Materials, water hydration capacity

Quinn, J.R. and Paton, D. 1979. A practical measurement of water hydration capacity of protein materials. Cereal Chem. 56 38-40. 

The water-absorbing capacity of an enzyme support material may be characterized by the term aquaphilicity (Aq), which is the ratio of the amount of water on the support to the amount of water in the solvent under standard conditions (41). Support materials with high Aq are hydrophilic, and hence might deprive the enzyme of its essential water of hydration. Lipase activity is generally higher with hydrophobic (i.e., essentially nonpolar) supports such as celite and Bonopore (42). 

Until now, developments achieved in cement materials have shown great progress for humanity because of their usefulness in infrastructure, housing and transportation [66]. Cement is a combination of minerals especially formulated to react with water, following a series of chemical and physical processes known as hydration. Water is a substance strongly involved in preparation of cement materials, therefore the hydrophilic character and water holding capacity of micro and nanofibers of cellulose [83], is a property of great interest for cement materials. Properties of micro and nanofibers of... 

The hydration status of the clay or earth material may affect the adsorption capacity of nonpolar (or slightly polar) toxic chemicals. Continuing with parathion as a case study, Fig. 8.33 shows the increase adsorbed parathion on attapulgite from a hexane solution, as the adsorbed water on the clay surface decreases. This behavior may be explained by the competition for adsorption sites between the polar water and the slightly polar parathion. Possibly, however, the reduction in adsorption due to the presence of water is caused by the increased time required for parathion molecules to diffuse through the water film to the adsorption sites. 

It has been demonstrated that mixed oxides obtained from calcined LDHs have the ability to act as sorbents for a variety of anionic compounds from aqueous solution. This ability is because of the propensity for the mixed oxide to hydrate and re-form an LDH in such conditions and is of particular interest for the decontamination of waste-water. Hermosin et al. have found, for example, that MgAl-LDHs calcined at 500 °C are potential sorbents for the pollutants trinitrophenol and trichlorophenol from water [208, 209]. The adsorption mechanism was shown, using PXRD, to involve reconstruction of the LDH, with the uptake of the phenolate anions into the interlayers. Similarly, the ability of calcined MgAl-LDHs to remove nitriloacetate anions from solution has been demonstrated [210]. Calcined LDHs have been utilized also for the sorption of radioactive anions, such as 111, from aqueous solution [211]. A particularly attractive feature of the use of calcined LDHs for the remediation of waste-water is that the sorption capacity of the material may be regenerated via calcination of the rehydrated LDH. 

Another approach is to apply a material that forms an insulating layer around the fibre at temperatures below the fibre pyrolysis temperature. Boric acid and its hydrated salts function in this capacity (Fig. 8.4). When heated, these low melting compounds release water vapour and produce a foamed glassy surface on the fibre, insulating the fibre from the apphed heat and oxygen. 

T Tydrogels are a class of synthetic polymers of diverse chemical nature distinguished from other polymers by the capacity to imbibe relatively large amounts of water in their structure. The water content of these materials varies from about 30 to 90 wt % depending on both the chemical nature and physical structure of the polymer. Many natural or biocompatible polymers are also highly hydrated, e.g. 30-50 wt % water is bound by globular proteins (I). Partly for this reason, hydrogels... 

Due to protein-water binding, human skin has the capacity to absorb five to six times its weight in water. The extent of skin hydration is directly related to the penetration rate of toxic materials. Controversy exists about whether hair follicles contribute to increased penetration, but some studies do show increased absorption through hairy skin. Inflammation in the skin leads to vasodilatation and increased blood flow and subsequently increased penetration of toxic material. Aging contributes to decreased lipid barrier protection and decreased intercellular cohesion and increased penetration of toxic material. 

When a material can crystallize into a different polymorph, the chemical nature of the species remains identical, however, the physical properties of the material can be different. For example, properties such as density, heat capacity, melting point, thermal conductivity, and optical activity can vary from one polymorph to another. Table 2.3 lists common materials that exhibit polymorphism. Looking at Table 2.3 we can see that density varies significantly for the same materials when the crystal structure has changed. In addition, the change in the crystal structure often means a change in the external shape of the crystal, which is often an important parameter in industrial crystallization that has to be controlled. Many substances crystallize into structure in which the solvent is present as part of the crystal lattice. These crystals are known as solvates (or hydrates when the solvent is water). A substance can have multiple solvates with different crystal structures as well as a solvent free crystal form with a unique crystal structure. The solvates are often referred to as pseudopolymorphs. They are not true polymorphs because of the addition of the solvent molecule(s) to the crystal lattice. Conformational polymorphism refers to the situation where the molecular conformation of the molecules of a given substance are different in each polymorph. 

Pluronic poloxamers can be suitable carrier materials for this purpose due to their capacity to enhance the absorption of water-insoluble compounds by formation of micelles in aqueous environment that can host such hydrophobic compounds. Different authors have described the formation of quercetin-loaded Pluronic micelles by thin-film hydration methods and have shown that the resulting micelles enhanced the solubilization of the active compound. Ghanem et al. described the encapsulation of quercetin in Pluronic F127 via spray drying. ... 

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