Ronald
    Smith, Paul J.
    Havelius, Kajsa G. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Hughes, Joseph L.
    Debono, Lesley
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Krausz, Elmars
    Pace, Ron J.
    The S-1 split signal of photosystem II: a tyrosine-manganese coupled interaction2009In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1787, no 7, p. 882-889Article in journal (Refereed)
    Abstract [en]

    Detailed optical and EPR analyses of states induced in dark-adapted PS II membranes by cryogenic illumination permit characterization and quantification of all pigment derived donors and acceptors, as well as optically silent (in the visible, near infrared) species which are EPR active. Near complete turnover formation of Q(A)(-) is seen in all centers, but with variable efficiency, depending on the donor species. In minimally detergent-exposed PS II membranes, negligible (<5%) oxidation of chlorophyll or carotenoid centers occurs for illumination temperatures 5-20 K. An optically silent electron donor to P680(+) is observed with the same decay kinetics as the S-1 split signal. Cryogenic donors to P680(+) seen are: (i) transient (t(1/2)similar to 150 s) tyrosine related species, including 'split signals' (similar to 15% total centers), (ii) reduced cytochrome b(559) (similar to 30-50% centers), and (iii) an organic donor, possibly an amino acid side chain, (similar to 30% centers).

  • 15.
    Daniel, Quentin
    et al.
    KTH Royal Inst Technol.
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Fan, Ting
    KTH Royal Inst Technol.
    Wang, Ying
    KTH Royal Inst Technol.
    Duan, Lele
    KTH Royal Inst Technol.
    Wang, Lei
    KTH Royal Inst Technol.
    Li, Fusheng
    KTH Royal Inst Technol.
    Rinkevicius, Zilvinas
    KTH Royal Inst Technol.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ahlquist, Marten S. G.
    KTH Royal Inst Technol.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Sun, Licheng
    KTH Royal Inst Technol; Dalian Univ Technol.
    Rearranging from 6-to 7-coordination initiates the catalytic activity: An EPR study on a Ru-bda water oxidation catalyst2017In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 346, p. 206-215Article, review/survey (Refereed)
    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.

  • 16. Danielsson, Ravi
    et al.
    Suorsa, Marjaana
    Paakkarinen, Virpi
    Albertsson, Per-Ake
    Styring, Stenbjörn
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Aro, Eva-Mari
    Mamedov, Fikret
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Dimeric and monomeric organization of photosystem II. Distribution of five distinct complexes in the different domains of the thylakoid membrane.2006In: J Biol Chem, ISSN 0021-9258, Vol. 281, no 20, p. 14241-9Article in journal (Refereed)
  • 17. Faunce, Thomas
    et al.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Wasielewski, Michael R.
    Brudvig, Gary W.
    Rutherford, A. William
    Messinger, Johannes
    Lee, Adam F.
    Hill, Craig L.
    deGroot, Huub
    Fontecave, Marc
    MacFarlane, Doug R.
    Hankamer, Ben
    Nocera, Daniel G.
    Tiede, David M.
    Dau, Holger
    Hillier, Warwick
    Wang, Lianzhou
    Amal, Rose
    Artificial photosynthesis as a frontier technology for energy sustainability2013In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 6, no 4, p. 1074-1076Article in journal (Other academic)
  • 18.
    Feyziyev, Yashar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Deak, Zsuzsanna
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjorn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Bernat, Gabor
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Electron transfer from Cyt b (559) and tyrosine-D to the S-2 and S-3 states of the water oxidizing complex in photosystem II at cryogenic temperatures2013In: Journal of Bioenergetics and Biomembranes, ISSN 0145-479X, E-ISSN 1573-6881, Vol. 45, no 1-2, p. 111-120Article in journal (Refereed)
    Abstract [en]

    The Mn4CaO5 cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with Tyrosine(Z) and P-680, which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine(D) (Y-D) and Cytochrome b (559) (Cyt b (559)) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b (559) and Y-D to the S-2 and S-3 states at 195 K. First, Y-D (aEuro cent) and Cyt b (559) were chemically reduced. The S-2 and S-3 states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S-1 state. EPR signals of the WOC (the S-2-state multiline signal, ML-S-2), Y-D (aEuro cent) and oxidized Cyt b (559) were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S-2 population decayed to S-1 in the S-2 samples by following a single exponential decay. Differently, S-3 samples showed an initial increase in the ML-S-2 intensity (due to S-3 to S-2 conversion) and a subsequent slow decay due to S-2 to S-1 conversion. In both cases, only a minor oxidation of Y-D was observed. In contrast, the signal intensity of the oxidized Cyt b (559) showed a two-fold increase in both the S-2 and S-3 samples. The electron donation from Cyt b (559) was much more efficient to the S-2 state than to the S-3 state.

