Spectroscopic Investigation on the Interaction of Pyrimidine Derivative, 2-Amino-6-hydroxy-4-(3,4-dimethoxyphenyl)-pyrimidine-5-carbonitrile with Human Serum Albumin: Mechanistic and Conformational Study

Abstract

In the present study, fluorescence spectroscopy in combination with UV–vis absorption spectroscopy and synchronous fluorescence spectroscopy (SFS) was employed to investigate the binding affinity of pyrimidine derivative, 2-amino-6-hydroxy-4-(3,4-dimethoxyphenyl)-pyrimidine-5-carbonitrile (AHDMPPC) to human serum albumin (HSA) under the physiological conditions. In the mechanism discussion, it was proved that the fluorescence quenching of HSA by AHDMPPC is a result of the formation of AHDMPPC–HSA complex. The quenching mechanism and number of binding sites (n ≈ 1) were obtained by fluorescence titration data. Binding parameters calculated from Stern–Volmer method showed that the AHDMPPC bind to HSA with the binding affinities of the order 104 L mol–1. The thermodynamic parameters studies revealed that the binding was characterized by negative enthalpy and positive entropy changes −13.06 kJ/mol and 51.34 J/mol K–1 (from the Van’t Hoff equation) and suggest that the binding reaction was exothermic and hydrophobic interaction is the predominant intermolecular forces stabilizing the complex. The specific binding distance (r = 2.25 nm) between donor HSA and acceptor AHDMPPC was obtained according to fluorescence resonance energy transfer (FRET). Furthermore, the synchronous spectral result, three–dimensional fluorescence spectra and circular dichroism (CD) indicates that the secondary structure of HSA was changed in the presence of AHDMPPC.