Extended chain conformation

Crystallites occurring in PET fibers can assume two kinds of morphological forms. The first form represents the crystallite formed by molecules of folded conformation, while the other is formed from molecules of extended-chain conformation. The first form is sometimes called a flexural morphological form, whereas the other is called a straightened morphological form. The flexural form is the typical and prevailing morphological form in PET fibers. However, it should be stressed that no... 

Viscosimetric studies of organotin copolymer solutions allow the changes in the shape of the macromolecules to be followed as a function of the electrostatic charge. From the plot of the intrinsic viscosity of copolymers in DMFA solution against the degree of dilution it is seen that increasing dilution results in a rise of viscosity, probably due to an extension of macromolecular chains accompanied by conformational transformations. Naturally, this rise in viscosity with dilution cannot proceed infinitely since a coiled chain cannot be extended more than a completely extended chain conformation, due to intramolecular repulsion. 

An anomalojs character of the dependence of the viscosity on dilution may be explained by the course of conformational changes before a stable extended chain conformation has been formed after which the linearity of the viscosity-dilution relationship is restored. 

The existence of an extended chain conformation is also suggested from a consideration of the surface coverage data. Results for the surface area occupied by each PDMS chain (9j indicate that total coverage of the particles may be assumed, that the area occupied by a given PDMS chain is similar on both... 

The sequence His-Cys-His has an extended chain conformation. In this sequence, the cysteine binds type 1 and the two histidines, two separate copper atoms of the trinuclear cluster, thus making the shortest distance from the type 1 copper to the trinuclear cluster 13 A. Within the cluster, the Cu-Cu distances are 3.4, 3.9, and 4 A. It should be noted that none of the histidines bridges the copper atoms, unlike SOD, in which a histidine bridges the copper and zinc. The pattern of histidine binding to the trinuclear cluster is rather clever two His-X-His pairs from separate domains, His-Cys-His (507-509) and His-Gly-His (106-108), bind the... 

The copolymers, water soluble and hydrophilic, usually show an extended chain conformation below their LCSTs, undergoing a phase transition to an insoluble and hydrophobic aggregate above the LCSTs. This phase transition for PIPAAm remarkably occurs with narrow temperature changes through the LCST and is reversible corresponding to temperature changes (Chung et al., 1999). 

A completely different approach to polymer crystallisation in extended-chain conformation became possible with the coming of a new class of polymers the para-para type aromatic polymers. These polymers possess inherently rigid molecular chains in an extended conformation (Preston, 1975 Magat, 1980 Northolt, 1974, 1980, 1985 Dobb, 1985). Theoretically they should give rise to high orientation in fibre form without the necessity of subjecting the as spun filaments to the conventional drawing process. 

For flexible synthetic polymers, the chain conformation is commonly controlled by the degree of polymerization (DP), with low-DP polymers having a rather extended chain conformation and high-DP polymers adopting random coil conformations in solution. Recently, Percec, Moller et al. reported extensive studies concerning the chain conformation and supramolecular structure of dendron-substituted polystyrene and polymethacrylate [23], Remarkably, at low DP... 

The thermochromic effect in solutions of poly(3-alkylthiophene)s has been attributed to an intramolecular conformational transition to an extended chain conformation, principally on the basis of an observed isosbestic point <1987PSB1071, 1992MM2141>, but evidence for supramolecular aggregates was noted <1987PSB1071>. 

Notice that if the chain is arranged in a zig-zag or extended chain conformation, as found in the crystal structures of polyethyl-... 

The proportion of a-helix in native proteins is variable and sometimes not very great. It is a mistake to over emphasize its role in interfacial structures, but where it is present its radial distribution of side chains means that its orientation in the interface will be governed by its over-all hydrophobicity. The presence of hydrophobic groups directed into the water is then possible as well as others contributing to cohesion between adjacent molecules as in the monolayers considered here. Those directed into the water may function as sites for the binding of other molecules in the aqueous phase. This is also a possibility for the p conformation but not for extended chain conformations where under pressure the hydrophobic side chains are directed away from the surface and the hydrophilic ones into the water. While this latter model has been accepted by surface chemists 37), the conformation appears unlikely both from a biological and a stereochemical standpoint. Indeed except where there is a regular alternation of hydrophobic and hydrophilic side chains, the conformation is probably not one acceptable within the usual criteria for polypeptide structures (5). 

The p form and the p form are of an extended chain conformation with orthorhombic and triclinic subcell structures, respectively. In the p form alternating fatty acid chain axes are oppositely oriented, whereas in the p form all fatty acid chain axes are oriented in one way (9, 10). 

Fig. 4. Schematic representation of chain conformations in flexible linear high polsrmers. A represents the limiting conformation found in melt, solution, or glass, B the folded chain conformation from melt or solution crystallization, C the extended chain conformation found preferentially on crystallization during polymerization. The area of the triangle represents the large variation of intermediate...

P2i2i2i Z = 4, Dx = 1.701 R = 0.034 for 2,821 neutron intensities. The D-gluconate ion has the extended-chain conformation, with an intramolecular hydrogen-bond between the st/n-diaxial hydroxyl... 

While the interlamellar forces in n-alkanes are weak and their contribution to the LAM frequencies is small, in systems with strongly interacting chain ends the effect can be very pronounced.44 For example, while in n-alkanes, the ratio v Jv is around 2.8, quite close to 3 as expected from eq 1, vjjv is only 2.1—2.3 for monodisperse oligo(oxyethylenes) and PEO fractions.45-46 In PEO fractions, this effect makes it difficult to distinguish between LAM-3 of the extended chain conformation and LAM-1 of the once folded chain, and peak assignment must be made with caution. The helical conformation of PEO accounts for its low elastic modulus (25 GPa), as obtained from LAM frequencies.47... 

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