The effect of temperature on lipid-n-alkane interactions in lipid bilayers (original) (raw)
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The organization of n-alkanes in lipid bilayers
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1980
The interaction of n-alkanes (C6--C16) with phosphatidylcholine has been studied by the combined use of differential scanning calorimetry, X-ray diffraction and monolayer techniques. It has been found that the thermal properties and ultrastructure of lipid-alkane vesicles are strongly dependent on the length of the n-alkanes. Long alkanes, such as tetradecane and hexadecane, increase the transition temperature of dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine, while the X-ray data indicate that these long alkanes align parallel to the lipid acyl chains. In contrast, shorter alkanes, such as hexane and octane, decrease and broaden the thermal transition and electron density profiles show that these alkanes increase bilayer width by partitioning between the apposing monolayers of the bilayer. For lipids in the gel and liquid crystalline states, the short alkanes form an alkane region in the geometric center of the bilayer.
Communication: Rigidification of a lipid bilayer by an incorporated n-alkane
The Journal of chemical physics, 2016
Towards a greater understanding of the effects of organic molecules in biomembranes, the effects of a flexible alkyl chain on the morphologies of phospholipid vesicles are investigated. Vesicles composed of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine and tetradecane (TD) rupture during cooling from the liquid-crystalline phase to the gel phase. A model calculation based on the size-dependent rupture probability indicates that the bending rigidity of the bilayer in the gel phase is more than 10 times higher than that without TD, resulting in the rupture arising from elastic stress. The rigidification is caused by the denser molecular packing in the hydrophobic region by TD. There is little change of the rigidity in the liquid-crystalline phase. Additionally, the rigidification produces a characteristic morphology of the ternary giant vesicles including TD. Reported thermal behaviors imply that molecules with a linear and long alkyl chain, such as trans fatty acids, universally exhib...
Lipid concentration affects the kinetic stability of dielaidoylphosphatidylethanolamine bilayers
Chemistry and Physics of Lipids, 1993
The bilayer to hexagonal phase transition temperature (Th) of dielaidoylphosphatidylethanolamine is 65.5°C as measured by DSC heating scans at lipid concentrations below 100 mg/ml and at scan rates ranging from 1.7 to 45°C/h. However, at lipid concentrations above 100 mg/ml and at scan rates of 1-3°C/h the measured T h decreases below 65.5°C. At a lipid concentration of 500 mg/ml and a heating scan of 1.2°C/h the transition to the hexagonal phase occurs at 62.7°C. However, this same sample scanned at a rate of 34°C/h has a transition temperature of 64.6°C. Thus a combination of high lipid concentration and slow scan rate is required to significantly lower the hexagonal phase transition temperature below 65°C. These results demonstrate that the rate of conversion of the bilayer to the hexagonal phase is dependent on the concentration of the lipid suspension even under conditions of full hydration. Furthermore, a 100 mg/ml suspension of this lipid which has a Th of 64.3°C at a scan rate of 3.2°C/h has a lower hexagonal phase transition temperature of 62.8°C after pelleting the lipid with low-speed centrifugation but retaining the same amount of solvent in the supernatant above the pellet. Pelleting of the lipid also has a marked effect on the isothermal rate of conversion of the bilayer to hexagonal phase as observed by 3~p NMR. The conversion is highly temperature-dependent and is orders of magnitude more rapid for the pelleted sample than for the suspension. The NMR results also demonstrate that the lowering of the temperature of transition to non-bilayer phases is not caused by the formation of a stable cubic phase. We have demonstrated that subtle changes in the morphology of lipid suspensions, probably altering the extent of bilayer-bilayer contact, can have effects on the measured value of Th. These changes do not affect the La to L~ transition temperature. Over a wide variety of conditions, T h for dielaidoylphosphatidylethanolamine is found to be 65.6°C, but the L~ phase in the region 63-65°C is metastable.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2011
The structural parameters of fluid phase bilayers composed of phosphatidylcholines with fully saturated, mixed, and branched fatty acid chains, at several temperatures, have been determined by simultaneously analyzing small-angle neutron and X-ray scattering data. Bilayer parameters, such as area per lipid and overall bilayer thickness have been obtained in conjunction with intrabilayer structural parameters (e.g. hydrocarbon region thickness). The results have allowed us to assess the effect of temperature and hydrocarbon chain composition on bilayer structure. For example, we found that for all lipids there is, not surprisingly, an increase in fatty acid chain trans-gauche isomerization with increasing temperature. Moreover, this increase in trans-gauche isomerization scales with fatty acid chain length in mixed chain lipids. However, in the case of lipids with saturated fatty acid chains, trans-gauche isomerization is increasingly tempered by attractive chain-chain van der Waals interactions with increasing chain length. Finally, our results confirm a strong dependence of lipid chain dynamics as a function of double bond position along fatty acid chains. Crown j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / b b a m e m
Lipid bilayers: thermodynamics, structure, fluctuations, and interactions
Chemistry and Physics of Lipids, 2004
This article, adapted from our acceptance speech of the Avanti Award in Lipids at the 47th Biophysical Society meeting in San Antonio, 2003, summarizes over 30 years of research in the area of lipid bilayers. Beginning with a theoretical model of the phase transition (J.F.N.), we have proceeded experimentally using dilatometry and density centrifugation to study volume, differential scanning calorimetry
Gauging the Effect of Impurities on Lipid Bilayer Phase Transition Temperature
The Journal of Physical Chemistry B, 2006
We report on the gel-to-fluid phase transition behavior of unilamellar vesicles formed with 1,2-dimyristoylsn-phosphatidylcholine (14:0 DMPC). We have interrogated the gel-to-fluid transition temperature of these bilayer structures using the chromophore perylene incorporated in their nonpolar region. We observe a discontinuous change in the reorientation time of perylene sequestered within the bilayer at the known melting transition temperature of 14:0 DMPC, 24°C. The perylene reorientation data reveal a local viscosity of 14.5 (2.5 cP in the gel phase, and 8.5 (1.5 cP in the fluid phase. We have also incorporated small amounts of 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (14:1 DMPC) into these unilamellar vesicles and find that the melting transition temperature for these bilayers varies in a regular manner with the amount of 14:1 DMPC present. These data demonstrate that very little "contaminant" is required to cause a substantial change in the gel-to-fluid transition temperature, even though these contaminants do not alter the viscosity of the bilayer sensed by perylene, either above or below the melting transition.
