Interaction of 4-imidazolemethanol with a copper electrode revealed by isotope-edited SERS and theoretical modeling

Abstract

Adsorption of 4-imidazolemethanol (ImMeOH) on a copper electrode has been investigated by in situ isotope-edited (H/D and ⁶³Cu/⁶⁵Cu) surface enhanced Raman spectroscopy (SERS) in aqueous solutions at physiological pH (7.0) in a potential window from −0.500 to −1.100 V. Theoretical modeling by DFT calculations at the B3LYP/6-311++G(d,p) level for light atoms and LANL2DZ with ECP for copper atoms have been employed for the interpretation of experimental data. The copper surface was modeled by a cluster of 6 atoms. It was found that the imidazole ring adopts Tautomer-I form in the adsorbed state and coordinates with the Cu surface through the N3 atom. Linear potential-dependence of ν(C4C5) mode with the slope of (15 ± 1) cm⁻¹ V⁻¹ was experimentally observed. The imidazole ring mode near 1492 cm⁻¹ primarily due to ν(C2–N3) + β(C2H) vibration has also showed a considerable decrease in frequency at more negative electrode potentials with the slope of (9 ± 2) cm⁻¹ V⁻¹. Both modes can be used as sensitive probes for analysis of interaction of the imidazole ring with the metal surface. In agreement with experimental data theoretical modeling has predicted higher stability of surface bound Tautomer-I compared with Tautomer-II. The formation of a covalent bond between the metal and adsorbate was experimentally evidenced by metal isotopic (⁶³Cu/⁶⁵Cu) frequency shift of ν(Cu–N) mode at 222 cm⁻¹, combined with theoretical modeling of the surface complex.