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Nele V, Holme MN, Rashid MH, Barriga HMG, Le TC, Thomas MR, Doutch JJ, Yarovsky I, Stevens MM. Design of Lipid-Based Nanocarriers via Cation Modulation of Ethanol-Interdigitated Lipid Membranes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:11909-11921. [PMID: 34581180 DOI: 10.1021/acs.langmuir.1c02076] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Short-chain alcohols (i.e., ethanol) can induce membrane interdigitation in saturated-chain phosphatidylcholines (PCs). In this process, alcohol molecules intercalate between phosphate heads, increasing lateral separation and favoring hydrophobic interactions between opposing acyl chains, which interpenetrate forming an interdigitated phase. Unraveling mechanisms underlying the interactions between ethanol and model lipid membranes has implications for cell biology, biochemistry, and for the formulation of lipid-based nanocarriers. However, investigations of ethanol-lipid membrane systems have been carried out in deionized water, which limits their applicability. Here, using a combination of small- and wide-angle X-ray scattering, small-angle neutron scattering, and all-atom molecular dynamics simulations, we analyzed the effect of varying CaCl2 and NaCl concentrations on ethanol-induced interdigitation. We observed that while ethanol addition leads to the interdigitation of bulk phase 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers in the presence of CaCl2 and NaCl regardless of the salt concentration, the ethanol-induced interdigitation of vesicular DPPC depends on the choice of cation and its concentration. These findings unravel a key role for cations in the ethanol-induced interdigitation of lipid membranes in either bulk phase or vesicular form.
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Affiliation(s)
- Valeria Nele
- Department of Materials, Department of Bioengineering and Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ, U.K
| | - Margaret N Holme
- Department of Materials, Department of Bioengineering and Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ, U.K
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden
| | - M Harunur Rashid
- School of Engineering, RMIT University, Melbourne, Victoria 3001, Australia
- Department of Mathematics and Physics, North South University, Bashundhara, Dhaka 1229, Bangladesh
| | - Hanna M G Barriga
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden
| | - Tu C Le
- School of Engineering, RMIT University, Melbourne, Victoria 3001, Australia
| | - Michael R Thomas
- Department of Materials, Department of Bioengineering and Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ, U.K
- London Centre for Nanotechnology and Department of Biochemical Engineering, University College London, 17-19 Gordon Street, London WC1H 0AH, U.K
| | - James J Doutch
- ISIS Neutron and Muon Source, STFC, Rutherford Appleton Laboratory, Didcot OX11 ODE, U.K
| | - Irene Yarovsky
- School of Engineering, RMIT University, Melbourne, Victoria 3001, Australia
| | - Molly M Stevens
- Department of Materials, Department of Bioengineering and Institute of Biomedical Engineering, Imperial College London, London SW7 2AZ, U.K
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden
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2
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Cheu C, Yang L, Nieh MP. Refining internal bilayer structure of bicelles resolved by extended-q small angle X-ray scattering. Chem Phys Lipids 2020; 231:104945. [PMID: 32621811 DOI: 10.1016/j.chemphyslip.2020.104945] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Revised: 06/18/2020] [Accepted: 06/26/2020] [Indexed: 11/15/2022]
Abstract
The internal profile across the bilayer reveals important structural information regarding the crystallinity of acyl chains or the positions of encapsulated species. Here, we demonstrate that a simple five-layer-core-shell discoidal model can be employed to best fit the extended-q small angle X-ray scattering (SAXS) data and resolve the bilayer internal structure (with sub-nanometer resolution) of a nanoscale discoidal system comprised of a mixture of long- and short- chain lipids (known as "bicelles"). In contrast to the traditional core-shell discoidal model, the detailed structure in the hydrophobic core such as the methylene and methyl groups can be distinguished via this model. The refined model is validated by the SAXS data of bicelles whose electron scattering length density of the hydrophobic core is adjusted by the addition of a long-chain lipid with a fluorine-end group. The higher resolution of the bilayer internal structure can be employed to advance our understanding of the interaction and conformation of the membrane and associated molecules, such as membrane-associated proteins and locations of entrapped species in the lipid nanoparticles.
