Contribution to the establishment of temperature-concentration curves of homogeneous nucleation in solutions of some cryoprotective agents
Rasmussen, D.; Luyet, B.
Biodynamica 11(223): 33-44
1970
ISSN/ISBN: 0006-3010 PMID: 5490673 Document Number: 5140
1. In an inquiry on the mode of action of cryoprotective substances, the question has been raised of the possibility that, in the case of rapid cooling, their efficiency may be due in part to their ability to lower the temperatures of homogeneous nucleation. 2. To evaluate this possibility, solutions of various concentrations of ethylene glycol, glycerol and polyvinyl pyrrolidone in deionized distilled water were emulsified in silicon oil, and small aliquots of the emulsion placed in capillary tubes were cooled in a differential thermal analysis apparatus which recorded the thermograms indicative of nucleation and ice formation and of melting. 3. Each solution gave two exotherms at temperatures quite far apart; these exotherms are interpreted as representing, respectively, the crystallization of the droplets that contained heterogeneous nuclei and the crystallization of the remaining droplets from homogeneously generated nuclei. 4. The data recorded led to the construction of "phase diagrams" in which the temperatures of homogeneous nucleation in terms of solute concentration for the three cryoprotectants studied are some 40 to 65 degrees C. below the melting temperatures. 5. The energetics determining the homogeneous nucleation temperature might be based in part on the colligative depression by the solute, but there are indications for the intervention of other factors. 6. The observations reported contribute to correlate the effects of the fundamental factors in nucleation and in ice formation: the degree of thermal agitation, the viscosity of the medium and the solute concentration, with the actual occurrence or the non-occurrence of phase transitions.
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