The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform

Dudley H. Williams - One of the best experts on this subject based on the ideXlab platform.

  • kinetic analysis of high mobility group proteins hmg 1 and hmg i y binding to cholesterol tagged dna on a supported Lipid Monolayer
    Nucleic Acids Research, 2000
    Co-Authors: Carl I Webster, Dudley H. Williams, Mark E. Cooper, Leonard C Packman, John C Gray
    Abstract:

    High-mobility-group proteins HMG-1 and HMG-I/Y bind to multiple sites within a 268 bp A/T-rich enhancer element of the pea plastocyanin gene (PetE). Within a 31 bp region of the enhancer, the binding site for HMG-1 overlaps with the binding site for HMG-I/Y. The kinetics of binding and the affinities of HMG-1 and HMG-I/Y for the 31 bp DNA were determined using surface plasmon resonance. Due to very high non-specific interactions of the HMG proteins with a carboxymethyl–dextran matrix, a novel method using a cholesterol tag to anchor the DNA in a supported Lipid Monolayer on a thin gold film was devised. The phosphatidylcholine Monolayer produced a surface that reduced background interactions to a minimum and permitted the measurement of highly reproducible protein–DNA interactions. The association rate constant (ka) of HMG-I/Y with the 31 bp DNA was ~5-fold higher than the rate constant for HMG-1, whereas the dissociation constant (KD) for HMG-I/Y (3.1 nM) was ~7-fold lower than that for HMG-1 (20.1 nM). This suggests that HMG-I/Y should bind preferentially at the overlapping binding site within this region of the PetE enhancer.

  • Kinetic analysis of antibody-antigen interactions at a supported Lipid Monolayer.
    Analytical biochemistry, 1999
    Co-Authors: Mark E. Cooper, Dudley H. Williams
    Abstract:

    Modified phosphoLipids possessing carboxyl head groups synthesized from phosphatidylethanolamine were incorporated into supported Lipid Monolayers on top of a thin gold film. A monoclonal antibody was chemically coupled to the modified Lipids in these Monolayers and the kinetics of antigen binding were determined by surface plasmon resonance. The binding could be analyzed using a conventional 1:1 binding algorithm and the derived kinetic and affinity constants were almost identical to those reported for the same interaction on a dextran hydrogel-based sensor chip. When an antigen was chemically coupled to a modified Lipid Monolayer, the binding of a monoclonal antibody to this surface was biphasic. A two-step algorithm describing the formation of a 1:2 antibody:antigen complex was developed which accurately described the data and enabled differentiation of the two binding steps. The binding was assayed varying both the concentration of antibody in solution and the density of antigen on the surface. The affinities determined by Scatchard analysis of equilibrium binding levels were similar to those values obtained from an ELISA.

  • Surface plasmon resonance analysis at a supported Lipid Monolayer
    Biochimica et biophysica acta, 1998
    Co-Authors: Mark E. Cooper, Andrew C. Try, Joe Carroll, David J. Ellar, Dudley H. Williams
    Abstract:

    Methods for the formation of supported Lipid Monolayers on top of a hydrophobic self assembled Monolayer in a surface plasmon resonance instrument are described. Small unilamellar vesicles absorb spontaneously to the surface of the hydrophobic self-assembled Monolayer to form a surface which resembles the surface of a cellular membrane. Lipophilic ligands, such as small acylated peptides or glycosylphosphatidylinositol-anchored proteins, were inserted into the absorbed Lipid and binding of analytes to these ligands was analysed by surface plasmon resonance. Conditions for the formation of Lipid Monolayers have been optimised with respect to Lipid type, chemical and buffer compatibility, ligand stability and reproducibility.

  • surface plasmon resonance analysis of glycopeptide antibiotic activity at a model membrane surface
    Chemical Communications, 1997
    Co-Authors: Mark E. Cooper, Dudley H. Williams
    Abstract:

    Affinity constants of glycopeptide antibiotics for peptides anchored in a Lipid Monolayer measured by surface plasmon resonance show a correlation with in vitro antimicrobial activity.

Mark E. Cooper - One of the best experts on this subject based on the ideXlab platform.

  • kinetic analysis of high mobility group proteins hmg 1 and hmg i y binding to cholesterol tagged dna on a supported Lipid Monolayer
    Nucleic Acids Research, 2000
    Co-Authors: Carl I Webster, Dudley H. Williams, Mark E. Cooper, Leonard C Packman, John C Gray
    Abstract:

    High-mobility-group proteins HMG-1 and HMG-I/Y bind to multiple sites within a 268 bp A/T-rich enhancer element of the pea plastocyanin gene (PetE). Within a 31 bp region of the enhancer, the binding site for HMG-1 overlaps with the binding site for HMG-I/Y. The kinetics of binding and the affinities of HMG-1 and HMG-I/Y for the 31 bp DNA were determined using surface plasmon resonance. Due to very high non-specific interactions of the HMG proteins with a carboxymethyl–dextran matrix, a novel method using a cholesterol tag to anchor the DNA in a supported Lipid Monolayer on a thin gold film was devised. The phosphatidylcholine Monolayer produced a surface that reduced background interactions to a minimum and permitted the measurement of highly reproducible protein–DNA interactions. The association rate constant (ka) of HMG-I/Y with the 31 bp DNA was ~5-fold higher than the rate constant for HMG-1, whereas the dissociation constant (KD) for HMG-I/Y (3.1 nM) was ~7-fold lower than that for HMG-1 (20.1 nM). This suggests that HMG-I/Y should bind preferentially at the overlapping binding site within this region of the PetE enhancer.

