During freezing membrane

It is appropriate to consider the toxicities of different ions toward membranes. During freezing of thylakoids, anion toxicity decreases in the order 1 > Br > N03 > CT > F > acetate. This is reminiscent of the Hofmeister lyotropic power series, which was originally observed with regard to denaturation of euglobulins, then for blood clotting, then for... 

From these results it can be concluded that damage to mitochondrial membranes, as observed in this study, was more closely related to the extent of ice formation than to the size of ice crystals. Therefore, this damage might not be caused by mechanical injury of membranes but rather by removal of water from the membranes during freezing or, in other words, by a dehydration process. Water is necessary for the... 

LABBfi c, CROWE L M and CROWE J H (1997) Stability of the lipid component of trout sperm plasma membrane during freeze-thawing. Cryobiology, 34,176-182. 

Anchordoguy, T.J., Rudolph, A.S., Carpenter, J.F., Crowe, J.H. (1987). Modes of interaction of cryoprotectants with membrane phospholipids during freezing. Cryobiol. 24,324-331. 

Rudolph, A. S., and Crowe, J. H. (1985). Membrane stabilization during freezing The role of two natural cryoprotectants, trehalose and proline, Cryobiology, 22, 367-377. 

De Antoni et al. [1.23] demonstrated, that the addition of trehalose during freezing and thawing of two strains of Lactobacillus bulgaricus improved the survival rate differentially, but in both cases considerably. The samples (1 mL) were frozen at 18 °C/min to -60 °C and thawed to 37 °C at 15 °C/min. The solution consisted of distilled water, culture medium and 10 % milk with or without trehalose. It was shown, that after three freezingthawing cycles, milk alone resulted in a survival rate of 24 % or 65 %, while with trehalose this was can be improved to 32 % and 100 % respectively. The efficacy in the case of both strains was clearly different. De Antoni et al. suggested, that the efficiency of milk was related to its Ca2+ content, while the trehalose could replace water molecules in the phospholipids of the membranes. However no mention was made wether other sugar molecules in milk showed any effect. 

The total pressure during freeze drying may be measured by several methods, though only two are mostly used heat conductivity, and the membrane pressure difference gauge. Their operating principles and their advantages and disadvantages are described below. 

Ausbom, M Schreier, H Brezesinnski, G., Fabian, H., Meyer, H. W.. Nuhn, P. The protective effect of free and membrane-bound cryoprotctants during freezing and freeze drying of liposomes. J. Controlled Release, 30 (2), p. 105-116, 1994... 

Proper water management in proton exchange membrane fuel cells (PEMFCs) is critical to PEMFC performance and durability. PEMFC performance is impaired if the membrane has insufficient water for proton conduction or if the open pore space of the gas diffusion layer (GDL) and catalyst layer (CL) or the gas flow channels becomes saturated with liquid water, there is a reduction in reactant flow to the active catalyst sites. PEMFC durability is reduced if water is left in the CL during freeze/thaw cycling which can result in CL or GDL separation from the membrane,1 and excess water in contact with the membrane can result in accelerated membrane thinning.2... 

P. The protective effect of free and membrane-bound cryoprotectants during freezing and freeze-drying of liposomes./. Controlled Release 30,105-116,... 

Fig. 18. Diagrams illustrating the differences and difficulties during freezing of cells in suspension (a) and on surfaces (b, c and d). In both cases, large ice crystal formation must be avoided, this means that freezing must be rapid and often involves the use of cryo-protectants. In suspension, the use of hypertonic solutions to shrink cells by osmosis helps to avoid membrane rupture. But with cells fixed to surfaces, shrinkage can lead to rupture of the filopodia or to parts of cytoskeleton or cell membrane (c). Additionally, animal cells under stress (including this kind of osmotic stress) tend to build up into a spherical shape. This means they would lose many of their surface contacts before freezing and disappear into solution after re-thawing. Cryo-con-servation of adhered cells in defined positions requires very precise control of the conditions...

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