Bound crystal water

In addition, zirconium phosphate (ZrP) was also reported as a promising filler in Nafion membrane due to the additional H+ ions of the phosphate moiety and bound crystal water (Bauer and Porada 2004). Bauer and Porada reported that in the... 

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. 

The X-ray crystal structure of the hexachloride salt of the protonated macrocycle shows that it adopts a cleft-like conformation as shown in the diagram, and modelling studies support the existence of this conformation in solution. The electrostatic nature of the anion binding by 4.12-nH+ means that it binds particularly strongly to multiply changed anions, and ATP, with its 4- charge, is bound in water at pH 4, with logXn = 11 for the hexaprotonated host. 

Fig. 1. Simulation procedure before starting the dissolution of a crystal in water (a) water in the box (b) water molecules and a crystal in which ions are strongly bound and water molecules are equilibrated with the crystal (c) the potential function between ions in the crystal is replaced by the function employed in the simulation. The dissolution of the crystal then starts.

A crystal structure of the 1 1 adduct of 1,10-phenanthroline and the seven coordinate species, [Mn(199)(H20)2](C104)2, indicates that the phenanthroline molecule is not coordinated to the manganese but is sandwiched between [Mn(I99)(H20)2]2+ units in a lamellar structure.136 The phenanthroline nitrogens are hydrogen bound to water molecules in adjacent complex ions the structure also appears to be held together by it donor/rc acceptor and dispersion forces. 

The category of bound moisture comprises water retained in small capillaries in the solid, water absorbed on solid surfaces, water bound as solutions in cells or fiber walls, and water bound as crystal water in chemical combination with the solid. Bound water exerts an equilibrium vapor pressure lower than that of pure water at the same temperature. 

Freeze drying, i.e., sublimation drying of the ice content and desorption drying of the bound or crystal water content... 

Free water, shown in Table 4, represented moisture not bound as water of crystallization. No pattern for the seepage of water through the stacks was apparent from the data. The maximum free water content for each core occurred at depth intervals from 3 to 27 m, but also the minimum occurred at depth intervals from 0 to 27 m. The wettest and driest depth intervals even occurred adjacent to each other. For example, in Core BI, the 18 to 21 m interval was the wettest and the 21 to 24 m interval the driest. In Core BI the first sample was like mud the second was like rock. Analysis of variance (ANOVA) of the data showed there was no significant difference in free water among depths and there was a significant difference among cores. 

Repeat experiment 16.1 using KCl. Note the initial loss of free (adsorbed) water and then the loss of bound interstitial water up to temperatures above 200°C. Could temperaffires below 200°C be used to dry KCl crystals successfully ... 

In most cases, both mechanisms contribute to the overall displacement effect although to different extents. Because displacement drying is based on the surface phenomena, it is clear that internally bound water at molecular level, osmotically bound water or crystal water cannot be removed by this technique. It is possible, however, to remove water held in small pores. 

The extremely small size of these nano-crystals, separated from each other and bound with water, and their mostly electropositive relative electric charges, arranged along the axis of the molecule, allow this polyglucoside to remain stably suspended in water solutions, ready to bind with other molecules via ionic bonding (Revol et al. 1996) (Figure 37.3). 

The oil-in-water (o/w) type of creams (Fig. 1) are systems of four components their main elements are the hydrophilic and lipophilic gel phases. Both phases are composed of bilayers of mixed crystals. Water molecules are enclosed between the surfactant and alcoholic groups of the emulsifier molecules. In the gel phase, water molecules in interlamellar binding are in equilibrium with water molecules bound as bulk water. Both aqueous phases constitute the coherent (outer) phase of the system. The surplus of cetostearyl alcohol, which is not part of the hydrophilic gel phase, forms a matrix of lipophilic character called the lipophilic gel phase. The disperse or inner phase is mechanically not removable from the lipophilic gel phase. The lipophilic gel phase is constituted exclusively by cetostearyl alcohol, which can form only a semihydrate water layer [1,2]. 

Water is present in most natural foods, at levels up to 90-95% w/w in some fruits (oranges) and vegetables (tomatoes). Most beverages contain high proportions of water. Water exists in foods in various forms free water, water droplets, water adsorbed on a surface, chemically bound water, crystal water, and composition water. Often water is removed from processed foods to improve their keeping quality or to reduce their weight and volume. In most cases, however, part of this water is extremely difficult to remove, so even dehydrated foods may contain 2-3% residual water. The physics of water, as a pure substance and as part of biological systems, has been studied by many workers [16-18] the basic phenomena are described in a volume edited by Franks [19]. 

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