Backbone configuration

There is a basic difference between rupture above the glass transition temperature (where the polymer backbones have an opportunity to change their configurations before the material fails) and well below Tg (where the backbone configurations are essentially immobilised within the period of observation brittle materials). 

Table I shows the molecular weights and the relative photographic speed results of the amorphous p-methoxycinnamate polymer films. The difference in the photographic speed between polymers X and XIA, XIB could be attributed to the difference in the backbone configuration and the effect it has on the orientation of the cinnamate chromophore as well as the M.W. difference.

The ball-and-stick model and skeletal model best show the bonding arrangements and the backbone configurations of biomolecules the inclusion of the numerous hydrogen atoms would obscure the very features revealed by these models. 

C.-H. Luan, J. laggard, R.D. Harris, and D.W. Urry, On the Source of Entropic Elastomeric Force in Polypeptides and Proteins Backbone Configurational vs. Side Chain Solvational Entropy. Int. J. Quant. Chem. Quant. Biol. Symp., 16,235-244,1989. 

Here, we discuss the scaling behavior of the distribution functions of the end-to-end distances, analogously to Section 4. For SAWs on backbone substrates, the results are presented both in - and r-space to allow for a direct comparison. The quantities are hence (Pb(, A )) and (Pb( ", A)), averaged over many backbone configurations, where Pb i, A) di is the probability that after A steps the topological end-to-end distance of a SAW on a single backbone is between I and and PB(r, A) dr is the respective quan-... 

Ramachandran plot A plot that constitutes a map of all possible backbone configurations for an amino acid in a polypeptide. The axes of the plot consist of the rotation angles of the two backbone bonds that are free to rotate (j) and ij/, respectively) each point ( >, ij/ on the plot thus represents a conceivable amino acid backbone configuration. 

Fig. 2. Schematic illustration of side-chain polymer crystals where (1) represents the polymer backbone, (2) represents the alkylene spacer and (3) represents the different side-group moieties. In a real polymer the backbone would not generally be in the rigid configuration shown. For example, with an SiO backbone the alkylene chains are attached to each Si atom (for a fully substituted system) and rotational isomerism due to free rotation about the linking oxygen would ensure a random backbone configuration. Typical spacer groups consist of between 4 and 12 methylene units and the side-group moieties contain several bulky phenylene units. Therefore, in three-dimensional space the molecules would look more like a bottle brush with random bristles attached to a flexible backbone stem.

Figure 44 Proposed formation mechanism of polythiophene/protein wire bundles (a) structural image of polythiophene with an all trans backbone configuration (left). Structure of BI monomer (PDB file lAPH) with a tyrosine side chain shown for comparison (right), (b) Proposed interaction between a partially unfolded BI monomer (gray) and two polythiophenes (green), (c) Transmission electron microscopy of the wires after incubation for 6h at 65 °C and proposed structure, (d) Left Two fiuorescence micrographs of the corresponding poly thiophenes shown on the right (scale bar 20 pm). (Reproduced with permission from Ref. 78. Wiley-VCH, 2005.)...

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