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- Temperature-Controlled Structure and Kinetics of Ripple Phas...Temperature-Controlled Structure and Kinetics of Ripple Phases in One- and Two-Component Supported Lipid Bilayers
Biophysical Journal, Volume 85, Issue 1, 1 July 2003, Pages 350-360
Thomas Kaasgaard, Chad Leidy, John H. Crowe, Ole G. Mouritsen and Kent Jørgensen
AbstractTemperature-controlled atomic force microscopy (AFM) has been used to visualize and study the structure and kinetics of ripple phases in one-component dipalmitoylphosphatidylcholine (DPPC) and two-component dimyristoylphosphatidylcholine-distearoylphosphatidylcholine (DMPC-DSPC) lipid bilayers. The lipid bilayers are mica-supported double bilayers in which ripple-phase formation occurs in the top bilayer. In one-component DPPC lipid bilayers, the stable and metastable ripple phases were observed. In addition, a third ripple structure with approximately twice the wavelength of the metastable ripples was seen. From height profiles of the AFM images, estimates of the amplitudes of the different ripple phases are reported. To elucidate the processes of ripple formation and disappearance, a ripple-phase DPPC lipid bilayer was taken through the pretransition in the cooling and the heating direction and the disappearance and formation of ripples was visualized. It was found that both the disappearance and formation of ripples take place virtually one ripple at a time, thereby demonstrating the highly anisotropic nature of the ripple phase. Furthermore, when a two-component DMPC-DSPC mixture was heated from the ripple phase and into the ripple-phase/fluid-phase coexistence temperature region, the AFM images revealed that several dynamic properties of the ripple phase are important for the melting behavior of the lipid mixture. Onset of melting is observed at grain boundaries between different ripple types and different ripple orientations, and the longer-wavelength metastable ripple phase melts before the shorter-wavelength stable ripple phase. Moreover, it was observed that the ripple phase favors domain growth along the ripple direction and is responsible for creating straight-edged domains with 60° and 120° angles, as reported previously.
Abstract | Full Text | PDF (3946 kb) - A Differential Scanning Calorimetry Study of Phosphocholines...A Differential Scanning Calorimetry Study of Phosphocholines Mixed with Paclitaxel and Its Bromoacylated Taxanes
Biophysical Journal, Volume 78, Issue 1, 1 January 2000, Pages 246-256
Shaukat Ali, Sharma Minchey, Andrew Janoff and Eric Mayhew
AbstractHigh sensitivity differential scanning calorimetry (DSC) was used to investigate the thermotropic phase properties of binary mixtures of disaturated phosphocholines (PCs) and -bromoacyl taxane derivatives. The -bromoacyl taxanes were synthesized as hydrolyzable hydrophobic prodrugs of paclitaxel. The PCs used were 1,2-dimyristoyl--glycero-3-phosphatidyl-choline (DMPC), 1,2-dipalmitoyl--glycero-3-phosphatidylcholine (DPPC) and 1,2-distearoyl--glycero-3-phosphatidylcholine (DSPC). The bromoacyl chain lengths of the taxane prodrugs were varied from 6 to 12 or 16 carbons. For comparison, paclitaxel and PC mixtures were also examined. DSC data from DPPC and bromoacyl taxane mixtures showed a complete abolition of the pretransition and significant broadening of the main phase transition with increasing amounts of bromoacyl taxane prodrugs. The effects were more pronounced with the long-chain compared to the short-chain prodrugs. Under equivalent DSC conditions, the short-chain DMPC showed greater changes in thermotropic phase behavior than with DPPC on taxane addition, suggesting an enhanced degree of association with the fluid-type bilayers. Under similar conditions, the long-chain DSPC bilayers showed a far less significant change in phase behavior on taxane addition than DPPC. These changes were also chain length-dependent for both the PCs and the taxane prodrugs. In contrast, PC and paclitaxel (lacking the acyl chain) mixtures under similar conditions showed insignificant changes in the endotherms, suggesting only slight insertion of the molecule into the PC bilayers. From the DSC data it is apparent that taxane prodrugs solvated in DMPC bilayers more than in DPPC and DSPC bilayers, and taxane prodrugs with longer acyl chains were able to associate with PCs better than those with shorter chain prodrugs. DSC data also suggest that paclitaxel was poorly associated with any of the PCs. In general, the amount of taxane association with bilayers decreased in order: DMPC>DPPC ≫ DSPC. In contrast, the transition enthalpy (ΔH) of DMPC, DPPC, and DSPC mixtures with paclitaxel showed significantly lower enthalpies than with taxane prodrugs. Taken together, the DSC data suggest that the acyl chains of paclitaxel prodrugs have some access into the bilayers via alignment with the acyl chain of the PC component.
