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3. Temperature-induced mobility in Octacalcium Phosphate impacts crystal symmetry: water dynamics studied by NMR crystallography

Author

Nelson, Adam, primary, Papawassiliou, Wassilios, additional, Paul, Subhradip, additional, Hediger, Sabine, additional, Hung, Ivan, additional, Gan, Zhehong, additional, Venkatesh, Amrit, additional, Franks, W. Trent, additional, Smith, Mark E., additional, Gajan, David, additional, De Paëpe, Gaël, additional, Bonhomme, Christian, additional, Laurencin, Danielle, additional, and Gervais, Christel, additional

Published
2024
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4. From single-site tantalum complexes to nanoparticles of Ta x N y and TaO x N y supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy

Author

Mohandas, Janet C, Abou-Hamad, Edy, Callens, Emmanuel, Samantaray, Manoja K, Gajan, David, Gurinov, Andrei, Ma, Tao, Ould-Chikh, Samy, Hoffman, Adam S, Gates, Bruce C, and Basset, Jean-Marie

Subjects
Bioengineering, Nanotechnology, Chemical Sciences
Abstract

Air-stable catalysts consisting of tantalum nitride nanoparticles represented as a mixture of Ta x N y and TaO x N y with diameters in the range of 0.5 to 3 nm supported on highly dehydroxylated silica were synthesized from TaMe5 (Me = methyl) and dimeric Ta2(OMe)10 with guidance by the principles of surface organometallic chemistry (SOMC). Characterization of the supported precursors and the supported nanoparticles formed from them was carried out by IR, NMR, UV-Vis, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopies complemented with XRD and high-resolution TEM, with dynamic nuclear polarization surface enhanced NMR spectroscopy being especially helpful by providing enhanced intensities of the signals of 1H, 13C, 29Si, and 15N at their natural abundances. The characterization data provide details of the synthesis chemistry, including evidence of (a) O2 insertion into Ta-CH3 species on the support and (b) a binuclear to mononuclear transformation of species formed from Ta2(OMe)10 on the support. A catalytic test reaction, cyclooctene epoxidation, was used to probe the supported nanoparticles, with 30% H2O2 serving as the oxidant. The catalysts gave selectivities up to 98% for the epoxide at conversions as high as 99% with a 3.4 wt% loading of Ta present as Ta x N y /TaO x N y .

Published
2017

6. Highly Selective and Efficient Perdeuteration of n‐Pentane via H/D Exchange Catalyzed by a Silica‐Supported Hafnium‐Iridium Bimetallic Complex

Author

Pichugov, Andrey V., primary, Escomel, Léon, additional, Lassalle, Sébastien, additional, Petit, Julien, additional, Jabbour, Ribal, additional, Gajan, David, additional, Veyre, Laurent, additional, Fonda, Emiliano, additional, Lesage, Anne, additional, Thieuleux, Chloé, additional, and Camp, Clément, additional

Published
2024
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7. Reversible transformation of sub-nanometer Ga-based clusters to isolated [4]Ga(4Si) sites creates active centers for propane dehydrogenation

Author

Chen, Zixuan, primary, Serykh, Alexander I., additional, Kierzkowska, Agnieszka, additional, Gajan, David, additional, Docherty, Scott R., additional, Yakimov, Alexander V., additional, Abdala, Paula M., additional, Copéret, Christophe, additional, Florian, Pierre, additional, Fedorov, Alexey, additional, and Müller, Christoph R., additional

Published
2024
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8. The Nature of Secondary Interactions at Electrophilic Metal Sites of Molecular and Silica-Supported Organolutetium Complexes from Solid-State NMR Spectroscopy

Author

Conley, Matthew P, Lapadula, Giuseppe, Sanders, Kevin, Gajan, David, Lesage, Anne, del Rosal, Iker, Maron, Laurent, Lukens, Wayne W, Copéret, Christophe, and Andersen, Richard A

Subjects
Inorganic Chemistry, Chemical Sciences, General Chemistry, Chemical sciences, Engineering
Abstract

