Potential and Limitations of 2D 1H-1H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids

Brus, Jiřı́; Petříčková, Hana; Dybal, Jiřı́

doi:10.1007/978-3-7091-3715-4_7

Cited by 4 publications

(5 citation statements)

References 77 publications

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“…While the H-H distances in a CH 3 or NH 3 group are similarly close as compared to that in a CH 2 group, there is usually a fast rotation of the CH 3 or NH 3 group about the CÀC or N-C bond direction at room temperature. 94,95 Such a fast rotation causes a scaling of the H-H dipolar coupling by a factor of |(1/2)(3cos 2 b À 1)|, where b is the angle between the internuclear vector and the axis of rotation, i.e., the intra-CH 3 or intra-NH 3 H-H dipolar couplings are scaled by a factor of 0.5, since b = 901. As a consequence, there is a reduced perturbing effect due to CH 3 or NH 3 groups as compared to the case for a rigid CH 2 group.…”

Section: Resultsmentioning

confidence: 99%

Determining relative proton–proton proximities from the build-up of two-dimensional correlation peaks in 1H double-quantum MAS NMR: insight from multi-spin density-matrix simulations

Bradley

Tripon

Filip

et al. 2009

Phys. Chem. Chem. Phys.

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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).

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Section: Resultsmentioning

confidence: 99%

Determining relative proton–proton proximities from the build-up of two-dimensional correlation peaks in 1H double-quantum MAS NMR: insight from multi-spin density-matrix simulations

Bradley

Tripon

Filip

et al. 2009

Phys. Chem. Chem. Phys.

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“…This can be achieved by using a very short CP contact time; however, this prevents magnetization from reaching isolated non‐protonated carbons (such as unprotonated aromatic or carboxyl carbons). A promising alternative is the LG‐CP method, which greatly suppresses the 1 H‐ 1 H dipolar interactions, as confirmed by the observation of intense transient dipolar oscillation, and is further corroborated by the observation of multiplets consistent with the number of J ‐coupled protons (Brus et al, 2002). Thus, LG‐CP suppresses 1 H‐ 1 H dipolar interactions which, in turn, greatly suppress spin diffusion, allowing one to study intra‐ molecular correlations.…”

Section: Methodsmentioning

confidence: 81%

“…This arises from 1 H‐ 1 H spin exchange occurring for both z and spin‐locked transverse 1 H magnetization (as is the case under Hartmann‐Hahn CP conditions) (Hartmann and Hahn, 1962). Under sample rotation the dipolar coupling is scaled by 50% in the locked field, leading to a slowdown in the spin‐exchange by 50% during the CP processes in comparison to that experienced during standard spin‐exchange, which takes place in the z direction (Brus et al, 2002). Thus, spin diffusion takes place at a slower rate during the CP process.…”

Section: Methodsmentioning

confidence: 99%

Studying Organic Matter Molecular Assemblage within a Whole Organic Soil by Nuclear Magnetic Resonance

et al. 2008

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This work shows the applicability of two-dimensional (2D) (1)H-(13)C heteronuclear correlation (HETCOR) nuclear magnetic resonance (NMR) spectroscopy to the characterization of whole soils. A combination of different mixing times and cross polarization (CP) methods, namely Lee-Goldberg (LG)-CP and Ramp-CP are shown to afford, for the first time, intra- and inter- molecular connectivities, allowing for molecular assemblage information to be obtained on a whole soil. Our results show that, for the brackish marsh histosol under study, two isolated domains could be detected. The first domain consists of O-alkyl and aromatic moieties (lignocellulose material), while the second domain is comprised of alkyl type moieties (cuticular material). The role of these domains is discussed in terms of hydrophobic organic compound sorption within soil organic matter (SOM), including the possible effects of wetting and drying cycles.

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“…The possible formation of a 50:50 mixture between two polymorphs was ruled out by 1 H T 1 measurements which provided the same value for all 1 H atoms. 15 Indeed, according to a simplified but reliable approach, 28 the spin diffusion process averages 1 H T 1 when protons belong to the same phase or in the case of homogeneous samples on a nanometer scale. 29 On the other hand, protons with different relaxation times belong to different domains with an average 20 linear dimension of greater than about 100 Å and vice versa.…”

Section: Figmentioning

confidence: 99%

Improvement of the water solubility of tolfenamic acid by new multiple-component crystals produced by mechanochemical methods

Gaglioti¹,

Chierotti²,

Grifasi³

et al. 2014

CrystEngComm

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Tolfenamic acid (HTA) is a drug characterized by very poor water solubility (13.6 nM under acidic\ud conditions) and moderate solubility in ethanol (0.17 M). A series of new multicomponent crystals have been\ud obtained by applying mechanochemical methods (i.e. kneading) to mixtures of HTA with sodium acetate,\ud sodium carbonate, sodium hydroxide and imidazole. These reactions resulted in two salts (NaTA·0.5H2O\ud and NaTA HT Form), a co-crystal of salts (NaTA·HTA·0.5NaAc·2H2O) and two salt co-crystals\ud (NaTA·HTA·H2O/NaHCO3 and IMH-TA·HTA). Due to the lack of suitable crystals for single-crystal X-ray\ud diffraction analysis, the structural features of the samples have been characterized by solid-state NMR\ud (1H MAS, 13C CPMAS, 1H-13C FSLG LG-CP HETCOR and 15N CPMAS), IR(ATR) and Raman spectroscopy,\ud VT-XRPD and elemental analysis. The evaluation of thermal stability and dissolution behavior was\ud performed using thermogravimetry, differential scanning calorimetry and dissolution kinetic tests. The new\ud solid-state forms show better thermal stability than pure HTA and an improved dissolution rate, which is\ud most pronounced in NaTA·HTA·H2O/NaHCO3, NaTA HT Form and NaTA·0.5H2O

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Potential and Limitations of 2D 1H-1H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids

Cited by 4 publications

References 77 publications

Determining relative proton–proton proximities from the build-up of two-dimensional correlation peaks in 1H double-quantum MAS NMR: insight from multi-spin density-matrix simulations

Determining relative proton–proton proximities from the build-up of two-dimensional correlation peaks in 1H double-quantum MAS NMR: insight from multi-spin density-matrix simulations

Studying Organic Matter Molecular Assemblage within a Whole Organic Soil by Nuclear Magnetic Resonance

Improvement of the water solubility of tolfenamic acid by new multiple-component crystals produced by mechanochemical methods

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