Chiral recognition of 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate using fluorescence anisotropy

The photophysical properties of 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate (BNP) have been examined with particular emphasis to the effects of the chiral recognition of BNP by α-, β-, and γ-cyclodextrins (CDs). Fluorescence spectra and anisotropy values of the BNP enantiomers were measured in the presence and absence of the CDs under various conditions and the chiral recognition behavior are discussed based on the acquired fluorescence data. Small spectral shifts in the fluorescence emission allowed evaluation of the binding constant and enantioselectivity of the binding in β-, and γ-cyclodextrin, but significant shifts were not observed in the case of α-cyclodextrin. Fluorescence anisotropy proved to be an effective technique to study the enantioselective interactions, even in the case of α-cyclodextrin where a smaller binding constant and enantiodiscrimination were confirmed. The differential thermodynamics of binding were examined by fluorescence anisotropy and are discussed with reference to the general structural characteristic of the cyclodextrins examined. Interestingly, BNP was found to exhibit opposite thermodynamic trends for β-cyclodextrin at low (1 mM) and high (11 mM) cyclodextrin concentrations, indicating the possibility of complex of even different modes of enantiodiscrimination in this system.