Polyelectrolyte chains confined by macroions bearing electrostatic charges of opposite sign can mediate an effective attraction between the macroions. This polyelectrolyte mediated attraction is usually referred to as the bridging interaction. The polyelectrolyte bridging interaction comprises feature of electrostatics as well as polymer elasticity that conferrs effecrtive attractions between nominally equally charged bodies.

Polyelectrolyte bridging interactions show in the dependence of the second virial coefficient on ionic strength. The second virial coefficient of the nucleosomal core particles (NCP) in low density regime has been measured extensively and shows this effect as the N-tails of the histone core contract or expand in response to the varying salt concentration. NCPs represent the lowest level of the chromatin organization in eucaryotes and have recently been resolved at an atomic resolution. They consist of a histone protein octamer core with 146 bp of DNA tightly wrapped around it, giving it an approximate cylindrical shape of a radius 55 Angstroms, a height of 57 Angstroms and a structural charge of -250. The charged histone N-termini or N-tails can desorb from this complex and basically play the role of grafted flexible polyelectrolyte chains of an approximate total charge of +90.

Computation of the bridging interaction shows that it gives a substantial contribution to the second virial coefficient of the nucleosomal core particles in solution.

R.Podgornik, Two-body polyelectrolyte mediated bridging interactions, J. Chem. Phys. 118 (2003) 11286-11296.

R.Podgornik, Polyelectrolyte-mediated bridging interactions, Journal of Polymer Science Part B: Polymer Physics Volume 42, Issue 19 , Pages 3539 - 3556.

Top of Page