Interactions of highly charged colloidal cylinders with applications to double-stranded DNA

✍ Scribed by Dirk Stigter

• Publisher: Wiley (John Wiley & Sons)
• Year: 1977
• Tongue: English
• Weight: 762 KB
• Volume: 16
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1977.360160705

✦ Synopsis

This paper presents new applications of the McMillat-Mayer solution theory to dispersions of highly charged colloidal cylinders in monovalent salt solutions. The thermodynamic so- lution properties are given in terms of the virial expansions relating to a Donnan membrane equilibrium. General expressions are derived for the second Donnan pressure virial coefficient Rz and for the first two salt distribution coefficients A1 and A*. The effect of electric interactions is represented as an increased effective diameter d~ or d A of the colloidal cylinder. This yields the simple excluded volume expressions Bz = r d ~L ~/ 4

and A 1 = r d A 2L/4 for hard cylinders of length L and diameter d B and d A , respectively. The coefficient A2 is derived from the dependence of Rz on the salt concentration.

Computations are made for double-stranded DNA in sodium chloride solutions with the DNA model developed in the preceding paper: a uniformly charged cylinder, with size and charge consistent with transport experiments, and surrounded by a Gouy double layer. In 1-0.005M sodium chloride solutions d~ is found to vary from 29 A to about 220 A, and da from 30 A to about 170 A, with little sensitivity to the uncertainties in the kinetic diameter d = 24 A and the experimental {potentials of DNA. Corresponding results predicted by the classical Donnan theory are 6-167 times too high for Rz.

Values of A2 are relatively small, in line with the expected rapid convergence of the virial expansion for the salt distribution. This is consistent with a phase transition from random to parallel orientation of the cylinders predicted first by Onsager for hard cylinders on the basis of Rz, but not yet observed for DNA in simple salt solutions.