A Gravimetric Study of Hydration of Polynucleotides

The hydration of soluble ribonucleic acid, of two forms of polyriboadenylic acid, and of nucleohistone was determined gravimetrically as a function of relative humidity (r.h.). The curves are smooth functions of r.h., similar to those obtained earlier for deoxyribonucleic acid. The general similarity of the hydration curves of the polynucleotides so far investigated is in agreement with the suggestion that the ionic phosphate groups are the primary hydration sites in polynucleotides. The hydration data fit the Brunauer–Emmett–Teller equation up to about 75% r.h. and the Harkins–Jura equation at higher values. Both equations yield a value of about 2.0 molecules of H2O per nucleotide for the "monolayer content" for all the polynucleotides investigated.