The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Electra Gizeli - One of the best experts on this subject based on the ideXlab platform.
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Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
The Analyst, 2009Co-Authors: Kathryn A. Melzak, Electra GizeliAbstract: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.
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Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
Analyst, 2008Co-Authors: Kathryn A. Melzak, Electra GizeliAbstract: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.
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Probing Mechanical Properties of Liposomes Using Acoustic Sensors
Langmuir, 2008Co-Authors: Kathryn A. Melzak, F. Bender, A Tsortos, Electra GizeliAbstract: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...
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Probing mechanical properties of liposomes using acoustic sensors
Langmuir, 2008Co-Authors: Kathryn A. Melzak, F. Bender, A Tsortos, Electra GizeliAbstract: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 beta-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 surface density of the lipid bilayer was indeed observed in the acoustic data, but the resulting change in signal was larger than expected from the change in surface density. In addition, increasing the bilayer resistance to stretching was found to lead to a greater dissipation of the acoustic energy. The acoustic response is assessed in terms of the possible distortions of the liposomes and the known effects of cholesterol on the mechanical properties of the lipid bilayer that encloses the aqueous core of the liposome. To aid the interpretation of the acoustic response, it is discussed how the above changes in the lipid bilayer will affect the effective viscoelastic properties of the entire liposome/solvent film on the scale of the acoustic wavelength. It was found that the acoustic device is very sensitive to the mechanical properties of lipid vesicles; the response of the acoustic device is explained, and the basic underlying mechanisms of interaction are identified.
Kathryn A. Melzak - One of the best experts on this subject based on the ideXlab platform.
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Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
The Analyst, 2009Co-Authors: Kathryn A. Melzak, Electra GizeliAbstract: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.
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Relative activity of cholesterol in OPPC/cholesterol/sphingomyelin mixtures measured with an acoustic sensor.
Analyst, 2008Co-Authors: Kathryn A. Melzak, Electra GizeliAbstract: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.
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Probing Mechanical Properties of Liposomes Using Acoustic Sensors
Langmuir, 2008Co-Authors: Kathryn A. Melzak, F. Bender, A Tsortos, Electra GizeliAbstract: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...
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Probing mechanical properties of liposomes using acoustic sensors
Langmuir, 2008Co-Authors: Kathryn A. Melzak, F. Bender, A Tsortos, Electra GizeliAbstract: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 beta-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 surface density of the lipid bilayer was indeed observed in the acoustic data, but the resulting change in signal was larger than expected from the change in surface density. In addition, increasing the bilayer resistance to stretching was found to lead to a greater dissipation of the acoustic energy. The acoustic response is assessed in terms of the possible distortions of the liposomes and the known effects of cholesterol on the mechanical properties of the lipid bilayer that encloses the aqueous core of the liposome. To aid the interpretation of the acoustic response, it is discussed how the above changes in the lipid bilayer will affect the effective viscoelastic properties of the entire liposome/solvent film on the scale of the acoustic wavelength. It was found that the acoustic device is very sensitive to the mechanical properties of lipid vesicles; the response of the acoustic device is explained, and the basic underlying mechanisms of interaction are identified.
Barbara J. Finlayson-pitts - One of the best experts on this subject based on the ideXlab platform.
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Nitrite-Induced Oxidation of Organic Coatings on Models for Airborne Particles†
Journal of Physical Chemistry A, 2009Co-Authors: Federico Karagulian, Christopher W. Dilbeck, Barbara J. Finlayson-pittsAbstract: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 ― .
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Unusual oxidation of organics at interfaces from the bottom up and atmospheric implications.
Journal of the American Chemical Society, 2008Co-Authors: Federico Karagulian, Christopher W. Dilbeck, Barbara J. Finlayson-pittsAbstract: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.
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A new mechanism for ozonolysis of unsaturated organics on solids: phosphocholines on NaCl as a model for sea salt particles
Physical Chemistry Chemical Physics, 2007Co-Authors: Federico Karagulian, Christopher W. Dilbeck, Barbara J. Finlayson-pittsAbstract: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.
