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

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.

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“…The impact of nonelectrostatic interactions, as well as the correlation of the size of hydrated cations with CO adsorption sites and Stark tuning rates, is further supported by changing the nature of cations through chelation. 18-Crown-6 is a crown ether known to effectively chelate an equimolar solution of K + ions (60). Thus, the nature of the cation can largely be changed by introducing the crown ether to the KOH electrolyte (crown: K + = 1:1) to form a chelated complex, referred to as C-K + (Fig.…”

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“…As KOH, CsOH·H 2 O, and t -BuOK produced product 2a in similar yields, KOH was chosen for the next experiments, considering its lower cost, ready availability, and easier handling. Further experiments also showed that the reaction was faster when 10 mol % of dibenzo-18-crown-6 was used as an additive (Table , entry 12), which suggests that its recognized binding affinity to the potassium cation played a role in this system. However, the reaction yield of 2a did not improve.…”

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“…The geometry of the 15- crown -5 head with an attached benzene group and the complex formed with Au 3+ were optimized using the B3LYP functional 48 , which was implemented in the GAUSSIAN09 program (G09) 49 . The B3LYP density functional has been used to model the crown ether in other works 50,51 . The 6–31 + G(d) basis set was used to describe all of the electrons in the system.…”