An NMR crystallography study of the hemihydrate of 2′, 3′-O-isopropylidineguanosine

Abstract

An NMR crystallography study of the hemihydrate of 2', 3'-O-isopropylidineguanosine (Gace) is presented, together with powder X-ray diffraction and thermogravimetric analysis. (1)H double-quantum and (14)N-(1)H HMQC spectra recorded at 850MHz and 75kHz MAS (using a JEOL 1mm probe) are presented together with a (1)H-(13)C refocused INEPT spectrum recorded at 500MHz and 12.5kHz MAS using eDUMBO-122(1)H homonuclear decoupling. NMR chemical shieldings are calculated using the GIPAW (gauge-including projector augmented wave) method; good two-dimensional agreement between calculation and experiment is observed for (13)C and (1)H chemical shifts for directly bonded CH and CH3 peaks. There are two Gace molecules in the asymmetric unit cell: differences in specific (1)H chemical shifts are rationalised in terms of the strength of CH-π and intermolecular hydrogen bonding interactions.

Co‐existence of Distinct Supramolecular Assemblies in Solution and in the Solid State

“…Specifically, 1 H NMR chemical shifts are markedly sensitive to intermolecular NH⋅⋅⋅N and NH⋅⋅⋅O hydrogen bonding interactions which interconnect Hoogsteen faces, such that structurally different assemblies (herein quartet and ribbon‐like) exhibit distinct 1 H DQ‐SQ spectral patterns, facilitating a direct identification of quartet and ribbon‐like assemblies 9c, 23. For example, 1 H DQ‐SQ correlation NMR spectra have been presented for guanosine dihydrate (G⋅2H 2 O),23b isopropylidene‐guanosine (Gace)23c and 3′, 5′‐dipropanoyl deoxyguanosine dG(C3) 2 ,23a in which there are crystal structures exhibiting different types of ribbon‐like self‐assembly. A 1 H DQ‐SQ correlation spectrum has also been presented for a lyophilised guanosine borate hydrogel in the presence of K + ions, whereby a 1 H DQ “signature” (Figure 1 of ref.…”

“…For the GaceC10⋅K⋅ Eth 8:1 complex, the observation of two sets of 1 H DQ peaks for the NH resonance at 14.8 ppm is likely due to proximity to both an NH2 and a CH8 proton (compare, for example, the 1 H DQ spectrum of Gace presented in Figure 7 of ref. 23c). …”

Determination of a complex crystal structure in the absence of single crystals: analysis of powder X-ray diffraction data, guided by solid-state NMR and periodic DFT calculations, reveals a new 2′-deoxyguanosine structural motif

“…This phenomenon is well known and can be addressed empirically either by establishing the calculated chemical shifts using eqn (2) and the least-squares fitting procedure (in which the gradient m may deviate from unity) described in the Methods section, or by using different reference shieldings for the high-ppm region and the low-ppm region of the spectrum. 11,23,81 As shown in Fig. S3,‡ when the calculated 13 C chemical shifts are established using eqn (2), the RMS deviation between calculated and experimental 13 C chemical shifts is decreased to 2.51 ppm.…”

Combining Nuclear Magnetic Resonance Spectroscopy and Density Functional Theory Calculations to Characterize Carvedilol Polymorphs

“…GIPAW method has been widely used to calculate chemical shielding constants of pharmaceutical compounds with very good accuracy. [37][38][39][40][41][42] Regarding carvedilol, which has three polymorphs and other solvates, the 13 C CP MAS spectra of forms II, III, and hydrate show that the compounds are not the same, but they are very similar. The difference between 13 C chemical shifts from solution-state and 13 C solid-state chemical shift (Fig.…”