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1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine

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Electra Gizeli – 1st expert on this subject based on the ideXlab platform

  • Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
    The Analyst, 2009
    Co-Authors: Kathryn A. Melzak, Electra Gizeli

    Abstract:

    Acoustic devices are sensitive to the mole fraction of cholesterol present in liposomes adsorbed to the device surface as a result of the different mechanical properties of the liposomes. This fact was exploited to develop an acoustic assay to determine the relative affinity of cholesterol for different lipid mixtures. In the assay described here, the initial rate of beta-cyclodextrin-induced removal of cholesterol was measured for liposomes having a range of compositions. The initial rate of cholesterol removal was found to be directly proportional to the concentration of beta-cyclodextrin (betaCD) present over the range of 0-7.5 mg/ml (0-6.6 mM), consistent with other assays measuring the betaCD-accelerated transfer of cholesterol between liposomes. The affinity of cholesterol for 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) liposomes with a sphingomyelin mole fraction, chi(SPM), of 0.2 was found to be 1.4x higher than that for pure OPPC liposomes. For liposomes composed only of OPPC and cholesterol in varying ratios, the initial rate of cholesterol removal was determined as a function of cholesterol mole fraction (chi(C)). The initial rate of removal showed an increase at chi(C) = 0.13, consistent with phase diagrams showing the start of liquid ordered domain formation, but no such increase at chi(C) = 0.25, in contrast to the predictions of the umbrella model for OPPC/cholesterol interactions.

  • Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
    Analyst, 2008
    Co-Authors: Kathryn A. Melzak, Electra Gizeli

    Abstract:

    Acoustic devices are sensitive to the mole fraction of cholesterol present in liposomes adsorbed to the device surface as a result of the different mechanical properties of the liposomes. This fact was exploited to develop an acoustic assay to determine the relative affinity of cholesterol for different lipid mixtures. In the assay described here, the initial rate of β-cyclodextrin-induced removal of cholesterol was measured for liposomes having a range of compositions. The initial rate of cholesterol removal was found to be directly proportional to the concentration of β-cyclodextrin (βCD) present over the range of 0–7.5 mg/ml (0–6.6 mM), consistent with other assays measuring the βCD-accelerated transfer of cholesterol between liposomes. The affinity of cholesterol for 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) liposomes with a sphingomyelin mole fraction, χSPM, of 0.2 was found to be 1.4× higher than that for pure OPPC liposomes. For liposomes composed only of OPPC and cholesterol in varying ratios, the initial rate of cholesterol removal was determined as a function of cholesterol mole fraction (χC). The initial rate of removal showed an increase at χC = 0.13, consistent with phase diagrams showing the start of liquid ordered domain formation, but no such increase at χC = 0.25, in contrast to the predictions of the umbrella model for OPPC/cholesterol interactions.

  • Probing Mechanical Properties of Liposomes Using Acoustic Sensors
    Langmuir, 2008
    Co-Authors: Kathryn A. Melzak, F. Bender, A Tsortos, Electra Gizeli

    Abstract:

    Acoustic devices were employed to characterize variations in the mechanical properties (density and viscoelasticity) of liposomes composed of 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (POPC) and cholesterol. Liposome properties were modified in three ways. In some experiments, the POPC/cholesterol ratio was varied prior to deposition on the device surface. Alternatively, the ratio was changed in situ via either insertion of cholesterol or removal of cholesterol with β-cyclodextrin. This was done for liposomes adsorbed directly on the device surface and for liposomes attached via a biotin-terminated poly(ethylene glycol) linker. The acoustic measurements make use of two simultaneous time-resolved signals: one signal is related to the velocity of the acoustic wave, while the second is related to dissipation of acoustic energy. Together, they provide information not only about the mass (or density) of the probed medium but also about its viscoelastic properties. The cholesterol-induced increase in the…

Kathryn A. Melzak – 2nd expert on this subject based on the ideXlab platform

  • Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
    The Analyst, 2009
    Co-Authors: Kathryn A. Melzak, Electra Gizeli

    Abstract:

    Acoustic devices are sensitive to the mole fraction of cholesterol present in liposomes adsorbed to the device surface as a result of the different mechanical properties of the liposomes. This fact was exploited to develop an acoustic assay to determine the relative affinity of cholesterol for different lipid mixtures. In the assay described here, the initial rate of beta-cyclodextrin-induced removal of cholesterol was measured for liposomes having a range of compositions. The initial rate of cholesterol removal was found to be directly proportional to the concentration of beta-cyclodextrin (betaCD) present over the range of 0-7.5 mg/ml (0-6.6 mM), consistent with other assays measuring the betaCD-accelerated transfer of cholesterol between liposomes. The affinity of cholesterol for 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) liposomes with a sphingomyelin mole fraction, chi(SPM), of 0.2 was found to be 1.4x higher than that for pure OPPC liposomes. For liposomes composed only of OPPC and cholesterol in varying ratios, the initial rate of cholesterol removal was determined as a function of cholesterol mole fraction (chi(C)). The initial rate of removal showed an increase at chi(C) = 0.13, consistent with phase diagrams showing the start of liquid ordered domain formation, but no such increase at chi(C) = 0.25, in contrast to the predictions of the umbrella model for OPPC/cholesterol interactions.

  • Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
    Analyst, 2008
    Co-Authors: Kathryn A. Melzak, Electra Gizeli

    Abstract:

    Acoustic devices are sensitive to the mole fraction of cholesterol present in liposomes adsorbed to the device surface as a result of the different mechanical properties of the liposomes. This fact was exploited to develop an acoustic assay to determine the relative affinity of cholesterol for different lipid mixtures. In the assay described here, the initial rate of β-cyclodextrin-induced removal of cholesterol was measured for liposomes having a range of compositions. The initial rate of cholesterol removal was found to be directly proportional to the concentration of β-cyclodextrin (βCD) present over the range of 0–7.5 mg/ml (0–6.6 mM), consistent with other assays measuring the βCD-accelerated transfer of cholesterol between liposomes. The affinity of cholesterol for 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) liposomes with a sphingomyelin mole fraction, χSPM, of 0.2 was found to be 1.4× higher than that for pure OPPC liposomes. For liposomes composed only of OPPC and cholesterol in varying ratios, the initial rate of cholesterol removal was determined as a function of cholesterol mole fraction (χC). The initial rate of removal showed an increase at χC = 0.13, consistent with phase diagrams showing the start of liquid ordered domain formation, but no such increase at χC = 0.25, in contrast to the predictions of the umbrella model for OPPC/cholesterol interactions.

  • Probing Mechanical Properties of Liposomes Using Acoustic Sensors
    Langmuir, 2008
    Co-Authors: Kathryn A. Melzak, F. Bender, A Tsortos, Electra Gizeli

    Abstract:

    Acoustic devices were employed to characterize variations in the mechanical properties (density and viscoelasticity) of liposomes composed of 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (POPC) and cholesterol. Liposome properties were modified in three ways. In some experiments, the POPC/cholesterol ratio was varied prior to deposition on the device surface. Alternatively, the ratio was changed in situ via either insertion of cholesterol or removal of cholesterol with β-cyclodextrin. This was done for liposomes adsorbed directly on the device surface and for liposomes attached via a biotin-terminated poly(ethylene glycol) linker. The acoustic measurements make use of two simultaneous time-resolved signals: one signal is related to the velocity of the acoustic wave, while the second is related to dissipation of acoustic energy. Together, they provide information not only about the mass (or density) of the probed medium but also about its viscoelastic properties. The cholesterol-induced increase in the…

Barbara J. Finlayson-pitts – 3rd expert on this subject based on the ideXlab platform

  • Nitrite-Induced Oxidation of Organic Coatings on Models for Airborne Particles†
    Journal of Physical Chemistry A, 2009
    Co-Authors: Federico Karagulian, Christopher W. Dilbeck, Barbara J. Finlayson-pitts

    Abstract:

    The UV photolysis at λ ≥ 290 nm in air of a mixture of NaNO 2 /NaCl coated with 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) was followed in real time in the absence and presence of water vapor by using diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) at 23 °C. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was used to confirm the identification of the products. Photolysis of NO 2 ― is known to generate O ― , which in the presence of water forms OH + OH-. Irradiation of the OPPC/NaNO 2 /NaCl mixture led to a loss of nitrite and the formation of organic nitrates and carbonyl compounds. In the absence of added water vapor, carboxylate ions were also formed. These products are due to oxidation of OPPC by O ― and OH radicals. The organic products formed per calculated O ― /OH generated by photolysis increased with relative humidity, consistent with a competition between OPPC and NO 2 ― for OH. This suggests a new mechanism of oxidation of organics on particles and on surfaces in air that have nitrite ions available for photolysis. Similar chemistry is likely to occur for nitrate ions, which also photolyze to generate O ― .

  • Unusual oxidation of organics at interfaces from the bottom up and atmospheric implications.
    Journal of the American Chemical Society, 2008
    Co-Authors: Federico Karagulian, Christopher W. Dilbeck, Barbara J. Finlayson-pitts

    Abstract:

    Photolysis of a mixture of NaNO2 with NaCl with an adsorbed coating of 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) is shown to lead to oxidation of the OPPC. This oxidation “from the bottom up” is due to the generation of the OH free radical from nitrite ion photochemistry in the presence of water and its addition to the OPPC double bond. Such chemistry may be important in the lower atmosphere.

  • A new mechanism for ozonolysis of unsaturated organics on solids: phosphocholines on NaCl as a model for sea salt particles
    Physical Chemistry Chemical Physics, 2007
    Co-Authors: Federico Karagulian, Christopher W. Dilbeck, Barbara J. Finlayson-pitts

    Abstract:

    The ozonolysis of an approximately one monolayer film of 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) on NaCl was followed in real time using diffuse reflection infrared Fourier transform spectrometry (DRIFTS) at 23 °C. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and Auger electron spectroscopy were used to confirm the identification of the products. Ozone concentrations ranged from 1.7 × 1012 to 7.0 × 1013 molecules cm–3 (70 ppb to 2.8 ppm). Upon exposure to O3, there was a loss of CC accompanied by the formation of a strong band at ∼1110 cm–1 due to the formation of a stable secondary ozonide (1,2,4-trioxolane, SOZ). The yield of the SOZ was smaller when the reaction was carried out in the presence of water vapor at concentrations corresponding to relative humidities between 2 and 25%. The dependencies of the rate of SOZ formation on the concentrations of ozone and water vapor are consistent with the initial formation of a primary ozonide (1,2,3-trioxolane, POZ) that can react with O3 or H2O in competition with its thermal decomposition to a Criegee intermediate and aldehyde. Estimates were obtained for the rate constants for the POZ thermal decomposition and for its reactions with O3 and H2O, as well as for the initial reaction of O3 with OPPC. The SOZ decomposed upon photolysis in the actinic region generating aldehydes, carboxylic acids and anhydrides. These studies show that the primary ozonide has a sufficiently long lifetime when formed on a solid substrate that direct reactions with O3 and H2O can compete with its thermal decomposition. In dry polluted atmospheres, ozone–alkene reactions may lead in part to the formation of stable secondary ozonides whose chemistry, photochemistry and toxicity should be taken into account in models of such regions.