Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Michel Bardet is active.

Publication


Featured researches published by Michel Bardet.


Journal of Wood Chemistry and Technology | 1984

Structural Changes in Lignin During Kraft Cooking Part 3. On the Structure of Dissolved Lignins

Danielle Robert; Michel Bardet; Göran Gellerstedt; Eva Lisa Lindfors

Abstract Two series of pine kraft lignins were prepared by a) normal kraft cooks to different pulp yield levels and precipitation of the lignins from the black liquors by acidification and b) by successive acidification of the black liquor obtained from a flow-through cook. All the lignins were extensively purified, subjected to elemental and methoxyl analysis and subsequently acetylated. Quantitative 13C-NMR analysis was carried out on acetylated samples and the results were combined with the results of phenolic group determination by means of aminolysis and with elemental analysis data. The various acetylated lignins were also subjected to analysis by size exclusion chromatography. All results are discussed with reference to known features of kraft cooking and of kraft lignins.


Journal of the American Chemical Society | 2012

Enhanced solid-state NMR correlation spectroscopy of quadrupolar nuclei using dynamic nuclear polarization.

Daniel Lee; Hiroki Takahashi; Aany Sofia Lilly Thankamony; Jean-Philippe Dacquin; Michel Bardet; Olivier Lafon; Gaël De Paëpe

By means of a true sensitivity enhancement for a solid-state NMR spectroscopy (SSNMR) experiment performed under dynamic nuclear polarization (DNP) conditions, corresponding to 4-5 orders of magnitude of time savings compared with a conventional SSNMR experiment, it is shown that it is possible to record interface-selective (27)Al-(27)Al two-dimensional dipolar correlation spectra on mesoporous alumina, an advanced material with potential industrial applications. The low efficiency of cross-polarization and dipolar recoupling for quadrupolar nuclei is completely negated using this technique. The important presence of pentacoordinated Al has not only been observed, but its role in bridging interfacial tetra- and hexacoordinated Al has been determined. Such structural information, collected at low temperature (∼103 K) and 9.4 T with the use of DNP, would have been impossible to obtain under standard conditions, even using a higher magnetic field. However, here it is demonstrated that this information can be obtained in only 4 h. This work clearly opens a new avenue for the application of SSNMR to quadrupolar nuclei and notably the atomic-scale structure determination of catalysis materials such as mesoporous alumina.


Journal of the American Chemical Society | 2013

Solid-state NMR on bacterial cells: selective cell wall signal enhancement and resolution improvement using dynamic nuclear polarization.

Hiroki Takahashi; Isabel Ayala; Michel Bardet; Gaël De Paëpe; Jean-Pierre Simorre; Sabine Hediger

Dynamic nuclear polarization (DNP) enhanced solid-state nuclear magnetic resonance (NMR) has recently emerged as a powerful technique for the study of material surfaces. In this study, we demonstrate its potential to investigate cell surface in intact cells. Using Bacillus subtilis bacterial cells as an example, it is shown that the polarizing agent 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL) has a strong binding affinity to cell wall polymers (peptidoglycan). This particular interaction is thoroughly investigated with a systematic study on extracted cell wall materials, disrupted cells, and entire cells, which proved that TOTAPOL is mainly accumulating in the cell wall. This property is used on one hand to selectively enhance or suppress cell wall signals by controlling radical concentrations and on the other hand to improve spectral resolution by means of a difference spectrum. Comparing DNP-enhanced and conventional solid-state NMR, an absolute sensitivity ratio of 24 was obtained on the entire cell sample. This important increase in sensitivity together with the possibility of enhancing specifically cell wall signals and improving resolution really opens new avenues for the use of DNP-enhanced solid-state NMR as an on-cell investigation tool.


Solid State Nuclear Magnetic Resonance | 1997

Two-dimensional spin-exchange solid-state NMR studies of 13C-enriched wood☆

Michel Bardet; Lyndon Emsley; Marc Vincendon

Two-dimensional high-resolution solid-state NMR has been used to study 13C-enriched wood. Wood is a complex material containing three major polymers: cellulose, hemicelluloses and lignin. The use of an enriched 13C-compound allows the observation of intra-molecular spin-diffusion driven by dipolar couplings. Correlations between spins at progressively longer distances have been obtained as the mixing time is increased, corresponding, for each of the separate polymer chains, to intra-unit and then to inter-unit interactions, and in the case of cellulose to inter-chain interactions. A straightforward qualitative analysis of the spin diffusion spectra is shown to yield the assignment of the carbon-13 spectrum. The cellulose resonances can all be sequentially assigned using the spin diffusion experiment. Using the experiments it is shown that, at least on a distance scale of several nanometres explored by the spin diffusion process, the three main components of wood occur in separate phases. Also, a question concerning the structure of the hemicellulose units is resolved by locating the O-acetyl group at the 2-position of the xylan chains.


