Globule polymer conformation

An excluded-volume random-coil conformation will be achieved when the solvent quality exceeds the theta point, the temperature or denatu-rant concentration at which the solvent-monomer interactions exactly balance the monomer—monomer interactions that cause the polymer to collapse into a globule under more benign solvent conditions. A number of lines of small-angle scattering—based evidence are consistent with the suggestion that typical chemical or thermal denaturation conditions are good solvents (i.e., are beyond the theta point) and thus that chemically or thermally unfolded proteins adopt a near random-coil conformation. 

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. 

Macrosyneresis, in which the network polymer is contained only in one phase is not the only possibility for phase equilibria in networks. Under favorable conditions two polymer phases can coexist in a network with a diluent phase (50). The two polymer phases in equilibrium differ in the conformations of the network chains. The transition resembles the condensation of a real gas or, in macromolecules, an intramolecular transition due to long-range net attraction between segments in a poor solvent (coil-globule type transition [139)). 

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