Clathrate compound

An example is the complex with argon which can be kept indefinitely in an ordinary bottle, although the equilibrium pressure of argon over the crystal amounts to several atmospheres at room temperature. Powell31 named these complexes "clathrate compounds, which according to him are those compounds "in which two or more components are associated without ordinary chemical union but through complete enclosure of one set of molecules in a suitable structure formed by another. ... 

Not only hydroquinone, but also phenol and a number of related substances have been reported20,21 33,44 to form clathrate compounds of a similar type. But this class of substances proves to be... 

According to these authors all gas hydrates crystallize in either of two cubic structures (I and II) in which the hydrated molecules are situated in cavities formed by a framework of water molecules linked together by hydrogen bonds. The numbers and sizes of the cavities differ for the two structures, but in both the water molecules are tetrahedrally coordinated as in ordinary ice. Apparently gas hydrates are clathrate compounds. 

A common feature of all clathrates discussed so far is a host lattice, by itself thermodynamically unstable, which is stabilized by inclusion of the second component. The forces binding this component must be similar in nature to the intermolecular forces in liquids. It seems natural, therefore, to regard a clathrate compound as a solid solution of the second component in the (meta-stable) host lattice. 

In the next section we shall give a brief account of the crystal structure of the hydroquinone clathrates and of the gas hydrates, as far as is needed for a proper understanding of the subsequent parts. The reader who is interested in the phenomenology of other clathrate compounds should consult one of the many review articles7,8 39 on inclusion compounds. 

Among other hosts for inclusion and/or clathrate compounds are deoxycholic... 

Recent and most comprehensive representation of this topic. A complete reference list of mono-graphies and reviews on clathrate compounds is found in Chapter 1 of Vol. 140 of this series (Molecular Inclusion and Molecular Recognition — Clathrates I)... 

Radon forms a series of clathrate compounds (inclusion compounds) similar to those of argon, krypton, and xenon. These can be prepared by mixing trace amounts of radon with macro amounts of host substances and allowing the mixtures to crystallize. No chemical bonds are formed the radon is merely trapped in the lattice of surrounding atoms it therefore escapes when the host crystal melts or dissolves. Compounds prepared in this manner include radon hydrate, Rn 6H20 (Nikitin, 1936) radon-phenol clathrate, Rn 3C H 0H (Nikitin and Kovalskaya, 1952) radon-p-chlorophenol clathrate, Rn 3p-ClC H 0H (Nikitin and Ioffe, 1952) and radon-p-cresol clathrate, Rn bp-CH C H OH (Trofimov and Kazankin, 1966). Radon has also been reported to co-crystallize with sulfur dioxide, carbon dioxide, hydrogen chloride, and hydrogen sulfide (Nikitin, 1939). 

Trofimov, A. M. and Kazankin, Yu. N., Clathrate Compounds of p-Cresol with Noble Gases. II. Compound of p-Cresol with Krypton and Radon, Radiokhim. 8 720-723 (1966). 

In contrast to carbon, which forms structures derived from both sp2 and sp3 bonds, silicon is unable to form sp2 related structures. Since one out of four sp3 bonds of a given atom is pointing out of the cage, the most stable fullerene-like structure in this case is a network of connected cages. This kind of network is realized in alkali metal doped silicon clathrate (19), which were identified to have a connected fullerene-like structure (20). In these compounds, Si polyhe-dra of 12 five-fold rings and 2 or 4 more six-fold rings share faces, and form a network of hollow cage structures, which can accommodate endohedral metal atoms. Recently, the clathrate compound (Na,Ba), has been synthesized and demonstrated a transition into a superconductor at 4 K (21). The electronic structure of these compounds is drastically different from that of sp3 Si solid (22). 

Among other hosts108 for inclusion and/or clathrate compounds are deoxycholic acid,101 cholic acid,102 small ring compounds such as 29,103 perhydrotriphenylene,104 and the compound 30, which has been called a carcerand.105... 

The induction of unconsciousness may be the result of exposure to excessive concentrations of toxic solvents such as carbon tetrachloride or vinyl chloride, as occasionally occurs in industrial situations (solvent narcosis). Also, volatile and nonvolatile anesthetic drugs such as halothane and thiopental, respectively, cause the same physiological effect. The mechanism(s) underlying anesthesia is not fully understood, although various theories have been proposed. Many of these have centered on the correlation between certain physicochemical properties and anesthetic potency. Thus, the oil/water partition coefficient, the ability to reduce surface tension, and the ability to induce the formation of clathrate compounds with water are all correlated with anesthetic potency. It seems that each of these characteristics are all connected to hydrophobicity, and so the site of action may be a hydrophobic region in a membrane or protein. Thus, again, physicochemical properties determine biological activity. 

Finally we have the completely three-dimensionally joined structure with hydrogen bonds, which is characteristic of all the polyhydroxy compounds from glycerol to the sugars, and by extension even the polymerized sugars, the carbohydrates (Fig. 9). A particularly interesting subsection of this type of structures is that in which the hydrogen-bonded framework is continuous, but extended, leaving holes in which the other types of atom molecule can be placed. These are the clathrate compounds already discussed. 

Compounds of this sort, in which molecules are entrapped by a lattice formed by other molecules, are called clathrate compounds. Often the lattice is formed by molecules linked to one another by hydrogen bonds. The structures of many of these substances have been determined by Powell and his cowQrkers.6 An especially interesting class is tliat formed by quinol, p-dihydroxybenzene. The hydroxyl groups... 

Certain differences in numerical data reported in various publications can be justified to some extent by differences in the analytical methods used. On the other hand, the values given by Lhoste seem to show that the sulphuric acid in nitrocotton could be combined with nitrocellulose molecules less firmly than in an ester group. For instance, it is not out of the question that sulphuric add may be bound with nitrocellulose as an inclusion (clathrate) compound. (Attention was also drawn to this point by Miles [15] in his monograph on cellulose nitrate.)... 

Chlorophyll, and photosynthenc reaction center. 917-919 Chromium carbonyl complexes, bond lengths in, 427 Circular dichrotsm ICD). 496-499 Claasen, H. H., 70 Clathrate compounds, 304-306 Claihro-chelates, 530 Clays. 750 Clementi, E., 31, 32 Closo structures, 798-800. 807 Clostridium pasieurianttm, 934 Clusters, 738, 807-819 Coenzyme, 919 Coenzymes, vitamin B,-,... 

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