Valence tautomerism and recyclisation of type B mesoionic tetrazoles: a computational study

The energy profiles for ring opening of representative type B mesoionic 2,3-diphenyl-1,2,3,4-tetrazolium-5-olates, -thiolates, -aminides and –methylides and for alternative recyclisation pathways are investigated using ab initio MP2 calculations. The energetics of initial ring opening are found to be comparable for all systems, but the tetrazolium-5-olates are anomalous in that no alternative reaction pathway is accessible. The influence of solvent is explored using the polarised continuum model (PCM) method to simulate aqueous solvation. The only significant solvent effect is found to be solvation of the mesoionic precursors. This solvent effect correlates with dipole moment and disfavours initial valence tautomerism both kinetically and thermodynamically.

Graphical Gaussian Process Regression Model for Aqueous Solvation Free Energy Prediction of Organic Molecules in Redox Flow Battery

The solvation free energy of organic molecules is a critical parameter in determining emergent properties such as solubility, liquid-phase equilibrium constants, and pKa and redox potentials in an organic redox...

Pressure dependence of solvation of non-polar solute in simple model of water

We modelled the aqueous solvation of a nonpolar solute as a function of the radius, temperature and pressure. In this study a simple two-dimensional Mercedes-Benz (MB) water model was used in NPT Monte Carlo simulations. This model has previously been shown to qualitatively predict the volume anomalies of pure water and the free energy, enthalpy, entropy, heat capacity, and volume change in order to insert a nonpolar solute into water. Here, we extended the studies of solvation of nonpolar solute to examine the pressure dependence and broader range of temperature and size dependence. The model shows two different mechanisms, one for the solvation of large nonpolar solutes bigger than water and the second for smaller solutes.

Dependency of solvation effects on metal identity in surface reactions

Solvent interactions with adsorbed moieties involved in surface reactions are often believed to be similar for different metal surfaces. However, solvents alter the electronic structures of surface atoms, which in turn affects their interaction with adsorbed moieties. To reveal the importance of metal identity on aqueous solvent effects in heterogeneous catalysis, we studied solvent effects on the activation free energies of the O–H and C–H bond cleavages of ethylene glycol over the (111) facet of six transition metals (Ni, Pd, Pt, Cu, Ag, Au) using an explicit solvation approach based on a hybrid quantum mechanical/molecular mechanical (QM/MM) description of the potential energy surface. A significant metal dependence on aqueous solvation effects was observed that suggests solvation effects must be studied in detail for every reaction system. The main reason for this dependence could be traced back to a different amount of charge-transfer between the adsorbed moieties and metals in the reactant and transition states for the different metal surfaces.

Estudo da Energia Livre de Formação das Ligações de Hidrogênio da Dopamina em Solução Aquosa Usando CPMD

Dopamine is an important neurotransmitter belonging to the catecholamine family, which acts on the central nervous system. This catecholamine plays a key role in regulating a variety of functions, such as motor and cognitive functions. This class of neurotransmitters is important for normal neurophysiology and is also the target of a broad spectrum of therapeutic and illicit agents. Evaluating the interaction of these neurotransmitters, in particular, dopamine with water molecules, is crucial for a better understanding of the conformational preferences of dopamine in solution, which consequently assists in the design of new drugs for the treatment of diseases associated with a malfunction of the system, and direct measurement, which is particularly essential for early warning of certain diseases. In this sense, the objective of this work is to examine the effects of aqueous solvation on the geometric and electronic parameters of dopamine using Car-Parrinelo Molecular Dynamics. The Car-Parrinello Molecular Dynamics simulation was performed using the CPMD program package (Version 4.1). The results indicate that dopamine interact swith several water molecules, with the formation of hydrogen bonds. In particular, there are two hydrogen bonds (H5···Owf and N3···Hwd) with an infinite residence time that strongly suggests the protonation of these groups.

Estudo Teórico do Mecanismo de Complexação do Íon Cobalto II com a Glucosamina Usando Dinâmica Molecular de Car-Parrinello

Cobalt II is essential for the body and is one of the components of vitamin B12. However, in excess, it is toxic. It is present in various industrial and nuclear reactor waste; removing it is necessary. Among the various processes for removing heavy metals from wastewater, adsorption stands out, economical, easy to apply, and efficient. Modified chitosan has shown promise in the adsorption of cobalt II from contaminated waters. Although experimental studies show cobalt II adsorption by chitosan, the adsorption mechanism by chitosan is still unclear. This work aimed to study cobalt coordination with glucosamine (chitosan monomer) in the gas phase and aqueous solvation using the Car-Parrinello Molecular Dynamics. The results show that cobalt can coordinate strongly with the amino group of glucosamine in both the gaseous and aqueous environments. The QTAIM analysis was performed to characterize the interactions. In the gas phase, a partially covalent interaction was observed, while in the aqueous medium, the interaction of Co with glucosamine can be classified as covalent. Understanding the coordination mechanism of cobalt II with glucosamine can help remove cobalt from wastewater.