KINETICALLY ACCESSIBLE COMPACT CONFORMATIONS OF CHAIN MOLECULES

The kinetic accessibility of various compact conformations of chain mo lecules is studied using a short self-avoiding chain on a three-dimens ional cubic lattice. The kinetic accessibility of a compact conformati on depends on the conformational energy and the distances from the oth er conformations along kinetically possible trajectories. We focus on the kinetic distances. We consider a chain in a poor solvent, having m ultiple lowest-energy compact conformations. The chain collapse from a n arbitrary conformation to one of the lowest energy conformations is investigated. Though the lowest energy states would be occupied with t he same probability in equilibrium, the probabilities for a first hit are not necessarily all the same and they indeed are not. We show that the hit probability at low temperature can be used as a measure of th e kinetic distances from other conformations. The hit probability is i nvestigated under two kinetic processes. One is a Monte Carlo dynamic process and the other is a ''contact-set stepping'' process, in which kinetic distances between conformations are defined based on sets of c ontacts. The two kinetic processes exhibit similar results showing tha t both processes well reproduce the kinetic behavior of chain molecule s. Through the characterization of the states with large hit probabili ty at low temperature, we show that the influence of the kinetic dista nces on the kinetic accessibility can be explained by domain structure or locality of contacts. (C) 1998 American Institute of Physics. [S00 21-9606(98)51620-0].