| 1. |
- Evertsson, H., et al.
(författare)
-
NMR self diffusion measurements of the monooleoylglycerol/poly ethylene glycol/water L-3 phase
- 2002
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 26:02-jan, s. 21-29
-
Tidskriftsartikel (refereegranskat)abstract
- The monooleoylglycerol (GMO)/poly ethylene oxide (PEG)/water sponge (L-3) phase has been investigated by pulsed-gradient spin-echo NMR self-diffusion. The data allow the L-3 phase to be modeled as a bicontinuous system with respect to the lipid and water domains. It is proposed by using the interconnected rod model that the solvent PEG mainly distributes to the water domain, but has a higher weight fraction partition to the lipid head groups of the local GMO bilayer than water. The data is put in relation to earlier self-diffusion measurements on the binary GMO/water cubic phase, as well as earlier conductivity and X-ray diffraction measurements on the very same L-3 phase.
|
|
| 2. |
- Persson, Gerd, et al.
(författare)
-
Phase Behavior of 1-Alkylpyridinium Octane-1-sulfonates : Effect of the 1-Alkylpyridinium Counterion Size
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:4, s. 1168-1179
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature-versus-composition phase diagrams of eight different 1-alkylpyridinium octane-1-sulfonates (APOSs) in water were studied by 1H NMR, 2H NMR, pulsed gradient spin−echo NMR, small-angle X-ray diffraction, differential scanning calorimetry, surface tension and conductivity measurements, and polarizing microscopy. The number of carbons (nc) in the hydrocarbon chain of the pyridinium counterions was varied from nc = 1 to nc = 8 to study how the phase behavior of the APOS/2H2O systems was affected by a change in the chain length of the counterion. The sodium octane-1-sulfonate (NaOS)/water system was used as a reference. This system formed an isotropic micellar solution (L1) phase and a normal hexagonal (HI) phase. All APOSs were readily soluble in water and formed L1 phases. The surface tension above the critical micelle concentration for nc between 1 and 3 was higher than that for NaOS, and it decreased steadily for the different APOSs with increasing chain length. The area per molecule at the air/solution interfaces was rather constant at 68 Å2 for nc between 1 and 7. For 1-octylpyridinium octane-1-sulfonate (OPOS), it was about 5 Å2 smaller, which was just outside the estimated error. However, the smallest area was obtained for NaOS. At higher surfactant concentrations, liquid crystalline phases formed. Both cubic and HI phases were found for nc = 1 and 2, while for nc between 3 and 5 only an HI phase was observed. HI and lamellar liquid crystalline (Lα) phases formed for nc = 6 and 7. The only liquid crystalline phase found in the OPOS system was a Lα phase. The NaOS HI phase was the only liquid crystalline phase that showed a linear relation between the 2H2O NMR quadrupolar splitting (ΔW) and Xsurf/XW, where Xsurf and XW are the mole fractions of surfactant and water. The OPOS lamellae were found to be much thinner than expected, indicating a defect lamellar structure. This was further supported by the behavior of the quadrupolar splitting of deuterated OPOS. The anomalous behaviors of the 2H2O NMR quadrupolar splitting observed in the Lα phases of 1-heptylpyridinium octane-1-sulfonate and OPOS were interpreted in terms of changes in the population of the water molecules residing in different sites combined with a continuous rearrangement of the lamellae surface with the possible development of holes. The appearances of the phase diagrams were discussed in terms of surfactant molecular geometry and the packing of the amphiphiles in the aggregates formed.
|
|
| 3. |
- Persson, Gerd, et al.
(författare)
-
Thermal Behaviour of Cubic Phases Rich in 1-monooleoyl-rac-glycerol in the ternary system 1-monooleoyl-rac-glycerol / n-octyl-b-D-glucoside / Water.
