Hydrates inclusion

The many polymorphs of ice [422, 423] and the wide variety of ice-like hydrate inclusion compounds provide a source of information about 0H---0 hydrogen bonds where the water molecules are the structure-determining molecular species... 

Unfortunately, none of the hydrate inclusion compounds which have less regular structures, such as the tetrabutyl and isoamylammonium salt hydrates [432] and the amine semi-clathrates [433, 434], has been studied by neutron dif-... 

Hydrogen-bonding patterns in crystal structures of the cydodextrins and the simpler carbohydrates differ. The infinite, homodromic chains are common both in the low molecular-weight carbohydrates and in the cydodextrins. The principal difference lies in the frequency of occurrence of the homodromic and antidromic cycles, which are common in the cyclodextrin crystal structures and rare in the mono-, di-, and trisaccharides. The cyclic patterns are the rule in the clathrate hydrates and in the ices. From this point of view, the hydrogen-bonding patterns of the hydrated cydodextrins lie between those of the simpler hydrated carbohydrates and those of the hydrate inclusion compounds, discussed in Part IV, Chapter 21. 

The alkylamine hydrate inclusion compounds form a large variety of structures. Phase diagram studies at the end of the last century [7651 (see Tkble 21.3), and an extensive series of phase diagram studies carried out between 1970 and 1981 [798], showed that aliphatic amines form a large variety of hydrates. Relatively few of these have been studied by X-ray crystal structure analysis and none by neutron diffraction [433, 799]. These hydrates differ from the gas hydrates and the alkyl ammonium salt hydrates in that there appear to be no definite structural types into which several hydrates can be classified. Hitherto, a different crystal structure has been observed for every alkylamine hydrate studied. In this respect, they resemble low hydrated crystals. 

Jeffrey GA (1984) Hydrate inclusion compounds. Chap 5. In Atwood JL, Davies JED, MacNicol DD (eds) Inclusion compounds, vol. 1. Academic Press, London, pp 135-190... 

In general, polymorphs of a given compound have different physicochemical properties, such as melting point, solubility and density, so that the occurrence of polymorphism has important formulation, biopharmaceutical and chemical process implications. In addition to polymorphs, solvates (inclusion of the solvent of crystallization), hydrates (inclusion of water of crystallization) and amorphous forms (where no long-range order exists) may also exist. Figure 3.8 shows an example of the polymorphism of estrone (Busetta et al. 1973). 

Such three-dimensional networks of perfectly disordered hydrogen bonds are rare, but they are also found in the low-pressure cubic form of ice and in some of the high pressure forms [74], Proton disorder also occurs in some of the hydrate inclusion compounds in which the water molecules form regular three-dimensional arrangements. These structures have been reviewed by Jeffrey and Saenger [10]. 

Jeffrey, G.A., Hydrate Inclusion Compounds, in Inclusion Compounds, Atwood, J.W., Davies, J.E.D., MacNicol, D.D (eds.). Academic Press, London, 1984... 

Jeffrey. G.A. Hydrate Inclusion Compounds. In Comprehensive Supramolecular Chemistry, Vol. 6 MacNicol. 

Hofmann-type clathrates Werner clathrates clathrate hydrates inclusion compounds of urea, thiourea, and selenourea cyclodextrins calixarenes gossypol hexa-hosts hydroquinone phenol and Dianin s compounds graphite intercalates natural and pillared clays and others. Such studies contributed to the birth of supramolecular chemistry, with relevance to a new understanding of the world of materials that was emphasized with a Nobel Prize. 

The template theory can be understood from the close structural analogy between the structures of ice and Si02 [27], hydrate inclusion compounds [28] and the various clathrasils [29] these analogies illustrate the fact that H2O and Si02 tetrahedra can both form three-dimensional four-connected nets. Figure 7. 

Mixed hydrates with monodentate ligands [e.g., [U02(H20)(urea)4] " (Dailey et al. 1972)] have a similar structure to that of binary hydrates. Inclusion of bidentate ligands in the equatorial plane can lead to expansion of the coordination number of the uranyl ion to six (Dailey et al. 1971, Taylor and Mueller 1965, Hallet al. 1965, Bombieri et al. 1976, Eller and Penneman 1976, Ritger et al. 1983), as in the structure of the neutral [U02(H20)2(N03)2] unit. The U O (water) distances in these compounds ranges from 2.42 to 2.47 A. 

The addition of a liquid to a grinding mixture of two co-crystal components can sometimes enable co-crystallisation through the formation of a product that incorporates the molecules of the liquid as a constituent. For this reason, grinding in the presence of liquids is a versatile technique for searching for three-component co-crystals e.g. co-crystal hydrates, inclusion compounds ). In some... 

Salts, and more recently co-crystals, have attracted much interest in the pharmaceutical industry for their promise in tailoring the physical properties of an active pharmaceutical ingredient (API) to meet the needs of the drug product and ultimately the patient.Salt forms, produced by add (A)-base (B) reactions in the solid state, are multi-component solids comprising minimally an A B pair they may be crystalline or amorphous. The term co-crystal, on the other hand, refers specifically to crystalline molecular complexes, which may include an A B pair among the different components and by definition necessarily include solvates (hydrates), inclusion compounds, clathrates and solid solutions. 

The topic of hydrogen bonding of carbohydrates and hydrate inclusion compounds has been surveyed as have the topics of intramolecular hydrogen bonding and molecular association in monosaccharides and natural cellulose. Other reviews on physical aspects of carbohydrates have dealt with liquid crystal compounds and with molecular dynamics simulations in the field. ... 

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