1. Vitrification of Cryoprotectant Solutions(Lectures presented at the Meeting on the 30th Anniversary of Japanese Society for Research of Freezing and Drying(in part))

Abstract

Vitrification, or glass formation, is a feature of the low temperature phase behaviour of many aqueous solutions. Here the physical conditions favouring glass formation are reviewed and discussed in terms of a number of well known aqueous solution systems. The discussion will also consider the conditions under which devitrification (crystallization during warming) and recrystallization (ie. ripening) are also important. The role of the solute in promoting glass formation has also been the subject of study in recent years, in an effort to develop improved solutes which support glass formation at lower solute concentrations. It has been observed that one of the functions of a solute which strongly promotes glass formation is to break down the highly structured regions which tend to build up in pure water at temperatures below 0℃. This occurs via strong specific interactions between the solute and water molecules, however in the extreme of very strong interactions solute hydrate compound formation can interfere with vitrification by providing an alternate crystalline phase other than ice. The nature of the solute-water interactions depend strongly on the chemical structure of the solute and detailed trends are beginning to emerge as a result of spectroscopic studies. For example, in the family of diol compounds related to ethane 1, 2 diol it has been observed, by nuclear magnetic resonance studies, that the addition of an alkyl group to the hydroxy carbon produces a more basic hydroxy group. This results in a stronger hydrogen bond between the solute and water, and hence provides the structural disruption in the solution required to promote glass formation.