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Kathryn F Lanoue - One of the best experts on this subject based on the ideXlab platform.

  • a method of determining Electrical Potential Gradient across mitochondrial membrane in perfused rat hearts
    American Journal of Physiology-heart and Circulatory Physiology, 1993
    Co-Authors: B Wan, Chris Doumen, J Duszynski, G Salama, Kathryn F Lanoue
    Abstract:

    The Electrical Potential Gradient across the mitochondrial membrane (delta psi m) in perfused rat hearts was estimated by calculating the equilibrium distribution of the lipophilic cation tetraphenylphosphonium (TPP+), using measured kinetic constants of uptake and release of TPP+. First-order rate constants of TPP+ uptake were measured during 30-min perfusions of intact rat hearts with tracer amounts (5.0 nM) of tritium-labeled TPP+ ([3H]TPP+) in the perfusate. This was followed by a 30-min washout, during which the first-order rate constant of efflux was estimated. Values of [3H]TPP+ outside the heart and total [3H]TPP+ inside the heart at equilibrium were calculated. From this information and separately estimated time-averaged plasma membrane Potentials (delta psi c) it was possible to calculate free cytosolic [3H]TPP+ at equilibrium. It was also possible to calculate free intramitochondrial [3H]TPP+ at equilibrium as the difference between total tissue [3H]TPP+ minus free cytosolic TPP+ and the sum of all the bound [3H]TPP+. Bound [3H]TPP+ was determined from [3H]TPP+ binding constants measured in separate experiments, using both isolated mitochondria and isolated cardiac myocytes under conditions where both delta psi m and delta psi c were zero. Delta psi m was calculated from the intramitochondrial and cytosolic free TPP+ concentrations using the Nernst equation. Values of delta psi m were 144.9 +/- 2.0 mV in hearts perfused with 5 mM pyruvate and 118.2 +/- 1.4 mV in hearts perfused with 11 mM glucose, in good agreement with delta psi m obtained from isolated rat heart mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)

  • effects of cardiac work on Electrical Potential Gradient across mitochondrial membrane in perfused rat hearts
    American Journal of Physiology-heart and Circulatory Physiology, 1993
    Co-Authors: B Wan, Chris Doumen, J Duszynski, G Salama, Thomas C Vary, Kathryn F Lanoue
    Abstract:

    The myocardium responds to alterations in cardiac work by changing its rate of O2 consumption. This reflects an increase in the oxidative synthesis of ATP to meet the contractile demand for ATP. Ho...

Ivars Neretnieks - One of the best experts on this subject based on the ideXlab platform.

  • determination of sorption properties of intact rock samples new methods based on electromigration
    Journal of Contaminant Hydrology, 2009
    Co-Authors: Magnus André, Maria Malmström, Ivars Neretnieks
    Abstract:

    Abstract Two new methods for determining sorption coefficients in large rock samples have been developed. The methods use electromigration as a means to speed up the transport process, allowing for fast equilibration between rock sample and tracer solution. An Electrical Potential Gradient acts as a driving force for transport in addition to the concentration Gradient and forces the cations through the rock sample towards the cathode. The Electrical Potential Gradient induces both electromigration and electroosmotic flow with a resulting solute transport that is large compared to diffusive fluxes. In one of the methods, the solute is driven through the sample and collected at the outlet side. In the other, simpler method, the rock sample is equilibrated by circulating the solute through the sample. The equilibration of rock samples, up to 5 cm in length, with an aqueous solution has been accomplished within days to months. Experiments using cesium as a sorbing tracer yield results consistent with considerably more time demanding in-diffusion experiments. These methods give lower distribution coefficients than those obtained using traditional batch experiments with crushed rock.

