[Optical properties and molecular structure of nucleic acids and their components. X. Infrared spectra and molecular structure of denatured DNA with different water content and degree of protonation].

IR-spectra (4000-900 cm-minus-1) of heat denatured DNA (d-DNA) of calf thymus have been obtained in the range of relative humidity of 0-93% and of the guota of protoned bases alpha of 0-0,5. fron these spectra the diagram of d-DNA states is plotted as the relationships of intensities and the location of some bands with and relative humidity. At alpha approximately 0,2 a compact structure S2-1 with firm hydrogen bonds between protoned and unprotoned bases which is similar to those observed earlier while protoning homopolynucleotides poly-A and poly-C. At G1'-large values of alpha S2-1-conformation destroyed and a loose structure (alpha approximately 0,35) appears. the latter is characterized by a minimum H-binding of the base and increased hydration. Further increase of alpha brings about the formation of sufficiently compact G2-1-STRUCTURE WHICH IS CHARACTERIZED BY SOLID H-bonds between PO2-groups and protoned bases. A specific effect of the structures found on the state of absorbed water and the structure of hydrate envelope is revealed.