Conformation of polyelectrolyte chains in dilute aqueous solutions investigated by conductometry, 1 - Influence of the degree of polymerization on the conformation of flexible vinylic polyanions and rigid native DNA

The temperature dependencies of the conductivities of dilute salt-free aqueous solutions of flexible vinylic polyelectrolytes - sodium poly(acrylate) and sodium poly(styrene sulfonate) - with different degrees of polymerization (DP) were investigated. Analogous dependencies were obtained for solutions of rigid native DNA with different degrees of polymerization (i.e. with a different number of base pairs (bp) in the chain) in 0.001 mol·L-1 NaCl as a supporting electrolyte. On the basis of Manning's polyelectrolyte theory, the mean charge spacing b in the polyion chains was calculated from these data. The determined b values were used to estimate the conformational changes of the charged chains. For all studied polyanions, b increased with the shortening of the chains, indicating a transition from coil-like to rod-like regimes. For both vinylic polyanions, the transition was observed practically in the same DP region, i.e. ≈ 102-103, whereas rigid native double-stranded DNA molecules underwent the conformational change at substantially higher DP values, namely of the order of 103-104. The obtained results show that the used conductometric approach is appropriate for the estimation of the conformational changes of polyions in dilute aqueous solutions. © Wiley-VCH Verlag GmbH, 2001.