Glasses in aqueous systems

ABSTRACTS, 24th ANNUAL and reflection coefficient. o, to obtain an optimum correlation of the simulation with the experimental data. Experiments were performed in the temperature range from -7 to - lO”C, with an observed decrease in L, and a defined activation energy AE for cells which had been equilibrated in the Me,SO solution prior to examination. It was found that the movement of Me,SO across the plasma membrane was insufficient in magnitude to achieve the sensitivity required for evaluation of the parameters o and cr. (Sponsored by a grant from the Texas Advanced Technology Research Program.) SYMPOSIUM II-AQUEOUS SOLUTIONS AT LOW TEMPERATURES 13. Glasses in Aqueous Systems. TIMOTHY W. SCHENZ (Technical Center, General Foods Corp., 555 S. Broadway, Tarrytown, New York 10591). The characteristics and attributes of aqueous systems at low temperatures depend to a great extent on the physicochemical and thermomechanical properties of the unfrozen, amorphous matrix that surrounds the ice crystals. If this matrix is maintained as a kinetically metastable mechanical solid (a glass), then the changes that typically occur at higher temperatures can be prevented or greatly retarded. The optimum storage temperature or optimum formulation for a particular system is dictated by the characteristic glass transition temperature, T8’, of the aqueous system. The formation of aqueous glasses and their properties is influenced primarily by the nature and composition of the solutes in the unfrozen aqueous phase. The relationships between glass formation and the properties of the solutes, methodology for the measurement of glass transitions, and the functional uses of glasses in aqueous systems will be reviewed. 14. Antifreeze

Proteins

and Their Mode of Action ut

rhe Ice Surf&e. ROBERTFEENEY (Department of Food Science, University of California).

qf Ice during Systems. D. S. REID

15. Facrors Involved in the Propagation the Freezing ofBiological

(Department of Food Science, University of California, Davis). For ice to be present in a frozen system, a complex sequence of events has had to take place. Nucleation, the initiation of growth, is necessary. The nucleation process is affected by the composition of the system and by the presence or absence of a variety of catalytic moieties which can induce the heterogeneous nucleation process. Nucleation per se is a necessary but not sufficient prerequisite for the formation of ice in quantity in a frozen system. Ice has to propagate from the nuclei. The growth or propagation of ice is a process which is affected by system composition, by

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system temperature, and by the rate at which conditions are changing. The interrelationships between the kinetics of nucleus formation and the kinetics of crystal propagation are important in the light of the current understanding of the processes contributing to the observed phenomena. SESSION II-AQUEOUS SOLUTIONS AT LOW TEMPERATURES 16. Application of Silver Iodide as an Inducer of Ice Formation in Cryopreservation of Mammulian Embryos. T. KOJIMA, T. SOMA, AND N. OGURI

(Department of Animal Reproduction, National Institute of Animal Industry, Tsukuba Science City, Ibaraki, Japan). A method was devised for inducing ice crystal formation in extracellular solution using silver iodide. A latent heat occurred immediately before the temperature of the sample reached -7”C, when a 70-mm column of I .5 M dimethyl sulfoxide (Me,SO) was aspirated into a plastic straw followed by 3 mm of air and 10 mm of 1% suspension of silver iodide in distilled water (1% AgI). To examine the effect of silver iodide as an inducer of ice crystal formation in extracellular solution on in vitro development of frozen-thawed rabbit morulae, the straws were filled by successive aspiration of the following fractions: 175 pl of 1.5 M Me,SO containing the embryos, 7.5 pl of air, and 25 JLI of 1% AgI. The straws were cooled to -7°C at I”C/ min and held at -7°C for 10 min without initiating seeding. They were then cooled again to -30°C at l”C/min and plunged into liquid nitrogen. After rapid thawing, 100 of 109 (92%) embryos that were recovered developed into expanding blastocysts. To examine the viability of bovine Day 7 embryos frozen using the silver iodide seeding procedure after cervical transfer to appropriate heifers, the straws were loaded by successive aspiration of the following fractions: 175 pJ of 10% (v/v) glycerol containing the embryo, 7.5 p1 of air, and 25 pl of 1% AgI. The straws were cooled to - 7°C at 1”Cimin and held at - 7°C for 10 min without initiating seeding. They were then cooled to - 35°C at 0.3”Cimin and plunged into liquid nitrogen. After rapid thawing, the embryos recovered were immersed in 1.O M sucrose solution for 10 min and washed by modified PBS. The seven embryos were transferred to the total seven recipients simultaneously. Two pregnancies were produced, and then two normal male calves were born. The silver iodide method does not require special equipment or a manual procedure for seeding and avoids extreme temperature fluctuation of the samples that can accompany seeding procedures. Using the silver iodide method, it may be possible to seed simultaneously a large number of samples and to set samples horizontally in a cooling bath because of nonlimitation in setting of samples. This method may also make it possible to employ freezing vessels other than plastic straws. We need only to cool samples to a con-