Martin Edwards - Profile on Academia.edu (original) (raw)
Papers by Martin Edwards
Physical Chemistry Chemical Physics, 2023
A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a ... more A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a planar electrode for a 1e outer-sphere redox process, which fully accounts for cell electrostatics, including ohmic potential drop, ion migration, and the structure of the potential-dependent electric double layer. Both reversible and quasi-reversible redox reactions are treated. The simulations compute the time-dependent electric potential and ion distributions across the entire cell during a voltammetric scan. In this way, it is possible to obtain the interdependent faradaic and non-faradaic contributions to a CV and rigorously include all effects of the electric potential distribution on the rate of electron transfer and the local concentrations of the redox species O z and R zÀ1 . Importantly, we demonstrate that the driving force for electron transfer can be different to the applied potential when electrostatic interactions are included. We also show that the concentrations of O z and R zÀ1 at the plane of electron transfer (PET) significantly depart from those predicted by the Nernst equation, even when the system is characterised by fast electron transfer/diffusion control. A mechanistic rationalisation is also presented as to why the electric double layer has a negligible effect on the CV response of such reversible systems. In contrast, for quasi-reversible electron transfer the concentrations of redox species at the PET are shown to play an important role in determining CV wave shape, an effect also dependant on the charge of the redox species and the formal electrode potential of the redox couple. Failure to consider electrostatic effects could lead to incorrect interpretation of electron-transfer kinetics from the CV response. Simulated CVs at scan rates between 0.1 and 1000 V s À1 are found to be in good agreement with experimental data for the reduction of 1.0 mM Ru(NH 3 ) 6 3+ at a 2 mm diameter gold disk electrode in 1.0 M potassium nitrate.
ResearchOnline at James Cook University (James Cook University), Jun 1, 2009
Langmuir, May 30, 2018
Nanobubble nucleation is a problem that affects efficiency in electrocatalytic reactions since th... more Nanobubble nucleation is a problem that affects efficiency in electrocatalytic reactions since those bubbles can block the surface of the catalytic sites. In this article, we focus on the nucleation rate of O 2 nanobubbles resulting from the electrooxidation of H 2 O 2 at Pt disk nanoelectrodes. Bubbles form almost instantaneously when a critical peak current, i nb p , is applied, but for lower currents, bubble nucleation is a stochastic process in which the nucleation (induction) time, t ind , dramatically decreases as the applied current approaches i nb p , a consequence of the local supersaturation level, ζ, increasing at high currents. Here, by applying different currents below i nb p , nanobubbles take some time to nucleate and block the surface of the Pt electrode at which the reaction occurs, providing a means to measure the stochastic t ind . We study in detail the different conditions in which nanobubbles appear, concluding that the electrode surface needs to be preconditioned to achieve reproducible results. We also measure the activation energy for bubble nucleation, E a , which varies in the range from (6 to 30)kT, and assuming a spherically cap-shaped nanobubble nucleus, we determine the footprint diameter L = 8-15 nm, the contact angle to the electrode surface θ = 135-155°, and the number of O 2 molecules contained in the nucleus (50 to 900 molecules).
Angewandte Chemie, Aug 20, 2020
Achieving control over the size distribution of metal-organic-framework (MOF) nanoparticles is ke... more Achieving control over the size distribution of metal-organic-framework (MOF) nanoparticles is key to biomedical applications and seeding techniques. Electrochemical control over the nanoparticle synthesis of the MOF, HKUST-1, is achieved using a nanopipette injection method to locally mix Cu 2+ salt precursor and benzene-1,3,5-tricarboxylate (BTC 3À ) ligand reagents, to form MOF nanocrystals, and collect and characterise them on a TEM grid. In situ analysis of the size and translocation frequency of HKUST-1 nanoparticles is demonstrated, using the nanopipette to detect resistive pulses as nanoparticles form. Complementary modelling of mass transport in the electric field, enables particle size to be estimated and explains the feasibility of particular reaction conditions, including inhibitory effects of excess BTC 3À . These new methods should be applicable to a variety of MOFs, and scaling up synthesis possible via arrays of nanoscale reaction centres, for example using nanopore membranes.
