Kinetic conformational properties

Kinetics of Intramolecular Cross-Linking and Conformational Properties of Cross-Linked Chains... 

The method of mathematical simulation has many advantages, and is very close to the physical experiment. However the further development of this approach /a consideration of volume effects, reversible reactions and so onj can be rather difficult because it will reau.ire too much computer time, therefore it is expedient to search some simple analytical or semianalytical approximate approaches to the calculation of cross-linking kinetics and conformational properties of cross-linked macromolecules. The results obtained bv the Fonte Carlo calculation can serve as criteria of the accuracy of such approximation. 

Thus the approach described can be apolied to the description of the kinetics of intramolecular cross-linking and the conformational properties of cross-linked products. 

The reaction of thioacetals with two equivalents of peroxy acids generally affords epimeric gem-disulfoxides, the ratio of epimers being subject to kinetic and/or equilibrium control (70). However, Poje, Sikirica, Vickovic, and Bruvo (71) have reported the first example of a stereospecific oxidation in the gem-disulfide series. They found that 2,2-bis(methylthio)-l,3-diphe-nylpropane is smoothly oxidized to the corresponding meso-disulfoxide with m-chloroperbenzoic acid. The study of conformational properties in solution by nmr indicated that the meso-disulfoxide exists in conformation 119 which... 

Table 8). This permits the interpretation of experimental data by using the electro-optical properties of flexible-chain polymers in terms of a worm-like chain model However, EB in solutions of polyelectrolytes is of a complex nature. The high value of the observed effect is caused by the polarization of the ionic atmosphere surrounding the ionized macromolecule rather than by the dipolar and dielectric structure of the polymer chain. This polarization induced by the electric field depends on the ionic state of the solution and the ionogenic properties of the polymer chain whereas its dependence on the chain structure and conformation is slight. Hence, the information on the optical, dipolar and conformational properties of macromoiecules obtained by using EB data in solutions of flexible-chain polyelectrolytes is usually only qualitative. Studies of the kinetics of the Kerr effect in polyelectrolytes (arried out by pulsed technique) are more useful since in these... 

The orientational mechanism of EB in solutions of r id-chain polymers and the possibility of determining rotatory diffusion constants of their molecules from dispersion curves may be utilized for the characterization of equilibrium conformational properties of their drains. The theory of rotational friction of kinetically rigid molecules developed by Hearst makii% use of the statistics of worm-like chains can be employed for this purposes. The results of this theory for the two limiting cases of molecular conformation refering to the slightly bent rod and the worm-like coil are expressed by Eqs. (27) and (28) (Sect. 2.3). 

Just as the equilibrium conformational properties of macromolecules, the theory of which has been developed in well-known classical works by Kuhn, Flory, Volken-stein and others the kinetic properties of polymer chains can be determined by two main mechanisms of intramolecular mobility. First, it is the discrete rotational isomeric (rotameric) mechanism of mobility caused by the jump of small-chain segments (kinetic units) from certain energically stable allowed conformers into others is4-i6S) gg ond it is the continuous mechanism of motion deter-... 

Table I. Comparison of Kinetic, Binding, and Conformational Properties Between WT and Y50F...

The brief review of the basic crystallite structure has centered on the nature of the lamellar habit. There are several points that should be emphasized. The molecular basis for the formation of lamellae can be developed in a natural way, based on the conformational properties of long chains. It is not necessary to invoke any inherent propensity of chains to fold or to arbitrarily draw upon monomeric nucleation theory. The structure of the equilibrium interphase has been quantitatively described. Although the number of chains that return to the crystallite from which they emanate is relatively large, the number that return in adjacent positions is small. These equilibrium considerations will be tempered in general by kinetic factors and by the melt structure at high molecular weights. The amount of adjacent reentry will be further reduced while the residual melt structure will enhance the value of the interfacial free energy. 

The possibility of conformational changes in chains between chemical junctions for weakly crosslinked CP in ionization is confirmed also by the investigation of the kinetic mobility of elements of the reticular structure by polarized luminescence [32, 33]. Polarized luminescence is used for the study of relaxation properties of structural elements with covalently bonded luminescent labels [44,45]. For a microdisperse form of a macroreticular MA-EDMA (2.5 mol% EDMA) copolymer (Fig. 9 a, curves 1 and 2), as compared to linear PM A, the inner structure of chain parts is more stable and the conformational transition is more distinct. A similar kind of dependence is also observed for a weakly crosslinked AA-EDMA (2.5 mol%) copolymer (Fig. 9b, curves 4 and 5). 

Possible modes of regulation of filament assembly may be anticipated from the basic properties of actin. We have shown that the tightly bound divalent metal ion (Ca or Mg ) interacts with the P- and y-phosphates of ATP bound to actin, and that the Me-ATP bidentate chelate is bound to G-actin in the A configuration. The nature of the bound metal ion affects the conformation of actin, the binding kinetics of ATP and ADP, and the rate of ATP hydrolysis. 

The most interesting properties are exhibited by thin films, where rapid changes in doping level, conductivity, and optical transmission can be obtained. Thicker films exhibit vastly slower kinetics, which is due to slow counterion transport and, to some extent, to slow conformation changes. 

Polymer properties, influence of ions, 258 Polymer surface reactions, kinetics, 322-323 Polymer transformation reactions configurational effect, 38 conformational effects, 38 hydrolysis of polyfmethyl methacrylate), 38 neighboring groups, 37-38 quaternization of poly(4-vinyl pyridine), 37-38 Polymerization, siloxanes, 239... 

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