Polymer conformational stability, transitions

Dugic, M., Rakovic, D., and Plavsic, M., The polymer conformational stability and transitions a quantum decoherence theory approach, in Finely Dispersed Particles Micro-, Nano- and Atto-Engineering, Spasic, A.M., Hsu, J.P., Eds., Marcel Dekker/CRC Press/Taylor Francis, Chap. 9. 

In this chapter, we describe the problem of polymer conformational stability and transitions in the framework of the so-called quantum decoherence theory. We propose a rather qualitative scenario yet bearing generality in the context of the quantum decoherence theory, enabling us to reproduce both, existence and stability of the polymers conformations, and the short time scales for the quantum-mechanical processes resulting effectively in the conformational transitions. The... 

Introduces the quantum decoherence theory approach to polymer conformational stability and transitions... 

Part II continues with a section on various approaches and transitions. Chapter 6 covers polymer networks and transitions from nano- to macroscale by Plavsic. The following chapter is on the atomic scale imaging of oscillation and chemical waves at catalytic surface reactions by Elokhin and Gorodetskii. Then next chapter relates the characterization of catalysts by means of an oscillatory reaction written by Kolar-Anic, Anic, and Cupic. Then Dugic, Rakovic, and Plavsic address polymer conformational stability and transitions based on a quantum decoherence theory approach. Chapter 10 of this section, by Jaric and Kuzmanovic, presents a perspective of the physics of interfaces from a standpoint of continuum physics. 

The stabilization of the planar conformation in these materials is due primarily to intramolecular hydrogen bonding between the N-H and C=0 (urethane) groups on adjacent R groups. The resulting polymer conformation is shown schematically in Figure 3. This explanation of the color transition is clearly evident from infrared spectra (12), which will not be discussed here. 

The stereochemistry of products derived from reactions of coordinated olefins and the stereochemistry of polymers formed in reactions catalyzed by transition metals are ultimately determined by the conformational stability of 7r-complexed intermediates. For example, the cisitrans ratios and the relative amounts of 1,2- versus 1,4-polymer units obtained in diene polymerization are determined by stabilities of syn and anti isomers of vr-allyls and the relative stabilities of various orientations of substituted olefins bound to metals (105). The interconversion rates of these isomers and the thermodynamic preferences of olefin-metal conformations should explain observed product distributions and provide a rational basis for catalyst design. 

In the wetting transition, elastic polymers with stretchable bonds can form perfectly icosahedral morphologies. This would additionally stabilize the polymer conformation and... 

The immobilization of enzymes for sensing purposes frequently provides several important advantages an increase of its stability, operational reusability and greater efficiency in consecutive multistep reactions. Sometimes immobilization is accompanied by a certain degree of denaturalization however, the enzyme-matrix interactions may assist in stabilization preventing conformational transitions that favor such process. In some cases excessive bond formation affects the conformation of the active site and the steric hindrances caused by the polymer matrix may render an inactive sensor. 

The transition state was shown to have a four-centered nonplanar structure and the product showed a strong jS-agostic interaction.59 Molecular-mechanics (MM) calculations based on the structure of the transition state indicated that the regioselectivity is in good agreement with the steric energy of the transition state rather than the stability of the 7r-complex. The MM study also indicated that the substituents on the Cp rings determine the conformation of the polymer chain end, and the fixed polymer chain end conformation in turn determines the stereochemistry of olefin insertion at the transition state.59... 

Polymers designed with this technique have a number of important aspects in common with proteins. First of all, the transition from a liquid-like globule into a frozen state occurs as a first order phase transition. Further, the frozen state itself has an essential stability margin, which is determined by the design parameters. As in real proteins, neither a large variation of temperature or other environmental conditions, nor a mutational substitution of several monomers leads to any change in basic state conformation. In this respect the ability of sequence design to capture certain essential characteristics of proteins seems quite plausible. 

The kinetics and equlibria of the complexation between PAA and PEO or PVPo were studied by Morawetz s group [ 13-15], and it was shown that the complex formation consisted of an initial diffusion-controlled hydrogen-bonding process with a small activation energy and an extensive conformational transition of the two polymer chains which induces additional hydrogen bonding, thus stabilizing the complex. 

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