Seydina Ibrahima Kebe

Bio: Seydina Ibrahima Kebe is an academic researcher from University of Paris. The author has contributed to research in topics: Capillary electrochromatography & Monolith. The author has an hindex of 4, co-authored 6 publications receiving 47 citations.

Gold nanoparticles-supported histamine-grafted monolithic capillaries as efficient microreactors for flow-through reduction of nitro-containing compounds

Abstract: A histamine functionalized monolith was synthesized within a micro-sized channel as a permeable support for the immobilization of 5, 20 and 100 nm-sized gold nanoparticles and the resulting nanostructured hybrid monoliths were applied as microreactors for the catalytic reduction of nitro-derivatives. The whole synthetic pathway of the composite materials relies on (i) UV-induced polymerization of N-acryloxysuccinimide and ethylene glycol dimethacrylate in toluene, (ii) surface grafting of histamine through nucleophilic substitution of hydroxysuccinimide leaving groups, and (iii) specific adsorption of citrate-stabilized colloidal gold nanoparticles. The achievement of the successive synthetic steps was ascertained by using a combination of experimental techniques providing information about the chemical composition (FTIR, Raman, and EDX) and porosity and surface-dispersion (SEM) of gold nanoparticles. Of particular interest, it is shown that surface-grafted histamine units exhibit strong affinity towards gold nanoparticles and allow homogeneous and dense dispersion of 5 and 20 nm sized nanoparticles. Consequently, the gold nanoparticle size-dependence of the catalytic activity (conversion of nitro and di-nitro aromatic compounds into the corresponding amino and di-amino-derivatives) was demonstrated, highlighting the utmost importance of controlling the dispersion of nano-catalysts on the support surface, while histamine protonation was also evidenced as a parameter of paramount importance regarding nanogold surface density and thus resulting catalytic activity. Histamine protonation notably allows the generation of electrostatic interactions between citrate-coated gold nanoparticles and thus-formed positive charges at the monolith surface.

Thiol–ene click chemistry for the design of diol porous monoliths with hydrophilic surface interaction ability: a capillary electrochromatography study

Abstract: A monolithic material with dual functionality was successfully synthesized through the combination of UV-initiated free radical copolymerization, nucleophilic substitution reaction and thiol–ene radical photoaddition. Firstly, poly(N-acryloxysuccinimide-co-ethylene dimethacrylate) was prepared by non-solvent induced phase separation occurring within the course of the polymerization of the respective monomers. Toluene was selected as a porogen providing percolating pores in the micrometer range. Secondly, N-hydroxysuccinimide units on the monolith surface were converted into ene functionality through covalent immobilization of allylamine. Finally, thioglycerol served as a hydrophilizing agent of the pore surface via surface confined thiol–ene click grafting. All the preparation steps were performed, in situ, i.e. within the confines of UV-transparent capillary channels, affording a micro-column with electro-osmotic flow generation and hydrogen bond forming abilities. Raman microspectrocopy confirmed that all the synthetic steps were accomplished successfully. Investigation of the electrochromatographic retention behavior of hydrophobic and hydrophilic solutes revealed the possibility of tuning the interfacial character of the diol-functionalized monolithic stationary phases with respect to the water content in the surrounding liquid phase. For the acetonitrile-rich mobile phase, the diol-monolith interface exhibited highly hydrophilic character allowing fast and efficient separation of phenol and aniline derivatives, as well as methylxanthines and pyrimidic bases. Moreover, the relative standard deviation of the retention factor values was less than 3.3%.

Covalent Attachment and Detachment by Reactive DESI of Sequence-Coded Polymer Taggants.

Abstract: The use of sequence-defined polymers is an interesting emerging solution for materials identification and traceability. Indeed, a very large amount of identification sequences can be created using a limited alphabet of coded monomers. However, in all reported studies, sequence-defined taggants are usually included in a host material by non-covalent adsorption or entrapment, which may lead to leakage, aggregation or degradation. To avoid these problems, sequence-defined polymers were covalently-attached in the present work to the mesh of model materials, namely acrylamide hydrogels. To do so, sequence-coded polyurethanes containing a disulfide linker and a terminal methacrylamide moiety were synthesized by stepwise solid-phase synthesis. These methacrylamide macromonomers were afterwards copolymerized with acrylamide and bisacrylamide in order to achieve crosslinked hydrogels containing covalently-bound polyurethane taggants. It is shown herein that these taggants can be selectively detached from the hydrogel mesh by reactive desorption electrospray ionization. Using dithiothreitol the disulfide linker that link the taggant to the gel can be selectively cleaved. Ultimately, the released taggants can be decoded by tandem mass spectrometry. This article is protected by copyright. All rights reserved.

