Lipophilic cavity

An example of a cyclophane-type cavity is the azacyclophane CP66 supra-molecular system which provides a lipophilic cavity with an internal width of approximately 6.5 A, as well as positive charges which accelerate and increase the selectivity of the process. The Diels-Alder reaction of cyclopentadiene with diethylfumarate at 20 °C in 10% and 50 To dioxane-water is accelerated by the presence of CP66 by 2.9 and 1.5 times, respectively [65c] (Equation 4.12). 

SCHEME 9.6 A macrocyclic oligosaccharide cyclodextrin forming a torus-shaped structure of cyclodextrin with rigid lipophilic cavities. (Adapted from Polyakov, N.E., Free Rad. Biol. Med., 36, 872, 2004. With permission.)... 

The considerable interest in the design of container molecules [26, 27, 30], for their potential application as nano-scale chemical reactors has particularly received much attention [97]. In this sense, supramolecular catalysis allowing the chemical transformation of a substrate selectively entrapped within a molecular receptor, will behave as a chemical reactor [98]. One way to obtain a supramolecular catalysis, is to design a molecular receptor containing a lipophilic cavity allowing selective substrate binding, and specific sites for metal ion coordination [97, 99]. Attempts in this direction have... 

Schneider and coworkers investigated the capability of the tetraazonia cyclophane 51 to bind nucleosides and nucleotides in water [72]. Its two diphenylmethane units border a lipophilic cavity for the uptake of likewise lipophilic molecules or subunits. As evidenced by HNMR studies of the complexes, only in the case of the purine derived nucleosides and nucleotides (A, G, AXP, GMP) the base moiety is included inside the host cavity but not in the case of the pyrimidine analogues (U, C, UMP, CMP, TMP). Due to their hydrophilic nature, the sugar and phosphate groups remain outside the niche. 

Inspection of the crystal structure of compound III bound to the active site of HIV PR revealed lipophilic cavities extending off the Sl/ST subsites adjacent to the /-butyl groups of the benzamidine moiety. The cavities are bordered by flexible loops around Pro81/8T and previous crystallographic studies indicated that both loops can move back by up to 2.5 A, extending the size and... 

Neutral molecules are carried between two organic phases through a water layer by water-soluble receptors containing a lipophilic cavity [6.40, 6.41]. Urea and nucleosides are transported using a metallocarrier [6.42a] and complementary basepairing agents [6.42b], respectively. 

Another commonly used cyclodextrin Capfi oiulfobutylether ofi-CD (SBE-ft-CD), is a polyanionicp-cyclodextrin derivative with a sodium sulfonate salt separated from the lipophilic cavity by a butyl ether spacer group, or sulfobutylether. BotfHBGPand sulfobutylether qf-CD (SBE-p-CD) are widely used cyclodextrins for solubility-enhancing purpose. 

Other groups have used the cyclotriveratrylene cone both as a shaping unit and as a lipophilic cavity for designing and constructing hollow molecules of various types. 

Inclusion complexes have also been shown to aid excimer formation provided that the cavity dimensions and polarity are appropriate. Thus Ueno et al. (1980) have shown that the lipophilic cavity of y-cyclodextrin can accommodate two molecules of sodium (l-naphthyl)methyl acetate and that this leads to enhanced excimer emission. Excimer formation by diaryl-methylammonium salts is promoted by y-cyclodextrin but not by a- and P-cyclodextrins (Emert et al., 1981a). The best results were obtained with compounds having fairly large aryl groups e.g. 4-biphenylyl and 1-naphthyl. The hydrophobic character of these groups helped to solubilise the compounds in the interior of the cyclodextrin. 

Catalytic reactions in aqueous solution can be modified by changes in the supramolecular state of the medium in which they are conducted. One approach to using medium changes to influence catalytic reactions is to introduce host molecules, such as cyclodextrins, into the reaction mixtures. Cyclodextrins have inner lipophilic cavities enclosed by hydrophilic surfaces. A cyclodextrin can bind a hydrophilic terminal alkene into its... 

According to Horvath, the problems arising from the limited reciprocal solubilities of the water phase and higher olefins should be overcome by application of the SAPC technique [138, 144]. For this and other biphasic - but nonaqueous -processes, see Sections 3.1.1.2 and 3.1.1.3. A new concept concerning inner lipophilic cavities and hydrophilic surfaces of a-cyclodextrins may offer new possibilities for the hydroformylation of higher olefins [142]. Asymmetric hydro-formylations are dealt with in Section 2.9. 

Molecular Structures with Large Lipophilic Cavities... 

D3)-Bis(cyclotriveratrylene) derivatives [35] as new macrocage hosts (13) (Structure 7) possess roughly spherical and considerably rigid lipophilic cavities. They have strong complexing ability toward neutral guests, namely poly-halomethanes, in water [36] and even in lipophilic media [37-39]. Stability... 

In 1980, Koga and coworkers reported the inclusion complexation of benzene and naphthalene derivatives by 14 (Fig. 3) in aqueous HCl. To inspect the driving forces for inclusion complexation by completely lipophilic cavities in detail. Diederich and coworkers investigated a series of cyclophanes (15a-c) displaying the following features ... 

---