INFRARED-SPECTROSCOPY AND INFRARED LINEAR DICHROISM OF NUCLEIC-ACIDS

The activities of this laboratory in the field of infrared spectroscopy of nucleic acids since 1964 are summarized. Vibrations of deoxyribonucleic acid (DNA) were assigned by inspection of spectra of DNA's differing in their base composition. The "melting" of DNA dissolved in D2O has been studied by infrared spectroscopy, and the base composition of DNA samples from different microorganisms has been determined both from absorbance differences of base vibrations and by measurements of the "melting" temperature. Further studies have dealt with the structure of the copper (II)-DNA complex and the assignment of the out-of-plane NH vibration bands of the DNA bases. It was shown that the purine H-8 atoms undergo slow isotopic exchange at elevated temperature (55-degrees-C), allowing preparation of deuterium-labelled native DNA. The introduction of infrared linear dichroism enabled the B-A transition of oriented DNA films to be monitored as a function of the relative humidity. An infrared band at 1185 cm-1 was described as a new "marker" band for A-DNA. The infrared linear dichroism results were treated quantitatively to determine the phosphate group geometry of B-DNA and A-DNA, and to calculate the ligand-induced "freezing" of a fraction of the DNA in the B form. A new drug assay was presented based upon this "freezing" effect.