Clathrate inclusion complex

Fig. 2. Classification/nomenclature of host—guest type inclusion compounds, definitions and relations (/) coordinative interaction, (2) lattice barrier interaction, (J) monomolecular shielding interaction (I) coordination-type inclusion compound (inclusion complex), (II) lattice-type inclusion compound (multimolecular/extramolecular inclusion compound, clathrate), (III) cavitate-type inclusion compound (monomolecular/intramolecular inclusion...

Even less expected, perhaps, are the reactions involving gas-solid addition of HBr, Cl2, and Br2 to a, 3-unsaturated acid guest species in a- and P-cyclodextrin inclusion complexes (242). Although the chemical yields are not high, the optical yields in some cases are extraordinary. Thus, chlorine addition to methacrylic acid in a-cyclodextrin yields (- )-2,3-dichloro-2-methylpropanoic acid in nearly quantitative optical yield. The 3-cyclodextrin methacrylic acid clathrate undergoes chlorine addition to yield preferentially the enantiomeric (+ )-product, with an e.e. of 80%. 

An important advantage of the inclusion complexes of the cyclodextrins over those of other host compounds, particularly in regard to their use as models of enzyme-substrate complexes, is their ability to be formed in aqueous solution. In the case of clathrates, gas hydrates, and the inclusion complexes of such hosts as urea and deoxycholic acid, the cavity in which the guest molecule is situated is formed by the crystal lattice of the host. Thus, these inclusion complexes disintegrate when the crystal is dissolved. The cavity of the cyclodextrins, however, is a property of the size and shape of the molecule and hence it persists in solution. In fact, there is evidence that suggests that the ability of the cyclodextrins to form inclusion complexes is dependent on the presence of water. Once an inclusion complex has formed in solution, it can be crystallized however, in the solid state, additional cavities appear in the lattice, as in the case of the hosts previously mentioned, which enable the inclusion of further guest molecules. ... 

Pb azide, Pb nitrophenols, Pb triethanol-ammonium perchlorate and PETN or RDX, with a sheath spun from filaments of a thermo plastic material or a ductile metal such as bronze) Ad 159) J.F. Kenney, USP 3293091(1966) CA 67, 7089(1967) [Primary expl mixts contg 46% of complex clathrate inclusion salts (as shown by X-ray diffraction data) of basic lead picrate, such as Pb(C5H2N3O7)2-Pb(OH)2-Pb(N03)2.-Pb(OAc)2, 50% Ba nitrate 4% Tetracene]... 

Figure 7.32 Single crystal transformations between the 1 1 and 1 2 toluene inclusion complexes of p-f-butylcalix[4]arene. The transformation of the the toluene or benzene clathrates to the guest-free a-form causes crumbling of the crystal (reproduced by permission of The Royal Society of Chemistry).

Crystalline inclusion complexes (IC s) have been also formed between polymers and another small-molecules, host clathrated provide a unique environment for observing the solid - state behavior of isolated polymer chains. In their IC s with small-molecule, host clathrates, such as urea (U) [1] and perhydrotriphenylene (PHTP) [57], the included polymer chains are confined to occupy narrow channels (ca. 5.4 A in diameter) where they are extended and separated from neighboring chains by the channel walls, which are composed exclusively of the host clathrate, crystalline matrix. Choi et al. [58] have been studied the behavior of isolated, extended polymer chains included in their IC s with U and PHTP by a combination of molecular modeling [59,60] and experimental observations in an effort to determine their conformations and mobilities in these well-defined, containing environments. 

One rarely used but powerful means of maximizing both content uniformity (as mentioned above) and stability aspects of low-dose pharmaceuticals is the formation of inclusion complexes to increase both the drug load in the formulation as well as the stability of the API. One specific example is the complexation of ethinyl estradiol in the form of its /3-cyclodextrin clathrate for use in pharmaceutical formulations.23 This inclusion complex has been successfully applied in the development of an ultralow-dose formulation of this steroid.24... 

The explosive ingredient in Sinoxyd-type primers is lead styphnate (lead trinitroresorcinate), which is very sensitive to static electricity, and fatalities have resulted from handling the dry salt. Preparation of the pure salt is difficult, and many patented preparations, including basic modifications, exist. Some claim special crystalline forms and/or reduced static electricity hazard. Explosive ingredient substitutes for lead styphnate were sought that would be easier to make and safer to use. These included lead azide, diazonitrophenol, lead salts of many organic compounds, complex hypophosphite salts, pic-rate-clathrate inclusion compounds, and pyrophoric metal alloys. 

In 1962 Kenney applied for patents on many complex, basic lead pic-rate-clathrate inclusion compounds which did not have the static electricity hazard of lead styphnate. Of 44 compounds listed in his patent, monobasic lead picrate-lead nitrate-lead acetate was preferred for primers, although monobasic lead picrate-lead nitrate-lead hypophosphite dibasic lead pic-rate-lead nitrate-lead acetate and monobasic lead picrate-lead nitrate-lead acetate-lead hypophosphite were also suitable. Glass was thought to damage the bore of the firearm and was considered by some to be undesirable. A glassless rimfire mixture was ... 

Host — A - molecular entity that forms an -> inclusion complex with organic or inorganic -> guests, or a - chemical species that can accommodate guests within cavities of its crystal structure. Examples include cryptands and crowns (where there are -> ion-dipole interactions between heteroatoms and positive ions), hydrogen-bonded molecules that form clathrates (e.g., hydroquinone and water), and host molecules of inclusion compounds (e.g., urea or thiourea). The - van der Waals forces and hydrophobic interactions (- hydrophobic effect) bind the guest to the host molecule in clathrates and inclusion compounds. 

Figure 3 Schematic representation of the formation of inclusion complexes based on the recognition of a guest molecule by a host receptor (a), of a clathrate based on the inclusion of guest molecules within cavities generated upon packing of clathrands in the solid state (b), and of a 1-D inclusion molecular network named koilate formed through interconnection of hollow tectons (koilands) by connector molecules (c).

Starch-guest molecule compounds in inclusion complexes are usually nonstoichiometric species. On the other hand, in the case of amylose such compounds are stoichiometric, but their composition is not repeatable. Starch complexes may consist of partly physical mixtures, adsorbates, and true inclusion complexes formed by direct involvement of dipolar interactions, host-guest hydrogen bonds, and/or clathration-like interactions within the starch matrix. 

A simple possibility for the synthesis of esters, the reaction of an acid chloride with an alcohol, was used by Schrage and Vogtle [58] for a two-step synthesis of the macrocycle 63 from the alcohol 61 and the acid chloride 62. Compound 63, an example from the field of host/guest chemistry, forms a cavity, as studied with CPK-models, which could include planar, aromatic guests. Crystals obtained from benzene/ -heptane point to a 1 2 stoichiometry of 63 and benzene according to NMR-spectroscopic data. However, whether this is a molecular inclusion complex or just a clathrate is not yet known. 

Clathrate An inclusion complex formed when molecules of one kind are trapped in the crystalline network formed by molecules of a different kind. 

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