Abstract
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 ribbon-like supramolecular structures of three different guanosine derivatives: guanosine dihydrate (G), 3′,5′-O-dipropanolyl deoxyguanosine (dG(C3)2), and 3′,5′-O-isopropylideneguanosine 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...
Highlights
Molecular self-assembly can be exploited to engineer biomimetic and functional materials in aqueous and organic solutions, on surfaces and in the solid state.[1−4] Characterization of noncovalent interactions such as hydrogen bonding and CH−π interactions at the molecular level is crucial to better understand the delicate balance between the forces that hold together supramolecular structure, to establish structure−property relationships and to improve their design and function
density functional theory (DFT) calculations performed on the full crystal and extracted isolated molecules, we here investigate the role of noncovalent interactions driving the ribbon-like self-assembly in three guanosine derivatives: guanosine dihydrate G, 3′,5′-O-dipropanolyl deoxyguanosine dG(C3)[2], and 3′,5′-O-isopropylideneguanosine hemihydrate Gace
Solid-state magic-angle spinning (MAS) NMR spectroscopy has been used to identify the mode of self-assembly of guanosine derivatives; notably, 1H and 15N double-quantum (DQ) spectral patterns were used to assign quartet- and ribbonlike structures based on distinct intermolecular N−H···N and N−H···O hydrogen bonding interactions, including cases where it was not possible to obtain X-ray diffraction structures.[13,20,23]
Summary
Molecular self-assembly can be exploited to engineer biomimetic and functional materials in aqueous and organic solutions, on surfaces and in the solid state.[1−4] Characterization of noncovalent interactions such as hydrogen bonding and CH−π interactions at the molecular level is crucial to better understand the delicate balance between the forces that hold together supramolecular structure, to establish structure−. Guanosine derivatives; notably, 1H and 15N double-quantum (DQ) spectral patterns were used to assign quartet- and ribbonlike structures based on distinct intermolecular N−H···N and N−H···O hydrogen bonding interactions, including cases where it was not possible to obtain X-ray diffraction structures.[13,20,23] Figure 3 illustrates how a suite of one- and two-dimensional solid state MAS NMR spectra can be applied to characterize ribbon-like self-assembly in G. The amino protons in the type A molecule form similar hydrogen bonds with O8′(B) in the neighboring ribbon, N−H2a(A)···O8′(B) (Figure 6, side view−gray shading), though the hydrogen-bonding distance is longer (3.13 Å as compared to 2.99 Å), resulting in a difference in the ΔδiCso−M values for H2a of nearly 2 ppm. A NMR crystallography approach has been employed to quantitatively unravel the role of specific intermolecular interaction by means of GIPAW DFT calculated NMR chemical shifts on full crystal vs isolated molecules for the two crystallographically independent molecules in each guanosine derivative.
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