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Multidimensional NOESY experiments targeting correlations between exchangeable imino and amino protons provide valuable information about base pairing in nucleic acids. It has been recently shown that the sensitivity of homonuclear correlations involving RNA's labile imino protons can be significantly enhanced, by exploiting the repolarization brought about by solvent exchanges. Homonuclear correlations, however, are of limited spectral resolution, and usually incapable of tackling relatively large homopolymers with repeating structures like RNAs. This study presents a heteronuclear-resolved version of those NOESY experiments, in which magnetization transfers between the aqueous solvent and the nucleic acid protons are controlled by selecting specific chemical shift combinations of a coupled 1 H- 15 N spin pair. This selective control effectively leads to a pseudo-3D version of HSQC-NOESY, but with cross-peaks enhanced by ∼2-5× as compared with conventional 2D NOESY counterparts. The enhanced signal sensitivity as well as access to both 15 N- 1 H and 1 H- 1 H NOESY dimensions can greatly facilitate RNA assignments and secondary structure determinations, as demonstrated here with the analysis of genome fragments derived from the SARS-CoV-2 virus.

While 13 C-based Incredible Natural Abundance DoublE QUAntum Transfer Experiment (INADEQUATE) experiments offer an attractive alternative for establishing molecular structures, they suffer from low sensitivities arising from the scarcity of spin pairs present at natural abundance. Herein we demonstrate that dissolution dynamic nuclear polarization (dDNP) provides sufficient sensitivity to acquire 1D 13 C INADEQUATE spectra in a single scan and at natural abundance. Moreover, if steps are adopted to endow sub-Hertz precision to these measurements, they allow one to measure carbon-carbon J couplings over both one and multiple bonds for each chemical site. As these J CC -couplings are usually sufficiently distinct to enable univocal pairing of the nuclei involved, essentially the same information as in 2D INADEQUATE can be obtained. The feasibility of the method is demonstrated for a range of compounds, including natural products such as α-pinene, menthol and limonene. Features and extensions of this approach are briefly discussed.