| 1. |
- Huang, Ping, et al.
(författare)
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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-bipyridine
- 2002
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 91:1, s. 159-172
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
- Sun, Licheng C., et al.
(författare)
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Towards an artificial model for Photosystem II : a manganese(II,II) dimer covalently linked to ruthenium(II) tris-bipyridine via a tyrosine derivative
- 2000
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 78:1, s. 15-22
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Tidskriftsartikel (refereegranskat)abstract
- In order to model the individual electron transfer steps from the manganese cluster to the photooxidized sensitizer P-680(+) in Photosystem II (PS II) in green plants, the supramolecular complex 4 has been synthesized. In this complex, a ruthenium(II) tris-bipyridine type photosensitizer has been linked to a manganese(II) dimer via a substituted L-tyrosine, which bridges the manganese ions. The trinuclear complex 4 was characterized by electron paramagnetic resonance (EPR) and electrospray ionization mass spectrometry (ESI-MS). The excited state lifetime of the ruthenium tris-bipyridine moiety in 4 was found to be about 110 ns in acetonitrile, Using flash photolysis in the presence of an electron acceptor (methylviologen), it was demonstrated that in the supramolecular complex 4 an electron was transferred from the excited state of the ruthenium tris-bipyridine moiety to methylviologen, forming a methylviologen radical and a ruthenium(III) tris-bipyridine moiety. Next, the Ru(III) species retrieved the electron from the manganese(II/II) dimer in an intramolecular electron transfer reaction with a rate constant k(ET)>1.0X10(7) s(-1), generating a manganese(II/III) oxidation state and regenerating the ruthenium(II) photosensitizer. This is the first example of intramolecular electron transfer in a supramolecular complex, in which a manganese dimer is covalently linked to a photosensitizer via a tyrosine unit, in a process which mimics the electron transfer on the donor side of PS II.
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| 4. |
- Olofsson, J., et al.
(författare)
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Picosecond Kerr-gated time-resolved resonance Raman spectroscopy of the Ru(phen)(2)dppz (2+) interaction with DNA
- 2002
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 91:1, s. 286-297
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the basis of the 'light-switch' effect, the solvent dependence of the Kerr-gated picosecond-time resolved resonance Raman (TR3) spectra of [Ru(bpy),dppz](2+), [Ru(phen)(2)dppz](2+), and the modified complex [Ru(phen)(2)cpdppzOMe](2+) and a dimer [mu-C4(cpdppz)(2)-(phen)(4)Ru-2](4+) were studied. The investigation focussed on comparing the behaviour of [Ru(phen)(2)dppz](2+) in acetonitrile, ethanol, H2O, D2O, and DNA. The data are consistent with a model wherein excitation induces metal-to-ligand charge transfer (MLCT) to any of the ligands (termed the 'precursor' state) which, by interligand electron transfer (ILET), produces an excited state localised on the dppz ligand, MLCT1. In water this state relaxes with a characteristic time of similar to6 ps to a non-emissive state (MLCT2). The TR3 spectra in water, acetonitrile and DNA are all distinctly different. However. the early (4 ps) water spectrum resembles the spectrum in DNA. This interesting observation suggests that the DNA-bound excited state of the complex can be thought of as a model for the initial, poorly solvated state in water.
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| 5. |
- Arkhypchuk, Anna I., et al.
(författare)
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Investigation of the demetallation of 10-aryl substituted synthetic chlorins under acidic conditions
- 2020
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Ingår i: Journal of Inorganic Biochemistry. - : ELSEVIER SCIENCE INC. - 0162-0134 .- 1873-3344. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- The acidic demetallation of a series of sparsely substituted Zn(II) chlorins is reported. The chlorins were functionalized in the 10-position with substituents ranging from strongly electron donating mesityl and p-methoxyphenyl to electron-withdrawingp-nitrophenyl and pentafluorophenyl groups. The demetallation kinetics were investigated using UV-Visible absorption spectroscopy. Demetallation was carried out by exposing the metallochlorins dissolved in CH2Cl2 to an excess of trifiuoroacetic acid. Reasonable correlation was found between the Hammett constant of the 10-substituent and the rate constant of the loss of the metal ion. The largest differences were observed between the p-methoxyphenyl and p-nitrophenyl-substituted Zn(II) chlorins, undergoing loss of Zn(II) with pseudo first order rate constants of 0.0789 x 10(-3) and 3.70 x 10(-3) min(-1), respectively. Taken together, these data establish the dramatic influence even subtle changes can have in altering the electronic properties of chlorins, which in turn impacts metallochlorin function.
