Change in the elasticity of a random heteropolymer chain induced by freezing

– We consider a simple model of a random heteropolymer chain that is known to undergo the freezing transition. We investigate the change in the elastic properties of the chain upon freezing. The elastic constants are evaluated and it is shown that they acquire a non-trivial contribution in the frozen phase. The goal of this letter is to investigate the elasticity of a random heteropolymer chain and, in particular, its change upon freezing. Macroscopic elastomeric response is one of the fundamental properties of cross-linked polymeric systems [1]. It originates from the presence of an infinite network. On a macroscopic level uncrosslinked polymeric systems exhibit a viscous flow rather than an elastic recovery behavior. However, on a microscopic level a single polymer chain is endowed with an elastic response [2]. This is a combined effect of both the chain connectivity and the huge number of possible conformations. Here we examine the elasticity of a single random heteropolymer chain that undergoes a freezing transition. This transition leads to a non-ergodic phase characterized by a highly rugged topography of the free-energy landscape with multiple multidimensional minima. Different chain conformations are separated by high-energy barriers. This effectively reduces the number of accessible chain conformations and thus should result in a change of the elastic properties of the heteropolymer chain. It should be emphasized here that the model random heteropolymer and its freezing transition which are considered in this work are very similar to those discussed in the context of protein folding. Thus, the method we are using to investigate an emerging additional contribution to the heteropolymer chain elasticity can be used to study the elasticity or stiffness of a folded protein. In general, elastic properties may be related to the structure and the stability of the ground state (note that elastic constants are determined by the curvature of the free energy). Under certain conditions [3] elastic constants may even be considered as order (∗) E-mail: [email protected] (∗∗) E-mail: [email protected]