Freezing in polyampholyte globules: Influence of the long-range nature of the interaction

TL;DR

This paper investigates how long-range Coulomb interactions influence the freezing transition in polyampholyte globules, revealing that beyond a certain length scale, freezing behavior resembles that of short-range interactions due to self-screening effects.

Contribution

It demonstrates that long-range interactions do not induce freezing at all scales in polyampholyte globules, contrasting with short-range interaction models, and highlights the importance of self-screening in this process.

Findings

Freezing occurs only at length scales shorter than the self-screening length.

Long-range interactions do not cause large-scale freezing due to self-screening.

Insufficient frustration prevents freezing in non-maximally compact globules.

Abstract

In random heteropolymer globules with short-range interactions between the monomers, freezing takes place at the microscopic length scale only, and can be described by a 1-step replica symmetry breaking. The fact that the long-range Coulomb interaction has no intrinsic length scale suggests that freezing in random polyampholyte globules might take place at all length scales, corresponding to an overlap parameter q(x) that increases continuously from zero to its maximum value. Study of the polyampholyte globule within the independent interaction approximation seems to confirm this scenario. However, the independent interaction model has an important deficiency: it cannot account for self-screening, and we show that the model is only reliable at length scales shorter than the self-screening length. Using the more realistic sequence model we prove that in the general case of a random heteropolymer globule containing two types of monomers such that unlike monomers attract each other, freezing at arbitrarily large length scales is not possible. For polyampholyte globules this implies that beyond the self-screening length, the freezing behavior is qualitatively the same as in the case of short-range interactions. We find that if the polyampholyte globule is not maximally compact, the degree of frustration is insufficient to obtain freezing.