Affinity capillary electrophoresis and quantum mechanical calculations applied to the investigation of hexaarylbenzene-based receptor binding with lithium ion

In this study, two complementary approaches, affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations, have been employed for quantitative characterization and structure elucidation of the complex between hexaarylbenzene (HAB)‐based receptor R and lithium ion Li⁺. First, by means of ACE, the apparent binding constant of Li R ⁺ complex (K) in methanol was determined from the dependence of the effective electrophoretic mobilities of Li R ⁺ complex on the concentration of lithium ions in the 25 mM Tris/50 mM chloroacetate background electrolyte (BGE) using non‐linear regression analysis. Prior to regression analysis, the effective electrophoretic mobilities of the Li R ⁺ complex were corrected to reference temperature 25°C and constant ionic strength 25 mM. The apparent binding constant of the Li R ⁺ complex in the above methanolic BGE was evaluated as logK = 1.15±0.09. Second, the most probable structures of nonhydrated Li R ⁺ and hydrated Li R ⁺·3H₂O complexes were derived by DFT calculations. The optimized structure of the hydrated Li R ⁺·3H₂O complex was found to be more realistic than the nonhydrated Li R ⁺ complex because of the considerably higher binding energy of Li R ⁺·3H₂O complex (500.4 kJ/mol) as compared with Li R ⁺ complex (427.5 kJ/mol).