  • Determining sorption coefficients in intact rock using an Electrical Potential Gradient as a driving force for migration
    MRS Proceedings, 2006
    Co-Authors: Magnus André, Maria Malmström, Ivars Neretnieks
    Abstract:

    The transport of radionuclides in indigenous rock is greatly affected by the sorption of cations in the porous rock matrix. For the determination of sorption coefficients, batch experiments have traditionally been used. For these experiments, the rock sample is crushed into fine particles to reduce the experimental time. However, this procedure increases the specific surface area of the sample and the new surfaces created could have different sorption qualities than the naturally occurring surfaces, which may impair the results of sorption coefficient determinations. A new method for determining sorption coefficients in intact rock is being developed, using electromigration as a means to speed up the transport process, thereby allowing for faster equilibration between the rock sample and the tracer solution. Here, we report results from preliminary experiments, using cesium as a sorbing tracer, showing a consistent difference between sorption coefficients obtained using electromigration methods on intact rock samples and traditional batch experiments on crushed samples.

  • a conceivable technique of measuring sorption coefficients in intact rock using an Electrical Potential Gradient as the driving force for migration
    27th Symposium on Scientific Basis for Nuclear Waste Management Location: Kalmar SWEDEN Date: JUN 15-19 2003, 2004
    Co-Authors: Martin Löfgren, Ivars Neretnieks
    Abstract:

    Sorption coefficients are traditionally obtained in batch experiments if the sorbent is strongly or intermediately sorbing. In a batch experiment the rock is crushed and this could increase the sur ...

  • A Conceivable Technique of Measuring Sorption Coefficients in Intact Rock Using an Electrical Potential Gradient as the Driving Force for Migration
    MRS Proceedings, 2003
    Co-Authors: Martin Löfgren, Ivars Neretnieks
    Abstract:

    ABSTRACTSorption coefficients are traditionally obtained in batch experiments if the sorbent is strongly or intermediately sorbing. In a batch experiment the rock is crushed and this could increase the surface area as well as induce new and fresh surfaces. Therefore there is some concern whether sorption coefficients obtained in batch experiments represents those of intact rock. Performing sorption experiment by diffusion in intact rock with intermediately and strongly sorbing species seems impossible in practice due to extremely long experimental times. In this paper the possibility of increasing the migration rate in the rock by two of three orders, thus enabling KD measurements of intermediately sorbing species in intact rock, is discussed. The increase in migration ratehas already been achieved successfully in so called through electromigration experiments using non-sorbing species. Here a Potential Gradient acts as the main driving force. In our experiments the migration rate was increased 320 times by using a Potential drop of only 9 volts.

B Wan - One of the best experts on this subject based on the ideXlab platform.

  • a method of determining Electrical Potential Gradient across mitochondrial membrane in perfused rat hearts
    American Journal of Physiology-heart and Circulatory Physiology, 1993
    Co-Authors: B Wan, Chris Doumen, J Duszynski, G Salama, Kathryn F Lanoue
    Abstract:

    The Electrical Potential Gradient across the mitochondrial membrane (delta psi m) in perfused rat hearts was estimated by calculating the equilibrium distribution of the lipophilic cation tetraphenylphosphonium (TPP+), using measured kinetic constants of uptake and release of TPP+. First-order rate constants of TPP+ uptake were measured during 30-min perfusions of intact rat hearts with tracer amounts (5.0 nM) of tritium-labeled TPP+ ([3H]TPP+) in the perfusate. This was followed by a 30-min washout, during which the first-order rate constant of efflux was estimated. Values of [3H]TPP+ outside the heart and total [3H]TPP+ inside the heart at equilibrium were calculated. From this information and separately estimated time-averaged plasma membrane Potentials (delta psi c) it was possible to calculate free cytosolic [3H]TPP+ at equilibrium. It was also possible to calculate free intramitochondrial [3H]TPP+ at equilibrium as the difference between total tissue [3H]TPP+ minus free cytosolic TPP+ and the sum of all the bound [3H]TPP+. Bound [3H]TPP+ was determined from [3H]TPP+ binding constants measured in separate experiments, using both isolated mitochondria and isolated cardiac myocytes under conditions where both delta psi m and delta psi c were zero. Delta psi m was calculated from the intramitochondrial and cytosolic free TPP+ concentrations using the Nernst equation. Values of delta psi m were 144.9 +/- 2.0 mV in hearts perfused with 5 mM pyruvate and 118.2 +/- 1.4 mV in hearts perfused with 11 mM glucose, in good agreement with delta psi m obtained from isolated rat heart mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)

  • effects of cardiac work on Electrical Potential Gradient across mitochondrial membrane in perfused rat hearts
    American Journal of Physiology-heart and Circulatory Physiology, 1993
    Co-Authors: B Wan, Chris Doumen, J Duszynski, G Salama, Thomas C Vary, Kathryn F Lanoue
    Abstract:

    The myocardium responds to alterations in cardiac work by changing its rate of O2 consumption. This reflects an increase in the oxidative synthesis of ATP to meet the contractile demand for ATP. Ho...

