SPECTROSCOPIC STUDIES OF SOLID ALPHA-ALPHA TREHALOSE

Infrared, Raman and high-resolution solid-state C-13 NMR spectra are r eported for the crystalline hydrate and anhydrous forms of solid alpha -alpha trehalose. A new form of anhydrous crystalline trehalose is als o reported which has been identified from its vibrational and NMR char acteristics. These show that it is distinct from the previously known anhydrous form. Detailed assignments of the spectra for all three soli ds are given. Whilst the vibrational spectra have been shown to be con sistent with the crystal structures reported for the individual disach aride molecules, the NMR results sugest that solid-stale NMR spectra a re primarily determined by packing effects rather than by inequivalenc ies within the disaccharide molecule. The longer-range effects affect different carbon atoms to different extents, having a negligible effec t on the C1,C1' atoms of the hydrated form, which displays one singlet resonance. The results obtained indicate, therefore, that the presenc e of a singlet resonance in a solid-state C-13 NMR spectrum cannot be taken as evidence of the existence of only one environment for the car bon atoms corresponding to that resonance, and may simply reflect a lo wer sensitivity of solid-state NMR to local environments.