| 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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| 11. |
- Chen, Shilu, et al.
(författare)
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Reaction mechanism of the binuclear zinc enzyme glyoxalase II : A theoretical study
- 2009
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 103:2, s. 274-281
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Tidskriftsartikel (refereegranskat)abstract
- The glyoxalase system catalyzes the conversion of toxic methylglyoxal to nontoxic d-lactic acid using glutathione (GSH) as a coenzyme. Glyoxalase II (GlxII) is a binuclear Zn enzyme that catalyzes the second step of this conversion, namely the hydrolysis of S-d-lactoylglutathione, which is the product of the Glyoxalase I (GlxI) reaction. In this paper we use density functional theory method to investigate the reaction mechanism of GlxII. A model of the active site is constructed on the basis of the X-ray crystal structure of the native enzyme. Stationary points along the reaction pathway are optimized and the potential energy surface for the reaction is calculated. The calculations give strong support to the previously proposed mechanism. It is found that the bridging hydroxide is capable of performing nucleophilic attack at the substrate carbonyl to form a tetrahedral intermediate. This step is followed by a proton transfer from the bridging oxygen to Asp58 and finally C–S bond cleavage. The roles of the two zinc ions in the reaction mechanism are analyzed. Zn2 is found to stabilize the charge of tetrahedral intermediate thereby lowering the barrier for the nucleophilic attack, while Zn1 stabilizes the charge of the thiolate product, thereby facilitating the C–S bond cleavage. Finally, the energies involved in the product release and active-site regeneration are estimated and a new possible mechanism is suggested.
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| 12. |
- Czapla-Masztafiak, Joanna, et al.
(författare)
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Mechanism of hydrolysis of a platinum(IV) complex discovered by atomic telemetry
- 2018
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Ingår i: Journal of Inorganic Biochemistry. - : ELSEVIER SCIENCE INC. - 0162-0134 .- 1873-3344. ; 187, s. 56-61
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Tidskriftsartikel (refereegranskat)abstract
- Herein we report on the hydrolysis mechanism of [Pt{N(p-HC6F4)CH2}(2)(NC5H5)(2)(OH)(2)], a platinum(IV) complex that exhibits anti-cancer properties. Atomic telemetry, an in situ technique based on electron structure sensitive X-ray spectroscopy, revealed that hydrolysis preceded any reduction of the metal center. The obtained results are complemented with F-19 NMR measurements and theoretical calculations and support the observation that this Pt-II complex does not reduce spontaneously to Ptll in HEPES buffer solution at pH 7.4 and after 24 h incubation. These results are of importance for the design of novel Pt-based coordination complexes as well as understanding their behavior under physiological conditions.
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| 13. |
- Das, Biswanath, et al.
(författare)
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A dinuclear zinc(II) complex of a new unsymmetric ligand with an N(5)0(2) donor set; A structural and functional model for the active site of zinc phosphoesterases
- 2014
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 132, s. 6-17
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Tidskriftsartikel (refereegranskat)abstract
- The dinuclear complex [Zn-2(DPCPMP)(pivalate)](C10(4)), where DPCPMP is the new unsymmetrical ligand [2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin2-y1)methyl)amino)acetic acid], has been synthesized and characterized. The complex is a functional model for zinc phosphoesterases with dinuclear active sites. The hydrolytic efficacy of the complex has been investigated using bis-(2,4-dinitrophenyl)phosphate(BDNPP), a DNA analog, as substrate. Speciation studies using potentiometric titrations have been performed for both the ligand and the corresponding dizinc complex to elucidate the formation of the active hydrolysis catalyst; they reveals that the dinuclear zinc(II) complexes, [Zn-2(DPCPMP)](2) and [Zn-2(DPCPMP)(OH)1 predominate the solution above pH 4. The relatively high pKa of 8.38 for water deprotonation suggests that a terminal hydroxide complex is formed. Kinetic investigations of BDNPP hydrolysis over the pH range 5.5-11.0 and with varying metal to ligand ratio (metal salt:ligand = 0.5:1 to 3:1) have been performed. Variable temperature studies gave the activation parameters triangle H double dagger = 95.6 kJ mol(-1), triangle S double dagger = 44.8 J mo1(-1) K-1, and 6,triangle G double dagger = 108.0 kJ mo1-1. The cumulative results indicate the hydroxido-bridged dinuclear Zn(II) complex [Zn-2(DPCPMP)(mu-OH)] (+) as the effective catalyst. The mechanism of hydrolysis has been probed by computational modeling using density functional theory (DFF). Calculations show that the reaction goes through one concerted step (S(N)2 type) in which the bridging hydroxide in the transition state becomes terminal and performs a nucleophilic attack on the BDNPP phosphorus; the leaving group dissociates simultaneously in an overall inner sphere type activation. The calculated free energy barrier is in good agreement with the experimentally determined activation parameters.
