Complexation of dimethyl 2,3-naphthalenedicarboxylate with 2-hydroxypropyl-alpha-, -beta- and -gamma-cyclodextrins in aqueous solution by fluorescence, circular dichroism and molecular mechanics

Fluorescence, circular dichroism and molecular mechanics have been used to study the complexation of 2,3-dimethyl naphthalenedicarboxylate with 2-hydroxypropyl-alpha-, -beta and -gamma-cyclodextrins (HPCDs) in aqueous solution. Emission spectra upon excitation of the naphthalenedicarboxylate group show two bands whose intensity ratio R is quite sensitive to polarity. From the change of R and lifetimes averages with HPCD concentration and temperature were obtained the stoichiometry, the association constants and the enthalpy and entropy changes during the complexation. R, and the fluorescence anisotropies (r) extrapolated at [HPCD]-->infinity allows us to estimate the polarity and microviscosity of the media surrounding the guest when complexed. In addition, the analysis of quenching and induced circular dichroism experiments and molecular mechanics calculations in the presence of water, provide information about the forces responsible for the complexation and the geometry of the complexes.