Single and Double Binding of 1,10-Phenanthroline and 4,7-Dimethyl-1,10-phenanthroline to HMeQ7: Contrasting pKa Shifts Induced by HMeQ7

摘要

By using UV-vis absorption, we ascertained the HMeQ7 induced supramolecular pKa shifts of 1,10-phenanthroline (guest 1) and 4,7-dimethyl-1,10-phenanthroline (guest 2), which are completely different. Based on the pKa values of guests 1 and 2, the binding behaviors of HMeQ7 with guests 1 and 2 at a specified solution pH were investigated by NMR spectroscopy and ITC techniques. NMR data indicate that the complexation of HMeQ7 with guests 1 and 2 may generate half-inclusion complex 1 subset of HMeQ7 and double binding complex 2 subset of HMeQ7boolean OR 2. The later one possesses two binding modes simultaneously, one being endo binding and the other one being exo binding, which is not observed in conventional host - guest complex. Such mixed double binding behavior for guest 2 should be one of the reasons for its large pKa shift. ITC experiments further confirmed the formation of the 1 : 1 and 1 : 2 host - guest complexes.