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| 6. |
- Aureliano, M., et al.
(författare)
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Decavanadate in vitro and in vivo effects : facts and opinions
- 2014
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 137, s. 123-130
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Tidskriftsartikel (refereegranskat)abstract
- This review covers recent advances in the understanding of the in vitro and in vivo effects of decavanadate, (V10O28)(6-), particularly in mitochondria. In vivo toxicological studies involving vanadium rarely account for the fact that under physiological conditions some vanadium may be present in the form of the decavanadate ion, which may behave differently from ortho- and metavanadates. It has for example been demonstrated that vanadium levels in heart or liver mitochondria are increased upon decavanadate exposure. Additionally, in vitro studies have shown that mitochondrial depolarization (IC50, 40 nM) and oxygen consumption (IC50, 99 nM) are strongly affected by decavanadate, which causes reduction of cytochrome b (complex III). We review these recent findings which together suggest that the observed cellular targets, metabolic pathway and toxicological effects differ according to the species of vanadium present. Finally, the toxicological effects of decavanadate depend on several factors such as the mode of administration, exposure time and type of tissue. (C) 2014 Elsevier Inc. All rights reserved.
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| 7. |
- Blomberg, Margareta R. A., 1946-, et al.
(författare)
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Reduction of molecular oxygen in flavodiiron proteins - Catalytic mechanism and comparison to heme-copper oxidases
- 2024
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 255
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Tidskriftsartikel (refereegranskat)abstract
- The family of flavodiiron proteins (FDPs) plays an important role in the scavenging and detoxification of both molecular oxygen and nitric oxide. Using electrons from a flavin mononucleotide cofactor molecular oxygen is reduced to water and nitric oxide is reduced to nitrous oxide and water. While the mechanism for NO reduction in FDPs has been studied extensively, there is very little information available about O2 reduction. Here we use hybrid density functional theory (DFT) to study the mechanism for O2 reduction in FDPs. An important finding is that a proton coupled reduction is needed after the O2 molecule has bound to the diferrous diiron active site and before the O–O bond can be cleaved. This is in contrast to the mechanism for NO reduction, where both N–N bond formation and N–O bond cleavage occurs from the same starting structure without any further reduction, according to both experimental and computational results. This computational result for the O2 reduction mechanism should be possible to evaluate experimentally. Another difference between the two substrates is that the actual O–O bond cleavage barrier is low, and not involved in rate-limiting the reduction process, while the barrier connected with bond cleavage/formation in the NO reduction process is of similar height as the rate-limiting steps. We suggest that these results may be part of the explanation for the generally higher activity for O2 reduction as compared to NO reduction in most FDPs. Comparisons are also made to the O2 reduction reaction in the family of heme‑copper oxidases.
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| 8. |
- Blomberg, Margareta R. A.
(författare)
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The mechanism for oxygen reduction in the C family cbb(3) cytochrome c oxidases - Implications for the proton pumping stoichiometry
- 2020
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 203
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Tidskriftsartikel (refereegranskat)abstract
- Cytochrome c oxidases (CcOs) couple the exergonic reduction of molecular oxygen to proton pumping across the membrane in which they are embedded, thereby conserving a significant part of the free energy. The A family CcOs are known to pump four protons per oxygen molecule, while there is no consensus regarding the proton pumping stoichiometry for the C family cbb(3) oxidases. Hybrid density functional theory is used here to investigate the catalytic mechanism for oxygen reduction in cbb(3) oxidases. A surprising result is that the barrier for O-O bond cleavage at the mixed valence reduction level seems to be too high compared to the overall reaction rate of the enzyme. It is therefore suggested that the O-O bond is cleaved only after the first proton coupled reduction step, and that this reduction step most likely is not coupled to proton pumping. Furthermore, since the cbb3 oxidases have only one proton channel leading to the active site, it is proposed that the activated E-H intermediate, suggested to be responsible for proton pumping in one of the reduction steps in the A family, cannot be involved in the catalytic cycle for cbb(3), which results in the lack of proton pumping also in the E to R reduction step. In summary, the calculations indicate that only two protons are pumped per oxygen molecule in cbb(3) oxidases. However, more experimental information on this divergent enzyme is needed, e.g. whether the flow of electrons resembles that in the other more well-studied CcO families.