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| 14. |
- Das, Biswanath, et al.
(författare)
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A dinuclear zinc(II) complex of a new unsymmetric ligand with an N5O2 donor set; A structural and functional model for the active site of zinc phosphoesterases.
- 2014
-
Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 1873-3344 .- 0162-0134. ; 132:Online 13 August 2013, s. 6-17
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Tidskriftsartikel (refereegranskat)abstract
- The dinuclear complex [Zn2(DPCPMP)(pivalate)](ClO4), where DPCPMP is the new unsymmetrical ligand [2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino)acetic acid], has been synthesized and characterized. The complex is a functional model for zinc phosphoesterases with dinuclear active sites. The hydrolytic efficacy of the complex has been investigated using bis-(2,4-dinitrophenyl)phosphate (BDNPP), a DNA analog, as substrate. Speciation studies using potentiometric titrations have been performed for both the ligand and the corresponding dizinc complex to elucidate the formation of the active hydrolysis catalyst; they reveals that the dinuclear zinc(II) complexes, [Zn2(DPCPMP)](2+) and [Zn2(DPCPMP)(OH)](+) predominate the solution above pH4. The relatively high pKa of 8.38 for water deprotonation suggests that a terminal hydroxide complex is formed. Kinetic investigations of BDNPP hydrolysis over the pH range 5.5-11.0 and with varying metal to ligand ratio (metal salt:ligand=0.5:1 to 3:1) have been performed. Variable temperature studies gave the activation parameters ΔH(‡)=95.6kJmol(-1), ΔS(‡)=-44.8Jmol(-1)K(-1), and ΔG(‡)=108.0kJmol(-1). The cumulative results indicate the hydroxido-bridged dinuclear Zn(II) complex [Zn2(DPCPMP)(μ-OH)](+) as the effective catalyst. The mechanism of hydrolysis has been probed by computational modeling using density functional theory (DFT). Calculations show that the reaction goes through one concerted step (SN2 type) in which the bridging hydroxide in the transition state becomes terminal and performs a nucleophilic attack on the BDNPP phosphorus; the leaving group dissociates simultaneously in an overall inner sphere type activation. The calculated free energy barrier is in good agreement with the experimentally determined activation parameters.
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| 15. |
- Dimitrakopoulou, Anastasia, et al.
(författare)
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Synthesis, structure and interactions with DNA of novel tetranuclear, [Mn-4(II/II/II/IV)] mixed valence complexes
- 2008
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 1873-3344 .- 0162-0134. ; 102:4, s. 618-628
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of Mn(II) with phenoxyalkanoic acids and di-2-pyridyl ketone oxime (Hpko) leads to neutral tetranuclear complexes of the general formula Mn-4(O)(pko)(4)(phenoxyalkanoato)(4) (phenoxyalkanoic acids: H-mcpa = 2-methyl-4-chloro-phenoxy-acetic acid, H-2,4,5-T = 2,4.5-trichloro-phenoxy-acetic acid or H3,4-D = 3,4-dichloro-phenoxy-acetic acid). The compounds were synthesized by adding di2-pyridyl ketone oxime to MnCl2 in the presence of the sodium salts of the alkanoic acids in methanol. The crystal structure of Mn-4(II/II/ II/IV)(O)(pko)4(()2,4,5-T)(4) . 2.5CH(3)OH . 0.25H(2)O 1 shows that the complex consists of a [Mn-4( mu(4)-O)](8+) core with a Mn(IV) and 3 Mn(II) ions in octahedral environment and a mu(4)-O atom bridging the four manganese ions. Spectroscopic studies of the interaction of these tetranuclear clusters with DNA showed that these compounds bind to dsDNA. The binding strength of the Mn-4(II/II/II/ IV)(O)(pko)(4)(2,4,5-T)(4) complex for calf thymus DNA is equal to 1.1 X 10(4) M-1. Among the deoxyribonucleotides they bind preferentially to deoxyguanylic acid (dGMP). Competitive studies with ethidium bromide (EthBr) showed that the Mn-4(II/II/II/ IV)(O)(pko)(4)(2,4,.5-T)(4) complex exhibited the ability to displace the DNA-bound EthBr indicating that the complex binds to DNA via intercalation in strong competition with EthBr for the intercalative binding site. Additionally, DNA electrophoretic mobility experiments showed that all three complexes, at low cluster concentration, are obviously capable of binding to pDNA causing its cleavage (relaxation) at physiological pH and temperature. At higher cluster concentration, catenated dimer forms of pDNA was formed.
