Céline Moreau

Cellulose Nanocrystal-Assisted Dispersion of Luminescent Single- Walled Carbon Nanotubes for Layer-by-Layer Assembled Hybrid Thin Films

Highly stable single-walled carbon nanotube (SWNT) dispersions are obtained after ultrasonication in cellulose nanocrystal (CN) aqueous colloidal suspensions. Mild dispersion conditions were applied to preserve the SWNT length in order to facilitate the identification of hybrid objects. This led to a moderate dispersion of 24% of the SWNTs. Under these conditions, atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments succeeded in demonstrating the formation of hybrid particles in which CNs are aligned along the nanotube axis by a self-assembly process. These SWNT/CN dispersions are used to create multilayered thin films with the layer-by-layer method using polyallylamine hydrochloride as a polyelectrolyte. Homogeneous films from one to eight bilayers are obtained with an average bilayer thickness of 17 nm. The presence of SWNTs in each bilayer is attested to by characteristic Raman signals. It should be noted that these films exhibit a near-infrared luminescence signal due to isolated and well-separated nanotubes. Furthermore, scanning electron microscopy (SEM) suggests that the SWNT network is percolating through the film.

Elaboration of spin-coated cellulose-xyloglucan multilayered thin films.

In the context of developing a biomimetic model of the primary cell wall, our aim was to produce multilayered thin films composed of cellulose nanocrystals (CN) and xyloglucan (XG). We investigated the effect of XG concentrations ranging from 0.5 g/L to 10 g/L. The choice of concentration was based on rheological investigation of the XG solutions which indicated that the two lower concentrations (0.5 and 1 g/L) correspond to a semidilute regime where the polymer chains are not entangled, whereas they are entangled at the highest concentrations (5 and 10 g/L). Several processes of film preparation were tested (dipping or spin-coating, with or without a rinsing step). The film growth profiles obtained for different XG concentrations by mechanical profilometry showed that spin-coating without rinsing was the most efficient process. Results showed that at high XG concentrations (XG = 5 g/L and XG = 10 g/L) plateau values were reached after the formation of 3 or 4 bilayers, whereas growth of the multilayer structure was linear at the lower XG concentrations (XG = 0.5 g/L and XG = 1 g/L). The thickness of one CN/XG bilayer corresponded to a single layer of CN covered by a thin XG layer, despite the absence of a rinsing step between successive coatings. The importance of the XG concentration was confirmed by determining by neutron reflectivity the film architecture obtained from four XG solutions after eight successive paired coatings. The results are discussed in relation to the role of XG in the plant cell wall.

Interactions between β-Lactoglobulin and Aroma Compounds : Different Binding Behaviors as a Function of Ligand Structure

Interactions between beta-lactoglobulin (BLG) in its monomeric form and a wide range of aroma compounds were investigated by Fourier transform infrared (FT-IR) and 2D nuclear magnetic resonance (NMR) spectroscopies. A screening of the ligands was carried out by FT-IR through the amide I region changes of BLG upon binding. The location of two binding sites was determined by 2D NMR from the study of 10 selected ligands with different structures. All of the data suggest at least two binding behaviors as a function of the chemical class, the hydrophobicity, or the structure of the ligands. The binding of the elongated aroma compounds, such as 2-nonanone or ethyl pentanoate, within the central cavity involves residues located at the entrance of the calyx and Trp19. The binding onto the protein surface of aroma compounds that have or adopt a compact structure occurs in a site located between strand beta-G, alpha helix, and strand beta-I.

