1H MAS NMR

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Klaus Gawrisch - One of the best experts on this subject based on the ideXlab platform.

  • NMR detection of lipid domains.
    Methods in molecular biology (Clifton N.J.), 2007
    Co-Authors: Ivan V Polozov, Klaus Gawrisch
    Abstract:

    Methods for detection of lateral domains by solid-state 2H nuclear magnetic resonance (NMR) and 1H magic angle spinning (MAS)-NMR in model- and biomembranes are presented. 2H NMR has been used for decades to distinguish between liquid-ordered and solid-ordered lamellar phases of phospholipids with deuterated hydrocarbon chains. More recently, it was shown that superposition of liquid-ordered and -disordered phases is detected as well, taking advantage of the large differences in chain order parameters between them. Experiments require preparation of samples with deuterated lipids. In contrast, 1H MAS-NMR utilizes the natural proton NMR signals of lipids in model- and biomembranes. Very good resolution of resonances according to their chemical shifts is achieved by rapid spinning of samples at the "magic angle" (54.7 degrees) to the main magnetic field. Phase transitions to ordered states are detected as broadening of resonances. The method distinguishes liquid-disordered, liquid-ordered, and solid-ordered phases, has much higher sensitivity than 2H NMR, and does not require labeling. In combination with pulsed magnetic field gradients, 1H MAS-NMR yields diffusion rates that may report confinement of lipids to domains with submicrometer dimensions.

  • domains in binary sopc pope lipid mixtures studied by pulsed field gradient 1H MAS NMR
    Biophysical Journal, 2004
    Co-Authors: Ivan V Polozov, Klaus Gawrisch
    Abstract:

    We studied domain formation in mixtures of the monounsaturated lipids SOPC and POPE as a function of temperature and composition by NMR. Magic angle spinning at kHz frequencies restored resolution of 1H NMR lipid resonances in the fluid phase, whereas the linewidth of gel-phase lipids remained rather broad and spinning frequency dependent. In regions of fluid- and gel-phase coexistence, spectra are a superposition of resonances from fluid and gel domains, as indicated by the existence of isosbestic points. Quantitative determination of the amount of lipid in the coexisting phases is straightforward and permitted construction of a binary phase diagram. Lateral rates of lipid diffusion were determined by 1H MAS NMR with pulsed field gradients. At the onset of the phase transition near 25°C apparent diffusion rates became diffusion time dependent, indicating that lipid movement is obstructed by the formation of gel-phase domains. A percolation threshold at which diffusion of fluid-phase lipid becomes confined to micrometer-size domains was observed when ∼40% of total lipid had entered the gel phase. The results indicate that common phosphatidylethanolamines may trigger domain formation in membranes within a physiologically relevant temperature range. This novel NMR approach may aid the study of lipid rafts.

  • liquid domains in vesicles investigated by NMR and fluorescence microscopy
    Biophysical Journal, 2004
    Co-Authors: Sarah L Veatch, Ivan V Polozov, Klaus Gawrisch, S Keller
    Abstract:

    We use 2H-NMR, 1H-MAS NMR, and fluorescence microscopy to detect immiscibility in three particular phospholipid ratios mixed with 30% cholesterol: 2:1 DOPC/DPPC, 1:1 DOPC/DPPC, and 1:2 DOPC/DPPC. Large-scale (≫160 nm) phase separation into liquid-ordered (Lo) and liquid-crystalline (Lα) phases is observed by both NMR and fluorescence microscopy. By fitting superimposed 2H-NMR spectra, we quantitatively determine that the Lo phase is strongly enriched in DPPC and moderately enriched in cholesterol. Tie-lines estimated at different temperatures and membrane compositions are based on both 2H-NMR observations and a previously published ternary phase diagram. 2H- and 1H-MAS NMR techniques probe significantly smaller length scales than microscopy experiments (submicron versus micron-scalp), and complex behavior is observed near the miscibility transition. Fluorescence microscopy of giant unilamellar vesicles shows micrometer-scale domains below the miscibility transition. In contrast, NMR of multilamellar vesicles gives evidence for smaller (∼80 nm) domains just below the miscibility transition, whereas large-scale demixing occurs at a lower temperature, Tlow. A transition at Tlow is also evident in fluorescence microscopy measurements of the surface area fraction of ordered phase in giant unilamellar vesicles. Our results reemphasize the complex phase behavior of cholesterol-containing membranes and provide a framework for interpreting 2H-NMR experiments in similar membranes.

