Ratio guest/water

The ideal guest/water ratio is G 5%H20 for molecules that can occupy both cavities of structure I, and G-7(2/3 )H20 for occupants of only the 51262 of structure I. As indicated in Figure 2.13 molecules of transitional size (shaded region) such as cyclopropane (Majid et al., 1969) and trimethylene oxide (Hawkins and Davidson, 1966) with diameters of 5.8 and 6.1 A, respectively, may form either structure. 

Semilogarithmic plots of formation pressure versus reciprocal absolute temperature yield straight lines, over limited temperature ranges, for hydrate formation from either liquid water, or ice. From Equation 4.13 such linear plots either indicate (1) relatively constant values of the three factors (a) heat of formation, AH, (b) compressibility factor, z, (c) stoichiometry ratios of water to guest or (2) cancellation of curvilinear behavior in these three factors. 

Historically, two periods occurred for the determination of the number of hydrate water molecules per guest molecule. In the first century (1778-1900) after the discovery of hydrates, the hydration number was determined directly. That is, the amounts of hydrated water and guest molecules were each measured via various methods. The encountered experimental difficulties stemmed from two facts (1) the water phase could not be completely converted to hydrate without some occlusion and (2) the reproducible measurement of the inclusion of guest molecules was hindered by hydrate metastability. As a result, the hydrate numbers differed widely for each substance, with a general reduction in the ratio of water molecules per guest molecule as the methods became refined with time. After an extensive review of experiments of the period, Villard (1895) proposed Villard s Rule to summarize the work of that first century of hydrate research ... 

To prevent water occlusion. Without agitation, Villard (1896) showed, for example, that nitrous oxide hydrate formation was continuous for a period longer than 15 days under a pressure of 2 MPa. Villard also determined that in previous research the ratio of water to guest molecules had been analyzed as greater than G 6H20 (Villard s Rule) due to either occlusion of water within the hydrate mass, or due to the loss of the guest component. 

Another major difference between conventional solute transfer and supramolecular association is the crucial influence of the shape of the guest molecule in the latter case. This is clearly demonstrated upon complexation of P-CD with 2- and 3-phenylbutyric acids. The apparently trivial variation in the methyl position results in a profound difference in complexation thermodynamics. Despite virtually the same hydrophobicity (i.e., the distribution ratio between water and nonpolar organic solvent), the affinity of 3-phenylbutyric acid toward P-CD ( =402-430 M ) is more than four times larger than... 

ABSTRACT. A number of complexes [M(4-MePy)jj(NCS)2], where M = Co(II), Ni(II), Zn(II), Cd(II) n = 2 or 4 have been synthesized and phase diagrams [M(4-MePy)2(NCS)2]-4-MePy have been studied. The forming compounds have been obtained and described with the help of IR-spectroscopy and thermal analysis. The structure of a molecular type with variable section channels, filled by two types guest-molecules (by a water molecule in the narrow part of the channel and by two 4-methylpyridine molecules in the broad part of the channel, with a total ratio guest host being 1 3) for [Cd(4-MePy)it(NCS)2] 0.67(4-MePy).O.33H2O has been defined by X-ray method. This clathrate is isostructural CX-ray powder diffractogram) to the anhydrous compound [Cd(4-MePy)i (NCS)2 0.67(4-MePy). 

The guest molecules experience different potential depending on the nature and the spatial distribution of the ions and the structural modifications in the aluminosilicate framework associated with the Si-Al substitution. Accordingly, the diffusive process can be different [1], The efficiency of migration of guest molecules depends on several factors the Si/Al ratio, the nature of the extra framework cations, the presence of sorbed water molecules, the temperature, and the sorbate concentration [1]. 

The zeolites are aluminosilicate framework minerals of general formula M", [AI4Sil0lr+>JJ -zH20.y They are characterized by open structures that permit exchange of catioas and water molecules (Fig. 16.2). In the synthetic zeolites the aperture and channel sizes may sometimes be controlled by a sort of template synthesis—the zeolite is synthesized around a particular organoammonium canon. This yields channels of the desired size. The zeolite framework thus behaves in some ways like a clathrate cage about a guest molecule (Chapter 8). The synthesis of zeolites also involves several other factors such as the Al/Si ratio, the pH. the temperature and pressure, and the presence or absence of seed crystals - ... 

The work in Table 1.2 illustrates one of the early research difficulties that is still present—namely, the direct measurement of the water to gas ratio in hydrates (hydration number, n = water molecules per guest). Whereas many solids... 

The copolymerization of a rue thy latcd-/ -cy c 1 odextri n 1 1 host-guest compound of styrene with various molar ratios of sodium 4-(acrylamido)-phenyldiazosulfonate carried out in water with free radical initiator is described [40]. Depending on the amount of sodium 4-(aciylamido)-phenyldiazosulfonate incorporated in the copolymer, water- or DMF-soluble copolymers of high molar mass were obtained. Irradiation of the copolymers with UV light in solution resulted in rapid decomposition of the azo chromophore. Irradiation of the polymers as films led to crosslinking and thus to insolubility. 

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