Study of the Enantioselective Interaction of Diclofop and Human Serum Albumin by Spectroscopic and Molecular Modeling Approaches In Vitro

In this contribution, the enantioselective interactions between diclofop (DC) and human serum albumin (HSA) were explored by steady-state and 3D fluorescence, ultraviolet-visible spectroscopy (UV-vis), and molecular modeling. The binding constants between R-DC and HSA were 0.9213x10(5), 0.9118x10(5), and 0.9009x10(5)Lmol(-1) at 293, 303, 313K, respectively. Moreover, the binding constants of S-DC for HSA were 1.4766x10(5), 1.2899x10(5), and 1.0882x10(5)Lmol(-1) at 293, 303, and 313K individually. Such consequences markedly implied the binding between DC enantiomers and HSA were enantioselective with higher affinity for S-DC. Steady-state fluorescence study evidenced the formation of DC-HSA complex and there was a single class of binding site on HSA. The thermodynamic parameters (H, S, G) of the reaction clearly indicated that hydrophobic effects and H-bonds contribute to the formation of DC-HSA complex, which was in excellent agreement with molecular simulations. In addition, both site-competitive replacement and molecular modeling suggested that DC enantiomers were located within the binding pocket of Sudlow's site II. Furthermore, the alterations of HSA secondary structure in the presence of DC enantiomers were verified by UV-vis absorption and 3D fluorescence spectroscopy. This study can provide important insight into the enantioselective interaction of physiological protein HSA with chiral aryloxyphenoxy propionate herbicides and gives support to the use of HSA for chiral pesticides ecotoxicology and environmental risk assessment. Chirality 25:719-725, 2013. (c) 2013 Wiley Periodicals, Inc.