Department of Chemistry and Biochemistry, University of California-Santa Cruz, Santa Cruz, California 95064, USA.
J Phys Chem B. 2013 Apr 25;117(16):4325-31. doi: 10.1021/jp306669t. Epub 2012 Oct 23.
Molecular dynamics simulations are used to calculate several free energy profiles relevant to the recombination/dissociation and transport of individual ions and ion pairs across the water/chloroform interface. Tetra methyl ammonium (TMA(+)) and tetra butyl ammonium (TBA(+)) (typically used as phase transfer catalysts) and a chloride ion (as an example of a transferred nucleophile) are considered. The free-energy profiles for the transfer of the three ions and the two ion pairs (TMA(+)Cl(-) and TBA(+)Cl(-)) across the interface, as well as the potential of mean force for the dissociation of these two ion pairs at different interface locations, are calculated and correlated with structural and energetic changes at the interface. These equilibrium calculations, together with nonequilibrium trajectory calculations, provide molecular insight into the mechanism of phase transfer catalysis. In particular, water surface fluctuations are strongly coupled to the ion-pair location along the interface normal and the ion-pair bond length.
分子动力学模拟被用于计算与单个离子和离子对在穿过水/氯仿界面时的重组/解离和传输相关的几个自由能分布。考虑了四甲基铵（TMA(+)）和四丁基铵（TBA(+)）（通常用作相转移催化剂）以及氯离子（作为转移亲核试剂的一个例子）。计算了三个离子和两个离子对（TMA(+)Cl(-)和 TBA(+)Cl(-)）穿过界面的转移的自由能分布，以及这两个离子对在不同界面位置解离的平均力势，并将其与界面处的结构和能量变化相关联。这些平衡计算，结合非平衡轨迹计算，为相转移催化的机制提供了分子见解。特别是，水表面的波动与沿界面法向的离子对位置和离子对键长强烈耦合。