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| 16. |
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| 17. |
- Dong, Weibing, et al.
(författare)
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Preparation, structures and electrochemical property of phosphine substituted diiron azadithiolates relevant to the active site of Fe-only hydrogenases
- 2007
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 101:3, s. 506-513
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Tidskriftsartikel (refereegranskat)abstract
- Mono- and di-phosphine diiron azadithiolate complexes [{(mu-SCH2)(2)N(4-NO2C6H4)}Fe-2(CO)(5)(PMe3)] (2), [{(mu-SCH2)(2)N(4NO(2)C(6)H(4))} {Fe(CO)(2)L}(2)] (3, L = PMe3; 4, PMe2Ph) and the mu-hydride diiron complex [3(FeHFe)](+)[PF6](-) were prepared as biontimetic models of the active site of Fe-only hydrogenases. The complexes 2-4 and [3(FeHFe)](+)[PF6](-) were characterized by IR P-31, H-1 and C-13 NMR spectra and their molecular structures were determined by single crystal X-ray analyses. The PMe3 ligand in complex 2 lies on the basal position. The PMe3-disubstituted complex 3 exists as two configuration isomers, transoid basal/basal and apical/basal, in the crystalline state, while two PMe2Ph ligands of 4 are in an apical/basal orientation. The variable temperature P-31 NMR spectra of 2 and 3 were made to have an insight into the existence of the possible conformation isomers of 2 and 3 in solution. The [3(FeHFe)](+) cation possesses the sole transoid ba/ba geometry as other reported mu-hydride diiron analogues. The electrocatalytic property of {(mu-SCH2)(2)NC6H5}[Fe(CO)(2)PMe3](2) (5) was studied for proton reduction in the presence of HOAc.
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| 18. |
- Dyrssen, David, et al.
(författare)
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Complexation of aluminum with DNA.
- 1987
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Ingår i: Journal of inorganic biochemistry. - 0162-0134 .- 1873-3344. ; 29:1, s. 67-75
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Tidskriftsartikel (refereegranskat)abstract
- The extent of complexation of aluminum(III) with DNA (Calf thymus, Sigma type I) was estimated by means of two experimental techniques: potentiometric titration with a fluoride selective indicator electrode and dialysis followed by aluminum determination by graphite furnace AAS. Both types of experiments indicate that aluminum(III) is bound to DNA. The data are treated by assuming an ion exchange reaction with the phosphate diester groups. Using Rt to denote the concentration of these groups the values of log [AlMn-3R]/(Rt-3[AlMn-3R])[Al3+] decrease from approx. 7.6 to 5.6 when the concentration of sodium chloride is increased from 1 to 100 mM. In the pH range 4.5-5.5 the ion exchange constant increases approximately 0.5 log units. Dialysis gives lower values for the complex formation constant than potentiometry.
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| 19. |
- Flock, Ulrika, et al.