Abstract | Full Text | PDF (187 kb) - Comparative Calorimetric and Spectroscopic Studies of the Ef...Comparative Calorimetric and Spectroscopic Studies of the Effects of Lanosterol and Cholesterol on the Thermotropic Phase Behavior and Organization of Dipalmitoylphosphatidylcholine Bilayer Membranes
Biophysical Journal, Volume 91, Issue 9, 1 November 2006, Pages 3327-3340
David A. Mannock, Ruthven N.A.H. Lewis and Ronald N. McElhaney
AbstractWe carried out comparative DSC and Fourier transform infrared spectroscopic studies of the effects of cholesterol and lanosterol on the thermotropic phase behavior and organization of DPPC bilayers. Lanosterol is the biosynthetic precursor of cholesterol and differs in having three rather than two axial methyl groups projecting from the -face of the planar steroid ring system and one axial methyl group projecting from the -face, whereas cholesterol has none. Our DSC studies indicate that the incorporation of lanosterol is more effective than cholesterol is in reducing the enthalpy of the pretransition. Lanosterol is also initially more effective than cholesterol in reducing the enthalpies of both the sharp and broad components of the main phase transition. However, at sterol concentrations of 50mol %, lanosterol does not abolish the cooperative hydrocarbon chain-melting phase transition as does cholesterol. Moreover, at higher lanosterol concentrations (∼30–50mol %), both sharp and broad low-temperature endotherms appear in the DSC heating scans, suggestive of the formation of lanosterol crystallites, and of the lateral phase separation of lanosterol-enriched phospholipid domains, respectively, at low temperatures, whereas such behavior is not observed with cholesterol at comparable concentrations. Our Fourier transform infrared spectroscopic studies demonstrate that lanosterol incorporation produces a less tightly packed bilayer than does cholesterol, which is characterized by increased hydration in the glycerol backbone region of the DPPC bilayer. These and other results indicate that lanosterol is less miscible in DPPC bilayers than is cholesterol, but perturbs their organization to a greater extent, probably due primarily to the rougher faces and larger cross-sectional area of the lanosterol molecule and perhaps secondarily to its decreased ability to form hydrogen bonds with adjacent DPPC molecules. Nevertheless, lanosterol does appear to produce a lamellar liquid-ordered phase in DPPC bilayers, although this phase is not as tightly packed as comparable cholesterol/DPPC mixtures.
Abstract | Full Text | PDF (254 kb) - …more
Copyright © 1975 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 15, Issue 11, 1117-1124, 1 November 1975
doi:10.1016/S0006-3495(75)85888-7
Research Article
Tilted hydrocarbon chains of dipalmitoyl lecithin become perpendicular to the bilayer before melting
R.P. Rand, D. Chapman and K. Larsson
Abstract
Differential scanning calorimetry studies of dipalmitoyl lecithin show two reversible transitions as the temperature is changed between 20 and 50 degrees C. A pretransition endotherm occurs at 35 degrees C prior to the main chain melting endotherm which occurs at 42 degrees C. X-ray diffraction studies show that below 33 degrees C the chains of the lecithin are fully extended, packed in a hexagonal crystalline lattice but tilted with respect to the plane of the bilayer. Between 35 and 42 degrees C the chains are similarly packed but oriented perpendicular to the bilayer plane. Above 44 degrees C the chains are "melted" or disordered. Monolayer studies of dipalmitoyl lecithin using continuous recording of pressure with molecular area reveal the existence of two solid condensed phases corresponding to these tilted and verticle chain structures. The tilted to perpendicular transition would account for the pretransition endotherm of the lipid; the crystalline to melted change corresponds to the larger transition observed at 42 degrees C.
