Water tightly bound

Figure 6 Temperature dependence of the DNP enhancement of water protons in an aqueous suspension of hardwood char. The dramatic change with temperature is due to the interplay between translational motion and the exchange rates of water tightly bound to the char. Amax = Emax + 1. Reproduced with permission from Ref. [34].

In soil samples, pores are sometimes classified by how easily water can be removed. Transmission pores (> 50 pm) are readily drainable storage pores (0.2 to 50 pm) maintain water available for plant root systems, and residual pores (<0.2 pm) have the water tightly bound and therefore unavailable. Soils with high sand components would typify the first classification and soils with high clay components would typify the latter, with other soil types being intermediate in value and distributions of pore sizes. Assume that soil samples are hydrophilic with a contact angle... 

Water proton T-2 in dense collagenous tissues such as tendons and ligaments, in cortical bone, or water tightly bound to collagen, was not ordinarily detectable by MRI, because of T-2 less than Ims. Recent advances in instrumentation in conjunction with non-Cartesian imaging strategies allow center of k-space to be scanned lOOis or less after excitation. In vivo MRI of submillisecond T-2 species was demonstrated with 2-D and 3-D radial sequences and applied to the measurement of cortical bone water. The performance of two radial pulse sequences, a 2D sequence with half-pulse excitation and a new 3D hybrid sequence with variable-eeho Cartesian encoding in the third dimension, was examined on a whole-body 3 T scanner. 

The ability of a PEM to operate at high temperature (> 100 C) and low relative humidity. These conditions are desirable from a system layout and design perspective. They require the design of PEMs that could provide sufficient proton conductivity with a minimal amount of water tightly bound to the polymeric host. 

Different samples of aqueous solution containing radionuclides of Co and Eu were prepared at different copper sulphate concentrations and constant polymer concentrations (pAM) of 15 mg/1. The addition of salt to the system was done to reduce both the repulsion forces between the radionuclides and the interaction between the polymeric chains [7]. The polymer efficiency for the prepared samples was determined, results are shown in Fig. 15. It is clear that the polymer efficiency for Eu " is higher than for Co. This can be explained by the difference in the tightly bound structured water associated with different cationic species [14,107]. On this basis, we expect that Co is more hydrated than Eu. This is due to the difference in the ionic size. The hydra-... 

The acceleration by anions under both conditions was attributed to displacement of one of the water molecules presumed to be tetrahedrally coordinated with the mercuric ion, the subsequent reaction being then envisaged as displacement of the anion or water molecule by the aromatic the anions which cause reaction to take place more slowly were presumed to be more tightly bound to the mercuric ion than water. It has, however, been pointed out that less tightly bound anions would be unlikely to displace the more tightly bound water molecules in the first place438. 

Water occurs in glass-ionomer and related cements in at least two different states (Wilson McLean, 1988 Prosser Wilson, 1979). These states have been classified as evaporable and non-evaporable, depending on whether the water can be removed by vacuum desiccation over silica gel or whether it remains firmly bound in the cement when subjected to such treatment (Wilson Crisp, 1975). The alternative descriptions loosely bound and tightly bound have also been applied to these different states of water combination. In the glass-poly(acrylic acid) system the evaporable water is up to 5 % by weight of the total cement, while the bound water is 18-28 % (Prosser Wilson, 1979). This amount of tightly bound water is equivalent to five or six molecules of water for each acid group and associated metal cation. Hence at least ten molecules of water are involved in the hydration of each coordinated metal ion at a carboxylate site. 

Glass-ionomer cements become less susceptible to desiccation as they age, because a greater proportion of the water in older cements has become tightly bound . Early contact with moisture is also damaging, and this problem is overcome clinically to some extent by using some sort of protection such as clear nail varnish to seal the cement during its early life (Wilson McLean, 1988). However, this does not give perfect results, and as yet there is no ideal barrier material for this purpose (Earl, Hume Mount, 1985). 

The structure of this water can be affected by ion binding. If the counterions are tightly bound at the sites of individual charged groups, the... 

Scanning electron microscopy shows the cement to consist of zinc oxide particles embedded in an amorphous matrix (Smith, 1982a). As with the zinc phosphate cement, a separate globular water phase exists since the cement becomes uniformly porous on dehydration. Porosity diminishes as the water content is decreased. Wilson, Paddon Crisp (1979) distinguish between two types of water in dental cements non-evaporable (tightly bound) and evaporable (loosely bound). They found, in the example they examined, that the ratio of tightly bound to loosely bound water was 0-22 1-0, the lowest for all dental cements. They considered that loosely bound water acted as a plasticizer and weakened the cement. 

Wilson, Paddon Crisp (1979) have shown that the water present in the cement can be divided, somewhat arbitrarily, into boimd water of hydration (non-evaporable) and loosely held (evaporable) water. The amount of tightly bound water increases as the cement ages and in one example reached 42 % of the total water. 

As mentioned previously, the cement contains both tightly bound and loosely bound water. The set cement can both lose and gain water depending on its environment. Under drying conditions (say 50 % relative humidity) it loses water and shrinks. When placed in water there is an... 

The sorption of water by excipients derived from cellulose and starch has been considered by numerous workers, with at least three thermodynamic states having been identified [82]. Water may be directly and tightly bound at a 1 1 stoichiometry per anhydroglucose unit, unrestricted water having properties almost equivalent to bulk water, or water having properties intermediate between these two extremes. The water sorption characteristics of potato starch and microcrystalline cellulose have been determined, and comparison of these is found in Fig. 11. While starch freely adsorbs water at essentially all relative humidity values, microcrystalline cellulose only does so at elevated humidity values. These trends have been interpreted in terms of the degree of available cellulosic hydroxy groups on the surfaces, and as a function of the amount of amorphous material present [83]. 

In contrast to the strong and bulky DMSO nucleophile, the small HCN molecule is a weak donor compared to water (vide supra) and can be easily replaced by H20. HCN on the one hand is a water-like solvent, without much application because of its toxicity. On the other hand, it is employed as a simplified model to perform quantum chemical studies on CH3CN. Our calculations corroborated the experimental work that the first coordination sphere around Li+ consists of four tightly bound CH3CN and HCN... 

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