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The oxidation of l-serine by chloro and chlorohydroxo complexes of gold(III) was spectrophotometrically investigated in acidic buffer media in the absence and presence of the anionic surfactant sodium dodecyl sulfate (SDS). The oxidation rate decreases with increase in either [H] or [Cl]. Gold(III) complex species react with the zwitterionic form of serine to yield acetaldehyde (principal reaction product) through oxidative decarboxylation and subsequent deamination processes. A reaction pathway involving one electron transfer from serine to Au(III) followed by homolytic cleavage of α-C-C bond with the concomitant formation of iminic cation intermediate has been proposed where Au(III) is initially reduced to Au(II). The surfactant in the submicellar region exhibits a catalytic effect on the reaction rate at [SDS] ≤ 4 mM; however, in the postmicellar region an inhibitory effect was prominent at [SDS] ≥ 4 mM. The catalytic effect below the critical micelle concentration (cmc) may be attributable to the electrostatic attraction between serine and SDS that, in turn, enhances the nucleophilicity of the carboxylate ion of the amino acid. The inhibition effect beyond cmc has been explained by considering the distribution of the reactant species between the aqueous and the micellar pseudophases that restricts the close association of the reactant species. The thermodynamic parameters Δ H and Δ S associated with the binding between serine and SDS micelle were calculated to be -14.4 ± 2 kJ mol and -6.3 ± 0.5 J K mol, respectively. Water structure rearrangement and micelle-substrate binding play instrumental roles during the transfer of the reactant species from aqueous to micellar pseudophase.

Oxidative degradation of l‐isoleucine (Ileu) by Au3+ complexes has been studied spectrophotometrically in weakly acid medium (acetic acid–sodium acetate buffer, pH range 3.72–4.80) in the temperature range 288–308 K. The reaction is first order with respect to AuIII but complex order (<1) with respect to isoleucine. Ionic strength has no significant effect on the reaction kinetics. Both H+ and Cl− ions have been found to show inhibiting effect on the reaction rate. Decreasing solvent polarity exerts an adverse effect on the reaction. Au3+ complexes react with the zwitterion form of isoleucine in a one‐step two‐electron transfer redox process. The reaction passes through intermediate formation of iminic cation, which hydrolyzes to produce 2‐methyl butanal, identified by 1H NMR. The activation parameters ΔH≠ and ΔS≠ related to the rate‐limiting step of the reaction are evaluated. The derived rate law is in excellent agreement with the experimental results. The kinetic and activation parameters of this investigation have been compared and analyzed with those of the oxidation of l‐leucine by gold(III).