Multinuclear NMR Investigations of the Oxygen, Water, and Hydroxyl Environments in Sodium Hexaniobate

Alam, Todd M.; Nyman, May; Cherry, Brian R.; Segall, Judith M.; Lybarger, Leslie E.

doi:10.1021/ja0398159

Cited by 102 publications

(88 citation statements)

References 48 publications

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“…2 This resolution is sufficient, for example, to identify correlation peaks due to proton-proton proximities in two-dimensional 1 H double-quantum ͑DQ͒ MAS spectra, with applications including probing hydrogen bonding in self-assembled polymeric structures, 3 pharmaceutical systems, 4 small biomolecules 5 and inorganic complexes, 6 as well as the role of aromatic -interactions in determining packing 7,8 and host-guest interactions for a molecular tweezer. 9 Understanding the factors that determine 1 H resolution in solid-state NMR is key to further applications of 1 H NMR to new structural problems.…”

Section: Introductionmentioning

confidence: 99%

Origins of linewidth in H1 magic-angle spinning NMR

Zorin

Brown

Hodgkinson

2006

The Journal of Chemical Physics

125

116

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A detailed study of the factors determining the linewidth (and hence resolution) in H1 solid-state magic-angle spinning NMR is described. Although it has been known from the early days of magic-angle spinning (MAS) that resolution of spectra from abundant nuclear spins, such as H1, increases approximately linearly with increasing sample rotation rate, the difficulty of describing the dynamics of extended networks of coupled spins has made it difficult to predict a priori the resolution expected for a given sample. Using recently developed, highly efficient methods of numerical simulation, together with experimental measurements on a variety of test systems, we propose a comprehensive picture of H1 resolution under MAS. The “homogeneous” component of the linewidth is shown to depend primarily on the ratio between an effective local coupling strength and the spin rate, modified by geometrical factors which loosely correspond to the “dimensionality” of the coupling network. The remaining “inhomogeneous” component of the natural linewidth is confirmed to have the same properties as in dilute-spin NMR. Variations in the NMR frequency due to chemical shift effects are shown to have minimal impact on H1 resolution. The implications of these results for solid-state NMR experiments involving H1 and other abundant-spin nuclei are discussed.

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Section: Introductionmentioning

confidence: 99%

Origins of linewidth in H1 magic-angle spinning NMR

Zorin

Brown

Hodgkinson

2006

The Journal of Chemical Physics

125

116

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“…However, advances such as fast MAS and improved homonuclear decoupling techniques have led to increased resolution for organic compounds. [6] In particular, 1 H double-quantum (DQ) MAS NMR spectroscopy [6][7][8] has become a powerful approach, providing valuable information about, for example, a molecular tweezer host-guest complex, [9] intramolecular hydrogen-bonding in a biological molecule, [10] water and hydroxy-group environments in polyoxoniobate materials, [11] and surface organometallic species.[12] More recently, the 1 H DQ CRAMPS (combined rotation and multiple-pulse spectroscopy) technique [13][14][15] has been shown to dramatically increase resolution, thus allowing well-resolved spectra to be obtained for model compounds. [13][14][15][16] Herein, we show how the presence of a specific pseudopolymorph of an API containing about 20 carbon atoms is identified in a tablet formulation using 1 H DQ CRAMPS NMR spectroscopy.…”

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confidence: 99%

Distinguishing Anhydrous and Hydrous Forms of an Active Pharmaceutical Ingredient in a Tablet Formulation Using Solid‐State NMR Spectroscopy

2007

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The phenomena of polymorphism and pseudopolymorphism (the formation of hydrates/solvates) and their influence on the chemical and physical properties of molecular crystals are well known.[1] This is especially true for pharmaceutical compounds, where polymorphic or pseudopolymorphic changes in active pharmaceutical ingredients (APIs) can have significant effects on bioavailability.[2] Identification and characterization of (pseudo-)polymorphs is therefore essential during all stages of the development and manufacture of pharmaceuticals; of key importance is the form adopted in a tablet formulation in which the API is combined with a mixture of filler compounds (excipients).13 C cross-polarization (CP) magic-angle spinning (MAS) solid-state NMR spectroscopy has proven itself as a powerful workhorse experiment for this purpose; [3][4][5] however, very little use has been made of 1 H solid-state NMR spectroscopy due to the large anisotropic broadening that results from extensive dipolar-coupled proton networks. However, advances such as fast MAS and improved homonuclear decoupling techniques have led to increased resolution for organic compounds. [6] In particular, 1 H double-quantum (DQ) MAS NMR spectroscopy [6][7][8] has become a powerful approach, providing valuable information about, for example, a molecular tweezer host-guest complex, [9] intramolecular hydrogen-bonding in a biological molecule, [10] water and hydroxy-group environments in polyoxoniobate materials, [11] and surface organometallic species.[12] More recently, the 1 H DQ CRAMPS (combined rotation and multiple-pulse spectroscopy) technique [13][14][15] has been shown to dramatically increase resolution, thus allowing well-resolved spectra to be obtained for model compounds. [13][14][15][16] Herein, we show how the presence of a specific pseudopolymorph of an API containing about 20 carbon atoms is identified in a tablet formulation using 1 H DQ CRAMPS NMR spectroscopy. This is demonstrated for an API currently under development, using only 30 mg of sample, and with no need for special preparation (that is, isotopic labeling). We present high-resolution 2D NMR spectra recorded in under two hours, a time equivalent to that needed for a high-quality 1D 13 C CP MAS spectrum. 1 H DQ CRAMPS NMR spectra, recorded using the pulse sequence in reference [15], of pure anhydrous and monohydrate forms of the API are shown in Figure 1 a and 1 b, respectively. For the monohydrate form, broader signals indicate a slightly less crystalline sample. X-ray single-crystal structure analyses reveal different intermolecular hydrogen- Figure 1. 600 MHz 1 H DQ CRAMPS NMR spectra together with skyline projections of a) the anhydrous and b) the monohydrate form of the API under consideration. The pair of DQ signals in both spectra corresponding to the intramolecular proximity of hydrogen-bonded protons with high-ppm resonance signals to the same nearby proton are highlighted. Each spectrum was recorded in 105 min. Base contours are shown at 11 % of maximum intensity. All axe...

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“…16,19,[35][36][37] The species NbO 3 − is a hypothetical species which was mentioned in few solubility studies 38,39 Equilibria involving hexaniobates and other minor species which would be more extractible cannot be excluded, but given the current knowledge on polyoxoniobate chemistry, the extraction of hexaniobates seems the most likely mechanism at a pH higher than ∼10. Therefore, reaction (5) can be considered to be a rational basis to describe the extraction of Nb(V) with methyltrioctylammonium chloride from alkaline media.…”

Section: Solvent Extraction Proceduresmentioning

confidence: 99%