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159 results on '"Le Brun, Anton P."'

12. pH-dependent interactions of coacervate-forming histidine-rich peptide with model lipid membranes

Author

Gudlur, Sushanth, primary, Ferreira, Filipe Viana, additional, Ting, Javier Shu Ming, additional, Domene, Carmen, additional, Maricar, Syed, additional, Le Brun, Anton P., additional, Yepuri, Nageshwar, additional, Moir, Michael, additional, Russell, Robert, additional, Darwish, Tamim, additional, Miserez, Ali, additional, and Cárdenas, Marité, additional

Published
2024
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15. Nanometer-Thick ITIC Bulk Heterojunction Films as Non-Fullerene Acceptors in Organic Solar Cells.

Author

Huang, Tzu-Yen, Le Brun, Anton P., Sochor, Benedikt, Wu, Chun-Ming, Bulut, Yusuf, Müller-Buschbaum, Peter, Roth, Stephan V., and Yang, Yan-Ling

Abstract

The nanomorphology of bulk heterojunctions (BHJs) plays a critical role in determining the performance of non-fullerene organic solar cells (OSCs). Thermal annealing is commonly used to reorganize the donor and acceptor phases within the BHJs. In this study, we investigate the vertical morphology of BHJ blend films incorporating the poly-[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di-(2-octyldodecyl)-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) polymer as the donor and 3,9-bis-(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis-(4-hexylphenyl)-dithieno-[2,3-d:2′,3′-d′]-s-indaceno-[1,2-b:5,6-b′]-dithiophene (ITIC) as the acceptor. Neutron reflectivity patterns and scattering length density profiles reveal that the surface of the BHJ films became diffuse when the annealing temperature was above 150 °C. We further find that mitigated agglomeration of PffBT4T-2OD side chains exhibits minimal impact on morphology post-annealing. Instead, ITIC molecules trigger aggregations, accompanied by interface diffusion and increased film roughness. X-ray scattering confirms a 5-fold increase in aggregated ITIC nanodomains after annealing. Our findings highlight that unstable ITIC phases dominate the BHJ morphology of thin films, leading to the thermal instability of OSCs. This study enhances our understanding of the BHJ morphology and offers insights into improving the performance of energy conversion devices. [ABSTRACT FROM AUTHOR]

Published
2024
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23. Underscreening in concentrated electrolytes: re-entrant swelling in polyelectrolyte brushes.

Author

Robertson, Hayden, Elliott, Gareth R., Nelson, Andrew R. J., Le Brun, Anton P., Webber, Grant B., Prescott, Stuart W., Craig, Vincent S. J., Wanless, Erica J., and Willott, Joshua D.

Abstract

Hypersaline environments are ubiquitous in nature and are found in myriad technological processes. Recent empirical studies have revealed a significant discrepancy between predicted and observed screening lengths at high salt concentrations, a phenomenon referred to as underscreening. Herein we investigate underscreening using a cationic polyelectrolyte brush as an exemplar. Poly(2-(methacryloyloxy)ethyl)trimethylammonium (PMETAC) brushes were synthesised and their internal structural changes and swelling response was monitored with neutron reflectometry and spectroscopic ellipsometry. Both techniques revealed a monotonic brush collapse as the concentration of symmetric monovalent electrolyte increased. However, a non-monotonic change in brush thickness was observed in all multivalent electrolytes at higher concentrations, known as re-entrant swelling; indicative of underscreening. For all electrolytes, numerical self-consistent field theory predictions align with experimental studies in the low-to-moderate salt concentration regions. Analysis suggests that the classical theory of electrolytes is insufficient to describe the screening lengths observed at high salt concentrations and that the re-entrant polyelectrolyte brush swelling seen herein is consistent with the so-called regular underscreening phenomenon. [ABSTRACT FROM AUTHOR]

Published
2023
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32. Targeted Delivery of Lm22a-4 by Cubosomes Protects Retinal Ganglion Cells in an Experimental Glaucoma Model

Author

Ding, Yue, primary, Chow, Seong Hoong, additional, Chen, Jinying, additional, Le Brun, Anton P., additional, Wu, Chun-Ming, additional, Duff, Anthony P., additional, Wang, Yajun, additional, Wong, Vickie HY, additional, Zhao, Da, additional, Lee, Tzong-Hsien, additional, Conn, Charlotte E., additional, Hsu, Hsien-Yi, additional, Bui, Bang V., additional, Liu, Guei-Sheung, additional, and Shen, Hsin-Hui, additional

