Hydration of nucleosides in dilute aqueous solutions. Ultrasonic velocity and density measurements

The values of the concentration increments of the ultrasound velocity and their temperature slopes, apparent molar volumes, apparent molar expansibilities, apparent molar adiabatic compressibilities and their temperature gradients for 12 nucleosides and their analogs, as well as for ribose and deoxyribose, have been obtained using precision measurements of ultrasound velocity and density. The following hydration parameters for the atomic groups of the nucleosides, reflecting the state of water in the hydration shells of these groups, have been analyzed: (1) the contribution of ribose to the values of the concentration increment of ultrasound velocity A, the apparent molar volumes phi v and apparent molar adiabatic compressibilities phi ks of nucleosides; (2) contributions of the CH3, NH2 and O = ... -H groups of nucleic bases to the A, phi v and phi ks values of nucleosides and free nucleic bases; (3) contributions of the 2'-OH group of ribose to the values of A, phi v and phi ks nucleosides; (4) changes in the A values of nucleosides and free nucleic bases upon their protonation and deprotonation. Data have been obtained on the mutual influence of the atomic groups of nucleosides on their hydration. It is shown that the GC pairs of free deoxynucleosides undergo hydration more vigorously than the AT pairs, which contrasts with the relation of the degree of hydration of the GC and AT pairs of the double helix.