  • 19. Garcia-Bosch, Isaac
    et al.
    Company, Anna
    Cady, Clyde W.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Browne, Wesley R.
    Ribas, Xavi
    Costas, Miquel
    Evidence for a Precursor Complex in C-H Hydrogen Atom Transfer Reactions Mediated by a Manganese(IV) Oxo Complex2011In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 25, p. 5648-5653Article in journal (Refereed)
  • 20. Grasse, Nicole
    et al.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Becker, Kristin
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Roegner, Matthias
    Nowaczyk, Marc M.
    Role of Novel Dimeric Photosystem II (PSII)-Psb27 Protein Complex in PSII Repair2011In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, no 34, p. 29548-29555Article in journal (Refereed)
    Abstract [en]

    The multisubunit membrane protein complex Photosystem II (PSII) catalyzes one of the key reactions in photosynthesis: the light-driven oxidation of water. Here, we focus on the role of the Psb27 assembly factor, which is involved in biogenesis and repair after light-induced damage of the complex. Weshow that Psb27 is essential for the survival of cyanobacterial cells grown under stress conditions. The combination of cold stress (30 degrees C) and high light stress (1000 mu mol of photons x m(-2) x s(-1)) led to complete inhibition of growth in a Delta psb27 mutant strain of the thermophilic cyanobacterium Thermosynechococcus elongatus, whereas wild-type cells continued to grow. Moreover, Psb27-containing PSII complexes became the predominant PSII species in preparations from wild-type cells grown under cold stress. Two different PSII-Psb27 complexes were isolated and characterized in this study. The first complex represents the known monomeric PSII-Psb27 species, which is involved in the assembly of PSII. Additionally, a novel dimeric PSII-Psb27 complex could be allocated in the repair cycle, i.e. in processes after inactivation of PSII, by (15)N pulse-label experiments followed by mass spectrometry analysis. Comparison with the corresponding PSII species from Delta psb27 mutant cells showed that Psb27 prevented the release of manganese from the previously inactivated complex. These results indicate a more complex role of the Psb27 protein within the life cycle of PSII, especially under stress conditions.

  • 21.
    Hammarstrom, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Styring, Stenbjorn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Splitting with a difference2009In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 1, no 3, p. 185-186Article in journal (Refereed)
  • 22.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Coupled electron transfers in artificial photosynthesis2008In: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, E-ISSN 1471-2970, Vol. 363, no 1494, p. 1283-1291Article in journal (Refereed)
    Abstract [en]

    Light-induced charge separation in molecular assemblies has been widely investigated in the context of artificial photosynthesis. Important progress has been made in the fundamental understanding of electron and energy transfer and in stabilizing charge separation by multi-step electron transfer. In the Swedish Consortium for Artificial Photosynthesis, we build on principles from the natural enzyme photosystem II and Fe-hydrogenases. An important theme in this biomimetic effort is that of coupled electron-transfer reactions, which have so far received only little attention. (i) Each absorbed photon leads to charge separation on a single-electron level only, while catalytic water splitting and hydrogen production are multi-electron processes; thus there is the need for controlling accumulative electron transfer on molecular components. (ii) Water splitting and proton reduction at the potential catalysts necessarily require the management of proton release and/or uptake. Far from being just a stoichiometric requirement, this controls the electron transfer processes by proton-coupled electron transfer (PCET). (iii) Redox-active links between the photosensitizers and the catalysts are required to rectify the accumulative electron-transfer reactions, and will often be the starting points of PCET.

  • 23.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Proton-coupled electron transfer of tyrosines in Photosystem II and model systems for artificial photosynthesis: the role of a redox-active link between catalyst and photosensitizer2011In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 4, no 7, p. 2379-2388Article in journal (Refereed)
    Abstract [en]

    Water oxidation in Photosystem II is dependent on a particular amino acid residue, Tyrosine(Z). This is a redox intermediate in steady state oxygen evolution and transfers electrons from the water splitting CaMn4 cluster to the central chlorophyll radical P-680(+). This Perspective discusses the functional principles of Tyrosine(Z) as a proton-coupled redox active link, as well as mechanistic studies of synthetic model systems and implications for artificial photosynthesis. Experimental studies of temperature dependence and kinetic isotope effects are important tools to understand these reactions. We emphasize the importance of proton transfer distance and hydrogen bond dynamics that are responsible for variation in the rate of PCET by several orders of magnitude. The mechanistic principles discussed and their functional significance are not limited to tyrosine and biological systems, but are important to take into account when constructing artificial photosynthetic systems. Of particular importance is the role of proton transfer management in water splitting and solar fuel catalysis.

  • 24.
    Hammarström, Leif
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics.
    Winkler, Jay R.
    Gray, Harry B.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Shedding Light on Solar Fuel Efficiencies2011In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 333, no 6040, p. 288-288Article in journal (Refereed)
  • 25.
    Han, Guangye
    et al.
    Institute of Botany, The Chinese Academy of Sciences.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Havelius, Kajsa G. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Morvaridi, Susan F.
    Department of Chemistry and Biochemistry, University of California-Los Angeles,.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Direct quantification of the four individual S states in Photosystem II using EPR spectroscopy2008In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1777, no 6, p. 496-503Article in journal (Refereed)
    Abstract [en]

    Car, carotenoid; Chl, chlorophyll; ChlZ, secondary chlorophyll electron donor to P680+; Cytb559, cytochrome b559; EPR, electron paramagnetic resonance; DMSO, dimethylsulfoxide; MES, 2-(N-morpholino) ethanesulfonic acid; NIR, near-infrared; OEC, oxygen evolving complex; P680, primary electron donor chlorophylls in PSII; PpBQ, phenyl-p-benzoquinone; PSII, Photosystem II; QA and QB, primary and secondary plastoquinone acceptors of Photosystem II; YD, tyrosine 161 of the PSII D2 polypeptide; YZ, tyrosine 161 of the PSII D1 polypeptide

  • 26. Han, Guangye
    et al.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Misses during Water Oxidation in Photosystem II Are S State-dependent2012In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 287, no 16, p. 13422-13429Article in journal (Refereed)
    Abstract [en]

