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Water is the most eccentric molecule in our ecosystem. It is quadrupolar, with two positive and two negative charges at the vertices of an almost regular tetrahedron. Because of the particular hybridisation of the molecular orbitals, H2O is unable to form covalent bonds. Its interactions are confined to weak hydrogen bonds. In this respect, carbohydrates, whose structures can be written as Cm(H2O)n, closely resemble water. The hydrogen bond orientations of their –OH groups are also tetrahedral in space, and hydrogen bond lengths, angles and energies in crystalline sugars coincide almost completely with those of ice Like ice, the crystals can form chains, rings and infinite three dimensional networks, all linked (and kept apart) by hydrogen bonds.

Like inorganic molecules, they can also interact with water in the form of crystal hydrates, e.g. glucose.H2O, α,α-trehalose.2H2O or β.β-trehalose.4H2O, which can be dehydrated. But, unlike their inorganic counterparts, such transitions occur very slowly and proceed via long-lived intermediate and noncrystalline (amorphous) states. They therefore do not exhibit characteristic transition temperatures. Thus, the dehydrations appear to be irreversible in real time which may cause problems in some processes, like water removal, that employ carbohydrates as stabilisers.

Because of their useful rheological properties, the long-lived supersaturated carbohydrate/water mixtures find uses in the processing of labile materials, yielding solid mixtures with useful shelf lives, but coupled with adjustable water solubilities. The material science of such ‘water soluble glasses’ still remains to be put on a firmer basis.

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