Reversible dehydration of trehalose and anhydrobiosis: from solution stateto an exotic crystal?

Physico-chemical properties of the trehalose-water system are reviewed with special reference to the transformations that may shed light on the mechan ism of trehalose bio-protection. Critical analysis of solution thermodynami cs is made in order to scrutinize trehalose properties often called 'anomal ous' and to check the consistency of literature results. Discussion on the conversion between the solid state polymorphic forms is given, with a speci al emphasis of the transformations involving the newly identified anhydrous crystalline form of alpha,alpha -trehalose, TREalpha. This exotic crystal is almost 'isomorphous' with the dihydrate crystal structure, and possesses the unique feature of reversibly absorbing water to produce the dihydrate, without changing the main structural features. The reversible process coul d play a functional role in the well-known ability of this sugar to protect biological structures from damage during desiccation. The final aim of the paper is to add some new insights into and to reconcile previous hypothese s for the peculiar 'in vivo' action of trehalose. (C) 2001 Elsevier Science Ltd. All rights reserved.