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Affiliation(s)
- Catherine Cheu
- Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA
| | - Lin Yang
- Brookhaven National Laboratory, PO Box 5000, Upton, NY 11973-5000, USA
| | - Mu-Ping Nieh
- Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA; Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269, USA; Department of Biomedical Engineering, University of Connecticut, Storrs, CT 06269, USA.
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3
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Shah SWH, Schwieger C, Kressler J, Blume A. Monolayer behavior of pure F-DPPC and mixed films with DPPC studied by epifluorescence microscopy and infrared reflection absorption spectroscopy. Chem Phys Lipids 2020; 230:104918. [PMID: 32417099 DOI: 10.1016/j.chemphyslip.2020.104918] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Revised: 04/19/2020] [Accepted: 05/04/2020] [Indexed: 12/27/2022]
Abstract
The monolayer behavior of a l-DPPC derivative with a single fluorination in one of its terminal methyl groups (F-DPPC) at air-water interface was investigated by epifluorescence microscopy and infrared reflection absorption spectroscopy (IRRAS). Epifluorescence microscopy was utilized to study the shape and morphology of liquid-condensed (LC) domains observed upon compression of the film. IRRAS was employed for the determination of chain order and orientation. The shapes of LC-domains in a monolayer of F-DPPC are more dependent on the rate of compression than those of DPPC. The LC domains of F-DPPC display pronounced fractal growth patterns depending on the compression speed. The evolution of LC domain occurs under dominating electrostatic dipolar forces in F-DPPC. IRRAS measurements with the analysis of the frequency of the methylene stretching vibrations as a function of film compression show that the acyl chains in an F-DPPC monolayer in the LE-phase are more disordered than those in a DPPC film. The reason for the higher chain disorder in LE phase F-DPPC monolayers is a back folding of the fluorinated sn-2 chain terminus towards the air-water interface leading to larger molecular area requirement. Angular dependent IRRA spectra of monolayers at a surface pressure of 30 mN m-1 show that in the LC phase DPPC and F-DPPC exhibit a similar tilt of the acyl chains of ca. 28-30 ° relative to the surface normal. F-DPPC is ideally miscible with l-DPPC-d62 having the same chirality, as indicated by epifluorescence images and by IRRAS. However, the LC domains in an equimolar mixture of d-DPPC and F-DPPC having opposite chirality show multi-lobed complex domain patterns indicating chiral phase separation within LC domains.
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Affiliation(s)
- Syed W H Shah
- Institute of Chemistry, Martin Luther University Halle-Wittenberg, 06120, Halle (Saale), Germany; Department of Chemistry, Hazara University, 21120, Mansehra, Pakistan.
| | - Christian Schwieger
- Institute of Chemistry, Martin Luther University Halle-Wittenberg, 06120, Halle (Saale), Germany; Integrative Research Center HALOmem, Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, 06120, Halle (Saale), Germany
| | - Jörg Kressler
- Institute of Chemistry, Martin Luther University Halle-Wittenberg, 06120, Halle (Saale), Germany
| | - Alfred Blume
- Institute of Chemistry, Martin Luther University Halle-Wittenberg, 06120, Halle (Saale), Germany
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4
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Gagnon MC, Auger M, Paquin JF. Progress in the synthesis of fluorinated phosphatidylcholines for biological applications. Org Biomol Chem 2018; 16:4925-4941. [DOI: 10.1039/c8ob00991k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Fluorinated phospholipids have attracted a lot of interest over the past 40 years. While mono- and polyfluorinated analogs are mostly designed to be used as 19F NMR probes, highly fluorinated phospholipids are mainly developed as drug delivery devices and oxygen carriers. This review describes their synthetic pathways, their properties and potential applications.
