Randomly charged polymers

  • Mehran Kardar
  • Yacov Kantor
Conference paper
Part of the Lecture Notes in Physics book series (LNP, volume 492)


Polyampholytes (PAs) are polymers with a random sequence of positive and negative charges along their backbone. We have studied systematically the dependence of internal energy and shape of the PA on its excess charge by combining analytic arguments, Monte Carlo simulations, and exact enumeration of all configurations of short chains. The results indicate that the overall excess charge, Q, is the main determinant of the size of the PA. A polymer composed of a mixture of N positive and negative charges ±qo, is compact for Q<Q cqoN, and expanded otherwise. The transition between the two states at low temperatures is reminiscent of the Rayleigh shape instability of a charged drop. A uniform excess charge causes the breakup of a fluid drop; we show that a uniformly charged polymer stretches out to a necklace shape. The inhomogeneities in charge distort the shape away from an ordered necklace. The freezing transition of a PA, and its relevance to proteins is also discussed.


Monte Carlo Simulation Coulomb Interaction Compact Globule Excess Charge Charged Drop 
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Copyright information

© Springer-Verlag 1997

Authors and Affiliations

  • Mehran Kardar
    • 1
  • Yacov Kantor
    • 2
  1. 1.Department of PhysicsMassachusetts Institute of TechnologyCambridgeUSA
  2. 2.School of Physics and AstronomyTel Aviv UniversityTel AvivIsrael

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