  • Kinetic analysis of antibody-antigen interactions at a supported Lipid Monolayer.
    Analytical biochemistry, 1999
    Co-Authors: Mark E. Cooper, Dudley H. Williams
    Abstract:

    Modified phosphoLipids possessing carboxyl head groups synthesized from phosphatidylethanolamine were incorporated into supported Lipid Monolayers on top of a thin gold film. A monoclonal antibody was chemically coupled to the modified Lipids in these Monolayers and the kinetics of antigen binding were determined by surface plasmon resonance. The binding could be analyzed using a conventional 1:1 binding algorithm and the derived kinetic and affinity constants were almost identical to those reported for the same interaction on a dextran hydrogel-based sensor chip. When an antigen was chemically coupled to a modified Lipid Monolayer, the binding of a monoclonal antibody to this surface was biphasic. A two-step algorithm describing the formation of a 1:2 antibody:antigen complex was developed which accurately described the data and enabled differentiation of the two binding steps. The binding was assayed varying both the concentration of antibody in solution and the density of antigen on the surface. The affinities determined by Scatchard analysis of equilibrium binding levels were similar to those values obtained from an ELISA.

  • Surface plasmon resonance analysis at a supported Lipid Monolayer
    Biochimica et biophysica acta, 1998
    Co-Authors: Mark E. Cooper, Andrew C. Try, Joe Carroll, David J. Ellar, Dudley H. Williams
    Abstract:

    Methods for the formation of supported Lipid Monolayers on top of a hydrophobic self assembled Monolayer in a surface plasmon resonance instrument are described. Small unilamellar vesicles absorb spontaneously to the surface of the hydrophobic self-assembled Monolayer to form a surface which resembles the surface of a cellular membrane. Lipophilic ligands, such as small acylated peptides or glycosylphosphatidylinositol-anchored proteins, were inserted into the absorbed Lipid and binding of analytes to these ligands was analysed by surface plasmon resonance. Conditions for the formation of Lipid Monolayers have been optimised with respect to Lipid type, chemical and buffer compatibility, ligand stability and reproducibility.

  • surface plasmon resonance analysis of glycopeptide antibiotic activity at a model membrane surface
    Chemical Communications, 1997
    Co-Authors: Mark E. Cooper, Dudley H. Williams
    Abstract:

    Affinity constants of glycopeptide antibiotics for peptides anchored in a Lipid Monolayer measured by surface plasmon resonance show a correlation with in vitro antimicrobial activity.

Anne Charrier - One of the best experts on this subject based on the ideXlab platform.

  • Femtomolar detection of Cu2+ ions in solution using super-Nernstian FET-sensor with a Lipid Monolayer as top-gate dielectric
    Sensors and Actuators B: Chemical, 2020
    Co-Authors: A. Kenaan, F. Brunel, J.-m. Raimundo, Anne Charrier
    Abstract:

    The development of ions sensors with low limit of detection and high sensitivity and selectivity is required in many fields of application and still remains a challenge. We report on the first dual-gated field effect transistor sensor with an engineered Lipid Monolayer as top gate dielectric. The sensor was designed and fabricated for the specific detection of Cu 2+ using the Di-2-picolylamine as recognition unit. The Lipid Monolayer was reticulated to achieve high mechanical and dielectric stability over device operation. The resulting sensor exhibits exceptional performances with a limit of detection at 10 femtomolar, with a linear dependency over 10 decades and a super-Nernstian sensitivity of ~100 mV/decade. We also show that the Lipid layer forms a good barrier to ions trapping, hence providing a high stability of the sensor over measurements.

  • Supported Lipid Monolayer with Improved Nanomechanical Stability: Effect of Polymerization
    The journal of physical chemistry. B, 2012
    Co-Authors: Racha El Zein, Herve Dallaporta, Anne Charrier
    Abstract:

    We study the effect of polymerization on the nanomechanical stability of supported Lipid Monolayers consisting of 1,2-di-(10Z,12Z-tricosadiynoyl)-sn-glycero-3-phosphocholine by means of force mapping using an atomic force microscope. For both nonpolymerized and polymerized Lipid Monolayers, we investigate the break-through forces required to rupture the Monolayers for a whole range of loading velocities. We show that the average break-through force exerted by the tip and required to penetrate the Monolayer has a logarithmic dependence on the loading rate. Both Young moduli and intrinsic Gibbs energies have been determined for the nonpolymerized and polymerized Lipid Monolayers, and we show a drastic effect of polymerization on the nanomechanical stability of the Monolayer with an increase by a factor of ∼100 for the young modulus and ∼3 for the intrinsic Gibbs activation energy.

