Inclusion complex/compound

The solubility of aromatic Pis could be enhanced by the introduction of kinks such as ether, bulky side groups, alicyclic groups [6], long flexible chains [7] meta- or ortho-oriented phenylene rings [8], cardo rings [9] and inclusion complex compounds [10]. Fluorination of... 

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...

Fig. 4. Chiroselective inclusion formation of racemic l-phenylethylammonium salt ((R/S)-14) using optically active crown compound ((i, 5)-13) [53955-48-9]. The diastereomeric inclusion complex (R)-(14) is more stable than (3, 3)-(13)-(3)-(14) (top views, dotted lines represent hydrogen...

Absorption, metaboHsm, and biological activities of organic compounds are influenced by molecular interactions with asymmetric biomolecules. These interactions, which involve hydrophobic, electrostatic, inductive, dipole—dipole, hydrogen bonding, van der Waals forces, steric hindrance, and inclusion complex formation give rise to enantioselective differentiation (1,2). Within a series of similar stmctures, substantial differences in biological effects, molecular mechanism of action, distribution, or metaboHc events may be observed. Eor example, (R)-carvone [6485-40-1] (1) has the odor of spearrnint whereas (5)-carvone [2244-16-8] (2) has the odor of caraway (3,4). 

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. 

Chiral Chromatography. Chiral chromatography is used for the analysis of enantiomers, most useful for separations of pharmaceuticals and biochemical compounds (see Biopolymers, analytical techniques). There are several types of chiral stationary phases those that use attractive interactions, metal ligands, inclusion complexes, and protein complexes. The separation of optical isomers has important ramifications, especially in biochemistry and pharmaceutical chemistry, where one form of a compound may be bioactive and the other inactive, inhibitory, or toxic. 

It has been established, that both DN and Ibp form complex compounds with ions Eu(III), Sm(III), Tb(III) and Dy(III), possessing luminescent properties. The most intensive luminescence is observed for complex compounds with ion Tb(III). It has been shown, that complexation has place in low acidic and neutral water solutions at pH 6,4-7,0. From the data of luminescence intensity for the complex the ratio of component Tb Fig was established equal to 1 2 by the continuous variations method. Presence at a solution of organic bases 2,2 -bipyridil, (Bipy) and 1,10-phenanthroline (Phen) causes the analytical signal amplification up to 250 (75) times as a result of the Bipy (Phen) inclusion in inner coordination sphere and formation of different ligands complexes with component ratio Tb Fig Bipy (Phen) = 1 2 1. 

A relative of the latter class of compounds are the macrotricyclic quaternary ammonium salts which have been reported by Schmidtchen. The bridges may contain either methylenes or ethyleneoxy units and the nitrogens are quaternarized. The underlying principle is to provide a cavity suitable for solvating or at least trapping anions. Schmidtchen presents evidence which suggests the formation of halide inclusion complexes. The synthesis of these molecules is accomplished along more or less traditional lines Such a species is illustrated above as compound 19. 

Macrocyclic tetraammonium compounds VIII and IX 611 form stable 1 1 inclusion complexes with anionic molecules in aqueous solutions 62). The anions are halides, carbonate, phosphate, AMP, ATP etc. The stability of the inclusion complexes hepends on electrostatic as well as hydrophobic interactions. Whereas the complexes of VIII are dominated by the electfostatic component, the hydrophobic interaction plays the main part in complexes of IX. 

A different non-classical approach to the resolution of sulphoxides was reported by Mikolajczyk and Drabowicz269-281. It is based on the fact that sulphinyl compounds very easily form inclusion complexes with /1-cyclodextrin. Since /1-cyclodextrin as the host molecule is chiral, its inclusion complexes with racemic guest substances used in an excess are mixtures of diastereoisomers that should be formed in unequal amounts. In this way a series of alkyl phenyl, alkyl p-tolyl and alkyl benzyl sulphoxides has been resolved. However, the optical purities of the partially resolved sulphoxides do not exceed 22% after... 

The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of y-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules present in a mixture. For example, perylene is extracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. 

On the other hand, the crystallization process of diolefin compounds often plays a significant role in determining their topochemical behaviour, by changing their crystal structure or by forming solvent inclusion complexes. Furthermore, topochemical photoreactions of crystals with )8-type packing are accompanied by thermal processes under moderate control by the reacting crystal lattice (see p. 140). These factors seriously complicate the whole reaction scheme. 

For example, the same dimer complex which contains two molar equivalents of ethanol, underwent photoreaction to give a higher molecular weight polymer (M = 12 000). The formation of such inclusion complexes with the solvent is rather generally observed with similar types of dimers formed with alcohols and some other solvents and, consequently, this enhances photopolymerizability. Such complex formation with a solvent may be one of the promising techniques that can be used for diolehn compounds in order to obtain polymers with high molecular weights. 

Enantioselective bromination of cyclohexene (11) in an inclusion complex with the optically active host compound, (i, i )-(-)-trans-4,5-bis(hydroxy-diphenylmethyl)-2,2-dimethyl-l,3-dioxacyclopentane (10a) was accomplished. 

An enantioselective Michael addition reaction was also accomplished in an inclusion complex with a chiral host compound. Treatment of a 1 1 complex of 10c and 66b with 2-mercaptopyridine (137) in the solid state gave (+)-138 of 80% ee in 51% yield. By a similar method, 3-methyl-3-buten-2-one (139) gave (+)-140 of 49% ee in 76% yield [30]. 

It is not easy to control the steric course of photoreactions in solution. Since molelcules are ordered regularly in a crystal, it is rather easy to control the reaction by carrying out the photoreaction in a crystal. However, molecules are not always arranged at an appropriate position for efficient and stereoselective reaction in their crystals. In these cases inclusion chemistry is a useful technique, as it can be employed to position molecules appropriately in the host-guest structure. Chiral host compounds are especially useful in placing prochiral and achiral molecules in suitable positions to yield the desired product upon photoirradiation. Some controls of the steric course of intramolecular and intermolelcular photoreactions in inclusion complexes with a host compound are described. 

Reaction Control of Guest Compounds in Host-Guest Inclusion Complexes... 

Fig. 3. Stereoview of the inclusion complex between a hydrogen-bonded dimer of host 3 with water and methylene chloride as guests. The crystal structure of this compound contains two additional species, a disordered CH Clj and fractional water (donated by S ). Both lie outside the complex between the bound water and an adjacent host unit (taken from Ref.28>)...

The wheel-and-axle design as source for host-guest compounds was originally proposed by Toda and Hart in 1981 for hosts containing hydroxyl functions 481 (see Ch. 3, Sect. 2.1 of Vol. 140). The l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol (24) provides a representative compound. It forms 1 2 crystalline inclusion complexes with a large number of small guest molecules, including a variety of ketones, amines, amides and a sulfoxide 48). 

When guest molecules are arranged together in the channel of a host-guest inclusion complex, intermolecular reactions of the guest compound may proceed stereoselec-tively and efficiently. An enantioselective reaction is expected when optically active host compounds are used. 

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