Ishizuka Ryosuke, Matubayasi Nobuyuki, Tu Kai-Min, Umebayashi Yasuhiro
Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
J Phys Chem B. 2015 Jan 29;119(4):1579-87. doi: 10.1021/jp5101957. Epub 2015 Jan 8.
Cation and anion effects were investigated in the energetics of CO2 solvation in room-temperature ionic liquids. The solvation free energy in 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C4mim][NTf2]) was calculated with three types of force fields by molecular dynamics simulations combined with the energy-representation (ER) method, and the interaction responsible for the CO2 stability was examined in terms of the average sum of the solute-solvent interaction energy and its electrostatic and van der Waals components. A key role of the van der Waals component was found for the cation contribution, and the electrostatic component was seen to be minor in the anion contribution. The solvation free energy of CO2 was also investigated in ionic liquids of the form 1-n-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Cnmim][NTf2]) with varying alkyl-chain lengths of n = 4, 6, 8, and 12 by the ER method. The free energy was found to depend weakly on n, in agreement with experiments, and the cation and anion contributions and the electrostatic and van der Waals interaction components acted similarly at all values of n examined. The alkyl-chain length was found not to affect the local structure around CO2 strongly, and its effect on the interaction energy with CO2 appeared mainly through the bulk density.
研究了阳离子和阴离子对室温离子液体中二氧化碳溶剂化能的影响。采用分子动力学模拟结合能量表示（ER）方法，用三种类型的力场计算了1-正丁基-3-甲基咪唑双（三氟甲基磺酰）亚胺（[C4mim][NTf2]）中的溶剂化自由能，并根据溶质-溶剂相互作用能及其静电和范德华分量的平均和，研究了对二氧化碳稳定性起作用的相互作用。发现范德华分量对阳离子贡献起关键作用，而静电分量在阴离子贡献中较小。还通过ER方法研究了具有不同烷基链长度n = 4、6、8和12的1-正烷基-3-甲基咪唑双（三氟甲基磺酰）亚胺（[Cnmim][NTf2]）形式的离子液体中二氧化碳的溶剂化自由能。发现自由能对n的依赖性较弱，这与实验结果一致，并且在所研究的所有n值下，阳离子和阴离子贡献以及静电和范德华相互作用分量的作用相似。发现烷基链长度对二氧化碳周围的局部结构影响不大，其对与二氧化碳相互作用能的影响主要通过体密度体现。
