Reactivity of disulfide peptide l-cystine with iodido (diethylenetriamine)platinum(II) and synthesis of products in the presence of an iodide ion

Abstract

Substitution reactions of complex [PtI(dien)]+ (where, dien=diethylenetriamine ) with sulfur-containing peptide l-cystine has been studied in 1.0×10−1 M aqueous perchlorate or acetate medium between 298≤T (K)≤323 and 2.30≤pH≤4.45 using a UV–visible spectrophotometer. Products obtained have characterized from their physico-chemical and spectroscopic methods at various pH and temperatures. From this characterization, products have indicated that [PtI(dien)]+ has formed a complex with l-cystine and acts as a bidentate ligand, through Pt–S bond at 2.30≤pH≤3.30 and through Pt–N and Pt–S bond of cystine in 3.95≤pH≤4.45. At 2.30≤pH≤3.30, ring opening and closing of dien have occurred at 308 and 323 K, respectively, and the same has happened at pH≥3.95. All reactions have followed the rate law – d[mixture]/dt=(k 1+k 2 [cystine]) [Pt(II)], where k 2 denotes the second-order rate constant. Activation parameters E a , Δ H # and Δ S # have been determined. Product formation and reversible and forward reaction rate constants have also been evaluated.