Intrinsic cavities

Fig. 23. Scanning electron micrograph of intrinsic cavities in preoriented polycarbonate (AOj = 0.034)...

A detailed investigation is described of dendritic effects in transition metal catalysed organic transformations. Small dye molecules were loaded into the intrinsic cavities of the backbone of dihydroxybenzyl alcohol based dendrimers which led to a change in physical properties of both the dye and the dendrimer. The use of dendrimers as templates to prepare network carriers containing cavities of predetermined size and disposition was also investigated. 21 refs. 

From the single X-ray crystal analysis, H5.1 formed intra- and inter-molecular hydrogen bonds, which resulted in the formation of ID extrinsic channels with a diameter of 7.10 A, slit channels of 5.14 A by 9.14 A, and an intrinsic cavity of 6.76 A. The multiple hydrogen bonds stabilized the supra-molecular structure even after removal of the trapped solvents by heating under reduced pressure. The supramolecular assembly of the activated H5.1 took up CO2, but did not accommodate CH4 and N2, indicating that the activated H5.1 can selectively capture CO2. The activated porous crystals of H5.1 showed remarkable CO2 selectivity over CH4 (375 1) and N2 (339 l). " ... 

All of above results suggest that such pillararene-based SOF materials with permanent porosity can be expected to have potential application in gas absorption. As displayed by the gas sorption isotherms measured up to 1 atm at 298 K, P5-SOF exhibits remarkably higher absorption capacity for CO2 through the dipole-dipole interactions between CO2 and hydrojyl groups, compared with CH4 and N2 under the same condition. The selectivity for CO2 is estimated to be 339 1 over N2, and 375 1 over CH4. It is also worth mentioning that this is the first report of a pillararene-based SOF material with a permanent porous stmcture and with extraordinarily selective and reversible absorption capacity for CO2 compared with that of most of the reported SOF materials with intrinsic cavities. Furthermore, it also provides a glimpse into the novel potential of P5-SOF materials in gas capture and further environmental engineering. 

Leahy, D. E. (1986) Intrinsic molecular volume as a measure of the cavity term in linear solvation energy relationships octanol-water partition coefficients and aqueous solubilities. J. Pharm. Sci. 75, 629-636. 

A very powerful method for the evaluation of solubility differences between polymorphs or solvates is that of intrinsic dissolution, which entails measurements of the rates of solution. One method for this work is to simply pour loose powder into a dissolution vessel, and to monitor the concentration of dissolved solute as a function of time. However, data obtained by this method are not readily interpretable unless they are corrected by factors relating to the surface area or particle size distribution of the powder. In the other approach, the material to be studied is filled into the cavity of a circular dissolution die, compressed until it exhibits the effective planar surface area of the circular disc, and then the dissolution rate is monitored off the surface of the rotating disc in the die [130],... 

Continuum models remove the difficulties associated with the statistical sampling of phase space, but they do so at the cost of losing molecular-level detail. In most continuum models, dynamical properties associated with the solvent and with solute-solvent interactions are replaced by equilibrium averages. Furthermore, the choice of where the primary subsystem ends and the dielectric continuum begins , i.e., the boundary and the shape of the cavity containing the primary subsystem, is ambiguous (since such a boundary is intrinsically nonphysical). Typically this boundary is placed on some sort of van der Waals envelope of either the solute or the solute plus a few key solvent molecules. 

Most network structures are effective host structures for small guest molecules, often the solvent. Exceptions arise when there is a high degree of interpenetration, i.e. where two or more networks are entangled [7]. This type of host-guest behaviour is not intrinsic to the molecular components themselves, but occurs in cavities or clefts created by the assembly of the network structure. Mol-... 

In addition to the classification of liquid chromatographic enantioseparation methods by technical description, these methods could further be classified according to the chemical structure of the diverse CSPs. The chiral selector moiety varies from large molecules, based on natural or synthetic polymers in which the chirality may be based on chiral subunits (monomers) or intrinsically on the total structure (e.g., helicity or chiral cavity), to low molecular weight molecules which are irreversibly and/or covalently bound to a rigid hard matrix, most often silica gel. 

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