    The period of four oscillation of the S state intermediates of the water oxidizing complex in Photosystem II (PSII) is commonly analyzed by the Kok parameters. The important miss factor determines the efficiency for each S transition. Commonly, an equal miss factor has been used in the analysis. We have used EPR signals which probe all S states in the same sample during S cycle advancement. This allows, for the first time, to measure directly the miss parameter for each S state transition. Experiments were performed in PSII membrane preparations from spinach in the presence of electron acceptor at 1 degrees C and 20 degrees C. The data show that the miss parameter is different in different transitions and shows different temperature dependence. We found no misses at 1 degrees C and 10% misses at 20 degrees C during the S-1 -> S-2 transition. The highest miss factor was found in the S-2 -> S-3 transition which decreased from 23% to 16% with increasing temperature. For the S-3 -> S-0 transition the miss parameter was found to be 7% at 1 degrees C and decreased to 3% at 20 degrees C. For the S-0 -> S-1 transition the miss parameter was found to be approximately 10% at both temperatures. The contribution from the acceptor side in the form of recombination reactions as well as from the donor side of PSII to the uneven misses is discussed. It is suggested that the different transition efficiency in each S transition partly reflects the chemistry at the CaMn4O5 cluster. That consequently contributes to the uneven misses during S cycle turnover in PSII.

  • 27. Han, Guangye
    et al.
    Morvaridi, Susan
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    S-state dependence of misses in the OEC probed by EPR spectroscopy of individual S-states2008In: Photosynthesis. Energy from the Sun / [ed] Allen J.F., Gant E., Golbeck J.H. and Osmond B., Springer , 2008, p. 419-422Conference paper (Refereed)
  • 28.
    Harlang, Tobias C. B.
    et al.
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Liu, Yizhu
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden.;Lund Univ, Dept Chem, Ctr Anal & Synth, SE-22100 Lund, Sweden..
    Gordivska, Olga
    Lund Univ, Dept Chem, Ctr Anal & Synth, SE-22100 Lund, Sweden..
    Fredin, Lisa A.
    Lund Univ, Dept Chem, Theoret Chem Div, SE-22100 Lund, Sweden..
    Ponseca, Carlito S., Jr.
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Chabera, Pavel
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Kjaer, Kasper S.
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden.;Tech Univ Denmark, Dept Phys, DK-2800 Lyngby, Denmark..
    Mateos, Helena
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Uhlig, Jens
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Wallenberg, Reine
    Lund Univ, nCHREM, SE-22100 Lund, Sweden..
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Persson, Petter
    Lund Univ, Dept Chem, Theoret Chem Div, SE-22100 Lund, Sweden..
    Sundstroem, Villy
    Lund Univ, Dept Chem Phys, SE-22100 Lund, Sweden..
    Waernmark, Kenneth
    Lund Univ, Dept Chem, Ctr Anal & Synth, SE-22100 Lund, Sweden..
    Iron sensitizer converts light to electrons with 92% yield2015In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 7, no 11, p. 883-889Article in journal (Refereed)
    Abstract [en]

    Solar energy conversion in photovoltaics or photocatalysis involves light harvesting, or sensitization, of a semiconductor or catalyst as a first step. Rare elements are frequently used for this purpose, but they are obviously not ideal for large-scale implementation. Great efforts have been made to replace the widely used ruthenium with more abundant analogues like iron, but without much success due to the very short-lived excited states of the resulting iron complexes. Here, we describe the development of an iron-nitrogen-heterocyclic-carbene sensitizer with an excited-state lifetime that is nearly a thousand-fold longer than that of traditional iron polypyridyl complexes. By the use of electron paramagnetic resonance, transient absorption spectroscopy, transient terahertz spectroscopy and quantum chemical calculations, we show that the iron complex generates photoelectrons in the conduction band of titanium dioxide with a quantum yield of 92% from the 3MLCT (metal-to-ligand charge transfer) state. These results open up possibilities to develop solar energy-converting materials based on abundant elements.

  • 29.
    Havelius, Kajsa G. V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Sjöholm, Johannes
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Metalloradical EPR Signals from the Y-Z center dot S-State Intermediates in Photosystem II2010In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 37, no 1-4, p. 151-176Article, review/survey (Refereed)
    Abstract [en]

    The redox-active tyrosine residue (Y-Z) plays a crucial role in the mechanism of the water oxidation. Metalloradical electron paramagnetic resonance (EPR) signals reflecting the light-induced Y-Z center dot in magnetic interaction with the CaMn4-cluster in the particular S-state, Y-Z center dot S-X intermediates, have been found in intact photosystem II. These so-called split EPR signals are induced by illumination at cryogenic temperatures and provide means to both study the otherwise transient Y-Z center dot and to probe the S-states with EPR spectroscopy. The illumination used for signal induction grouped the observed split EPR signals in two categories: (i) Y-Z in the lower S-states was oxidized by P680(+) formed via charge separation, while (ii) Y-Z in the higher S-states was oxidized by an excited, highly oxidizing Mn species. Applied mechanistic studies of the Y-Z center dot S-X intermediates in the different S-states are reviewed and compared to investigations in photosystem II at physiological temperature. Addition of methanol induced S-state characteristic changes in the split signals' formation which reflect changes in the magnetic coupling within the CaMn4-cluster due to methanol binding. The pH titration of the split EPR signals, on the other hand, could probe the proton-coupled electron transfer properties of the Y-Z oxidation. The apparent pK (a)s found for decreased split signal induction were interpreted in the fate of the phenol proton.

