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

In random heteropolymer globules with short-range interactions between the monomers, freezing takes place at the microscopic length scale only, and ca n be described by a one-step replica symmetry breaking. The fact that the l ong-range Coulomb interaction has no intrinsic length scale suggests that f reezing in random polyampholyte globules might take place at all length sca les, 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. H owever, the independent interaction model has an important deficiency: it c annot account for self-screening, and we show that the model is only reliab le 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 hete ropolymer globule containing two types of monomers such that unlike monomer s attract each other, freezing at arbitrarily large length scales is not po ssible. For polyampholyte globules this implies that beyond the self-screen ing length, the freezing behavior is qualitatively the same as in the case of short-range interactions. We find that if the polyampholyte globule is n ot maximally compact, the degree of frustration is insufficient to obtain f reezing. (C) 1999 American Institute of Physics. [S0021-9606(99)50525-4].