PHASE-DIAGRAM ANALYSIS OF RANDOM HETEROPOLYMERS WITH COMPOSITION SPECIFIC AND QUENCHED CROSS-LINKS

We study the conformational organization of a novel class of soft matt er, random heteropolymers (RHPs) with composition specific and quenche d cross-links by replica field theory. These technologically relevant materials carry an essentially quenched sequence distribution of dispa rate segments, and also a fixed distribution of composition specific c ross-links. The chain connectivity of the linear RHPs is captured most generally by a continuous microscopic RHP Hamiltonian, while the quen ched character of the cross-links is enforced by spatial constraints o n segments of a prescribed composition, and by allowing fluctuations i n the total number of composition specific cross-links around an exper imentally controlled average. The replica theory, a formalism widely u sed in the study of linear RHPs, is extended in the present work to an alysis of systems with multiform disorder that have interdependent dis order components. By numerically analyzing the free energy and its sta bility we predict the occurrence of frozen phase formation wherein few conformations are sampled. By systematically varying the sequence/cro ss-link fluctuations, temperature, and the RHP interaction parameters we show that two conformational transitions can occur in the frozen ph ase. The low temperature conformational transition resembles to a larg e extent the reduction in chain conformations which occurs during the folding of proteins with fixed disulfide bonds. The frozen phase domai n microstructure formation is discussed in context of the recently elu cidated phase diagram of a close related system, RHPs with annealed cr oss-links. Explicit connection is made with possible experiments and c omputer simulations methods to test our predictions. (C) 1998 American Institute of Physics.