Solution Equilibria and Structures of Disulfhydryl-containing Peptide-Indium (III) and Gallium (III) Complex Species

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Solution equilibria of the In (III) and Ga (III) complex species of 2,3-dimercaptopropionylglycine (DMPG) and 2-mercaptopropionyl-L-cysteine (MPC) have been investigated by potentiometry in aqueous solution. The formation constants of various species and their distribution as a function of pH were evaluated with a non-linear leastsquares treatment of the potentiometric data. The structural features and the complexation mechanisms were proposed through the interpretation of the results of the potentiometric and infrared spectral (in D_2O) studies. In the various protonated species formed in the In (III) solutions of DMPG and MPC, the carboxyl and sulfhydryl groups are protonated, respectively. In the 1 : 1 DMPG-In (III) system, the stable In (OH) L species formed even in the alkaline solution. Ga (III) resists complexation with monosulfhydrylcontaining ligands in contrast to In (III), but forms the complex with disulfhydryl-containing ligands in spite of the occurrence of the hydrolytic precipitation during part of the titration of the MPC-Ga (III) solution. Once formed Ga (III) complex is stable as well as In (III). Two sulfhydryl groups of peptides were required for complexation, even in the In (III) case. In all cases, no deprotonation of the peptide-amide proton was observed. The potentiometric calculations gave the large values of the equilibrium constants of the complexes, indicating that the disulfhydryl-containing peptides are remarkably effective towards the formation of the complexes of In (III) and Ga (III) in aqueous solution.
社団法人日本薬学会の論文
1978-02-25

Solution Equilibria and Structures of Disulfhydryl-containing Peptide-Indium (III) and Gallium (III) Complex Species

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