  • Domains in Binary SOPC/POPE Lipid Mixtures Studied by Pulsed Field Gradient 1H MAS NMR
    Biophysical journal, 2004
    Co-Authors: Ivan V Polozov, Klaus Gawrisch
    Abstract:

    We studied domain formation in mixtures of the monounsaturated lipids SOPC and POPE as a function of temperature and composition by NMR. Magic angle spinning at kHz frequencies restored resolution of (1)H NMR lipid resonances in the fluid phase, whereas the linewidth of gel-phase lipids remained rather broad and spinning frequency dependent. In regions of fluid- and gel-phase coexistence, spectra are a superposition of resonances from fluid and gel domains, as indicated by the existence of isosbestic points. Quantitative determination of the amount of lipid in the coexisting phases is straightforward and permitted construction of a binary phase diagram. Lateral rates of lipid diffusion were determined by (1)H MAS NMR with pulsed field gradients. At the onset of the phase transition near 25 degrees C apparent diffusion rates became diffusion time dependent, indicating that lipid movement is obstructed by the formation of gel-phase domains. A percolation threshold at which diffusion of fluid-phase lipid becomes confined to micrometer-size domains was observed when approximately 40% of total lipid had entered the gel phase. The results indicate that common phosphatidylethanolamines may trigger domain formation in membranes within a physiologically relevant temperature range. This novel NMR approach may aid the study of lipid rafts.

Toshihide Baba - One of the best experts on this subject based on the ideXlab platform.

  • Proton Exchange Reaction between Hydroxyl Groups in the Supercage and Those in the Sodalitecage of Y Zeolite As Studied by Variable Temperature 1H MAS NMR
    The Journal of Physical Chemistry C, 2012
    Co-Authors: Naoki Asakawa, Ken Motokura, Tatsuaki Yashima, To-ru Koyama, Toshinori O-nuki, Akimitsu Miyaji, Toshihide Baba
    Abstract:

    Proton-exchanged Y zeolite (H–Y zeolite) has two types of bridging hydroxyl groups; one exists in the supercage and the other exists in the sodalitecage. The dynamic property of protons due to these hydroxyl groups was investigated by variable temperature 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR). Proton exchange between two types due to these hydroxyl groups proceeded at temperatures higher than ca. 500 K. The temperature dependence of the spectra was explained using the McCornell equation. The activation energy of the proton exchange was estimated to be 50 kJ mol–1.

  • Dynamic properties of protons in solid acids as studied by variable temperature 1H MAS NMR
    Applied Catalysis A: General, 1999
    Co-Authors: Toshihide Baba, Yoshio Ono
    Abstract:

    Abstract The temperature dependence of the line width of 1 H MAS NMR reveals that the acidic protons in H-ZSM-5 become mobile at temperature as low as ∼370 K, though not mobile at 298 K. Substitution of a small part of protons with Na+ or K+ ions sharply decreases the mobility as well as the catalytic activity of the remaining protons, suggesting that a long-range interaction exists among the acid sites. In H-[B,Al]-ZSM-5, two types of protons from the bridging hydroxyl groups, B–OH–Si and Al–OH–Si are observed separately, indicating that the nature of protons are determined by the local environment of the acid sites. However, the local migration of the protons around Al-based acid sites is suppressed by boron introduction to the framework. Two types of protons are observed at 6.4 and 9.3 ppm when Ag3PW12O40 is reduced with hydrogen. The protons at 6.4 ppm exist only when hydrogen is present in the gas phase. They are mobile even at room temperature and catalytically more active than the protons at 9.3 ppm. Upon raising temperature, the exchange of protons between the two kinds of protons proceeds.

