1,721,001 research outputs found
Metallacrowns of α-picolinehydroxamate and Cu2+, Ni2+ or Zn2+: self-assembly in solution
No full textDoes the reduction of c heme trigger the conformational change of crystalline nitrite reductase?
No full textThe structures of nitrite reductase from Paracoccus denitrificans GB17 (NiR-Pd) and Pseudomonas aeruginosa (NiR-Pa) have been described for the oxidized and reduced state (Fulop, V., Moir, J. W. B., Ferguson, S. J., and Hajdu, J. (1995) Cell 81, 369-377; Nurizzo, D., Silvestrini, M. C., Mathieu, M., Cutruzzola, F., Bourgeois, D., Fulop, V., Hajdu, J., Brunori, M., Tegoni, M., and Cambillau, C. (1997) Structure 5, 1157-1171; Nurizzo, D., Cutruzzola F., Arese, M., Bourgeois, D., Brunori, M., Cambillau, C., and Tegoni, M. (1998) Biochemistry 37, 13987-13996). Major conformational rearrangements are observed in the extreme states although they are more substantial in NiR-Pd. The four structures differ significantly in the c heme domains. Upon reduction, a His(17)/ Met(106) heme-ligand switch is observed in NiR-Pd together with concerted movements of the Tyr in the distal site of the d(1) heme (Tyr(10) in NiR-Pa, Tyr(25) in NiR-Pd) and of a loop of the c heme domain (56-62 in NiR-Pa, 99-116 in NiR-Pd). Whether the reduction of the c heme, which undergoes the major rearrangements, is the trigger of these movements is the question addressed by our study. This conformational reorganization is not observed in the partially reduced species, in which the c heme is partially or largely (15-90%) reduced but the d(1) heme is still oxidized. These results suggest that the d(1) heme reduction is likely to be responsible of the movements. We speculate about the mechanistic explanation as to why the opening of the d(1) heme distal pocket only occurs upon electron transfer to the d(1) heme itself, to allow binding of the physiological substrate NO2- exclusively to the reduced metal center
Copper(II) 15-Metallacrown-5 complexes of (S)-α-alaninehydroxamic acid with europium(III) and gadolinium(III)
No full textFormation thermodynamics of copper(II) metallacrowns with alpha-, beta- and gamma-aminohydroxamic acids in aqueous solution
No full textSolution equilibria of copper(II) 15-metallacrown-5 complexes of (S)-alpha-alaninehydroxamic acid with lantanides(III)
No full textMetallacrowns of copper(II) and aminohydroxamates: Thermodynamics of self assembly and host–guest equilibria
No full textMetallacrowns (MCs) of copper(II) and aminohydroxamic acids have been extensively studied during the past few decades. Although their discovery dates back more than twenty years, systematic studies on the thermodynamics of self assembly of MCs and of their capability to act as guests for anions and cations are quite recent. This review focuses on the solution studies of these metallamacrocycles and, in particular, the following aspects are discussed: (i) the thermodynamics of self-assembly of 12-MC-4 complexes; (ii) the thermodynamics of self-assembly and core metal substitution of 15-MC-5 species; (iii) the thermodynamics of host–guest equilibria between 15-MC-5 complexes and anions. The overall thermodynamic parameters for the formation of a wide number of 12-MC-4 species of α-, β- and γ-aminohydroxamates are discussed together with the most relevant structural, spectroscopic and reactivity features reported in the literature for copper(II) metallacrowns. These data provide a thermodynamic quantitation of the “metallacrowns structural paradigm”, and show the possibility to devise new MCs with desired stabilities in different medium conditions through an appropriate choice of metal coordinating moieties and ligand dimensions. The thermodynamics of self-assembly of 15-MC-5 is discussed for Ca2+ and Ln3+ as core metals, and the overall formation constants are used to evaluate the copious literature data regarding the stability of these species in solution. The relative stability of 15-MC-5 complexes of different Ln3+ ions is also discussed, showing the extraordinary capability of these complexes to discriminate different Ln3+ ions on the basis of their dimensions. Finally, the thermodynamics of host–guest equilibria of 15-MC-5 complexes as receptors for carboxylates is presented: the binding affinities of different carboxylates for the 15-MC-5 species with Ln3+ as the core metal are discussed on the basis of guests hydrophobicity, dimension and basicity, and in terms of core metal Lewis acidity
Unespected 12-metallacrown-4 in the speciation of copper(II)/(S)-glutamic-gamma-hydroxamic acid system
No full textStructure and Solution Self-Assembly Equilibria of Copper(II) Metallacrowns of Aminohydroxamic Acids
No full textElectrochemical study of the intermolecular electron transfer to Pseudomonas aeruginosa cytochrome cd1 nitrite reductase
No full textThe kinetics of electron transfer reaction between cytochrome cd(1) nitrite reductase (NiR) from Pseudomonas aeruginosa and various physiological/non physiological redox partners was investigated using cyclic voltammetry at the pyrolytic graphite electrode. While NiR did not exchange electron with the electrode, cytochrome c(551) and azurin, both from Ps. aeruginosa, behaved as fast electrochemical systems. The intermolecular electron transfers between NiR and cytochrome c(551) or azurin as electron shuttles, in the presence of nitrite, were studied. Second order rate constants of 2 x 10(6) and 1.4 x 10(5) M-1 s(-1) are calculated for cytochrome c(551) and azurin, respectively. The dependence of the second-order rate constant on ionic strength and pH is discussed. Finally, the effect of the global charge of the electron shuttles was explored using differently charged species (proteins or small ions). The experimental results suggest involvement of polar interactions as well as of hydrophobic contacts in the protein recognition prior to the intermolecular electron transfer. As the cross-reaction between Ps. nautica cytochrome c(552) and Ps. aeruginosa NiR was shown to be as efficient as the catalytic reaction involving the physiological partners, it is concluded to a 'pseudo-specificity' in the recognition between NiR and the electron donor
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