CONICET | Buscador de Institutos y Recursos Humanos

Dopamine (DA) is a catecholamine that binds and activates cell surface receptors in humans and mammalians. This neurotransmitter plays an important physiological role in the central nervous, renal and hormonal systems. It is of great medical and pharmacological interest to study chemical interactions in which this molecule is involved. According to the pH value of the solvent medium, dfferent forms of catecholamine molecules have been reported, including neutral, zwitterionic, cationic and anionic species. Recently, several proposals for DA detection have published based on cyclic voltammetry and surface-enhanced Raman spectroscopy where the use of colloidal Ag nanoparticles as substrate for DA adsorption allows a better detection of this molecule. In this work, the adsorption of the zwitterionic (Z-DA), protonated (P-DA) and deprotonated (DP-DA) species on the surface of Ag(111) and Ag (110) was studied using the Vienna Ab Initio Simulation Package (VASP) in the context of the Density Functional Theory (DFT) formalism. The repeated slabs representing the Ag(110) and Ag(111) surfaces contain five and four layers of atoms, respectively, and a vacuum gap in the normal direction. The adsorbed species and at the same time the first and second atomic layers for Ag(110) were allowed to relax. In the case of the Ag(111) surface only the first atomic layers was relaxed. For the adsorption of DA species a horizontal orientation was considered, with the aromatic ring parallel to each Ag surface. The adsorbate-substrateinteraction was evaluated by computing the electronic charge-density difference and the DEEC6 atomic-charge analysis, showing an important reorganization of electronic charge. The effect of an homogeneous electric field on the adsorption of Z-DA on Ag systems was also studied.