  • 30.
    Havelius, Kajsa G. V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    pH Dependent Competition between YZ and YD in Photosystem II Probed by Illumination at 5 K2007In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 46, no 26, p. 7865-7874Article in journal (Refereed)
    Abstract [en]

    The photosystem II (PSII) reaction center contains two redox active tyrosines, YZ and YD, situated on the D1 and D2 proteins, respectively. By illumination at 5 K, oxidation of YZ in oxygen-evolving PSII can be observed as induction of the Split S1 EPR signal from YZ* in magnetic interaction with the CaMn4 cluster, whereas oxidation of YD can be observed as the formation of the free radical EPR signal from YD*. We have followed the light induced induction at 5 K of the Split S1 signal between pH 4-8.5. The formation of the signal, that is, the oxidation of YZ, is pH independent and efficient between pH 5.5 and 8.5. At low pH, the split signal formation decreases with pKa approximately 4.7-4.9. In samples with chemically pre-reduced YD, the pH dependent competition between YZ and YD was studied. Only YZ was oxidized below pH 7.2, but at pH above 7.2, the oxidation of YD became possible, and the formation of the Split S1 signal diminished. The onset of YD oxidation occurred with pKa approximately 8.0, while the Split S1 signal decreased with pKa approximately 7.9 demonstrating that the two tyrosines compete in this pH interval. The results reflect the formation and breaking of hydrogen bonds between YZ and D1-His190 (HisZ) and YD and D2-His190 (HisD), respectively. The oxidation of respective tyrosine at 5 K demands that the hydrogen bond is well-defined; otherwise, the low-temperature oxidation is not possible. The results are discussed in the framework of recent literature data and with respect to the different oxidation kinetics of YZ and YD.

  • 31. Havelius, Kajsa G V
    et al.
    Su, Ji-Hu
    Feyziyev, Yashar
    Mamedov, Fikret
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Spectral resolution of the split EPR signals induced by illumination at 5 K from the S1, S3, and S0 states in photosystem II.2006In: Biochemistry, ISSN 0006-2960, Vol. 45, no 30, p. 9279-90Article in journal (Refereed)
  • 32.
    Havelius, Kajsa G. V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Su, Ji-Hu
    Han, Guangye
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    The formation of the split EPR signal from the S-3 state of Photosystem II does not involve primary charge separation2011In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1807, no 1, p. 11-21Article in journal (Refereed)
    Abstract [en]

    Metalloradical EPR signals have been found in intact Photosystem II at cryogenic temperatures. They reflect the light-driven formation of the tyrosine Z radical (Y-z(center dot)) in magnetic interaction with the CaMn4 cluster in a particular S state. These so-called split EPR signals, induced at cryogenic temperatures, provide means to study the otherwise transient Y-z(center dot) and to probe the S states with EPR spectroscopy. In the S-0 and S-1 states, the respective split signals are induced by illumination of the sample in the visible light range only. In the S-3 state the split EPR signal is induced irrespective of illumination wavelength within the entire 415-900 nm range (visible and near-IR region) [Su, J. H., Havelius, K. G. V., Ho, F. M., Han, G., Mamedov, F., and Styring, S. (2007) Biochemistry 46. 10703-10712]. An important question is whether a single mechanism can explain the induction of the Split S-3 signal across the entire wavelength range or whether wavelength-dependent mechanisms are required. In this paper we confirm that the Y-z(center dot) radical formation in the S-1 state, reflected in the Split S-1 signal, is driven by P680-centered charge separation. The situation in the S-3 state is different. In Photosystem II centers with pre-reduced quinone A (Q(A)), where the P680-centered charge separation is blocked, the Split S-3 EPR signal could still be induced in the majority of the Photosystem II centers using both visible and NIR (830 nm) light. This shows that P680-centered charge separation is not involved. The amount of oxidized electron donors and reduced electron acceptors (Q(A)(-)) was well correlated after visible light illumination at cryogenic temperatures in the S-1 state. This was not the case in the S-3 state, where the Split S-3 EPR signal was formed in the majority of the centers in a pathway other than P680-centered charge separation. Instead, we propose that one mechanism exists over the entire wavelength interval to drive the formation of the Split S-3 signal. The origin for this, probably involving excitation of one of the Mn ions in the CaMn4 cluster in Photosystem II, is discussed.

  • 33. Havelius, Kajsa
    et al.
    Su, Ji-Hu
    Ho, Felix
    Han, Guangye
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    The mechanism behind the formation of the “Split S3” EPR signal in photosystem II induced by visible or near-infrared light2008In: Photosynthesis. Energy from the Sun / [ed] Allen J.F., Gant E., Golbeck J.H. and Osmond B., Springer , 2008, p. 423-426Conference paper (Refereed)
  • 34.
    Ho, Felix M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Morvaridi, Susan F.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Enhancement of Y-D(center dot) spin relaxation by the CaMn4 cluster in photosystem II detected at room temperature: A new probe for the S-cycle2007In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1767, no 1, p. 5-14Article in journal (Refereed)
    Abstract [en]

