Amino acid ester salt recognition by ferrocene-based ditopic receptor bearing oligoethylene glycol with pendant bipy subunits: CV, UV-vis and ESR studies

Abstract

The novel ferrocene-based ditopic receptor 1 was synthesized. This receptor bears two oligoethylene glycol arms with pendant 2,2′-bipyridine unit at the identical cyclopentadienyl rings, Cu^I cation binds to 1 to form the 1 : 1 complex (1·Cu^I) with the cavity consisting of polyether, and the resulting complex acts as a receptor for amino acid ester salts to give the ditopic complex (1·Cu^I·AAOMe–HCl). The ¹H NMR spectrum of 1·Cu^I·LeuOMe–HCl exhibits strong broadening at the bipyridine region, and the ESR spectrum of the same sample gives the signals assigned as Cu^II species. With these data, the binding of 1·Cu^I towards AAOMe·HCl leads to the conformational change, and the Cu^I complex is simultaneously oxidized to the Cu^II complex.