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 ((LaL2)-L-III) 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 (LaL2)-L-III. It was found that the fluorescence quenching of BSA by (LaL2)-L-III resulted mainly from the formation of a (LaL2)-L-III-BSA complex. The enthalpy change (Delta H) and entropy change (Delta S) were found to be -41.03 kJ/mol and -32.61 J/moI/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 ((LaL2)-L-III) was found to be 4.35 nm, according to Forster theory of non-radioactive energy transfer. Moreover, the conformational changes of BSA by (LaL2)-L-III 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 (LaL2)-L-III. Copyright (C) 2008 John Wiley & Sons, Ltd.