Guillaume Gerbaud

Nuclear Magnetic Resonance and Electron Paramagnetic Resonance as Analytical Tools To Investigate Structural Features of Archaeological Leathers

Archaeological waterlogged leathers dated from the 13th to 17th century have been analyzed using carbon-13 high-resolution solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). The NMR and EPR spectra have been compared to modern vegetable-tanned leathers and crude hide. Both techniques allowed us to fully characterize the samples and better understand the changes occurring during aging in water environment. The main features of the archaeological leathers are the high contents in iron and the absence of residual vegetable tannins. Traces of lubricants could not be detected either. The accumulation of iron oxides may have played a role in the conservation of the archaeological objects and explain the surprising good conservation state of the leather samples as was observed in the NMR spectra. The absence of tannins and lubricants in the studied archaeological samples is also discussed. It may be a consequence of aging in water-rich environment. The analysis strategy described in this paper can be systematically applied to characterize archaeological or historical leather samples.

Exploring intrinsically disordered proteins using site-directed spin labeling electron paramagnetic resonance spectroscopy.

Proteins are highly variable biological systems, not only in their structures but also in their dynamics. The most extreme example of dynamics is encountered within the family of Intrinsically Disordered Proteins (IDPs), which are proteins lacking a well-defined 3D structure under physiological conditions. Among the biophysical techniques well-suited to study such highly flexible proteins, Site-Directed Spin Labeling combined with EPR spectroscopy (SDSL-EPR) is one of the most powerful, being able to reveal, at the residue level, structural transitions such as folding events. SDSL-EPR is based on selective grafting of a paramagnetic label on the protein under study and is limited neither by the size nor by the complexity of the system. The objective of this mini-review is to describe the basic strategy of SDSL-EPR and to illustrate how it can be successfully applied to characterize the structural behavior of IDPs. Recent developments aimed at enlarging the panoply of SDSL-EPR approaches are presented in particular newly synthesized spin labels that allow the limitations of the classical ones to be overcome. The potentialities of these new spin labels will be demonstrated on different examples of IDPs.

Dynamics property recovery of archaeological-wood fibers treated with polyethylene glycol demonstrated by high-resolution solid-state NMR

We used high-resolution Solid-State 13C NMR to better understand and optimize the conservation process of archaeological waterlogged woods by polyethylene glycol (PEG) impregnation via the study of the molecular interactions between PEG and residual celluloses. By both deconvoluting NMR spectra and analyzing the behavior of 13C magnetization build-up under proton to carbon cross-polarization conditions, we were able to quantify PEG penetration and extract parameters sensitive to molecular dynamics such as proton spin lattice-relaxation-time constants in the rotating frame T1ρH and the cross-relaxation time constant TCH. By exploring a large range of PEG concentrations for the impregnating solutions we show that the PEG penetrates inside the fibers and interacts at a molecular level with the cellulose fibrils thus restoring the dynamics properties of the damaged molecular cell wall network. At high PEG concentration, the polymer accumulates in the remaining free volume with more and looser molecular interactions with the residual wood components. This feature explains the facility for these hydroscopic materials to exude from the wood and led to deleterious consequences for the restored artefacts.Graphical Abstractxa0

Application of 7 Li NMR to characterize the evolution of intercalated and non-intercalated lithium in LiFePO 4 -based materials for Li-ion batteries

Different synthesis batches of LiFePO4/C materials were prepared, and their electrochemical properties as positive cathodes for lithium-ion batteries were evaluated. Using standard solid-state NMR conditions, such as a 7-mm magic-angle-spinning probe performing at low spinning rates, information on both intercalated and non-intercalated (stored on the grain boundaries) lithium was obtained. A sharp signal assigned to non-intercalated lithium could be observed by diluting the active material in silica. Correlations could be, thus, obtained between the amount of each type of lithium and the electrochemical history and state of the material, revealing that the relative amount of surface lithium in a pristine LiFePO4/C material is rather constant and cannot be used as a criterion for its further specification. However, a drastic increase of this surface lithium was observed in the cathode materials of out-of-order batteries. As the cathode material recovered from the batteries after electrochemical testing was carefully washed before analysis, we can conclude that the non-intercalated lithium is strongly bound to the active material probably inside the so-called solid electrolyte interface layer at the surfaces of LiFePO4 particles. This work illustrates that solid-state lithium NMR can allow rapid characterization and testing of LiFePO4/C cathode materials.

Microscopic structure of heterogeneous lipid-based formulations revealed by 13C high-resolution solid-state and 1H PFG NMR methods

Lipid-based formulations such as lip glosses that are very alike on the base of their components may have significant differences in their expected macroscopic properties as cosmetics. To differentiate such formulations, high-resolution (13)C NMR was performed under magic angle spinning to investigate the properties at both molecular and microscopic levels. Temperature studies were carried out and no polymorphism in the solid domains could be evidenced after the thermal treatment performed for obtaining the commercial lip glosses. (13)C NMR spectra also showed that some waxes remain partially solubilized in the oils of formulations. The microscopic structure of the wax-oil liquid domains was worked out on the basis of restricted diffusion properties obtained with proton pulsed-field gradient NMR. Changing a single wax component, in two identical formulations, yields significant morphological differences. In the first one the liquid phase appears as a continuum whereas in the second one, the liquid phase is fractionated into micrometric droplets.