| 1. |
- Bryskhe, Karin, et al.
(författare)
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Spontaneous vesicle formation in a block copolymer system
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:28, s. 9710-9719
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the formation of vesicles in the binary system of a triblock copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) with the average composition EO5PO68EO5 in water. Vesicles are formed when a solution of unimers is heated into a two-phase region where, at equilibrium, a concentrated lamellar phase coexists with a dilute solution of unimers. The vesicles were characterized by cryo-TEM, static and dynamic light scattering, and NMR experiments. The average vesicle radius is approximately 60 nm, with an exponential size distribution, and the concentration of vesicles depends strongly on the temperature. The vesicles remain stationary on the time scale of hours. A striking observation is that, on this time scale, both the vesicle size distribution and the concentration of vesicles are reversible with respect to temperature cycles. However, on the time scale of weeks a sedimentation is observed in the solutions.
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| 2. |
- Cárdenas, Marité, et al.
(författare)
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DNA compaction by cationic surfactant in solution and at polystyrene particle solution interfaces: a dynamic light scattering study
- 2004
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 6:7, s. 1603-1607
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Tidskriftsartikel (refereegranskat)abstract
- The effect of cationic surfactant on the compaction of DNA both in bulk solution and on polystyrene particles has been studied by dynamic light scattering. DNA undergoes a transition from a semiflexible coil to a more compact globule in aqueous solution as a consequence of cationic surfactant binding. Thus the hydrodynamic radius of DNA decreases from 107 nm to about 50 nm in the presence of cationic surfactant. Such compaction is also observed on DNA coated polystyrene particles. In this case, the hydrodynamic layer thickness of DNA coated particles is reduced from 36 to 5 nm in the presence of cetyltrimethylammonium bromide.
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| 3. |
- Jansson, Jörgen, et al.
(författare)
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The interaction between PEO-PPO-PEO triblock copolymers and ionic surfactants in aqueous solution studied using light scattering and calorimetry
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:1, s. 82-92
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Tidskriftsartikel (refereegranskat)abstract
- Properties of nonionic triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) (EOnPOmEOn) in aqueous solution and their interaction with the ionic surfactants sodium dodecyl sulfate and hexadecyltrimethylammonium chloride have been investigated by static and dynamic light scattering, high sensitivity differential scanning, and isothermal titration calorimetry. The studied copolymers (denoted P123 and F127) have the same hydrophobic PPO central block (m = 68), but different length of the endblocks, n = 20 and 97. At 40degreesC, the copolymers are associated into micelles with hydrodynamic radius of 9.8 nm (P123) and 12.5 nm (F127) composed of a hydrophobic PPO core and a water-swollen PEO corona. The different copolymer/surfactant systems have been investigated at a constant copolymer concentration of 1 wt % and with varying surfactant concentration up to about 120 mM. When ionic surfactants are added to the PEO-PPO-PEO block copolymer micellar systems, three concentration regimes are observed in the results from the complementary experimental techniques. At low surfactant concentrations ( < 1-2 mM), single surfactant molecules associate with the copolymer micelle forming a large copolymer-rich complex that becomes increasingly charged. The relaxation time distributions from dynamic light scattering are monomodal and the electrostatic interaction is evidenced in both the static and the dynamic light scattering results. In the intermediate surfactant concentration regime, two types of copolymer-surfactant complexes coexist, one large copolymer-rich complex and one small complex consisting of one or a few copolymer chains and rich in surfactant. This indicates a peel-off mechanism behind the disintegration of the copolymer micelles. The titration calorimetric data present an exothermic signal as the PPO blocks become rehydrated when the copolymer micelles breakup. At high surfactant concentrations, only the small surfactant-rich complexes are present in the systems.
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| 4. |
- Jansson, Jörgen
(författare)
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The Interaction between Triblock Copolymers and Surfactants in Dilute Aqueous Solution
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The solution properties of dilute aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers and their interaction with surfactants have been investigated using static and dynamic light scattering, combined with small angle X-ray scattering, calorimetry and nuclear magnetic resonance techniques. In aqueous solution, the triblock copolymers P123 and F127 (EO20PO68EO20 and EO97PO68EO97, respectively) form micelles with a PPO core and a PEO corona. The triblock copolymer L121 (EO5PO68EO5) forms vesicles, that are quasi-stationary, by increasing the temperature into a two-phase region. The P123 and the F127 micelles interact with a cationic (hexadecyltrimethylammonium chloride), an anionic (sodium dodecyl sulfate) and a nonionic [hexa(ethylene oxide) monododecyl ether] surfactant. The interaction behavior can be divided into three different surfactant concentration intervals. At low surfactant concentrations the copolymers and surfactants form a spherical mixed complex, which resembles a block copolymer micelle. In the ionic surfactant cases, the low surfactant concentration regime is followed by a narrow concentration interval, where two coexisting complexes (a large block copolymer micelle-surfactant complex and a small surfactant-copolymer complex) are found. At high ionic surfactant concentrations, the copolymer micelles are broken up due to the electrostatic interaction and only small surfactant-copolymer complexes are left. The surfactant-copolymer complex resembles a pure surfactant micelle. In the case of the nonionic surfactant, a single mixed complex is formed over the whole surfactant concentration range investigated. This complex undergoes a structural change and grows in one dimension into a rod-like complex at elevated temperatures (40 °C and above) and at high surfactant concentrations.