- 2003
-
Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 270:1, s. 56-65
-
Tidskriftsartikel (refereegranskat)abstract
- Using synchrotron X-ray diffraction the thermal behaviour was studied of the cubic phases in the 1-monooleoyl-rac -glycerol (MO)/n-octyl-beta-d-glucopyranoside (OG)/(2) H-2 O system with 58 or 45 wt % MO concentration and varying OG/(H2O)-H-2 contents. These MO contents correspond to a Pn3m cubic single-phase or a Pn3m cubic phase in excess water on the binary MO/water axis of the ternary phase diagram. The cubic liquid crystalline phases are stable with small fractions of OG, while higher OG concentrations trigger a cubic-to-lamellar phase transition. Moreover, with increasing OG concentration the initial Pn3m structure is completely converted to an Ia3d structure prior to the L-alpha phase being formed. Upon heating this effect is reversed, resulting in an Ia3d -to-Pn3m phase transition. For some samples additional peaks were observed in the diffractograms upon heating, resulting from the metastability notoriously shown by bicontinuous cubic phases. This judgement is supported by the fact that upon cooling these peaks were absent. Remarkably, both the Ia3d and the Pn3m cubic structures could be in equilibrium with excess water in this ternary system. A comparison is made with previous results on n -dodecyl-beta-d-maltoside (DM), showing that cubic phases with OG have higher thermal and compositional stability than with DM
|
|
| 4. |
- Ben-Menachem, Gil, et al.
(författare)
-
The physico-chemical characteristics of the phosphocholine-containing glycoglycerolipid MfGL-II govern the permeability properties of Mycoplasma fermentans
- 2001
-
Ingår i: The FEBS Journal, European Journal of Biochemistry. - : Wiley. ; 268:13, s. 3694-3701
-
Tidskriftsartikel (refereegranskat)abstract
- Mycoplasma fermentans seems to be involved in several pathogenic condtions in humans, and is among other things capable of fusing with T-cells and lymphocytes. The choline-containing phosphoglycolipid 6'-O-(3"-phosphocholine-2"-amino-1"-phospho-1",3"-propanediol)-α-d-glucopyranosyl-(1'→3)-1,2-diacylglycerol (MfGL-II) in the membrane of M. fermentans has been suggested to enhance the fusion process, and the characteristics of MfGL-II were therefore investigated. When a cell culture ages the fraction of MfGL-II increases, and the fraction of the other major membrane lipid, phosphatidylglycerol (PtdGro), decreases concomitantly. Swelling experiments showed that the permeability and osmotic fragility are markedly reduced in aged cells. MfGL-II is selectively released into the surrounding medium when aged M. fermentans cells are incubated in buffer containing EDTA. The physico-chemical properties of MfGL-II were studied by NMR spectroscopy and differential scanning calorimetry, and they can explain the biochemical results. The temperature for the transition between gel and lamellar liquid crystalline (Lα) phases is 35–45 °C higher for MfGL-II than for PtdGro, which most probably gives rise to the reduced permeability in aged cells. At high water contents MfGL-II forms an Lα phase and isotropic aggregates which were interpreted to be vesicles with a radius of ≈ 450 Å. It is proposed that MfGL-II forms vesicles in the surrounding medium when it is released from the cell membrane. Neither EDTA nor Ca2+ ions have a significant influence on the aggregate structures formed by MfGL-II. Our results indicate that MfGL-II has no fusogenic properties. It is more probable that a recently identified lysolipid in the M. fermentans membrane acts as a fusogen.
|
|
| 5. |
- Binder, Hans, et al.
(författare)
-
A Molecular View on the Interaction of the Trojan Peptide Penetratin with the Polar Interface of Lipid Bilayers
- 2004
-
Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495. ; 87, s. 332-43
-
Tidskriftsartikel (refereegranskat)abstract
- Penetratin belongs to the family of Trojan peptides that effectively enter cells and therefore can be used as cargos for agents that are unable to penetrate the cell membrane. We applied polarized infrared spectroscopy in combination with the attenuated total reflection technique to extract information before penetratin binding to lipid membranes with molecular resolution. The amide I band of penetratin in the presence of zwitterionic dimyristoylphosphatidylcholine and of anionic lipid membranes composed of dioleoylphosphatidylcholine and dioleoylphosphatidylglycerol shows the characteristics of an antiparallel ß-sheet with a small fraction of turns. Both signatures have been interpreted in terms of a hairpin conformation. The infrared linear dichroism of the amide I band indicates that the peptide chain orients in an oblique fashion whereas the plane of the sheet aligns virtually parallel with respect to the membrane surface. The weak effect of the peptide on dimyristoylphosphatidylcholine gives indication of its superficial binding where the charged lysine and arginine side chains form H-bonds to the phosphate oxygens of the surrounding lipids. The determinants for internalization of penetratin appear to be a peptide sequence with a distribution of positively charged residues along a ß-sheet conformation, which enables the anchoring of the peptide in the polar part of the membranes and the effective compensation of anionic lipid charges.
|
|
| 6. |
- Byström, Tomas, et al.