(författare)
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Exploring the terminal region of the proton pathway in the bacterial nitric oxide reductase
- 2009
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 103:5, s. 845-850
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Tidskriftsartikel (refereegranskat)abstract
- The c-type nitric oxide reductase (cNOR) from Paracoccus (P.) denitrificans is an integral membrane protein that catalyzes NO reduction; 2NO+2e(-)+2H(+)-->N(2)O+H(2)O. It is also capable of catalyzing the reduction of oxygen to water, albeit more slowly than NO reduction. cNORs are divergent members of the heme-copper oxidase superfamily (HCuOs) which reduce NO, do not pump protons, and the reaction they catalyse is non-electrogenic. All known cNORs have been shown to have five conserved glutamates (E) in the catalytic subunit, by P. denitrificans numbering, the E122, E125, E198, E202 and E267. The E122 and E125 are presumed to face the periplasm and the E198, E202 and E267 are located in the interior of the membrane, close to the catalytic site. We recently showed that the E122 and E125 define the entry point of the proton pathway leading from the periplasm into the active site [U. Flock, F.H. Thorndycroft, A.D. Matorin, D.J. Richardson, N.J. Watmough, P. Adelroth, J. Biol. Chem. 283 (2008) 3839-3845]. Here we present results from the reaction between fully reduced NOR and oxygen on the alanine variants of the E198, E202 and E267. The initial binding of O(2) to the active site was unaffected by these mutations. In contrast, proton uptake to the bound O(2) was significantly inhibited in both the E198A and E267A variants, whilst the E202A NOR behaved essentially as wildtype. We propose that the E198 and E267 are involved in terminating the proton pathway in the region close to the active site in NOR.
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| 20. |
- Fraqueza, Gil, et al.
(författare)
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Sarcoplasmic reticulum calcium ATPase interactions with decaniobate, decavanadate, vanadate, tungstate and molybdate
- 2012
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 107:1, s. 82-89
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Tidskriftsartikel (refereegranskat)abstract
- Over the last few decades there has been increasing interest in oxometalate and polyoxometalate applications to medicine and pharmacology. This interest arose, at least in part, due to the properties of these classes of compounds as anti-cancer, anti-diabetic agents, and also for treatment of neurodegenerative diseases, among others. However, our understanding of the mechanism of action would be improved if biological models could be used to clarify potential toxicological effects in main cellular processes. Sarcoplasmic reticulum (SR) vesicles, containing a large amount of Ca(2+)-ATPase, an enzyme that accumulates calcium by active transport using ATP, have been suggested as a useful model to study the effects of oxometalates on calcium homeostasis. In the present article, it is shown that decavanadate, decaniobate, vanadate, tungstate and molybdate, all inhibited SR Ca(2+)-ATPase, with the following IC(50) values: 15, 35, 50, 400 mu M and 45 mM, respectively. Decaniobate (Nb(10)), is the strongest P-type enzyme inhibitor, after decavanadate (V(10)). Atomic-absorption spectroscopy (AAS) analysis, indicates that decavanadate binds to the protein with a 1:1 decavanadate:Ca(2+)-ATPase stoichiometry. Furthermore, V10 binds with similar extension to all the protein conformations, which occur during calcium translocation by active transport, namely El, El P, E2 and E2P, as analysed by MS. In contrast, it was confirmed that the binding of monomeric vanadate (H(2)VO(4)(2-):V(1)) to the calcium pump is favoured only for the E2 and E2P conformations of the ATPase, whereas no significant amount of vanadate is bound to the E1 and E1P conformations. Scatchard plot analysis, confirmed a 1:1 ratio for decavanadate-Ca(2+)-ATPase, with a dissociation constant, k(d) of 1 mu M(-1). The interaction of decavanadate V(10)O(28)(6-) (V(10)) with Ca(2+)-ATPase is prevented by the isostructural and isoelectronic decaniobate Nb(10)O(28)(6-) (Nb(10)), whereas no significant effects were detected with ATP or with heparin, a known competitive ATP binding molecule, suggesting that V(10) binds non-competitively, with respect to ATP, to the protein. Finally, it was shown that decaniobate inhibits SR Ca(2+)-ATPase activity in a non competitive type of inhibition, with respect to ATP. Taken together, these data demonstrate that decameric niobate and vanadate species are stronger inhibitors of the SR calcium ATPase than simple monomeric vanadate, tungstate and molybdate oxometalates, thus affecting calcium homeostasis, cell signalling and cell bioenergetics, as well many other cellular processes. The ability of these oxometalates to act either as phosphate analogues, as a transition-state analogue in enzyme-catalysed phosphoryl group transfer processes and as potentially nucleotide-dependent enzymes modulators or inhibitors, suggests that different oxometalates may reveal different mechanistic preferences in these classes of enzymes. (C) 2011 Elsevier Inc. All rights reserved.
