Kinetics of the metallation of coproporphyrin-I in water with cadmium(II) and manganese(II)

The reaction of 3,8, 13,18-tetramethyl-21H,23H-porphine-2,7,12,17-tetraprop ionic acid or coproporphyrin-I (CPI) with cadmium(II) was studied spectroph otometrically and its kinetic and equilibrium constants were determined. Th e influence of temperature on the reaction rate was also studied. At differ ent ratios of [CPI][Cd(II)] two types of complex were formed: CdII(CPI) and (CdII)(2)(CPI); an investigation of the solution properties and the mechan ism of aggregation of (CdII)(2)(CPI) at different pH were performed. It is verified that cadmium(II) accelerates the reaction of the incorporation of manganese(II) into CPI by the substitution of cadmium(II) with manganese(II ) in the CdII(CPI) complex; the kinetics and mechanism of this substitution reaction at alkaline pH were studied. A sensitive kinetic method for the d etermination of cadmium(II) at ppb levels has been established; the molar a bsorptivity and the Sandell's sensitivity (for A = 0.001) of the recommende d procedure at 458 nm and 300 s after the start of the reaction are (6.175 +/- 0.026) x 10(5) 1 mol(-1) cm(-1) and (1.820 +/- 0.008) x 10(-4) mu g cm( -2) respectively. (C) 1998 John Wiley & Sons, Ltd.