An Experimental and Theoretical Study of Surface-Enhanced Raman Spectra of Sulfadiazine Adsorbed on Nanoscale Gold Colloids.

Abstract

Sulfadiazine, as a class of antibiotics, widely used in the world for decades, however, its surface-enhanced Raman spectra (SERS) on gold colloids is obviously different from ordinary Raman spectra in solid powder and liquid solution. To explore the reasons of such significant differences, we used density functional theory (DFT) calculations and normal mode analysis to investigate the effects of configuration, conformation, protonation, hydrogen bond interaction as well as adsorption configurations of sulfadiazine on gold clusters to check these different effects on the vibrational assignments. Our calculated results can summarize as two points. First, the Raman spectra strongly depend on configuration, conformation, protonation and hydrogen bond of sulfadiazine. Second, the wagging vibration displays a significant vibrational frequency shift and a very strong SERS peak responsible to the observed SERS signal when sulfadiazine adsorbed on gold clusters through the terminal amino group. This is different from another adsorption configuration through two oxygen atoms of the -SO2NH- group on gold clusters. Finally, we further investigate the potential energy surfaces along the wagging vibration and the binding interaction of -NH2 adsorbed at the different sites of gold surfaces.