Expression and Regulation of the SCD2 Desaturase in the Rat Ovary

Abstract Despite the significant role of the lipid reserve in cell structure and function, very few studies have provided detailed descriptions of unsaturated fatty acid synthesis in the ovary. In the present study, we have shown by RT-PCR, Northern blot, and Western blot analyses the mRNA and protein expression of SCD2 (stearoyl-coenzyme A desaturase 2; also named delta 9 desaturase) in rat ovary. We also have localized Scd2 mRNA by in situ hybridization, mainly in granulosa cells of antral follicles, cumulus oophorus, and corpus luteum. Interestingly, either no or very weak SCD2 expression was observed in primordial follicles and oocytes. After eCG injection for 24 h in immature rats (age, 22 days), the level of SCD2 expression and SCD activity in ovary was increased by approximately fourfold (P < 0.05), and the response was further increased 48 h after hCG treatment. As expected, eCG/hCG treatment increased expression of the steroidogenesis enzymes (CYP11A1 and HSD3B) and STAR. We also found a decrease in the SCD2 expression and SCD activity in the corpus luteum at Days 10 and 15 compared to Day 3 of gestation, paralleled by a decrease in the expression of the steroidogenesis enzymes and STAR. To investigate the molecular mechanisms involved in the regulation of SCD2 expression in ovary, we performed primary culture of rat granulosa cells. We observed that both insulin-like growth factor 1 (IGF1) (7.5 × 10−8g/ml) and FSH (350 × 10−8g/ml) increased SCD2 expression and SCD activity by approximately threefold. Using specific inhibitors, we demonstrated that the MAPK3/MAP1 and PIK3R1/AKT pathways are involved in the IGF1- and FSH-induced SCD2 expression, respectively. The SCD2 is expressed and active in rat ovary, and it may be involved in the regulation of follicular growth and/or the oocyte maturation.

Coloured Semi‐reflective Thin Films for Biomass‐hydrolyzing Enzyme Detection

A new enzymatic activity detection assay based on colour change of the semi-reflective films is presented. The method is based on the preparation of multilayered thin films of controlled thickness obtained by sequential deposition of cellulose nanocrystals and xyloglucan. The hydrolysis of the films leads to a decrease in layer thickness that enables to detect enzyme activity, to the naked eye, from the resulting colour changes in a span of few minutes. The method allows direct, fast, highly sensitive, and easy-to-use characterization of enzymatic activities.

Lytic polysaccharide monooxygenases disrupt the cellulose fibers structure

Lytic polysaccharide monooxygenases (LPMOs) are a class of powerful oxidative enzymes that breakdown recalcitrant polysaccharides such as cellulose. Here we investigate the action of LPMOs on cellulose fibers. After enzymatic treatment and dispersion, LPMO-treated fibers show intense fibrillation. Cellulose structure modifications visualized at different scales indicate that LPMO creates nicking points that trigger the disintegration of the cellulose fibrillar structure with rupture of chains and release of elementary nanofibrils. Investigation of LPMO action using solid-state NMR provides direct evidence of modification of accessible and inaccessible surfaces surrounding the crystalline core of the fibrils. The chains breakage likely induces modifications of the cellulose network and weakens fibers cohesion promoting their disruption. Besides the formation of new initiation sites for conventional cellulases, this work provides the first evidence of the direct oxidative action of LPMOs with the mechanical weakening of the cellulose ultrastructure. LPMOs can be viewed as promising biocatalysts for enzymatic modification or degradation of cellulose fibers.

Xyloglucan-cellulose nanocrystal multilayered films: effect of film architecture on enzymatic hydrolysis.

Understanding the hydrolysis process of lignocellulosic substrates remains a challenge in the biotechnology field. We aimed here at investigating the effect of substrate architecture on the enzymatic degradation process using two different multilayered model films composed of cellulose nanocrystals (CNCs) and xyloglucan (XG) chains. They were built by a spin-assisted layer-by-layer (LbL) approach and consisted either of (i) an alternation of CNC and XG layers or of (ii) layers of mixed (CNC/XG) complexes alternated with polycation layers. Neutron reflectivity (NR) was used to determine the architecture and composition of these films and to characterize their swelling in aqueous solution. The films displayed different [XG]/[CNC] ratios and swelling behavior. Enzymatic degradation of films was then performed and investigated by quartz crystal microbalance with dissipation monitoring (QCM-D). We demonstrated that some architectural features of the substrate, such as polysaccharide accessibility, porosity, and cross-links, influenced the enzymatic degradation.

