Studies on complexation of cobalt with bioligand

The present work discusses the complexation behavior of bioligand cysteine with cobalt and the immobilization of this complex (Co-Cys) onto a biocompatible ligand and common drug base, polyvinylpyrrolidone (PVP). The complexation behavior has been studied by radiometric method and UV-Vis spectrophotometry. The radiometric method involves dialysis of 60Co-Cys-PVP complex against triple distilled water which subsequently gives the dynamic dissociation constant (kd) of the complex. The half life of 60Co-Cys-PVP complex calculated from kd value is 22.6 h against triple distilled water at pH 8.5. The UV-Vis spectra analysis confirms the complexation of Co with cysteine at this pH and also indicates that the cysteine ligated Co(II) centers easily get oxidised to Co(III) centers (low spin, d6) in the presence of air at alkaline pH showing no d-d transitions. (author)