Resorcinarene molecules structures

In the case of another aUylic acid included within a solid host structure, only photoisomerization is observed. Specifically, 3-chloroacryfic acid guest molecules in the C-ethylcalix[4]resorcinarene host structure (host N in Figure 24) undergo photoisomerization in a single-crystal to... 

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)... 

The three structures shown at the right of the second line represent important families of receptor molecules that have been extensively studied in their own right. The aromatic spherand grew out of crown ether chemistry while calixarene chemistry developed on a separate evolutionary pathway. Still, their similarity is apparent. The structures of calixarenes and resorcarenes (also resorcinarenes) are included here because they have often been fused to macrocycles to form complex receptor systems. A few examples of fused receptor systems are discussed below. 

C60 and Cyo fullerenes are able to form complexes with resorcinarene [80]. In this case, the host molecule can guest only one fullerene molecule in its inclusion complex structure. The n-n, CH-n and n-n interactions were observed by CPMAS and FTIR analysis data. Chattopadyay and coworkers [81] investigated the ability of C o and Cyo fullerenes to form ICs with a series of crown ethers. They showed that fullerenes can form 1 1 molecular complexes with crown ethers, but two of them, dibenzeno-24-crown-8 and dibenzeno-30-crown-10, are able to form complexes only with C6o fullerene, not with Cjq. 

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. 

Figure 12.5 The structure of the nanotube showing resorcinarenes, tV-7, in stick representation and diquaternary cations B-18, shown with Van der Waals radii. Anions, water molecules, non-hydrogen bonding hydrogens of resorcinarenes, and disorder of the cations are omitted for clarity, a) The asymmetric unit, b) A view of the tube along the crystallographic a axis. Reprinted with permission from [46]. Copyright 2004 Wiley-VCH Verlag CmbH Co. KCaA...

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... 

Figure 24 Molecular structures of the cis-3-chloroacrylic acid and fraws-3-chloroacrylic acid guest molecules and the host molecule N (C-ethylcalix[4]resorcinarene).

FIGURE 7.4 Dimeric structure of resorcinarene with eight alcohol molecules. 

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