Supramolecular structures characterization

Two approaches to the attainment of the oriented states of polymer solutions and melts can be distinguished. The first one consists in the orientational crystallization of flexible-chain polymers based on the fixation by subsequent crystallization of the chains obtained as a result of melt extension. This procedure ensures the formation of a highly oriented supramolecular structure in the crystallized material. The second approach is based on the use of solutions of rigid-chain polymers in which the transition to the liquid crystalline state occurs, due to a high anisometry of the macromolecules. This state is characterized by high one-dimensional chain orientation and, as a result, by the anisotropy of the main physical properties of the material. Only slight extensions are required to obtain highly oriented films and fibers from such solutions. 

Especially notable is also the synthesis and structural characterization of an unusual antimony(III) guanidinate. 1,2,3-Tiiisopropylguanidine, Pr N = C(NHPr )2,was found to react with 1 molar equivalent of Sb(NMe2)3 in toluene under formation of a yellow solution, from which the novel compound Sb[Pr NC(NPr )2][Pr NHC(NPr )2] could be isolated in 10% yield as highly air-sensitive crystals. In the solid state, the complex adopts a heavily distorted trigonal-bipyramidal molecular structure in which the Sb is chelated by a [CfNPr ls] dianion and a [Pr NHC(NPr )2] monoanion (Figure 16). Supramolecular... 

Socaciu, C. et al.. Carotenoid-rich fractions in sea buckthorn berry oleosomes separation, characterization and stability in colloid supramolecular structures, Proc. 4th Int. Congr. Pigments in Food, October 9-12, 2006, Shaker Verlag GmbH, Stuttgart, Germany. 

Square-planar zinc compounds predominate with these ligand types as would be predicted. This is in contrast to the prevalence of tetrahedral or distorted tetrahedral geometries for four-coordinate species that have been discussed thus far. Zinc porphyrin complexes are frequently used as building blocks in the formation of supramolecular structures. Zinc porphyrins can also act as electron donors and antenna in the formation of photoexcited states. Although the coordination of zinc to the porphyrin shows little variation, the properties of the zinc-coordinated compounds are extremely important and form the most extensively structurally characterized multidentate ligand class in the CSD. The examples presented here reflect only a fraction of these compounds but have been selected as recent and representative examples. Expanded ring porphyrins have also... 

The nanometer- to micrometer-scale dimensions of supramolecular assemblies present many challenges to rigorous compositional and structural characterization. Development of adequate structure-property relationships for these complex hierarchical systems will require improved measurement methods and techniques. The following areas constitute critical thrusts in instrument development. 

Arsenic dithiocarbamates, As(S2CNR2)3 (R = Bu, CH2Ph),399 and toluene-3,4-dithiolato arsenic and bismuth dithiocarbamato derivatives, (MeC6H3S2) M(S2CNR2) (M = As, Bi R = Me, Et, CH2CH2)400 have been structurally characterized and the supramolecular self-assembly in Sb(III) dithiocarbamates has been carefully examined.401... 

At shorter distances, particularly those characteristic of H-bonded and other charge-transfer complexes, the concepts of partial covalency, resonance, and chemical forces must be extended to intramolecular species. In such cases the distinction between, e.g., the covalent bond and the H-bond may become completely arbitrary. The concept of supramolecular clusters as fundamental chemical units presents challenges both to theory and to standard methods of structural characterization. Fortunately, the quantal theory of donor-acceptor interactions follows parallel lines for intramolecular and intermolecular cases, allowing seamless description of molecular and supramolecular bonding in a unified conceptual framework. In this sense, supramolecular aggregation under ambient thermal conditions should be considered a true chemical phenomenon. 

When rotaxanes and catenanes contain redox-active units, electrochemical techniques are a very powerful means of characterization. They provide a fingerprint of these systems giving fundamental information on (i) the spatial organization of the redox sites within the molecular and the supramolecular structure, (ii) the entity of the interactions between such sites, and (iii) the kinetic and thermodynamic stabilities of the reduced/oxidized and charge-separated species. 

This hydrogen-bond-driven large-scale structural organization has parallels in abiotic systems as well. For example, 1 1 mixtures of ra -l,2-diaminocyclohexane and C2 symmetric 1,2-diols self-assemble into well-defined supramolecular structures which have been characterized by X-ray diffraction analysis. The structures, some of which are stable to sublimation, are helical, the handedness of the helices being determined by the handedness of the 1,2-diamine [222]. 

Dozol, H., Berthon, C. 2007. Characterization of the supramolecular structure of malon-amides by application of pulsed field gradients in NMR spectroscopy. The Royal Society of Chemistry. Physical Chemistry Chemical Physics 9 5162-5170. 

Dimeric complex was prepared by interaction of 642 (Z=1,4-C6H4) with copper acetate in methanol and structurally characterized [99], meanwhile the reaction of 643 with the same salt in ethanol yields, according to x-ray diffraction data, tetra-nuclear supramolecular structures [100]. 

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