Structure and dynamics of Na+ and Cl− solvation shells in liquid DMSO: molecular dynamics simulations

Ionic effects on supramolecular hosts: solvation and counter-ion binding in polar media

For the progress of synthetic supramolecular chemistry in aqueous solution the design of host molecules soluble in this medium is essential. A possible route is the introduction of ionic residues, with the additional advantage that also electrostatic interactions can be used to form supramolecular architectures. In this work we study the effect of different ionic substituents on a resorcin[4]arene host on solvation and counterion binding in water and dimethyl sulfoxide (DMSO). To do so, we combine dielectric relaxation spectroscopy (DRS) at 298.15 K and dilute-solution conductivity measurements covering 278.15-308.15 K. The results indicate that studied substituents lead to a comparable increase in solubility in both water and the dipolar-aprotic DMSO. However, solvation and counterion binding not only depend on the nature of the ionic substituent but also on the solvent. Although intrinsically hydrophobic in nature, resorcin[4]arenes with ionic substituents also show strong hydrophilic hydration in water, with the extent depending on the nature of the ionic group. In contrast to that, solvophobicity apparently dominates the interactions of DMSO with the solute. Counterion binding was found for both solvents and is essentially determined by solvent polarity. It appears that, compared to neat DMSO, the solubility of the cationic resorcin[4]arene with dimethylamine substituents is strongly increased in water-DMSO mixtures due to the formation of hydrogen bonds between two DMSO molecules and one water molecule.

FT-Raman spectroscopic evidences for the preferential solvation of sodium tetrafluorobrate in acetonitrile-based mixed solvents

Solutions of sodium tetrafluorobrate in acetonitrile-dimethylformamide, and acetonitrile-dimethylsulfoxide mixtures have been studied by FT-Raman spectroscopy for three solvent compositions, respectively. New bands due to solvent molecules in the first solvation shell of Na(+) were detected in the region of the O=C--N deformation and CH(3) rocking mode for amide and of the S=O and C--S stretching modes for sulfoxide. The individual solvation numbers of sodium cation in different environment were deduced. In all the cases, it is found that the sodium ion was preferentially solvated by DMF or DMSO in respective binary solvents. This result was further supported by ab initio calculations.