Glutamate adsorption on the Au(111) surface at different pH values

Abstract

Adsorbed amino acids can modulate the behavior of metal nanoparticles in advanced applications. Using a combination of electrochemical experiments, FTIR spectroscopy, and DFT calculations, glutamate species interacting with the Au(111) surface in solution are here investigated. Electrochemical results indicate that the adsorption behavior depends on the solution pH (which controls the glutamate ionization) and on the charge of the surface. Glutamate adsorption starts at potentials slightly negative to the potential of zero charge. The thermodynamic analysis of these results indicates that two electrons are exchanged per molecule, implying that both carboxylic groups become deprotonated upon adsorption. The FTIR spectra reveal that carboxylate groups are bonded to the surface in a bidentate configuration (with both oxygen atoms attached to the surface).Plausible adsorbed configurations, consistent with the whole of these insights, were found using DFT. Moreover, it was observed that glutamate oxidation only takes place when the surface is oxidized, which suggests that this oxidation process involves the transfer of an oxygen group to the molecule, though, according to the FTIR spectra, the main chain remains intact.

Glutamate adsorption on gold electrodes at different pH values

“…2). On the other hand, some signs of Glu oxidation can be appreciated at the upper potential, in agreement with what is observed for the Au(1 1 1) [22] and Au(1 0 0) electrodes.…”

“…The adsorption behavior of Glu on the considered electrodes is divided into two potential regions: up to 1.2 V, in the so-called double-layer region, and up to 1.7 V (the oxide region). In the first region, Glu species are expected to adsorb, as has been already observed on Au (1 1 1) [22]. In the second region, the specific adsorption of OH and its subsequent oxidation to form surface gold oxides [33][34][35] may lead to the oxidation of Glu [22].…”

“…In the first region, Glu species are expected to adsorb, as has been already observed on Au (1 1 1) [22]. In the second region, the specific adsorption of OH and its subsequent oxidation to form surface gold oxides [33][34][35] may lead to the oxidation of Glu [22]. In any case, the complex behavior of the single crystal surfaces of gold, which are prone to reconstruct, should be taken into account.…”

“…2B). When the Glu adsorption behavior on the Au(1 1 0) surface is compared to that on the Au(1 1 1) [22] and Au(1 0 0) surfaces, a significant difference can be observed. The Glu adsorption processes on the Au(1 1 1) and Au(1 0 0) electrodes increase their potential in the RHE scale as the pH increases.…”

“…These results not only provide a better understanding of the adsorption behavior of Glu on gold, facilitating the application of Glu modified gold nanoparticles, but they also help to comprehend the mechanism giving rise to preferentially shaped colloidal nanoparticles of this metal when Glu is used as the growing mediator. Given that it was found in our previous research on the adsorption behavior of Glu on Au(1 1 1) [22] that the specific adsorption of OH at high enough potentials may lead to the oxidation of Glu, the present study is divided into two potential regions: up to 1.2 V vs. RHE, in the so-called doublelayer region, and up to 1.7 V vs. RHE (the oxide region). It should be noted that citrate and Glu present a similar structure, with a main chain formed by two terminal carboxylic groups separated by 3 carbon atoms, differing only by their side groups.…”