Category Archives: natural abundance

Structural Elucidation of Amorphous Photocatalytic Polymers from Dynamic Nuclear Polarization Enhanced Solid State NMR #DNPNMR

Brownbill, Nick J., Reiner Sebastian Sprick, Baltasar Bonillo, Shane Pawsey, Fabien Aussenac, Alistair J. Fielding, Andrew I. Cooper, and Frédéric Blanc. “Structural Elucidation of Amorphous Photocatalytic Polymers from Dynamic Nuclear Polarization Enhanced Solid State NMR.” Macromolecules 51, no. 8 (April 24, 2018): 3088–96. 

https://doi.org/10.1021/acs.macromol.7b02544

Dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (NMR) offers a recent approach to dramatically enhance NMR signals and has enabled detailed structural information to be obtained in a series of amorphous photocatalytic copolymers of alternating pyrene and benzene monomer units, the structures of which cannot be reliably established by other spectroscopic or analytical techniques. Large 13C cross-polarization (CP) magic angle spinning (MAS) signal enhancements were obtained at high magnetic fields (9.4− 14.1 T) and low temperature (110−120 K), permitting the acquisition of a 13C INADEQUATE spectrum at natural abundance and facilitating complete spectral assignments, including when small amounts of specific monomers are present. The high 13C signal-to-noise ratios obtained are harnessed to record quantitative multiple contact CP NMR data, used to determine the polymers’ composition. This correlates well with the putative pyrene:benzene stoichiometry from the monomer feed ratio, enabling their structures to be understood.

High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy

Rossini, A.J., et al., High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy. J Magn Reson, 2015. 259: p. 192-8.

http://www.ncbi.nlm.nih.gov/pubmed/26363582

We demonstrate that high field (9.4 T) dynamic nuclear polarization (DNP) at cryogenic ( approximately 100 K) sample temperatures enables the rapid acquisition of natural abundance (1)H-(2)H cross-polarization magic angle spinning (CPMAS) solid-state NMR spectra of organic solids. Spectra were obtained by impregnating substrates with a solution of the stable DNP polarizing agent TEKPol in tetrachloroethane. Tetrachloroethane is a non-solvent for the solids, and the unmodified substrates are then polarized through spin diffusion. High quality natural abundance (2)H CPMAS spectra of histidine hydrochloride monohydrate, glycylglycine and theophylline were acquired in less than 2h, providing direct access to hydrogen chemical shifts and quadrupolar couplings. The spectral resolution of the (2)H solid-state NMR spectra is comparable to that of (1)H spectra obtained with state of the art homonuclear decoupling techniques.

Hyperpolarized NMR of plant and cancer cell extracts at natural abundance

Dumez, J.N., et al., Hyperpolarized NMR of plant and cancer cell extracts at natural abundance. Analyst, 2015. 140(17): p. 5860-3.

http://www.ncbi.nlm.nih.gov/pubmed/26215673

Natural abundance (13)C NMR spectra of biological extracts are recorded in a single scan provided that the samples are hyperpolarized by dissolution dynamic nuclear polarization combined with cross polarization. Heteronuclear 2D correlation spectra of hyperpolarized breast cancer cell extracts can also be obtained in a single scan. Hyperpolarized NMR of extracts opens many perspectives for metabolomics.

High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy

Rossini, A.J., et al., High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy. J. Magn. Reson., 2015. 259: p. 192-198.

http://dx.doi.org/10.1016/j.jmr.2015.08.020

We demonstrate that high field (9.4 T) dynamic nuclear polarization (DNP) at cryogenic (∼100 K) sample temperatures enables the rapid acquisition of natural abundance 1H–2H cross-polarization magic angle spinning (CPMAS) solid-state NMR spectra of organic solids. Spectra were obtained by impregnating substrates with a solution of the stable DNP polarizing agent TEKPol in tetrachloroethane. Tetrachloroethane is a non-solvent for the solids, and the unmodified substrates are then polarized through spin diffusion. High quality natural abundance 2H CPMAS spectra of histidine hydrochloride monohydrate, glycylglycine and theophylline were acquired in less than 2 h, providing direct access to hydrogen chemical shifts and quadrupolar couplings. The spectral resolution of the 2H solid-state NMR spectra is comparable to that of 1H spectra obtained with state of the art homonuclear decoupling techniques.

Quantitative Structural Constraints for Organic Powders at Natural Isotopic Abundance Using Dynamic Nuclear Polarization Solid-State NMR Spectroscopy

Mollica, G., et al., Quantitative Structural Constraints for Organic Powders at Natural Isotopic Abundance Using Dynamic Nuclear Polarization Solid-State NMR Spectroscopy. Angewandte Chemie, 2015. 127(20): p. 6126-6129.

http://dx.doi.org/10.1002/ange.201501172

A straightforward method is reported to quantitatively relate structural constraints based on 13C–13C double-quantum build-up curves obtained by dynamic nuclear polarization (DNP) solid-state NMR to the crystal structure of organic powders at natural isotopic abundance. This method relies on the significant gain in NMR sensitivity provided by DNP (approximately 50-fold, lowering the experimental time from a few years to a few days), and is sensitive to the molecular conformation and crystal packing of the studied powder sample (in this case theophylline). This method allows trial crystal structures to be rapidly and effectively discriminated, and paves the way to three-dimensional structure elucidation of powders through combination with powder X-ray diffraction, crystal-structure prediction, and density functional theory computation of NMR chemical shifts.

Natural Abundance N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine-Carboxyl-Linked Immobilized Dirhodium Catalyst

Gutmann, T., et al., Natural Abundance N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine-Carboxyl-Linked Immobilized Dirhodium Catalyst. Chemistry, 2015: p. n/a-n/a.

http://www.ncbi.nlm.nih.gov/pubmed/25620003

A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh2 (OAc)4 ) units, which are covalently linked to amine- and carboxyl-bifunctionalized mesoporous silica (SBA-15NH2 COOH). It shows good efficiency in catalyzing the cyclopropanation reaction of styrene and ethyl diazoacetate (EDA) forming cis- and trans-1-ethoxycarbonyl-2-phenylcyclopropane. To characterize the structure of this catalyst and to confirm the successful immobilization, heteronuclear solid-state NMR experiments have been performed. The high application potential of dynamic nuclear polarization (DNP) NMR for the analysis of binding sites in this novel catalyst is demonstrated. Signal-enhanced 13 C CP MAS and 15 N CP MAS techniques have been employed to detect different carboxyl and amine binding sites in natural abundance on a fast time scale. The interpretation of the experimental chemical shift values for different binding sites has been corroborated by quantum chemical calculations on dirhodium model complexes.

Towards structure determination of self-assembled peptides using dynamic nuclear polarization enhanced solid-state NMR spectroscopy

Takahashi, H., et al., Towards structure determination of self-assembled peptides using dynamic nuclear polarization enhanced solid-state NMR spectroscopy. Angew Chem Int Ed Engl, 2013. 52(27): p. 6979-82.

http://www.ncbi.nlm.nih.gov/pubmed/23564735

Bio-inspired self-assemblies made of peptide building blocks have great potential for nanotechnology ranging from biological and pharmaceutical applications to (opto)electronics. With these goals, a variety of peptide nanoassemblies have been studied and designed over the last few decades. Inevitably, structural studies at an atomic scale are crucial to unravel the mechanisms that drive nanoassembly formation as well as to relate these structures to their physical and chemical properties. However, structure determination at an atomic level is challenging essentially because of the difficulty associated with using X-ray crystallography on such nanoassemblies.

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