Solvent effects on the interaction between alkali metal cations and 1,3-Diisopropoxycalix [4] arenecrown-6: Nuclear magnetic resonance spectroscopy and Independent Gradient Model Non-Covalent interactions analysis

Abstract

The combination of 1,3-Diisopropoxycalix [4] arenecrown-6 (BPC6) and alkali metal ions were studied in different solvents by 1H and 133Cs Nuclear magnetic resonance (NMR) spectra, gmx_MMPBSA, and Independent Gradient Model (IGM) non-covalent interactions analysis based on Molecular Dynamics (MD) Simulations. The binding energy of BPC6·M+ complex follows the order: BPC6·Cs+ > BPC6·Rb+ > BPC6·K+ in CHCl3, which is completely reverse to that in vacuum. In addition, the coordination properties depend on solvent polarity: In the low polarity solvent such as CHCl3, all the oxygens in crown ether chain of BPC6 are involved in the coordination with Cs+ ions. By comparison, in the high polarity solvents such as CH3CN and CH3OH, the number of oxygens participates in the complexation decreases, and the cation-π interaction areas of complexes are also reduced. That is because the contribution of electrostatic interactions in complexation is weakened by solvent effect. The cation-π interaction plays a very important role in selectivity among alkali metal cations and coordination stability of BPC6·M+ complex in different solvents.