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Depuis quelques années, la modification de surface est une méthode efficace qui permet de contrôler les interactions entre un matériau et son environnement. Ce domaine de recherche ouvre la voie au développement de nouvelles surfaces « intelligentes » aux propriétés fonctionnelles. Dans ce manuscrit, nous présentons la conception d’un revêtement capable de contrôler l’auto-assemblage de peptides exclusivement à la surface d’un matériau. L'auto-assemblage est initié par un stimulus enzymatique localisé à la surface qui permet la transformation de peptides précurseurs en peptides gélateurs, ayant la propriété de s’auto-assembler pour former des structures fibrillaires enchevêtrées pour former un hydrogel. Les surfaces enzymatiques ont été obtenues par adsorption d’enzyme spécifique en utilisant la méthode « couche par couche ». Dans une première approche, la croissance du réseau de fibres est initiée par accumulation d’oligopeptides (KL)nOEt confinés sur un film enzymatique d’α-chymotrypsine. Ce processus d’hydrogélation peut être contrôlé dans le temps (en ajustant le temps de latence) en changeant la concentration en peptides KLOEt et la densité de surface en enzyme. Dans une deuxième approche, le film multicouche bioactif contenant l’alcaline phosphatase a été fonctionnalisé par une couche d’ensemencement composée d’acide poly(acrylique) modifié par une séquence peptidique Fmoc-FFC aux propriétés gélatrices. La modification de la densité de peptides gélatrices en surface a permis de contrôler le processus d’auto-assemblage du peptide gélateur Fmoc-FFY depuis la surface. Lorsque le film bioactif est mis en contact avec le peptide précurseur, i.e. Fmoc-FFY(PO42-) substrat de l’alcaline phosphatase, le peptide gélateur se forme et s’auto-assemble sous forme de nanofibres à partir de la surface. Grâce à ces deux études nous avons démontré qu'un film précurseur enzymatique ou une couche bioactive d'ensemencement sont des matériaux permettant d’initier et de contrôler l’auto-assemblage de peptides en surface afin de former un hydrogel. / Since the middle of the last century, the functionalization of surfaces has emerged as a convenient method to control interactions between a material and its surrounding environment. This recent research field paves the way to the design of surfaces bearing original “smart” functionalities. Herein, we present the design and control of peptide self-assembly taking place exclusively at or near a surface in response to an enzymatic stimulus. The localized enzyme-assisted self-assembly (LEASA) of peptides led to the growth of micrometric hydrogels from the surface. The enzymatic surface was obtained by adsorption of specific enzymes using the layer-by-layer method. In a first strategy, we developed the growth of fibrillary networks resulting from the accumulation of oligopeptides (KL)nOEt produced from a confined enzymatic layer of α-chymotrypsine at the interface. This process of gelation was tuned in time (lag time) by controlling the peptide KLOEt concentration and the enzymatic surface density. In a second strategy, alkaline phosphatase was embedded into a multilayer film to obtain a bioactive surface on which a seed-layer, i.e a poly(acrylic acid) covalently modified with a hydrogelator peptide, was adsorbed. This layer allows to control the self-assembly of the fiber network by changing the peptide density anchored on the seed layer. When this bioactive and seeding film is brought into contact with the peptide substrate, i.e. Fmoc-FFY(PO42-), of alkaline phosphatase, an efficient self-assembly of Fmoc-FFY is obtained leading to nanofibers growing from the surface. We demonstrated that an enzymatic precursor film or a more sophisticated bioactive seeding layer can self-instruct the self-assembly of small peptides sequences and influence buildup of a micrometric hydrogel from the surface.

Understanding the supramolecular interactions governing the self-assembly of molecular building blocks upon surfaces is fundamental to the design of new devices such as sensors or catalysts. Successful heterogeneous enantioselective catalysts have relied upon the adsorption of ‘chiral modifiers’, usually chiral amino acids, onto reactive metal surfaces. One of the most researched examples is the hydrogenation of β-ketoesters using nickel-based catalysts. The stability of the chiral modifiers upon catalyst surfaces is a major obstacle to the industrial scale-up of this reaction. In this study, the replacement of conventional modifiers with porous, chiral and functionalised self-assembled networks is investigated. Perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) and melamine (1,3,5-triazine,-2,4,6-triamine) have been shown to form hydrogen bonded networks on Ag-Si(111)√3x√3R30° in ultra-high vacuum (UHV) and Au(111) substrates in UHV and ambient conditions, these networks are capable of hosting guest molecules. These networks are investigated further in this study. In UHV, the behaviour of the components and network formation on Ni(111) is probed using scanning tunnelling microscopy (STM) and temperature-programmed desorption (TPD). The stability of the PTCDI-melamine network on Au(111) was analysed using TPD. Metal coordination interactions between each of the network components and nickel upon the Au(111) surface were examined by STM before testing the ability of the network to act as a template for metal growth. Finally, a number of polymerisation reactions are investigated with a view to replacing chiral modifiers with porous, chiral, functionalised covalent networks. Periodic covalent networks should possess the greater chemical and thermal stability required for more widespread use. In UHV and ambient conditions, STM is used to monitor the progress of surface-confined reactions on Au(111) and characterise the resultant covalent structures.

No description available.