КИНЕТИЧЕСКИЕ ХАРАКТЕРИСТИКИ ЗАМЫКАНИЯ И РАЗМЫКАНИЯ ЦИСТЕИНОВЫХ ЦИКЛОВ В КОМПЛЕКСАХ ХРОМА (III)

Abstract

The absorption spectra of chromium complexes (III) with a cysteine-containing mono- and bidentate coordinated amino acid were studied: [Cr(H₂L)₂Cl₂(H₂O)₂]⁺, [Cr(H₂L)₃Cl₂H₂O]⁺, [Cr(H₂L)₅Н₂О]³⁺, [Cr(H₂L)₆]³⁺, [Cr(HL)₃], [Cr(HL)(H₂L)₂ClH₂O]⁺, [Cr(H₂L)₂(HL)₂]⁺, [Cr(H₂L)₄НL]²⁺. In the electronic absorption spectrum there are three bands of d-d transitions, that allowed at spin -⁴T₁g ← ⁴A₂g, ⁴T₂g ← 4A2g, ⁴T₁g (P) ←⁴A₂g.. Parameters of the crystal field were calculated. It is shown that in the process of opening cycles cysteine complex [Cr(HL)₃], molar absorption coefficient band width ⁴T_lg(Р) ←⁴A_2g is decreasing.
The kinetics of the process opening and closing aminoacid cycles of cysteinatahroma (III) was studied with a spectrophotometric method. Reactions of opening and closing aminoacid cycles cysteinatahroma (III) have first order in the complex. Kinetics circuit cycles cysteine was studied on the example selected, alone complexes of chromium (III) coordinated with monodentate cysteine [Cr(H₂L)₅Н₂О]³⁺, [Cr(H₂L)₆]³⁺. For these complexes have shown that the relationship cysteine with chromium (III) is carried out by oxygen atoms COO- group and ring closure takes place at the nitrogen group NH₂. It was shown that the reaction proceeds by dissociative mechanism. Apparent rate constants of the reaction cycle formation in [Cr(H₂L)₅Н₂О]³⁺ , [Cr(H₂L)₆]³⁺.were determined. Rate constant is independent of the solutions pH : for [Cr(H₂L)₅Н₂О]³⁺ + when pH= 3.72m value κ_kazh = 0.0429 min^-1; when pH=3.85, value κ_kazh = 0.0389 min^-1; when pH= 4.10 value κ_kazh = 0.0388 min^-1; when pH=4.31 value κ_kazh = 0.0367 min^-1; for [Cr(H₂L)₆]³⁺ ions when pH=3.52 value κ_kazh = 0.0434 min^-1; when pH=3.81 value κ_kazh = 0.0401 min^-1; when pH=4.12 value κ_kazh = 0.0379 min^-1; when pH=4.45 value κ_kazh = 0.0426 min^-1.
Apparent rate constant of reaction cycles by opening a bi-mercapto tsisteinatohromate (III) [CrL₂] [Cr(Hl)(L)] solution by the action of acidic reagents were shown. The values of the rate constants are decreasing when solutions pH is increasing : when pH=3.8 value κ_kazh = 0.314 min^-1; when pH= 4.15 value κ_kazh = 0.242 min^-1; when pH=4.43 value κ_kazh = 0.219 min^-1; when pH=4.60 value k_kazh = 0.195 min^-1.