Intrachain connectivity

Moreover, the ratios Tj/Xj obtained at different temperatures are similar to the values obtained for labell polybutadiene in dilute solution in toluene (= 30). Thus, the surrounding chains seem to affect local dynamics only at the level of the friction coefficient. Intrachain connectivity remains the essential non isotropic constraint on local dynamics in bulk polymers and models for the isolated chain are applicable. This is consistent with the idea that topological interchain effects only act on a... 

Disulfides. As shown in Figure 4, the and h-chains of insulin are connected by two disulfide bridges and there is an intrachain cycHc disulfide link on the -chain (see Insulin and other antidiabetic drugs). Vasopressin [9034-50-8] and oxytocin [50-56-6] also contain disulfide links (48). Oxidation of thiols to disulfides and reduction of the latter back to thiols are quite common and important in biological systems, eg, cysteine to cystine or reduced Hpoic acid to oxidized Hpoic acid. Many enzymes depend on free SH groups for activation—deactivation reactions. The oxidation—reduction of glutathione (Glu-Cys-Gly) depends on the sulfhydryl group from cysteine. 

Fig. 16.—Antiparallel packing arrangement of 3-fold sodium pectate (13) helices, (a) Stereo view of two unit cells roughly normal to the fcc-plane. The helix at the center (open bonds) is antiparallel to the two in the front (tilled bonds). Intrachain hydrogen bonds stabilize each helix. Sodium ions (crossed circles) and water molecules (open circles) connect adjacent helices, (b) A view of the unitcell contents down the t -axis highlights the ions and water molecules located between the helices.

When the disulfide connectivity of a short peptide, consisting of about 20 amino acid residues or less with two intrachain disulfide bonds, has to be determined, the task is generally carried by synthesizing the three possible disulfide isomers (globule/ribbon/beads) and subsequent chromatographic comparison with the natural peptides. The isomers are synthesized by the two-step selective disulfide forming methods based on orthogonal cysteine... 

The a-D-glucopyranose residues are present in the Cl (d) conformation (Ia2e3e4e5e), and an intrachain hydrogen bond connects 0-2 and 0-3 of adjacent D-glucopyranose residues. A direct, interchain hydrogen-bond connects 0-2 and 0-6, and 0-2 and 0-5 have a water molecule lying between them to which both are hydrogen-bonded. However, this water molecule is randomly replaced by a potassium ion. 

Unlike the thermomechanical inversion of heat, the inversion of internal energy is possible only for chains with d In 0/dT 0. It is also evident from Eq. (48) that for d In 1 and vice versa. For values a = (6 — 10) x 10"4 K 1 and d In polymeric networks, XtJ = 1.3 — 2.2 for extension and X,j > 0.5 for compression. It must be emphasized that this thermomechanical inversion of internal energy is not connected with the stress-induced crystallization and arises from the different signs of inter- and intrachain contributions to the internal energy. The extreme of the internal energy occurs at the deformation... 

In this connection, it is very interesting that the volume and intrachain changes obtained by various experimental methods 24,29,85) [Eq. (101)] agree well with Eq. (56) following from the Tobolsky-Shen semiempirical equation of state or the related phenomenological Eq. (76). The values of y determined from the data are rather small (0.1-0.3). As has been mentioned above, according to the semiempirical approach by Tobolsky and Shen one can formally suggest that the front-factor in Eq. (28) is pressure dependent. If it is really so, then the parameter y for rubbers can be considered as an experimental coefficient similar to the coefficient of thermal expansion and compressibility 29). 

It is not easy to mimic the shuffling of domains in vitro by manipulation of genes. For example, each catalytic polypeptide chain of the multimeric E. coli aspartate transcarbamoylase (ATCase) is composed of two globular domains connected by two interdomain helixes. The E. coli enzyme ornithine transcarbamoylase (OTCase) is 32% identical in sequence and thus of presumably similar structure (see section D8). None of the chimeras in which a domain from one enzyme was attached to the corresponding partner in the other is active. The specific intrachain and interchain side-chain interactions also have to evolve for the Correcting packing.32... 

The connection of the effective intrachain g-ology couplings with the intramolecular or one-site repulsive interaction and the screened long-range Coulomb matrix element have been discussed in detail by Barisic et al. [110-112]. For gi, g2 and g, one has the following result. 

Figure 20. The structure of EHEYUL [Nd(CgH404)3(CgH504)(H20)]. Three distinct coordination modes of 1,3-BDC groups are shown. Type 1 connects the chains of NdOio polyhedra Type 2 decorates the chains as one group remains unbound Type 3 is an intrachain coordination.

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