13C-detected NMR experiments for measuring chemical shifts and coupling constants in nucleic acid bases

The paper presents a set of two-dimensional experiments that utilize direct 13 C detection to provide proton-carbon, carbon-carbon and carbon-nitrogen correlations in the bases of nucleic acids. The set includes a C-13-detected proton-carbon correlation experiment for the measurement of C-13-C-13 couplings, the CaCb experiment for correlating two quaternary carbons, the HCaCb experiment for the C-13-C-13 correlations in cases where one of the carbons has a proton attached, the HCC-TOCSY experiment for correlating a proton with a network of coupled carbons, and a C-13-detected C-13-N-15 correlation experiment for detecting the nitrogen nuclei that cannot be detected via protons. The IPAP procedure is used for extracting the carbon-carbon couplings and/or carbon decoupling in the direct dimension, while the (SE)-E-3 procedure is preferred in the indirect dimension of the carbon-nitrogen experiment to obtain the value of the coupling constant. The experiments supply accurate values of (13) C and N-15 chemical shifts and carbon-carbon and carbon nitrogen coupling constants. These values can help to reveal structural features of nucleic acids either directly or via induced changes when the sample is dissolved in oriented media.