Published
2020
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37. Investigating the interaction of octapeptin A3 with model bacterial membranes

Author

Han, Mei-Ling, Shen, Hsin-Hui, Hansford, Karl A., Schneider, Elena. K., Sivanesan, Sivashangarie, Kade, Roberts, D., Thompson, Philip E., Le Brun, Anton P., Zhu, Yan, Sani, Marc-Antoine, Separovic, Frances, Blaskovich, Mark A.T., Baker, Mark A., Moskowitz, Samuel M., Cooper, Matthew A., Li, Jian, and Velkov, Tony

Subjects
0301 basic medicine, 1,2-Dipalmitoylphosphatidylcholine, medicine.drug_class, Polymyxin, 030106 microbiology, Lipid Bilayers, Phospholipid, Biology, Article, Cell membrane, Lipid A, 03 medical and health sciences, chemistry.chemical_compound, Lipopeptides, Drug Resistance, Multiple, Bacterial, medicine, Carbohydrate Conformation, Lipid bilayer, Unilamellar Liposomes, Polymyxin B, Cell Membrane, 030104 developmental biology, Infectious Diseases, medicine.anatomical_structure, Membrane, chemistry, Biochemistry, Pseudomonas aeruginosa, lipids (amino acids, peptides, and proteins), Neutron reflectometry, Bacterial outer membrane, Protein Binding
Abstract

Octapeptins are cyclic lipopeptides that do not exhibit cross-resistance with polymyxins and have a broader spectrum of activity that includes fungi and Gram-positive bacteria. In the present study we investigated the interaction of octapeptin A3 with asymmetric outer membrane models of the Gram-negative pathogen Pseudomonas aeruginosa, using neutron reflectometry, together with fluorimetric and calorimetry methods. For the first time our neutron reflectometry results reveal that the interaction of octapeptin A3 with the Gram-negative outer membrane involves an initial transient polar interaction with the phospholipid and lipid A head groups, followed by the penetration of the entire octapeptin molecule into the fatty acyl core of the outer membrane. This mechanism contrasts that of polymyxin B which specifically targets lipid A, whereas octapeptins appear to target both lipid A and phospholipids. Furthermore, the mechanism of octapeptins does not appear to be highly dependent on an initial complimentary electrostatic interaction with lipid A, which accounts for their ability to bind to the lipid A of polymyxin-resistant Gram-negative bacteria which is modified with cationic moieties that act to electrostatically repel the cationic polymyxin molecule. The presented findings shed new light on the mechanism whereby octapeptins penetrate the outer membrane of polymyxin-resistant Gram-negative pathogens and highlight their potential as candidates for development as new antibiotics against problematic multi-drug resistant pathogens.

Published
2017

40. Electrochemical and Electrostatic Cleavage of Alkoxyamines

Author

Zhang, Long, Laborda, Eduardo, Darwish, Nadim A, Noble, Benjamin B, Tyrell, Jason, Pluczyk, Sandra, Le Brun, Anton P, Wallace, Gordon G, Gonzalez, Joaquin, Coote, M, Ciampi, Simone, Zhang, Long, Laborda, Eduardo, Darwish, Nadim A, Noble, Benjamin B, Tyrell, Jason, Pluczyk, Sandra, Le Brun, Anton P, Wallace, Gordon G, Gonzalez, Joaquin, Coote, M, and Ciampi, Simone

