Showing papers in "Journal of the American Chemical Society in 1965"

Correlations in the Ultraviolet Spectra of the Purine and Pyrimidine Bases1

Abstract: In order for optical studies (e.g., absorption spectrophotometry, optical rotatory dispersion) of the nucleic acids to be useful for structure determination, it is necessary to understand the optical properties of the isolated nucleic acid bases. A knowledge of the transition energies and polarization directions of the individual bases allows predictions of the optical properties of possible dimers, oligomers, and polymers of nucleotides, These predictions can be compared with experimental measurements to learn about the conformation and structure of these polynucleotides. The absorption and rotation of light by helical oligomers have been treated by assuming values and orientations of the transition moments in each r e ~ i d u e . ~ ~ ~ The change in light absorption of polynucleotides which occurs on transition from a disordered to an ordered state (hypochromism) has been similarly treated. 4-6 The examination of the ultraviolet absorption spectra of the purine and pyrimidine bases has been very extensive. Noteworthy is the work of Mason,7 Stewart and Davidson,* and Rosa and S i m p ~ o n . ~ Aqueous solution spectra to 185 mp of many of the bases have recently been published by Voet, et al. lo The present work is an effort to systematize and characterize the spectral bands of the purine and pyrimidine bases which are important constituents in the nucleic acids. A correlation (or assignment scheme) is developed which not only relates the absorption bands in the various compounds but also is consistent with spectral changes due to p H variation.