Chain unfolding

The hydrogenation of unsaturated polymers like polyisoprene is based on the mobility of a soluble catalyst in the reaction medium. In the hydrogenation of such unsaturated polymers the soluble catalyst brings its active site to the C=C bonds in the polymer chain. In contrast, a heterogeneous catalyst requires that the polymer chain unfold to gain access to a catalytically active site on the surface of a metal particle. 

Flg. lOa-c. Chain unfolding and cis to Irons isomoization of polyamide (d) in iV,iV-dimethylacetamide solution (0.31 g/ dl) [2. The oscUlogianis illustrate changes of light scattering intensity (a,c) at 514 nm and optical absorption at 514 nm (b) during and after 20 ns flash of 530 nm light. Traces a and b polyamide (6) trace c model compound... 

The tightly folded polypeptide chain unfolds to form an extended rod, with the polypeptide at the core being coated with negatively charged SDS molecules. 

Magonov, S.N. et al., Chain unfolding in single crystals of ultralong alkane C390H782 and polyethylene An atomic force microscopy study, Macromolecules 36 (15), 5637-5649, 2003. 

By applying, a second time, this chain unfolding technique to a chain E1, we can construct a chain Ei for which xJJ x 1 < xj, for any j. By proceeding as above, we can show that... 

At low concentrations of the denatured collagen peptides (less than 0.1 mg/ml) renaturation is a first-order process with respect to protein concentration (39). This suggests that refolding is entirely an intramolecular process resulting in formation of single-stranded structures folded back upon themselves. If the renaturation temperature is substantially below the Tu for chain unfolding, the renaturation will occur rapidly with many nucleation sites, and maximization of noncovalent... 

To correlate the macroscopic properties and the structural changes occurring dtuing deformation the orientation functions evaluated from Eqs. (20 a—c) have been plotted in dependence of strain in Fig. 14. Onc and Asada have discussed in detail the expected changes of infrared dichroism and orientation functions due to the different molecular processes of lamellar orientation and chain unfolding. 

Form thermally irreversible gels on heating. The protein chains unfold and reassociate to form aggregates which in turn generate a three-dimensional network. 

With enzyme-catalysed reactions, although the rate at which the reaction comes to equilibrium increases with temperature, there is a second effect of temperature — denaturation of the enzyme protein, leading to irreversible loss of activity (section 4.4.2. As the temperature increases, so the movement of parts of the protein molecules relative to each other increases, leading eventually to dismption of the hydrogen bonds that maintain the folded structure of the protein. When this happens, the protein chain unfolds and the active site is lost. As the temperature increases furthei so the denatured protein becomes insoluble, and precipitates out of solution. 

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