ACS Sensors, 2020
An electrochemical sensor that contains patterned regions of sp 2 -carbon in a boron doped diamon... more An electrochemical sensor that contains patterned regions of sp 2 -carbon in a boron doped diamond (BDD) matrix is presented for the quantitative detection of hypochlorite (OCl -) at high concentrations in the alkaline, chemically oxidizing environment associated with bleach. As BDD itself is unresponsive to OCl -reduction within the solvent window, by using a laser micromachining process it is possible to write robust electrochemically active regions of sp 2 -carbon into the electrochemically inert sp 3 BDD electrode. In this work, four different laser patterned BDD electrodes are examined and their response compared across a range of OCl -concentrations (0.02 M to 1.50 M). A single macro-spot (0.37 mm diameter disk) electrode and a closely spaced micro-spot (46 m diameter disk) hexagonal array electrode, containing the same surface area of sp 2 -carbon, are shown to provide the most linear response towards OCl -reduction. Finite element modelling (FEM) is employed to better understand the electrochemical system, due to the complexity of the electrode geometry, as well as the need to include contributions from migration and Ohmic drop at these high concentrations. FEM data suggest that only a small percentage (~ 1×10 -3 %) of the total laser-machined sp 2 area is active towards the OCl -reduction process and that this process is kinetically very sluggish (~ k eff = 1×10 -12 cm s -1 ). The sensitivity at the micro-array electrode (-0.127 ± 0.004 mA M -1 ; R 2 = 0.992) is higher than that at the single-spot (-0.075 ± 0.002 mA M -1 ; R 2 = 0.996) due to the enhanced effect of transport to the edges of the micro-spots, shown via simulation. The electrodes returned a relatively stable response over a > three-month period of use in the OCl - solutions, demonstrating these hybrid sp 2 -BDD electrodes show promise for long-term monitoring applications in the harsh environments associated with bleaching applications.
Langmuir, 2019
We report the observation of transient bipolar electrochemical coupling on freely-moving 40 nm si... more We report the observation of transient bipolar electrochemical coupling on freely-moving 40 nm silver nanoparticles. The use of an asymmetric nanoelectrochemical environment at the nanopore orifice, e.g., an acid inside the pipette and halide ions in the bulk, enabled us to observe unusually large current blockages of single Ag nanoparticles. We attribute these current blockages to the formation of H 2 nanobubbles on the surface of Ag nanoparticles due to the coupled faradaic reactions, in which the reduction of protons and water is coupled to the oxidation of Ag and water under potentials higher than 1 V. The appearance of large current blockages was strongly dependent upon the applied voltage and the choice of anions in the bulk solution. The correlation between large current blockages with the oxidation of Ag nanoparticles and their nanopore translocation was further supported by simultaneous fluorescence and electric recordings. This study demonstrates that transient bipolar electrochemistry can take place on small metal nanoparticles below 50 nm when they pass through nanopores where the electric field is highly localized. The use of a nanopore and the resistive-pulse sensing method to study transient bipolar electrochemistry of nanoparticles may be extended to the future studies in ultrafast electrochemistry, nanocatalyst screening, and gas nucleation on nanoparticles.
Biophysical Journal, 2014
and single-molecular force spectroscopy (SMFS) were applied. Direct highresolution imaging of the... more and single-molecular force spectroscopy (SMFS) were applied. Direct highresolution imaging of the outer surface of T. forsythia wild-type cells by AFM revealed a p4 structure with a lattice constant of ~9.0 nm. In contrast, on S-layer mutant cells, no periodic lattice could be visualized. Additionally, SMFS was used to probe specific interaction forces between an anti-TfsA antibody coupled to the AFM tip and the S-layer as present on T. forsythia wild-type and mutant cells displaying TfsA-GP alone. Unbinding forces between the antibody and wild-type cells were greater than with mutant cells. This indicated that the TfsA-GP is less strongly attached to the mutant cell surface when the co-assembling TfsB-GP is missing. Altogether, our data confirm the current model of the S-layer architecture with two intercalating S-layer glycoproteins and TfsA-GP mainly outwardly orientated. This study was funded by a Marie Curie International Incoming Fellowship of the 7 th European Community Framework Program (to Y. J. O.). Financial support came from the Austrian Science Fund FWF projects P20605-B12 and P24317-B22 (to C.S.). Board B284 Specific Role of Glycolipids in the Regular Stacking of Membranes Reconstituted from Thylakoid Lipid Extracts Bruno Deme ´1, Ce ´line Cataye 2 , Maryse Block 2 , E ´ric Mare ´chal 2 , Juliette Jouhet 2 .
