The build-up of intensity-as a function of the number, n(rcpl), of POST-C7 elements used for the excitation and reconversion of double-quantum (DQ) coherence (DQC)-is analysed for the fifteen distinct DQ correlation peaks that are observed experimentally for the eight separate (1)H resonances in a (1)H (500 MHz) DQ CRAMPS solid-state (12.5 kHz MAS) NMR spectrum of the dipeptide beta-AspAla (S. P. Brown, A. Lesage, B. Elena, and L. Emsley, J. Am. Chem. Soc., 2004, 126, 13230). The simulation in SPINEVOLUTION (M. Veshtort and R. G. Griffin, J. Magn. Reson., 2006, 178, 248) of t(1) ((1)H DQ evolution) FIDs for clusters of eight dipolar-coupled protons gives separate simulated (1)H DQ build-up curves for the CH(2)(a), CH(2)(b), CH(Asp), CH(Ala), NH and OH (1)H single-quantum (SQ) (1)H resonances. An analysis of both the simulated and experimental (1)H DQ build-up leads to the following general observations: (i) considering the build-up of (1)H DQ peaks at a particular SQ frequency, maximum intensity is observed for the DQC corresponding to the shortest H-H distance; (ii) for the maximum intensity (1)H DQ peak at a particular SQ frequency, the recoupling time for the observed maximum intensity depends on the corresponding H-H distance, e.g., maximum intensity for the CH(2)(a)-CH(2)(b) (H-H distance = 1.55 A) and OH-CH(Asp) (H-H distance = 2.49 A) DQ peaks is observed at n(rcpl) = 2 and 3, respectively; (iii) for DQ peaks involving a CH(2) proton at a non-CH(2) SQ frequency, there is much reduced intensity and a maximum intensity at a short recoupling time; (iv) for the other lower intensity (1)H DQ peaks at a particular SQ frequency, maximum intensity is observed for the same (or close to the same) recoupling time, but the relative intensity of the DQ peaks is a reliable indicator of the relative H-H distance-the ratio of the maximum intensities for the peaks at the CH(Ala) SQ frequency due to the two DQCs with the NH and OH protons are found to be approximately in the ratio of the squares of the corresponding dipolar coupling constants. While the simulated (1)H DQ build-up curves reproduce most of the features of the experimental curves, maximum intensity is often observed at a longer recoupling time in simulations. In this respect, simulations for two to eight spins show a trend towards a faster decay for an increasing number of considered spins. Finally, simulations show that increasing either the Larmor frequency (to 1 GHz) or the MAS frequency (to 125 kHz) does not lead to changes in the marked differences between the (1)H DQ build-up curves at the CH(Asp) SQ frequency for DQCs to the CH(2)(a) and OH protons that correspond to similar H-H distances (2.39 A and 2.49 A, respectively).

14N–1H heteronuclear multiple-quantum correlation (HMQC) solid-state magic-angle spinning (MAS) NMR spectra recorded at a 1H Larmor frequency of 850 MHz are presented for the dipeptide β-AspAla. A modified version of the pulse sequence presented by Gan et al. (Chem. Phys. Lett. 435 (2007) 163) that utilises rotary resonance recoupling (R3) at the n = 2 condition (ν 1 = 2ν R ) is employed. Spectra recorded with a short recoupling period (under 200 μs) show two correlation peaks corresponding to the NH and NH3 moieties in the dipeptide. The quadrupolar product, P Q = C Q √ [1 + (η Q 2/3)], is determined experimentally as 3.1 MHz (NH) and 1.0 MHz (NH3) by a comparison of the 14N and 15N isotropic chemical shifts which differ due to the isotropic second-order quadrupolar shift for the spin I = 1 14N nucleus. It is shown that the peak sensitivities increase markedly upon increasing the MAS frequency from 30 to 45 to 60 kHz due to a combination of the reduced residual dipolar broadening of the 1H resonances and a lengthening of the coherence lifetimes under R 3 recoupling. Increasing the recoupling period leads to the observation of additional peaks corresponding to longer range intra- and intermolecular NH proximities. Reasonable agreement is evident upon comparing the experimental build-up of correlation peak intensity to that observed for eight-spin density-matrix simulations.

An NMR crystallography approach that combines experimental solid-state magic-angle-spinning (MAS) NMR with calculation is applied to the  polymorph of the pharmaceutical molecule, indomethacin. First-principles calculations (GIPAW) for the full crystal structure and an isolated molecule show changes in the 1 H chemical shift for specific aliphatic and aromatic protons of over 1 ppm that are due to intermolecular CH- interactions. For the OH proton, 1 H double-quantum (DQ) CRAMPS (combined rotation and multiple-pulse spectroscopy) spectra reveal intermolecular H-H proximities to the OH proton of the carboxylic acid dimer as well as to specific aromatic CH protons.

Commercially available palladium acetate often contains two major impurities, whose presence can impact the overall catalytic efficacy. This systematic study provides a comparison of the differences in catalytic activity of pure palladium acetate, Pd3(OAc)6, with the two impurities: Pd3(OAc)5(NO2) and polymeric [Pd(OAc)2]n in a variety of cross-coupling reactions. The solid state (13)C NMR spectra of all three compounds in conjunction with DFT calculations confirm their reported geometries.

