Choi Chang Min, Heo Jiyoung, Kim Nam Joon
Department of Chemistry, Chungbuk National University, Chungbuk, 361-763, South Korea.
Chem Cent J. 2012 Aug 8;6(1):84. doi: 10.1186/1752-153X-6-84.
Dibenzo-18-crown-6 (DB18C6) exhibits the binding selectivity for alkali metal cations in solution phase. In this study, we investigate the main forces that determine the binding selectivity of DB18C6 for the metal cations in aqueous solution using the density functional theory (DFT) and the conductor-like polarizable continuum model (CPCM).
The bond dissociation free energies (BDFE) of DB18C6 complexes with alkali metal cations (M+-DB18C6, M = Li, Na, K, Rb, and Cs) in aqueous solution are calculated at the B3LYP/6-311++G(d,p)//B3LYP/6-31 + G(d) level using the CPCM. It is found that the theoretical BDFE is the largest for K+-DB18C6 and decreases as the size of the metal cation gets larger or smaller than that of K+, which agrees well with previous experimental results.
The solvation energy of M+-DB18C6 in aqueous solution plays a key role in determining the binding selectivity of DB18C6. In particular, the non-electrostatic dispersion interaction between the solute and solvent, which depends strongly on the complex structure, is largely responsible for the different solvation energies of M+-DB18C6. This study shows that the implicit solvation model like the CPCM works reasonably well in predicting the binding selectivity of DB18C6 in aqueous solution.
二苯并 - 18 - 冠 - 6（DB18C6）在溶液相中对碱金属阳离子表现出结合选择性。在本研究中，我们使用密度泛函理论（DFT）和类导体极化连续介质模型（CPCM）研究了决定DB18C6在水溶液中对金属阳离子结合选择性的主要作用力。
在B3LYP/6 - 311++G(d,p)//B3LYP/6 - 31 + G(d)水平下，使用CPCM计算了DB18C6与碱金属阳离子（M⁺ - DB18C6，M = Li、Na、K、Rb和Cs）在水溶液中的键解离自由能（BDFE）。发现K⁺ - DB18C6的理论BDFE最大，并且当金属阳离子的尺寸大于或小于K⁺时，BDFE会降低，这与先前的实验结果非常吻合。
M⁺ - DB18C6在水溶液中的溶剂化能在决定DB18C6的结合选择性方面起着关键作用。特别是，溶质与溶剂之间的非静电色散相互作用强烈依赖于配合物结构，在很大程度上导致了M⁺ - DB18C6不同的溶剂化能。本研究表明，像CPCM这样的隐式溶剂化模型在预测DB18C6在水溶液中的结合选择性方面表现良好。
