Affinity capillary electrophoresis and density functional theory applied to binding constant determination and structure elucidation of hexaarylbenzene-based receptor complex with ammonium cation

Affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations have been employed for the investigation of noncovalent interactions between hexaarylbenzene-based receptor (R) and ammonium cation NH4+. Firstly, by means of ACE, the binding constant of the NH4R+ complex in methanol was estimated from the dependence of the effective electrophoretic mobility of the receptor R (in advance corrected by our earlier developed procedure to a reference temperature of 25 °C) on the concentration of ammonium ion in the background electrolyte using non-linear regression analysis. The logarithmic form of the apparent binding (stability) constant of NH4R+ complex in the methanolic background electrolyte (25 mM Tris, 50 mM chloroacetate, pHMeOH 7.8) was evaluated as log KNH4R=4.03±0.15KNH4R=4.03±0.15. Secondly, the structural characteristics of NH4R+ complex were determined by DFT calculations.