Lu[CH(SiMe3)2]3 reacts with [SiO2-700] to give [(≡SiO)Lu[CH(SiMe3)2]2] and CH2(SiMe3)2. [(≡SiO)Lu[CH(SiMe3)2]2] is characterized by solid-state NMR and EXAFS spectroscopy, which show that secondary Lu···C and Lu···O interactions, involving a γ-CH3 and a siloxane bridge, are present. From X-ray crystallographic analysis, the molecular analogues Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 0-2) also have secondary Lu···C interactions. The (1)H NMR spectrum of Lu[CH(SiMe3)2]3 shows that the -SiMe3 groups are equivalent to -125 °C and inequivalent below that temperature, ΔG(⧧)(Tc = 148 K) = 7.1 kcal mol(-1). Both -SiMe3 groups in Lu[CH(SiMe3)2]3 have (1)JCH = 117 ± 1 Hz at -140 °C. The solid-state (13)C CPMAS NMR spectrum at 20 °C shows three chemically inequivalent resonances in the area ratio of 4:1:1 (12:3:3); the J-resolved spectra for each resonance give (1)JCH = 117 ± 2 Hz. The (29)Si CPMAS NMR spectrum shows two chemically inequivalent resonances with different values of chemical shift anisotropy. Similar observations are obtained for Lu[CH(SiMe3)2]3-x[O-2,6-tBu-C6H3]x (x = 1 and 2). The spectroscopic data point to short Lu···Cγ contacts corresponding to 3c-2e Lu···Cγ-Siβ interactions, which are supported by DFT calculations. Calculated natural bond orbital (NBO) charges show that Cγ carries a negative charge, while Lu, Hγ, and Siβ carry positive charges; as the number of O-based ligands increases so does the positive charge at Lu, which in turns shortens the Lu···Cγ distance. The change in NBO charges and the resulting changes in the spectroscopic and crystallographic properties show how ligands and surface-support sites rearrange to accommodate these changes, consistent with Pauling's electroneutrality concept.

Published
2016

12. Catalyst‐Free Transfer Hydrogenation from Amine‐Borane Small Oligomers.

Author

Le Moigne, Louis, Posenato, Tommaso, Gajan, David, Lesage de la Haye, Jennifer, Raynaud, Jean, and Lacôte, Emmanuel

Subjects
TRANSFER hydrogenation, OLIGOMERS, DIMERS, ALKENES, DEHYDROGENATION, MOIETIES (Chemistry), POLYCONDENSATION
Abstract

Amine‐borane dimers and oligomers with varied steric and electronic profiles were prepared via capping agent‐controlled AA/BB polycondensations. They were used for transfer hydrogenations to aldehydes, ketones, imines as well as electron‐poor alkene/alkyne moieties. The amine‐borane Lewis‐paired oligomers and the congested bis(amine‐borane)s provided the highest yields. This was likely helped by facilitated dissociation (oligomers) or H‐bond assistance. In the case of the oligomers, the second equivalent of H2 present was also engaged in the reaction. Solid‐state NMR characterization provides evidence that the boron‐containing materials obtained after transfer dehydrogenation are highly similar to those obtained from thermal dehydrogenation. The oligomers bridge the gap between simple amine‐borane molecular reductants and the poly‐amine‐boranes and provide a full picture of the reactivity changes at the different scales. [ABSTRACT FROM AUTHOR]

Published
2024
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13. Structure, Location, and Spatial Proximities of Hydroxyls on γ-Alumina Crystallites by High-Resolution Solid-State NMR and DFT Modeling: Why Edges Hold the Key

Author

Batista, Ana T. F., primary, Pigeon, Thomas, additional, Meyet, Jordan, additional, Wisser, Dorothea, additional, Rivallan, Mickael, additional, Gajan, David, additional, Catita, Leonor, additional, Diehl, Fabrice, additional, Gay, Anne-Sophie, additional, Chizallet, Céline, additional, Lesage, Anne, additional, and Raybaud, Pascal, additional

Published
2023
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14. Reversible transformation of sub-nanometer Ga-based clusters to isolated [4]Ga(4Si)sites creates active centers for propane dehydrogenationElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3cy01446k

Author

Chen, Zixuan, Serykh, Alexander I., Kierzkowska, Agnieszka, Gajan, David, Docherty, Scott R., Yakimov, Alexander V., Abdala, Paula M., Copéret, Christophe, Florian, Pierre, Fedorov, Alexey, and Müller, Christoph R.

