Guest mobility

This behaviour may be easily understood with the aid of Equation 1. Inspection of the well-known structure of the cavity in Dianin s compound suggests that the guest molecule should be able to librate around the three-fold axis much more easily than around an axis perpendicular to the three-fold axis. Such a libration has no component of 0 or Oy for the axial chlorine nucleus but does for the three equatorial nuclei. When the rotation occurs rapidly enough, the equatorial resonance disappears entirely. The resonance from the axial nucleus is affected only by librations around the perpendicular axis and these occur much less readily. The slope of the temperature/frequency curve for CCI4 in six inclusion compounds that all have cavities with three-fold symmetry axes show an excellent correlation with the ratio between the volume of the carbon tetrachloride molecule and the cavity volume [20]. 

For these inclusion compounds where the cavity has a three-fold symmetry axis the normal coordinates are symmetry-determined and it becomes possible to analyse the temperature-dependence of the NQR frequencies completely. The practical difficulty is that the theoretical relationship between frequency and temperature applies to constant volume conditions [10,11] while the experimental data are usually obtained at constant pressure. 

The similarity of the curves and their convergence to the same value at OK demonstrates that the guest is in essentially the same environment in all four complexes. The slope of the curves at high temperatures, however, progressively increases in the 

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The diffusion, or percolation,41 of a molecule within the channels of CyD or FAU inclusion compounds is expected to be much less than that in conventional solvents. Often, the decay rate (k0) of a carbene in a nonviscous organic solvent is diffusion limited, cf. kd(MeOH) = 1.20 x 1010M-1 s-1 25°C.67 Therefore, limited guest mobility not only will hamper intermolecular reactions but it should also prolong the lifetime (Y) of the carbene reaction intermediate, if intramolecular modes of decay are not accessible. 

Solid state NMR experiments on LP/urea indicate a high de e of guest mobility under ambient conditions, a result consistent with similar studies of long-chain hydrocarbon/urea clathrates. ... 

Gonzalez J, Devi RN, TunstaU DP, Cox PA, Wright PA. Deuterium NMR studies of framework and guest mobility in the metal—organic framework compound MOF-5, Zn OfO CC H CO lj. Microporous Mesoporous Mater 2005 84 97-104. 

Immobilization. The abiUty of cyclodextrins to form inclusion complexes selectively with a wide variety of guest molecules or ions is well known (1,2) (see INCLUSION COMPOUNDS). Cyclodextrins immobilized on appropriate supports are used in high performance Hquid chromatography (hplc) to separate optical isomers. Immobilization of cyclodextrin on a soHd support offers several advantages over use as a mobile-phase modifier. For example, as a mobile-phase additive, P-cyclodextrin has a relatively low solubiUty. The cost of y- or a-cyclodextrin is high. Furthermore, when employed in thin-layer chromatography (tic) and hplc, cyclodextrin mobile phases usually produce relatively poor efficiencies. 

The second way in which an electroactive species such as lithium can be incorporated into the structure of an electrode is by a topotactic insertion reaction. In this case the guest species is relatively mobile and enters the crystal structure of the host phase so that no significant change in the structural configuration of the host lattice occurs. 

The configurational entropy of the mobile guest ions, assuming random mixing and a concentration x, residing in x° lattice sites of equal energy, is... 

The primary question is the rate at which the mobile guest species can be added to, or deleted from, the host microstructure. In many situations the critical problem is the transport within a particular phase under the influence of gradients in chemical composition, rather than kinetic phenomena at the electrolyte/electrode interface. In this case, the governing parameter is the chemical diffusion coefficient of the mobile species, which relates to transport in a chemical concentration gradient. 

JC° number of lattice sites occupied by mobile guest ions III. 4... 

In a typical SPR experiment real-time kinetic study, solution flows over the surface, so desorption of the guest immobilized on the surface due to this flow must be avoided.72 In the first stage of a typical experiment the mobile reactant is introduced at a constant concentration ([H]0) into the buffer flowing above the surface-bound reactant. This favors complex association, and the progress of complex formation at the surface is monitored. The initial phase is then followed by a dissociation phase where the reactant is removed from the solution flowing above the surface, and only buffer is passed over the surface to favor dissociation of the complex.72 74 The obtained binding curves (sensograms) contain information on the equilibrium constant of the interaction and the association and dissociation rate constants for complex formation (Fig. 9). 

Liquid-liquid chromatographic runs with RR-1284] in CHC13 in the mobile phase and racemic guest in the aqueous stationary phase ... 

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