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, d^5′(¹C²G³⁴G⁵Ā⁶A⁷T⁸⁹C¹⁰Ḡ¹¹C¹²G)₂^3′, (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, d^5′(¹C²G³C⁴G⁵A⁶A⁷T⁸T⁹C¹⁰G¹¹C¹²G)₂^3′, 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.