Ultrasonic Absorption in Aqueous Solutions of Deoxyribose Nucleic Acid

The ultrasonic absorption of aqueous deoxyribose nucleic acid (salmon sperm, M≃106) solutions were studied as a function of pH in the acidic region over the frequency range 5–50 MHz at 10° and 25°C. The alkaline pH range has previously been investigated [J. Chim. Phys. 66, 81 (1969)]. The double helical structure of the DNA molecule breaks down as a result of the acid and alkaline titrations causing the base‐base hydrogen bonds to be substituted for base‐solvent hydrogen bonds. The ultrasonic absorption titration curves for DNA show peaks around pH 2.6 and 12 which are attributed to hydrogen bond transfer. Proton transfer, which has been implicated in aqueous protein solutions, is considered unimportant as the mechanism responsible for the DNA absorption peaks. [This work is supported by the Institute of General Medical Sciences, National Institute of Health.]