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| 21. |
- Glans, Lotta, et al.
(författare)
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Synthesis, characterization and antimalarial activity of new chromium arene-quinoline half sandwich complexes.
- 2011
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 1873-3344 .- 0162-0134. ; 105:7, s. 985-990
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Tidskriftsartikel (refereegranskat)abstract
- Organometallic analogs of chloroquine (CQ) are of interest as drug candidates that may be able to overcome the widespread chloroquine resistance developed by malaria parasites. Two new chromium arene CQ-analogs: [η(6)-N-(7-chloroquinolin-4-yl)-N'-(2-dimethylamino-methylbenzyl)-ethane-1,2-diamine]tricarbonylchromium 4 and [η(6)-N-(7-chloroquinolin-4-yl)-N'-(2-dimethylaminobenzyl)-ethane-1,2-diamine]tricarbonylchromium 9 have been synthesized and characterized. In addition, X-ray crystal structures of the intermediates (η(6)-benzyldimethylamine)tricarbonylchromium 2, [η(6)-2-((dimethylamino)methyl) benzaldehyde]tricarbonylchromium 3 and p-(η(6)-dimethylaminobenzaldehyde)tricarbonyl chromium 8 are reported. Compound 4 was more active than chloroquine against both CQ-sensitive and CQ-resistant strains of Plasmodium falciparum when antimalarial activity was tested in vitro. The activity of 4 against the CQ-resistant parasite strain was twice as high as for the organic ligand alone (IC(50) values of 33.9nM versus 63.1nM).
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| 22. |
- González-Mendoza, Victor M., et al.
(författare)
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Biochemical characterization of phospholipases C from Coffea arabica in response to aluminium stress
- 2020
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- Signal transduction in plants determines their successful adaptation to diverse stress factors. Our group employed suspension cells to study the phosphoinositide pathway, which is triggered by aluminium stress. We investigated about members of the PI-specific phospholipase C (PLC) family and evaluated their transcription profiles in Coffea arabica (Ca) suspension cells after 14 days of culture when treated or not with 100 μM AlCl3. The four CaPLC1-4 members showed changes in their transcript abundance upon AlCl3 treatment. The expression profiles of CaPLC1/2 exhibited a rapid and transitory increase in abundance. In contrast, CaPLC3 and CaPLC4 showed that transcript levels were up-regulated in short times (at 30 s), while only CaPLC4 kept high levels and CaPLC3 was reduced to basal after 3 h of treatment. CaPLC proteins were heterologously expressed, and CaPLC2 and CaPLC4 were tested for in vitro activity in the presence or absence of AlCl3 and compared to Arabidopsis PLC2 (AtPLC2). A crude extract was isolated from coffee cells. CaPLC2 showed a similar inhibition (30%) as in AtPLC2 and in the crude extract, while in CaPLC4, the activity was enhanced by AlCl3. Additionally, we visualized the yellow fluorescent protein PH domain of human PLCδ1 (YFP-PHPLCδ1) subcellular localization in cells that were treated or not with AlCl3. In non-treated cells, we observed a polar fluorescence signal towards the fused membrane. However, when cells were treated with AlCl3, these signals were disrupted. Finally, this is the first time that PLC activity has been shown to be stimulated in vitro by AlCl3.
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| 23. |
- Gorzsás, András, et al.