F1000Research, 2014
Ectonucleotidases are membrane-bound or secreted proteins that hydrolyze extracellular nucleotide... more Ectonucleotidases are membrane-bound or secreted proteins that hydrolyze extracellular nucleotides. Recently, we identified three ectonucleotidases that hydrolyze extracellular adenosine 5’-monophosphate (AMP) to adenosine in primary somatosensory neurons. Currently, it is unclear which ectonucleotidases hydrolyze ATP and ADP in these neurons. Ectonucleoside triphosphate diphosphohydrolases (ENTPDs) comprise a class of enzymes that dephosphorylate extracellular ATP and ADP. Here, we found that ENTPD3 (also known as NTPDase3 or CD39L3) was located in nociceptive and non-nociceptive neurons of the dorsal root ganglion (DRG), in the dorsal horn of the spinal cord, and in free nerve endings in the skin. To determine if ENTPD3 contributes directly to ATP and ADP hydrolysis in these tissues, we generated and characterized an Entpd3 knockout mouse. This mouse lacks ENTPD3 protein in all tissues examined, including the DRG, spinal cord, skin, and bladder. However, DRG and spinal cord...
Biophysical Journal, 2013
We present what is, to our knowledge, the first experimental demonstration of dielectric constant... more We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization forces which were measured using an electrostatic force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of ε r ~3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (ε r ~2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane electrostatics and other bioelectric phenomena.
Figshare documentation (Figshare (United Kingdom)), Jul 21, 2020
Chemical Communications, 2016
Faraday Discussions, organised by the Royal Society of Chemistry (RSC), bring the concept of the ... more Faraday Discussions, organised by the Royal Society of Chemistry (RSC), bring the concept of the flipped classroom to scientific conferences, promoting lively debate and discussion with the opportunity to hear complementary and contrasting views on topics spanning physical chemistry. The Faraday Discussion on the topic of single entity electrochemistry, in the picturesque setting of the University of York (31 st August to 2 nd September, 2016), presented an opportunity for researchers pushing at the lower limits of electrochemistry to engage in such lively discourse. The topic single entity was chosen to be as inclusive as possible, and proved to be so, with researchers probing single nanoparticles, nanopores, nanorods, vesicles and even single molecules, with a wide range of electrochemical techniques, both experimental and theoretical.
bioRxiv (Cold Spring Harbor Laboratory), Aug 18, 2022
Solid-state nanopores have been widely employed in the detection of biomolecules, but low signal-... more Solid-state nanopores have been widely employed in the detection of biomolecules, but low signal-to-noise ratios still represent a major obstacle to enable the discrimination of short nucleic acid and protein sequences. The addition of 50% polyethylene glycol (PEG) to the bath solution was recently demonstrated as a simple way to enhance the detection of such biomolecules translocating through a model solid-state nanopore. Here, we provide a comprehensive description of the physics describing a nanopore measurement carried out in 50% PEG that is supported by finite-element modelling and experiments. We demonstrate that the addition of PEG to the external solution introduces a strong imbalance in the transport properties of cations and anions, drastically affecting the characteristic current response of the nanopore. We further show that the strong asymmetric current response is due to a polarity-dependent ion distribution and transport at the nanopipette tip region, leading to either ion depletion or enrichment for few tens of nanometers across the aperture. Under negative potential, when double-stranded DNA molecules translocate, the depleted region (sensing region) significantly improves the sensitivity compared to systems without PEG. We then introduce a displacement of the interface between pore and external solution to simulate the mechanical interactions between analyte and PEG molecules. We found that this displacement affects the ion distribution in the sensing region, enhancing the detection current during the translocation of biomolecules. .