    The long-lived, light-induced radical Y-D(.) of the Tyr161 residue in the D2 protein of Photosystem 11 (PSII) is known to magnetically interact with the CaMn4 cluster, situated similar to 30 angstrom away. In this study we report a transient step-change increase in YD EPR intensity upon the application of a single laser flash to S, state-synchronised PSII-enriched membranes from spinach. This transient effect was observed at room temperature and high applied microwave power (100 mW) in samples containing PpBQ, as well as those containing DCMU. The subsequent decay lifetimes were found to differ depending on the additive used. We propose that this flash-induced signal increase was caused by enhanced spin relaxation of YD by the OEC in the S-2 state, as a consequence of the single laser flash turnover. The post-flash decay reflected S-2 -> S-1 back-turnover, as confirmed by their correlations with independent measurements of S-2 multiline EPR signal and flash-induced variable fluorescence decay kinetics under corresponding experimental conditions. This flash-induced effect opens up the possibility to study the kinetic behaviour of S-state transitions at room temperature using YD as a probe.

  • 35.
    Ho, Felix M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Access channels and methanol binding site to the CaMn4 cluster in Photosystem II based on solvent accessibility simulations, with implications for substrate water access2008In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1777, no 2, p. 140-153Article in journal (Refereed)
    Abstract [en]

    Given the tightly packed environment of Photosystem II (PSII), channels are expected to exist within the protein to allow the movement of small molecules to and from the oxygen evolving centre. In this report, we calculate solvent contact surfaces from the PSII crystal structures to identify such access channels for methanol and water molecules. In a previous study of the effects of methanol on the EPR split S-1-, S-3-, and S-0-signals [Su et al. (2006) Biochemistry 45, 7617-7627], we proposed that methanol binds to one and the same Mn ion in all S-states. We find here that while channels of methanol dimensions were able to make contact with the CaMn4 cluster, only Mn-3 and Mn-4 were accessible to methanol. Combining this observation with spectroscopic data in the literature, we propose that Mn-3 is the ion to which methanol binds. Furthermore, by calculating solvent contact surfaces for water, we found analogous and more extensive water accessible channels within PSII. On the basis of their structure, orientation, and electrostatic properties, we propose functional assignments of these channels as passages for substrate water access to the CaMn4 cluster, and for the exit of O-2 and H+ that are released during water oxidation. Finally, we discuss the possible existence of a gating mechanism for the control of substrate water access to the CaMn4 cluster, based on the observation of a gap within the channel system that is formed by Ca2+ and several mechanistically very significant residues in the vicinity of the cluster.

  • 36.
    Huang, P.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Kurz, Philipp
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    EPR investigations of synthetic manganese complexes as bio-mimics of the water oxidation complex in photosystem II2007In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 31, no 1-2, p. 301-320Article in journal (Refereed)
    Abstract [en]

    Research in the Swedish Consortium for Artificial Photosynthesis aims to construct a supramolecular system containing synthetically connected D (electron donor), S (photosensitizer), and A (electron acceptor) compartments. These are intended to carry out catalytic water oxidation on the donor side and catalytic hydrogen formation on the acceptor side, driven by light energy absorbed by the photosensitizer. In this minireview, we focus our attention on our spectroscopic and electrochemical studies of a series of manganese complexes partially mimicking the water-oxidizing manganese complex in the natural photosystem II (PSII), using ruthenium(II) tris(bypyridine) as the photosensitizer. The manganese complexes we discuss fall in three categories: monomeric manganese systems covalently linked to the ruthenium(II) tris(bypyridine) center, dimeric manganese complexes that are not covalently connected to ruthenium(II) tris(bypyridine) and dimeric manganese complexes covalently bound to a ruthenium(II) tris(bypyridine) center via an amide bound. The review focuses on the use of electron paramagnetic resonance spectroscopy in the studies of our manganese compounds.

  • 37.
    Huang, Ping
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Abrahamsson, Malin
    Tamm, Markus
    Sun, Licheng
    van Rotterdam, Bart
    Park, Jonathan
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Åkermark, Björn
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Photo-induced oxidation of a dinuclear Mn-2(II,II) complex to the Mn-2(III,IV) state by inter- and intramolecular electron transfer to Ru-III tris-bipyridine2002In: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 91, no 1, p. 159-172Article in journal (Refereed)
    Abstract [en]

    To model the structural and functional parts of the water oxidizing complex in Photosystem 11, a dimeric manganese(II,11) complex (1) was linked to a ruthenium(II)tris-bipyridine (Ru-II(bpy)3) complex via a substituted L-tyrosine, to form the trinuclear complex 2 [J. Inorg. Biochem. 78 (2000) 15]. Flash photolysis of 1 and Ru-II(bpy), in aqueous solution, in the presence of an electron acceptor, resulted in the stepwise extraction of three electrons by Ru-III(bpy), from the Mn-2(II,II) dimer, which then attained the Mn-2(III,IV) oxidation state. In a similar experiment with compound 2, the dinuclear Mn complex reduced the photo-oxidized Ru moiety via intramolecular electron transfer on each photochemical event. From EPR it was seen that 2 also reached the Mn-2(III,IV) state. Our data indicate that oxidation from the Mn-2(II,II) state proceeds stepwise via intermediate formation of Mn-2(II,III) and Mn-2(III,III). In the presence of water, cyclic voltammetry showed an additional anodic peak beyond Mn-2(II,III/III,III) oxidation which was significantly lower than in neat acetonitrile. Assuming that this peak is due to oxidation to Mn-2(III,IV), this suggests that water is essential for the formation of the Mn-2(III,IV) oxidation state. Compound 2 is a structural mimic of the water oxidizing complex, in that it links a Mn complex via a tyrosine to a highly oxidizing photosensitizer. Complex 2 also mimics mechanistic aspects of Photosystem 11, in that the electron transfer to the photosensitizer is fast and results in several electron extractions from the Mn moiety. (C) 2002 Elsevier Science Inc. All rights reserved.

