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Water nonfreezing, hydration

It is well known that at low moisture uptakes, the water associated with the cellulose exhibits properties that differ from those of liquid water and it has been called by such terms as bound water, nonsolvent water, hydrate water, and nonfreezing water. From a review of the literature, which included determinations by such techniques as NMR and calorimetry, Zeronian [303] concluded that between 0.10 and 0.20 g/g of the water present in the fiber cell wall appeared to be bound. Such regains are obtained at RVPs between 0.85 and 0.98. [Pg.83]

The amount of water that does not freeze near 0°C in a protein—water system is a useful measure of the hydration water (Kuntz and Kauz-mann, 1974). Such estimates are self-consistent, in that different methods for determining nonfreezing water give closely similar values, and are reliable, in that they agree with other thermodynamic estimates of hydration. [Pg.54]

Measurements of model polypeptides were consistent with the non-freezing water being primarily associated with ionic groups of the protein (Kuntz, 1971). A set of amino acid hydration values, constructed to calculate the amount of nonfreezing water according to the amino acid composition of a protein, gave estimates in close agreement with measurement (Kuntz, 1971). [Pg.55]

The determination of nonfreezing water is perhaps the most simple and straightforward way to estimate hydration. Scanning calorimetric and NMR measurements are made with equipment that is commonly available, and these methods should continue to be widely used. [Pg.56]

Harvey and Hoekstra (1972) determined the dielectric constant and loss for lysozyme powders as a function of hydration level in the frequency range 10 —10 Hz. At water contents less than 0.3 h, they found a dispersion at 170 MHz, which increased somewhat with increasing hydration, and a new dispersion at about 10 Hz that develops at high hydration. These dispersions, detected by time-domain techniques, remain measurable down to the lowest temperature studied, — 60°C. Water mobility in the hydration shell below 0 C is in line with other observations of nonfreezing water. Above 0.3 h, in the stage of the hydration process at which condensation completes the surface monolayer, water motion increased strongly with increased hydration (Fig. 11). [Pg.62]

One manifestation of strong solnte-solvent interactions is the inability of affected waters to freeze when the temperature falls well below the freezing point. Nnclear magnetic resonance (NMR), infrared spectroscopy, and low-temperatnre calorimetry have been employed to characterize the number of nonfreezing waters in the hydration shell of DNA (6-9). Based on their infrared measnrements of DNA films, Falk et al. (6) have concluded that about 10 water molecules per nucleotide are incapable of freezing with an additional 3 waters that show... [Pg.1342]

FIGURE 7.53 H NMR spectra of water in partially hydrated bones at different temperatures in (a) air and (b) CDCI3. (Adapted from Colloids Surf. B Biointerfaces, 48, Turov, V.V., Gun ko, V.M., Zarko, V.I. et al.. Weakly and strongly associated nonfreezable water bound in bones, 167-175, 2006a, Copyright 2006, with permission from Elsevier.)... [Pg.837]

In some cases, both NMR and DSC techniques have been used to determine the amount of nonfreezable water. For example, pulsed NMR relaxation data for the hydrated copolymer poly(A-vinyl-2-pyrrolidone/methyl methacrylate) allow one to estimate the relative fractions of three distinguishably different types of water [147] (1) tightly bound (type B) at specific polymer sites, such as carbonyl groups (2) more loosely bound (type A) that is more moderately influenced by the polymer matrix, for example, multilayer water and water in interstices and, in samples with water content in excess of about 76 wt%, (3) bulk-like water that freezes at the vicinity of 273 K. Both type A and type B, which have nearly the same energy, are nonfreezable in the accepted sense of the term but undergo glasslike transitions at 170-200 K. NMR is sensitive to both type A and type B, whereas DSC is sensitive only to type A and correspondingly predicts a lower estimate for the amount of nonfreezable water [147]. [Pg.90]

From differential scanning calorimetric measurements a marked cooling-heating cycle hysteresis has been observed, showing that water encapsulated in AOT reversed micelles is only partially freezable and that the freezable fraction displays marked supercooling behavior as a consequence of the very small size of the micellar core. The nonfreezable fraction has been identified as the water hydrating the AOT ionic heads [56,57]. [Pg.10]

Finally, we discuss the role of interlamellar water in lipid phase transitions. As shown in Fig. 36, the phase behavior of the lipid in the DMPE-water system is complex in the absence of freezable interlamellar water [21], Presumably, in a region of such low water content, the lipid bilayers exist as hydrated crystals containing only nonfreezable interlamellar water. However, with the appearance of freezable interlamellar water (curves d-m), the lipid phase transition comes to be characterized by a certain peak that is gradually shifted to lower temperatures with increasing water content and finally converges to a fixed temperature, generally ascribed to the gel-to-liquid crystal phase transition. Such phase behavior suggests that freezable interlamellar water is absolutely necessary for the formation of the gel phase of lipid-water systems. In this respect, another noticeable point is that the fixed peak of the gel-to-liquid crystal transition is obtained above a certain water content where a maximum uptake of the freezable interlamellar... [Pg.287]

On the other hand, as discussed above, the L-subgel phase of the DPPC-water system involves the extra nonfreezable interlamellar water up to one molecule of HjO per molecule of lipid, compared with the gel phase. This nonfreezable interlamellar water comes from the freezable interlamellar water present in the gel phase, indicating the critical role of this freezable water in the conversion of the gel to the L-subgel phase. In fact, as shown in Fig. 25B, the conversion to the L-subgel phase by annealing is not realized for a gel sample at < 5 (see curve a), i.e., when there is no freezable interlamellar water (see Fig. 14). Furthermore, as shown in Fig. 25B, the fixed peak of the L-subgel-to-gel phase transition is observed above 12-13 where the subgel phase is fully hydrated (see... [Pg.290]


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See also in sourсe #XX -- [ Pg.54 , Pg.55 ]




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