Adsorption of dopamine species on Ag(110): a theoretical perspective

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

Congreso; 42do Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2016; 2016

Table 1. Adsorption energy of DA and ZDA. Electrostatic and deformation energies of the systems studied.   Eads(eV) Eelec(eV) EDA,def(eV) EAg,def(eV) DA/Ag(110) -4.76 -5.75 0.21 0.25 ZDA/Ag(110) -6.14 -7.31 0.14 0.25   Dopamine (DA) is a neurotransmitter that plays animportant physiological role in the central nervous, renal and hormonal systems.It is therefore of great medical and pharmacological interest to study chemicalinteractions in which this molecule is involved. Recently, the DA interactionwith the surface of colloidal nanoparticles coated with a layer of Ag has been experimentallyinvestigated [1]. In this work, the adsorption of dopamine and its zwitterionicspecies (ZDA) on the surface of Ag (110) was studied using the Vienna Ab InitioSimulation Package (VASP) in the context of the Density Functional Theory (DFT)formalism. The Ag(110) substrate is modeled using a slab of five metal layers,allowing the first atomic layer to be relaxed. Several geometricalconfigurations for the adsorption of DA and ZDA were considered, noting that theadsorption of these molecules in a horizontal orientation is more stable. The adsorptionof ZDA on the surface of Ag(110) is benefited by 1.38 eV with respect to DA. Thepresence of DA on Ag causes a local distortion of the surface, as quantified bythe analysis of deformation energies performed on the systems studied (See Table1). The adsorbate-substrate interaction was evaluated by computing the electroniccharge-density difference and the Voronoi atomic-charge changes of the molecule (ΔQ)with respect to separated fragments. It was observedthat an important electron transfer occurs from the Ag substrate to themolecules with a relevant electrostatic interaction (See Eelec energyin Table 1). The vibration frequencies of DA and ZDA on Ag(110) were also considered.For comparison, complementary calculations were performed for DA and ZDAadsorbed on the Ag(111) surface.