A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a ... more A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a planar electrode for a 1e outer-sphere redox process, which fully accounts for cell electrostatics, including ohmic potential drop, ion migration, and the structure of the potentialdependent electric double layer. Both reversible and quasi-reversible redox reactions are treated. The simulations compute the time-dependent electric potential and ion distributions across the entire cell during a voltammetric scan. In this way, it is possible to obtain the interdependent faradaic and non-faradaic contributions to a CV and rigorously include all effects of the electric potential distribution on the rate of electron transfer and the local
Bipyridine complexes of Ni are used as catalysts in a variety of reductive transformations. Here,... more Bipyridine complexes of Ni are used as catalysts in a variety of reductive transformations. Here, the electroreduction of [Ni(Mebpy)3]2+ (Mebpy = 4,4’-dimethyl-2,2’-bipyridine) in dimethylformamide is reported, with the aim of determining the redox mechanism and oxidation states of products formed under well-controlled electrochemical conditions. Results from cyclic voltammetry, steady-state voltammetry (SSV) and chronoamperometry demonstrate that [Ni(Mebpy)3]2+ undergoes two sequential 1e reductions at closely separated potentials (E0’1 = -1.06 ± 0.01 V and E0’2 = -1.15 ± 0.01 V vs Ag/AgCl (3.4 M KCl)). Homogeneous comproportionation to generate [Ni(Mebpy)3]+ is demonstrated in SSV experiments in low ionic strength solutions. The comproportionation rate constant is determined to be > 106 M-1s-1, consistent with rapid outer-sphere electron transfer. Consequentially, on voltammetric time scales, the 2e reduction of [Ni(Mebpy)3]2+ results in formation of [Ni(Mebpy)3]1+ as the predo...
Chemical Science, 2020
Nanoparticles mimicking the three-dimensional architecture of enzymes where the reaction occurs d... more Nanoparticles mimicking the three-dimensional architecture of enzymes where the reaction occurs down a channel isolated from bulk solution, referred here as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions.
Journal of the American Chemical Society, 2019
Below is the automatically generated Comsol "model report", which describes in detail the boundar... more Below is the automatically generated Comsol "model report", which describes in detail the boundary conditions, geometry, mesh, solver configuration, etc., used in the finite element simulations of the 3-phase interface reported in this work and described in Supporting Information, section 6.
C-N cross-coupling is one of the most valuable and widespread transformations in organic synthesi... more C-N cross-coupling is one of the most valuable and widespread transformations in organic synthesis. Largely dominated by Pd-and Cu-based catalytic systems, it has proven to be a staple transformation for those in both academia and industry. The current study presents the development and mechanistic understanding of an electrochemically driven, Ni-catalyzed method for achieving this reaction of high strategic importance. Through a series of electrochemical, computational, kinetic, and empirical experiments the key mechanistic features of this reaction have been unraveled, leading to a second generation set of conditions that is applicable to a broad range of aryl halides and amine nucleophiles, including complex examples on oligopeptides, medicinally-relevant heterocycles, natural products, and sugars. Full disclosure of the current limitations as well as procedures for both batch and flow scale-ups (100 gram) are also described.
Faraday Discussions, 2018
The stochastic nature of very fast single-entity events challenges current electrochemical method... more The stochastic nature of very fast single-entity events challenges current electrochemical methods and modern electronics, as illustrated using recent experiments from the authors’ laboratory.
ACS nano, Jan 27, 2018
The oxidation of catecholamine at a microelectrode, following its release from individual vesicle... more The oxidation of catecholamine at a microelectrode, following its release from individual vesicles, allows interrogation of the content of single nanometer vesicles with vesicle impact electrochemical cytometry (VIEC). Previous to this development, there were no methods available to quantify the chemical load of single vesicles. However, accurate quantification of the content is hampered by uncertainty in the proportion of substituent molecules reaching the electrode surface (collection efficiency). In this work, we use quantitative modeling to calculate this collection efficiency. For all vesicles except those at the very edge of the electrode, modeling shows that ∼100% oxidation efficiency is achieved when employing a 33 μm diameter disk microelectrode for VIEC, independent of the location of the vesicle release pore. We use this to experimentally determine a precise distribution of catecholamine in individual vesicles extracted from PC12 cells. In contrast, we calculate that when...
