Florence Babonneau

First-Principles Calculation of NMR Parameters Using the Gauge Including Projector Augmented Wave Method: A Chemist’s Point of View

Including Projector Augmented Wave Method: A Chemist’s Point of View Christian Bonhomme,*,† Christel Gervais,*,† Florence Babonneau,† Cristina Coelho,‡ Fred́eŕique Pourpoint,† Thierry Azaïs,† Sharon E. Ashbrook,* John M. Griffin, Jonathan R. Yates,* Francesco Mauri, and Chris J. Pickard †Laboratoire de Chimie de la Matier̀e Condenseé de Paris, Universite ́ Pierre et Marie Curie, Paris 06, CNRS UMR 7574, Colleg̀e de France, 75005 Paris, France ‡IMPC, Institut des Mateŕiaux de Paris Centre, FR2482, UPMC Universite ́ Pierre et Marie Curie Paris 06, Colleg̀e de France, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France School of Chemistry and EaStCHEM, University of St. Andrews, North Haugh, St. Andrews KY16 9ST, United Kingdom Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom Laboratoire de Mineŕalogie Crystallographie, UMR CNRS 7590, Universite ́ Pierre et Marie Curie, UPMC, 75015 Paris, France Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom

Hydrothermal Carbon from Biomass: Structural Differences between Hydrothermal and Pyrolyzed Carbons via 13C Solid State NMR

The objective of this paper is to better describe the structure of the hydrothermal carbon (HTC) process and put it in relationship with the more classical pyrolytic carbons. Indeed, despite the low energetic impact and the number of applications described so far for HTC, very little is known about the structure, reaction mechanism, and the way these materials relate to coals. Are HTC and calcination processes equivalent? Are the structures of the processed materials related to each other in any way? Which is the extent of polyaromatic hydrocarbons (PAH) inside HTC? In this work, the effect of hydrothermal treatment and pyrolysis are compared on glucose, a good model carbohydrate; a detailed single-quantum double-quantum (SQ-DQ) solid state (13)C NMR study of the HTC and calcined HTC is used to interpret the spectral region corresponding to the signal of furanic and arene groups. These data are compared to the spectroscopic signatures of calcined glucose, starch, and xylose. A semiquantitative analysis of the (13)C NMR spectra provides an estimation of the furanic-to-arene ratio which varies from 1:1 to 4:1 according to the processing conditions and carbohydrate employed. In addition, we formulate some hypothesis, validated by DFT (density functional theory) modeling associated with (13)C NMR chemical shifts calculations, about the possible furan-rich structural intermediates that occur in the coalification process leading to condensed polyaromatic structures. In combination with a broad parallel study on the HTC processing conditions effect on glucose, cellulose, and raw biomass (Falco, C.; Baccile, N.; Titirici, M.-M. Green Chem., 2011, DOI: 10.1039/C1GC15742F), we propose a broad reaction scheme and in which we show that, through HTC, it is possible to tune the furan-to-arene ratio composing the aromatic core of the produced HTC carbons, which is not possible if calcination is used alone, in the temperature range below 350 °C.

Water-mediated structuring of bone apatite

It is well known that organic molecules from the vertebrate extracellular matrix of calcifying tissues are essential in structuring the apatite mineral. Here, we show that water also plays a structuring role. By using solid-state nuclear magnetic resonance, wide-angle X-ray scattering and cryogenic transmission electron microscopy to characterize the structure and organization of crystalline and biomimetic apatite nanoparticles as well as intact bone samples, we demonstrate that water orients apatite crystals through an amorphous calcium phosphate-like layer that coats the crystalline core of bone apatite. This disordered layer is reminiscent of those found around the crystalline core of calcified biominerals in various natural composite materials in vivo. This work provides an extended local model of bone biomineralization.

