Fig. 3. 19F (A) and 1H/1H DQFCOSY (B) NMR spectra of single-stranded RNA 5′-GGCAG(2′-OCF3-A)GGC. For the 2′-OCF3 adenosine moiety, the 3-bond scalar coupling constant of H1′ and H2′ (3JH1′-H2′) was extracted from the corresponding crosspeak and amounted to 5.9 Hz. Assuming a pure C2′/C3′-endo equilibrium, this value is correlated to a C2′-endo (South) population of 58%.38,40 (C) 1H NMR spectrum of the self-complementary 8 nt RNA with 2′-OCF3-A group (red); 3JH1′–H2′ is smaller than 1 Hz, consistent with prevalent C3′-endo conformation in the double helix. Conditions: c(RNA) = 0.3 mM; 15 mM Na[AsO2(CH3)2]·3H2O, 25 mM NaCl, 3 mM NaN3, in D2O, pH 6.5, 296 K.
