Bound water associated with

Elliott et al.i applied classical MD simulations to study the dynamics of small molecules in a model Nafion membrane for A= 1, 3.8, and 9.7. They observed wafer segregafion info "bound" water associated with the sulfonate groups and more loosely attached "free" water. 

The amount of bound water associated with the PNF was measured using a Perkin Elmer DSC II equipped with a subambient stage. The samples were scanned from 227 to 303 K at 10 K/min under dry nitrogen. The heats of fusion of the sorbed water were calculated relative to the heats of fusion of indium (12). 

Differential scanning calorimetry (DSC) was used to ascertain the degree, if any, of bound water associated with the PNF polymer. As seen in Table II, the virgin PNF contained 0.01 mg bound water/mg polymer, which increased to 0.05 mg bound water/mg polymer. The reasons for the increase in bound water content as a function of irradiation are currently under investigation (11). This change may be tied to the oxidation level of the polymer. 

Hatakeyama T, Nakamura K, Hatakeyama H (2000) Vaporization of bound water associated with cellulose fibres. Thermochim Acta 352-353 233-239... 

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 amounts of water associated with various components in a typical reaction mixture are shown in Table 1.2. Most of the water is dissolved in the reaction medium, and the amount of water bound to the enzyme is obviously just a minor fraction of the total amount of water. If the solvent was changed to one able to dissolve considerably more water and the same total amount of water was present in the system, the amount of water bound to the enzyme would decrease considerably and thereby its catalytic activity as well. Changing solvent at fixed water activity would just increase the concentration of water in the solvent and not the amount bound to the enzyme. Comparing enzyme activity at fixed enzyme hydration (fixed water activity) is thus the proper way of studying solvent effects on enzymatic reactions. 

Excipients both typically contain water and are required to interact with it. The water associated with excipients can exist in various forms. Studies with different materials have shown that water can exist in association with excipients in at least four forms that may be termed free water, bound water, structural water, and water of crystallization. Water associated with a particular excipient may exist in more than one form (26). The type of water will govern how it is implicated in interactions between the excipient and the API or another excipient. The so-called free water is the form that is most frequently implicated in excipient interactions. Bound water is less easily available for interaction, and structural water is usually the least available one. Water of crystallization can be very tightly bound into the crystal structure however, there are some comparatively labile hydrates, e.g., dibasic calcium phosphate dihydrate (see above). If water of crystallization remains tightly bound within the crystal structure, it is unlikely to participate in an excipient interaction. However, any material that is in equilibrium with air above 0% RH will have some free moisture associated with it. In reality, below about 20% RH, the amount of moisture will probably be insufficient to cause problems. However, if sufficient moisture is present (e.g., at a higher RH), it can facilitate the interaction between components of the formulation. 

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. 

Changes in the moisture content of the wood cell wall have a major effect on the mechanical properties of wood [5]. At moisture contents from oven-dry (OD) to the fiber saturation point (FSP), water accumulates in the wood cell wall (bound water). Above the FSP, water accumulates in the wood cell cavity (free water) and there is no tangible strength effect associated with a change in free water content. However, at moisture contents between OD and the FSP, water does affect strength. Increased amounts of bound water interfere with and reduce hydrogen bonding between the polymers of the cell... 

NMR has provided the most useful information on the state and mobility of water in keratins (2, 3, 4). It was shown (4) that the water associated with the stratum corneum seems to exist in two distinct states a bound fraction and a free fraction. This type of information could be obtained conveniently by the new technique using desorption kinetics under a wide range of experimental conditions. Also, it would be of interest to examine the effect of various agents, which are known to produce structural changes in the corneum, on the ability of the corneum to hold water and to retain it under a variety of conditions. 

Bound moisture Water associated with a solid exhibiting a vapor pressure less than P. 

The effects of drought, i.e., the quantitative properties of water in fresh and dry leaves of durum wheat were tested by the relation between the water status and the properties of bound water (BW) with different strengths to ionic, polar, or hydrophobic sites of macromolecules [56]. An increase in tissue affinity for strongly bound water implied a simultaneous increase in the affinity for weakly bound water. The qualitative properties of bound water may be particularly important for drought adaptation in durum wheat, which is associated with solute potential plots of differential energies of water sorption (Figure 4). 

Water associated with proteins and other macromolecules has traditionally been referred to as bound water. However, to designate such water as bound can be misleading because, for the most part, the water molecules are probably only transiently associated, and at least a portion of the associated water has to be constantly rearranged, due to the thermal perturbations of weak hydrogen bonds. 

Weakly bound low-density water, associated with the dense water layers. 

Permeation Studies. Matsuura and co-workers have made use of liquid chromatography to estimate the extent of partitioning between free solution and the membrane phase (48>87-89)> the magnitude of A-M and B-M interactions due to electrostatic repulsion and van der Waals attraction (48,49,89-91), the thickness of bound or interfacial water associated with the membrane (87-89), as well as the average size and size distribution of the transport corridor on the membrane surface (92-94). 

The water of hydration and hydroxyl water associated with the MOC 5-form and 3-form are 44 and 49%, respectively. When heated to 297°C, the chemically bound water will be converted to steam with an energy requirement of about 1000 Btu per pound of water released. The MOC cement beneath the surface exposed to the heat will not be heated above this temperature until all of the water has been released and driven from the cement. Because of the high energy requirement for this process to occur, the insulative effect from the water of hydration is considerable and constitutes the principle means of insulation (Monde and Mayhan, 1973). Thermally decomposed MOC cement is primarily MgO and as such has a high reflectivity, which is also a significant factor in the overall insulative capability of magnesium oxychloride cement. It has been calculated that a 5-cm thickness of typical MOC cement with a density of 960 kg m-3, containing approximately 35% bound water and no fillers, requires over 6h for the nonheated face to reach a temperature of 1000°F (538°C). 

Various terms have been used to characterize the water associated with cellulose fibers. Bound water, imbibed water, water of constitution, adsorbed water, fiber saturation point are some of the terms that have been used to describe the water in pulps and papers. The origin of each term can be traced to either theoretical considerations or to the experimental method of measurement. Bound water has been the most popular term used to describe the associated water. Bulk water or free water is that portion of water not associated (or not bound) with the fibers. Two measurement techniques may not yield identical values of bound water. 

Offer and Knight (1988b) concluded that muscle protein molecules in an aqueous solution interact with water, and when it moves through the solvent it carries some water with it. Part of this bound water is believed to be hydrogen-bonded to the surface of the protein molecule, while part may be present in clefts or pockets. Both are in dynamic exchange with free water. These authors stated that the amount of water associated with proteins in this way can be measured by a variety of techniques. However, it amounts to only about 0.5 g of water per gram protein. The total concentration of protein in muscle is about 200 mg/ml, so that as emphasized by Hamm (1960,1986), only about a 10th of the water in muscle can be considered to be closely bound with the proteins. 

There is a problem of bound water both in hfeless nature and in biological systems at various levels of the stractural hierarchy. In this regard we can talk about the existence of the phenomenon of bound water with different from hulk water strac-tures and properties [17-19]. Let us consider a model of water associated with biopolymer. The basis of this model is the fact that water molecule can be represented as a distorted tetrahedron because an ideal tetrahedron bond angle is 109.28, and free water molecule bond angle is 104.5. The model assumes that the water may produce a continuous three-dimensional netwoik of tetrahedral particles. 

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