Search results for "solution"

The electrochemical reduction of thioisonicotinamide in an aqueous medium

1998

Abstract The electrochemical reduction of thioisonicotinamide NRCSNH 2 has been examined in an aqueous medium between H 0 =−1 and pH=13.7. As shown by cyclic voltammetry and polarography, a global 2e − reversible transfer is followed by two successive first-order chemical reactions and a 2e − , 2H + reduction (EC 1 C 2 E process). A mechanism is proposed, beginning with the 2e − reduction of NRCSNH 2 to the formal diionized form NRC − (SH)(NH 3 + ), the first chemical reaction, C 1 , being a formal proton transfer which yields the 4- gem aminosulfanylmethylpyridine; the rate constant of this reaction is 2×10 4  s −1 in acidic medium and diminishes in neutral medium. The second process, C 2 …

Catalytic Reaction Mechanism in Native and Mutant Catechol- O-methyltransferase from the Adaptive String Method and Mean Reaction Force Analysis.

2018

Catechol- O-methyltransferase is an enzyme that catalyzes the methylation reaction of dopamine by S-adenosylmethionine, increasing the reaction rate by almost 16 orders of magnitude compared to the reaction in aqueous solution. Here, we combine the recently introduced adaptive string method and the mean reaction force method, in combination with the structural and electronic descriptors to characterize the reaction mechanism. The catalytic effect of the enzyme is addressed by the comparison of the reaction in the human wild-type enzyme, in the less effective Y68A mutant, and in aqueous solution. The influence of these different environments at different stages of the chemical process and th…

Electroreduction of aliphatic chlorides at silver cathodes in water

2010

The effect of water on the reduction of aliphatic chlorides at silver cathodes was investigated by cyclovoltammetric experiments in acetonitrile, water and their mixture and focused electrolyses in water solutions. The addition of water to acetonitrile gives rise to the formation of new peaks and/or the displacement of pre-existent peaks at dramatically less negative potentials. In a water medium, silver shows a very large electrocatalytic effect towards the reduction of chlorinated aliphatic compounds belonging to the classes of chloromethanes, chloroethanes and chloroethenes, dramatically higher than that observed in aprotic solvents such as dimethylformamide (DMF) or acetonitrile (ACN). …

Theoretical study of phosphodiester hydrolysis in nucleotide pyrophosphatase/phosphodiesterase. Environmental effects on the reaction mechanism.

2010

We here present a theoretical study of the alkaline hydrolysis of methyl p-nitrophenyl phosphate (MpNPP(-)) in aqueous solution and in the active site of nucleotide pyrophosphatase/phosphodiesterase (NPP). The analysis of our simulations, carried out by means of hybrid quantum mechanics/molecular mechanics (QM/MM) methods, shows that the reaction takes place through different reaction mechanisms depending on the environment. Thus, while in aqueous solution the reaction occurs by means of an A(N)D(N) mechanism, the enzymatic process takes place through a D(N)A(N) mechanism. In the first case, we found associative transition-state (TS) structures, while in the enzyme TS structures have dissoc…

Nanoscale etching of III-V semiconductors in acidic hydrogen peroxide solution: GaAs and InP, a striking contrast in surface chemistry

2019

In this study of nanoscale etching for state-of-the-art device technology, the importance of surface chemistry, in particular the nature of the surface oxide, is demonstrated for two III-V materials. Striking differences in etching kinetics were found for GaAs and InP in sulphuric and hydrochloric acidic solutions containing hydrogen peroxide. Under similar conditions, etching of GaAs was much faster, while the dependence of the etch rate on pH, and on H2O2 and acid concentrations also differed markedly for the two semiconductors. Surface analysis techniques provided information on the product layer present after etching: strongly non-stoichiometric porous (hydr)oxides on GaAs and a thin st…

ChemInform Abstract: Oxidative Transformation of Aryls Using Molybdenum Pentachloride

2012

Molybdenum pentachloride combines a strong Lewis acid character with an unusually high oxidation potential creating a powerful reagent for oxidative transformations. Since the oxidative coupling reaction of aryls is induced at an extraordinarily high reaction rate, a variety of labile groups, e.g. iodo, tert-alkyl, etc., are tolerated on the aromatic core. Furthermore, the co-formed molybdenum salts can either be exploited for template effects to obtain uncommon geometries in a preferred manner, or redox-play starts after aqueous workup. Therefore MoCl5 represents a unique and easily available reagent.

1987

1987

LINKING TEACHER PROFESSIONAL DEVELOPMENT NEEDS WITH APPROPRIATE SOLUTIONS: INSIGHTS FROM AN INIATIVE IN LATVIA

2021

International surveys have stated that each year teachers spend, on average, more than 10 days engaged in different professional development activities. The purpose for this investment in teacher professional development (TPD) is clear: teachers’ competence must develop according to changes in curriculum and 21st century requirements. In previous research we have developed a theoretical teacher competence framework, implemented it to identify teacher (N=263) groups competence gaps and professional development needs. The goal of this research is to link identified professional development needs related to the instruction of 21st century skills (criteria - instructional design, learning goals…

Development of a biosensor for copper detection in aqueous solutions using an Anemonia sulcata recombinant GFP.

2014

Fluorescent proteins from marine organisms represent potential candidates for biosensor development. In this paper, we described the isolation of a native green fluorescent protein from Anemonia sulcata and the cloning and purification of its equivalent as a recombinant protein in Escherichia coli. Furthermore, the spectroscopic behaviours of the native and recombinant GFPs were investigated as a function of Cu2+, Cd2+, Pb 2+ and Ni2+ concentration. Our results suggest the high selectivity of both proteins at copper than the other metals and, for the recombinant protein, a great sensitivity at a very low concentration (0.1-1 μM). Moreover, starting from these data, using the combination of …