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| 9. |
- Blomberg, Margareta R. A.
(författare)
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The structure of the oxidized state of cytochrome c oxidase - experiments and theory compared
- 2020
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 206
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Tidskriftsartikel (refereegranskat)abstract
- Cytochrome c oxidase (CcO), the terminal enzyme in the respiratory chain, reduces molecular oxygen to water. Experimental data on the midpoint potentials of the heme iron/copper active site cofactors do not match the overall reaction energetics, and are also in conflict with the observed efficiency of energy conservation in CcO. Therefore it has been postulated that the ferric/cupric intermediate (the oxidized state) exists in two forms. One form, labelled O-H, is presumably involved during catalytic turnover, and should have a high Cu-B midpoint potential due to a metastable high energy structure. When no more electrons are supplied, the O-H state supposedly relaxes to the resting form, labelled O, with a lower energy and a lower midpoint potential. It has been suggested that there is a pure geometrical difference between the O-H and O states, obtained by moving a water molecule inside the active site. It is shown here that the difference between the two forms of the oxidized state must be of a more chemical nature. The reason is that all types of geometrically relaxed structures of the oxidized intermediate have similar energies, all with a high proton coupled reduction potential in accordance with the postulated O-H state. One hypothesized chemical modification of the O-H state is the transfer of an extra proton, possibly internal, into the active site. Such a protonated state has several properties that agree with experimental data on the relaxed oxidized state, including a decreased midpoint potential.
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| 10. |
- Brindell, M, et al.
(författare)
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Mechanistic information on the reaction of cis- and trans-[RuCl2(DMSO)(4)] with d(T(2)GGT(2)) derived from MALDI-TOF and HPLC studies
- 2004
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 1873-3344 .- 0162-0134. ; 98:8, s. 1367-1377
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Tidskriftsartikel (refereegranskat)abstract
- Reactions of trans and cis isomers of the Ru-II complex [RuCl2(DMSO)(4)] with single-stranded hexanucleotide d(T(2)GGT(2)) were studied in aqueous solutions in the absence and presence of excess chloride by high performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionisation time of flight mass spectrometry (MALDI-TOF MS). Despite the different reactive species formed from the two isomers in aqueous solution, similar reaction products are obtained in their interaction with d(T(2)GGT(2)). Both [RuCl2(DMSO)(4)] isomers bind to the oligonucleotide in the bidentate mode to form thermodynamically stable bis-guanosine adducts, Ru(G-N7)(2), Significant differences were observed in the reaction rates, however the reaction with trans[RuCl2(DMSO)(4)] is ca. 5-10 times faster in comparison to that observed for the cis analogue. This difference is interpreted in terms of different rate-limiting steps for the trans and cis complexes, respectively. It is suggested that the rate of the reaction with the trans isomer is controlled by dissociation of a Cl- ligand from the initially formed trans, cis, cis-[RuCl2(DMSO)(2)(H2O)(2)]. In the contrast, release of a dimethyl sulfoxide molecule from the reactive species cis,fac-[RuCl2(DMSO)(3)(H2O)] is likely to be rate limiting for the cis analogue. Significant influence of electrostatic interactions on the reaction rate was observed for the trans isomer. Mechanistic interpretation of the observed reactivity trends based on data obtained from UV-Vis spectroscopy, HPLC and MALDI-TOF MS studies is presented and discussed within the paper.
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