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- ItemEffect of alkanethiol chain length on the oxidation resistance of self-assembled monolayer passivated Ge(100) surfaces(Elsevier B.V., 2023-06-08) Garvey, Shane; Maccioni, Barbara; Serino, Andrew C.; Holmes, Justin D.; Nolan, Michael; Draeger, Nerissa; Long, Brenda; Enterprise Ireland; Lam ResearchThe use of self-assembled monolayers (SAMs) of heteroalkanes as passivation layers to protect against oxidation has been studied on a variety of materials. However, typically heteroalkanes with C8 and longer have been used, since the contributing van der Waals between the carbon chains is a significant stabilising force and the longer the chain the greater the force. The industry requirement for passivating semiconducting materials is that they remain oxide free for a queue time of 24 h. The remit of this study is to explore whether passivation using shorter chain alkanethiols, which would be beneficial for reducing carbon, will work to prevent re-oxidation over this time frame. A series of 1-alkanethiols, with chain lengths from C2 to C12 are used to create SAMs on Ge(100) and a study of the re-oxidation of the passivated Ge upon exposure to ambient conditions is undertaken in an effort to determine how chain length effects oxidation resistance of the passivated Ge. X-ray photoelectron spectroscopy is used, complimented by water contact angle measurements to show that the longer thiol molecules outperform their shorter-chain counterparts at inhibiting re-oxidation over 168 h of exposure to ambient. Nonetheless, Ge surfaces passivated by the short-chain thiols, down to C4, still display acceptable resistance to re-oxidation. Finally, a detailed summary of density functional theory simulations whereby the most stable SAM structures and coverages are explored.
- ItemLigand-aided glycolysis of PET using functionalized silica-supported Fe2O3 nanoparticles(ACS Publications, 2023-10-18) Rimola, Albert; Holmes, Justin D.; Collins, Gillian; Casey, Éadaoin; Breen, Rachel; Gómez, Jennifer S.; Kentgens, Arno P. M.; Pareras, Gerard; Science Foundation Ireland; Horizon 2020; Fundación Margarita Salas; Ministerio de Economía y CompetitividadThe development of efficient catalysts for the chemical recycling of poly(ethylene terephthalate) (PET) is essential to tackling the global issue of plastic waste. There has been intense interest in heterogeneous catalysts as a sustainable catalyst system for PET depolymerization, having the advantage of easy separation and reuse after the reaction. In this work, we explore heterogeneous catalyst design by comparing metal-ion (Fe3+) and metal-oxide nanoparticle (Fe2O3 NP) catalysts immobilized on mesoporous silica (SiO2) functionalized with different N-containing amine ligands. Quantitative solid-state nuclear magnetic resonance (NMR) spectroscopy confirms successful grafting and elucidates the bonding mode of the organic ligands on the SiO2 surface. The surface amine ligands act as organocatalysts, enhancing the catalytic activity of the active metal species. The Fe2O3 NP catalysts in the presence of organic ligands outperform bare Fe2O3 NPs, Fe3+-ion-immobilized catalysts and homogeneous FeCl3 salts, with equivalent Fe loading. X-ray photoelectron spectroscopy analysis indicates charge transfer between the amine ligands and Fe2O3 NPs and the electron-donating ability of the N groups and hydrogen bonding may also play a role in the higher performance of the amine-ligand-assisted Fe2O3 NP catalysts. Density functional theory (DFT) calculations also reveal that the reactivity of the ion-immobilized catalysts is strongly correlated to the ligand-metal binding energy and that the products in the glycolysis reaction catalyzed by the NP catalysts are stabilized, showing a significant exergonic character compared to single ion-immobilized Fe3+ ions.
- ItemSynthesis and evaluation of aromatic BDSF bioisosteres on biofilm formation and colistin sensitivity in pathogenic bacteria(Elsevier, 2023-09-23) Gómez, Andromeda-Celeste; Horgan, Conor; Yero, Daniel; Bravo, Marc; Daura, Xavier; O'Driscoll, Michelle; Gibert, Isidre; O'Sullivan, Timothy P.; Irish Research Council; Ministerio de Ciencia e Innovación; Agència de Gestió d'Ajuts Universitaris i de RecercaThe diffusible signal factor family (DSF) of molecules play an important role in regulating intercellular communication, or quorum sensing, in several disease-causing bacteria. These messenger molecules, which are comprised of cis-unsaturated fatty acids, are involved in the regulation of biofilm formation, antibiotic tolerance, virulence and the control of bacterial resistance. We have previously demonstrated how olefinic N-acyl sulfonamide bioisosteric analogues of diffusible signal factor can reduce biofilm formation or enhance antibiotic sensitivity in a number of bacterial strains. This work describes the design and synthesis of a second generation of aromatic N-acyl sulfonamide bioisosteres. The impact of these compounds on biofilm production in Acinetobacter baumannii, Escherichia coli, Burkholderia multivorans, Burkholderia cepacia, Burkholderia cenocepacia, Pseudomonas aeruginosa and Stenotrophomonas maltophilia is evaluated, in addition to their effects on antibiotic tolerance. The ability of these molecules to increase survival rates on co-administration with colistin is also investigated using the Galleria infection model.
- ItemOrganocatalytic asymmetric peroxidation of g,d-unsaturated ß-keto esters - A novel route to chiral cycloperoxides(2023-05-24) Hennessy, Mary C.; Hirenkumar, Gandhi; O'Sullivan, Timothy P.; Irish Research Council; Science Foundation IrelandA methodology for the asymmetric peroxidation of g,d-unsaturated ß-keto esters is presented. Using a cinchona-derived organocatalyst, the target d-peroxy-ß-keto esters were obtained in high enantiomeric ratios of up to 95:5. Additionally, these d-peroxy esters can be readily reduced to chiral d-hydroxy-ß-keto esters without impacting the ß-keto ester functionality. Importantly, this chemistry opens up a concise route to chiral 1,2-dioxolanes, a common motif in many bioactive natural products, via a novel P2O5-mediated cyclisation of the corresponding d-peroxy-ß-hydroxy esters.
- ItemThickness control of dispersion in opal photonic crystals(Elsevier B.V., 2023-06-28) Grant, Alex; Lonergan, Alex; O'Dwyer, Colm; Irish Research Council; Horizon 2020; European Regional Development Fund; Enterprise IrelandOpals are naturally occurring photonic crystals which can be formed easily using low-cost self-assembly methods. While the optical behaviour of opals has received significant attention over the last number of decades, there is limited information on the effect of crystal thickness on the optical properties they display. Here, the relationship between volume fraction and crystal thickness is established with an evaporation-induced self-assembly (EISA) method of formation. The extent to which thickness can be used to manipulate the optical properties of the crystals is explored, focusing on the change in the photonic band gap (PBG). Microscopical structural characterization and angle-resolved transmission spectroscopy are used to examine the quality of the photonic crystals formed using different volume fractions of polystyrene spheres, with thicknesses up to 37 layers grown from volume fractions of 0.125%. This work provides a direct correlation between sphere solution volume fraction and crystal thickness, and the associated optical fingerprint of opal photonic crystals. Maximum thickness is examined, which is shown to converge to a narrow range over several evaporation rates. We identify the criteria required to achieve thickness control in relatively fast evaporation induced self-assembly while maintaining structural quality, and the change to the spectroscopic signature to the (111) stopband and higher order (220) reflections, under conditions where a less ordered photonic crystals are formed.