Surface-induced dimerization of 2-thiazoline-2-thiol on silver and gold nanoparticles: A surface enhanced Raman scattering (SERS) and density functional theoretical (DFT) study

Abstract

The adsorption behavior of an anti-thyroid agent, 2-thiazoline-2-thiol (TT) on silver (Ag) and gold (Au) nanoparticles (NPs) was studied using surface enhanced Raman scattering (SERS) and density functional theory (DFT). The tautomers of TT involved in the surface adsorption processes were identified. Raman scattering studies indicated the predominance of the thione form in solid and the thiol tautomer in aqueous solution. SERS studies of TT functionalized Ag (TT-Ag) and Au NPs (TT-Au) showed maximum enhancement for 1 μM concentration, suggesting monolayer coverage. Surface induced dimerization of TT was evident from SERS and DFT. The appearance of prominent peaks at 484 (SS stretch) and 317 (CSS bend) cm−1 for TT-Ag revealed the formation of disulphide dimer, while the emergence of a distinct band at 2124 cm−1 (H-bonded SH stretch) for TT-Au indicated the development of H-bonded dimer. Thus, in the present study, selective formation of disulphide dimer and the H-bonded dimer was observed on the surface of Ag and Au NPs, respectively. In addition, the thiol tautomer was found to be exclusively bound to the metal surface, via the thiazoline ring N atom. In this work, a qualitative relation between the strength of TT-metal charge transfer complex and inter-molecular association of TT on the surface of metal NPs was established. This study, thus paves the way for designing novel metal nanosubstrates that can be exploited for studying interesting surface phenomenon, viz. surface induced dimerization or rearrangement reactions, surface catalysis, etc. as well as for designing valuable drugs suitable for chelation therapy.