Abstract

Ga-based propane dehydrogenation (PDH) catalysts are explored in industry as an alternative to PtSn and CrOx-based catalysts. Yet, at present, there is only limited understanding of the structural dynamics of surface sites in Ga-based PDH catalysts. Here, we employ atomic layer deposition (ALD) to engineer a sub-monolayer of Ga species on dehydroxylated silica, which serves as a model PDH catalyst. While the ALD-grown shell contains, after calcination at 500 °C, tetra- and pentacoordinate Ga3+sites with both Si and Ga atoms in the second coordination sphere (i.e., [4]Ga(Si/Ga)and [5]Ga(Si/Ga)sites), its exposure to ambient air leads to sub-nanometer GaxOy(OH)zclusters with [4]Ga(Ga)and [6]Ga(Ga)sites, due to the hydrolysis of the Ga–O–Si linkages by the moisture of ambient air. When calcining the material at 650 °C, the [4]Ga(Ga)and [6]Ga(Ga)sites evolve leading to a silica surface dominated by isolated tetracoordinate [4]Ga(4Si)sites, that is, [(SiO)3Ga(XOSi)] sites, where X is H or Si. Exposure of the dehydroxylated material with [4]Ga(4Si)sites to ambient air reforms the sub-nanometer GaxOy(OH)zclusters, indicating the reversibility of the Ga dispersion and agglomeration as a function of the extent of silica (de)hydroxylation. The presence of [4]Ga(4Si)sites coincides with a high performance in PDH, achieving an initial turnover frequency of ca.12 h−1and propene selectivity of ca.85%, while deactivating by only 34% over 20 h of time on stream. Overall, our results highlight the dynamic nature of the dispersion and agglomeration of Ga3+sites during the dehydroxylation (by calcination) and rehydration (ambient air exposure).

Published
2024
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16. Speciation and Structures in Pt Surface Sites Stabilized by N-Heterocyclic Carbene Ligands Revealed by Dynamic Nuclear Polarization Enhanced Indirectly Detected 195 Pt NMR Spectroscopic Signatures and Fingerprint Analysis

Author

Wang, Zhuoran, Völker, Laura A., Robinson, Thomas C., Kaeffer, Nicolas, Menzildjian, Georges, Jabbour, Ribal, Venkatesh, Amrit, Gajan, David, Rossini, Aaron J., Copéret, Christophe, Lesage, Anne, Centre de RMN à très hauts champs de Lyon (CRMN), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Department of Chemistry and Applied Biosciences [ETH Zürich] (D-CHAB), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich), Iowa State University (ISU), and European Project: 101008500,PANACEA

Subjects
Colloid and Surface Chemistry, DNP MAS NMR, surface catalysts, [CHIM]Chemical Sciences, DNP, General Chemistry, 195Pt NMR, DFT calculations, Biochemistry, Catalysis, NMR
Abstract

N-Heterocyclic carbenes (NHCs) are widely used ligands in transition metal catalysis. Notably, they are increasingly encountered in heterogeneous systems. While a detailed knowledge of the possibly multiple metal environments would be essential to understand the activity of metal-NHC-based heterogeneous catalysts, only a few techniques currently have the ability to describe with atomic-resolution structures dispersed on a solid support. Here, we introduce a new DNP surface enhanced solid-state NMR approach that, in combination with advanced DFT calculations, allows the structure characterization of isolated silica-supported Pt-NHC sites. Notably, we demonstrate that the signal amplification provided by DNP in combination with fast magic angle spinning enables the implementation of sensitive 13 C-195 Pt correlation experiments. By exploiting 1 J(13 C-195 Pt) couplings, 2D NMR spectra were acquired revealing two types of Pt sites. For each of them, 1 J(13 C-195 Pt) values were determined as well as 195 Pt chemical shift tensor parameters. To interpret the NMR data, DFT calculations were performed on an extensive library of molecular Pt-NHC complexes. While one surface site was identified as a bis-NHC compound, the second site most likely contains a bidentate 1,5 cyclooctadiene ligand, pointing to various parallel grafting mechanisms. The methodology described here represents a new step forward in the atomic-level description of catalytically relevant surface metal-NHC complexes. In particular, it opens up innovative avenues for exploiting the spectral signature of platinum, one of the most widely used transition metals in catalysis, but whose use for solid-state NMR remains difficult. Our results also highlight the sensitivity of 195 Pt NMR parameters to slight structural changes.