  • 38.
    Huang, Ping
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Shaikh, Nizamuddin
    Anderlund, Magnus F
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Styring, Stenbjörn
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Hammarström, Leif
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics. Physics, Department of Physics and Materials Science, Chemical Physics.
    Consistent simulation of X- and Q-band EPR spectra of an unsymmetric dinuclear Mn2(II,III) complex.2006In: J Inorg Biochem, ISSN 0162-0134, Vol. 100, no 5-6, p. 1139-46Article in journal (Refereed)
  • 39.
    Johansson, Anh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Abrahamsson, Malin
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Mårtensson, Jerker
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Sun, Licheng
    Åkermark, Björn
    Synthesis and Photophysics of One Mononuclear Mn(III) and One Dinuclear Mn(III,III) Complex Covalently Linked to a Ruthenium(II) Tris(bipyridyl) Complex2003In: Inorganic Chemistry, Vol. 42, p. 7502-7511Article in journal (Refereed)
    Abstract [en]

    The preparation of donor (D)-photosensitizer (S) arrays, consisting of a manganese complex as D and a ruthenium tris(bipyridyl) complex as S has been pursued. Two new ruthenium complexes containing coordinating sites for one (2a) and two manganese ions (3a) were prepared in order to provide models for the donor side of photosystem II in green plants. The manganese coordinating site consists of bridging and terminal phenolate as well as terminal pyridyl ligands. The corresponding ruthenium-manganese complexes, a manganese monomer 2b and dimer 3b, were obtained. For the dimer 3b, our data suggest that intramolecular electron transfer from manganese to photogenerated ruthenium(III) is fast, k(ET) > 5 x 10(7) s(-1).

  • 40. Karonen, Maarit
    et al.
    Mattila, Heta
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Tyystjarvi, Esa
    A Tandem Mass Spectrometric Method for Singlet Oxygen Measurement2014In: Photochemistry and Photobiology, ISSN 0031-8655, E-ISSN 1751-1097, Vol. 90, no 5, p. 965-971Article in journal (Refereed)
    Abstract [en]

    Singlet oxygen, a harmful reactive oxygen species, can be quantified with the substance 2,2,6,6-tetramethylpiperidine (TEMP) that reacts with singlet oxygen, forming a stable nitroxyl radical (TEMPO). TEMPO has earlier been quantified with electron paramagnetic resonance (EPR) spectroscopy. In this study, we designed an ultra-high-performance liquid chromatographictandem mass spectrometric (UHPLC-ESI-MS/MS) quantification method for TEMPO and showed that the method based on multiple reaction monitoring (MRM) can be used for the measurements of singlet oxygen from both nonbiological and biological samples. Results obtained with both UHPLC-ESI-MS/MS and EPR methods suggest that plant thylakoid membranes produce 3.7x10(-7) molecules of singlet oxygen per chlorophyll molecule in a second when illuminated with the photosynthetic photon flux density of 2000molm(-2)s(-1).

  • 41. Koroidov, Sergey
    et al.
    Anderlund, Magnus F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Thapper, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Messinger, Johannes
    First turnover analysis of water-oxidation catalyzed by Co-oxide nanoparticles2015In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 8, no 8, p. 2492-2503Article in journal (Refereed)
    Abstract [en]

    Co-oxides are promising water oxidation catalysts for artificial photosynthesis devices. Presently, several different proposals exist for how they catalyze O2 formation from water. Knowledge about this process at molecular detail will be required for their further improvement. Here we present time-resolved 18O-labelling isotope-ratio membrane-inlet mass spectrometry (MIMS) experiments to study the mechanism of water oxidation in Co/methylenediphosphonate (Co/M2P) oxide nanoparticles using [Ru(bpy)3]3+ (bpy = 2,2'-bipyridine) as chemical oxidant. We show that 16O–Co/M2P-oxide nanoparticles produce 16O2 during their first turnover after simultaneous addition of H218O and [Ru(bpy)3]3+, while sequential addition with a delay of 3 s yields oxygen reflecting bulk water 18O-enrichment. This result is interpreted to show that the O–O bond formation in Co/M2P-oxide nanoparticles occurs via intramolecular oxygen coupling between two terminal Co–OHn ligands that are readily exchangeable with bulk water in the resting state of the catalyst. Importantly, our data allow the determination of the number of catalytic sites within this amorphous nanoparticular material, to calculate the TOF per catalytic site and to derive the number of holes needed for the production of the first O2 molecule per catalytic site. We propose that the mechanism of O–O bond formation during bulk catalysis in amorphous Co-oxides may differ from that taking place at the surface of crystalline materials.

