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

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 approximate to 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 10(4) 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.