Probing the Adsorption Sites of 5‐amino‐2‐mercaptobenzimidazole Conformations on Colloidal Gold Nanoparticles Investigated by SERS and DFT

Abstract Gold nanoparticles (AuNP) have shown great potential in biomedical applications due to their unique and tunable properties. Understanding the ligand conformation on AuNP has profound interest in nanoparticle research leading to a precise drug delivery system. Colloidal AuNPs were synthesized using trisodium citrate as reducing agent. Normal Raman spectrum (NRS) in solid and aqueous phase identifies that 5‐amino‐2‐mercaptobenzimidazole (5A2MBI) mainly exist as thione form. Surface enhanced Raman scattering (SERS) investigation of 5A2MBI depending on pH was performed to explore the adsorption mechanism of thiolate and thione conformations on AuNPs. Density functional theory (DFT) calculations were used to find the band assignments and molecular electrostatic potential (MEP) mapping to identify the electron rich site where metal can interact preferentially. Using SERS spectral analysis and DFT results, surface adsorption scheme was proposed. At basic pH, 5A2MBI adsorbs on AuNP as thiolate form bidentately via Sulfur and nitrogen atom of imidazole ring with tilted geometry. However, in acidic condition the thione form adsorbs on nanosurface with perpendicular orientation.