Molecular and macroscopic properties of trehalose and sucrose, related to biomaterial

M F. MAZZOBRE; M.P. LONGINOTTI; H.R. CORTI; P. BUERA

Zichron Yaakov, Israel

Simposio; ISOPOW 2000. 8th International Symposium on the properties of water.; 2000

The stabilization of biomaterials by their incorporation into protective carbohydrate solutions before drying or freezing is an known preservative procedure. Crystallization of the sugars or ice in the amorphous (dehydrated or frozen) system leads to the loss of the protective effects of the matrices. Evidence exists on the modification of some physical properties of sugars by salts. A critical point is to understand how molecular relaxations are affected by suprastructural relaxations or vice versa. In order to explore the effects of different salts on the properties of aqueous sugar systems, experiments were performed at critical conditions for sugar or ice crystallization. Sugar or ice crystallization were evaluated by DSC. Electrical conductivity and viscosity measurements were performed on supercooled or freeze-dried solutions containing trehalose or sucrose, or mixtures sugar-salt (MgCl2, ZnCl2, CsCl, NaCl, LiCl, KCl). Crystallization of sugar or ice was delayed in systems containing salts. The electrical conductivity measurements of NaCl or MgCl2  in concentrated trehalose solutions revealed that the ion mobility was higher than that predicted by the continuum model of viscous friction. This effect was very pronounced in MgCl2 systems and it could be ascribed to the local viscosity (around Mg2+ ions) much smaller than the bulk viscosity. The modification of the properties of sugars in the presence of salts was explained as a consequence of changes occurring at structural level (modification of water sorption behavior and on the delay of sugar and ice crystallization) and in the dynamic behavior, which we manifeste also in the crystallization of sugar and ice, and on anomalities in transport properties due to the existence of inhomogeinitiesat molecular level.