Critical cooling rates to avoid ice crystallization in solutions of cryoprotective agents

Abstract

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.