Electrochemical study about zinc electrodeposition onto GCE and HOPG substrates

We carried out an electrochemical study about zinc electrodeposition onto GCE and HOPG substrates from an electrolytic plating bath containing 0.01M ZnSO4 + 1M (NH4)2SO4 at pH 7. Under our experimental conditions the predominant chemical species was the complex [ZnSO4(H2O)5]. The chronoamperometric study showed that zinc electrodeposition follows a typical 3D nucleation mechanism in both substrates. The average dG calculated for the stable nucleus formation was 6.92 x 10-21 J nuclei"1 and 1.35 x 10-20 J nuclei"1 for GCE and HOPG, respectively. The scanning electron microscopy (SEM) images showed different nucleation and growth processes on GCE and HOPG substrates at same overpotential

Kinetical study about the cobalt electrodeposition onto polycrystalline platinum

An electrochemical study of Co electrodeposition onto polycrystalline Pt from an aqueous solution containing 10-2 M CoCl2 + 1 M NH4CI (pH = 9.3) was conducted at overpotential conditions. The current density transients showed two maxima that corresponded to two nucleation and growth processes. The entire transient behavior was adequately predicted considering the contribution to the total current of four different processes: a Langmuir-type adsorption process, a diffusion-controlled two-dimensional instantaneous nucleation, and two three-dimensional nucleation and growth processes

An In Silico Approach to Enzymatic Synthesis of Fucooligosaccharides Using α-L-Fucosidase from Thermotoga maritima

Abstract: Fucooligosaccharides comprise the primary group of human milk oligosaccharides. Due to their beneficial properties, a series of synthetic methods have been proposed to obtain them. Enzy- matic methods show great promise, and α-L-fucosidase from Thermotoga maritima has emerged as a powerful catalyst for their production. Nonetheless, the enzyme’s limited substrate scope has de- layed its wider application. The present work aims to compare the relative reactivity of fucose, pNP-fucose, and ethyl-fucose, while also exploring the molecular interactions of these fucosyl-donors with the enzyme through a combination DFT and docking analysis. The HOMO-LUMO band gaps range from −7.14571 to −4.24429 eV, with α/β-pNP-fucose and α-fucose being the three most reactive compounds. Moderate association energies between −6.4 to −5.5 kcal·mol−1 were found in the dock- ing analysis, with α-pNP-fucose and both anomers of ethyl-fucose demonstrating the poorest affinity. In the case of α/β-lactose affinity to the β-fucose/enzyme complex, no significant differ- ences were shown. We conclude that the best fucosyl-donors for transfucosylation are those that maintain an enzyme affinity and reactivity similar to pNP-fucose

A DFT study of the chemical reactivity of thiobencarb and its oxidized derivatives in aqueous phase

In the present work, the global and local reactivity of S-(4-chlorobenzyl)- N,N-diethylthiocarbamate (TB) and its oxidized derivatives (sulfone (TBSu) and sulfoxide (TBS) were analyzed. In addition, the chemical reactivities of the dechlorinated forms of TB (DTB), TBSu (DTBSu) and TBS (DTBS) were studied. The calculations were performed at the wB97XD/6- -311++G(2d,2p) level of theory in the aqueous phase. The condensed Fukui functions indicated that for TB and DTB, the most preferred sites for donating electron in a reaction are located on the S and N atoms, while the most reactive sites for accepting electrons are associated with the aromatic ring (AR). For TBS and DTBS, the more reactive sites are located on AR, S and AR for nucleophilic, electrophilic and free radical attacks, respectively. In the case of TBSu and DTBSu, the results showed AR to be the more reactive zone for the three kinds of attacks. These last results suggest that cleavage of the C–S bond in TB, TBS and their dechlorinated forms is favored by electrophilic attacks. Additionally, the obtained results suggest that in TB, it is plausible that the cleavage of the C–N is favored on attack of this molecule by electrophiles

Chemical Reactivity of Isoproturon, Diuron, Linuron, and Chlorotoluron Herbicides in Aqueous Phase: A Theoretical Quantum Study Employing Global and Local Reactivity Descriptors

We have calculated global and local DFT reactivity descriptors for isoproturon, diuron, linuron, and chlorotoluron herbicides at the MP2/6-311++G(2d,2p) level of theory. The results suggest that, in aqueous conditions, chlorotoluron, linuron, and diuron herbicides may be degraded by elimination of urea moiety through electrophilic attacks. On the other hand, electrophilic, nucleophilic, and free radical attacks on isoproturon may cause the elimination of isopropyl fragment

Estudio de factibilidad y propuesta de un proceso de gestión que permita implementar el b-learning en la asignatura Electroquímica.

