Resonance Raman spectroscopic studies of 2-(4′-hydroxyphenylazo)-benzoic acid and some substituted analogs—II. Binding to avidin and bovine serum albumin

Abstract

Resonance Raman spectroscopic studies unequivocally indicate that the absorption band at about 500 nm, observed when 2-(4′hydroxyphenylazo)-benzoic acid (HABA) interacts with either avidin or bovine serum albumin in neutral aqueous solution, originates from the protein-bound hydrazone form of the dye. Spectroscopic comparison of the protein-bound and unbound hydrazone forms enables some of the ligand—protein interactions to be defined. Studies with HABA and some selected analogs in aqueous solution, in buffer-doped dimethyl sulfoxide ( d 6), and in the presence of α-cyclodextrin indicate that two important factors responsible for stabilising the hydrazone forms of HABA analogs are the ring substitution pattern, and intramolecular hydrogen bonding. A possible model for the HABA—protein interaction is proposed.