Solid State Inclusion of the Nonionic Surfactant C 12 E 4 in β-Cyclodextrin, at Various Humidities: A Combined Raman and 13 C CP MAS NMR Study

The inclusion of the nonionic surfactant α- n -dodecyl-ω-hydroxytetra(oxyethylene), C 12 E 4, in β-cyclodextrin (βCD), has been prepared in the solid state and its structure characterized by powder X-ray diffraction, thermogravimetry, and Raman and 13 C CP/MAS NMR spectroscopies. Stepwise dehydration was observed in the thermogram, indicating the presence of energetically distinct water molecules. Comparison of the dispersions of 13 C chemical shift values for C1 and C4 atoms of the βCD macrocycle, within a series of inclusion compounds of C n E m homologues, reveals a rather complete symmetrization of the βCD macrocycle, and the dispersions of 13 C shifts for C6 atoms point to the particular sensitivity of these atoms to hydrogen-bonding type of interactions. The integrated intensity of the O−H Raman stretching band for the βCD inclusion compound of C 12 E 4 is approximately constant for humidities between 20% and 80%. In passing from 15% to 20% of humidity, one observes abrupt relative intensity variations of some Raman bands, in particular at 926 cm -1, and the sudden decrease of the dispersions of 13 C chemical shift values for all carbon atoms of the βCD macrocycle. Overall, the above findings converge to stress the structural relevance of hydration water in the βCD inclusion compound of C 12 E 4 .