ABSTRACT
A new water-soluble single- and double-chain surfactant–cobalt(III) complexes, [Co(dien)(TA)Cl2]ClO4 (1) and [Co(dien)(TA)2Cl](ClO4)2 (2), where dien =is diethylenetriamine and TA is =tetradecylamine, have been synthesized. The structure of the complexes was characterized by UV–visible (UV–vis), Fourier transform infrared, NMR, and electrospray ionization mass spectrometry. Hydrophobicity of these surfactant–cobalt(III) complexes was investigated by partition-coefficient method. The critical micelle concentration (CMC) values of these surfactant metal complexes in aqueous solution were obtained from conductivity measurements at five different temperatures. The biophysical interaction of these amphiphilic molecules with bovine serum albumin (BSA) has been examined by fluorescence, synchronous, three-dimensional (3D) fluorescence, UV–vis, and circular dichroism (CD) techniques at pH 7.4. The results of hydrophobicity and CMC values indicate that double-chain surfactant–cobalt(III) complex has more hydrophobicity compared to single-chain surfactant–cobalt(III) complex. The fluorescence titration at three different temperatures has shown that the interaction between surfactant–cobalt(III) complexes and BSA was mainly a static quenching process. Interestingly, on increasing temperature, binding constant and number of binding sites get decreased for single-chain system whereas increased for double-chain system, due to the changes in the mode of protein–complex interaction. The observed thermodynamic parameters clearly showed that surfactant–cobalt(III) complexes with single-chain system prefer electrostatic binding, whereas those with double-chain system prefer hydrophobic interaction. Moreover, the results from UV–vis absorption, synchronous fluorescence, 3D fluorescence, and CD indicate that conformational and some microenvironmental changes occurred in BSA.
