Strongly coupled polyelectrolyte-macroion complexes

We review the problem of complex formation between a macroion and an oppositely charged polyelectrolyte on the linear level. We study the effect of changing the ionic strength and the valency of the macroion on the complexed polymer configuration. Distinguishing four different configurational symmetry classes, we are able to map out the global configurational phase diagram. We also study the interaction between two complexes of macroion and polyelectrolyte, which gives rise to configurational changes of two complexes as they approach each other. Most of these calculations are performed on the ground-state level and are thus accurate only for very stiff polymers or highly charged and therefore strongly bound systems. We also give a short outlook into the problem of thermal fluctuations around the polymer ground state configuration as it is wrapped around the macroion. This problem is tackled by a normal-mode analysis. All calculations are performed for parameters corresponding to DNA-histone complexes, which are the basic building blocks of the nucleosomal genetic structure.