Institute of Applied Radiation Chemistry, Technical University of Lodz, Zeromskiego 116, 90-924 Lodz, Poland.
J Chem Phys. 2012 Feb 14;136(6):064510. doi: 10.1063/1.3683436.
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. Liquid and supercritical water above the critical density exhibit the radical localization in cavities existing in the solvent structure. A change of mechanism has been found at supercritical conditions below the critical density. Instead of cavity localization, we have identified accumulation of water molecules around (●)OH associated with the formation of a strong H-donor bond and diminution of non-homogeneity in the solvent structure. For all the systems investigated, the computed hydration number and the internal energy of hydration Δ(h)U showed approximately linear decrease with decreasing density of the solvent but a degree of radical-water hydrogen bonding exhibited non-monotonic dependence on density. The increase in the number of radical-water H-acceptor bonds is associated with diminution of extended nets of four-bonded water molecules in compressed solution at ~473 K. Up to 473 K, the isobaric heat of hydration in compressed liquid water remains constant and equal to -40 ± 1 kJ mol(-1).
已经在分子动力学模拟中采用了包括氢原子短程相互作用的自由基和水分子的灵活模型，以理解在具有技术重要性的水相体系中（●）OH 水合的机制。已经确定了水分子氢键连接模式的关键作用。（●）OH(aq) 的行为强烈依赖于水的密度，并与由热力学条件驱动的水的氢键结构的拓扑变化相关联。在临界密度以上的液态和超临界水中，自由基在溶剂结构中存在的腔体内局部化。在低于临界密度的超临界条件下，已经发现了机制的变化。我们已经确定，自由基周围水分子的积累与强 H 供体键的形成以及溶剂结构中非均相性的减少有关，而不是空腔定位。对于所有研究的系统，计算出的水合数和水合内能Δ(h)U 都表现出与溶剂密度降低近似线性的下降，但自由基-水氢键的程度表现出非单调依赖于密度。自由基-水 H-接受键数量的增加与在~473 K 的压缩溶液中四键结合水分子扩展网络的减少有关。在 473 K 以下，压缩液态水中的恒压水化热保持恒定，等于-40 ± 1 kJ mol(-1)。