  • 42.
    Kurz, Philipp
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Anderlund, Magnus F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Shaikh, Nizamuddin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Styring, Stenbjorn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Redox reactions of a dinuclear manganese complex: the influence of water2008In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 5, p. 762-770Article in journal (Refereed)
    Abstract [en]

    The redox properties of the dinuclear manganese complex [(Mn2L)-L-III,III(mu-OAC)(2)](+) (1) (where L is the trianion of the heptadentate ligand 2,6-bis{[(3,5-di-tert-butyl-2-hydroxybenzyl)(2-pyridylmethyl)amino]methy l)-4-methylphenol) were studied in acetonitrile solutions containing different concentrations of water. Electrochemical reactions as well as reactions with different chemical and photochemical redox reagents were monitored, using a variety of analytical techniques, namely cyclic voltammetry, UV/Vis spectroelectrochemistry, and EPR spectroscopy. We found that even small concentrations of water influence the compound's redox behaviour significantly, especially the oxidation reactions. As a consequence, the presence of water reduces the overall potential span needed to reach the highest oxidation state observed for 1 (M-2(III,IV)) from its most reduced state (Mn-2(II,II)) to about 1.1 V Higher oxidation states of I are stabilized, most likely by water coordination and the formation of mu-oxido bridge(s) between the two manganese atoms. For reducing conditions, an unprecedented 25-line EPR signal was observed, which might originate from reduced 1 in its Mn-2(II,II) or Mn-2(II,II) state after considerable ligand rearrangement. As complexes like I have been designed to act as potential water oxidation catalysts, the complicated redox- and ligand-exchange chemistry found for 1 in the presence of water, its intended substrate, might be exemplary for many of the dinuclear manganese compounds currently under investigation.

  • 43.
    Kurz, Philipp
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Berggren, Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Anderlund, Magnus F.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Oxygen evolving reactions catalysed by synthetic manganese complexes: A systematic screening2007In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 38, p. 4258-4261Article in journal (Refereed)
    Abstract [en]

    A set of six multinuclear manganese complexes was screened for the ability to catalyse reactions yielding O(2) under coherent experimental conditions; we identify a much larger number of manganese compounds than previously known that catalyse oxygen formation.

  • 44.
    Liu, Si
    et al.
    Shaanxi Normal Univ, Key Lab Macromol Sci Shaanxi Prov, Sch Chem & Chem Engn, Xian 710119, Shaanxi, Peoples R China.
    Lei, You-Jia
    Shaanxi Normal Univ, Key Lab Macromol Sci Shaanxi Prov, Sch Chem & Chem Engn, Xian 710119, Shaanxi, Peoples R China.
    Xin, Zhi-Juan
    Shaanxi Normal Univ, Key Lab Macromol Sci Shaanxi Prov, Sch Chem & Chem Engn, Xian 710119, Shaanxi, Peoples R China.
    Xiang, Rui-Juan
    Shaanxi Normal Univ, Key Lab Macromol Sci Shaanxi Prov, Sch Chem & Chem Engn, Xian 710119, Shaanxi, Peoples R China.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Thapper, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Wang, Hong-Yan
    Shaanxi Normal Univ, Key Lab Macromol Sci Shaanxi Prov, Sch Chem & Chem Engn, Xian 710119, Shaanxi, Peoples R China.
    Ligand modification to stabilize the cobalt complexes for water oxidation2017In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, no 50, p. 29716-29724Article in journal (Refereed)
    Abstract [en]

    Ligand modifications with electron-withdrawing and electron-donating groups were applied to afford three novel mononuclear cobalt-based catalysts [Co(TPA-R)]2+ (TPA = tris(2-pyridylmethyl) amine; R = tri-α F, 1; R = tri-αOMe, 2; R = mono-αF, 3) for water oxidation. Characterization of the catalysts shows that steric and electronic factors play important roles in inhibiting spontaneous intermolecular dimerization of two cobalt centers, and influence the catalytic behavior. Complex 1 exhibits the best catalytic ability and stability, showing a good efficiency with TOF of 6.03 ± 0.02 mol (O2)/(mol (cat)*s) in photo-induced water oxidation experiments using Ru (bpy)3 2+ as photosensitizer and Na2S2O8 as electron acceptor. The bulky electron donating groups in 2 led to degradation of the complex and formation of CoOx particles acting as the real catalyst. Electron-withdrawing substituents on the TPA ligand can stabilize the catalyst under both electrochemical and photo-induced conditions, with the enhancement increasing with the number of the electron-withdrawing groups. © 2017 Hydrogen Energy Publications LLC.

  • 45.
    Lomoth, Reiner
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Sjödin, Martin
    Huang, Ping
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Chemical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mimicking the electron donor side of Photosystem II in artificial photosynthesis.2006In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, p. 1-16Article in journal (Refereed)
  • 46.
    Magnuson, Ann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Anderlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Johansson, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Lindblad, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Lomoth, Reiner
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Polivka, Tomas
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Stensjö, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Sundström, Villy
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Biomimetic and Microbial Approaches to Solar Fuel Generation2009In: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 42, no 12, p. 1899-1909Article, review/survey (Refereed)
    Abstract [en]

