Dynamic studies of transnitrosation of thiols of biological importance by the nitrosated 4,4',4'',4'''-tetrasulfophthalocyaninecobaltate(III) anion in aqueous solution.

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 degrees 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 (DeltaH(not equal) and DeltaS(not equal)) 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: DeltaH(double dagger) = DeltaG(0)(double dagger) + beta(0)DeltaS(double dagger) where DeltaG(o)(double dagger) is the intrinsic free energy of activation, and beta(o) the isokinetic temperature. The plot which showed very good linearity (R(2) = 0.997), gave values of DeltaG(o)(double dagger) (61+/-1 J K(-1) mol(-1)) from the intercept, and beta(o) (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.