Interaction studies of a novel Co(II)-based potential chemotherapeutic agent with human serum albumin (HSA) employing biophysical techniques

Novel macrocyclic cobalt(II) complex C36H24N8O4S4CoCl2 with a butterfly topology was synthesized and characterized by spectroscopic (IR, H-1, C-13 NMR, EPR, UV-Vis, ESI-MS) and analytical methods. The complex exhibits distorted octahedral geometry around Co(II) metal ion, which was confirmed by EPR measurements with g(a), g(b), and g(c) values (8.01, 2.20, and 1.66), respectively, and molar extinction coefficient epsilon = 58 M(-1)cm(-1). The Interaction studies with human serum albumin (HSA) in phosphate buffer (0.1 M, pH 7.0) were studied by electronic absorption titration, fluorescence titration, circular dichroism, and cyclic voltammetry. Hyperchromism in fluorescence intensity indicates binding of complex with HSA near tryptophan residue in IIA subdomain leading to less polar microenvironment around tryptophan and more at tyrosine. The intrinsic binding constant K (b) obtained from absorption spectral titrations was found to be 9.3 x 10(4) M-1, suggesting medium binding affinity of HSA with complex. CD spectrum indicates alpha-helical structure up to beta-pleated secondary structure. CV data confirmed medium reversible binding with HSA. The binding of complex with HSA shows typical reversible mode of binding, which enables the delivery of drug candidate to the tissue enzymes and receptors in an efficient manner, and thereby affects the uptake of the drug.