Physical Chemistry Chemical Physics, 2023
A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a ... more A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a planar electrode for a 1e outer-sphere redox process, which fully accounts for cell electrostatics, including ohmic potential drop, ion migration, and the structure of the potential-dependent electric double layer. Both reversible and quasi-reversible redox reactions are treated. The simulations compute the time-dependent electric potential and ion distributions across the entire cell during a voltammetric scan. In this way, it is possible to obtain the interdependent faradaic and non-faradaic contributions to a CV and rigorously include all effects of the electric potential distribution on the rate of electron transfer and the local concentrations of the redox species O z and R zÀ1 . Importantly, we demonstrate that the driving force for electron transfer can be different to the applied potential when electrostatic interactions are included. We also show that the concentrations of O z and R zÀ1 at the plane of electron transfer (PET) significantly depart from those predicted by the Nernst equation, even when the system is characterised by fast electron transfer/diffusion control. A mechanistic rationalisation is also presented as to why the electric double layer has a negligible effect on the CV response of such reversible systems. In contrast, for quasi-reversible electron transfer the concentrations of redox species at the PET are shown to play an important role in determining CV wave shape, an effect also dependant on the charge of the redox species and the formal electrode potential of the redox couple. Failure to consider electrostatic effects could lead to incorrect interpretation of electron-transfer kinetics from the CV response. Simulated CVs at scan rates between 0.1 and 1000 V s À1 are found to be in good agreement with experimental data for the reduction of 1.0 mM Ru(NH 3 ) 6 3+ at a 2 mm diameter gold disk electrode in 1.0 M potassium nitrate.
ResearchOnline at James Cook University (James Cook University), Jun 1, 2009
Langmuir, May 30, 2018
Nanobubble nucleation is a problem that affects efficiency in electrocatalytic reactions since th... more Nanobubble nucleation is a problem that affects efficiency in electrocatalytic reactions since those bubbles can block the surface of the catalytic sites. In this article, we focus on the nucleation rate of O 2 nanobubbles resulting from the electrooxidation of H 2 O 2 at Pt disk nanoelectrodes. Bubbles form almost instantaneously when a critical peak current, i nb p , is applied, but for lower currents, bubble nucleation is a stochastic process in which the nucleation (induction) time, t ind , dramatically decreases as the applied current approaches i nb p , a consequence of the local supersaturation level, ζ, increasing at high currents. Here, by applying different currents below i nb p , nanobubbles take some time to nucleate and block the surface of the Pt electrode at which the reaction occurs, providing a means to measure the stochastic t ind . We study in detail the different conditions in which nanobubbles appear, concluding that the electrode surface needs to be preconditioned to achieve reproducible results. We also measure the activation energy for bubble nucleation, E a , which varies in the range from (6 to 30)kT, and assuming a spherically cap-shaped nanobubble nucleus, we determine the footprint diameter L = 8-15 nm, the contact angle to the electrode surface θ = 135-155°, and the number of O 2 molecules contained in the nucleus (50 to 900 molecules).
Angewandte Chemie, Aug 20, 2020
Achieving control over the size distribution of metal-organic-framework (MOF) nanoparticles is ke... more Achieving control over the size distribution of metal-organic-framework (MOF) nanoparticles is key to biomedical applications and seeding techniques. Electrochemical control over the nanoparticle synthesis of the MOF, HKUST-1, is achieved using a nanopipette injection method to locally mix Cu 2+ salt precursor and benzene-1,3,5-tricarboxylate (BTC 3À ) ligand reagents, to form MOF nanocrystals, and collect and characterise them on a TEM grid. In situ analysis of the size and translocation frequency of HKUST-1 nanoparticles is demonstrated, using the nanopipette to detect resistive pulses as nanoparticles form. Complementary modelling of mass transport in the electric field, enables particle size to be estimated and explains the feasibility of particular reaction conditions, including inhibitory effects of excess BTC 3À . These new methods should be applicable to a variety of MOFs, and scaling up synthesis possible via arrays of nanoscale reaction centres, for example using nanopore membranes.
