1-(Naphthalen-1-yl)-5-phenyl-1H-1,2,3-triazole (NPTA), a novel synthesized triazole compound has been characterized for its photophysical properties and bioactivity. The structure of NPTA was optimized by semi-empirical PM3 method using the Polak-Ribiere algorithm. Molecular modeling was furtherly performed to reveal the binding mode and site to human serum albumin (HSA). The spectroscopic properties and the binding to HSA of NPTA were investigated by absorption spectra, synchronous fluorescence, 3D fluorescence spectra and fluorescence polarization. The results indicated that the characteristic absorption and fluorescence spectrum could be attributed to the conjugated polyene π bond of NPTA. Molecular docking showed NPTA moiety bound to the hydrophobic cavity of HSA and there are four hydrogen bonds interactions between NPTA and the residues Arg222. Fluorescent displacement measurements confirmed that NPTA bound HSA on site II. The 2D and 3D fluorescence spectroscopes of NPTA-HSA system indicated that NPTA quenched strongly the intrinsic fluorescence of HSA and induced a conformational change of the protein. The absorption and synchronous fluorescence spectra showed that NPTA could quench the fluorescence of tryptophan mainly and have effect on the microenvironment around HSA in aqueous solution. The low anisotropy values suggested that NPTA molecules were bound in a motionally unrestricted environment introduced by HSA. The binding constants (10⁴ magnitude) and the number of binding sites (n≈1) between NPTA and HSA at different temperatures (299, 309 and 319 K) were calculated from relevant fluorescence titration data, which indicated the strong binding between NPTA and HSA. Meanwhile, from the thermodynamic parameter calculation, it could be shown that the acting force was mainly the hydrophobic interactions, which was in good agreement with molecular modeling studies. Under the conditions studied, the values of the negative charge density (δ), the dissociation constants (K_d) and quantum yield (Ф) of NPTA-HSA system were calculated.

Key words: NPTA, human serum albumin (HSA), spectroscopy, binding