THE HYDROLYSIS PRODUCTS OF CIS-DIAMMINEDICHLOROPLATINUM(II) .5. THE ANATION KINETICS OF CIS-PT(X)(NH3)2(OH2)+ (X = CL, OH) WITH GLYCINE, MONOHYDROGEN MALONATE AND CHLORIDE

The spectrophotometrically determined rate constants, k(obs) (s-1), for the anation of cis-PtCl(NH3)2(OH2)+ with glycine (Nu = gly at pH = 7.4), or sodium hydrogen malonate (Nu = Hmal- at pH = 4.3) can be represented by the equation k(obs) = k(o) + k(Nu)[Nu], where k(o) is an hydrolysis rate constant independent of the nucleophile concentration but dependent on pH, and K(Nu) is a nucleophile dependent path. With Nu = Hmal-, k(o) approximately 0 and the first step is monodentate coordination, followed by a second (k(cy)), nucleophile independent path, due to ring closure. With Nu = gly, the ring closure reaction is sufficiently fast as to appear synchronous with coordination and k(o) is the base hydrolysis rate constant for cis-PtCl(OH)(NH3)2 at pH = 7.4. Kinetic parameters associated with the anation are k(Hmal) (25.0-degrees-C, pH = 4.3, I = 1.0 M) = 9.90 x 10(-4) M-1 s-1, DELTA-H not-equal = 74.8 kJ mol-1, DELTA-S not-equal = -52 J K-1 mol-1; k(gly) (25.0-degrees-C, pH = 7.4, I = 1.0 M) = 2.75 x 10(-4) M-1 s-1, DELTA-H not-equal = 62.7 kJ mol-1, DELTA-S not-equal = -103 J K-1 mol-1; k(cy) (25.0-degrees-C, pH = 4.3, I = 1.0 M) = 1.03 x 10(-5) s-1, DELTA-H not-equal = 88.9 kJ mol-1, DELTA-S not-equal = -42 J K-1 mol-1. The rate (k3, s-1) of the chloride release from cis-PtCl(OH)(NH3)2 to give cis-Pt(OH)NH3)2(OH2)+ and rate of chloride uptake (k-3, M-1 s-1) have been measured at pH = 7.4. Kinetic parameters are k3 = 2.39 x 10(-5) s-1 (25.0-degrees-C, pH = 7.4, I = 1.0 M) DELTA-H not-equal = 82.4 kJ mol-1, DELTA-S not-equal = -57 J K-1 mol-1 and k-3 = 9.37 x 10(-4) M-1 s-1 (25.0-degrees-C, pH = 7.4, I = 1.0 M), DELTA-H not-equal = 61.7 kJ mol-1, DELTA-S not-equal = -96 J K-1 mol-1. From these rate constants, K3 = (k3[k-3]-1) is calculated to be 2.55 x 10(-2) at 25.0-degrees-C. These data have been used to comment on the nucleophilicity of cis-PtCl(NH3)2(OH2)+.