Neocembrene A, a major component of the trail-following pheromone in the genus Prorhinotermes (Insecta, Isoptera, Rhinotermitidae)

Summary.The diterpene neocembrene A or (1E,5E,9E,12R)-1,5,9-trimethyl-12-(1-methylethenyl)-1,5,9-cyclotetradecatriene, known as the trail-following pheromone of the advanced Termitidae Nasutitermitinae Nasutitermes exitiosus and Trinervitermes bettonianus, has been identified after SPME-GC/MS as the major component of the trail-following pheromone of the Rhinotermitidae Prorhinotermitinae, Prorhinotermes canalifrons and P. simplex. In all the other Rhinotermitidae studied until now, the major component of their trail pheromones is dodecatrienol ((3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol). This biochemical data further add to the anatomical and molecular characteristics that give a special status to the taxon Prorhinotermes among Rhinotermitidae. In Prorhinotermes canalifrons and P. simplex, neocembrene A was the only secretory compound specific to the sternal gland surface that could be detected after SPME. It elicited orientation as well as recruitment behavioral effects. However, the comparison of the respective biological activities triggered by neocembrene A and by sternal gland secretion suggests that minor components of the latter are acting in synergy with neocembrene A.

Tuning the Architecture of Cellulose Nanocrystal–Poly(allylamine hydrochloride) Multilayered Thin Films: Influence of Dipping Parameters

Multilayered thin films consisting of alternating cationic polyelectrolyte, poly(allylamine hydrochloride) (PAH), and anionic cellulose nanocrystals (CNs) were constructed using the dipping procedure by screening different experimental parameters: the drying step between each layer adsorption, the dipping time, the ionic strength of the PAH solution, and the concentration of CNs dispersion. We showed that the drying process and the ionic strength of PAH solution were crucial parameters for the successful construction of 8-bilayer films. Film thickness is mainly influenced by dipping time and CN concentration when using the dipping procedure without drying. Two architectures of adsorbed CN layers-a single or a double layer of CNs-were revealed on the basis of the thickness increment per bilayer, depending on experimental conditions. The layer adsorption process was investigated in real-time using quartz crystal microbalance with dissipation (QCM-D) experiments in an aqueous environment or by incorporating a drying step. On the basis of in situ construction of PAH-CN films in wet media, QCM-D data were indicative of highly hydrated films for which the progressive layer stacking is disturbed or prevented. QCM-D monitoring of CNs and PAH layer adsorption was monitored by incorporating a drying process. The impact of experimental parameters on PAH-CN multilayered construction and on CN layer configuration is discussed. This study offers new opportunities for tailoring the architecture of CN-based multilayer films.

Site-Selective Surface Modification Using Enzymatic Soft Lithography

Surface modification with functional polymers or molecules offers great promise for the development of smart materials and applications. Here, we describe a versatile and easy-to-use method of site-selective surface modification based on the ease of microcontact printing and the exquisite selectivity of enzymatic degradation. A micropatterned poly-L-lysine (PLL) layer on solid substrates was prepared by enzymatic degradation using trypsin enzyme immobilized on a prestructured poly(dimethlylsiloxane) (PDMS) stamp. After the enzymatic degradation of PLL and the removal of the degradation products, very well defined patterning was revealed over a large scale by fluorescence microscopy and atomic force microscopy (AFM). We investigate the advantage of our method by comparison with traditional microcontact printing and found that lateral diffusion was reduced, yielding a more accurate reproduction of the master. We also demonstrate that the stamp can be reused without reinking. The patterned surface was used for site-selective modification. The strategy was applied to two applications: the first is dedicated to the creation of amino-silane patterned surfaces, and the second illustrates the possibility of patterning polyelectrolyte multilayered thin films.