Published
2022
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17. Speciation and Structures in Pt Surface Sites Stabilized by N-Heterocyclic Carbene Ligands Revealed by Dynamic Nuclear Polarization Enhanced Indirectly Detected 195Pt NMR Spectroscopic Signatures and Fingerprint Analysis

Author

Wang, Zhuoran, primary, Völker, Laura A., additional, Robinson, Thomas C., additional, Kaeffer, Nicolas, additional, Menzildjian, Georges, additional, Jabbour, Ribal, additional, Venkatesh, Amrit, additional, Gajan, David, additional, Rossini, Aaron J., additional, Copéret, Christophe, additional, and Lesage, Anne, additional

Published
2022
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19. Off-the-Shelf Gd(NO3)3 as an Efficient High-Spin Metal Ion Polarizing Agent for Magic Angle Spinning Dynamic Nuclear Polarization

Author

Elliott, Stuart J., primary, Duff, Benjamin B., additional, Taylor-Hughes, Ashlea R., additional, Cheney, Daniel J., additional, Corley, John P., additional, Paul, Subhradip, additional, Brookfield, Adam, additional, Pawsey, Shane, additional, Gajan, David, additional, Aspinall, Helen C., additional, Lesage, Anne, additional, and Blanc, Frédéric, additional

Published
2022
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20. Multiple Surface Site Three-Dimensional Structure Determination of a Supported Molecular Catalyst

Author

Jabbour, Ribal, primary, Renom-Carrasco, Marc, additional, Chan, Ka Wing, additional, Völker, Laura, additional, Berruyer, Pierrick, additional, Wang, Zhuoran, additional, Widdifield, Cory M., additional, Lelli, Moreno, additional, Gajan, David, additional, Copéret, Christophe, additional, Thieuleux, Chloé, additional, and Lesage, Anne, additional

Published
2022
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24. Spectroscopic Signature and Structure of the Active Sites in Ziegler–Natta Polymerization Catalysts Revealed by Electron Paramagnetic Resonance

Author

Ashuiev, Anton, primary, Humbert, Matthieu, additional, Norsic, Sébastien, additional, Blahut, Jan, additional, Gajan, David, additional, Searles, Keith, additional, Klose, Daniel, additional, Lesage, Anne, additional, Pintacuda, Guido, additional, Raynaud, Jean, additional, Monteil, Vincent, additional, Copéret, Christophe, additional, and Jeschke, Gunnar, additional

Published
2021
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26. Atomic-Scale Structure and Its Impact on Chemical Properties of Aluminum Oxide Layers Prepared by Atomic Layer Deposition on Silica

Author

Kaushik, Monu, primary, Leroy, César, additional, Chen, Zixuan, additional, Gajan, David, additional, Willinger, Elena, additional, Müller, Christoph R., additional, Fayon, Franck, additional, Massiot, Dominique, additional, Fedorov, Alexey, additional, Copéret, Christophe, additional, Lesage, Anne, additional, and Florian, Pierre, additional

Published
2021
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27. The Structure of Molecular and Surface Platinum Sites Determined by DNP-SENS and Fast MAS 195Pt Solid-State NMR Spectroscopy

Author

Venkatesh, Amrit, Lund, Alicia, Rochlitz, Lukas, Jabbour, Ribal, Gordon, Christopher P., Menzildjian, Georges, Viger-Gravel, Jasmine, Gajan, David, Coperet, Christophe, Lesage, Anne, and Rossini, Aaron

Subjects
NMR data, pulse sequences
Abstract

Pulse sequences, raw 1D and 2D NMR data., Fast MAS solid-state NMR spectroscopy experiments and data analysis (AV and AJR) were supported by the National Science Foundation under Grant No. 1709972 to AJR. AV and AJR acknowledge additional support from Donors of the American Chemical Society Petroleum Research Fund (58627-DNI6). AJR acknowledges additional support from the Alfred P. Sloan Foundation through a Sloan research fellowship. LR and CPG thank the SNF (SNSF fond number: 200021_169134) and the Scholarship Fund of the Swiss Chemical Industry (SSCI) for funding, respectively. Financial support from ANR-17-CE29-0006-01 is also gratefully acknowledged.

