In the present study the interaction of various thiols (L-glutathione, L-cysteine, N-acetyl cysteine and D-penicillamine) with LaCl3 was studied in vitro by modified Ellman’s method. Experiments carried out at various concentrations inferred gradual decrease in thiol concentration with the increase in La3+ concentration in aqueous solutions. Maximum interac-tion between thiols and La3+ was observed at pH 7.5 and 35°C as indicated by the lowest values of residual thiol con-centration. The order of reactivity was DPA>GSH>NAC>Cys, where reactivity increased with increasing pKa of their thiol group. The possible products of reaction are proposed to be La(RS)3 complex or oxidized form with disulfide bond (RSSR).
Key words: Chelation, Ellman’s modified method, lanthanum, thiols.