Introducing ecodesign in silica sol–gel materials

Over the last decade, ecodesign has been introduced as a concept and a methodological framework to identify and improve sustainability in product development. In this context, the 12 principles of green chemistry provide suitable guidelines for the elaboration of molecules and materials in conditions that meet some ecodesign-related criteria. Sol–gel chemistry is an interesting domain to be examined in this perspective because it was early identified as an eco-friendly process compared to traditional routes to ceramics and glasses. Thus it is not surprising that many recent developments in sol–gel technology have, explicitly or not, addressed sustainability issues. In this review, we present an overview of these advances, focusing on the chemistry of silica. Starting from the typical reaction involving tetraethoxysilane hydrolysis and condensation in hydro-alcoholic media in the presence of inorganic catalysts, the current alternatives in terms of precursors, solvents, catalysts and activation sources are presented. As an example of hybrid materials, the synthesis of surfactant-based mesostructured silica is commented. Manufacturing methods to nanoproducts, including sol–gel technology are also discussed in terms of sustainability. Finally, the recyclability and degradation of sol–gel silica are briefly commented on. As a conclusion, some perspectives and current limitations for the development of a “greener” sol–gel chemistry are provided, extending the discussion to non-silica materials.

Unusual, pH-induced, self-assembly of sophorolipid biosurfactants

An increasing need exists for simple, bioderived, nontoxic, and up-scalable compounds with stimuli-responsive properties. Acidic sophorolipids (SL) are glucose-based biosurfactants derived from the yeast broth of Candida bombicola (teleomorph: Starmerella bombicola). The specific design of this molecule, a sophorose head with a free end-COOH group at the end of the alkyl chain, makes it a potentially interesting pH-responsive compound. We have specifically investigated this assumption using a combination of small angle neutron scattering (SANS), transmission electron microscopy under cryogenic conditions (Cryo-TEM), and nuclear magnetic resonance (NMR) techniques and found a strong dependence of SL self-assembly on the degree of ionization, α, of the COOH group at concentration values as low as 5 and 0.5 wt %. At least three regimes can be identified where the supramolecular behavior of SL is unexpectedly different: (1) at low α values, self-assembly is driven by concentration, C, and micelles are mainly identified as nonionic objects whose curvature decreases (sphere-to-rod) with C; (2) at mid α values, the formation of COO(-) groups introduces negative charges at the micellar surface inducing an increase in curvature (rod-to-sphere transition). Repulsive electrostatic long-range interactions appear at this stage. In both regimes 1 and 2, the cross-section radius of the micelles is below 25 Å. This behavior is concentration independent. (3) At α = 1, individual micelles seem to favor the formation of large netlike tubular aggregates whose size is above 100 nm. Such a complex behavior is very unique as it is generally not observed for common alkyl-based surfactants in concentration ranges below 5-10 wt %.

Accurate characterization of pure silicon-substituted hydroxyapatite powders synthesized by a new precipitation route

This paper presents a new aqueous precipitation method to prepare silicon-substituted hydroxyapatites Ca10(PO4)6-y(SiO4)y(OH)2-y(VOH)y (SiHAs) and details the characterization of powders with varying Si content up to y=1.25molmolSiHA(-1). X-ray diffraction, transmission electron microscopy, solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to accurately characterize samples calcined at 400°C for 2h and 1000°C for 15h. This method allows the synthesis of monophasic SiHAs with controlled stoichiometry. The theoretical maximum limit of incorporation of Si into the hexagonal apatitic structure is y<1.5. This limit depends on the OH content in the channel, which is a function of the Si content, temperature and atmosphere of calcination. These results, particularly those from infrared spectroscopy, raise serious reservations about the phase purity of previously prepared and biologically evaluated SiHA powders, pellets and scaffolds in the literature.

Investigation of the interface in silica-encapsulated liposomes by combining solid state NMR and first principles calculations.

In the context of nanomedicine, liposils (liposomes and silica) have a strong potential for drug storage and release schemes: such materials combine the intrinsic properties of liposome (encapsulation) and silica (increased rigidity, protective coating, pH degradability). In this work, an original approach combining solid state NMR, molecular dynamics, first principles geometry optimization, and NMR parameters calculation allows the building of a precise representation of the organic/inorganic interface in liposils. {(1)H-(29)Si}(1)H and {(1)H-(31)P}(1)H Double Cross-Polarization (CP) MAS NMR experiments were implemented in order to explore the proton chemical environments around the silica and the phospholipids, respectively. Using VASP (Vienna Ab Initio Simulation Package), DFT calculations including molecular dynamics, and geometry optimization lead to the determination of energetically favorable configurations of a DPPC (dipalmitoylphosphatidylcholine) headgroup adsorbed onto a hydroxylated silica surface that corresponds to a realistic model of an amorphous silica slab. These data combined with first principles NMR parameters calculations by GIPAW (Gauge Included Projected Augmented Wave) show that the phosphate moieties are not directly interacting with silanols. The stabilization of the interface is achieved through the presence of water molecules located in-between the head groups of the phospholipids and the silica surface forming an interfacial H-bonded water layer. A detailed study of the (31)P chemical shift anisotropy (CSA) parameters allows us to interpret the local dynamics of DPPC in liposils. Finally, the VASP/solid state NMR/GIPAW combined approach can be extended to a large variety of organic-inorganic hybrid interfaces.

