Probing the Interaction Between a Surfactant-Cobalt(III) Complex and Bovine Serum Albumin

The mechanism of binding of the surfactant-cobalt(III) complex, cis-[Co(phen) 2(C 14H 29NH 2)Cl](ClO 4) 2{dot operator}3H 2O (phen = 1,10-phenanthroline, C 14H 29NH 2 = tetradecylamine) with bovine serum albumin (BSA) was investigated by UV-vis absorption, circular dichroism (CD) and fluorescence spectroscopic techniques. The results of fluorescence titration revealed that the surfactant-cobalt(III) complex quenched the intrinsic fluorescence of BSA through a combination of static and dynamic quenching. The apparent binding constant (K a) and number of binding sites (n) were calculated below and above the critical micelle concentration (CMC). The thermodynamic parameters determined by the van't Hoff analysis of the constants (ΔH {ring operator}=14.87 kJ{dot operator}mol -1; ΔS {ring operator}=152.88 J{dot operator}mol -1{dot operator}K -1 below the CMC and 25.70 kJ{dot operator}mol -1 and 243.14 J{dot operator}mol -1{dot operator}K -1, respectively, above the CMC) clearly indicate that the binding is entropy-driven and enthalpically disfavored. Based on Förster's theory of non-radiation energy transfer, the binding distance, r, between donor (BSA) and the acceptor (surfactant-cobalt(III) complex) was evaluated. UV-vis, CD and synchronous fluorescence spectral results showed that the binding of the surfactant-cobalt(III) complex to BSA induced conformational changes in BSA. © 2012 Springer Science+Business Media, LLC.