Thermal perturbation differential spectra of ribonucleic acids. I. Hydration effects.

A relatively important change in UV absorption is observed upon thermal perturbation of nucleotide solutions. Comparison of these thermal perturbation spectra of nucleic acid residues with solvent perturbation spectra of the same compounds suggests that this spectral change can most probably be attributed to temperature induced hydration change of the bases. This conclusion is confirmed by the results obtained from acid-base perturbation spectra of these nucleotides as well as thermal perturbation spectra of nucleotides containing modified bases. It is shown that this temperature dependent change in UV absorption is also present in dinucleoside monophosphates. In that case, this effect is superimposed upon the well known change in absorbance due to the unstacking of the bases during heating.