Journal of The Electrochemical Society | 2007

Comparison Between E-beam and Ultraviolet Curing to Perform Porous a-SiOC : H

V. Jousseaume; Aziz Zenasni; L. Favennec; G. Gerbaud; Michel Bardet; Jean-Paul Simon; A. Humbert

Porous ultralow-k films are required by the microelectronics industry as interlayer dielectrics for 65 nm technologies and below. These porous insulating films can be deposited by plasma-enhanced chemical vapor deposition using a porogen approach. It consists of the codeposition of a matrix precursor and a sacrificial organic porogen, and then on a post-treatment to remove the organic porogen phase and create porosity in the film. In this work, an e-beam assisted thermal curing was compared to an ultraviolet-assisted thermal curing. Basic film properties such as k, film shrinkage, porosity, pore size, and pore size distribution were evaluated. NMR and Fourier transform infrared analyses were used to study the chemical modifications induced by the post-treatment. These analyses show that the post-treatment impact depends on the radiation used. Both treatments lead to a removal of terminal nonbridging bonds such as Si-OH, Si-H, and Si-CH 3 and can contribute to a subsequent formation of Si-O-Si crosslinks. Both treatments remove methyls from Si-CH 3, but the e-beam induces a Si-H bond increase while the UV bulb used decreases the Si-H contribution. The cross-linking improvement induces an increase of Youngs modulus, the elastic properties being mainly correlated to the Si-O-Si volumic bond concentration in the film.


Journal of the American Chemical Society | 2014

Untangling the Condensation Network of Organosiloxanes on Nanoparticles using 2D 29Si–29Si Solid-State NMR Enhanced by Dynamic Nuclear Polarization

Daniel Lee; Guillaume Monin; Nghia Tuan Duong; Isabel Zamanillo Lopez; Michel Bardet; Vincent Mareau; Laurent Gonon; Gaël De Paëpe

Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with organosiloxanes. Information about the surface coverage and the nature, if any, of organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear (29)Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of (29)Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D (29)Si-(29)Si correlation experiments, it is shown that the required reaction conditions favor lateral polymerization and domain growth. Moreover, the natural abundance correlation experiments permitted the estimation of (2)J(Si-O-Si)-couplings (13.8 ± 1.4 Hz for surface silica) and interatomic distances (3.04 ± 0.08 Å for surface silica) since complications associated with many-spin systems and also sensitivity were avoided. The work detailed herein not only demonstrates the possibility of using MAS-DNP to greatly facilitate the acquisition of 2D (29)Si-(29)Si correlation spectra but also shows that this technique can be used in a routine fashion to characterize surface grafting networks and gain structural constraints, which can be related to a systems chemical and physical properties.


Journal of Colloid and Interface Science | 2011

Preparation and characterization of highly stable lipid nanoparticles with amorphous core of tuneable viscosity

Thomas Delmas; Anne-Claude Couffin; Pierre‑Alain Bayle; François de Crécy; Emmanuelle Neumann; Françoise Vinet; Michel Bardet; Jérôme Bibette; Isabelle Texier

Lipid nanoparticles (LNP) have been designed based on low cost and human-use approved excipients, and manufactured by an easy, robust, and up-scalable process. Fluid colloidal dispersions or gel viscous formulations of highly stable nanoparticles (more than 12 month stability is achieved for some formulations) can be obtained. Their physicochemical properties are studied by Dynamic Light Scattering, Differential Scanning Calorimetry, and NMR. The results picture nanoparticles with a non-crystalline core, which viscosity can be finely tuned by the lipid composition and the temperature. A design of experiments has been used to investigate the limits of the system colloidal stability. The impact of core and surfactant weight fractions have been explored both experimentally and using the design of experiments. The versatility of this physicochemical system could open the way to a wide range of future pharmaceutical applications.


