Study of solvent effects on the stability constant and ionic mobility of the dibenzo-18-crown-6 complex with potassium ion by affinity capillary electrophoresis.

The effect of solvent on the strength of noncovalent interactions and ionic mobility of the dibenzo-18-crown-6 complex with K+ in water/organic solvents was investigated by using affinity capillary electrophoresis. The proportion of organic solvent (methanol, ethanol, propan-2-ol, and acetonitrile) in the mixtures ranged from 0 to 100 vol.%. The stability constant, KKL , and actual ionic mobility of the dibenzo-18-crown-6-K+ complex were determined by the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of dibenzo-18-crown-6 on the concentration of K+ (added as KCl) in the background electrolyte (25 mM lithium acetate, pH 5.5, in the above mixed hydro-organic solvents). Competitive interaction of the dibenzo-18-crown-6 with Li+ was observed and quantified in mixtures containing more than 60 vol.% of the organic solvent. However, the stability constant of the dibenzo-18-crown-6-Li+ complex was in all cases lower than 0.5 % of KKL . The log KKL increased approximately linearly in the range 1.62-4.98 with the increasing molar fraction of organic solvent in the above mixed solvents and with similar slopes for all four organic solvents used in this study. The ionic mobilities of the dibenzo-18-crown-6-K+ complex were in the range (6.1-43.4) × 10-9 m2 V-1 s-1 .