En este trabajo se reportan los resultados obtenidos mediante una investigación de tipo cuantitativo, enfocada a identificar y reconocer los estilos de aprendizaje y las competencias digitales que poseen los alumnos que se inscriben en el curso denominado Electroquímica; y que se imparte dentro de la Licenciatura en Química en la Universidad Autónoma del Estado de Hidalgo. La información necesaria se recolectó mediante la aplicación de encuestas elaboradas en este trabajo. Al analizar las competencias digitales de los estudiantes se encontró que la totalidad de ellos emplean los teléfonos inteligentes para comunicarse, continuamente navegan en internet con fines didácticos, recreativos y ocupacionales, emplean de manera básica los procesadores de textos, hojas de cálculo y presentaciones electrónicas

Cobalt electrodeposition onto highly oriented pyrolytic graphite (HOPG) electrode from ammonium sulfate solutions

It was carried out an electrochemical study of the cobalt electrodeposition onto HOPG electrode from an aqueous solution containing 10-2 M of CoSO4 + 1M (NH4)2SO4. Nucleation parameters such as nucleation rate, density of active nucleation sites, saturation nucleus and the rate constant of the proton reduction reaction (kPR) were determined from potentiostatic studies. An increase in kPR values with the decrease in the applied potential suggested a competition between H+ and Co2+ by the active sites on the surface. The ΔG energy calculated for the formation of stable nucleus was 8.21x10-21 J/nuclei. The AFM study indicated the formation of small clusters of 50-400 nm in diameter and 2-120 nm in height

Kinetic study of the cobalt electrodeposition onto glassy carbon electrode from ammonium sulfate solutions

We carried out an electrochemical study of the cobalt electrodeposition onto glassy carbon electrode from an aqueous solution containing 10-2 M of CoSO4 + 1 M (NH4)2SO4 at natural pH 4.5. The potentiostatic study indicated a progressive 3D nucleation and growth during the deposition process. The average diffusion coefficient calculated for this system was 2.65 X 10-6 cm² s-1 while the ΔG for the formation of stable nucleus was 6.50 X 10-20 J/nuclei. The scanning electron microscopy images indicated the formation of small and homogeneous nucleus onto GCE of approximately 300 nm

The Effect of pH on the Electrodeposition of Pd Clusters onto Highly Ordered Pyrolytic Graphite—A Kinetic and Morphological Study

In this study, we carried out an electrochemical investigation of the palladium electrodeposition process at pH 5 and 8, evaluating the kinetic parameters related to its nucleation and growth processes on a Highly Oriented Pyrolytic Graphite (HOPG) electrode from a plating bath containing 1 mM of Pd and 1 M NH4Cl. The voltammetric study allowed us to identify the potential values at which palladium can be electrodeposited, along with the adsorption and desorption processes of hydrogen absorbed on the deposited Pd. Analysis of the peak currents of the deposited Pd indicated diffusional control at both pH values. The evaluation of kinetic parameters, such as the number of active nucleation sites (N0), the nucleation rate (A), and the rate constant of the proton reduction process (kPR), was determined via potentiostatic studies, revealing their dependence on the applied potential to the electrode. The number of active nucleation sites predicted by the nucleation model correlated well with the number of nuclei observed via Scanning Electron Microscopy (SEM). SEM images revealed that at pH 5, the Pd clusters had an average diameter of 27 nm and a height of 39 nm, while at pH 8, the clusters had an average diameter of 12.8 nm and a height of 16.6 nm. At pH 5, homogeneous and dispersed Pd clusters were obtained, while at pH 8, agglomeration of Pd clusters was observed

A DFT study of the chemical reactivity of cimetidine A, C and D in the gas, H2O, MeOH and EtOH solvents

% Fukui % DFT s KR nema In the present work, we have analyzed the chemical reactivity of cimetidine A, C and D in different solvents; through the evaluation of global and local DFT reactivity descriptors. In the gas, MeOH and EtOH phases, cimetidine A, C and D exhibit energy differences of 3-11 kcal mol-1. But, in the aqueous phase, cimetidine A and D are approximately isoenergetic. The values of the hardness indicate that cimetidine A, C and D are more reactive in the presence of a solvent than in the gas phase. Also, our results suggest that CimC and CimD are better nucleophiles that CimA. The Fukui Function values suggest that the more reactive sites of CimA are not modified in the different solvents. In the case of CimC, the more reactive sites to electrophilic and free radical attacks are located on the thioether sulfur. For CimD, the number and place of the electrophilic and free radical sites are independent of the solvent