  • mobility of the acidic protons in h zsm 5 as studied by variable temperature 1H MAS NMR
    Journal of Physical Chemistry B, 1998
    Co-Authors: Toshihide Baba, Norito Komatsu, Yoshio Ono, Hisashi Sugisawa
    Abstract:

    The dynamic nature of the protons in H−ZSM-5 was examined by the temperature dependence of 1H MAS NMR in the range 298−473 K. The line width of 1H MAS NMR of acidic protons increased, and through maximum it decreased. The intensity of the spinning sidebands monotonically decreased, and they almost disappeared upon raising the temperature. This temperature dependence of the spectrum was explained by the thermal motion of protons. The correlation times and the activation energies for proton mobility were estimated. The estimated values of the activation energy are 17−20 kJ mol-1.

Elaine Holmes - One of the best experts on this subject based on the ideXlab platform.

  • High-resolution 1H NMR and magic angle spinning NMR spectroscopic investigation of the biochemical effects of 2-bromoethanamine in intact renal and hepatic tissue
    Magnetic resonance in medicine, 2001
    Co-Authors: S. Garrod, Manfred Spraul, Susan C. Connor, Jeremy K. Nicholson, E. Humpher, J.c. Connelly, Elaine Holmes
    Abstract:

    The metabolic consequences of xenobiotic-induced toxicity were investigated using high-resolution magic angle spinning (MAS) NMR spectroscopy of intact tissue. Renal papillary necrosis (RPN) was induced in Sprague-Dawley rats (n = 12) via a single i.p. dose of 250 mg/kg 2-bromoethanamine (BEA) hydrobromide. At 2, 4, 6, and 24 h after treatment with BEA, three animals were killed and tissue samples were obtained from liver, renal cortex, and renal medulla. Tissue samples were also removed at 2 and 24 h from matched controls (n = 6). 1H MAS NMR spectroscopic techniques were used to analyze samples of intact tissue (∼10 mg). Decreased levels of nonperturbing renal osmolytes (glycerophosphocholine, betaine, and myo-inositol) were observed in the renal papilla of BEA-treated animals at 6 and 24 h postdose (p.d.), concomitant with a relative increase in the tissue concentration of creatine. Increased levels of glutaric acid were found in all tissues studied in BEA-treated animals at 4 and 6 h p.d., indicating the inhibition of mitochondrial fatty acyl CoA dehydrogenases and mitochondrial dysfunction. Increased levels of trimethylamine-N-oxide occurred in the renal cortex at 6 h p.d. Changes in the metabolite profile of liver included an increase in the relative concentrations of triglycerides, lysine, and leucine. The novel application of 1H MAS NMR to the biochemical analysis of intact tissues following a toxic insult highlights the potential of this technique as a toxicological probe in providing a direct link between urinary biomarkers of toxicity and histopathological evaluation of toxicological lesions. Magn Reson Med 45:781–790, 2001. © 2001 Wiley-Liss, Inc.

  • high resolution magic angle spinning 1H NMR spectroscopic studies on intact rat renal cortex and medulla
    Magnetic Resonance in Medicine, 1999
    Co-Authors: S. Garrod, Eberhard Humpfer, Manfred Spraul, Susan C. Connor, S. Polley, John Connelly, John C. Lindon, Jeremy K. Nicholson, Elaine Holmes
    Abstract:

    High-resolution magic angle spinning 1H NMR (MAS-NMR) spectroscopy was used to investigate the biochemical composition of normal renal cortex and renal papilla samples from rats, and results were compared with those from conventional 1H NMR analysis of protein-free tissue extracts. 1H MAS NMR spectra of samples obtained from inner and outer cortex were found to be broadly similar in terms of metabolite profile, and intra- and inter-animal variability was small. However, the MAS NMR spectra from renal papilla samples were qualitatively and quantitatively different from those obtained from cortex. High levels of free amino acids and several organic acids were detected in the cortex, together with choline, glucose, and trimethylamine-N-oxide. The dominant metabolite resonances observed in papillary tissue were from glycerophosphocholine (GPC), betaine, myo-inositol, and sorbitol. On increasing the magic angle spinning rate from 4,200 to 12,000 Hz, the lipid MAS 1H NMR signal profile remained largely unchanged in papillary tissue, whereas “new” resonances from triglycerides appeared in the spectra of cortical tissue, this effect being reversible on returning the spinning rate to 4,200 Hz. Further investigation into the behavior of the lipid components under different spinning rates suggested that the lipids in the cortex were present in more motionally constrained environments than those in the papilla. 1H MAS NMR spectra of tissues are of value both in interrogation of the biochemical composition of whole tissue, and in obtaining information on the mobility and compartmentalization of certain metabolites. Magn Reson Med 41:1108–1118, 1999. © 1999 Wiley-Liss, Inc.

