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The molecular interaction of polymer-anchored cobalt(III) complex, cis-[Co(bpy) 2 (BPEI)Cl]Cl 2 $4H 2 O (bpy ¼ 2,2 0 -bipyridine, BPEI ¼ branched polyethyleneimine) with two plasma proteins, human serum albumin (HSA) and bovine serum albumin (BSA) using various spectrophotomeric techniques has been investigated. The steady-state and time-resolved fluorescence spectra clearly demonstrated the static quenching mechanism. The calculated thermodynamic parameters revealed that the interaction between the polymer-cobalt(III) complex and HSA/BSA was driven mainly by van der Waals forces and hydrogen bonds. The results observed from three dimensional fluorescence and circular dichorism (CD) spectral studies manifested the conformational changes of HSA/BSA upon addition of the polymer-cobalt(III) complex. Furthermore, the antimicrobial result showed that the polymer-cobalt(III) complex exhibits good antibacterial and antifungal activities against certain human pathogenic microorganisms. In addition, the antiproliferative properties of the polymercobalt(III) complex on the HEp-2 human larynx cancer cells were determined using the MTT assay.The mode of cell death induced by the complex following treatment was analyzed adopting specific staining techniques. MTT assay revealed that the viability of the cells thus treated was significantly decreased and the cells succumbed to apoptosis as well as necrosis as reflected in changes in the nuclear morphology and cytoplasmic features by AO & EB and Hoechst staining methods.

The interaction of surfactant-cobalt(III) complexes [Co(bpy)(dien)TA](ClO4)3 · 3H2O (1) and [Co(dien)(phen)TA](ClO4)3 · 4H2O (2), where bpy = 2,2'-bipyridine, dien = diethylenetriamine, phen = 1,10-phenanthroline and TA = tetradecylamine with human serum albumin (HSA) under physiological conditions was analyzed using steady state, synchronous, 3D fluorescence, UV/visabsorption and circular dichroism spectroscopic techniques. The results show that these complexes cause the fluorescence quenching of HSA through a static mechanism. The binding constant (Kb ) and number of binding-sites (n) were obtained at different temperatures. The corresponding thermodynamic parameters (∆G°, ∆H° and ∆S°) and Ea were also obtained. According to Förster's non-radiation energy transfer theory, the binding distance (r) between the complexes and HSA were calculated. The results of synchronous and 3D fluorescence spectroscopy indicate that the binding process has changed considerably the polarity around the fluorophores, along with changes in the conformation of the protein. The antimicrobial and anticancer activities of the complexes were tested and the results show that the complexes have good activities against pathogenic microorganisms and cancer cells.

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