Clathrates analysis

Krypton clathrates have been prepared with hydroquinone and phenol. 85Kr has found recent application in chemical analysis. By imbedding the isotope in various solids, kryptonates are formed. The activity of these kryptonates is sensitive to chemical reactions at the surface. Estimates of the concentration of reactants are therefore made possible. Krypton is used in certain photographic flash lamps for high-speed photography. Uses thus far have been limited because of its high cost. Krypton gas presently costs about 30/1. 

Phase equilibria of the isothiazole-water system have been investigated by differential thermal analysis (76BSF1043), and it has been established that a stable crystalline clathrate (isothiazole-34H20) forms below 0 °C. 

As we have seen in Section I.B x-ray analysis of both hydroqui-none clathrates and hydrates has revealed that all cavities are approximately spherical and that their walls consist of a relatively large number of atoms. It is therefore plausible to suppose that the field of force acting on a solute molecule in its cage has a spherical symmetry, and, in addition to the aforementioned assumptions (a)-(d), to make the two further assumptions ... 

The search for suitable borides of alkali metals recently led to a new lithium boride with hexagonal Bs-octahedra framework unknown until now. Strong evidence for the existence of planar LiaB molecules in the wide channels of the framework is given by the structural analysis ( ). This compound points out another aspect involving reactions of solid phases namely, the possible release of small molecules, which are clathrate-like, locked in the structure and are therefore stabilized. 

In an oligonucleotide-drug hydrate complex, the appearance of a clathrate hydrate-like water structure prompt a molecular dynamics simulation (40). Again the results were only partially successful, prompting the statement, "The predictive value of simulation for use in analysis and interpretation of crystal hydrates remains to be established." However, recent molecular dynamics calculations have been more successful in simulating the water structure in Ae host lattice of a-cyclodextrin and P-cyclodextrin in the crystal structures of these hydrates (41.42). 

Figure 3.49 summarizes the oxygen isotope curve for the last 65 Ma. The most pronounced warming trend is expressed by a 1.5%o decrease in 8 0 and occurred early in the Cenozoic from 59 to 52 Ma, with a peak in Early Eocene. Coinciding with this event is a brief negative carbon isotope excursion, explained as a massive release of methane into the atmosphere (Norris and Rohl 1999). These authors used high resolution analysis of sedimentary cores to show that two thirds of the carbon shift occurred just in a few thousand years, indicating a catastrophic release of carbon from methane clathrates into the ocean and atmosphere. 

For clarity and because of space limitations, we will consider only examples of complexes in which the guest interacts with the host from above (or/and below) the cavity, and the structure has been confirmed by X-ray analysis. These complexes serve as models for the interaction of neutral molecules which are nearly concave/ convex complementary in their. spatial interaction. Although complementary in shape, some guest molecules simply fill spatial voids in the host lattice. These clathrate-like structures will not be considered. 

Kini (2002). The Raman data are based on the works by Sum (1996), Tulk et al. (1998), Subramanian (2000), and Hester (2007). To accompany these tables, select NMR and Raman spectra are given in Figures 6.13 through 6.19. These tables and sample spectra should serve as a useful reference to those embarking on spectroscopic measurements and analysis of clathrate hydrates. 

The process of guest release for the two types of inclusion compound of 9.4 can be followed by thermo-gravimetric analysis (TGA, Box 9.1). This reveals the clathrate-like behaviour of the y phase (trace 2) and contrasts significantly with the zeolite-like behaviour of the microporous /1-phase (trace 1), Figure 9.19b. The mass loss stages followed by both compounds after initial wetting in benzene are as follows ... 

Closely related to DSC is the much older technique of differential thermal analysis (DTA). DTA works on the simpler principle of measurement (via thermocouple) of temperature difference between a sample and reference as the same heating power is supplied to both. The DTA trace therefore represents a temperature effect, which is related only semiquantitatively to AH. A combined DTA-TGA trace for the Werner clathrate (Section 9.4) [Ni(NCS)2(4-phenylpyridine)4] CgHg is shown in Figure 9.22. The DTA trace shows that all three thermal events observed are endothermic. The first is associated with loss of the benzene guest, while the second and third relate to loss of the coordinated 4-Phpy ligands. Note the high temperature (about 350 °C) required to remove the enclathrated benzene. This is a clear indication of the thermal stability of the Werner clathrate family.18... 

Lavelle, L., Nassimbeni, L. R., Niven, M. L., Taylor, M. W., Studies in Werner Clathrates. 2. Structure and thermal-analysis of bis(isothiocyanato)tetrakis(4-phenylpyridine)nickel(n) benzene clathrate (1-4). Acta Crystallogr. Sect. C-Cryst. Struct. Commun. 1989, 45, 591-595. 

Here the layers contain only water molecules which form antidromic pentagons, quadrilaterals and homodromic hexagons (Fig. 21.10). Clathrate or semi-clathrate structures have been postulated for choline chloride hydrate, (H3Q3N+CH2CH2OH 2H20 CP, on the basis of similarities in the solid-state infrared spectra [162], but this has not been confirmed by crystal structure analysis. 

Structural analysis of the 1 1 cocrystal, as well as [69] the structures of several related compounds Structures of the 2 1 piperazine and 1 1 piperidine [70] cocrystals, and comparison of these with the known clathrate structures Structures of 11 new cocrystals, and elucidation [71] of the amide-acid and amide-amide hydrogen bonding in relation to synthon assembly... 

An X-ray analysis of the clathrate formed by 4-( )-hydroxy-phenyl)-2,2,4-trimethylthiochroman has been reported. 

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