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Real-Time Monitoring of the Kinetics and Gas-Phase Products of the Reaction of Ozone with an Unsaturated Phospholipid at the Air−Water Interface
Langmuir, 2000Co-Authors: Y. Wadia, Douglas J. Tobias, And R. Stafford, Barbara J. Finlayson-pittsAbstract:While the kinetics and mechanisms of the reaction of O3 with alkenes in the gas and condensed phases are reasonably well understood, those with unsaturated organics in the intermediate regime at the air−water interface are not. Studies of the reaction of ozone at room temperature with the unsaturated phospholipid, 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC) at the air−water interface, and, for comparison, the fully saturated dipalmitoyl-l-α-phosphatidylcholine (DPPC) were carried out. The phospholipids were exposed at varying surface areas per phosphocholine molecule on a water subphase to a flow of O3 in air (0.25−1 ppm), and atmospheric pressure ionization mass spectrometry (API-MS) was used to monitor the formation of gaseous products in real time. Nonanal was detected as a major gas-phase product of the reaction of ozone with OPPC; no volatile products were observed in the case of DPPC. The yield of nonanal, defined as the nonanal produced per phosphocholine molecule reacted at the air−wat...
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Interactions of monolayers of unsaturated phosphocholines with ozone at the air-water interface
Langmuir, 1994Co-Authors: S. H. Yang, Barbara J. Finlayson-pittsAbstract:The phosphocholines 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). 1-Oleoyl-2-Palmitoyl-Sn-Glycero-3-Phosphocholine (OPPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and 1-oleoyl-2-stearoyl-sn-glycero-3-phosphocholine (OSPC) were exposed as monolayers on a Langmuir trough to O 3 in O 2 at concentrations from 0.3 to 30 ppm for reaction times of 10-30 min. The changes in the surface pressure-area isotherms after ozone exposure are shown to be sensitive indicators of reaction. The most dramatic changes were observed at the largest extents of reaction using a basic subphase, suggesting an acid was a major product of the O 3 reaction under these conditions
J L Beauchamp - One of the best experts on this subject based on the ideXlab platform.
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cholesterol provides nonsacrificial protection of membrane lipids from chemical damage at air water interface
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Xinxing Zhang, Kevin M Barraza, J L BeauchampAbstract:The role of cholesterol in bilayer and monolayer lipid membranes has been of great interest. On the biophysical front, cholesterol significantly increases the order of the lipid packing, lowers the membrane permeability, and maintains membrane fluidity by forming liquid-ordered–phase lipid rafts. However, direct observation of any influence on membrane chemistry related to these cholesterol-induced physical properties has been absent. Here we report that the addition of 30 mol % cholesterol to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (POPG) monolayers at the air–water interface greatly reduces the oxidation and ester linkage cleavage chemistries initiated by potent chemicals such as OH radicals and HCl vapor, respectively. These results shed light on the indispensable chemoprotective function of cholesterol in lipid membranes. Another significant finding is that OH oxidation of unsaturated lipids generates Criegee intermediate, which is an important radical involved in many atmospheric processes.
Paweł Wydro - One of the best experts on this subject based on the ideXlab platform.
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Sphingomyelin/phosphatidylcholine/cholesterol monolayers - analysis of the interactions in model membranes and Brewster Angle Microscopy experiments
Colloids and Surfaces B: Biointerfaces, 2012Co-Authors: Paweł WydroAbstract:In this work the properties of two ternary sphingomyelin/phosphatidylcholine/cholesterol monolayers imitating erythrocyte membrane were studied at various content of sterol. Phosphatidylcholines chosen for experiments differ in the length of sn-1 saturated chain in the molecule (1-stearoyl-2-oleoyl- sn-glycero-3-phosphocholine-SOPC vs. 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine - POPC). Langmuir monolayer experiments combined with Brewster Angle Microscopy prove that for both investigated systems the most favorable effect of cholesterol appears at 30% of sterol in the film. However, the interactions between molecules at 50% of sterol are only slightly weaker as compared to those for 1:1:1 films. It was also found that only at higher sterol concentration appear differences in the ordering effect of cholesterol on the systems containing PC molecules of various length of sn-1 saturated chain. Although the differences in the properties of POPC versus SOPC-containing monolayers were found, similarities in the morphology of the respective systems and stoichiometry of thermodynamically the most favorable mixture allow one to conclude that both SM/POPC/Chol as well as SM/SOPC/Chol monolayer can be used to mimic raft systems. © 2012 Elsevier B.V.