Albert C Aragones - One of the best experts on this subject based on the ideXlab platform.

  • electrostatic catalysis of a diels alder reaction
    Nature, 2016
    Co-Authors: Albert C Aragones, Naomi L Haworth, Nadim Darwish, Simone Ciampi, Nathaniel J Bloomfield, Gordon G Wallace, Ismael Diezperez, Michelle L Coote
    Abstract:

    Theory suggests that many chemical reactions (not simply, as is often thought, redox reactions) might be catalysed by an applied electric field; experimental evidence for this is now provided from single-molecule studies of the formation of carbon–carbon bonds in a Diels–Alder reaction. Theory suggests that many chemical reactions — not simply, as is often thought, redox reactions — might be catalysed by an applied Electrical field. Experimental evidence for this is now provided from single-molecule studies of the formation of carbon–carbon bonds in a Diels–Alder reaction. In a series of scanning tunnelling microscopy break-junction experiments, the authors observe a fivefold increase in the frequency of single-molecule junction formation when the Electrical field is present and aligned in the direction to favour electron flow from the dienophile to the diene. The demonstration that it is possible to manipulate chemical reactions with electric fields offers proof-of-principle for a novel approach to heterogeneous catalysis. It is often thought that the ability to control reaction rates with an applied Electrical Potential Gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields could affect the outcomes of a range of chemical reactions, regardless of whether a redox system is involved1,2,3,4. This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an applied electric field is aligned in such a way as to electrostatically stabilize one of these minor forms, the degree of resonance increases, resulting in the overall stabilization of the molecule or transition state. This means that it should be possible to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field, as long as the orientation of the approaching reactants with respect to the field stimulus can be controlled. Here, we provide experimental evidence that the formation of carbon–carbon bonds is accelerated by an electric field. We have designed a surface model system to probe the Diels–Alder reaction, and coupled it with a scanning tunnelling microscopy break-junction approach5,6,7. This technique, performed at the single-molecule level, is perfectly suited to deliver an electric-field stimulus across approaching reactants. We find a fivefold increase in the frequency of formation of single-molecule junctions, resulting from the reaction that occurs when the electric field is present and aligned so as to favour electron flow from the dienophile to the diene. Our results are qualitatively consistent with those predicted by quantum-chemical calculations in a theoretical model of this system, and herald a new approach to chemical catalysis.

  • electrostatic catalysis of a diels alder reaction
    Nature, 2016
    Co-Authors: Albert C Aragones, Naomi L Haworth, Nadim Darwish, Simone Ciampi, Nathaniel J Bloomfield, Gordon G Wallace, Ismael Diezperez, Michelle L Coote
    Abstract:

    It is often thought that the ability to control reaction rates with an applied Electrical Potential Gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields could affect the outcomes of a range of chemical reactions, regardless of whether a redox system is involved. This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an applied electric field is aligned in such a way as to electrostatically stabilize one of these minor forms, the degree of resonance increases, resulting in the overall stabilization of the molecule or transition state. This means that it should be possible to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field, as long as the orientation of the approaching reactants with respect to the field stimulus can be controlled. Here, we provide experimental evidence that the formation of carbon-carbon bonds is accelerated by an electric field. We have designed a surface model system to probe the Diels-Alder reaction, and coupled it with a scanning tunnelling microscopy break-junction approach. This technique, performed at the single-molecule level, is perfectly suited to deliver an electric-field stimulus across approaching reactants. We find a fivefold increase in the frequency of formation of single-molecule junctions, resulting from the reaction that occurs when the electric field is present and aligned so as to favour electron flow from the dienophile to the diene. Our results are qualitatively consistent with those predicted by quantum-chemical calculations in a theoretical model of this system, and herald a new approach to chemical catalysis.