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Affiliation(s)
| | - Michèle Auger
- PROTEO
- CERMA
- CQMF
- Département de Chimie
- Université Laval
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5
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Shah SWH, Schwieger C, Li Z, Kressler J, Blume A. Effect of Perfluoroalkyl Endgroups on the Interactions of Tri-Block Copolymers with Monofluorinated F-DPPC Monolayers. Polymers (Basel) 2017; 9:polym9110555. [PMID: 30965858 PMCID: PMC6418721 DOI: 10.3390/polym9110555] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 10/20/2017] [Accepted: 10/21/2017] [Indexed: 12/16/2022] Open
Abstract
We studied the interaction of amphiphilic and triphilic polymers with monolayers prepared from F-DPPC (1-palmitoyl-2-(16-fluoropalmitoyl)-sn-glycero-3-phosphocholine), a phospholipid with a single fluorine atom at the terminus of the sn-2 chain, an analogue of dipalmitoyl-phosphatidylcholine (DPPC). The amphiphilic block copolymers contained a hydrophobic poly(propylene oxide) block flanked by hydrophilic poly(glycerol monomethacrylate) blocks (GP). F-GP was derived from GP by capping both termini with perfluoro-n-nonyl segments. We first studied the adsorption of GP and F-GP to lipid monolayers of F-DPPC. F-GP was inserted into the monolayer up to a surface pressure Π of 42.4 mN m−1, much higher than GP (32.5 mN m−1). We then studied isotherms of lipid-polymer mixtures co-spread at the air-water interface. With increasing polymer content in the mixture a continuous shift of the onset of the liquid-expanded (LE) to liquid-condensed (LC) transition towards higher molecular and higher area per lipid molecule was observed. F-GP had a larger effect than GP indicating that it needed more space. At a Π-value of 32 mN m−1, GP was excluded from the mixed monolayer, whereas F-GP stayed in F-DPPC monolayers up to 42 mN m−1. F-GP is thus more stably anchored in the monolayer up to higher surface pressures. Images of mixed monolayers were acquired using different fluorescent probes and showed the presence of perfluorinated segments of F-GP at LE-LC domain boundaries.
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Affiliation(s)
- Syed W H Shah
- Institute of Chemistry, Martin-Luther University Halle-Wittenberg, D 06099 Halle, Germany.
- Chemistry Department, Hazara University, 21120 Mansehra, Pakistan.
| | - Christian Schwieger
- Institute of Chemistry, Martin-Luther University Halle-Wittenberg, D 06099 Halle, Germany.
| | - Zheng Li
- Institute of Chemistry, Martin-Luther University Halle-Wittenberg, D 06099 Halle, Germany.
| | - Jörg Kressler
- Institute of Chemistry, Martin-Luther University Halle-Wittenberg, D 06099 Halle, Germany.
| | - Alfred Blume
- Institute of Chemistry, Martin-Luther University Halle-Wittenberg, D 06099 Halle, Germany.
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6
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Smith EA, Dea PK. The interdigitated gel phase in mixtures of cationic and zwitterionic phospholipids. Biophys Chem 2015; 196:86-91. [DOI: 10.1016/j.bpc.2014.10.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 10/14/2014] [Accepted: 10/14/2014] [Indexed: 11/26/2022]
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7
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Smith EA, Smith C, Tanksley B, Dea PK. Effects of cis- and trans-unsaturated lipids on an interdigitated membrane. Biophys Chem 2014; 190-191:1-7. [DOI: 10.1016/j.bpc.2014.03.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 03/14/2014] [Accepted: 03/14/2014] [Indexed: 11/25/2022]
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8
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Gagnon MC, Turgeon B, Savoie JD, Parent JF, Auger M, Paquin JF. Evaluation of the effect of fluorination on the property of monofluorinated dimyristoylphosphatidylcholines. Org Biomol Chem 2014; 12:5126-35. [DOI: 10.1039/c4ob00934g] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The synthesis and characterization of three monofluorinated dimyristoylphosphatidylcholines, with the fluorine atom located at the extremities of the acyl chain in position 2 of the glycerol (sn-2), is described.
