Fluorescence, induced circular dichroism and molecular mechanics of 1-methyl naphthalenecarboxylate complexes with 2-hydroxypropyl cyclodextrins.

Steady-state, time-resolved fluorescence, Circular Dichroism and Molecular Mechanics techniques were used to study the complexation of 1-methyl naphthalenecarboxylate (1MN) with the 2-hydroxylpropyl-alpha-, -beta- and -gammacyclodextrins (HPCDs). The emission spectrum of 1MN shows two bands whose intensity ratios (R) are sensitive to complexation. The stoichiometry, binding constants and thermodynamics parameters upon complexation were obtained from the variation of fluorescence intensity, R, and lifetime averages, [Formula: see text], with [HPCD] and temperature. They were then compared with the ones obtained for the complexation of 1MN with the non-substituted alpha-, beta- and gammaCDs. Like the 1MN:CD complexes, the 1MN:HPCD ones showed 1:1 stoichiometries, but they resulted relatively more stable. Molecular Mechanics calculations in the presence of water allowed us to understand the structure of the complexes and the possible driving forces responsible for the complexation. Geometry agrees with the experimental stoichiometry and the signs of enthalpy and entropy changes. R for the complexes, quenching, fluorescence depolarization measurements and induced circular dichroism spectra also supported the proposed structures.