Cooperative conformational transitions in linear macromolecules undergoing chiral perturbations

The conformation of a linear polymer chain in the unperturbed state undergoes a cooperative transition between an ordered and disordered states and/or between two different ordered states. Thus this transition is concerned with the conformation of an isolated chain. Typical examples discussed in this review are helix-coil transitions in polypeptides, helix reversals in chiral polyisocyanates, and order-disorder transition in a triple-helical polysaccharide schizophyllan in water, etc. They are linear cooperative systems and well treated theoretically in terms of the linear Ising model. First experimental systems studied are briefly reviewed. Then theories of the transitions based on the Ising model are re-organized with relevant conditions put for each case; both transition curves and global conformations are discussed. Numerical results are given to predict new possibilities. Finally, it is shown that these theories are used to analyze respective experimental data with the polymer molecular weight as the key bridge between experiment and theory, yielding important molecular parameters and thus exploiting the detailed molecular mechanism behind. (C) 2001 Elsevier Science Ltd. All rights reserved.