| 1. |
- Persson, Gerd, 1970-
(författare)
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Amphiphilic Molecules in Aqueous Solution
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to investigate amphiphilic molecules in aqueous solution. The work was divided into two parts. In the first part the effects of different counterions on phase behavior was investigated, while the second part concerns the 1-monooleoyl-rac-glycerol (MO)/n-octyl-β-D-glucoside (OG)/2H2O-system. The effects of mixing monovalent and divalent counterions were studied for two surfactant systems, sodium/calcium octyl sulfate, and piperidine/piperazine octanesulfonate. It was found that mixing monovalent and divalent counterions resulted in a large decrease in cmc already at very low fractions of the divalent counterion. Moreover, the degree of counterion binding for piperidine in the piperidine/piperazine octanesulfonate system was much higher than predicted, probably due to the larger hydrophobic moiety of piperidine. The effects of hydrophobic counterions were studied for eight alkylpyridinium octanesulfonates (APOS). The results were discussed in terms of packing constraints. The anomalous behavior of the 2H2O quadrupolar splittings in the lamellar phases was explained by the presence of two or more binding sites at the lamellae surface. The MO/OG/water system was studied in general and the MO-rich cubic phases in particular. When mixing MO and OG it was found that OG-rich structures (micelles, hexagonal and cubic phase of space group Ia3d) could solubilize quite large amounts of MO, while the MO-rich cubic structures where considerable less tolerant towards the addition of OG. The micelles in the OG-rich L1 phase were found to remain rather small and discrete in the larger part of the L1 phase area, but at low water concentration and high MO content a bicontinuous structure was indicated. Only small fractions of OG was necessary to convert the MO-rich cubic Pn3m structure to an Ia3d structure, and upon further addition of OG a lamellar (La) phase formed. Since the larger part of the phase diagram contains a lamellar structure (present either as a single La phase or as a dispersion of lamellar particles together with other phases), the conclusion was that introducing OG in the MO structures, forces the MO bilayer to become more flat. Upon heating the cubic phases, structures with more negative curvature were formed. The transformation between the cubic structures required very little energy, and this resulted in the appearance of additional peaks in the diffractograms.
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| 2. |
- Persson, Gerd, et al.
(författare)
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Phase Behavior of 1-Alkylpyridinium Octane-1-sulfonates : Effect of the 1-Alkylpyridinium Counterion Size
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:4, s. 1168-1179
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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.
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| 3. |
- Persson, Gerd, et al.
(författare)
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Phase behaviour of the 1-monooleoyl-rac-glycerol/n-octyl-beta-D-glucoside/water system
- 2004
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Ingår i: TRENDS IN COLLOID AND INTERFACE SCIENCE XVI. - : Springer. - 3540005536 ; , s. 36-39, s. 36-9
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Konferensbidrag (refereegranskat)abstract
- Obtaining high-quality crystals for X-ray diffraction from membrane proteins has proven to be a difficult task. One recently presented method utilises the cubic phases formed by 1-monooleoyl-rac-glycerol (MO). Removing the proteins from their native environment requires the use of surfactants. One commonly used surfactant is n-octyl-beta-D-glucopyranoside (OG). Using NMR techniques and visual observations, the ternary phase diagram of MO/OG/(H2O)-H-2 was outlined at 25 degreesC. The preliminary data show that all phases present in the binary systems at this temperature are also found in the ternary. Further, at the OG-rich side, an additional phase that appears to be hexagonal occurs. Addition of minor amounts (approximate to1.5 wt/wt %) of OG converts the cubic phases of MO to a lamellar structure, while the OG-rich cubic phase is able to dissolve about 15 wt/wt % MO. OG in water forms a large micellar solution phase;. Increasing the MO concentration at constant water content leads to a series of two- and three-phase areas in which one or two phases are in equilibrium with almost pure water.
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| 4. |
- Persson, Gerd, et al.
(författare)
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The 1-monooleoyl-rac-glycerol/n-octyl-beta-D-glucoside/water system : Phase diagram and phase structures determined by NMR and X-ray diffraction
- 2003
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:14, s. 5813-5822
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Tidskriftsartikel (refereegranskat)abstract
- Using SAXD and NMR techniques as well as visual observations, a detailed study of the extension of the phase regions and their structures has been performed for the ternary system 1-monooleoyl-rac-glycerol (MO)/n-octyl-β-d-glucopyranoside (OG)/2H2O at 25 °C. OG in water forms a large region of a micellar solution phase, in which substantial amounts of MO can be dissolved. Increasing the MO concentration at constant water content results in the formation of two- and three-phase areas, consisting of liquid, lamellar, or cubic phases in equilibrium with a very dilute water/OG solution. Besides the different phases previously reported for the binary systems, an additional hexagonal phase occurs at high OG contents. Addition of minor amounts (≈1.5 wt %) of OG converts the cubic phases present in the MO/2H2O system to an Lα phase, while the cubic phase in the OG/2H2O system is able to dissolve as much as 15 wt % MO. Since a major part of the phase diagram consists of planar bilayers, it is concluded that for most MO/OG ratios the spontaneous curvature is close to zero. The reason for this is discussed in terms of the molecular packing of MO and OG.
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| 5. |
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| 6. |
- Persson, Gerd, et al.
(författare)
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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
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 270:1, s. 56-65
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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
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