Synthesis and Structural Studies of a Self-complementary Decadeoxynucleotide D(AATTGCAATT). II.-Proton Magnetic Resonance Studies

Proton magnetic resonance spectra of the self-complementary decadeoxynucleotide d(AATTGCAATT) at 90 and 250 MHz have been obtained at different temperatures. The assignment of the different resonance lines to the base protons was obtained by combining the data derived from various methods: hydrogen in equilibrium with deuterium exchange at the H8 position of purines; comparison of NMR spectra obtained at high temperature with those of mononucleotides; comparison of the variations in chemical shifts obtained between 280 K and 360 K with calculated values; determination of half-transition temperatures for each base pair. On the basis of computed chemical shifts for stacked base-pairs it is concluded that the decadeoxynucleotide duplex exists in the B form in solution at 280 K. Propagation of the opening of the mini double helix from terminal to central base pairs if reflected in the variation of half-transition temperatures which vary between 306 K and 327 K.