Poly base proton chemical shifts

We observe similar base pair overlaps for poly(dA-dT) in 1 M Na+ and TMA+ solution based on a comparison of the base proton chemical shifts of the synthetic DNA in the duplex state as a function of counterion. 

Figure 3. The temperature dependence (5° to 95°C) of the base and sugar proton chemical shifts of poly(dA-dT) in 0.1 M phosphate, 1 mWl EDTA, -H.O, pH 7.0...

Nucleic Acid Base Resonances The chemical shifts of the nonexchangeable protons in poly(dA-dT), the Nuc/D = 24 complex and the Nuc/D = 8 complex in 1 M NaCl solution are plotted as a function of temperature in Figure 19. The nucleic acid nonexchangeable proton chemical shifts in the duplex state are either unperturbed (adenosine H-8, H-2, and thymidine CH3-5) or shift slightly upfield (thymidine H-6) on complex formation (Figure 19). By contrast, the thymidine H-3 exchangeable proton located in the center of the duplex resonates 0.35 ppm to higher field in the Nuc/D = 8 proflavine complex compared to its position in the... 

The temperature dependence of the chemical shifts of the base resonances in poly(dA-dT) and poly(dA-5brdU) are plotted in Figure 5. These data demonstrate that the adenosine H-8 and H-2 protons exhibit very similar behavior over the entire temperature range and are not perturbed by the substitution on the pyrimidine 5 position. 

There is no information to our knowledge on premelting transitions in RNA duplexes. We have therefore investigated the NMR parameters for the related synthetic RNA duplex poly(A-U) as a function of temperature. Typical 360 MHz aromatic proton region spectra for the poly(A-U) duplex in 0.1 M phosphate (tj, = 66.5°C) at 8.2° and 44.5°C are presented in Figure 7. It is clear that the chemical shifts of the base protons vary with... 

Phosphodiester Linkages The proton noise decoupled lp nmr spectra of the daunomycin poly(dA-dT) complex in 1 M NaCl solution at 67°C have been recorded at 1 antibiotic per 6 base pairs (Nuc/D = 11.8) and 1 antibiotic per A,3 base pairs (Nuc/D = 5.9). Resolved resonances are observed for the complex at both Nuc/D ratios (Figure 32). One of the resonances in the complex exhibits a chemical shift similar to that observed for poly(dA-dT) in 1 M NaCl alone ( 4.1 ppm) at this temperature while the other resonance is shifted downfield by 0.3 ppm in the Nuc/D = 11.8 complex and by 0.45 ppm in the NucD = 5.8 complex (Table XI). The results suggest that daunomycin intercalates at either the dTgdA or dApdT sites, resulting in a downfield shift of the 31p resonance of the corresponding phosphodiester grouping at the intercalation site. 

---