Optical properties of sixteen dinucleoside phosphates

Further studies of the optical properties of the dinucleoside phosphates of RNA have supported the prediction that the structure of these molecules can be understood in terms of “stacking” and “unstacking” of the bases. Optical rotatory dispersion and absorption parameters at 25 °C of the 16 dinucleoside phosphates at pH 1, 7 and 11.5 and an ionic strength of 0.1 have been measured. Using the value of hypochromism as a criterion, four dinucleoside phosphates are stacked at pH 1, eleven at pH 7 and eight at pH 11.5. The optical rotatory dispersion was found to be very dependent on sequence; therefore, measurements of optical rotatory dispersion could distinguish between sequence isomers, whereas the absorption measurements could not. The application of optical properties of the dinucleoside phosphates to the interpretation of the structure and properties of polynucleotides is discussed.