P.R. Bontchev

Linear-dichroic infrared spectral analysis of Cu(I)–homocysteine complex

The interaction between homocysteine (HCysSH) and Cu(II) leads to the formation of a yellow complex [Cu(I)(HCysS-SCysH)2]Cl (1) after redox processes in the Cu(II)-homocysteine system resulting in dimerization of the ligand and formation of a mononuclear Cu(I) complex with two dimers. The structure of (1) was obtained by IR-LD spectral analysis of a solid amorphous sample oriented in nematic liquid crystal medium. The original technique for orientation developed here and the polarized IR spectra thus obtained, permit the determination of the complexation sites and coordination mode of diamagnetic complexes. In the complex (1), Cu(I) is coordinated through the two O atoms of one COO- group of each of the ligands and the metal ion coordination sphere represents a distorted tetrahedron.

Chromium(V) coordination chemistry

Mecanisme de formation des complexes de Cr(V). Structure et liaison. Photochimie de la reduction de Cr(VI)

Catalytic reactions-I Mechanisms.

The mechanisms of some reactions used in catalytic analysis are discussed. The knowledge of the mechanism of a catalytic reaction can help in the development of new catalytic reactions and the choice of optimal conditions, and to show the possibilities for further increases in sensitivity.

Catalytic reactions—II: Activation

The activation of the homogeneous catalytic reactions used in analysis is discussed. The use of activators in catalytic methods permits increase in their sensitivity by 2-4 orders of magnitude and improvement in their selectivity as well. Many different mechanisms of activation are discussed and used as illustrations of the principles for choice of an appropriate activator.

Copper(II) interaction and complexation with 1-[2(S)-3-mercapto-3-methylpropionyl]-L-proline (captopril)

The redox processes between copper(II) and captopril, H2L, in a molar ratio 1:2 were studied. Copper(II) is reduced to Cu(I), which forms with the excess of captopril, a yellow complex, reoxidized by oxygen to a green complex CuIIL.H2O. The latter is studied using spectral (UV-Vis, IR), magnetochemical, EPR, DTA, and TGA methods. The coordination sites of the ligand are COO−, CO, and S−. In a solid state the complex exists mainly as a dimer, the bridging realized by the carboxylate group of the ligand. The complex is soluble in pyridine, forming the mononuclear adduct CuCapt(py)3.

Pulsed laser photolysis of the PtCl62−—creatinine system in methanol

Abstract The pulsed laser photolysis (excimer laser, XeCl; 308 nm) of the PtCl 6 2− —creatinine—methanol system was studied. The formation of an intermediate Pt III species (PtCl 5 2− cr, where cr = creatinine) was demonstrated and its decay kinetics were examined. Some kinetic and thermodynamic data of the photoinduced reaction were determined. The photolysis of the same system using stationary irradiation was also investigated allowing the end product of the reaction to be determined.

Mechanism of silver(I) catalysed sulphanilic acid oxidation by persulphate

The mechanism of sulphanilic acid oxidation with persulphate catalysed by silver(I) is reported. The first rate-limiting step of the process is a second-order reaction giving the active intermediates Ag(II) and SO4− which further oxidize sulphanilic acid. The uncatalysed reaction proceeds in a similar way with a second order interaction between the substrate and the oxidant. It is supposed that the second-order reactions of persulphate with the substrate (the uncatalysed reaction) or with the catalyst (the catalytic reaction) are processes of nucleophilic substitution on oxygen.

Copper–homocysteine complexes and potential physiological actions

During the last 2 decades it was proposed that atherogenesis was closely related to the homeostasis of homocysteine (hCys) and/or copper. We hypothesized that the physiological action of hCys may be connected with its ability to form complexes with Cu. Our results showed the presence of two different Cu-hCys complexes. At a molar ratio Cu:hCys 1:1, a blue complex most probably consistent with a tentative dimeric Cu(II)(2)(hCys)(2)(H(2)O)(2) formula was formed, with tetrahedral Cu coordination and anti-ferromagnetic properties. The redox processes between Cu(II) and hCys, in a molar ratio > or =1:3 led to formation of a second yellow Cu(I)hCys complex. Both Cu-hCys complexes affected the metabolism of extracellular thiols more than hCys alone and inhibited glutathione peroxidase-1 activity and mRNA abundance. The biological action of hCys and Cu-hCys complexes involved remodeling and phosphorylation of focal adhesion complexes and paxillin. The adhesive interactions of monocytes with an endothelial monolayer led to the redistribution of both paxillin and F-actin after all treatments, but the diapedesis of monocytes through endothelial cell monolayer was both greater and faster in the presence of the tentative Cu(II)(2)(hCys)(2)(H(2)O)(2) complex. Together, these observations suggest that Cu-hCys complexes actively participate in the biochemical responses of endothelial cells that are involved in the aethiopathogenesis of atherosclerosis.

Monomeric Pt(II) and Pd(II) complexes with Creatinine. Crystal structure of tetrakis-(Creatinine) platinum(II) diperchlorate

Abstract Pt(II) and Pd(II) complexes with creatinine, C3H2N2(O)(CH3)NH2, were synthesized. Potentiometric and IR spectroscopic analyses were carried out. A model for the coordination of the ligands to the central atoms was confirmed by X-ray structural investigation of Pt(creat)4(ClO4)2. The compound [Pt(C4H7N3O)(ClO4)2] crystallizes in the monoclinic crystal system, space group C2/c, a = 15.748(5), b = 15.763(7), c = 24.843(8) A, β = 106.84(4)°, V = 5902 A3, Z = 8. The refinement of the structure by the least-squares method gave R = 0.051 and Rw = 0.054 for 1527 observed reflections with I > 2σ(I). The structure consists of Pt(creat)42+ complex cations, possessing approximate D2 symmetry and rotationally disordered perchlorate anions. The Pt atom is square-planarly coordinated by the endocyclic N atoms of four creatinine ligands. The PtN bond lengths range from 2.00(2) to 2.03(1) A and the NPtN angles from 88.4(9) to 91.8(8)°. The ligands are almost planar and tilted towards the PtN4-plane by 82.1(8)–93.5(9)°.

Coordination chemistry of N6 macrocycles

Abstract The complexation ability of saturated and unsaturated N 6 macrocycles towards different metal ions, synthesis, thermodynamics and structure of the metal complexes (mono- and dinuclear) formed are discussed. The data concerning protonation processes of the saturated azamacrocycles, i.e. cyclic polyamines and their ability to react selectively with some anions (host-guest chemistry) are also reviewed.