Improving inclusion capabilities of permethylated cyclodextrins by appending a cap-like aromatic moiety

Steady-state and time-resolved fluorescence techniques have been employed in the study of the complexation of methyl 2-naphthalenecarboxylate (2MN), a fluorescent probe, with 2I,3I-O-(o-Xylylene)-per-O-Me-α-, -β-, and -γ-cyclodextrins (Xmα-, Xmβ-, and XmγCDs, respectively), which have also the capability of self-aggregate. The influence of the xylylene moiety was assessed by comparing the data of 2MN complexation by Xmα-, Xmβ-, and XmγCD with those obtained for their fully permethylated mα-, mβ-, and mγCD counterparts. The 2MN emission spectrum shows two overlapping electronic bands whose ratio of intensities, R, is very sensitive to the polarity of the surrounding medium. The stoichiometry, the complex formation constants and the ΔH0 and ΔS0 parameters upon inclusion were obtained from the variations in R and 〈τ〉 as a function of CD concentration and temperature. 2MN forms 1:1 stoichiometry complexes with all the CDs. Molecular Mechanics and Molecular Dynamics calculations were performed to simulate the complexation processes in the presence of water, determine their preferred structures, and ascertain the host-guest interactions at play.