Dynamic Studies of Transnitrosation of Thiols of Biological Importance by the Nitrosated 4,4',4'',4'''-Tetrasulfophthalocyaninecobaltate (III) Anion in Aqueous Solution

Document Type

Article

Publication Date

5-1-2009

Department

Chemistry and Biochemistry

School

Mathematics and Natural Sciences

Abstract

The kinetics of interaction of Co(III)TSPcNO (TSPc = 4,4′,4″,4′′′-tetrasulfophthalocyanine) with various thiols of biological relevance, e.g., reduced glutathione (GSH), captopril (CapSH), N-acetyl-L-cysteine (NALC), and L-cysteine ethyl ester (LCEE) have been investigated spectrophotometrically. The observed rate constants for transnitrosation are all first-order with respect to the respective thiols. The second-order rate constants which were determined at physiological temperature, 37 °C are 258 ± 8, 159 ± 3, 66.7 ± 1.3 and 37.4 ± 0.6 M− 1 s− 1, respectively. The second-order rate constants decreased according to the sequence LCEE > CapSH > GSH > NALC. The activation parameters (ΔH≠ and ΔS≠) were derived from the Eyring's equation. The experimental activation parameters were then correlated by an isokinetic plot, for the reduction of [Co(III)TSPc(NO−)]4− by the thiols, making use of the expression: ΔH‡ = ΔG0‡ + β0ΔS‡ where ΔGo‡ is the intrinsic free energy of activation, and βo the isokinetic temperature. The plot which showed very good linearity (R2 = 0.997), gave values of ΔGo‡ (61 ± 1 J K− 1 mol− 1) from the intercept, and βo (260 ± 11 K) from the slope. It is concluded that a common mechanism is adhered to in the reduction of Co(III)TSPcNO, irrespective of the type of thiol being used, to give the corresponding S-nitrosothiol, which is further confirmed by high performance liquid chromatography with mass spectrometric detector.

Publication Title

Biophysical Chemistry

Volume

141

Issue

41308

First Page

198

Last Page

202

Link to Full Text

Find in your library

Share

COinS