  • High-resolution magic angle spinning 1H NMR spectroscopic studies on intact rat renal cortex and medulla.
    Magnetic resonance in medicine, 1999
    Co-Authors: S. Garrod, Eberhard Humpfer, Manfred Spraul, Susan C. Connor, S. Polley, John Connelly, John C. Lindon, Jeremy K. Nicholson, Elaine Holmes
    Abstract:

    High-resolution magic angle spinning 1H NMR (MAS-NMR) spectroscopy was used to investigate the biochemical composition of normal renal cortex and renal papilla samples from rats, and results were compared with those from conventional 1H NMR analysis of protein-free tissue extracts. 1H MAS NMR spectra of samples obtained from inner and outer cortex were found to be broadly similar in terms of metabolite profile, and intra- and inter-animal variability was small. However, the MAS NMR spectra from renal papilla samples were qualitatively and quantitatively different from those obtained from cortex. High levels of free amino acids and several organic acids were detected in the cortex, together with choline, glucose, and trimethylamine-N-oxide. The dominant metabolite resonances observed in papillary tissue were from glycerophosphocholine (GPC), betaine, myo-inositol, and sorbitol. On increasing the magic angle spinning rate from 4,200 to 12,000 Hz, the lipid MAS 1H NMR signal profile remained largely unchanged in papillary tissue, whereas "new" resonances from triglycerides appeared in the spectra of cortical tissue, this effect being reversible on returning the spinning rate to 4,200 Hz. Further investigation into the behavior of the lipid components under different spinning rates suggested that the lipids in the cortex were present in more motionally constrained environments than those in the papilla. 1H MAS NMR spectra of tissues are of value both in interrogation of the biochemical composition of whole tissue, and in obtaining information on the mobility and compartmentalization of certain metabolites.

Michael Hunger - One of the best experts on this subject based on the ideXlab platform.

  • Disentangling Brønsted Acid Sites and Hydrogen-Bonded Silanol Groups in High-Silica Zeolite H-ZSM-5
    The Journal of Physical Chemistry C, 2020
    Co-Authors: Christian Schroeder, Michael Ryan Hansen, Michael Hunger, Vassilios Siozios, Hubert Koller
    Abstract:

    Hydrogen-bonded SiOH defects and Bronsted acidic bridging OH groups, defined as Bronsted acid sites (BAS), yield overlapping signals in 1H MAS NMR and FTIR spectroscopies. Here, a clear distinction...

  • Transformations of monoterpene hydrocarbons on ferrierite type zeolites
    Applied Catalysis A-general, 2012
    Co-Authors: R. Rachwalik, Michael Hunger, Bogdan Sulikowski
    Abstract:

    Abstract Transformations of α-pinene and limonene over hydrogen forms of commercial ferrierite type zeolites of different origin (Tosoh Corp. and Zeolyst Intern.) have been studied in the liquid phase at 313–363 K. The catalysts were characterized by XRD, sorption of nitrogen, scanning electron microscopy, FTIR and 27Al & 1H MAS NMR. The concentration of Bronsted acid sites has been determined by 1H MAS NMR and FTIR quantitative measurements, while their strength was estimated by adsorption of CO. The liquid-phase isomerization of α-pinene proceeds smoothly on the two zeolite catalysts, and the initial reaction rates have been compared. Camphene and limonene were the main products, while the selectivity to these hydrocarbons differed. Isomerization of pure limonene was also studied, showing large difference in activity over the two ferrierite catalysts. The selectivity of α-pinene transformations has been rationalized in terms of retarded consecutive isomerization of limonene over the zeolite from Zeolyst.

