Solid-state hydrates

Solid state hydrates 394 3.3. Solubility of lanthanide hydroxides 434... 

Salts are non-volatile and in the fused state or in solution eonduet an eleetrie eurrent. Many salts are hydrated in the solid state with water of erystallization. 

As is pointed out in the introduction to Section II, the presence or absence of water in the solid state gives no indication as to whether or not covalent hydration occurs in aqueous solution. However, many examples are known of substances which hydrate strongly in solution and also in the solid state. Thus, 2-hydroxy- and 6-hydroxy-pteridine crystallize with one molecule of water. On heating, the former loses water rapidly only at 180°, whereas the latter retains all of the water up to 180° where it begins to darken. ... 

In the 1930s when high-pressure natural gas (95% methane) pipelines were being built in the United States, it was found that the lines often became plugged in cold weather by a white, waxy solid that contained both water and methane (CFIJ molecules. Twenty years later. Walter Claussen at the University of Illinois deduced Ihe structure of that solid, a hydrate of methane. Notice (Figure B) that CH4 molecules are trapped within a three-dimensional cage of H20 molecules. 

C03-0152. Aluminum sulfate is used in the manufacture of paper and in the water purification industry. In the solid state, aluminum sulfate is a hydrate. The formula is AI2 (804)3 18 H2 O. (a) How many grams of sulfiar are there in 0.570 moles of solid aluminum sulfate (b) How many water molecules are there in a 5.1-g sample of solid aluminum sulfate (c) How many moles of sulfate ions are there in a sample of solid aluminum sulfate that contains 12.5 moles of oxygen atoms (d) An aqueous solution of aluminum sulfate contains 1.25% by mass aluminum and has a density of 1.05 g/mL. What is the molarity of aluminum ions in the solution ... 

Calcium sulfate, the substance used to absorb water in desiccators, provides an example of this temperature sensitivity. Anhydrous calcium sulfate absorbs water vapor from the atmosphere to give the hydrated salt. The reaction has a negative AS° because water molecules become more constrained when gaseous water molecules move into the solid state. The reaction also has a negative AH ° because of the electrical forces of attraction... 

One of the major uses of DTA has been to follow solid-state reactions as they occur. All decomposition reactions (loss of hydrates, water of constitution, decomposition of inorganic anions, e.g.- carbonate to carbon dioxide gas, etc.) are endothermic and irreversible. Likewise are the synthesis reactions such as... 

Figure 11. Solid-state C NMR spectrum of hydrated cell walls from Citrus peel, with high content of methyl-esterified pectia...

In addition to giving conformational information, solid state NMR relaxation experiments can be used to probe the thermal motion of polymers in the hydrated cell wall (5). The motion of the polymers can give us clues as to the environment of the polymer. When there are both rigid and mobile polymers within a composite material, NMR spin-diffusion experiments can be used to find out how far apart they are. 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

These methods approach gelation from the sol state. A gel may also be obtained from the solid state. If solid gelatin is immersed in water, it will imbibe enough solvent to form a gel. Hence, it should be realized that a gel is an intermediate state of hydration between a sol and a solid. 

Several enzymes like lipases, esterases, and dehydrogenases have been active in hydrophobic environments. Thermodynamic water activity is a good predictor of the optimal hydration conditions for catalytic activity [51]. Enzyme preparation can be equilibrated at a specific water activity before the reaction [52]. When water concentration is very low, enzyme is suspended in the solid state in the water-immiscible organic solvent [46]. Enzymes are easily recovered after the reaction by the method of filtration. 

F. Volke, A. Pampel 1995, (Membrane hydration and structure on a subnanometer scale as seen by high resolution solid state nuclear magnetic resonance POPC and P0PC/C12E04 model membranes), Biophys.J. 68, 1960-1965. 

Solid state 13C CPMAS NMR spectra of Wheat High Molecular Weight (W.HMW) subunits show well resolved resonances identical with spectra of dry protein and peptide samples [24], Most of the amino acids side-chain resonances are found in the 0-35 ppm region followed by the alpha resonances of the most abundant amino acids glycine, glutamine and proline at chemical shifts of 42, 52 and 60 ppm, respectively, and the carbonyl carbons show a broad peak in 172-177 ppm region. The CPMAS spectra of hydrated whole HMW provides important information on the structural characteristics. 

Free amine 36 was isolated as a hygroscopic hydrate which was very difficult to dry in the solid state and required azeotropic drying using THF (expensive and time consuming). 

The phenomenon of pseudopolymorphism is also observed, i.e., compounds can crystallize with one or more molecules of solvent in the crystal lattice. Conversion from solvated to nonsolvated, or hydrate to anhydrous, and vice versa, can lead to changes in solid-state properties. For example, a moisture-mediated phase transformation of carbamazepine to the dihydrate has been reported to be responsible for whisker growth on the surface of tablets. The effect can be retarded by the inclusion of Polyoxamer 184 in the tablet formulation [61]. 

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