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Affiliation(s)
- Marie-Claude Gagnon
- Department of Chemistry
- PROTEO
- CERMA
- Québec, Canada
- Canada Research Chair in Organic and Medicinal Chemistry
| | - Bianka Turgeon
- Department of Chemistry
- PROTEO
- CERMA
- Québec, Canada
- Canada Research Chair in Organic and Medicinal Chemistry
| | - Jean-Daniel Savoie
- Department of Chemistry
- PROTEO
- CERMA
- Québec, Canada
- Canada Research Chair in Organic and Medicinal Chemistry
| | - Jean-François Parent
- Department of Chemistry
- PROTEO
- CERMA
- Québec, Canada
- Canada Research Chair in Organic and Medicinal Chemistry
| | | | - Jean-François Paquin
- Canada Research Chair in Organic and Medicinal Chemistry
- Department of Chemistry
- PROTEO
- CGCC
- Québec, Canada
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9
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Yoshino M, Kikukawa T, Takahashi H, Takagi T, Yokoyama Y, Amii H, Baba T, Kanamori T, Sonoyama M. Physicochemical Studies of Bacteriorhodopsin Reconstituted in Partially Fluorinated Phosphatidylcholine Bilayers. J Phys Chem B 2013; 117:5422-9. [DOI: 10.1021/jp311665z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Masaru Yoshino
- Department of Chemistry and
Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu 376-8515, Japan
| | - Takashi Kikukawa
- Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan
| | - Hiroshi Takahashi
- Department of Chemistry and Chemical
Biology, Graduate School of Engineering, Gunma University, Maebashi 371-8510, Japan
| | - Toshiyuki Takagi
- Research Center for Stem Cell
Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan
| | - Yasunori Yokoyama
- Department of Applied Physics,
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
| | - Hideki Amii
- Department of Chemistry and
Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu 376-8515, Japan
| | - Teruhiko Baba
- Research Center for Stem Cell
Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan
| | - Toshiyuki Kanamori
- Research Center for Stem Cell
Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan
| | - Masashi Sonoyama
- Department of Chemistry and
Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu 376-8515, Japan
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10
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Lozano MM, Liu Z, Sunnick E, Janshoff A, Kumar K, Boxer SG. Colocalization of the ganglioside G(M1) and cholesterol detected by secondary ion mass spectrometry. J Am Chem Soc 2013; 135:5620-30. [PMID: 23514537 PMCID: PMC3639293 DOI: 10.1021/ja310831m] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The characterization of the lateral organization of components in biological membranes and the evolution of this arrangement in response to external triggers remain a major challenge. The concept of lipid rafts is widely invoked; however, direct evidence of the existence of these ephemeral entities remains elusive. We report here the use of secondary ion mass spectrometry (SIMS) to image the cholesterol-dependent cohesive phase separation of the ganglioside GM1 into nano- and microscale assemblies in a canonical lipid raft composition of lipids. This assembly of domains was interrogated in a model membrane system composed of palmitoyl sphingomyelin (PSM), cholesterol, and an unsaturated lipid (dioleoylphosphatidylcholine, DOPC). Orthogonal isotopic labeling of every lipid bilayer component and monofluorination of GM1 allowed generation of molecule specific images using a NanoSIMS. Simultaneous detection of six different ion species in SIMS, including secondary electrons, was used to generate ion ratio images whose signal intensity values could be correlated to composition through the use of calibration curves from standard samples. Images of this system provide the first direct, molecule specific, visual evidence for the colocalization of cholesterol and GM1 in supported lipid bilayers and further indicate the presence of three compositionally distinct phases: (1) the interdomain region; (2) micrometer-scale domains (d > 3 μm); (3) nanometer-scale domains (d = 100 nm to 1 μm) localized within the micrometer-scale domains and the interdomain region. PSM-rich, nanometer-scale domains prefer to partition within the more ordered, cholesterol-rich/DOPC-poor/GM1-rich micrometer-scale phase, while GM1-rich, nanometer-scale domains prefer to partition within the surrounding, disordered, cholesterol-poor/PSM-rich/DOPC-rich interdomain phase.