ACS Sensors, 2020
An electrochemical sensor that contains patterned regions of sp 2 -carbon in a boron doped diamon... more An electrochemical sensor that contains patterned regions of sp 2 -carbon in a boron doped diamond (BDD) matrix is presented for the quantitative detection of hypochlorite (OCl -) at high concentrations in the alkaline, chemically oxidizing environment associated with bleach. As BDD itself is unresponsive to OCl -reduction within the solvent window, by using a laser micromachining process it is possible to write robust electrochemically active regions of sp 2 -carbon into the electrochemically inert sp 3 BDD electrode. In this work, four different laser patterned BDD electrodes are examined and their response compared across a range of OCl -concentrations (0.02 M to 1.50 M). A single macro-spot (0.37 mm diameter disk) electrode and a closely spaced micro-spot (46 m diameter disk) hexagonal array electrode, containing the same surface area of sp 2 -carbon, are shown to provide the most linear response towards OCl -reduction. Finite element modelling (FEM) is employed to better understand the electrochemical system, due to the complexity of the electrode geometry, as well as the need to include contributions from migration and Ohmic drop at these high concentrations. FEM data suggest that only a small percentage (~ 1×10 -3 %) of the total laser-machined sp 2 area is active towards the OCl -reduction process and that this process is kinetically very sluggish (~ k eff = 1×10 -12 cm s -1 ). The sensitivity at the micro-array electrode (-0.127 ± 0.004 mA M -1 ; R 2 = 0.992) is higher than that at the single-spot (-0.075 ± 0.002 mA M -1 ; R 2 = 0.996) due to the enhanced effect of transport to the edges of the micro-spots, shown via simulation. The electrodes returned a relatively stable response over a > three-month period of use in the OCl - solutions, demonstrating these hybrid sp 2 -BDD electrodes show promise for long-term monitoring applications in the harsh environments associated with bleaching applications.
Langmuir, 2019
We report the observation of transient bipolar electrochemical coupling on freely-moving 40 nm si... more We report the observation of transient bipolar electrochemical coupling on freely-moving 40 nm silver nanoparticles. The use of an asymmetric nanoelectrochemical environment at the nanopore orifice, e.g., an acid inside the pipette and halide ions in the bulk, enabled us to observe unusually large current blockages of single Ag nanoparticles. We attribute these current blockages to the formation of H 2 nanobubbles on the surface of Ag nanoparticles due to the coupled faradaic reactions, in which the reduction of protons and water is coupled to the oxidation of Ag and water under potentials higher than 1 V. The appearance of large current blockages was strongly dependent upon the applied voltage and the choice of anions in the bulk solution. The correlation between large current blockages with the oxidation of Ag nanoparticles and their nanopore translocation was further supported by simultaneous fluorescence and electric recordings. This study demonstrates that transient bipolar electrochemistry can take place on small metal nanoparticles below 50 nm when they pass through nanopores where the electric field is highly localized. The use of a nanopore and the resistive-pulse sensing method to study transient bipolar electrochemistry of nanoparticles may be extended to the future studies in ultrafast electrochemistry, nanocatalyst screening, and gas nucleation on nanoparticles.
Biophysical Journal, 2014
and single-molecular force spectroscopy (SMFS) were applied. Direct highresolution imaging of the... more and single-molecular force spectroscopy (SMFS) were applied. Direct highresolution imaging of the outer surface of T. forsythia wild-type cells by AFM revealed a p4 structure with a lattice constant of ~9.0 nm. In contrast, on S-layer mutant cells, no periodic lattice could be visualized. Additionally, SMFS was used to probe specific interaction forces between an anti-TfsA antibody coupled to the AFM tip and the S-layer as present on T. forsythia wild-type and mutant cells displaying TfsA-GP alone. Unbinding forces between the antibody and wild-type cells were greater than with mutant cells. This indicated that the TfsA-GP is less strongly attached to the mutant cell surface when the co-assembling TfsB-GP is missing. Altogether, our data confirm the current model of the S-layer architecture with two intercalating S-layer glycoproteins and TfsA-GP mainly outwardly orientated. This study was funded by a Marie Curie International Incoming Fellowship of the 7 th European Community Framework Program (to Y. J. O.). Financial support came from the Austrian Science Fund FWF projects P20605-B12 and P24317-B22 (to C.S.). Board B284 Specific Role of Glycolipids in the Regular Stacking of Membranes Reconstituted from Thylakoid Lipid Extracts Bruno Deme ´1, Ce ´line Cataye 2 , Maryse Block 2 , E ´ric Mare ´chal 2 , Juliette Jouhet 2 .
