The spectra of a number of methylated xanthines have been determined in aqueous solution as a function of pH and have been found to fall into two distinct categories; that is, these derivatives may be placed into either of two spectral classes which are readily distinguishable regarding both the positions and the intensities of the bands. Correlation of the spectral shifts with pH has permitted an assignment for the sequence of ionization of the various hydrogen atoms.In the case of xanthine, for example, the first ionization is attributed to the removal of the 3-hydrogen while the second is due to the 7hydrogen. When the 3-position is substituted, the 7-hydrogen ionizes first; the 1-hydrogen next. When the l-position is substituted the order is identical to that of xanthine, and if the 7-position is substituted, the sequence is 3, 1. In general, the sequence of ionization of the three positions would be 3, 7, 1. The spectrally-determined apparent dissociation constants are found to be in good agreement with those obtained potentiometrically. Contrary to an earlier belief, it has been shown that xanthine, 7-methylxanthine and xanthosine each exhibit two dissociations in the pH range studied. The relative values of the various apparent dissociation constants are discussed in terms of structure.

Spectra of Pyrimidines and Purines 2587 increase in A1C1 concentration of over one hundred thousandfold was noted, when aluminum was added to aluminum trichloride, over that observed by thermal dissociation of aluminum trichloride alone.New Kensington, Pa.

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The effects of enzymatic attack and of shear during the isolation and deproteinization of DNA have been investigated. Different methods of disaggregating DNA have been studied, and conditions under which reaggregation can occur are discussed. It was found that shaking with chloroform-octanol does not degrade DNA from the seven sources studied; that light scattering yields valid weight-average molecular weights for these samples; and that, when disaggregated, the molecular weights of these samples are in the range 1.2-2.4 million and the length-to-mass ratios are high.