Deuterium isotope effects and fractionation factors of hydrogen-bonded A:T base pairs of DNA

Deuterium isotope effects and fractionation factors of N1...H3–N3 hydrogen bonded Watson–Crick A:T base pairs of two DNA dodecamers are presented here. Specifically, two-bond deuterium isotope effects on the chemical shifts of 13C2 and 13C4, 2Δ13C2 and 2Δ13C4, and equilibrium deuterium/protium fractionation factors of H3, Φ, were measured and seen to correlate with the chemical shift of the corresponding imino proton, δH3. Downfield-shifted imino protons associated with larger values of 2Δ13C2 and 2Δ13C4 and smaller Φ values, which together suggested that the effective H3–N3 vibrational potentials were more anharmonic in the stronger hydrogen bonds of these DNA molecules. We anticipate that 2Δ13C2, 2Δ13C4 and Φ values can be useful gauges of hydrogen bond strength of A:T base pairs.