Raman pH profiles for nucleic acid constituents I. Cytidine and uridine ribonucleosides

Raman spectra of aqueous solutions of uridine and cytidine have been recorded as a function of pH with the band intensities and vibrational frequencies monitored to determine bands which may be considered as diagnostic of the concentration of the various species. Quantitative band intensity measurements indicate that not all pH-sensitive bands can be considered as diagnostic of the pK value for the acid form of the nucleoside, and for the percent species in solution. Although the accuracy of the Raman band intensity method is inherently less than that of the titrimetric or visible-ultraviolet spectrophotometric methods, the pK values and percent species agree well with those obtained from these methods. The utility of the results obtained from the pH profiles for cytidine is discussed in terms of the effect of acidification on the structural and conformational characteristics of polycytidylic acid in solution.