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SynopsisThe field-dependent 23Na nuclear relaxation in aqueous DNA solutions has been obtained for a range of temperatures, including the DNA melting region. At least two correlation times are needed to characterize the spectral density function for the 23Na relaxation. For the slow process (with the largest correlation time), the temperature dependence of the coupling constant and the correlation time were determined, and important premelting effects were observed. Possible origins of the slow process are discussed. The last process is shown to be correlated with the properties of the hydration water of DNA as reflected by the *70 relaxation rates in these solutions. The influence of the polyelectrolyte and NaCl concentrations on the 23Na relaxation rate is compared with previous results from solutions of linear flexible polyelectrolytes.

Potentiometric titrations, pulsed field gradient NMR, and viscometry of poly(maleic acid) have been carried out in different salt solutions of varying ionic strength. The shape of the titration curve depends strongly on the type of cation used, especially beyond α = 0.5. Above 5 times excess salt concentration, the potentiometric titration curves can be fit satisfactorily to an equation derived on the basis of a random Ising model, using three free parameters:  the intrinsic dissociation constant K 0 and two excess free energies εr and εm describing the nearest-neighbor interaction across a racemic and mesomeric bond, respectively. The stereochemistry of PMA is modeled using an additional parameter P r, which is the probability of racemic propagation during synthesis. This parameter was determined by 13C NMR. The results compare favorably with those obtained for other poly(carboxylic acid)s. Except for a gradual expansion of the polymer coil upon charging, no conformational changes are observed by PFG-NMR and viscometry. Rather, attractive intermolecular interactions appear to play a role at high degrees of dissociation.