Capsules molecular

The concept of a well-stirred segregated reactor which also has an exponential residence time distribution function was introduced by Dankwerts (16, 17) and was elaborated upon by Zweitering (18). In a totally segregated, stirred tank reactor, the feed stream is envisioned to enter the reactor in the form of macro-molecular capsules which do not exchange their contents with other capsules in the feed stream or in the reactor volume. The capsules act as batch reactors with reaction times equal to their residence time in the reactor. The reactor product is thus found by calculating the weighted sum of a series of batch reactor products with reaction times from zero to infinity. The weighting factor is determined by the residence time distribution function of the constant flow stirred tank reactor. 

Cronin, L. (2006) Inorganic molecular capsules from structure to function. Angewandte Chemie-Intemational Edition, 45, 3576-3578. 

Recently, it has been found that the outcome of some cycloadditions can be altered remarkably when performed inside the cavity of cyclodextrins (288), self-assembled molecular capsules (289), or coordination cages (290). This fact intrigued us greatly and stimulated our interest in the Diels-Alder reactivity of the calixarene-like [M2(L19)(L )]+ complexes bearing unsaturated carboxylate coligands L (215). 

T. Heinz, D.M. Rudkevich, J. Rebek, Jr, Pairwise selection of guests in a cylindrical molecular capsule of nanometre dimensions , Nature 1998, 394,764-766. 

J. Kang, J. Rebek, Jr, Entropically driven binding in a self-assembling molecular capsule , Nature 1996, 382, 239-241. 

Molecular capsules composed of cavitands and able to form inclusion complexes have received much attention [29, 77, 78]. They can be formed covalently [78, 79] or reversibly through metal coordination [80-82] or H-bond-... 

To date, D coefficients of carbohydrates established with the PFGSE approactf - " have been undertaken to (1) validate the theoretical self-diffusion coefficients calculated from MD trajectories, (2) demonstrate the complexation of lanthanide cations by sugars,(3) probe the geometry of a molecular capsule formed by electrostatic interactions between oppositely charged P-cyclodextrins, (4) study the influence of concentration and temperature dependence on the hydrodynamic properties of disaccharides, and (5) discriminate between extended and folded conformations of nucleotide-sugars. ... 

Electrochemistry of Guests Inside Resorcinarene Molecular Capsules... 

Figure 3.8 Structures of the resorcinarenes 3 and 4 used in the formation of self-assembled, hexameric molecular capsules.

NMR spectroscopic data in CD2C12 solution verified the encapsulation of cobaltocenium inside a capsule composed of six molecules of resorcinarene 4. From NMR diffusion coefficient measurements, we concluded that the resorcinarene molecular capsules were preformed in CD2CI2 solution51 in the absence of cobaltocenium or any other cationic species. Similar results in CDC13 solution have been reported by Cohen and coworkers.52 53 It is now clear that cationic species are not required to seed the self-assembly of the capsules. 

Figure 3.9 Size comparison between cobatocenium (top left) and the hexameric molecular capsule formed by resorcinarene 3. Resorcinarene 4 would form a much larger capsule due to its longer undecyl feet compared to the methyl feet in 3. (See the color version of this figure in Color Plates section.)...

I n the latter two examples the EM values calculated from rate data are higher than the actual concentration of encapsulated reactants. This result indicates a favorable directional correlation of functionalities in the complex, but it is apparent that Rebek s capsule is less efficient than cucurbit[6]uril in promoting the productive geometry or stabilizing the TS. The molecular capsules not only concentrate reactants but also increase the time that the reacting function reside within critical distance (productive geometry) - both factors are determinant in achieving effective catalysis [24]. 

Kang, J., Santamaria, J., Hilmersson, G. and Rebek, f. fr. (1998) Self-assembled molecular capsule catalyzes a Diels-Alder reaction. J. Am. Chem. Soc.. 120. 7389-7390. Kang, J., Hilmersson, G., Santamaria, J. and Rebek, f. fr. (1998) Diels—Alder reactions through reversible encapsulation. J. Am. Chem. Soc., 120, 3650—3656. 

G. and Rebek, J. Jr (1998) Self-assembled molecular capsule catalyzes a Diels-Alder reaction. J. Am. Chem. Soc., 120 (29), 7389-7390. 

Among enzyme modified starch derivatives,cyclo dextrins behave as empty molecular capsules with the ability to entrap guest molecules of appropriate geometry and polarity.The included molecules are protected from surroundings light, heat,oxidation, etc. The flavor cyclodextrin com -plexes show the above advantageous properties while they are in the dry,solld state.On contact with water,cyclodextrin complexes release their flavor content. In Hungary,the spice flavor beta-cyclodextrin complexes have been on the market, since 1982. 

Figure 6.12 The molecular capsule 6.33b-6.34 held by interactions to cyclodextrins as a self-assembled monolayer on gold. (Reproduced by permission of The Royal Society of Chemistry).

Corbellini, F., van Leeuwen, F. W. B., Beijleveld, H., et al Multiple ionic interactions for noncovalent synthesis of molecular capsules in polar solvents , New J. Chem. 2005, 29, 243-248. 

Atwood et al. have gone on to prepare a truly enormous molecular capsule along these principles, which conforms to the geometry of a snub cube (structure (1) in Figure 10.47). Reaction of six equivalents of the octol [4] resorcarene (with either methyl or undecyl feet ) with eight water molecules results in... 

McKinlay, R. M., Thallapally, P. K., Atwood, J. L., Hexameric C-alkylpyrogallol[4]arene molecular capsules sustained by metal-ion coordination and hydrogen bonds. Chem. Commun. 2006, 2956-2958. 

Kobayashi, K., Shirasaka, T., Yamaguchi, K., Sakamoto, S., Horn, E., Furukawa, N., Molecular capsule constructed by multiple hydrogen bonds self-assembly of cavitand tetracarboxylic acid with 2-aminopyrimidine. Chem. Commun. 2000, 41-42. 

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