(författare)
-
Molecular packing in sphingomyelin bilayers and sphingomyelin/phospholid mixtures
- 2003
-
Ingår i: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. ; 59:9, s. 2191-5
-
Tidskriftsartikel (refereegranskat)abstract
- The molecular packing properties of sphingomyelin (SM) from egg yolk were studied. The influence of the spontaneous curvature of SM on the phase behaviour of SM/dodecane/water systems was investigated. A comparison was made to a previous study by Lindblom et al. (Liq. Cryst. 3 (1988) 783), of the phase behaviour of dipalmitoylphosphatidylcholine (DPPC)/dodecane/water systems, where a reversed hexagonal liquid crystalline was shown to form at high water contents (60–80%, w/w). In contrast, SM/dodecane/water systems mainly maintained a lamellar liquid crystalline phase at all compositions and temperatures >35 °C. This suggests that the spontaneous curvature of SM is larger than for DPPC. To further examine the packing properties of SM and DPPC, the phase behaviour of SM/dioleoylphosphatidylethanolamine (DOPE)/water and DPPC/DOPE/water systems were investigated. Aqueous dispersions of DOPE normally form a reversed hexagonal liquid crystalline phase, while an isotropic phase was formed at small additions (20 mol.%) of SM or DPPC and a lamellar liquid crystalline phase was maintained at higher fractions (>35 mol.%) of SM or DPPC.
|
|
| 7. |
- Byström, Tomas, et al.
(författare)
-
Orientation of a polyleucine-based peptide in phosphatidylcholine bilayers of different thickness. Solid-state NMR and CD spectroscopy
- 2003
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. ; 228:1-3, s. 37-42
-
Tidskriftsartikel (refereegranskat)abstract
- A study was performed of the orientation and secondary structure of the peptide pLeuD11 (KKGL7DL[15N]WL9KKA) in phosphatidylcholine (PC) bilayers. The lipid bilayer thickness was varied by using PCs with monounsaturated acyl chains of different lengths, ranging from 14 to 24 carbon atoms. The peptide/lipid molar ratio was kept at 1:30 for all systems with water content of 50 wt.%. The secondary structure was determined by circular dichroism (CD) spectroscopy. The peptide adopted a transmembrane orientation in all bilayers, independent on their thickness. The location of the peptide was determined by 15N solid-state magic angle spinning (MAS) NMR spectroscopy, exploiting the effects of paramagnetic lanthanide ions at the membrane surface. From static solid-state 31P NMR spectroscopy measurements it was concluded that all lipid/peptide systems formed a lamellar liquid crystalline phase. As found by CD the distribution of secondary structures in the peptide changed only slightly for the different lipid membranes. The fraction of -helix was highest (≈60%) in bilayers with lipids, having an acyl chain length of 18 and 22 carbon atoms, while for lipids with 14 and 24 carbon atoms the helical content decreased slightly to about 50%. This reduction was accompanied by an increase in the fraction of β-like structures.
|
|
| 8. |
- Danino, Dganit, et al.