Published
2020
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28. Spectroscopic Signature and Structure of Active Sites in Ziegler-Natta Polymerization Catalysts revealed by Electron Paramagnetic Resonance

Author

Ashuiev, Anton, primary, Humbert, Matthieu, primary, Gajan, David, primary, Norsic, Sebastien, primary, Blahut, Jan, primary, Searles, Keith, primary, Klose, Daniel, primary, Lesage, Anne, primary, Pintacuda, Guido, primary, Raynaud, Jean, primary, Monteil, Vincent, primary, Copéret, Christophe, primary, and Jeschke, Gunnar, primary

Published
2021
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33. The Structure of Molecular and Surface Platinum Sites Determined by DNP-SENS and Fast MAS 195Pt Solid-State NMR Spectroscopy

Author

Venkatesh, Amrit, primary, Lund, Alicia, additional, Rochlitz, Lukas, additional, Jabbour, Ribal, additional, Gordon, Christopher P., additional, Menzildjian, Georges, additional, Viger-Gravel, Jasmine, additional, Berruyer, Pierrick, additional, Gajan, David, additional, Copéret, Christophe, additional, Lesage, Anne, additional, and Rossini, Aaron J., additional

Published
2020
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34. Spectroscopic Signature and Structure of Active Centers in Ziegler-Natta Polymerization Catalysts revealed by Electron Paramagnetic Resonance

Author

Ashuiev, Anton, primary, Humbert, Matthieu, additional, Gajan, David, additional, Norsic, Sebastien, additional, Blahut, Jan, additional, Searles, Keith, additional, Klose, Daniel, additional, Lesage, Anne, additional, Pintacuda, Guido, additional, Raynaud, Jean, additional, Monteil, Vincent, additional, Copéret, Christophe, additional, and Jeschke, Gunnar, additional

Published
2020
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35. Atomic‐Scale Description of Interfaces between Antigen and Aluminum‐Based Adjuvants Used in Vaccines by Dynamic Nuclear Polarization (DNP) Enhanced NMR Spectroscopy

Author

Viger‐Gravel, Jasmine, primary, Paruzzo, Federico M., additional, Cazaux, Corine, additional, Jabbour, Ribal, additional, Leleu, Amandine, additional, Canini, Françoise, additional, Florian, Pierre, additional, Ronzon, Frédéric, additional, Gajan, David, additional, and Lesage, Anne, additional

Published
2020
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36. TinyPols: a family of water-soluble binitroxides tailored for dynamic nuclear polarization enhanced NMR spectroscopy at 18.8 and 21.1 T

Author

Lund, Alicia, primary, Casano, Gilles, additional, Menzildjian, Georges, additional, Kaushik, Monu, additional, Stevanato, Gabriele, additional, Yulikov, Maxim, additional, Jabbour, Ribal, additional, Wisser, Dorothea, additional, Renom-Carrasco, Marc, additional, Thieuleux, Chloé, additional, Bernada, Florian, additional, Karoui, Hakim, additional, Siri, Didier, additional, Rosay, Melanie, additional, Sergeyev, Ivan V., additional, Gajan, David, additional, Lelli, Moreno, additional, Emsley, Lyndon, additional, Ouari, Olivier, additional, and Lesage, Anne, additional

Published
2020
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38. Off-the-Shelf Gd(NO3)3as an Efficient High-Spin Metal Ion Polarizing Agent for Magic Angle Spinning Dynamic Nuclear Polarization

Author

Elliott, Stuart J., Duff, Benjamin B., Taylor-Hughes, Ashlea R., Cheney, Daniel J., Corley, John P., Paul, Subhradip, Brookfield, Adam, Pawsey, Shane, Gajan, David, Aspinall, Helen C., Lesage, Anne, and Blanc, Frédéric

Abstract

Magic angle spinning nuclear magnetic resonance spectroscopy experiments are widely employed in the characterization of solid media. The approach is incredibly versatile but deleteriously suffers from low sensitivity, which may be alleviated by adopting dynamic nuclear polarization methods, resulting in large signal enhancements. Paramagnetic metal ions such as Gd3+have recently shown promising results as polarizing agents for 1H, 13C, and 15N nuclear spins. We demonstrate that the widely available and inexpensive chemical agent Gd(NO3)3achieves significant signal enhancements for the 13C and 15N nuclear sites of [2-13C,15N]glycine at 9.4 T and ∼105 K. Analysis of the signal enhancement profiles at two magnetic fields, in conjunction with electron paramagnetic resonance data, reveals the solid effect to be the dominant signal enhancement mechanism. The signal amplification obtained paves the way for efficient dynamic nuclear polarization without the need for challenging synthesis of Gd3+polarizing agents.