  • Relation between acidity and local structure of dealuminated zeolites y investigated by solid-state NMR spectroscopy
    2011
    Co-Authors: Leizhi Wang, Yijiao Jiang, Jun Huang, Michael Hunger
    Abstract:

    Multi-nuclear (27Al, 29Si, 1H, 13C) solid-state NMR spectroscopy was carried out for investigating the relationship between acidity and local structure of a dealuminated zeolite Y. The generation of extra-framework aluminum species after mild steam treatment of a parent zeolite H,Na-Y was detected by 27Al MAS NMR spectroscopy. An increase of the framework nSi/nAl ratio from 2.7 to 5.4 was determined by simulation of the 29Si MAS NMR spectra. Via quantitative 1H MAS NMR spectroscopy, the concentration of Bronsted acid sites of zeolite deH-Y was found to decrease with steaming. Furthermore, after loading of deuterated acetonitrile, the 1H MAS NMR spectra show a significantly larger adsorbate-induced low-field shift Delta delta1H of the signal of bridging OH groups in zeolite deH-Y (5.6 ppm) in comparison with parent zeolite H,Na-Y (5.1 ppm). This larger low-field shift indicates an enhanced acid strength of Bronsted acid sites due to the decrease of the framework aluminum content. Finally, 13C MAS NMR spectroscopic studies gave hints for aldol reactions of 2-13C-acetone on zeolite deH-Y. However, no aldol reactions could be observed on zeolite H,Na-Y. This result indicates that dealumination enhances the reactivity of Y zeolites due to the stronger Bronsted acid sites and the formation of Lewis acid sites.

  • Handbook of Heterogeneous Catalysis - NMR Spectroscopy for the Characterization of Surface Acidity and Basicity
    Handbook of Heterogeneous Catalysis, 2008
    Co-Authors: Michael Hunger
    Abstract:

    The sections in this article are Introduction Investigation of Bronsted Acidic Hydroxyl Groups by 1H MAS NMR Spectroscopy Solid-State NMR Characterization of the Accessibility and Strength of Bronsted Acid Sites by Probe Molecules Solid-State NMR Investigations of Lewis Acid Sites by Probe Molecules Solid-State NMR Investigations of Base Sites in Solid Catalysts Keywords: solid-state nuclear magnetic resonance; acid sites; base sites; probe molecules

  • Sorption of methanol on zeolite HBeta investigated by in situ MAS NMR spectroscopy
    Catalysis Letters, 1997
    Co-Authors: Michael Hunger, Thomas Horvath
    Abstract:

    Methanol adsorption and desorption experiments were performed on acidic zeolites applying a new in situ MAS NMR technique. 1H MAS NMR spectra of dehydrated zeolites were recorded during injection of nitrogen gas loaded with methanol into the MAS rotor. The spectra indicated that in zeolite HBeta also silanol groups are involved in the adsorption of methanol which is in contrast to the behaviour of SiOH groups in zeolites HZSM-5 and HY. The desorption experiments show that about 70% of the methanol molecules contributing to adsorbate complexes in zeolite HBeta are weakly hydrogen-bonded at silanol groups.

Ivan V Polozov - One of the best experts on this subject based on the ideXlab platform.

  • NMR detection of lipid domains.
    Methods in molecular biology (Clifton N.J.), 2007
    Co-Authors: Ivan V Polozov, Klaus Gawrisch
    Abstract:

    Methods for detection of lateral domains by solid-state 2H nuclear magnetic resonance (NMR) and 1H magic angle spinning (MAS)-NMR in model- and biomembranes are presented. 2H NMR has been used for decades to distinguish between liquid-ordered and solid-ordered lamellar phases of phospholipids with deuterated hydrocarbon chains. More recently, it was shown that superposition of liquid-ordered and -disordered phases is detected as well, taking advantage of the large differences in chain order parameters between them. Experiments require preparation of samples with deuterated lipids. In contrast, 1H MAS-NMR utilizes the natural proton NMR signals of lipids in model- and biomembranes. Very good resolution of resonances according to their chemical shifts is achieved by rapid spinning of samples at the "magic angle" (54.7 degrees) to the main magnetic field. Phase transitions to ordered states are detected as broadening of resonances. The method distinguishes liquid-disordered, liquid-ordered, and solid-ordered phases, has much higher sensitivity than 2H NMR, and does not require labeling. In combination with pulsed magnetic field gradients, 1H MAS-NMR yields diffusion rates that may report confinement of lipids to domains with submicrometer dimensions.