F1000Research, 2014
Ectonucleotidases are membrane-bound or secreted proteins that hydrolyze extracellular nucleotide... more Ectonucleotidases are membrane-bound or secreted proteins that hydrolyze extracellular nucleotides. Recently, we identified three ectonucleotidases that hydrolyze extracellular adenosine 5’-monophosphate (AMP) to adenosine in primary somatosensory neurons. Currently, it is unclear which ectonucleotidases hydrolyze ATP and ADP in these neurons. Ectonucleoside triphosphate diphosphohydrolases (ENTPDs) comprise a class of enzymes that dephosphorylate extracellular ATP and ADP. Here, we found that ENTPD3 (also known as NTPDase3 or CD39L3) was located in nociceptive and non-nociceptive neurons of the dorsal root ganglion (DRG), in the dorsal horn of the spinal cord, and in free nerve endings in the skin. To determine if ENTPD3 contributes directly to ATP and ADP hydrolysis in these tissues, we generated and characterized an Entpd3 knockout mouse. This mouse lacks ENTPD3 protein in all tissues examined, including the DRG, spinal cord, skin, and bladder. However, DRG and spinal cord...
Biophysical Journal, 2013
We present what is, to our knowledge, the first experimental demonstration of dielectric constant... more We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization forces which were measured using an electrostatic force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of ε r ~3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (ε r ~2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane electrostatics and other bioelectric phenomena.
Figshare documentation (Figshare (United Kingdom)), Jul 21, 2020
Chemical Communications, 2016
Faraday Discussions, organised by the Royal Society of Chemistry (RSC), bring the concept of the ... more Faraday Discussions, organised by the Royal Society of Chemistry (RSC), bring the concept of the flipped classroom to scientific conferences, promoting lively debate and discussion with the opportunity to hear complementary and contrasting views on topics spanning physical chemistry. The Faraday Discussion on the topic of single entity electrochemistry, in the picturesque setting of the University of York (31 st August to 2 nd September, 2016), presented an opportunity for researchers pushing at the lower limits of electrochemistry to engage in such lively discourse. The topic single entity was chosen to be as inclusive as possible, and proved to be so, with researchers probing single nanoparticles, nanopores, nanorods, vesicles and even single molecules, with a wide range of electrochemical techniques, both experimental and theoretical.
bioRxiv (Cold Spring Harbor Laboratory), Aug 18, 2022
Solid-state nanopores have been widely employed in the detection of biomolecules, but low signal-... more Solid-state nanopores have been widely employed in the detection of biomolecules, but low signal-to-noise ratios still represent a major obstacle to enable the discrimination of short nucleic acid and protein sequences. The addition of 50% polyethylene glycol (PEG) to the bath solution was recently demonstrated as a simple way to enhance the detection of such biomolecules translocating through a model solid-state nanopore. Here, we provide a comprehensive description of the physics describing a nanopore measurement carried out in 50% PEG that is supported by finite-element modelling and experiments. We demonstrate that the addition of PEG to the external solution introduces a strong imbalance in the transport properties of cations and anions, drastically affecting the characteristic current response of the nanopore. We further show that the strong asymmetric current response is due to a polarity-dependent ion distribution and transport at the nanopipette tip region, leading to either ion depletion or enrichment for few tens of nanometers across the aperture. Under negative potential, when double-stranded DNA molecules translocate, the depleted region (sensing region) significantly improves the sensitivity compared to systems without PEG. We then introduce a displacement of the interface between pore and external solution to simulate the mechanical interactions between analyte and PEG molecules. We found that this displacement affects the ion distribution in the sensing region, enhancing the detection current during the translocation of biomolecules. .
