Binding Interaction of Organofluorine-Serum Albumin: A Comparative Ligand-Detected 19F NMR Analysis

In the present study, we attempt to characterize fluorinated ligand-serum albumin interaction in solution by a set of one-dimensional F-19 ligand-based experiments. In this regard, a model system diflunisal (DFL)-human serum albumin (HSA) has been chosen to benchmark the utility of F-19 relaxation and diffusion-based experiments in deciphering ligand-protein interactions. Further, we extend the application of a similar set of F-19 experiments to unravel the molecular interaction in an unexplored system of 2,6-difluorobenzoic acid (DFBA)-bovine serum albumin (BSA). Interaction analysis of DFBA-SA is of particular interest because DFBA is not only a stable metabolite of a number of pesticides but also used as the starting reagent of many fluorinated drugs. Observation of F-19-H-1 & H-1-H-1 saturation transfer difference effects confirmed binding of the ligands to SA. Further, these ligand-protein complexes were probed in terms of the dissociation constant (K-D), number of binding sites (n), bound fraction of the ligand (P-b), the complex lifetime (tau(res)) and exchange rate (K-ex). Although Carr-Purcell-Meiboom-Gill (CPMG)-based transverse relaxation and diffusion analysis quantified the former three quantities, the latter two were determined by the constant time fast pulsing CPMG method. Additionally, F-19 competition binding experiments performed with well characterized BSA site markers and DFBA indicated nonspecific binding of DFBA to BSA, whereas similar measurements in the case of HSA with DFL and DFBA revealed superior binding interaction of DFL with SA.