Liquid inclusion complexes

Because of the importance of aromatics/aliphatics separation and the problems associated with solvent extraction, possible alternatives have been studied. These include liquid membranes (Li, 1968 1971 Goswami et al., 1985), pervaporation (Hao et al., 1997), and the use of liquid inclusion complexes (Atwood, 1984). No selective sorbents are known for aromatics/aUphatics separation. It is, however, certainly possible to develop such sorbents based on jr-complexation. In the benzene molecule, the carbon atom is sp hybridized. Hence, each carbon has three sp orbitals and another Pz orbital. The six Pz orbitals in the benzene ring form the conjugative n bond. The Pz orbitals also form the antibonding n orbitals, which are not occupied. When benzene interacts with transition metals. 

The diluent portion also determines the form, or physical appearance, of the flavor, ie, Hquid, powder, or paste. Liquid flavor forms include water-soluble, oil-soluble, and emulsion forms powder flavor forms include plated (including dry solubles), extended, occluded, inclusion complexes, and other encapsulated forms and paste flavor forms include fat, protein, and carbohydrate-based paste. 

Nakajima et al. (1) prepared liquid crystalline polyrotaxane derivatives containing the mesogenic group 4-cyano-4 -hydroxybiphenyl attached to the a-cyclodextrin component of linear polyethylene glycol containing an a-cyclodextrin inclusion complex with an adamantane termini. 

Immobilization. The ability 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 liquid chromatography (hplc) to separate optical isomers. Immobilization of cyclodextrin on a solid support offers several advantages over use as a mobile-phase modifier. For example, as a mobile-phase additive, p-cyclodextrin has a relatively low solubility. The cost of y- or a-cyclodextrin is high. Furthermore, when employed in thin-layer chromatography (dc) and hplc, cyclodextrin mobile phases usually produce relatively poor efficiencies. 

Thus the boundaries of the enclosures in organized media may be of two types they may be stiff (i.e, none of the guest molecules can diffuse out and the walls do not bend), as in the case of crystals and some inclusion complexes, or flexible (i.e., some of the guest molecules may exit the cavity and the walls of the cavity are sufficiently mobile to allow considerable internal motion of the enclosed molecules), as in the case of micelles and liquid crystals. In these two extremes, free volume needed for a reaction is intrinsic (built into the reaction cavity) and latent (can be provided on demand). 

Chiral crown ethers based on IB-crown-6 I Fig. 4> can form inclusion complexes with ammonium ions and proionated primary amines. Immobilization of these chiral crown ethers on a chromatographic support provides a chiral stationary phase which can resolve most primary amino acids, amines and amino alcohols. However, the stereogenic center must be in fairly close proximity in the primary aininc lor successful chiral separalion. Significantly, ihe chiral crown ether phase is unique in that ii is one of the few liquid chromatographic chiral stationary phases that does not require the presence of an aromatic ring to achieve chiral separations. 

Another type of absorption enhancer, which has been shown to have a better safety profile, is cyclodextrin (CD) [39]. CDs have been shown to form inclusion complexes with lipophilic drugs, thereby improving their aqueous solubility and stability. A powdered insulin formulation containing dimethyl-(3-cyclodextrin improved the absolute bioavailability of insulin by 13% in rabbits compared to a control liquid formulation (1%) of insulin with dimethyl-(3-cyclodextrin [40]. Recently, hydroxypropyl (3-cyclodextrin has been shown to be more effective for enhancing the nasal absorption of acyclovir than a range of other absorption enhancers in vivo [41]. 

Oguchi and coworkers examined the decarboxylation behavior of -aminosalicylic acid (PAS) as a freeze-dried solid under thermal stress conditions (80°C) in the presence of the excipients pullulan (a linear polysaccharide which can not form inclusion complexes with PAS) and a-cyclodextrin (39). The solid-state stability was shown to correlate with the fraction of amorphous PAS. Increasing relative amounts of pullulan resulted in higher fractions of amorphous PAS. Rapid freezing (liquid nitrogen) was shown to result in a greater relative amount of amorphous drug, as expected. 

Eto, S., Noda, H., Noda, A., Chiral Separation of barbiturates and hydantoins by reversed-phase high-performance liquid-chromatography using a 25 or 50 mm short ods cartridge column via beta-cyclodextrin inclusion complexes. J. Chromatogr. 1992, 579, 253-258. 

Koscielski, T., Sybilska, D., and Jurczak, J. (1983) Separation of a- and / -pinene into enantiomers in gas-liquid chromatography systems via a-cyclodextrin inclusion complexes. J. Chromatogr. 280, 131-134. 

The use of cyclodextrins as the mobile phase components which impart stereoselectivity to reversed phase high performance liquid chromatography (RP-HPLC) systems are surveyed. The exemplary separations of structural and geometrical isomers are presented as well as the resolution of some enantiomeric compounds. A simplified scheme of the separation process occurring in RP-HPLC system modified by cyclodextrin is discussed and equations which relate the capacity factors of solutes to cyclodextrin concentration are given. The results are considered in the light of two phenomena influencing separation processes adsorption of inclusion complexes on stationary phase and complexation of solutes in the bulk mobile phase solution. 

To improve the effectiveness of the chromatographic separation, a comparison study has been carried out on cyclodextrin and liquid crystal stationary phases Both materials function as "ordered" media with cyclodextrins the inclusion complex formation predominates, whereas the liquid crystals enable interaction of compounds with the ordered structure of the mesophase ... 

Sorption of various gases (02, N2, C02, and He) on wheat flour, soybean flour, potato starch, and wheat starch has been investigated in order to study the effect of those gases on the functional properties of processed food products. Results indicate that such properties improved only after flour and starch were treated with chlorine.455,456 The adsorptivity of various gases by starch has been reexamined.457 Liquid ammonia quickly forms a gelatinous paste with starch.458 Tomasik et al.459 attempted to prepare inclusion complexes of starch with colloidal sulfur. A key result was that inclusion inside the starch matrix was only possible in small amounts because of the large relative size of the sulfur micelles. 

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