Aliphatic chain conformation

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

Fig. 32a and b. The conformation of the ligand 5c in its thiourea complex and the disorder of the chain ends. Side view of the 5e-thiourea complex showing hydrogen bond contacts (parts of the aliphatic chain have been omitted for clarity)421... 

NMR studies showed that in polar solvents (DMSO, DMF) catenane 45 adopts a supramolecular conformation (II) that allows the amide protons to interact via multiple hydrogen bonds with solvent molecules and at the same time buries the lipophilic chains in the center of the molecule (Figure 18). In contrast, NMR spectra in nonpolar solvents indicate that the aliphatic chains are situated on the outer sphere of the catenane, whereas the isophthaloyl units are arranged in a way that ensures optimal intramolecular hydrogen-bonding (I). 

These ligands, as exemplified by (12 Figure 2), were first reported by Zinke and Ziegler.31 Synthetic design has since then been modified and improved.64,65 133"135 The attachment of an aliphatic chain bridging two opposite para positions in the calix[4]arenes (i.e. those composed of four phenol groups) has been used to fix the cone conformation in these somewhat flexible molecules.136... 

For mesostructured aluminophosphates with lamellar structure WISE spectra indicate that template surfactant species have very restricted mobility as the ll wide lines are very broad.3 This is also consistent with the trans-conformation of the aliphatic chains. Other representatives of mesoporous A1PO exhibited template species with much narrower H resonances.2... 

Other WAXD starch patterns, known as V-types, are associated with the amylose fraction. In V-amylose, the chain conformation is a left-handed single helix with six residues per turn (V6) for complexes with aliphatic alcohols and monoacyl lipids with ligands bulkier than a hydrocarbon chain, helices of seven or eight glucose residues per turn are feasible.31 Aliphatic chains within amylose helices are rather locked... 

The conformations, can be detected by the changes in the intensity of sensitive bands in IR spectra by using model compounds (low-molecular-weight and linear polymers) and compare the results with networks. The differences in the behaviour of conformationally sensitive bands reflect the differences in the behaviour of aliphatic chains in different compounds. To detect the bands sensitive to the internal rotation, we have measured the spectra (50-4000 cm 1) of model compounds A and B. 

Which have in their structure aliphatic chains of the desired type. Both compounds are crystalline and their spectra give us the picture of the most stable conformations in the aliphatic chains. Spectral measurements of A and B in melt or CC14 solutions yield new bands which, undoubtedly, belong to the new conformers of the aliphatic fragments. 

The crystal-melt transition of compound A leads to a strong conformational change in aliphatic chains. The relative number of non crystalline conformers grows by 40-50%. 

R = R = OC12H25, R = H) molecular conformations likely predominate to satisfy the geometrical requirements. The supramolecular disks or columns thus result from the molecular association of two or three dendrimers (depending on the aliphatic chain substitution) in the appropriate conformation, as depicted in Fig. 52 and these columns are packed in a hexagonal lattice. Moreover, considering the diblock, alternated chemical nature of these octopus dendrimers, an onion morphology for the columns is most likely probable (Fig. 53) [264]. 

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