C, backbone of

The C—C backbone of SPS takes a planar zig-zag conformation in the crystal whereas IPS takes a 3/1 helical conformation in crystal. This difference in chain conformation in the crystal affects the crystallization rate of these polystyrenes. Table 18.1 [32] compares the crystallization parameters between SPS and IPS. The work of chain folding, Q, of SPS is smaller than that of IPS, which suggests that the chain folding of SPS can take place more easily than that of IPS. Also, SPS has a smaller surface free energy. These differences are related to the crystallization rate difference between SPS and IPS, which have different stereoregularities. 

The starting point for an analysis of the structure of linear polymers is the C-C backbone of an extended hydrocarbon chain, the simplest member of which is polyethylene. The... 

Fig. 12, The C backbones of CCP, LIP, ARP, and MPO, showing the location of the methionine, tryptophan, and tyrosine residues relative to the heme.

Fig. 15. The C backbone of horse heart cyt c, showing the location of the heme and the van der Waals surfaces of the 13 lysine residues surrounding the heme edge. The consensus map of the key lysines involved in CCP-cyt c interaction includes Lys8, 13, 27, 72, 79, 86, and 87. The van der Waals surfaces of these lysines are shown in bold. This diagram was generated using the X-ray coordinates of horse heart cyt c (162).

Fig. 14.17. Stereo view of the C backbone of the steroid-binding domain of cholesterol oxidase showing the proposed entrance to the active site. The FAD molecule is shown in thick lines. The mobile loops believed to be situated near the proposed entrance are also shown in thick lines [57]...

FIGURE 11.4. Computer graphics display of the C backbone of the GOx monomer, showing the location of the 15 lysine residues at the surface of glucose oxidase. (From Ref. 101). 

Based on the observation that the recombinant yeast expressing a cytosolic polymerase accumulate PHA monomers with C-backbones of different lengths than the fed fatty acids, we propose that P-oxidation can occur, at least partially, in the cytosol of S. cerevisiae (Figure 4). One possible explanation for this... 

X)GHz. hi the presence of microwave radiation, selective excitation of the polar bonds takes place. This results in their rupture/cleavage, thus leading to formation of free radical sites. The C—C backbone of the preformed polymer being relatively nonpolar remains unaffected by the miaowave radiation. Recently, the microwave-irradiated method of graft copolymer synthesis has been classified into two types based on the generation of free radical sites on polymeric backbone. These are as follows ... 

Methods have been developed to compare the folding of three-dimensional structure of proteins (Rossmann and Argos, 1975, 1976, 1977 Me Lachlan, 1972a,b, 1979a,b Remington and Matthews, 1978, 1980). Superposition of two chains and minimization of distances between corresponding C atoms are used to detect similarities between C backbones of proteins. 

PDMS is highly permeable to common gases such as oxygen and nitrogen [65]. This is due to the flexibility of the Si-O linkage, which results in high diffusion coefficients compared with the C-C backbone of many organic polymers. To prepare the PASs, calculated amounts of IPA and DAPE were used to form aramid dichloride with a desired Mn. An equal molar amount of PDMS was added to the aramid dichloride in situ. Copolymer combina-... 

Schematic diagram of deoxyribonucleic acid (DNA) showing the pairing of nitrogen bases (A-T C-G) between parts of two strands of DNA, the backbone of each strand being composed of alternately linked sugar and phosphate units.

Polyol Esters. Polyol esters are formed by the reaction of an alcohol having two or more hydroxyl groups, eg, a polyhydric alcohol and a monobasic acid. In contrast to the diesters, the polyol in the polyol esters forms the backbone of the stmcture and the acid radicals are attached to it. The physical properties maybe varied by using different polyols or acids. Trimethylolpropane [77-99-6] C H O, and pentaerythritol [115-77-5] are... 

All phosphoms oxides are obtained by direct oxidation of phosphoms, but only phosphoms(V) oxide is produced commercially. This is in part because of the stabiUty of phosphoms pentoxide and the tendency for the intermediate oxidation states to undergo disproportionation to mixtures. Besides the oxides mentioned above, other lower oxides of phosphoms can be formed but which are poorly understood. These are commonly termed lower oxides of phosphoms (LOOPs) and are mixtures of usually water-insoluble, yeUow-to-orange, and poorly characteri2ed polymers (58). LOOPs are often formed as a disproportionation by-product in a number of reactions, eg, in combustion of phosphoms with an inadequate air supply, in hydrolysis of a phosphoms trihahde with less than a stoichiometric amount of water, and in various reactions of phosphoms haUdes or phosphonic acid. LOOPs appear to have a backbone of phosphoms atoms having —OH, =0, and —H pendent groups and is often represented by an approximate formula, (P OH). LOOPs may either hydroly2e slowly, be pyrophoric, or pyroly2e rapidly and yield diphosphine-contaminated phosphine. LOOP can also decompose explosively in the presence of moisture and air near 150° C. 

C rbocyclic Azo Dyes. These dyes are the backbone of most commercial dye ranges. Based totally on benzene and naphthalene derivatives, they provide yellow, red, blue, and green colors for all the major substrates such as polyester, cellulose, nylon, polyacrylonitrile, and leather. Typical stmctures (26—30) are shown in Figure 4. 

With decreasing amounts of metal oxide, the degree of polymerisation increases. Chains of linked tetrahedra form, like the long chain polymers with a -C-C- backbone, except that here the backbone is an -Si-O-Si-O-Si- chain (Fig. 16.4c). Two oxygens of each tetrahedron are shared (there are two bridging oxygens). The others form ionic bonds between chains, joined by the MO. These are weaker than the -Si-O-Si- bonds which form the backbone, so these silicates are fibrous asbestos, for instance, has this structure. 

The binding model, suggested by Brian Matthews, is shown schematically in (a) with connected circles for the Ca positions, (b) A schematic diagram of the Cro dimer with different colors for the two subunits, (c) A schematic space-filling model of the dimer of Cro bound to a bent B-DNA molecule. The sugar-phosphate backbone of DNA is orange, and the bases ate yellow. Protein atoms are colored red, blue, green, and white, [(a) Adapted from D. Ohlendorf et al., /. Mol. Evol. 19 109-114, 1983. (c) Courtesy of Brian Matthews.]... 

Polypropylene differs from polyethylene in its chemical reactivity because of the presence of tertiary carbon atoms occurring alternately on the chain backbone. Of particular significance is the susceptibility of the polymer to oxidation at elevated temperatures. Some estimate of the difference between the two polymers can be obtained from Figure 1J.7, which compares- the rates of oxygen uptake of eaeh polymer at 93°C. Substantial improvements can be made by the inclusion of antioxidants and such additives are used in all commercial compounds. Whereas polyethylene cross-links on oxidation, polypropylene degrades to form lower molecular weight products. Similar effects are noted... 

Figure 8.12. A conjugated chain in poly(acetylene). (a) changes to (b) when a charge passes along the backbone of the molecule, (c) and (d) show chains of poly(acetylene) and poly(para phenylene) respectively, each containing solitons (after Windle 1996).

A stereochemical consequence of the way A T and G C base pairs form is that the sugars of the respective nucleotides have opposite orientations, and thus the sugar-phosphate backbones of the two chains run in opposite or... 

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