Conformational Features and Coordination Properties of Functionalized Cyclodextrins. Formation, Stability, and Structure of Proton and Copper(II) Complexes of Histamine-Bearing /8-Cyclodextrin in Aqueous Solution

The functionalized cyclodextrin 6-deoxy-6-(N-histamino)-beta-cyclodextrin was synthesized, and an NMR, EPR, pH-metric, and calorimetric investigation was carried out in aqueous solution in order to ascertain its behavior toward protonation and copper(II) complexation. Spectroscopic results as well as thermodynamic data give evidence of the influence of the beta-cyclodextrin cavity. In particular, the NMR spectra data show a protonation-promoted inclusion of the imidazole ring, while the copper(II) coordination is markedly affected by the presence of the cyclodextrin cavity, as shown by the A parallel-to value decrease, with respect to the analogous histamine complex.