Abstract

Alkoxyamines are heat-labile molecules, widely used as an in situ source of nitroxides in polymer and materials sciences. Here we show that the one-electron oxidation of an alkoxyamine leads to a cation radical intermediate that even at room temperature rapidly fragments, releasing a nitroxide and carbocation. Digital simulations of experimental voltammetry and current-time transients suggest that the unimolecular decomposition which yields the "unmasked" nitroxide (TEMPO) is exceedingly rapid and irreversible. High-level quantum computations indicate that the collapse of the alkoxyamine cation radical is likely to yield a neutral nitroxide radical and a secondary phenylethyl cation. However, this fragmentation is predicted to be slow and energetically very unfavorable. To attain qualitative agreement between the experimental kinetics and computational modeling for this fragmentation step, the explicit electrostatic environment within the double layer must be accounted for. Single-molecule break-junction experiments in a scanning tunneling microscope using solvent of low dielectric (STM-BJ technique) corroborate the role played by electrostatic forces on the lysis of the alkoxyamine C-ON bond. This work highlights the electrostatic aspects played by charged species in a chemical step that follows an electrochemical reaction, defines the magnitude of this catalytic effect by looking at an independent electrical technique in non-electrolyte systems (STM-BJ), and suggests a redox on/off switch to guide the cleavage of alkoxyamines at an electrified interface.

Published
2018

41. Electrochemical and Electrostatic Cleavage of Alkoxyamines

Author

Zhang, Long, primary, Laborda, Eduardo, additional, Darwish, Nadim, additional, Noble, Benjamin B., additional, Tyrell, Jason H., additional, Pluczyk, Sandra, additional, Le Brun, Anton P., additional, Wallace, Gordon G., additional, Gonzalez, Joaquin, additional, Coote, Michelle L., additional, and Ciampi, Simone, additional

Published
2018
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45. Investigating the Interaction of Octapeptin A3 with Model Bacterial Membranes

Author

Han, Mei-Ling, primary, Shen, Hsin-Hui, additional, Hansford, Karl A., additional, Schneider, Elena K., additional, Sivanesan, Sivashangarie, additional, Roberts, Kade D., additional, Thompson, Philip E., additional, Le Brun, Anton P., additional, Zhu, Yan, additional, Sani, Marc-Antoine, additional, Separovic, Frances, additional, Blaskovich, Mark A. T., additional, Baker, Mark A., additional, Moskowitz, Samuel M., additional, Cooper, Matthew A., additional, Li, Jian, additional, and Velkov, Tony, additional

Published
2017
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Author

Cortie, David L, Khaydukov, Y, Keller, T, Sprouster, David, Hughes, Jacob, Sullivan, James P, Wang, Xiaolin, Le Brun, Anton P, Bertinshaw, Joel, Callori, S J, Aughterson, Robert, James, Michael, Evans, P, Triani, Gerry, Klose, Frank, Cortie, David L, Khaydukov, Y, Keller, T, Sprouster, David, Hughes, Jacob, Sullivan, James P, Wang, Xiaolin, Le Brun, Anton P, Bertinshaw, Joel, Callori, S J, Aughterson, Robert, James, Michael, Evans, P, Triani, Gerry, and Klose, Frank

Abstract

High magnetizations are desirable for spintronic devices that operate by manipulating electronic states using built-in magnetic fields. However, the magnetic moment in promising dilute magnetic oxide nanocomposites is very low, typically corresponding to only fractions of a Bohr magneton for each dopant atom. In this study, we report a large magnetization formed by ion implantation of Co into amorphous TiO2-¿ films, producing an inhomogeneous magnetic moment, with certain regions producing over 2.5 ¿B per Co, depending on the local dopant concentration. Polarized neutron reflectometry was used to depth-profile the magnetization in the Co:TiO2-¿ nanocomposites, thus confirming the pivotal role of the cobalt dopant profile inside the titania layer. X-ray photoemission spectra demonstrate the dominant electronic state of the implanted species is Co0, with a minor fraction of Co2+. The detected magnetizations have seldom been reported before and lie near the upper limit set by Hund's rules for Co0, which is unusual because the transition metal's magnetic moment is usually reduced in a symmetric 3D crystal-field environment. Low-energy positron annihilation lifetime spectroscopy indicates that defect structures within the titania layer are strongly modified by the implanted Co. We propose that a clustering motif is promoted by the affinity of the positively charged implanted species to occupy microvoids native to the amorphous host. This provides a seed for subsequent doping and nucleation of nanoclusters within an unusual local environment.

