Proton transfer from heterocyclic compounds. Part III. Adenine and adenosine

Proton magnetic resonance studies on short duplexes. I. Helix formation by the duplex set GpApGpC:GpCpUpC

“…1. The shift assignments for the G and A residues in GA were consistent with those reported by Lee et al (10) and the positions of G(1)H-8 and A(2)H-8 were confirmed by a deuterium isotope exchange experiment (9). In GAG three of the signals in the aromatic region were virtually identical with those of GA and the new signal at 7.948 pprn therefore assigned to G(3)H-8.…”

“…The A(2)H-2 proton remained relatively sharp throughout the entire temperature range but the remaining aromatic protons showed line broadening at the lower temperatures of the order of 5-20 Hz. It was only by comparison of the spectra where the G(1)H-8, q(2)H-8, G(3)H-8, and G(4)H-8 protons had been replaced by deuterium (9) to the spectra of the fully protiated species that reasonable assignments of the remaining lowfield protons could be made. The shift changes with respect to temperature of the mixed tetranucleotides are shown in Fig.…”

Effect of aminoacyl transfer RNA synthetases on H-5 exchange of specific pyrimidines in transfer RNAs

“…In the case of the purine H-8 exchange reaction, it is believed to proceed through an ylide-type mechanism (Tomasz et al, 1972;Elvidge et al, 1973Elvidge et al, , 1974. In our investigations, we found that whenever a purine unit is bound to an enzyme or buried in the secondary or tertiary structure of the nucleic acid, the labeling rate is markedly retarded (Gamble et al, 1976;.…”

The Synthesis of Deuterionucleosides

“…The pH-dependent kinetic studies of exchange process have also been performed 52,71,83,[85][86][87][88] . It has been found, that within a certain pH range, the structure of the purine could be unchanged (neither protonated nor deprotonated).…”

“…This reaction consists of the OH -catalyzed abstraction of the hydrogen from the N7-protonated purine giving rise to an ylide type intermediate, which then is "reprotonated" at C8. In the case of guanosine, the protonation of the N7 can also occur due to the formation of a zwitterion [82][83][84][85] (Scheme 3).…”