Clathrate water cage

Mixture Models Broken-Down Ice Structures. Historically, the mixture models have received considerably more attention than the uniformist, average models. Somewhat arbitrarily, we divide these as follows (1) broken-down ice lattice models (i.e., ice-like structural units in equilibrium with monomers) (2) cluster models (clusters in equilibrium with monomers) (3) models based on clathrate-like cages (again in equilibrium with monomers). In each case, it is understood that at least two species of water exist—namely, a bulky species representing some... 

Clathrate-Cage Model. The final water model which is of major interest is based on clathrate hydrate cage structures. It was originally proposed by Pauling (116), who noted the existence of clathrate hydrates of many inert gases and suggested, by analogy to the chlorine hydrate,... 

Before proceeding, it is important to recall the significant feature which appears to distinguish the cluster model from the two other prominent mixture models—i.e., the broken-down ice lattice and the clathrate hydrate cage structures. The latter two theories allow for the existence of discrete sites in water, owing to the cavities present either in the ice... 

The importance of carefully considering anomalies when studying the behavior of solute-solvent interactions has been stressed. For aqueous solutions, many anomalous results presented in the literature suggest the existence of some type of discreteness in water structure. Discreteness is consistent with a view of water structure providing distinct sites such as those found in the models of water, implying a broken down ice lattice structure or clathrate hydrate cage-like structures. 

There are important differences between the literature models and our results. In our case, (i) the number of monomers is smaller than that in the Pauling model (where they are present in clathrate-like cages), and (ii) they coexist with a disturbed but still infinite, not disintegrated network of water molecules. In contrast, the models in refs 11 and 32 do not involve a network but only a distribution of clusters. 

Clathrate hydrates form when small (<0.9 nm) non-polar molecules contact water at ambient temperatures (typically <3(X) K) and moderate pressures (typically >0.6 MPa). On a molecular scale, single small guest molecules are encaged (enclathrated) by hydrogen-bonded water cavities in these non-stoichiometric hydrates. Guest repulsions prop open different sizes of water cages, which combine to form three well-defined unit crystals shown in Figure 1. 

Ocean disposal options fall into several categories, as illustrated in Fig. 1. One is to dilute the dissolved CO2 at a depth below the mixed layer. Carbon dioxide can be stored using this method for decades to centuries, but capacities are limited. Another approach is to form lakes of CO2 at the bottom of the ocean. Below 2700 m, compressed CO2 is denser than seawater and sinks to the bottom. In addition, CO2 reacts with seawater to form a clathrate, a cage structure with approximately six water molecules per C02- Clathrates are solids that can form at temperatures slightly higher than the melting point of water and thus form spontaneously in the presence of liquid CO2 near the bottom of the ocean. However, they are not stable, and as a result, they dissolve into ocean water once the... 

Clathrate hydrates are crystalline inclusion compounds composed of host water cages that trap guest molecule-. [-.The three most common types of clathrate hydrates are known as structure I, II, and H, which differ in the type of water cage they contain. The type of clathrate hydrate structure formed depends mainly on the size of the guest molecules present (for further details, see the article Clathrate Hydrates and Refs. [8,9]). The structures of these compounds were first determined from x-ray diffraction studieshowever, as mentioned previously, vibrational spectroscopy can provide important complementary information on the structures and dynamics of these compounds and can also detect the presence of any guest molecule-host lattice interactions. 

Clathrate Hydrates Clathrate structures in which the framework is composed of polyhedral water cages, capable of encapsulating neutral, non-polar guest species. 

OH radical and neutral H2O (recombination of the H20 ion with electrons leads essentially to dissociation to OH + H). In solid or gaseous form water has been found in a variety of astrophysical sites besides the ISM planets, satellites, comets, circumstellar disks, other galaxies and in our Sun and on our Moon. It also forms a matrix for trapping gases, as clathrates in which guest molecules are trapped within polyhedral water cages the most prominent example is that of methane hydrates which occur on ocean floors and in permafrost. 

Yet another question is how are small biologically important molecules normally aquated This is important when considering the distribution of such molecules within cells. It is probable that molecules such as Oj or NO are in clathrate-type cages in water. There is some evidence for weak hydrogen bonding for CO2 in water [54], although the normal view is that these molecules are also enclathrated [55]. 

Interest in the family of water clusters for n = 20 stems from the fact that one of the families of minima is the dodecahedron which has been proposed as a model for inclusion compounds and constitutes a budding block of type I ice clathrate (we will discuss this in detail in O section The First Few Water Cages ) The structure of (H2O)20 has been the subject of debate due to the existence of various major families of minima which are energetically in close proximity and the disagreement as to which was the global minimum (Fanourgakis et al. 2004). 

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