23Na nuclear magnetic resonance relaxation studies of sodium ion interaction with soluble RNA.

Interactions between (23)Na(+) and soluble RNA in aqueous solution are studied with the use of (23)Na nuclear magnetic resonance. At low concentrations of NaCl, the interactions obey a simple equilibrium model with a formation constant log (K(f))(3) = 2.8 +/- 0.3. The relaxation rate of the bound sodium is found to be T(1B) (-1) = 222 +/- 19 sec(-1) compared to that of free sodium T(1F) (-1) = 17.5 sec(-1). At high NaCl concentrations, the system deviates from the model, possibly owing to aggregation of the soluble RNA.