Measurement of T1 relaxation rates of natural abundant 13C at C2′ in a non-uniformly deuterium-labelled oligo-DNA
Abstract
The T1 relaxation rate of C2′ at natural abundance of four different stereoselectively C2′ deuterio-labelled nucleotide residues [2′-2H (S): ≈85 atom% 2H; 2″-2H (R): ≈15 atom% 2H; 3′- and 5′/5″-2H: >97 atom% 2H; 4′-2H: ≈65 atom% 2H] in duplex I, d5′(1C2G34G5Ā6A7T89C10Ḡ11C12G)23′, (1.13 mM) has been measured for the first time. Only the 13C nuclei bearing both proton and deuterium have been detected by 1H–13C 2D heteronuclear experiments by filtering away all other methylene 13C nuclei. A similar experiment performed without deuterium decoupling allows the observation of 13C(2′)–2H coupling, which semiquantitatively gives information regarding the dynamics of 2′-methylene fragments in deuterated DNA duplex II with natural 13C abundance, d5′(1C2G3C4G5A6A7T8T9C10G11C12G)23′, at 2.5 mM concentration [2′-2H (S): ≈85 atom% 2H; 2″-2H (R): ≈15 atom% 2H; 3′-2H: >97 atom% 2H; 5′-2H/5″-2H (R/S) ≈50∶50 atom% 2H]. It is noteworthy that despite the concentration increase of duplex II over duplex I by two-fold, only 13C(2′)–2H coupling was observable for the former but not the 13C(5′)–2H coupling because of the sensitivity problem owing to the proximity of C5′ to the water resonance.