A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a ... more A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a planar electrode for a 1e outer-sphere redox process, which fully accounts for cell electrostatics, including ohmic potential drop, ion migration, and the structure of the potentialdependent electric double layer. Both reversible and quasi-reversible redox reactions are treated. The simulations compute the time-dependent electric potential and ion distributions across the entire cell during a voltammetric scan. In this way, it is possible to obtain the interdependent faradaic and non-faradaic contributions to a CV and rigorously include all effects of the electric potential distribution on the rate of electron transfer and the local
Bipyridine complexes of Ni are used as catalysts in a variety of reductive transformations. Here,... more Bipyridine complexes of Ni are used as catalysts in a variety of reductive transformations. Here, the electroreduction of [Ni(Mebpy)3]2+ (Mebpy = 4,4’-dimethyl-2,2’-bipyridine) in dimethylformamide is reported, with the aim of determining the redox mechanism and oxidation states of products formed under well-controlled electrochemical conditions. Results from cyclic voltammetry, steady-state voltammetry (SSV) and chronoamperometry demonstrate that [Ni(Mebpy)3]2+ undergoes two sequential 1e reductions at closely separated potentials (E0’1 = -1.06 ± 0.01 V and E0’2 = -1.15 ± 0.01 V vs Ag/AgCl (3.4 M KCl)). Homogeneous comproportionation to generate [Ni(Mebpy)3]+ is demonstrated in SSV experiments in low ionic strength solutions. The comproportionation rate constant is determined to be > 106 M-1s-1, consistent with rapid outer-sphere electron transfer. Consequentially, on voltammetric time scales, the 2e reduction of [Ni(Mebpy)3]2+ results in formation of [Ni(Mebpy)3]1+ as the predo...
Chemical Science, 2020
Nanoparticles mimicking the three-dimensional architecture of enzymes where the reaction occurs d... more Nanoparticles mimicking the three-dimensional architecture of enzymes where the reaction occurs down a channel isolated from bulk solution, referred here as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions.
Journal of the American Chemical Society, 2019
Below is the automatically generated Comsol "model report", which describes in detail the boundar... more Below is the automatically generated Comsol "model report", which describes in detail the boundary conditions, geometry, mesh, solver configuration, etc., used in the finite element simulations of the 3-phase interface reported in this work and described in Supporting Information, section 6.
C-N cross-coupling is one of the most valuable and widespread transformations in organic synthesi... more C-N cross-coupling is one of the most valuable and widespread transformations in organic synthesis. Largely dominated by Pd-and Cu-based catalytic systems, it has proven to be a staple transformation for those in both academia and industry. The current study presents the development and mechanistic understanding of an electrochemically driven, Ni-catalyzed method for achieving this reaction of high strategic importance. Through a series of electrochemical, computational, kinetic, and empirical experiments the key mechanistic features of this reaction have been unraveled, leading to a second generation set of conditions that is applicable to a broad range of aryl halides and amine nucleophiles, including complex examples on oligopeptides, medicinally-relevant heterocycles, natural products, and sugars. Full disclosure of the current limitations as well as procedures for both batch and flow scale-ups (100 gram) are also described.
Faraday Discussions, 2018
The stochastic nature of very fast single-entity events challenges current electrochemical method... more The stochastic nature of very fast single-entity events challenges current electrochemical methods and modern electronics, as illustrated using recent experiments from the authors’ laboratory.
ACS nano, Jan 27, 2018
The oxidation of catecholamine at a microelectrode, following its release from individual vesicle... more The oxidation of catecholamine at a microelectrode, following its release from individual vesicles, allows interrogation of the content of single nanometer vesicles with vesicle impact electrochemical cytometry (VIEC). Previous to this development, there were no methods available to quantify the chemical load of single vesicles. However, accurate quantification of the content is hampered by uncertainty in the proportion of substituent molecules reaching the electrode surface (collection efficiency). In this work, we use quantitative modeling to calculate this collection efficiency. For all vesicles except those at the very edge of the electrode, modeling shows that ∼100% oxidation efficiency is achieved when employing a 33 μm diameter disk microelectrode for VIEC, independent of the location of the vesicle release pore. We use this to experimentally determine a precise distribution of catecholamine in individual vesicles extracted from PC12 cells. In contrast, we calculate that when...