N.M. Toan and C. Micheletti
Inferring the effective thickness of polyelectrolytes from stretching measurements at various ionic strengths: applications to DNA and RNA
J. Phys.: Condens. Matter 18 S269-S281 (2006)
Link to online article.
ABSTRACT
By resorting to the thick-chain model we discuss how the stretching
response of a polymer is influenced by the self-avoidance entailed by
its finite thickness. The characterization of the force versus
extension curve for a thick chain is carried out through extensive
stochastic simulations. The computational results are captured by an
analytic expression that is used to fit experimental stretching
measurements carried out on DNA and single-stranded RNA (poly-U) in
various solutions. This strategy allows us to infer the apparent
diameter of two biologically-relevant polyelectrolytes, namely DNA and
poly-U, for different ionic strengths. Due to the very different
degree of flexibility of the two molecules, the results provide
insight into how the apparent diameter is influenced by the interplay
between the (solution-dependent) Debye screening length and the
polymers' ``bare'' thickness. For DNA, the electrostatic contribution
to the effective radius, $\Delta$, is found to be about 5 times larger
than the Debye screening length, consistently with previous
theoretical predictions for highly-charged stiff rods. For the more
flexible poly-U chains the electrostatic contribution to $\Delta$ is
found to be significantly smaller than the Debye screening length.