CRITICAL COOLING RATES TO AVOID ICE CRYSTALLIZATION IN SOLUTIONS OF CRYOPROTECTIVE AGENTS

Emulsion isothermal calorimetry has been used to construct time-temperature-transformation (TTT) curves and hence continuous cooling (CT) curves for aqueous solutions of a number of established and potential cryoprotective agents, namely glycerol, dimethyl sulphoxide, (2R,3R)-(-)-butane--2,3-diol and mixtures of the meso isomer and racemate of butane-2,3-diol. The cooling rates required to avoid crystallization in these solutions are calculated from the TTT curves. The presence of the meso isomer of butane-2,3-diol at concentrations below 7% is shown not to affect the critical cooling rate for the racemic mixture. For vitrification at a cooling rate of 100 K min-1 the concentration of (2R,3R)-(-)-butane-2,3-diol required is 31.7% whilst for dimethyl sulphoxide the concentration is 42.1% and for glycerol 48.5%. (2R,3R)-(-)-butane-2,3-diol and mixtures of (+/-)-butane-2,3-diol with up to 7% of the meso isomer are thus shown to vitrify at cooling rates much lower than those for other cryoprotective agents.