Interplay of Noncovalent Interactions in Ribbon-like Guanosine Self-Assembly: An NMR Crystallography Study

An NMR crystallography study shows how intermolecular N−H··· O, N−H···N, O−H···N, O−H···O, and CH−π interactions stabilize the ribbonlike supramolecular structures of three different guanosine derivatives: guanosine dihydrate (G), 3′,5′-O-dipropanolyl deoxyguanosine (dG(C3)2), and 3′,5′-Oisopropylideneguanosine hemihydrate (Gace). Experimental solid-state 1H NMR spectra obtained at 20 T using fast magic-angle spinning (MAS), here at 75 kHz, are presented for a dihydrate of G. For each guanosine derivative, the role of specific interactions is probed by means of NMR chemical shifts calculated using the density functional theory (DFT) gauge-including projector-augmented wave (GIPAW) approach for the full crystal and extracted isolated single molecules. Specifically, the isolated molecule to full crystal transformations result in net changes in the GIPAW calculated 1H NMR chemical shifts of up to 8 ppm for O− H···O, up to 6.5 ppm for N−H···N and up to 4.6 ppm for N−H···O hydrogen bonds; notably, the presence of water molecules in G and Gace reinforces the molecular stacking through strong O−H···O hydrogen bonds. The sugar conformations are markedly different in G, dG(C3)2, and Gace, and it is shown that the experimental 13C solid-state NMR chemical shift at the C8 position is a reliable indicator of a “syn” (>135 ppm) or “anti” (<135 ppm) conformer.