Chain shape

The synthesis of cyclic compounds is a battle for the yield. The general synthetic strategies of CPOs are illustrated in Fig. 2. The first one involves one-pot synthesis using a porphyrin unit (method A), and the second one is the ringclosing reaction of the chain-shaped PO (method B) [11]. 

The SANS experiment is applicable to polymeric networks containing some deuterium labeled chains. The chain geometry can be probed not only in the unperturbed network, but changes in chain shape and size can be measured as a function of strain or swelling. This enhances the applicability of SANS experiments for elastomeric systems. 

In the same year in which Stoll et al. (1934) defined the cyclisation constant C, Kuhn (1934) laid the foundations of the theoretical approaches to the conformational statistics of hydrocarbon chains and considered the cyclisation probability of the chain as a fundamental, chain length dependent phenomenon related to chain shape. He proposed to view the specific rate kintra of an intramolecular reaction between a pair of reactive groups attached to the ends of a chain molecule as the product of the effective concentration Ceff of... 

A chain of vertex-sharing tetrahedra results when every tetrahedron has two terminal and two bridging atoms the composition is MX274X2A2 or MX3. The chain can be closed to form a ring as in [SOj], [PO3 Ij, ISiO I3 or [SiOf jg. Endless chains have different shapes depending on the mutual conformation of the tetrahedra (Fig. 16.19). They occur especially among silicates, where the chain shape is also determined by the interactions... 

M Drag, J Grembecka, M Pawelczak, P Kafarski (2005) alpha-aminoalkylphosphonates as a tool in experimental optimisation of PI side chain shape of potential inhibitors in S1 pocket of leucine - and neutral aminopeptidases, Eur J Med Chem 40(8) 764—771... 

Longer cellulose oligomers have been modeled with MD as well. Two studies have attempted to discuss the molecular shapes in aqueous solution as well as the solvent llo-dextrin and cellodextrin llodextrin interactions [191,192]. The first of these studies showed that chains were heavily solvated and not fully extended or in contact with other cellulose fragments. The simulation was proposed as a model for freshly prepared cellophane. The latter study was more in agreement regarding chain shapes with the results in Figure 5.16. In addition, that work showed, unlike the simulated cellotetraose molecules in the same study. 

Cellulose I(S and cellulose II have monoclinic, two-chain unit cells. Cellulose IIIj has a monoclinic one-chain cell [227], and the one-chain unit cell of la is triclinic with no 2i symmetry. Still, all of the chain shapes are very similar to each other. It had been speculated that cellulose chain linkage geometries would alternate between the quite different linkages found in crystalline p-cellobiose and in methyl 3-cellobioside [196]. That idea is now obsolete. Such a departure from symmetry would be far greater than indicated by the above high-resolution studies. When molecules from the high-resolution structures for all of the polymorphs are superimposed, differences in their backbone structures are barely visible. 

This is a novel type of polymer effect due to a polymer chain shape where chemical bond stability is impaired by superimposed random shearing forces at some definite site of the molecule. A similar effect has been reported by Oster upon sonic treatment of tabacco mosaic virus where the polymer aggregates are dissociated75). 

A look aside to other groups of elements and organisms the realm of chemical ecology and food chain shaping. 

Equation (32) uniquely relates the asymmetry of the shape of a worm-like chain Px to the relative chain length x and the asymmetry of the chain shape p in the conformation of a Gaussian coil. 

Actually, accordit to Eq. (32), at the limit of chain length (x -< 0) the asymmetry of chain shape increases infinitely (p— ). In theoretical Curves 1 and II in Fig. 23, p = > for all values of X. In fact, for any real polymer diain of length L and diameter d, the shape a mmetry cannot be greater than the value of L/d. This has been consider in Refs. where the calculation of the shape asymmetry of a chain molecule at low x according to Eq. (63) is proposed ... 

In the coordinate system fixed to a molecule in the origin the pattern of fluid flow looks like Fig. 2. Since the force on the molecule is proportional to the relative fluid velocity one can expect that the chain shape will be ellipsoidal in the coordinate system. 

Streptococcus (plural, streptococci), from a Greek word meaning chain-shaped. 

A chain-shape polyamine and ethylene glycol system favors the formation of layered aluminophosphates with an Al/P ratio of 3/4. For instance, ethylenediamine, diethylenetriamine, and triethylenetetramine combining with ethylene glycol solvent lead to the formation of layered aluminophosphates with an AFP ratio of 3/4 (see Table 3.9). Therefore, it is expected that using tetraethylenepentamine as template and ethylene glycol as solvent will result in the crystallization of a layered aluminophosphate with an AFP ratio of 3/4. Guided by this prediction, we did... 

Similarly, as shown in Figure 3.21 (b), (c), (d), and (e), there exists an excellent linear correlation between the charge/volume of the charged species encapsulated in the framework and the charge density of the anionic framework for the anionic aluminophosphates with Al/P ratio of 1/2 directed by arylamines, the anionic aluminophosphates with Al/P ratio of 2/3 directed by cyclic amines, the layered anionic aluminophosphates with Al/P ratio of 3/4 and 4,6,8-net topological sheet structure directed by chain-shape alkylamines, and the layered anionic aluminophosphates with Al/P ratio of 3/4 and 4,6,12-net topological sheet structure directed by chain-shape alkylamines as well. 

On the scientific side, considerable progress has been made on two fronts learning how the catalysts operate to make stereoregular polymers and learning how the properties of the polymers are controlled by chain shape, chain length, and, particularly, crystal habit. 

P2i Z = 2 Dx = 1.384 R = 0.071 for 3,427 intensities. Absolute configuration confirms that nogalose is a derivative of 6-deoxy-L-mannose. The molecule has an open-chain shape, with a sickle carbon-chain conformation, thereby permitting formation of an intramolecular hydrogen-bond between O-l-H and 0-5-H at either end of the chain. 

Chapter 3 discusses polymer chain shapes and packing in both crystalline and amorphous forms, while Chapter 6 explains the effect of polymer processing on the microstructure on a millimetre length scale. You should be able to synthesise these views, and use models on appropriate scales to explain the mechanical and physical properties of products. 

To evaluate the chain entropy, the number of distinguishable chain shapes W must be counted, then Eq. (3.9) used. The general shape of the relationship between W and r is first calculated for a short one-dimensional chain (Fig. 3.11), for which enumeration is easy. In this chain each link, of unit length, is either in the positive or negative x direction. If there are five links, there is... 

Figure 3.16 Projection of a 76 monomer polypropylene chain shape in the glassy state, with the parent...

The symmetry of the chain shape influences both and the abihty to form crystallites. Polyethylene and poly(tetrafluoroethylene) are both sufficiently symmetrical to be considered smooth stiff cylindrical rods. In the crystal, these rods tend to roll over each other and change position when thermally agitated. This motion within the crystal lattice, called premelting, increases the entropy of the crystal and effectively stabilizes it. Consequently, more thermal energy is required before the crystal becomes unstable, and is increased. Flat or irregularly shaped polymers, with bends and bumps in the chain, cannot move in this way without disrupting the crystal lattice, and so have lower values. This is only one aspect. 

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