Binding selectivity of dibenzo-18-crown-6 for alkali metal cations in aqueous solution: A density functional theory study using a continuum solvation model

Chang Min Choi,Jiyoung Heo,Nam Joon Kim

doi:10.1186/1752-153x-6-84

Chang Min Choi, Jiyoung Heo + Show 1 more

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https://doi.org/10.1186/1752-153x-6-84

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Abstract

BackgroundDibenzo-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).ResultsThe 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.ConclusionThe 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.

Highlights

Crown ether is one of the most well-known host molecules, which exhibits the binding selectivity for alkali metal and alkali earth metal cations in solution phase [1,2]
It is found that the solvation energy of M+-DB18C6 plays a key role in determining the relative bond dissociation free energies (BDFE) of M+-DB18C6 and the binding selectivity of DB18C6 in aqueous solution
This study shows that the inexpensive continuum solvation model like the conductor-like polarizable continuum model (CPCM) provides a tool to understand the binding selectivity of DB18C6 in aqueous solution on the basis of the followings: First, the strongest binding affinity of DB18C6 to K+ among other alkali metal cations as well as the decrease of the binding affinity with increasing or decreasing the size of the metal cation with respect to that of K+ are well reproduced by the calculations using density functional theory (DFT) and the CPCM

Summary

Introduction

Crown ether is one of the most well-known host molecules, which exhibits the binding selectivity for alkali metal and alkali earth metal cations in solution phase [1,2]. To understand the role of solvation and thereby the origin of the binding selectivity of crown ethers in solution phase, many experimental and theoretical studies have been performed.[9,10,11,12,13] A combined molecular mechanics and dynamics study on the cation selectivity of DB18C6 in methanol was carried out [12]. 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). Results: 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. This study shows that the implicit solvation model like the CPCM works reasonably well in predicting the binding selectivity of DB18C6 in aqueous solution

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