Spectroscopic studies of solid α-α trehalose

Abstract

Infrared, Raman and high-resolution solid-state 13C NMR spectra are reported for the crystalline hydrate and anhydrous forms of solid α-α trehalose. A new form of anhydrous crystalline trehalose is also reported which has been identified from its vibrational and NMR characteristics. These show that it is distinct from the previously known anhydrous form. Detailed assignments of the spectra for all three solids are given. Whilst the vibrational spectra have been shown to be consistent with the crystal structures reported for the individual disacharide molecules, the NMR results sugest that solid-state NMR spectra are primarily determined by packing effects rather than by inequivalencies within the disaccharide molecule. The longer-range effects affect different carbon atoms to different extents, having a negligible effect on the C1,C1′ atoms of the hydrated form, which displays one singlet resonance. The results obtained indicate, therefore, that the presence of a singlet resonance in a solid-state 13C NMR spectrum cannot be taken as evidence of the existence of only one environment for the carbon atoms corresponding to that resonance, and may simply reflect a lower sensitivity of solid-state NMR to local environments.