(författare)
-
Microstructures in the aqueous solutions of a hybrid anionic fluorocarbon/hydrocarbon surfactant
- 2003
-
Ingår i: Journal of Colloid and Interface Science. ; 259:2, s. 382-90
-
Tidskriftsartikel (refereegranskat)abstract
- The aqueous solutions of the anionic hybrid fluorocarbon/hydrocarbon surfactant sodium 1-oxo-1[4-(tridecafluorohexyl)phenyl]-2-hexanesulfate (FC6HC4) shows peculiar rheological behavior. At 25 °C the viscosity vs concentration curve goes successively through a maximum and a minimum, while the viscosity vs temperature curve of the 10 wt% aqueous FC6HC4 solution goes through a marked maximum at 36 °C [Tobita et al., Langmuir 13 (1997) 5054]. In an attempt to explain these properties the microstructure of aqueous solutions of FC6HC4 has been investigated by means of digital light microscopy, transmission electron microscopy at cryogenic temperature (cryo-TEM), rheology, and self-diffusion NMR. At 20 °C, the increase of the FC6HC4 concentration was found to result in a progressive change of structure of the surfactant assemblies from mainly spherical micelles at 0.5 wt% to mainly cylindrical micelles at 10 wt%. At intermediate concentrations small disklike micelles and small complete and incomplete vesicles coexisting with cylindrical micelles were visualized. The occurrence of stretched cylindrical micelles is responsible for the effect of the surfactant concentration on the solution viscosity. Cryo-TEM, rheology, and self-diffusion NMR all suggest that an increase of the temperature brings about a growth of the assemblies present in the 10 wt% solution of FC6HC4. The structure of the assemblies present at the temperature where the viscosity is a maximum could not be elucidated by cryo-TEM because of the probable occurrence of an on-the-grid phase transformation, the result of blotting during specimen preparation. Nevertheless, the results show that the observed large assemblies break up at higher temperature to give rise to a more labile bicontinuous structure that consists of multiconnected disordered lamellae, with many folds and creases, and that may well be the L3 phase.
|
|
| 9. |
- Filippov, Andrey, et al.
(författare)
-
Influence of Cholesterol and Water Content on Phospholipid Lateral Diffusion in Bilayers
- 2003
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:6397-400
-
Tidskriftsartikel (refereegranskat)abstract
- The dependence of lipid lateral diffusion on temperature, cholesterol, and water contents has been studied in oriented bilayers in three phosphatidylcholine lipid systems and one sphingomyelin system. The lateral diffusion of lipids is found to be reduced both by the addition of cholesterol and by decreasing the water content. This reduction can be ascribed to the increase in the ordering of the lipid acyl chains upon cholesterol addition and/or reduced water content. The dependence of the lateral diffusion coefficient on the water content is similar in both the liquid ordered and the liquid disordered phase, while the apparent activation energy for the diffusion process is larger in the liquid ordered phase. We also report an anomalous increase in the lipid diffusion upon small additions of cholesterol to bilayer systems at low water content and temperatures. The increased diffusion is tentatively explained by a reduction of lipid chain entanglements.
|
|
| 10. |
- Filippov, Andrey, et al.
(författare)
-
Lipid Lateral Diffusion in Ordered and Disordered Phases in Raft Mixtures
- 2004
-
Ingår i: Biophysical Journal. ; 86, s. 891-6
-
Tidskriftsartikel (refereegranskat)abstract
- Lipid lateral diffusion coefficients in the quarternary system of dioleoylphosphatidylcholine (DOPC), sphingomyelin, cholesterol, and water were determined by the pulsed field gradient NMR technique on macroscopically aligned bilayers. The molar ratio between dioleoylphosphatidylcholine and sphingomyelin was set to 1:1, the cholesterol content was varied between 0 and 45 mol %, the water content was 40 wt %, and the temperature was varied between 293 and 333 K. The diffusion coefficients were separated into fast and slow spectral components by using the CORE method for global analysis of correlated spectral data. A large two-phase region, tentatively assigned to the liquid disordered (ld) and the liquid ordered (lo) phases, was present in the phase diagram. The ld phase was enriched in dioleoylphosphatidylcholine and exhibited diffusion coefficients that were about three to five times larger than for the lo phase. Both the diffusion coefficients and the apparent activation energies for the quarternary systems were compatible with earlier reports on ternary phospholipid/cholesterol/water systems. However, in contrast to the latter ternary systems, the exchange of lipids between the lo and the ld phases was slow on the timescale for the diffusion experiment for the quarternary ones. This means that on the millisecond timescale fluid, ordered domains are floating around in a sea of faster diffusing lipids, assigned to consist of mainly dioleoylphosphatidylcholine.
|
|