The non-destructive separation of diverse astrobiologically relevant organic molecules by customizable capillary zone electrophoresis and monolithic capillary electrochromatography

Abstract: The in situ detection of organic molecules in space is key to understanding the variety and the distribution of the building blocks of life, and possibly the detection of extraterrestrial life itself. Gas chromatography mass spectrometry (GC-MS) has been the most sensitive analytical strategy for organic analyses in flight, and was used on missions from NASA's Viking, Phoenix, Curiosity missions to ESA's Rosetta space probe. While pyrolysis GC-MS revealed the first organics on Mars, this step alters or degrades certain fragile molecules that are excellent biosignatures including polypeptides, oligonucleotides and polysaccharides, rendering the intact precursors undetectable. We have identified a solution tailored to the detection of biopolymers and other biomarkers by the use of liquid-based capillary electrophoresis and electrochromatography. In this study, we show that a capillary electrochromatography approach using monolithic stationary phases with tailor-made surface chemistry can separate and identify various polycyclic aromatic hydrocarbons, nucleobases and aromatic acids that could be formed under astrophysically relevant conditions. In order to simulate flyby organic sample capture, we conducted hypervelocity impact experiments which consisted of accelerating peptide-soaked montmorillonite particles to a speed of 5.6 km s−1, and capturing them in an amorphous silica aerogel of 10 mg cm−3 bulk density. Bulk peptide extraction from aerogel followed by capillary zone electrophoresis led to the detection of only two stereoisomeric peptide peaks. The recovery rates of each step of the extraction procedure after the hypervelocity impact suggest that major peptide loss occurred during the impact. Our study provides initial exploration of feasibility of this approach for capturing intact peptides, and subsequently detecting candidate biomolecules during flight missions that would be missed by GC-MS alone. As the monolith-based electrochromatography technology could be customized to detect specific classes of compounds as well as miniaturized, these results demonstrate the potential of the instrumentation for future astrobiology-related spaceflight missions.

Enhanced Resolution of Chiral Amino Acids with Capillary Electrophoresis for Biosignature Detection in Extraterrestrial Samples

Abstract: Amino acids are fundamental building blocks of terrestrial life as well as ubiquitous byproducts of abiotic reactions. In order to distinguish between amino acids formed by abiotic versus biotic processes it is possible to use chemical distributions to identify patterns unique to life. This article describes two capillary electrophoresis methods capable of resolving 17 amino acids found in high abundance in both biotic and abiotic samples (seven enantiomer pairs d/l-Ala, -Asp, -Glu, -His, -Leu, -Ser, -Val and the three achiral amino acids Gly, β-Ala, and GABA). To resolve the 13 neutral amino acids one method utilizes a background electrolyte containing γ-cyclodextrin and sodium taurocholate micelles. The acidic amino acid enantiomers were resolved with γ-cyclodextrin alone. These methods allow detection limits down to 5 nM for the neutral amino acids and 500 nM for acidic amino acids and were used to analyze samples collected from Mono Lake with minimal sample preparation.

Ultralong hydroxyapatite nanowire-based layered catalytic paper for highly efficient continuous flow reactions

Abstract: Herein, we report a new kind of highly flexible hydroxyapatite nanowire (HAPNW)-based layered catalytic paper with a high thermal stability, excellent fire resistance, and high catalytic efficiency for continuous flow catalysis. A simple process has been developed for preparing and loading gold nanoparticles (AuNPs) on the fire-resistant HAPNW paper to obtain the HAPNW/AuNP layered catalytic paper. Oleic acid molecules adsorbed on the surface of HAPNWs can effectively reduce Au(III) ions to Au nanoparticles in situ in aqueous solution in the absence of an additional reducing reagent at room temperature. The size and weight percentage of AuNPs and surface hydrophilicity/hydrophobicity of the HAPNW/AuNP layered catalytic paper can be controlled. Benefiting from the nanoporous network and nanowire-based layered structure, the HAPNW/AuNP layered catalytic paper exhibits high catalytic activity for continuous flow reactions when the aqueous solution flows through the paper. Additionally, the HAPNW/AuNP layered catalytic paper can be easily recycled. Importantly, the HAPNW/AuNP layered catalytic paper shows excellent nonflammable properties and high catalytic stability after heat treatment. The HAPNW/AuNP layered catalytic paper has a high catalytic efficiency (100%), good recyclability, long-term stability, and high thermal stability in the continuous flow catalytic reduction of 4-nitrophenol. Furthermore, the catalytic degradation of organic dyes is also investigated. The HAPNW/AuNP layered catalytic paper is promising for applications in water treatment and high-temperature catalysis. In addition, the fire-resistant HAPNW-based paper can be used as an excellent support for various catalysts to prepare other kinds of catalytic paper for many applications.

The Molecular and Macromolecular Level of Carbon Nanotube Modification Via Diazonium Chemistry: Emphasis on the 2010s Years

Abstract: The present review focusses on the recent progress in the reductive grafting of diazotized big molecules and polymers on carbon nanotubes (CNTs). We briefly summarize the essentials on diazonium synthesis and discuss the CNT physical properties. The different routes for CNT covalent functionalization through diazonium salt interface chemistry are reviewed. The main analytical and spectroscopic techniques used to track carbon nanotube surface modification were cited as well as their advantages and limitations in the light of the information they provide. In this review, the emphasis is on big molecules such as dyes, crown ether, calixarene, cyclodextrin, fullerene and Ru-complex, and biomolecules such as biotin, proteins, and antibodies. The attachment of synthetic polymers to CNT via diazonium chemistry, or by preparing CNT-Polymer nanocomposites through: (1) in situ polymerization (controlled radical polymerization and click chemistry). (2) Oxidative polymerization of conjugated monomers. (3) Grafting onto method by Huisgen 1,3-cycloaddition click reaction and epoxy ring-opening were summarized and discussed. Throughout this review, we reported the recent advances using diazonium salt chemistry in numerous research areas (biomedicine, environment, energy conversion, sensors and actuators, structural composites,…).