Published
2017

47. Reproducible flaws unveil electrostatic aspects of semiconductor electrochemistry

Author

Vogel, Yan Boris, Zhang, Long, Darwish, Nadim A, Goncales, Vinicius R, Le Brun, Anton P, Gooding, J Justin, Molina, Angela, Wallace, Gordon G, Coote, M, Gonzalez, Joaquin, Ciampi, Simone, Vogel, Yan Boris, Zhang, Long, Darwish, Nadim A, Goncales, Vinicius R, Le Brun, Anton P, Gooding, J Justin, Molina, Angela, Wallace, Gordon G, Coote, M, Gonzalez, Joaquin, and Ciampi, Simone

Abstract

Predicting or manipulating charge-transfer at semiconductor interfaces, from molecular electronics to energy conversion, relies on knowledge generated from a kinetic analysis of the electrode process, as provided by cyclic voltammetry. Scientists and engineers encountering non-ideal shapes and positions in voltammograms are inclined to reject these as flaws. Here we show that non-idealities of redox probes confined at silicon electrodes, namely full width at half maximum < 90.6 mV and anti-thermodynamic inverted peak positions, can be reproduced and are not flawed data. These are the manifestation of electrostatic interactions between dynamic molecular charges and the semiconductor's space-charge barrier. We highlight the interplay between dynamic charges and semiconductor by developing a model to decouple effects on barrier from changes to activities of surface-bound molecules. These findings have immediate general implications for a correct kinetic analysis of charge-transfer at semiconductors as well as aiding the study of electrostatics on chemical reactivity.

Published
2017

48. Enhanced Magnetization of Cobalt Defect Clusters Embedded in TiO2−δ Films

Author

Cortie, David L., primary, Khaydukov, Yury, additional, Keller, Thomas, additional, Sprouster, David J., additional, Hughes, Jacob S., additional, Sullivan, James P., additional, Wang, Xiaolin L., additional, Le Brun, Anton. P., additional, Bertinshaw, Joel, additional, Callori, Sara J., additional, Aughterson, Robert, additional, James, Michael, additional, Evans, Peter J., additional, Triani, Gerry, additional, and Klose, Frank, additional

Published
2017
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49. TEMPO Monolayers on Si(100) Electrodes: Electrostatic Effects by the Electrolyte and Semiconductor Space-Charge on the Electroactivity of a Persistent Radical

Author

Zhang, Long, Vogel, Yan Boris, Noble, Benjamin B, Goncales, Vinicius R, Darwish, Nadim A, Le Brun, Anton P, Gooding, J Justin, Wallace, Gordon G, Coote, M, Ciampi, Simone, Zhang, Long, Vogel, Yan Boris, Noble, Benjamin B, Goncales, Vinicius R, Darwish, Nadim A, Le Brun, Anton P, Gooding, J Justin, Wallace, Gordon G, Coote, M, and Ciampi, Simone

Abstract

This work demonstrates the effect of electrostatic interactions on the electroactivity of a persistent organic free radical. This was achieved by chemisorption of molecules of 4-azido-2,2,6,6-tetramethyl-1-piperdinyloxy (4-azido-TEMPO) onto monolayer-modified Si(100) electrodes using a two-step chemical procedure to preserve the open-shell state and hence the electroactivity of the nitroxide radical. Kinetic and thermodynamic parameters for the surface electrochemical reaction are investigated experimentally and analyzed with the aid of electrochemical digital simulations and quantum-chemical calculations of a theoretical model of the tethered TEMPO system. Interactions between the electrolyte anions and the TEMPO grafted on highly doped, i.e., metallic, electrodes can be tuned to predictably manipulate the oxidizing power of surface nitroxide/oxoammonium redox couple, hence showing the practical importance of the electrostatics on the electrolyte side of the radical monolayer. Conversely, for monolayers prepared on the poorly doped electrodes, the electrostatic interactions between the tethered TEMPO units and the semiconductor-side, i.e., space-charge, become dominant and result in drastic kinetic changes to the electroactivity of the radical monolayer as well as electrochemical nonidealities that can be explained as an increase in the self-interaction "a" parameter that leads to the Frumkin isotherm.

Published
2016

50. Evidence of the Key Role of H3O+ in Phospholipid Membrane Morphology

Author

Cranfield, Charles G., primary, Berry, Thomas, additional, Holt, Stephen A., additional, Hossain, Khondker R., additional, Le Brun, Anton P., additional, Carne, Sonia, additional, Al Khamici, Heba, additional, Coster, Hans, additional, Valenzuela, Stella M., additional, and Cornell, Bruce, additional

Published
2016
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