Tang Wenxia

Synthesis, structure and properties of an imidazolate bridged copper, zinc binuclear complex:A model compound for Cu,Zn-SOD

Abstract A new imidazolate bridged Cu 2+ , Zn 2+ binuclear complex [(dtma) CuImZn (dtma)]ClO 4 · 2.5H 2 O taken as an active site model for Cu,Zn-SOD has been synthesized and its crystal structure has been determined. All the bond lengths, bond angles and the distance between copper and zinc atoms in the CuImZn core of the model complex are close to those in Cu,Zn-SOD. ESR parameters of the model complex as a function of pH show that the imidazolate bridge is stable in the pH range 10–12, and is broken on the zinc side at pH ∼ 9. With decreasing pH, the imidazole is released at pH ∼ 4 and the dtma ligand dissociates from the copper-containing fragment at pH ∼ 2.4.

Studies on the interaction between cytochrome c and cis-PtCl2(NH3)2☆

The interactions between cytochrome c and cis-PtCl2(NH3)2 under different conditions are reported. It is found that cis-PtCl2(NH3)2 is highly selective to bind to sulfur-containing Met residue and the interaction mode of cis-PtCl2(NH3)2 with cytochrome c is different from that of PtCl4(2-) with cytochrome c. The binding sites of platinum complex in the protein were characterized by analysis of the molar ratio of two metal atoms (Pt and Fe), 1H NMR spectra, UV-vis spectra, and differential pulse voltammetry.

The structure and magnetic properties of μ3-oxotriiron(III) complex [Fe3O(OBZ)6(CH3OH)3] (NO3)(CH3OH)2 (HOBZ = benzoic acid)

Abstract A new μ3-O triiron(III) complex [Fe3O(OBZ)6(CH3OH)3](NO3)(CH3OH)2 (HOBZ = benzoic acid) has been synthesized, its structure has been determined and variable temperature magnetic susceptibility has been measured. In the cation of the complex, three iron atoms form an equilateral triangle with μ3-O in the centre. An intramolecular antiferromagnetic exchange interaction occurs with J = −27.06 cm−1, and a weaker intermolecular antiferromagnetic exchange interaction occurs with zJ′ = −2.59 cm−1.

Structure of an imidazolate-bridged zinc dimer with tris(2-pyridyl)-methylamine ligand and magnetic properties of its copper dimer analogue

Abstract The compound [(tmpa)Zn(im)Zn(tmpa)](ClO 4 ) 3 [where tmpa is tris(2-pyridyl)-methylamine and im is imidazolate anion] was synthesized, and its crystal structure was determined by X-ray diffraction methods. The structure consists of a dimeric complex bridged by the deprotonated imidazole. The geometry of the coordination polyhedron around the zinc(II) ions is very near to trigonal bipyramidal. The electronic spectrum indicates the corresponding copper(II) dimer has the same geometrical structure as the zinc(II) dimer. Its ESR powder X-band spectrum shows features typical of an S = 1 system. Variable-temperature (4.2–300 K) magnetic susceptibility data give the antiferromagnetic interaction parameter J = −32.0 cm −1 . This behaviour is best accounted for by a super-exchange mechanism involving σ-exchange pathways.

Structure and magnetic exchange of an imidazolate-bridged copper dimer: [(dtma)Cu(im)Cu(dtma)]ClO4·2.5H2O

Abstract The compound of the formula [(dtma)Cu(im)Cu(dtma)]ClO4·2.5H2O (where dtmaH is 4-diethylenetriamineacetic acid and im is the imidazole anion) was synthesized and its crystal structure determined by X-ray diffraction methods. The structure consists of a dimeric complex bridged by the deprotonated imidazole. The geometries of the coordination polyhedron around the copper(II) ions are very near to tetragonal pyramid. The X-band ESR powder spectrum shows broad ΔM = 1 and weak ΔM = 2 absorptions. Variable-temperature (4.2–300 K) magnetic susceptibility data gave the antiferromagnetic interaction parameters J = −37 cm−1. This behaviour is best accounted for by a superexchange mechanism involving σ- and π-exchange pathways.

Vibrational Spectra and Normal Coordinate Analysis for an Imidazole Bridged Copper, Zinc Binuclear Complex

Abstract The normal coordinate analysis of a model compound for Cu, Zn-SOD: [(dtma)CuImZn(dtma)]CIO4 · 2.5H2O (where dtma = 4-diethylenetriamineacctate; Im = imidazolate) has been carried out by using a Urey-Bradley force field. According to the molecular structure, 240 internal coordinates were established and 174 theoretical vibrational frequencies were calculated. Due to introducing an appropriate set of internal coordinates and force constants in the course of calculation, the calculated frequencies agree well with the observed values, with the average difference 4.40cm−1 and the maximum deviation 24.2cm−1 between them, although the structure of the title compound is complicated. Some structural and spectral properties are here discussed.

Syntheses and Characterization of Coenzyme B12 Analogues Containing 2′-Deoxynucleosede

Abstract A new vitamin B12 coenzyme analogue 2′, 5′-dideoxyuridinyl-cobalamin and two other 2′, 5′-dideoxyribonucleosideccbalamins of adenosyl and thymidyl were synthesized by an improved method. It consists in direct tosylation of the nucleoside, followed by reaction with reduced hydroxocobalamin (vitamin B12a). All the three derivatives were characterized by UV -Vis and 1H NMR spectroscopy.

Vibrational spectra and normal coordinate analysis for cis-diamminetetrachloroplatinum

Abstract The normal coordinate analysis of cis -diamminetetrachloroplatinum has been carried out by using a modified Urey—Bradley force field. According to the molecular structure, 45 internal coordinates were established and 33 theoretical vibrational frequencies were calculated. Due to considering the interaction between non-neighbouring stretching vibrations and between bending vibrations and introducing an appropriate set of internal coordinates in the course of calculation, the calculated frequencies agree well with the observed values, with an average difference 3.61 cm −1 between them. The rationality and the reliability of the results are discussed and the questionable empirical assignment of ν(PtCl) in the literature is corrected.

Studies on the interaction between cytochrome c and [Pt-dien]2+☆

Abstract The reactions between cytochrome c and [Pt-dien] 2+ under different conditions are reported. It is found that the yield of modified protein derivatives as well as the likely binding sites for platinum complex in cytochrome c are sensitive to the reaction conditions. It is first reported that transition-metal complex [Pt-dien] 2+ can bind to Met 80 residue under mild conditions, which causes the FeS bond of ferricytochrome c to be broken. The binding sites of the platinum complex in the modified protein derivatives were identified by analysis of the molar ratio of the two metal atoms (Pt and Fe), 1 H NMR spectra, and UV-vis spectra.

Further studies on the interaction between cytochrome c and K2PtCl4

Abstract The products of the reaction of ferricytochrome c with K 2 PtCl 4 were separated and purified. Three kinds of cytochrome c derivatives—single-labeled monomer, triple-labeled dimer, and hexa-labeled trimer—were obtained. The binding sites of the platinum complex in these modified protein derivatives were identified by the measurement of the molecular weight, the analysis of the molar ratio of the two metal atoms (Pt and Fe), and the study of the reaction of the His-33 blocked cytochrome c with K 2 PtCl 4 .