Olivier Wattraint

Enzymatic hydrolysis of ionic liquid-pretreated celluloses: contribution of CP-MAS 13C NMR and SEM.

The supramolecular structure of four model celluloses was altered prior to their enzymatic saccharification using two ionic liquid pretreatments: one with the commonly used 1-ethyl-3-methylimidazolium acetate ([Emim](+)[CH(3)COO](-)) and the other with the newly developed 1-ethyl-3-methylimidazolium methylphosphonate ([Emim](+)[MeO(H)PO(2)](-)). The estimation of crystallinity index (CrI) by solid state (13)C nuclear magnetic resonance for each untreated/pretreated celluloses was compared with the performances of their enzymatic hydrolysis. For α-cellulose, both pretreatments led to a significant decrease in CrI from 25% to 5% but had no effect on glucose yields. In contrast, The [Emim](+)[MeO(H)PO(2)](-) pretreatment on the long fibers of cellulose had no significant effect on the CrI although a conversion yield in glucose of 88% is obtained versus 32% without pretreatment. However, scanning electron microscopy analysis suggested a loss of fiber organization induced by both ionic liquid pretreatments leading to a larger accessibility by cellulases to the cellulose surface.

Conformational and interfacial analyses of K3A18K3 and alamethicin in model membranes.

The involvement of membrane-bound peptides and the influence of protein conformations in several neurodegenerative diseases lead us to analyze the interactions of model peptides with artificial membranes. Two model peptides were selected. The first one, an alanine-rich peptide, K3A18K3, was shown to be in alpha-helix structures in TFE, a membrane environment-mimicking solvent, while it was mostly beta-sheeted in aqueous buffer as revealed by infrared spectroscopy. The other, alamethicin, a natural peptide, was in a stable alpha-helix structure. To determine the role of the peptide conformation on the nature of its interactions with lipids, we compared the structure and topology of the conformational-labile peptide K3A18K3 and of the alpha-helix rigid alamethicin in both aqueous and phospholipid environments (Langmuir monolayers and multilamellar vesicles). K3A18K3 at the air-water interface showed a pressure-dependent orientation of its beta-sheets, while the alpha-helix axis of alamethicin was always parallel to the interface, as probed by polarization modulation infrared reflection absorption spectroscopy. The beta-sheeted K3A18K3 peptide was uniformly distributed into DPPC condensed domains, while the helical-alamethicin insertion distorted the DPPC condensed domains, as evidenced by Brewster angle microscopy imaging of the air/interface. The beta-sheeted K3A18K3 interacted with DMPC multilamellar vesicles via hydrophilic interactions with polar heads and the helical-alamethicin via hydrophobic interactions with alkyl chains, as shown by infrared spectroscopy and solid state NMR. Our findings are consistent with the prevailing assumption that the conformation of the peptide predetermines the mode of interaction with lipids. More precisely, helical peptides tend to be inserted via hydrophobic interactions within the hydrophobic region of membranes, while beta-sheeted peptides are predisposed to interact with polar groups and stay at the surface of lipid layers.

A deeper investigation on carbohydrate cycling in Sinorhizobium meliloti

Recycling of triose‐phosphate and pentose‐phosphate was previously reported on glucose in Sinorhizobium meliloti, a polysaccharide‐synthesizing bacterium, but the metabolic basis of such processes remained unclear. In this work, we have used 13C‐labelling strategies to demonstrate that carbohydrate cycling in this organism is independent of the gluconate bypass, the alternative pathway for glucose assimilation involving its periplasmic oxidation into gluconate. Furthermore, carbohydrate cycling in S. meliloti is also observed on fructose, making the situation in this bacterium significantly different from that depicted for alginate‐synthesizing species.

Synthesis of lipophosphoramidyl-cyclodextrins and their supramolecular properties.

The synthesis of lipophosphoramidyl-β-CD was obtained by an Atherton-Todd (AT) reaction that involved dioleylphosphite and either functionalized permethylated or native β-cyclodextrin. This AT reaction that produced dioleylphosphoramide by making use of the amino group grafted on cyclodextrin, was optimized for these cyclic oligosaccharides. These new amphiphilic compounds were fully characterized, and their self-assembling properties were investigated: the mean size diameter and polydispersity measured by Dynamic Light Scattering (DLS) were affected by the nature of the aqueous media and the temperature of storage. The encapsulation properties of these nanoparticles have been evaluated using carboxyfluorescein and scopolamine derivatives as model of guests.

Interactions of two transmembrane peptides in supported lipid bilayers studied by a 31P and 15N MAOSS NMR strategy

(31)P and (15)N solid-state NMR with the magic angle-oriented sample spinning (MAOSS) strategy was used to investigate the effect of two model peptides on phospholipid bilayers mimicking biological membrane. One of the peptides, alamethicin, used as a reference of transmembrane alignment, has been shown to disrupt the lipid bilayer organisation, affecting the DMPC packaging. On the other hand, a alpha-helix alanine-rich peptide, K(3)A(18)K(3), with a (15)N labelled alanine, did not present any effect in the DMPC bilayer organisation. The mean orientation of this peptide in the bilayer gave a transmembrane alignment of about 80%.

Influence of the insertion of a cationic peptide on the size and shape of nanoliposomes: A light scattering investigation

Nanoliposomes are widely used for drug delivery in the human body. Cell-penetrating peptides are amphiphilic peptides inserting in the lipid bilayer of these lipid vesicles to induce the fusion with target cells. Separation by size exclusion chromatography coupled with the analysis by light scattering detectors provides both the hydrodynamic radius and the radius of gyration of all the liposomes in a sample. In this paper, the influence of the insertion of a cationic peptide, K2LA12, on the size and shape of anionic liposomes has been studied by this approach. The results obtained highlighted an increase in size and a slight deformation of the lipid vesicles depending on the concentration of peptides incorporated into the lipid bilayers.

Liposomal structure: A comparative study on light scattering and chromatography techniques

ABSTRACT Liposomes play an important role in medical and pharmaceutical science as, nanoscale drug carriers. One of the most important features is their size and size distribution, influencing both their bio-distribution and their targeting efficiency to tumors and also therapeutic activity of liposomal antitumor drugs. In this study, the effect of preparation method and molecular interaction on size and shape of liposome was studied. The size and shape characterization of liposomes was performed by asymmetrical flow field-flow fractionation coupled online with multi-angle light scattering (AF4-MALS). The size distributions obtained by AF4-MALS were compared to mean particle sizes and size distribution measured with other standard method such as Photon Correlation Spectroscopy (PCS). Furthermore, the effect of molecular interaction (hydrophilic and hydrophobic model drugs) on liposomal structure was assessed. GRAPHICAL ABSTRACT