Nuclear magnetic spectra of self complementary decanucleotides in solution; base sequence effect on the chemical...

The aim of this study was to attempt to determine the extent to which the chemical shifts of the nonexchangeable base protons of a DNA helix depend upon the base sequence. We measured the proton NMR spectra of twelve decadeoxynucleotides in order to carry out a "statistical" treatment. In the helices, the chemical shifts were found to be determined within +/- 0.04 ppm, largely by the nearest neighbor residues on the 5'-side, and to a smaller extent by the residue on the 3'-side. The theoretical chemical shift calculations reproduced very well the polymerization shifts measured for H2 protons of adenosines if the electrostatic field effect was taken into account. A fair agreement was also obtained for H8 protons of the adenosine and guanosine residues. However, theory underestimates the polarization effects of the base protons of cytidine. This discrepancy suggests that the conformation of this residue is different in the mononucleotides relative to double helices.