Concentrationhyphen;dependent collapse of a large polymer in a solution of incompatible polymers

摘要

DNA of high molecular weight is observed to collapse into a very compact particle in a salt solution in the presence of second neutral polymers, poly(ethylene oxide) lsqb;(EO)nrsqb; of lower molecular weight, above a certain critical concentration. We show in a statistical mechanical way that the phenomenon is caused by the repulsive interaction between the DNA and (EO)nrsquo;s. A selfhyphen;consistent (SC) potential is introduced to treat both intramolecular and intermolecular repulsive interactions of shorthyphen;range nature. Appearance of a bound state in this SC potential is necessary and sufficient condition for a collapsed state to be stable. The critical concentration of (EO)nis found to be proportional to the inverse degree of its polymerization. The average size of a DNA is expected to change fromN3/5toN1/3at the transition point, whereNis the number of base pairs in the DNA. The transition is of second kind.