    Photosynthesis is performed by a multitude of organisms, but in P nearly all cases, it is variations on a common theme: absorption of light followed by energy transfer to a reaction center where charge separation takes place, This initial form of chemical energy is stabilized by the biosynthesis of carbohydrates. To produce these energy-rich products, a substrate is needed that feeds in reductive equivalents, When photosynthetic microorganisms learned to use water as a substrate some 2 billion years ago, a fundamental barrier against unlimited use of solar energy was overcome. The possibility of solar energy use has inspired researchers to construct artificial photosynthetic systems that show analogy to parts of the intricate molecular machinery of photosynthesis. Recent years have seen a reorientation of efforts toward creating integrated light-to-fuel systems that can use solar energy for direct synthesis of energy-rich compounds, so-called solar fuels. Sustainable production of solar fuels is a long awaited development that promises extensive solar energy use combined with long-term storage. The stoichiometry of water splitting into molecular oxygen, protons, and electrons is deceptively simple; achieving it by chemical catalysis has proven remarkably difficult. The reaction center Photosystem II couples light-induced charge separation to an efficient molecular water-splitting catalyst, a Mn4Ca complex, and is thus an important template for biomimetic chemistry. In our aims to design biomimetic manganese complexes for light-driven water oxidation, we link photosensitizers and charge-separation motifs to potential catalysts in supramolecular assemblies. In photosynthesis, production of carbohydrates demands the delivery of multiple reducing equivalents to CO2. In contrast, the two-electron reduction of protons to molecular hydrogen is much less demanding. Virtually all microorganisms have enzymes called hydrogenases that convert protons to hydrogen, many of them with good catalytic efficiency. The catalytic sites of hydrogenases are now the center of attention of biomimetic efforts, providing prospects for catalytic hydrogen production with inexpensive metals. Thus, we might complete the water-to-fuel conversion: light + 2H(2)O -> 2H(2) + O-2 This reaction formula is to some extent already elegantly fulfilled by cyanobacteria and green algae, water-splitting photosynthetic microorganisms that under certain conditions also can produce hydrogen. An alternative route to hydrogen from solar energy is therefore to engineer these organisms to produce hydrogen more efficiently. This Account describes our original approach to combine research in these two fields: mimicking structural and functional principles of both Photosystem II and hydrogenases by synthetic chemistry and engineering cyanobacteria to become better hydrogen producers and ultimately developing new routes toward synthetic biology.

  • 47.
    Magnuson, Ann
    et al.
    Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University.
    Frapart, Yves
    Abrahamsson, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Horner, Olivier
    Åkermark, Björn
    Sun, Licheng
    Girerd, Jean-Jaques
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    A Biomimetic Model System for the Water Oxidizing Triad in Photosystem II1999In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 121, no 1, p. 89-96Article in journal (Refereed)
    Abstract [en]

    In plants, solar energy is used to extract electrons from water, producing atmospheric oxygen. This is conducted by Photosystem II, where a redox ”triad” consisting of chlorophyll, a tyrosine, and a manganese cluster, governs an essential part of the process. Photooxidation of the chlorophylls produces electron transfer from the tyrosine, which forms a radical. The radical and the manganese cluster together extract electrons from water, providing the biosphere with an unlimited electron source. As a partial model for this system we constructed a ruthenium(II) complex with a covalently attached tyrosine, where the photooxidized ruthenium was rereduced by the tyrosine. In this study we show that the tyrosyl radical, which gives a transient EPR signal under illumination, can oxidize a manganese complex. The dinuclear manganese complex, which initially is in the Mn(III)/(III) state, is oxidized by the photogenerated tyrosyl radical to the Mn(III)/(IV) state. The redox potentials in our system are comparable to those in Photosystem II. Thus, our synthetic redox “triad” mimics important elements in the electron donor ”triad” in Photosystem II, significantly advancing the development of systems for artificial photosynthesis based on ruthenium−manganese complexes.

  • 48.
    Magnuson, Ann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Krassen, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Stensjö, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Modeling Photosystem I with the alternative reaction center protein PsaB2 in the nitrogen fixing cyanobacterium Nostoc punctiforme2011In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1807, no 9, p. 1152-1161Article in journal (Refereed)
    Abstract [en]

    Five nitrogen fixing cyanobacterial strains have been found to contain PsaB2, an additional and divergent gene copy for the Photosystem I reaction center protein PsaB. In all five species the divergent gene, psaB2, is located separately from the normal psaAB operon in the genome. The protein, PsaB2, was recently identified in heterocysts of Nostoc punctiforme sp. strain PCC 73102. 12 conserved amino acid replacements and one insertion, were identified by a multiple sequence alignment of several PsaB2 and PsaB1 sequences. Several, including an inserted glutamine, are located close to the iron-sulfur cluster F(x) in the electron transfer chain. By homology modeling, using the Photosystem I crystal structure as template, we have found that the amino acid composition in PsaB2 will introduce changes in critical parts of the Photosystem I protein structure. The changes are close to F(x) and the phylloquinone (PhQ) in the B-branch, indicating that the electron transfer properties most likely will be affected. We suggest that the divergent PsaB2 protein produces an alternative Photosystem I reaction center with different structural and electron transfer properties. Some interesting physiologcial consequences that this can have for the function of Photosystem I in heterocysts, are discussed.

  • 49.
    Magnuson, Ann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Raleiras, Patricia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Laser flash photolysis induced electron transfer in the isolated uptake hydrogenase subunit HupS studied by EPR spectroscopy2014In: Journal of Biological Inorganic Chemistry, ISSN 0949-8257, E-ISSN 1432-1327, Vol. 19, no S2, p. 851-Article in journal (Other academic)
  • 50.
    Magnuson, Ann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Rova, Maria
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Fredriksson, P.-O.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Changes in the oxidation state of cytochrome b559 and tyrosine-D during in vivo photoactivation of photosystem II1998In: Photosynthesis: Mechanisms and Effects / [ed] Garab, G., Kluwer Academic Publishers, 1998, p. 1097-1100Conference paper (Refereed)
123 1 - 50 of 106
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