A carbonate-fluoride defect model for carbonate-rich fluorapatite

Abstract We propose a microscopic model of the dominant carbonate for phosphate substitution in fluorapatite. A well-crystallized sedimentary fluorapatite sample containing ~2.3 ± 0.8 wt% of carbonate was investigated using Fourier transform infrared spectroscopy (FTIR) and 13C and 19F magic angle spinning nuclear magnetic resonance (MAS NMR). About 75% of the carbonate groups replace the phosphate group (“B-site”), whereas a lesser contribution from carbonate groups located in the structural channels (“A-site”) is observed. Beside the dominant 19F NMR signal of channel ions at ~ -102 ppm, an additional signal corresponding to ~8% of fluoride ions is observed at -88 ppm. 19F double quantum-single quantum (DQ-SQ) MAS NMR and 13C{19F} frequency-selective Rotational Echo DOuble Resonance (REDOR) experiments prove that this additional signal corresponds to isolated fluoride ions in the apatite structure, located in close proximity of substituted carbonate groups. Density functional theory (DFT) calculations allow us to propose a composite carbonate-fluoride tetrahedron defect model accounting for these experimental observations. The planar carbonate ion lies in the sloping face of the tetrahedron opposite a fluoride ion occupying the remaining vertex, together replacing the tetrahedral phosphate ion. This “francolite-type” defect leads to a diagnostic narrow IR absorption band at 864 cm-1 that could be used as a guide to, e.g., detect the incipient transformation of fossil bone and teeth samples.

Sophorolipids: a yeast-derived glycolipid as greener structure directing agents for self-assembled nanomaterials

Sophorolipids, fully natural glycolipids, can form in water nanometre-size micelles of various geometries depending on their concentration as shown by small angle neutron scattering experiments. This property allows use of them, for the first time, as structure directing agents in the synthesis of nanostructured silica thin films via the evaporation induced self-assembly (EISA) process.

Heterogeneous structure and in vitro degradation behavior of wet-chemically derived nanocrystalline silicon-containing hydroxyapatite particles.

Nanocrystalline hydroxyapatite (HAp) and silicon-containing hydroxyapatite (SiHAp) particles were synthesized by a wet-chemical procedure and their heterogeneous structures involving a disordered phase were analyzed in detail by X-ray diffractometry (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The effects of heterogeneous structure on in vitro biodegradability and the biologically active Ca(II)- and Si(IV)-releasing property of SiHAp particles were discussed. The (29)Si NMR analysis revealed that the Si(IV) was incorporated in the HAp lattice in the form of Q(0)(SiO(4)(4-)orHSiO(4)(3-)) species, accompanied by the formation of condensed silicate units outside the HAp lattice structure, where the fraction and amount of Q(0) species in the HAp lattice depends on the Si content. The (31)P and (1)H NMR results agreed well with the XRD, TEM and FTIR results. NMR quantitative analysis results were explained by using a core-shell model assuming a simplified hexagonal shape of HAp covered with a disordered layer, where Si(IV) in Q(0) was incorporated in the HAp lattice and a disordered phase consisted of hydrated calcium phosphates involving polymeric silicate species and carbonate anions. With the increase in the Si content in the HAp lattice, the in vitro degradation rate of the SiHAps increased, while their crystallite size stayed nearly unchanged. The biologically active Ca(II)- and Si(IV)-releasing ability of the SiHAps was remarkably enhanced at the initial stage of reactions by an increase in the amount of Si(IV) incorporated in the HAp lattice but also by an increase of the amount of polymeric silicate species incorporated in the disordered phase.