Studies on the pH-independent ultrasonic relaxation in nucleotides and simple phosphates

The ultrasonic spectra of various nucleotides and some simple phosphates have been measured in the frequency range 6-300 MHz with both pulse and resonator methods. A pH-independent relaxation was found near 35 MHz in most cases. This effect has a concentration-independent relaxation frequency. The amplitude of the effect decreases with increased temperature. The amplitude is increased by addition of Mg²⁺. The relaxation frequency does not depend upon the nature of the nucleic base, the state of ionization of the sugar on the nucleotide, the phosphate chain length, or the nature of the cation. The data have been intrepreted by means of a multistep ion-pairing process. The observed effects are probably due to anionic desolvation. Several other possible explanations can be ruled out.