Published
2022
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39. Aromatic ring dynamics, thermal activation and transient conformations of a 468 kDa enzyme by specific labeling and fast-MAS NMR

Author

Gauto, Diego, Macek, Pavel, Barducci, Alessandro, Fraga, Hugo, Hessel, Audrey, Terauchi, Tsutomu, Gajan, David, Miyanoiri, Yohei, Boisbouvier, Jérôme, Lichtenecker, Roman Josef, Kainosho, Masatsune, Schanda, Paul, Institut de biologie structurale (IBS - UMR 5075 ), Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Biophysique Statistique, Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de RMN à très hauts champs de Lyon (CRMN), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), and ANR-17-EURE-0003,CBH-EUR-GS,CBH-EUR-GS(2017)

Subjects
[SDV.BBM.BP]Life Sciences [q-bio]/Biochemistry, Molecular Biology/Biophysics, [SDV.BBM.BS]Life Sciences [q-bio]/Biochemistry, Molecular Biology/Structural Biology [q-bio.BM], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2019
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40. Dendritic polarizing agents for DNP SENS† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc03139k Click here for additional data file

Author

Liao, Wei-Chih, Ong, Ta-Chung, Gajan, David, Bernada, Florian, Sauvée, Claire, Yulikov, Maxim, Pucino, Margherita, Schowner, Roman, Schwarzwälder, Martin, Buchmeiser, Michael R., Jeschke, Gunnar, Tordo, Paul, Ouari, Olivier, Lesage, Anne, Emsley, Lyndon, and Copéret, Christophe

Subjects
Chemistry
Abstract

Dendrimer-shielded polarizing agents for the application of DNP SENS to reactive surfaces., Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP SENS) is an effective method to significantly improve solid-state NMR investigation of solid surfaces. The presence of unpaired electrons (polarizing agents) is crucial for DNP, but it has drawbacks such as leading to faster nuclear spin relaxation, or even reaction with the substrate under investigation. The latter can be a particular problem for heterogeneous catalysts. Here, we present a series of carbosilane-based dendritic polarizing agents, in which the bulky dendrimer can reduce the interaction between the solid surface and the free radical. We thereby preserve long nuclear T′2 of the surface species, and even successfully enhance a reactive heterogeneous metathesis catalyst.

Published
2016

41. Atomic-level organization of vicinal acid–base pairs through the chemisorption of aniline and derivatives onto mesoporous SBA15† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc01229a

Author

Hamzaoui, Bilel, Bendjeriou-Sedjerari, Anissa, Pump, Eva, Abou-Hamad, Edy, Sougrat, Rachid, Gurinov, Andrei, Huang, Kuo-Wei, Gajan, David, Lesage, Anne, Emsley, Lyndon, and Basset, Jean-Marie

Subjects
Chemistry, Software_GENERAL
Abstract

The design of novel heterogeneous catalysts with multiple adjacent functionalities is of high interest to heterogeneous catalysis., The design of novel heterogeneous catalysts with multiple adjacent functionalities is of high interest to heterogeneous catalysis. Herein, we report a method to obtain a majority of bifunctional acid–base pairs on SBA15. Aniline reacts with SBA15 by opening siloxane bridges leading to N-phenylsilanamine–silanol pairs. In contrast with ammonia treated surfaces, the material is stable under air/moisture. Advanced solid state MAS NMR (2D 1H–1H double-quantum, 1H–13C HETCOR) experiments and dynamic nuclear polarization enhanced 29Si and 15N spectra demonstrate both the close proximity between the two moieties and the formation of a covalent Si–N surface bond and confirm the design of vicinal acid–base pairs. This approach was successfully applied to the design of a series of aniline derivatives of bifunctional SBA15. A correlation between the substituent effects on the aromatic ring (Hammett parameters) with the kinetics of a model Knoevenagel reaction is observed.

