Simulation Studies of the Dynamics and the Connectivity Patterns of Hydrogen Bonds in Water from Ambient to Supercritical Conditions.

Pressurized high-temperature water attracts attention as a promising medium for chemical synthesis, biomass processing or destruction of hazardous waste. Adjustment to the desired solvent properties requires knowledge on the behavior of populations of hydrogen-bonded molecules. In this work, the interconnection between the hydrogen bond (HB) dynamics and the structural rearrangements of HB networks have been studied by molecular dynamics simulation using the modified central force flexible potential and the HB definition controlling pair interaction energy, HB length and HB angle.

3D Characterization of the Molecular Neighborhood of OH Radical in High Temperature Water by MD Simulation and Voronoi Polyhedra.

Understanding the properties of the OH radical in aqueous environments is essential for biochemistry, atmospheric chemistry, and the development of green chemistry technologies. In particular, the technological applications involve knowledge of microsolvation of the OH radical in high temperature water. In this study, the classical molecular dynamics (MD) simulation and the technique based on the construction of Voronoi polyhedra were used to provide 3D characteristics of the molecular vicinity of the aqueous hydroxyl radical (OH).

Dynamics of Ion Pairing in Dilute Aqueous HCl Solutions by Spectroscopic Measurements of Hydroxyl Radical Conversion into Dichloride Radical Anions.

The rate of formation of dichloride anions (Cl) in dilute aqueous solutions of HCl (2-100 mmol·kg) was measured by the technique of pulse radiolysis over the temperature range of 288-373 K. The obtained Arrhenius dependence shows a concentration averaged activation energy of 7.3 ± 1.

Water-Triggered Photoinduced Electron Transfer in Acetonitrile-Water Binary Solvent. Solvent Microstructure-Tuned Reactivity of Hydrophobic Solutes.

The solvent-composition dependence of quenching triplet states of benzophenone (BP) by anisole in acetonitrile-water (ACN-HO) mixtures was investigated by laser flash photolysis over the water mole fraction () increasing from 0 to 0.92. Single exponential decay of BP was observed over the whole composition range.

Ionic-Equilibrium-Based Mechanism of OH Conversion to Dichloride Radical Anion in Aqueous Acidic Solutions by Kinetic and Theoretical Studies.

A new mechanism for the dichloride radical anion (Cl) formation in diluted acidic chloride solutions is proposed on the grounds of pulse radiolysis measurements of the optical absorption growth at 340 nm and the density functional theory and Hartree-Fock computations. We show that the rate of OH conversion into Cl is determined by the equilibrium concentration of the ionic pair HO·Cl. According to the proposed mechanism, the diffusional encounter of OH and HO·Cl is followed by fast concerted charge/proton transfer ( k(25 °C) = 6.

Mechanism of OH radical hydration: a comparative computational study of liquid and supercritical solvent.

Flexible models of the radical and water molecules including short-range interaction of hydrogen atoms have been employed in molecular dynamic simulation to understand mechanism of (●)OH hydration in aqueous systems of technological importance. A key role of H-bond connectivity patterns of water molecules has been identified. The behavior of (●)OH(aq) strongly depends on water density and correlates with topological changes in the hydrogen-bonded structure of water driven by thermodynamic conditions.

Molecular dynamics study of the hydration of the hydroxyl radical at body temperature.

Classical molecular dynamics (MD) simulation of ˙OH in liquid water at 37 °C has been performed using flexible models of the solute and solvent molecules. We derived the Morse function describing the bond stretching of the radical and the potential for ˙OH-H(2)O interactions, including short-range interactions of hydrogen atoms. Scans of the potential energy surface of the ˙OH-H(2)O complex have been performed using the DFT method with the B3LYP functional and the 6-311G(d,p) basis set.

Transition from patchlike to clusterlike inhomogeneity arising from hydrogen bonding in water.

Assembling of water molecules via hydrogen bonding has been studied by molecular dynamics simulations using flexible potential model. The relationship between the number of H-bonds per molecule, n(HB), the size of H-bonded nets, k, and the size of patches of four-bonded molecules, k(4), has been examined for several thermodynamic states of water ranging from ambient to supercritical conditions. Two kinds of structural inhomogeneity have been found: the patchlike associated with the mean n(HB)> 2.