Freezing biological water

The most significant kinetic isotope effect is the primary isotope effect, where a bond containing the atom or isotope of interest is broken or formed in the rate-determining step of the reaction. Secondary isotope effects refer to reactions where the isotopic atom is located next to the reactive bond [9], Many biological reactions and the rapid freezing of water are conunon examples of reactions that produce kinetic isotope fractionation [1,16]. 

Computer simulations, such as MD and Monte Carlo (MC), are useful tools for studying the structural and dynamic properties of ice and water at the molecular level. Simulations for the surfaces and interfaces of ice near the melting point (T ) have attracted a great deal of attention in connection with such issues as the pattern formation of snow and ice crystals [26], the freezing of water in biological systems [54], and the formation of acid snow [55]. 

Lyophilization. LyophiLization is essentially a drying technology. Some dmgs and biologicals are thermolabile and/or unstable in aqueous solution. Utilization of freeze drying permits the production of granules or powders that can be reconstituted by the addition of water, buffered solution, or mixed hydrophilic solvents just prior to use, eg, certain antibiotic suspensions. 

The molecular structure and dynamics of the ice/water interface are of interest, for example, in understanding phenomena like frost heaving, freezing (and the inhibition of freezing) in biological systems, and the growth mechanisms of ice crystals. In a series of simulations, Haymet and coworkers (see Refs. 193-196) studied the density variation, the orientational order and the layer-dependence of the mobilitity of water molecules. The ice/water basal interface is found to be a relatively broad interface of about... 

The fact that a certain amount of water cannot crystallize in a high concentrated solution, and that the molecules cannot move any more to the existing crystals, is important during the freezing of biological substances. Table 1.1 shows this for some food products. 

Nail, St. L., Johnson, W. Methodology for in-process determination of residual water in freeze-dried products. Developments in Biological Standardization, Vol. 74, p. 137-152. Acting Editors Joan C. May, F. Brown, S. Karger AG, CH-4009 Basel (Switzerland), 1992... 

Freeze drying is mostly done with water as solvent. Fig. 1.1 sows the phase diagram of water and the area in which this transfer from solid to vapor is possible. This step is difficult, even for pure water. If the product contains two or more components in true solutions or suspensions, the situation can become so complicated that simplified model substances have to be used. Such complex systems occur ubiquitously in biological substances. 

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