Michelle L Coote - One of the best experts on this subject based on the ideXlab platform.

  • electrostatic catalysis of a diels alder reaction
    Nature, 2016
    Co-Authors: Albert C Aragones, Naomi L Haworth, Nadim Darwish, Simone Ciampi, Nathaniel J Bloomfield, Gordon G Wallace, Ismael Diezperez, Michelle L Coote
    Abstract:

    Theory suggests that many chemical reactions (not simply, as is often thought, redox reactions) might be catalysed by an applied electric field; experimental evidence for this is now provided from single-molecule studies of the formation of carbon–carbon bonds in a Diels–Alder reaction. Theory suggests that many chemical reactions — not simply, as is often thought, redox reactions — might be catalysed by an applied Electrical field. Experimental evidence for this is now provided from single-molecule studies of the formation of carbon–carbon bonds in a Diels–Alder reaction. In a series of scanning tunnelling microscopy break-junction experiments, the authors observe a fivefold increase in the frequency of single-molecule junction formation when the Electrical field is present and aligned in the direction to favour electron flow from the dienophile to the diene. The demonstration that it is possible to manipulate chemical reactions with electric fields offers proof-of-principle for a novel approach to heterogeneous catalysis. It is often thought that the ability to control reaction rates with an applied Electrical Potential Gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields could affect the outcomes of a range of chemical reactions, regardless of whether a redox system is involved1,2,3,4. This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an applied electric field is aligned in such a way as to electrostatically stabilize one of these minor forms, the degree of resonance increases, resulting in the overall stabilization of the molecule or transition state. This means that it should be possible to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field, as long as the orientation of the approaching reactants with respect to the field stimulus can be controlled. Here, we provide experimental evidence that the formation of carbon–carbon bonds is accelerated by an electric field. We have designed a surface model system to probe the Diels–Alder reaction, and coupled it with a scanning tunnelling microscopy break-junction approach5,6,7. This technique, performed at the single-molecule level, is perfectly suited to deliver an electric-field stimulus across approaching reactants. We find a fivefold increase in the frequency of formation of single-molecule junctions, resulting from the reaction that occurs when the electric field is present and aligned so as to favour electron flow from the dienophile to the diene. Our results are qualitatively consistent with those predicted by quantum-chemical calculations in a theoretical model of this system, and herald a new approach to chemical catalysis.

  • electrostatic catalysis of a diels alder reaction
    Nature, 2016
    Co-Authors: Albert C Aragones, Naomi L Haworth, Nadim Darwish, Simone Ciampi, Nathaniel J Bloomfield, Gordon G Wallace, Ismael Diezperez, Michelle L Coote
    Abstract:

    It is often thought that the ability to control reaction rates with an applied Electrical Potential Gradient is unique to redox systems. However, recent theoretical studies suggest that oriented electric fields could affect the outcomes of a range of chemical reactions, regardless of whether a redox system is involved. This possibility arises because many formally covalent species can be stabilized via minor charge-separated resonance contributors. When an applied electric field is aligned in such a way as to electrostatically stabilize one of these minor forms, the degree of resonance increases, resulting in the overall stabilization of the molecule or transition state. This means that it should be possible to manipulate the kinetics and thermodynamics of non-redox processes using an external electric field, as long as the orientation of the approaching reactants with respect to the field stimulus can be controlled. Here, we provide experimental evidence that the formation of carbon-carbon bonds is accelerated by an electric field. We have designed a surface model system to probe the Diels-Alder reaction, and coupled it with a scanning tunnelling microscopy break-junction approach. This technique, performed at the single-molecule level, is perfectly suited to deliver an electric-field stimulus across approaching reactants. We find a fivefold increase in the frequency of formation of single-molecule junctions, resulting from the reaction that occurs when the electric field is present and aligned so as to favour electron flow from the dienophile to the diene. Our results are qualitatively consistent with those predicted by quantum-chemical calculations in a theoretical model of this system, and herald a new approach to chemical catalysis.