Christophe Méthivier

Grafting of Lysozyme and/or Poly(ethylene glycol) to Prevent Biofilm Growth on Stainless Steel Surfaces

In the aim of protecting stainless steel surfaces against protein and/or bacterial adhesion, thin films including the glycosidase hen egg white lysozyme (HEWL) and/or the synthetic polymer poly(ethylene glycol) (PEG) were covalently coated onto flat substrates by wet chemical processes. Chemical grafting of both species was carried out by covalent binding to surfaces pretreated by the polyamine poly(ethylene imine) (PEI). Surfaces were characterized at each step of functionalization by means of reflection-absorption infrared spectroscopy by modulation of polarization (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS) to determine the atomic and molecular composition of the interfaces, respectively. Then, the ability of the so-modified surfaces to prevent protein adsorption and bacterial adhesion together with their biocide properties were demonstrated by three local tests employing bovine serum albumin (BSA), and the bacteria Listeria ivanovii and Micrococcus luteus. A new test was implemented to assess the local enzymatic properties of HEWL. Cografting of PEG and HEWL resulted in a surface with both antiadhesion and antibacterial properties.

Co-grafting of amino-poly(ethylene glycol) and Magainin I on a TiO2 surface: tests of antifouling and antibacterial activities.

An antimicrobial peptide, Magainin I (Mag), was grafted to a titanium oxide surface, via an antiadhesive poly(ethylene glycol) (PEG) cross-linker. The latter plays a 2-fold part, being antiadhesive, and enabling the covalent immobilization of the peptide. The functionalization was characterized at each step by reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). The antiadhesive properties of PEG, and antibacterial activity of the anchored Magainin I, were individually tested toward adsorption of bovin serum albumin (BSA) proteins, and against Gram positive bacteria, Listeria ivanovii , respectively. The results reveal that adhesion of both proteins and bacteria have been considerably reduced, accompanied by an inhibition of the growth of remaining adhered bacteria. This work thus offers a novel approach to functionalize oxide surfaces against biofilms and to measure the so-obtained properties in each of the successive steps of a biofilm formation.

Characterization of two-dimensional chiral self-assemblies L- and D-methionine on Au(111).

A combination of XPS, in situ RAIRS, LEED, and STM experiments together with ab initio DFT calculations were used to elucidate the self-assembly properties at the atomic level, and enabled the interpretation of the expression of surface chirality upon adsorption of both enantiomers of methionine on a clean Au(111) surface under UHV conditions. The combination of experimental results, in particular, LEED and STM data with quantum chemical calculations is shown to be a successful setup strategy for addressing this challenge. It was found that the methionine molecular self-assembly consists of the first molecule lying parallel to the gold surface and the second interacting with the first methionine through a 2D H-bond network. The interaction with the gold surface is weak. The stability of the assembly is mainly due to the presence of intermolecular H bonds, resulting in the formation of ziplike dimer rows on the Au(111) surface. The methionine molecules interact with each other via their amino acid functional groups. The assembly shows an asymmetric pattern due to a slightly different orientation of the methionine molecules with respect to the surface. Simulations of the STM image of methionine assemblies were consistent with the experimental STM image. The present study shows another example of Au(111) stabilizing a self-assembled biological layer, which is not chemically perturbed by the surface.

Oxidation of NH3 on polycrystalline copper and Cu(1 1 0): a combined FT-IRAS and kinetics investigation

Abstract The kinetics of the reaction of oxidation of ammonia on polycrystalline copper, has been investigated, in a re-circulating reactor, and correlated to a characterisation of the catalyst surface at different extent of conversions. The rapid formation of a nitride or oxynitride phase and its reactivity have been demonstrated. Under oxidising conditions, P NH 3 = P O 2 , and up to 650xa0K, dinitrogen is the only product of the reaction; N 2 O being formed when T or P O 2 increases further. The correlation of these kinetics results to an in situ characterisation of the same reaction at RT by Fourier-transformed infrared reflection-absorption spectroscopy (FT-IRAS), on a well defined Cu(1xa01xa00) surface, led to the following conclusion: two reaction pathways contribute to the conversion of ammonia: (i) its decomposition on copper; (ii) the reaction between ammonia molecules and oxygen adsorbed from the gas phase. The major adsorbed species is oxygen; intermediate species are NH 2 , NH and possibly HNO formed when the oxygen surface concentration is sufficient. Increasing the pressure of oxygen induces, at high T , the formation of nitrous oxide; N 2 O results from an oxidation of the surface copper nitride or from the interaction of two surface HNO intermediates.

Interaction of NH3 and oxygen with Cu(1 1 0), investigated by FT-IRAS

Abstract Adsorption of ammonia, on the Cu(1xa01xa00) surface, has been investigated in situ, at room temperature, by Fourier-transformed infrared reflection–absorption spectroscopy (FT-IRAS). The role of oxygen in the reaction of oxy-dehydrogenation of ammonia was made clear by successively characterising the interaction of ammonia, co-adsorbed with oxygen on metallic Cu(1xa01xa00) or adsorbed on an oxygen-pre-dosed Cu(1xa01xa00) surface. Auger electron spectroscopy was used to check the chemical state of the surface after oxygen and/or ammonia exposure. NH 3 was observed to adsorb in a molecular form on the metallic Cu(1xa01xa00) surface. When co-adsorbed with ammonia or pre-adsorbed on the surface, oxygen favours abstraction of hydrogen from NH 3 , eventually yielding dinitrogen.

Tuning the Surface Chirality of Adsorbed Gly-Pro Dipeptide/Cu(110) by Changing Its Chemical Form via Electrospray Deposition

By changing the ultrahigh vacuum (UHV) deposition method, classical sublimation versus electrospray ionization, one can tune the chemistry of a chiral dipeptide molecule (Gly-Pro, GP), when adsorbed on a Cu(110) surface, from anionic to zwitterionic. This chemical shift will influence the adsorption mode of the dipeptide, either in a three-point fashion in the case of anionic GP molecules with a strong interaction among the copper surface, both O atoms of the carboxylate moiety, and the nitrogen atoms, or in the case of zwitterions GP, the adsorption mode relies on the sole interaction of one carboxylate oxygen atom. These different anchoring modes strongly modify the expression of surface 2D chirality and the supramolecular assemblies with two very distinct unit cells.