Supramolecular assemblies from channel

Most of the supramolecular assemblies have been constructed from the solutions of each component. More recently, the authors found that CD formed inclusion complexes with PEG with high selectivity only by mixing powdered crystals of CDs and polymer samples without any solvents under ambient conditions (Scheme 2) [120]. When crystals of a-CD and PEG (Mw = 400) were mixed without solvent (a-CD ethylene glycol unit =1 2), the X-ray powder patterns changed a peak at 26 = 22° characteristic for the cage type decreased, and a peak at 26 = 20° characteristic for the channel type appeared... 

Different stages of organization have been accomplished ranging from the spatial arrangements of dyes in the zeolite channels to the specific adsorption of molecules at the channel entrances as well as coupling of the dye-zeolite crystals to external devices. In most of the cases zeolites with LTA, FAU, MFI, AF1 and LTL type structures have been used for these supramolecular assemblies. 

Sidorenko et al. succeeded in fabrication of well-ordered nanostructures in thin polymer films by supramolecular assembly of PS-Zi-P4VP and 2-(4-hydro-xybenzeneazo) benzoic acid (HABA), consisting of cylindrical nanodomains formed by P4VP-HABA associates in a matrix of PS (Sidorenko et al., 2003). As shown in Scheme 12.7, extraction of HABA with a selective solvent results in nanochannel membranes with a hexagonal lattice of hollow channels in the diameter crossing the membrane from top to bottom. 

From the single X-ray crystal analysis, H5.1 formed intra- and inter-molecular hydrogen bonds, which resulted in the formation of ID extrinsic channels with a diameter of 7.10 A, slit channels of 5.14 A by 9.14 A, and an intrinsic cavity of 6.76 A. The multiple hydrogen bonds stabilized the supra-molecular structure even after removal of the trapped solvents by heating under reduced pressure. The supramolecular assembly of the activated H5.1 took up CO2, but did not accommodate CH4 and N2, indicating that the activated H5.1 can selectively capture CO2. The activated porous crystals of H5.1 showed remarkable CO2 selectivity over CH4 (375 1) and N2 (339 l). " ... 

The rational synthesis of peptide-based nanotubes by self-assembling of polypeptides into a supramolecular structure was demonstrated. This self-organization leads to peptide nanotubes, having channels of 0.8 nm in diameter and a few hundred nanometer long (68). The connectivity of the proteins in these nanotubes is provided by weak bonds, like hydrogen bonds. These structures benefit from the relative flexibility of the protein backbone, which does not exist in nanotubes of covalently bonded inorganic compounds. 

Figure 6 shows the proposed subunit assembly structure of the nicotinic acetylcholine receptor channel." The inner wall of the lower half part is surrounded by hydroxyl side chains from Ser and Thr, and by carboxylates or amides from Asp, Glu, and Gin at the mouth. Furthermore, a Lys residue seems to offer ion pairing with the carboxylate at the mouth. Considering the possibly similar stabilizing effect of ether and hydroxyl groups to cations, the proposed artificial supramolecular channel could be regarded as a good model of the acetylcholine receptor channel, which selects cations over anions, but does not discriminate between alkali metals. 

These observations suggest that the trans-azo ammonium can stabilize the supramolecular channel structure, which is formed by assembling relatively hydrophilic oligoether units based on the molecular recognition in the membrane phase. Compared to the extended molecular form of the trans-azo compound, which is appropriate for covering the hydrophilic component from the outside, the cis compound with a bulky structure cannot stabilize the structure and hence prohibits the assembly formation because it requites a large void structure in the membrane. Therefore, only leaky currents are observable (Figure 26). 

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