Resorcinarene molecules 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. 

Solvent molecules within the hexameric capsule can be displaced by sizable quaternary ammonium salts, and dissociation of at least one resorcinarene molecule from the hexamer is required for guest exchange. More details about the dynamic process of this assembly at nano- and micromolar concentrations were acquired using... 

Crystal structures for several of the corresponding pyrogallol[4]arenes 50 (Figure 3.23) have been solved. These also form hexameric capsules, which now contain an array of 72 hydrogen bonds (48 are intramolecular and 24 intermolecular, HB/ (N— 1) =4) and have no structural water molecules [64]. The increase in the ITm HB/(N— 1) value agrees very well with the fact that nanocapsules based on pyrogallol 50a are more stable in polar media than those derived from resorcinarene 49a. 

Fig. 39a, b Crystal structures of the capsule 52 between two tetracarboxylic acid resorcinarenes and four 2-aminopyrimidine molecules showing a the composition b the packing of the guests within the cavity (one aminopyrimidine is omitted to show interior)... 

Figure 3.7 The arrangement of the two resorcinarene monomers of type 36 in the corresponding dimeric capsule. The monomers are held together by a regular array of hydrogen bonds involving the phenolic hydrogens and eight propan-2-ol solvent molecules ...

Prompted by its crystal structure [34a] and the fact that some of these aggregates were formed in water-saturated chloroform solutions, the role of the water molecules in the formation of the hexameric capsules of 15c and 16c was also studied. Diffusion NMR was selected since the chemical shift of water protons in the presence of acidic compounds is very sensitive to the amount of water, the concentration of the acidic material, the exchange rate and solvent pH and is therefore not a predictable parameter. In addition, since water molecules are very small relative to the resorcinarene and pyrogallolarene hexamers, the water diffusion coefficient was anticipated to be a rather sensitive parameter to follow water interaction with these supramolecular structures. Indeed, when the water diffusion coefficient was followed as a function ofthe I5C/H2O ratio, a decrease in the diffusion coefficient of the water peak was observed with the increase of the 15c/H2O ratio, as shown in Fig. 6.12. Fig. 6.12a-d shows the signal decay of the water (Fig. 6.12a, c) and the... 

Molecular capsules are structurally elaborated receptors that completely surround the hosted molecule(s). Encapsulation based on covalent bonds yields permanent arrangements of molecules-within-molecules. Reversible encapsulation, on the other hand, is based on self-assembling through formation of weak supramolecular bonds and offers possibilities for a dynamic in out exchange of encapsulated molecules. Most of the dimeric capsules developed by Rebek and his group are obtained through reversible self-assembly of resorcinarene subunits. When simultaneously encapsulated in the cylindri-cally shaped inner space of these capsules, two reactant molecules are temporarily isolated from others in solution and display reactivity features different from those in bulk solution. The matter has been extensively reviewed,and will not be discussed here. 

The cavity of these calixarenes is usually too small to accommodate fullerenes, and is confirmed by solution, unless they have extended cavity walls as in calix[4]-naphthalenes. Nevertheless, some calix[4]arenes were shown to form stable crystalline complexes with C60 with the fullerene eno- to the calixarene cavity, and they include p-Ph-calix[4]arene, which has a toluene molecule in the cavity, the overall structure dominated by fullerene-fullerene and eso-calixarene fullerene interactions p-Br-calix[4]arene propyl ether, the structure showing very close interfullerene contacts in a columnar structure (Fig. 2d), which most likely results in opposing induced dipoles from the unidirectionally aligned calix-arenes " and /7-I-calix[4]arene benzyl ether, where the fullerenes are ordered without appreciable interfullerene interactions. There is also a calix[4]resorcinarene, R = CH2CH2Ph, 3, which has a molecular capsule derived from head-to-head hydrogen bonding of two resorcinar-enes and propan-2-01 molecules, with the fullerenes also... 

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