Understanding the link between the detection limit and the energy stability of two quercetin–antimony complexes by means of conceptual DFT

In view of the importance of quercetin and its derivatives in trace metal analyses, two organometallic complexes formed between quercetin (Q) and quercetin-5-sulfonic acid (QSA) with antimony metal, were theoretically studied via density functional theory (DFT) calculations. In this study, the concept of detection limit in electroanalysis was correlated to quantum chemical calculations for antimony trace analysis in aqueous solution by using Q and QSA as ligands. Based on two previous reports, the study was carried out experimentally using polarography where the working electrode was a dropping mercury electrode. The DFT calculations were performed with B3LYP and LSDA functionals as implemented in Gaussian 09 program and by employing the 6-31G(d) and 3-21G(d) basis sets, respectively. The results show a very strong relationship between the total energy of antimony complexes and the detection limit; thus, the more stable complex has a better detection limit value. Based on the Fukui functions, the calculated parameters such as local nucleophilicity indices and HOMO-1 electronic density of the ligands show a high interaction of antimony ion (III) with quercetin-5-sulfonic acid than that with quercetin. This finding was in good accord with the experimental results

Experimental and Theoretical Studies of Eosin Y Dye as Corrosion Inhibitors for Carbon Steel in Perchloric Acid Solution

The adsorption behavior and the inhibition performance of Eosin Y Dye for carbon steel corrosion in 1 M perchloric acid solution have been carried using weight loss and scanning electron micrograph (SEM) techniques as well theoretical calculations based on density functional theory (DFT). The studied inhibitor concentrations were between 5´10-5 M and 5´10-3 M. Results obtained revealed that Eosin Y is an effective inhibitor and its inhibition efficiency increases with increasing concentration to attain 96.91% at 5´10-3 M at 30 °C. Thermodynamic parameters such as adsorption heat, adsorption entropy and adsorption free energy were obtained from experimental data of the temperature studies of the inhibition process at five temperatures ranging from 20 to 60 °C. It was found that the adsorption of Eosin Y could prevent steel from weight loss and the adsorption accorded with the Langmuir adsorption isotherm. The free energy of adsorption showed that the corrosion inhibition takes place by spontaneous physicochemical adsorption of inhibitor molecules on the carbon steel surface. SEM and DFT studies confirm the adsorption of Eosin Y on carbon steel surface. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)