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Counterion correlations and attraction between like-charged macromolecules.

A Diehl1, H A Carmona, Y Levin

  • 1Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, CEP 60455-760, Fortaleza, Ceará, Brazil.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|July 20, 2001
PubMed
Summary

Like-charged polyions attract each other in polyelectrolyte solutions due to correlated counterion layers. This attraction, driven by counterion condensation, is short-range, particularly for DNA, appearing below 7 Angstroms separation.

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Area of Science:

  • Physical chemistry
  • Polymer science
  • Biophysics

Background:

  • Like-charged polyions typically repel due to electrostatic forces.
  • Polyelectrolyte solutions contain mobile counterions that can condense around polyions.
  • Counterion condensation can screen or even alter the effective interaction between polyions.

Purpose of the Study:

  • To model the emergence of attraction between like-charged polyions in a polyelectrolyte solution.
  • To investigate the role of counterion condensation in mediating inter-polyion attraction.
  • To quantify the conditions under which this attraction occurs.

Main Methods:

  • A simple theoretical model was developed for rigid cylindrical polyions in a dielectric solvent.
  • The model incorporates strong electrostatic interactions leading to counterion condensation.

Related Experiment Videos

  • Correlation functions for condensed counterions were calculated to analyze their interactions.

    • Main Results:

    • A model predicting attraction between like-charged polyions was presented.
    • Counterion condensation layers around closely spaced polyions can become correlated, inducing attraction.
    • The calculated correlations are of very short range.
    • For parameters mimicking double-stranded DNA, attraction is observed only at separations below 7 Angstroms.

    Conclusions:

    • Counterion condensation and correlation provide a mechanism for attraction between like-charged polyions.
    • This counterion-induced attraction is highly sensitive to the distance between polyions.
    • The findings are particularly relevant for understanding interactions involving DNA and similar macromolecules.