Magnetic Resonance in Chemistry | 1998

Distribution of erythro and threo forms of different types of β‐O‐4 structures in aspen lignin by 13C NMR using the 2D INADEQUATE experiment

Michel Bardet; Danielle Robert; Knut Lundquist; Sverker von Unge

Carbon–carbon connectivity spectra of 13C‐enriched aspen lignin recorded using the 2D INADEQUATE experiment revealed cross peaks which can be assigned to four types of arylglycerol β‐aryl ethers (β‐O‐4 structures): erythro forms of arylglycerol β‐syringyl ethers, threo forms of arylglycerol β‐syringyl ethers, erythro forms arylglycerol β‐guaiacyl ethers and threo forms of arylglycerol β‐guaiacyl ethers. The intensities of the cross peaks suggest larger amounts of β‐syringyl ethers than β‐guaiacyl ethers. The erythro isomers dominate among the β‐syringyl ethers. Erythro and threo forms of β‐guaiacyl ethers are present in similar amounts.


ACS Nano | 2012

Quenching Dynamics in CdSe Nanoparticles: Surface-Induced Defects upon Dilution.

Lucia Hartmann; Abhishek Kumar; Matthias Welker; Angela Fiore; Carine Julien-Rabant; Marina Gromova; Michel Bardet; Peter Reiss; Paul N.W. Baxter; Frédéric Chandezon; Robert B. Pansu

We have analyzed the decays of the fluorescence of colloidal CdSe quantum dots (QDs) suspensions during dilution and titration by the ligands. A ligand shell made of a combination of trioctylphosphine (TOP), oleylamine (OA), and stearic acid (SA) stabilizes the as-synthesized QDs. The composition of the shell was analyzed and quantified using high resolution liquid state 1H nuclear magnetic resonance (NMR) spectroscopy. A quenching of the fluorescence of the QDs is observed upon removal of the ligands by diluting the stock solution of the QDs. The fluorescence is restored by the addition of TOP. We analyze the results by assuming a binomial distribution of quenchers among the QDs and predict a linear trend in the time-resolved fluorescence decays. We have used a nonparametric analysis to show that for our QDs, 3.0 ± 0.1 quenching sites per QD on average are revealed by the removal of TOP. We moreover show that the quenching rates of the quenching sites add up. The decay per quenching site can be compared with the decay at saturation of the dilution effect. This provides a value of 2.88 ± 0.02 for the number of quenchers per QD. We extract the quenching dynamics of one site. It appears to be a process with a distribution of rates that does not involve the ligands.


Journal of Magnetic Resonance | 2014

Optimization of an absolute sensitivity in a glassy matrix during DNP-enhanced multidimensional solid-state NMR experiments.

Hiroki Takahashi; Carlos Fernández‐de‐Alba; Daniel Lee; Vincent Maurel; Serge Gambarelli; Michel Bardet; Sabine Hediger; Anne-Laure Barra; Gaël De Paëpe

Thanks to instrumental and theoretical development, notably the access to high-power and high-frequency microwave sources, high-field dynamic nuclear polarization (DNP) on solid-state NMR currently appears as a promising solution to enhance nuclear magnetization in many different types of systems. In magic-angle-spinning DNP experiments, systems of interest are usually dissolved or suspended in glass-forming matrices doped with polarizing agents and measured at low temperature (down to ∼100K). In this work, we discuss the influence of sample conditions (radical concentration, sample temperature, etc.) on DNP enhancements and various nuclear relaxation times which affect the absolute sensitivity of DNP spectra, especially in multidimensional experiments. Furthermore, DNP-enhanced solid-state NMR experiments performed at 9.4 T are complemented by high-field CW EPR measurements performed at the same magnetic field. Microwave absorption by the DNP glassy matrix is observed even below the glass transition temperature caused by softening of the glass. Shortening of electron relaxation times due to glass softening and its impact in terms of DNP sensitivity is discussed.

Collaboration


Dive into the Michel Bardet's collaboration.

Top Co-Authors

Avatar

Sabine Hediger

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar

Guillaume Gerbaud

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar

Gaël De Paëpe

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar

Daniel Lee

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Jean-Marie Mouesca

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar

Lionel Dubois

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar

Armel Guillermo

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar

Pierre-Alain Bayle

Centre national de la recherche scientifique

View shared research outputs
Top Co-Authors

Avatar

Knut Lundquist

Chalmers University of Technology

View shared research outputs
Researchain Logo
Decentralizing Knowledge