(författare)
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Speciation in Aqueous Vanadate – Ligand and Peroxovanadate – Ligand systems
- 2009
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 103:4, s. 517-526
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Tidskriftsartikel (refereegranskat)abstract
- In the present focused review, the speciation studies of aqueous vanadate-ligand (L) and peroxovanadate-L systems are addressed. The paper focuses solely on the systems studied at our department in the context of potential insulin-enhancing effects, including the following ligands: imidazole, alanylhistidine, alanylserine, lactate, picolinate, citrate, phosphate, maltol, and uridine. We summarise the results of detailed and thorough potentiometric (glass electrode) and 51V NMR (Bruker AMX-500 MHz) spectroscopic studies, performed at 25 °C in 0.150 M Na(Cl), a medium representing human blood. The importance of experimental conditions is discussed and illustrated. A detailed overview of our methodology, based on combining potentiometric and 51V integral and chemical shift data by means of the computer program LAKE, is also given. We list the important steps of equilibrium analysis and the kinds of information available from different sets of NMR spectra. The ligand picolinate is chosen to exemplify our working method, but conclusions are drawn from all systems, reviewing trends and common features. An overview of all systems is given in two tables, including e.g. types and number of species formed. Previously unpublished modelling results at physiological conditions are also shown for all peroxovanadate-ligand systems.
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| 24. |
- Hakobyan, Shoghik, et al.
(författare)
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Influence of Chelation Strength and Bacterial Uptake of Gallium Salicylidene Acylhydrazide on Biofilm Formation and Virulence by Pseudomonas aeruginosa
- 2016
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier. - 0162-0134 .- 1873-3344. ; 160, s. 24-32
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Tidskriftsartikel (refereegranskat)abstract
- Development of antibiotic resistance in bacteria causes major challenges for our society and has prompted a great need for new and alternative treatment methods for infection. One promising approach is to target bacterial virulence using for example salicylidene acylhydrazides (hydrazones). Hydrazones coordinate metal ions such as Fe(III) and Ga(III) through a five-membered and a six-membered chelation ring. One suggested mode of action is via restricting bacterial Fe uptake. Thus, it was hypothesized that the chelating strength of these substances could be used to predict their biological activity on bacterial cells. This was investigated by comparing Ga chelation strength of two hydrazone complexes, as well as bacterial Ga uptake, biofilm formation, and virulence in the form of production and secretion of a toxin (ExoS) by Pseudomonas aeruginosa. Equilibrium constants for deprotonation and Ga(III) binding of the hydrazone N′-(5-chloro-2-hydroxy-3-methylbenzylidene)-2,4-dihydroxybenzhydrazide (ME0329), with anti-virulence effect against P. aeruginosa, were determined and compared to bacterial siderophores and the previously described Ga(III) 2-oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (Ga-ME0163) and Ga-citrate complexes. In comparison with these two complexes, it was shown that the uptake of Ga(III) was higher from the Ga-ME0329 complex. The results further show that the Ga-ME0329 complex reduced ExoS expression and secretion to a higher extent than Ga-citrate, Ga-ME0163 or the non-coordinated hydrazone. However, the effect against biofilm formation by P. aeruginosa, by the ME0329 complex, was similar to Ga-citrate and lower than what has been reported for Ga-ME0163.
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| 25. |
- Hakobyan, Shoghik, et al.
(författare)
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Proton and gallium(III) binding properties of a biologically active salicylidene acylhydrazide
- 2014
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier. - 0162-0134 .- 1873-3344. ; 138, s. 9-15
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial biofilm formation causes a range of problems in our society, especially in health care. Salicylidene acylhydrazides (hydrazones) are promising antivirulence drugs targeting secretion systems used during bacterial infection of host cells. When mixed with the gallium ion they become especially potent as bacterial and biofilm growth-suppressing agents, although the mechanisms through which this occurs are not fully understood. At the base of this uncertainty lies the nature of hydrazone-metal interactions. This study addresses this issue by resolving the equilibrium speciation of hydrazone-gallium aqueous solutions. The protonation constants of the target 2-oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (ME0163) hydrazone species and of its 2,4,6-trihydroxybenzaldehyde and oxamic acid hydrazide building blocks were determined by UV-visible spectrophotometry to achieve this goal. These studies show that the hydrazone is an excessively strong complexing agent for gallium and that its antivirulence properties are predominantly ascribed to monomeric 1:1Ga-ME0163 complexes of various Ga hydrolysis and ME0163 protonation states. The chelation of Ga(III) to the hydrazone also increased the stability of the compounds against acid-induced hydrolysis, making this group of compounds very interesting for biological applications where the Fe-antagonist action of both Ga(III) and the hydrazone can be combined for enhanced biological effect.
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