Universality and Identity Ordering in Heteropolymer Coil-Globule Transition

The coil-globule transition of an energy polydisperse chain, a model heteropolymer system where the number of monomer species equals the total number of monomers, is studied by means of molecular dynamics simulations. In this study, we systematically explore the consequences of having different functional forms and variance of the energy distribution on the coil-globule transition in general. In particular, considering Gaussian (G) and uniform (U) distributions, the effect of varying polydispersity indices, (5, on the transition temperature 0*, chain size, and internal structure of the globule and kinetics of the folding are addressed. It is found that 0* for the model heteropolymer is lower than that for the homopolymer counterpart, and it increases with (5 (both G and U) and 0*(U) < 0*(G) consistently. The results of our study indicate that 0* is governed by the most probable value (rather than the width) of the pair-wise energy distribution. Interestingly, the nature of the collapse transition turns out to be universal, i.e., when scaled properly (irrespective of the functional form and variance), all of the swelling curves fall on a master curve, and it is well described by the same scaling form of the homopolymer counterpart. However, following quenching, the transition from the coil to the globule is relatively fast for the heteropolymer (with no significant difference between G and U systems and no significant (5 dependence within the considered range). On the other hand, an internal organization in the collapsed state, quantified through mean contact probability, shows distinct scaling regimes. Also, we observe the segregation of monomers based on their identities, which is more pronounced in the case of uniform distribution.