Binding interaction of quinclorac with bovine serum albumin: A biophysical study

Quinclorac (QUC) is a new class of highly selective auxin herbicides. The interaction between QUC and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy, synchronous fluorescence, three-dimensional fluorescence, CD spectroscopy and UV-vis absorption spectroscopy under simulative physiological condition. It was proved that the probable quenching mechanism of BSA by quinclorac was dynamic quenching. The Stern-Volmer quenching model has been successfully applied and the activation energy of the interaction as much as 8.03 kJ mol(-1), corresponding thermodynamic parameters Delta H-theta, Delta S-theta and Delta G(theta) were calculated. The results indicated that the acting forces between QUC and BSA were mainly hydrogen bonding and van der Waals forces. According to the Forster non-radiation energy transfer theory, the average binding distance between donor (BSA) and acceptor (QUC) was obtained (r = 3.12 nm). The alterations of protein secondary structure in the presence of QUC were confirmed by the evidences from three-dimensional fluorescence, synchronous fluorescence and CID spectroscopy. Furthermore, the site marker competitive experiments indicated that the binding of QUC to BSA primarily took place in Sudlow site 1. (C) 2009 Elsevier B.V. All rights reserved.