Mischa Bonn - One of the best experts on this subject based on the ideXlab platform.

  • interaction of a patterned amphiphilic polyphenylene dendrimer with a Lipid Monolayer electrostatic interactions dominate
    Langmuir, 2015
    Co-Authors: Masanari Okuno, Mischa Bonn, Markus Mezger, Rene Stangenberg, Martin Baumgarten, Klaus Mullen, Ellen H G Backus
    Abstract:

    Dendrimeric macromolecules with defined shape and size are promising candidates for delivering drug or DNA molecules into cells. In this work we study the influence of an amphiphilic polyphenylene dendrimer on a model cell membrane consisting of a condensed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) Lipid Monolayer. A small surface pressure decrease is observed when the dendrimer solution is injected into the aqueous phase below the Monolayer. X-ray reflectivity measurements show that the surface Monolayer remains intact. The molecular-scale picture is obtained with sum-frequency generation spectroscopy. With this technique, we observe that the tails of the surfactant molecules become less ordered upon interaction with the amphiphilic polyphenylene dendrimer. In contrast, the water molecules below the DPPC layer become more ordered. Our observations suggest that electrostatic interactions between the negative charge of the dendrimer and the positively charged part of the DPPC headgroup keep the dendrimer located below the headgroup. No evidence of dendrimer insertion into the membrane has been observed. Apparently before entering the cell membrane the dendrimer can stick at the hydrophilic part of the Lipids.

  • sensitive probing of dna binding to a cationic Lipid Monolayer
    Journal of the American Chemical Society, 2007
    Co-Authors: George W H Wurpel, Maria Sovago, Mischa Bonn
    Abstract:

    Cationic Lipids are promising candidates as transporters of genetic material into cells. Therefore, detailed knowledge on the molecular interaction between polynucleotides (DNA) and cationic Lipids is needed to improve our understanding of these so-called lipoplexes. Here, for the first time, we have investigated the role of water in DNA−Lipid interaction using vibrational sum-frequency generation (VSFG). We show that the DNA−Lipid complexation induces a dramatic restructuring of interfacial water, with less than one Monolayer of water remaining between the DNA and the Lipid; we also observe that the Lipid-bound water reorients upon interaction with DNA. This is apparent from the rather dramatic changes in the vibrational response of interfacial water. The approach presented here has a very high (picomolar) sensitivity and allows for the quantification of the DNA−Lipid association constant.

  • Phase transitions in a Lipid Monolayer observed with vibrational sum-frequency generation
    Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing X, 2003
    Co-Authors: Michiel Müller, Juleon M. Schins, Sylvie Roke, Mischa Bonn
    Abstract:

    Using both vibrational sum-frequency generation and fluorescence microscopy, the phase behavior of a DPPC Lipid Monolayer on water is investigated as a function of surface pressure. The vibrational specificity of the sum-frequency generation techniques permits determining the order of the alkyl chains, as well as the average orientation of the terminal methyl group. A novel -- and extremely sharp -- phase transition is observed at low compression, which is attributed to a curling of the alkyl chains due to increased exposure of the (hydrophobic) alkyl chains to the water surface.

Anne M. Charrier - One of the best experts on this subject based on the ideXlab platform.

  • Subpicomolar Iron Sensing Platform Based on Functional Lipid Monolayer Microarrays
    Analytical Chemistry, 2016
    Co-Authors: Ahmad Kenaan, Tuyen D. Nguyen, Herve Dallaporta, Jean-manuel Raimundo, Anne M. Charrier
    Abstract:

    We report herein the fabrication of novel micro-arrays based on air-stable functional Lipid Monolayers over silicon using a combination of e-beam lithography and lift-off. We demonstrate these microarrays can be use as ultrasensitive platform for Kelvin probe force microscopy in sensing experiments. Specificity of the detection is given by the functional group grafted at the Lipid headgroup. The arrays developed for the detection of ferric ions, Fe3+, using a gamma-pyrone derivative chelator, demonstrate subpicomolar limit of detection with high specificity. In addition, the technique takes advantage of the structure of the array with the silicon areas playing the role of reference for the measurement, and we determine critical pattern dimensions below which the probe size/shape impacts the measured results.

  • Subpicomolar Iron Sensing Platform Based on Functional Lipid Monolayer Microarrays
    2016
    Co-Authors: Ahmad Kenaan, Tuyen D. Nguyen, Herve Dallaporta, Jean-manuel Raimundo, Anne M. Charrier
    Abstract:

    We report herein the fabrication of novel microarrays based on air-stable functional Lipid Monolayers over silicon using a combination of e-beam lithography and lift-off. We demonstrate these microarrays can be use as ultrasensitive platform for Kelvin probe force microscopy in sensing experiments. Specificity of the detection is given by the functional group grafted at the Lipid headgroup. The arrays developed for the detection of ferric ions, Fe3+, using a γ-pyrone derivative chelator, demonstrate subpicomolar limit of detection with high specificity. In addition, the technique takes advantage of the structure of the array with the silicon areas playing the role of reference for the measurement, and we determine critical pattern dimensions below which the probe size/shape impacts the measured results