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Affiliation(s)
- Mónica M. Lozano
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
| | - Zhao Liu
- Department of Chemistry, Tufts University, Medford, Massachusetts 02155-5813
| | - Eva Sunnick
- Institute of Physical Chemistry, University of Göttingen, Tammannstr. 6, 37077 Göttingen, Germany
| | - Andreas Janshoff
- Institute of Physical Chemistry, University of Göttingen, Tammannstr. 6, 37077 Göttingen, Germany
| | - Krishna Kumar
- Department of Chemistry, Tufts University, Medford, Massachusetts 02155-5813
- Cancer Center, Tufts Medical Center, Boston, Massachusetts 02110
| | - Steven G. Boxer
- Department of Chemistry, Stanford University, Stanford, California 94305-5080
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11
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Takahashi H, Yoshino M, Takagi T, Amii H, Baba T, Kanamori T, Sonoyama M. Non-ideal mixing of dimyristoylphosphatidylcholine with its partially fluorinated analogue in hydrated bilayers. Chem Phys Lett 2013. [DOI: 10.1016/j.cplett.2012.12.067] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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12
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Smith EA, Dea PK. Influence of the interdigitated gel phase in mixtures of ether-linked and monofluorinated ester-linked phospholipids. Chem Phys Lipids 2012; 165:818-25. [DOI: 10.1016/j.chemphyslip.2012.10.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Revised: 10/25/2012] [Accepted: 10/26/2012] [Indexed: 10/27/2022]
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13
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Toimil P, Daviña R, Sabín J, Prieto G, Sarmiento F. Influence of temperature on the colloidal stability of the F-DPPC and DPPC liposomes induced by lanthanum ions. J Colloid Interface Sci 2012; 367:193-8. [DOI: 10.1016/j.jcis.2011.10.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Revised: 09/30/2011] [Accepted: 10/01/2011] [Indexed: 12/01/2022]
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14
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Smith EA, Wang W, Dea PK. Effects of cholesterol on phospholipid membranes: inhibition of the interdigitated gel phase of F-DPPC and F-DPPC/DPPC. Chem Phys Lipids 2011; 165:151-9. [PMID: 22200532 DOI: 10.1016/j.chemphyslip.2011.12.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2011] [Revised: 12/09/2011] [Accepted: 12/10/2011] [Indexed: 11/18/2022]
Abstract
Unlike the parent phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), the monofluorinated analog, 1-palmitoyl-2-(16-fluoropalmitoyl)sn-glycero-3-phosphocholine (F-DPPC), spontaneously forms an interdigitated gel phase (L(β)I) below the main transition temperature (T(m)). We have examined the effects of introducing cholesterol to F-DPPC and 1:1 F-DPPC/DPPC membranes using a combination of DSC, optical density, fluorescence intensity and polarization, (31)P NMR, and X-ray diffraction techniques. Cholesterol increases the fluidity of the gel phase, broadens the main transition, and decreases the main transition enthalpy. However, these results also reveal that there is an unusually large degree of phase coexistence between the L(β)I and non-interdigitated gel phases when cholesterol is added. Cholesterol encourages this phase segregation by partitioning into the thicker non-interdigitated domains. At higher cholesterol concentrations, the majority or all of the L(β)I phase of F-DPPC and 1:1 F-DPPC/DPPC is eliminated and is replaced by a non-interdigitated liquid-ordered (l(o)) phase with properties similar to DPPC/cholesterol. Consequently, cholesterol mitigates the influence the CF moiety has on the thermodynamic phase behavior of F-DPPC. Our findings demonstrate that there are multiple characteristics of cholesterol-rich membranes that disfavor interdigitation.
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Affiliation(s)
- Eric A Smith
- Department of Chemistry, Occidental College, Los Angeles, CA 90041, USA
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15
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Griffin KL, Cheng CY, Smith EA, Dea PK. Effects of pentanol isomers on the phase behavior of phospholipid bilayer membranes. Biophys Chem 2010; 152:178-83. [PMID: 20970239 DOI: 10.1016/j.bpc.2010.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Revised: 09/23/2010] [Accepted: 09/23/2010] [Indexed: 10/19/2022]
Abstract
Differential scanning calorimetry (DSC) was used to analyze the thermotropic phase behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers in the presence of pentanol isomers. The concentration of each pentanol isomer needed to induce the interdigitated phase was determined by the appearance of a biphasic effect in the main transition temperatures, the onset of a hysteresis associated with the main transition from the gel-to-liquid crystalline phase, and the disappearance of the pretransition. Lower threshold concentrations were found to correlate with isomers of greater alkyl chain length while branching of the alkyl chain was found to increase biphasic behavior. The addition of a methyl group to butanol systems drastically decreased threshold concentrations. However, as demonstrated in the DPPC/neopentanol system, branching of the alkyl chain away from the -OH group lowers the threshold concentration while maintaining a biphasic effect.
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Affiliation(s)
- Kathryn L Griffin
- Department of Chemistry, Occidental College, 1600 Campus Road, Los Angeles, CA 90041, USA
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