Spectroscopic studies on the interaction of lanthanum(III) 2-oxo-propionic acid salicyloyl hydrazone complex with bovine serum albumin.

The interaction of lanthanum(III) 2-oxo-propionic acid salicyloyl hydrazone complex (La(III)L(2)) with bovine serum albumin (BSA) was studied under physiological conditions. Fluorescence spectroscopy in combination with UV-vis absorption and circular dichroism (CD) spectroscopy were used to investigate the binding mechanism, binding constants and conformational changes of BSA in the presence of La(III)L(2). It was found that the fluorescence quenching of BSA by La(III)L(2) resulted mainly from the formation of a La(III)L(2)-BSA complex. The enthalpy change (delta H) and entropy change (deltaS) were found to be -41.03 kJ/mol and -32.61 J/mol/K, respectively, which indicated that van der Waals' interactions and hydrogen bonds were the predominant intermolecular force in stabilizing the complex. The distance r between the donor (BSA) and acceptor (La(III)L(2)) was found to be 4.35 nm, according to Förster theory of non-radioactive energy transfer. Moreover, the conformational changes of BSA by La(III)L(2) were analysed by means of synchronous fluorescence spectra, CD and three-dimensional fluorescence spectra. The experiment results confirmed some microenvironmental and conformational changes of BSA molecules in the presence of La(III)L(2). (c) 2008 John Wiley & Sons, Ltd.