Revisiting Volumes of Lipid Components in Bilayers
Journal of Physical Chemistry B, 2019
In addition to obtaining the highly precise volumes of lipids in lipid bilayers, it has been desirable to obtain the volumes of parts of each lipid, such as the methylenes and terminal methyls on the hydrocarbon chains and the headgroup. Obtaining such component volumes from experiment and from simulations is reexamined , first by distinguishing methods based on apparent versus partial molar volumes. While somewhat different, both these methods give results that are counterintuitive and that differ from results obtained by a more local method that can only be applied to simulations. These comparisons reveal differences in the average methylene component volume that result in larger differences in the headgroup component volumes. Literature experimental volume data for unsaturated phosphocholines and for alkanes have been used and new data have been acquired for saturated phosphocholines. Data and simulations cover extended ranges of temperature to assess both the temperature and chain length dependence of the component volumes. A new method to refine the determination of component volumes is proposed that uses experimental data for different chain lengths at temperatures guided by the temperature dependence determined in simulations. These refinements enable more precise comparisons of the component volumes of different lipids and alkanes in different phases. Finally, the notion of free volume is extended to components using the Lennard-Jones radii to estimate the excluded volume of each component. This analysis reveals that head group free volumes are relatively independent of thermodynamic phase, while both the methylene and methyl free volumes increase dramatically when bilayers transition from gel to fluid.
Effects of two double bonds on the hydrocarbon interior of a phospholipid bilayer
Chemical Physics Letters, 1995
A phospholipid bilayer was modelled by duplicating a monolayer system of 36 1 -palmitoyl-2-linoleoyl-sn-glycero-3phosphatidylcholine (PLPC) molecules (16 : O/ 18 : 2) plus 1368 water molecules and simulated using molecular dynamics. The analyses revealed distinct characteristics in the membrane structure due to polyunsaturation. The orientational behaviour of the fatty acid chains in the PLPC bilayer was found to be seemingly different from that in monounsaturated or in saturated phospholipid bilayers. The specific attributes responsible for the observed behaviour of the saturated and polyunsaturated chains are discussed and their relative importance assessed. 0009-2614/95/$09.50 6 1995 Elsevier Science B.V. All rights reserved SSDI 0009-2614(95)01113-7 M. Hyuiinen et al./Chemical Physics Letters 246 (1995) 300-306 301
Properties of hydrated unsaturated phosphatidylcholine (PC) lipid bilayers containing 40 mol % cholesterol and of pure PC bilayers have been studied. Various methods were applied, including molecular dynamics simulations, self-consistent field calculations, and the pulsed field gradient nuclear magnetic resonance technique. Lipid bilayers were composed of 18:0/18:1(n-9) cis PC, 18:0/18:2(n-6) cis PC, 18:0/18:3(n-3) cis PC, 18:0/20:4(n-6) cis PC, and 18:0/22:6(n-3) cis PC molecules. Lateral self-diffusion coefficients of the lipids in all these bilayers, mass density distributions of atoms and atom groups with respect to the bilayer normal, the C-H and C-C bond order parameter profiles of each phospholipid hydrocarbon chain with respect to the bilayer normal were calculated. It was shown that the lateral self-diffusion coefficient of PC molecules of the lipid bilayer containing 40 mol % cholesterol is smaller than that for a corresponding pure PC bilayer; the diffusion coefficients increase with increasing the degree of unsaturation of one of the PC chains in bilayers of both types (i.e., in pure bilayers or in bilayers with cholesterol). The presence of cholesterol in a bilayer promoted the extension of saturated and polyunsaturated lipid chains. The condensing effect of cholesterol on the order parameters was more pronounced for the double C=C bonds of polyunsaturated chains than for single C − C bonds of saturated chains .