Guest complexes formation

Control and Acceleration of Photoreactions via Host-Guest Complex Formation... 

Control and Acceleration of Photoreactions via Host-Guest Complex Formation by a Solid-Solid Reaction and Irradiation in the Solid State... 

A series of model siderophore molecular recognition studies coupled with host-guest carrier facilitated model membrane transport studies was reported (198-202). Three approaches were taken which incorporate (i) second coordination shell host-guest complexation, (ii) ternary complex formation, and (iii) a combination of ternary complex - second coordination shell host-guest complex formation. Examples of these approaches are described below. 

The dependence of 1/t on concentration can be explained by an extension to the equation for the two-step mechanism of one host-two guests complex-formation, that is,... 

Odashima, K., Itai, A., Iitaka, Y., Koga, K., Host-guest complex formation between a water soluble polyparacyclophane... 

Effective Optical Resolution of Bicyclic Enones Through Host-Guest Complex Formation, Tetrahedron Lett., 29, 551-554. 

Nassimbeni, L. R., Niven, M. L., Tanaka, K., and Toda, F. (1991) On the Optical Resolution of Bicyclic Enones Through Host-Guest Complex Formation The Crystallographic Result, J. Crystallograph. andSpectroscop. Res., 21, 451-457. 

Efficiency of the above discussed resolutions changed in a wide range 0 < S < 0.433 (Table 5). Menthol (28) and 2-halogenocyclohexanol (35, 36, 37) enantiomers were the best ligands of DBTA for chiral recognition during host-guest complex formation, therefore these model compounds were used for further elaboration of the resolution processes (point 3.4.). 

Toda, F., and Tanaka, K. Design of a new chiral host compound, trans-4,5-bis(hydroxydiphenylmethyl)-2,2-dimethyl-l,3-dioxacyclopentane. An effective optical resolution of bicyclic enones through host-guest complex formation, Tetrahedron Lett. 1988, 29, 551-554. 

Many plant secondary metabolites produced by cell cultures and substrates used in culture media are often hydrophobic and have low solubility in aqueous medium. Improving the production of metabolites in the plant cell system has also been attempted by enhancing the solubilities of metabolites by using the cyclodextrin-guest complex formation. There are two major approaches, one involves the improvement of substrate solubility and the other improves metabolite. 

Small structural changes are especially important in molecular recognition. It has been noted, e.g., that ... subtle changes of molecular structure may result in severe changes of inclusion behavior of a potential host molecule due to the complicated interplay of weak inter-molecular forces that govern host-guest complex formation [41],... 

Host/guest complex formation in solution can be simply described by the following equation,... 

Similar results have been reported for the host/guest complex formation between a tetracationic cyclophane host [=cyclobis(paraquat-p-phenylene)j and the planar het-eroarene indole. The binding constants Kg, determined in six solvents of different polarities, increase with increasing solvent polarity, being ca. 100-fold greater in water than in acetone [306]. Further examples of solvent-dependent cyclophane/guest complexation reactions can be found in reference [299],... 

K. Odashima, A. Itai, Y. litaka, K. Koga, Host-Guest Complex Formation between a Water-Soluble Polyparacyclophane and a Hydrophobic Guest Molecule , J. Am. Chem. Soc., 102,2504 (1980)... 

We have shown that the movement of molecules during the host-guest complex formation process in the solid state is easy. Some host-guest complexes can be formed simply by mixing host and guest compounds in the solid state or keeping a mixture of powdered host and guest at room temperature [2J. Therefore, the ease of oxidation in the solid state is not unexpected. 

Also, the discussion of the entropic contributions so far is valid for the isolated host-guest system. If placed in a solvent, solvent molecules that saturated the attractive contacts of the host and of the guest are liberated upon host-guest complex formation and can account for a significant entropy gain, as in the case of the well known chelate effect in coordination chemistry. 

Recently, the syntheses and some supramolecular properties of receptors with ribbon-type concave topology have been reported [17, 18]. Due to their ability to selectively bind electron-deficient aromatic and aliphatic substrates, these compounds can be regarded as molecular tweezers. This section is devoted to the temperature and pressure dependence of the host-guest complex formation of the naphthalene-spaced tweezer 2 and the diacetoxy substituted derivative 3 with the... 

If desolvation of the anionic nucleophile is to be the prominent factor in the molecular catalysis one would expect the most heavily solvated guest to display the largest rate enhancement factors at saturation in a given type of reaction. Heavy solvation of the anion may, however, impair host-guest complex formation so that the complete kinetic analysis with evaluation of every rate- or complex stability constant might not be possible. This turned out to be the case when the rate effects of different anionic nucleophiles in aromatic nucleophilic substitutions were studied The catalysis by the polyammonium host molecule 25 in most of these reactions could only be characterized by a Fig. of merit (FM = K ke ) but not by individual rate constants. 

Additionally, functional groups (-RCOOH) were added to a crown ether to probe the influence of tethering the counterion to the macrocyclic host and to determine the optimum tether length for stable host-guest complex formation. At an elevated pH, the substituted crown ether serves as host and counterion. It was experimentally... 

Toda F, Tanaka K, Sekikawa A. Host-guest complex formation by a solid-solid reaction. J Chem Soc Chem Commun 1987 279-80. 

Since these hosts are totally synthetic, design for selective and efficient artificial systems via host-guest complex formation is open as one of the most challenging and exciting fields in synthetic organic chemistry. 

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