Binary Stability Constants Studies of Cu and Mn-Complexes with Cysteine and Cephalexin

Binary complexes of Cu(II) and Mn(II) with cysteine and cephalexin have been studied potentiometrically at about 27    in aqueous medium using Irving-Rossotti titration technique for proton-ligand (P-L) and metal-ligand (M-L) stability constants evaluation. The proton-ligand stability constants for cysteine and cephalexin were: log K1H 8.4 (pKa for thiol group), log K2H 10.7 (pKa for NH2-group), log K1H 5.2 (pKa for carboxyl group), and log K2H 6.82 (pKa for amine group), respectively. The binary metal-ligand stability constant (logK) values for 1:1 were found in the order of Cu(II) > Mn(II) for both ligands in conformity to the Irving–Williams order of the divalent transition metals of the period 4. Though the redox-active nature of Cu(II)-Cysteine atmosphere likely compromised the Cu(II)-Cysteine stability constant. By and large, M-L stability constants of Mn and Cu with cysteine and cephalexin have been re-established. This finding agreed with previous studies claimed that cysteine is fit for use in transporting target metals. In general, the studies have strengthened the idea that drugs and amino acids are able to interact with metals in our body system to a specific extent in terms binding constant.