abstract
Solid-inclusion compounds of ethylene glycol butyl ether (C4E1), di(ethylene glycol) butyl ether (C4E2) and di(ethylene glycol) hexyl ether (C6E2) in beta-cyclodextrin (beta CD), with general formula represented by the notation {beta CD center dot CnEm}, were prepared from aqueous solution and characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-Raman and C-13 CP MAS NMR spectroscopies, at ambient humidity, as true hydrated microcrystalline inclusion compounds, pointing to a cage structure for {beta CD center dot C4E1} and a channel structure for both [beta CD center dot C4E2] and {beta CD center dot C6E2}. In addition, the inclusion compounds were investigated at several defined relative humidities (RHs). Several relative intensities of beta CD Raman bands generally ascribed to C-O stretching and CH2 bending vibrations are found to be influenced by the presence of guests in the beta CD cavity or the increase of ambient humidity, or by both of these factors. PXRD patterns show that crystalline structures are preserved for RHs equal or above 20%. Interestingly, important changes on the multiplicity of resonances and in the dispersions of C-13 CP MAS NMR chemical shifts values for all the carbon atoms of the beta CD macrocycle are observed in passing from RH 15% to 20%, suggesting amorphous structures below RH 20%. Overall, the above findings converge to stress the structural relevance of hydration water in the beta CD inclusion compounds, either with a cage packing arrangement or with a channel structure.
keywords
NONIONIC SURFACTANT C12E4; C-13 CHEMICAL-SHIFTS; CP-MAS NMR; WATER-MOLECULES; HIGH-RESOLUTION; REAL-TIME; COMPLEXES; DYNAMICS; DEHYDRATION; RAMAN
subject category
Chemistry
authors
Cunha-Silva, L; Teixeira-Dias, JJC
our authors
José J.C. Teixeira Dias
Full professorGroups