Ultrasonic Investigation of Solute—Solvent and Solute—Solute Interactions in Aqueous Solutions of Bases, Nucleosides, and Nucleotides. 3. Solute—Solute Interactions: Studies of Base Stacking by Ultrasonic Velocity Measurements

Hemmes P., Mayevski A. A., Buckin V. A. and Sarvazyan A. P.

J. Phys. Chem., 84, pp. 696 (1980)

The concentration dependence of ultrasonic velocity of dilute solutions of caffeine, 1-methyl-4-(methyl-amino)pyrazolo[3,4-d]pyrimidine, adenosine, and deoxyadenosine has been determined at a number of temperatures. The relative velocity changes are nonlinear functions of concentration. A method is proposed to use these data to obtain K and also obtain information on hydration of the species in solution. Stacking constants were obtained which are in good agreement with literature data. The data indicate that the intrinsic compressibility of the molecules may be high. When our model is used, properties of the stacks can be calculated. Hydration of both monomers and stacks can be calculated. Hydration of both monomers and stacks was reflected in the temperature dependence of the apparent compressibility. The stacks have a hydration shell which seems to contain more structured water than the monomers. This is in qualitative agreement with the known negative entropy change for stacking.

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