The anhydrous crystalline forms of Naproxen [(S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid], (NAPRO-A) and its sodium salt (NAPRO-S), widely used anti-inflammatory drugs, have been investigated by means of 1D and 2D MAS NMR and density functional theory (DFT) based calculations. From calculations, 1D 13 C CP MAS and 1 H CRAMPS and 2D 1 H− 13 C MAS-J-HMQC, refocused INEPT, FSLG-HETCOR, and 1 H− 1 H DQ-CRAMPS solid-state NMR experiments, 1 H and 13 C resonances have been fully assigned for NAPRO-A and -S. In the case of NAPRO-S, all of the nuclei belonging to the two inequivalent molecules of the asymmetric cell gave rise to distinct signals, which could be completely assigned. Interesting intermolecular ring current effects on 1 H chemical shifts have been experimentally observed for the two samples, even if with significant differences between the two cases. The measured and calculated proton chemical shift values showed a very good agreement for both NAPRO-A and -S, allowing us to correlate the different ring current effects with the crystal structures. The comparison between the proton chemical shifts calculated in the crystal structures and in vacuo allowed us to confirm the mainly intermolecular character of the ring current effects and to quantify them. ■ INTRODUCTIONThe elucidation of local structural features of molecules in the solid phase and of their crystal packing is of much interest for all of the applications involving solid systems, from both the chemical synthesis and crystal engineering point of view. 1 In the solid state, molecular interactions, ranging from strong hydrogen bonds to weak aromatic σ−π/π−π interactions, have been shown to define the molecular arrangement and consequently the properties of the material.Solid-state nuclear magnetic resonance spectroscopy (SSNMR) has established itself as a technique of primary importance for the investigation of structural properties and intermolecular interactions in solid systems. Moreover, the combination of SSNMR and suitable computational methods is at present a very powerful approach for the characterization of crystalline solids, as proven by the development of "NMR crystallography". 2 Important intermolecular aspects, for which SSNMR provides very detailed information, are the interactions involving the π electron density of aromatic moieties. The ring current effects of the π electron density are known since the beginning of proton NMR. Even if they have been extensively studied, their intermolecular actions in the solid state are still of noticeable interest. 3−5 Moreover, the study of ring current effects on proton chemical shifts in the solid state requires very high spectral resolution, 6−8 which can be achieved by specific techniques, based on fast magic angle spinning (MAS) and multiple pulse sequences for homonuclear decoupling, 9−13 which are currently continuously improved.Since most drug formulations are solid and different solid forms can show very different properties, the investigation of crystal structure is of particular int...

A microporous silicoaluminophosphate with a novel topology type, STA-20, has been prepared via a dual templating method using hexamethylene bisdiazabicyclooctane (diDABCO-C6) and trimethylamine as co-templates. Its structure has been solved and 2 confirmed using a multi-technique approach that included the use of a hypothetical zeolite database to obtain a candidate starting structure, followed by scanning transmission electron microscopy with annular dark field imaging and Rietveld refinement. STA-20 is a member of the ABC-6 family of zeotype structures. The structure has trigonal symmetry, P-31c, with a = 13.15497(18) Å and c = 30.5833(4) Å in the calcined form. It has a 12-layer stacking sequence of 6-rings (6Rs), AABAABAACAAC(A), which contains single and double 6R units. As well as d6r, can and gme cages, STA-20 possesses the longest cage observed in an ordered ABC-6 material, giving a 3D-connected pore system limited by 8R windows. Models for the location of the templates within cages of the framework were obtained by combining elemental analysis, 13 C MAS NMR, computer modelling and Rietveld refinement.

Small pore aluminosilicate zeolites are attractive targets for synthesis because of their activity as catalysts in important reactions, including ammonia-mediated selective catalytic reduction (SCR) of NOx in auto-exhaust emissions. Such a zeolite with SWY framework type, previously observed as a silicoaluminophosphate, has been prepared highly crystalline via designed syntheses employing organic 1,8-(1,4-diazabicyclo[2.2.2]octane)octyl (diDABCO-C8) and K + cations as templates. STA-30 (St Andrews microporous material 30) is an ABC-6 structure in the erionite-offretite family of zeolites that exhibits the 12-layer stacking sequence AABAABAACAAC. The framework, which can be prepared with controllable Si/Al ratio, possesses columns of alternating d6r units and can cages, the latter oriented to give an inter-column pore space comprising gme cages and swy cages connected via 8Rs. DiDABCO-C8 cations fill the swy cages of as-prepared STA-30 while K + cations display high occupancy in the can cages. Removal of template by calcination, followed by ammonium ion exchange 2 of K + cations residing outside the can cages and subsequent deammoniation, gives a highly crystalline zeolite (K3H6Al9Si72O144, P63/mmc, a = 12.9922(9) Å, c = 29.9624(12) Å) with solid acidity shown by solid state 1 H MAS NMR. Upon hydration, a portion of the Al adopts octahedral geometry, as demonstrated by two sharp resonances at −2.0 ppm and −3.1 ppm in the 27 Al MAS NMR. These octahedral species can be converted back to tetrahedral Al by ammonium exchange and are interpreted as distinct hydrated framework Al sites. The activated K,H-STA-30 is a small pore solid acid with a three-dimensionally connected micropore volume of 0.31 cm 3 g −1 . In the copper-loaded form it is an active catalyst for the SCR of NO by ammonia.

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