Encapsulated guest

Container molecules are of great interest because their encapsulated guests often exhibit novel and unusual properties, which are not observed in the free or solvated state (8,9). They are used today as probes of isolated molecules and of the intrinsic characteristics of the liquid state, and are capable of enantiose-lective recognition (10), reversible polymerization (11), isolation of reactive species (12-14), and promoting reactions within their interiors (15-18). For a valuable introduction to this area the reader is directed to some excellent review articles (15,19-21). 

Bottom right Upfield region of the 1H-NMR spectrum sule monomers, signals for the encapsulated guests are gen-... 

The diffusion of entrapped guest molecules out of dendritic boxes was un-measurably slow over a period of several months. However, Meijer and coworkers have demonstrated that the shape-selective liberation of encapsulated guests could be achieved by removing the closed shell in two steps (Scheme 3) [15]. First, hydrolysis of the tBOC groups of the dense shell with formic acid gave a partly open dendritic box . At this point, small guests such as p-nitroben-zoic acid and nitrophenol could diffuse out of the box by dialysis. Susequent and complete removal of the outer shell by refluxing with 12 AT HC1, lead to the... 

The possibilities for encapsulating guest molecules in dendritic hosts were first proposed by Maciejewski in 1982 [143], In 1990, Tomalia presented evidence for unimolecular encapsulation of guest molecules in dendrimers and pointed out that it was one of the possible future research areas in dendrimer chemistry [164],... 

Using information obtained from X-ray crystallography, we have described the structure of a chiral, spherical molecular assembly held together by 60 hydrogen bonds. [10] The host, which conforms to the structure of a snub cube, self-assembles in apolar media and encapsulates guest species within a cavity that possesses an internal volume of approximately 1.4 nm3. 

By manipulating the chemical properties of dendrimer functional groups, hydrophilic guest molecules can be dissolved in nonpolar solvents and hydro-phobic molecules can be dissolved in polar solution. This is possible because, independent of an encapsulated guest, dendrimers terminated in hydropho-... 

In addition to the hydrophobic interaction mentioned above to encapsulate guest molecules, other types of nonspecific interactions have also been explored to enhance binding. For example, block copolymer micelles based on PEO as hydrophilic segments and poly(/3-benzyl L-aspartate) as hydrophobic blocks have used to encapsulate doxombicin. The encapsulation efficiency of doxombicin, an aromatic anticancer drug molecule, has been found to be significantly higher. This observation has been attributed to the tt-tt interaction between the anthracycUne moiety of doxorubicin and the benzyl group of poly(/3-benzyl L-aspartate) (Cammas-Marion et al. 1999). 

Electrochemistry of Cavitand-Encapsulated Guests in Aqueous Solution... 

Nature often exploits large pJQ shifts in enzymes to effect chemical catalysis similarly, we hoped to apply the large shifts in the effective basicities of encapsulated guests to reaction chemistry. Initial studies focused on the hydrolysis of orthoformates, a class of molecules responsible for much ofthe formulation ofthe Bronsted theory of acids almost a century ago [98]. While orthoformates are readily hydrolyzed in acidic solution, they are exceedingly stable in neutral or basic solution [99]. However, in the presence of a catalytic amount of 1 in basic solution, small orthoformates are quickly hydrolyzed to the corresponding formate ester [38]. Addition of NEt4 to the reaction inhibited the catalysis but did not affect the hydrolysis rate measured in the absence of 1. With a limited volume in the cavity of 1, substantial size selectivity was observed in the orthoformate hydrolysis. Orthoformates smaller than tripentyl... 

Like many polymers, the fluidity or flow (rheological) properties of denrimers are of interest (Box 14.1). Dendrimers behave like soft, spherical particles, surrounded by a hard surface shell and hence are often described as core-shell type bodies. Hence the interior of dendrimers can be deformed according to the type of linkage and building blocks and my contain voids suitable for encapsulating guest species.2... 

For the C02 Cjo cluster, the translational frequencies e = 54 cm-1 and a [ = 122 cm-1 are smaller than for C2H2 C7o both these vibrations are coupled to the deformation vibrations of the guest and the cage. According to the Mulliken population analysis, there is some electron density redistribution and an increase of polarity of the both M-X bonds in the encapsulated guests, as compared to the free molecules BeF2 and CO2 (induced polarization). 

What kind of organic reactions can be carried out on encapsulated guests ... 

Different asymmetric residues with a different number of stereocenters attached with the same spacer to the resorcin[4]arene part showed an important influence on the encapsulated guest, even though the overall number of stereocenters changes drastically from 88 for 14-14 to only 8 for 12 12. These complementary experiments are undoubtedly proof of principle that magnetic desymmetrization of closed space can be performed by placing a chiral object outside the immediate environment. 

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