  • domains in binary sopc pope lipid mixtures studied by pulsed field gradient 1H MAS NMR
    Biophysical Journal, 2004
    Co-Authors: Ivan V Polozov, Klaus Gawrisch
    Abstract:

    We studied domain formation in mixtures of the monounsaturated lipids SOPC and POPE as a function of temperature and composition by NMR. Magic angle spinning at kHz frequencies restored resolution of 1H NMR lipid resonances in the fluid phase, whereas the linewidth of gel-phase lipids remained rather broad and spinning frequency dependent. In regions of fluid- and gel-phase coexistence, spectra are a superposition of resonances from fluid and gel domains, as indicated by the existence of isosbestic points. Quantitative determination of the amount of lipid in the coexisting phases is straightforward and permitted construction of a binary phase diagram. Lateral rates of lipid diffusion were determined by 1H MAS NMR with pulsed field gradients. At the onset of the phase transition near 25°C apparent diffusion rates became diffusion time dependent, indicating that lipid movement is obstructed by the formation of gel-phase domains. A percolation threshold at which diffusion of fluid-phase lipid becomes confined to micrometer-size domains was observed when ∼40% of total lipid had entered the gel phase. The results indicate that common phosphatidylethanolamines may trigger domain formation in membranes within a physiologically relevant temperature range. This novel NMR approach may aid the study of lipid rafts.

  • liquid domains in vesicles investigated by NMR and fluorescence microscopy
    Biophysical Journal, 2004
    Co-Authors: Sarah L Veatch, Ivan V Polozov, Klaus Gawrisch, S Keller
    Abstract:

    We use 2H-NMR, 1H-MAS NMR, and fluorescence microscopy to detect immiscibility in three particular phospholipid ratios mixed with 30% cholesterol: 2:1 DOPC/DPPC, 1:1 DOPC/DPPC, and 1:2 DOPC/DPPC. Large-scale (≫160 nm) phase separation into liquid-ordered (Lo) and liquid-crystalline (Lα) phases is observed by both NMR and fluorescence microscopy. By fitting superimposed 2H-NMR spectra, we quantitatively determine that the Lo phase is strongly enriched in DPPC and moderately enriched in cholesterol. Tie-lines estimated at different temperatures and membrane compositions are based on both 2H-NMR observations and a previously published ternary phase diagram. 2H- and 1H-MAS NMR techniques probe significantly smaller length scales than microscopy experiments (submicron versus micron-scalp), and complex behavior is observed near the miscibility transition. Fluorescence microscopy of giant unilamellar vesicles shows micrometer-scale domains below the miscibility transition. In contrast, NMR of multilamellar vesicles gives evidence for smaller (∼80 nm) domains just below the miscibility transition, whereas large-scale demixing occurs at a lower temperature, Tlow. A transition at Tlow is also evident in fluorescence microscopy measurements of the surface area fraction of ordered phase in giant unilamellar vesicles. Our results reemphasize the complex phase behavior of cholesterol-containing membranes and provide a framework for interpreting 2H-NMR experiments in similar membranes.

  • Domains in Binary SOPC/POPE Lipid Mixtures Studied by Pulsed Field Gradient 1H MAS NMR
    Biophysical journal, 2004
    Co-Authors: Ivan V Polozov, Klaus Gawrisch
    Abstract:

    We studied domain formation in mixtures of the monounsaturated lipids SOPC and POPE as a function of temperature and composition by NMR. Magic angle spinning at kHz frequencies restored resolution of (1)H NMR lipid resonances in the fluid phase, whereas the linewidth of gel-phase lipids remained rather broad and spinning frequency dependent. In regions of fluid- and gel-phase coexistence, spectra are a superposition of resonances from fluid and gel domains, as indicated by the existence of isosbestic points. Quantitative determination of the amount of lipid in the coexisting phases is straightforward and permitted construction of a binary phase diagram. Lateral rates of lipid diffusion were determined by (1)H MAS NMR with pulsed field gradients. At the onset of the phase transition near 25 degrees C apparent diffusion rates became diffusion time dependent, indicating that lipid movement is obstructed by the formation of gel-phase domains. A percolation threshold at which diffusion of fluid-phase lipid becomes confined to micrometer-size domains was observed when approximately 40% of total lipid had entered the gel phase. The results indicate that common phosphatidylethanolamines may trigger domain formation in membranes within a physiologically relevant temperature range. This novel NMR approach may aid the study of lipid rafts.