The interplay of the rate of water removal in the dehydration of alpha,alpha-trehalose

The removal of water from alpha,alpha-trehalose dihydrate, T-h, has been st udied both isothermally, at 130 degrees C, as a function of time, and as a function of the temperature at different scan rates by using differential s canning calorimetry. The protocols were chosen to discriminate the conditio ns that give rise to the formation of the anhydrous crystal form (T-beta) a nd those that, according to previous findings, generate another form, T-gam ma, characterised by a different X-ray powder diffraction pattern. Scrutiny of the thermal properties of T-gamma and of the carefully determined powde r diffraction patterns discloses that T-gamma is actually a mixture of the dihydrate and of the T-beta forms. On the basis of the scanning rate under which the formation of the T-gamma species occurs, the hypothesis is made t hat T-gamma contains a T-h hydrated core encapsulated by a T-beta anhydrous layer. (C) 1999 Elsevier Science Ltd. All rights reserved.