Dopamine species adsorbed on Ag: a DFT study of the degree of protonation and the effect of electric field

A. C. ROSSI; L. A. MEIER; N. J. CASTELLANI

Paris

Congreso; XLIII Congress of Theoretical Chemists of Latin Expression; 2017

Dopamine (DA) is a catecholamine that binds andactivates cell surface receptors in humans and mammalians. Thisneurotransmitter plays an important physiological role in the central nervous,renal and hormonal systems. It is of great medical and pharmacological interestto study chemical interactions in which this molecule is involved. According tothe pH value of the solvent medium, different forms of catecholamine moleculeshave been reported, including neutral, zwitterionic, cationic and anionicspecies. Recently, several proposals for DA detection have published based oncyclic voltammetry and surface-enhanced Raman spectroscopy where the use ofcolloidal Ag nanoparticles as substrate for DA adsorption allows a betterdetection 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) andAg (110) was studied using the Vienna Ab Initio Simulation Package (VASP) inthe context of the Density Functional Theory (DFT) formalism. The repeatedslabs representing the Ag(110) and Ag(111) surfaces contain _ve and four layersof atoms, respectively, and a vacuum gap in the normal direction. The adsorbedspecies 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 atomiclayers was relaxed. For the adsorption of DA species a horizontal orientation wasconsidered, with the aromatic ring parallel to each Ag surface. Theadsorbate-substrate interaction was evaluated by computing the electroniccharge-density difference and the DEEC6 atomic-charge analysis, showing animportant reorganization of electronic charge. The effect of an homogeneouselectric field on the adsorption of Z-DA on Ag systems was also studied.