Published
2016

42. BDPA-Nitroxide Biradicals for Efficient Dynamic Nuclear Polarization Enhanced Solid-State NMR at Magnetic Fields up to 21.1 T

Author

Gajan, David, Bussy, Agnès, Solid-State NMR Methods for Materials - Méthodes de RMN à l'état solide pour les matériaux, Institut des Sciences Analytiques (ISA), Institut de Chimie du CNRS (INC)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)

Subjects
[CHIM.ANAL] Chemical Sciences/Analytical chemistry, [CHIM.ANAL]Chemical Sciences/Analytical chemistry, [CHIM] Chemical Sciences, [CHIM]Chemical Sciences, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2018

43. From single-site tantalum complexes to nanoparticles of TaxNy and TaOxNy supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy

Author

Mohandas, Janet C., Abou-Hamad, Edy, Callens, Emmanuel, Manoja K. Samantaray, Gajan, David, Gurinov, Andrei, Ma, Tao, Ould-Chikh, Samy, Hoffman, Adam S., Gates, Bruce C., and Basset, Jean-Marie

Abstract

Air-stable catalysts consisting of tantalum nitride nanoparticles represented as a mixture of TaxNy and TaOxNy with diameters in the range of 0.5 to 3 nm supported on highly dehydroxylated silica were synthesized from TaMe5 (Me = methyl) and dimeric Ta-2(OMe)(10) with guidance by the principles of surface organometallic chemistry (SOMC). Characterization of the supported precursors and the supported nanoparticles formed from them was carried out by IR, NMR, UV-Vis, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopies complemented with XRD and high-resolution TEM, with dynamic nuclear polarization surface enhanced NMR spectroscopy being especially helpful by providing enhanced intensities of the signals of H-1, C-13, Si-29, and N-15 at their natural abundances. The characterization data provide details of the synthesis chemistry, including evidence of (a) O-2 insertion into Ta-CH3 species on the support and (b) a binuclear to mononuclear transformation of species formed from Ta-2(OMe)(10) on the support. A catalytic test reaction, cyclooctene epoxidation, was used to probe the supported nanoparticles, with 30% H2O2 serving as the oxidant. The catalysts gave selectivities up to 98% for the epoxide at conversions as high as 99% with a 3.4 wt% loading of Ta present as TaxNy/TaOxNy.

Published
2018
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46. Aromatic Ring Dynamics, Thermal Activation, and Transient Conformations of a 468 kDa Enzyme by Specific 1H–13C Labeling and Fast Magic-Angle Spinning NMR

Author

Gauto, Diego F., primary, Macek, Pavel, additional, Barducci, Alessandro, additional, Fraga, Hugo, additional, Hessel, Audrey, additional, Terauchi, Tsutomu, additional, Gajan, David, additional, Miyanoiri, Yohei, additional, Boisbouvier, Jerome, additional, Lichtenecker, Roman, additional, Kainosho, Masatsune, additional, and Schanda, Paul, additional

Published
2019
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47. Inside Back Cover: Preferential Siting of Aluminum Heteroatoms in the Zeolite Catalyst Al‐SSZ‐70 (Angew. Chem. Int. Ed. 19/2019)

Author

Berkson, Zachariah J., primary, Hsieh, Ming‐Feng, additional, Smeets, Stef, additional, Gajan, David, additional, Lund, Alicia, additional, Lesage, Anne, additional, Xie, Dan, additional, Zones, Stacey I., additional, McCusker, Lynne B., additional, Baerlocher, Christian, additional, and Chmelka, Bradley F., additional

Published
2019
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50. Innenrücktitelbild: Preferential Siting of Aluminum Heteroatoms in the Zeolite Catalyst Al‐SSZ‐70 (Angew. Chem. 19/2019)

Author

Berkson, Zachariah J., primary, Hsieh, Ming‐Feng, additional, Smeets, Stef, additional, Gajan, David, additional, Lund, Alicia, additional, Lesage, Anne, additional, Xie, Dan, additional, Zones, Stacey I., additional, McCusker, Lynne B., additional, Baerlocher, Christian, additional, and Chmelka, Bradley F., additional

Published
2019
Full Text
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