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| 5. |
- Nilsson, Anna, et al.
(författare)
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Tryptophan-tagged cutinase studied by steady state fluorescence for understanding of tag interactions in aqueous two-phase systems
- 2003
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Ingår i: Biochimica et Biophysica Acta - Proteins and Proteomics. - 1570-9639. ; 1646:1-2, s. 57-66
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Tidskriftsartikel (refereegranskat)abstract
- Genetic engineering has been used to construct fusion proteins of Fusarium solani pisi cutinase and tryptophan-based tags, expressed in Saccharomyces cerevisiae, to increase the partitioning in aqueous two-phase systems. The separation systems were composed of thermoseparating polymers (random copolymers of ethylene oxide and propylene oxide, EOPO) and detergents (C12EOn). In this study, the fluorescence behaviour of the peptide-tagged protein, free peptide tag and tryptophan was investigated. The tryptophan-tagged proteins, cutinase-(WP)4 and cutinase-TGGSGG-(WP)4, showed emission spectra similar to the free peptides and tryptophan, indicating solvent exposure of the tag. The influence of polymers and detergents on the fluorescence of tagged proteins was examined. When peptides and tagged proteins were exposed to polymer, a slight blue shift of the emission maximum was observed. Larger blue shifts of the emission maximum were observed when C12EOn detergents were utilised. The results correlate with aqueous two-phase partitioning where addition of C12EOn detergents results in more extreme partitioning compared to systems containing only polymers. Dynamic light scattering (DLS) measurements of the EOPO copolymers were carried out, showing that the polymers did not aggregate at concentrations used in aqueous two-phase systems. Quenching of fluorescence with iodide for both proteins and peptide tags was studied. Plots according to the Stern-Volmer equation resulted in a linear fit, indicating exposed tryptophan residues for both free peptides and fusion proteins. The quenching constants were similar for both tagged protein and free peptide tag. The fluorescence results indicated that the tryptophan residues in the tag were exposed to the solvent and could interact with detergents and polymers in the two-phase systems.
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| 6. |
- Said, Safwat, et al.
(författare)
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Stålarmering av Väg 600, Sundom
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- REFLEX är ett EU-projekt där syftet har varit att utveckla stålarmerade vägkonstruktioner som kan förstärka en beläggnings hållbarhet. Det förväntade resultatet utifrån hela projektet är att öka livslängden i vägkroppen och därmed minska livscykelkostnaderna. Ett lämpligt objekt i samband med detta ansågs vara väg 600, Sundom, i Norrbottens län. Vägen valdes med tanke på att det är en väg som har breddats, har stora ojämnheter, tjälsprickor och bärighetsskador. Totalt 7 vägsträckor byggdes med olika konstruktioner.Inledande mätningar av tjällyftning och grundvattennivåer visar inte på några nämnvärda skillnader mellan armerad och oarmerad sträcka. Resultaten från vägytemätningarna visar ännu så länge inte heller några nämnbara skillnader mellan armerade och oarmerade sträckor. Resultaten från fallviktsmätningarna visar att bärigheten förbättrats något efter de utförda åtgärderna men de visar inga större skillnader mellan de olika sträckorna. Okulärbesiktningen visar att stålarmering utformad enligt kapitel 3 inte kan förhindra tvärgående sprickor uppkomna genom ojämna korta tjällyftningar i vägens längdriktning t.ex. vid trummor. Däremot finns det klara tendenser till att stålarmering utformad enligt kap. 3 kan förhindra längsgående sprickbildning uppkommen genom ojämn tjällyftning tvärs vägen. Det har konstaterats att armeringen har förmågan att styra ut sprickorna till beläggningskanterna. Det konstateras att det är kort tid, ca två år, för att dra slutliga slutsatser och avgöra armeringens effekt på vägens bärighet. Det vore nyttigt att följa upp vägens nedbrytning under några år framåt.
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| 7. |
- Tivesten, Åsa, 1969, et al.
(författare)
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Liver-derived insulin-like growth factor-I is involved in the regulation of blood pressure in mice.
- 2002
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Ingår i: Endocrinology. - 0013-7227. ; 143:11, s. 4235-42
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Tidskriftsartikel (refereegranskat)abstract
- IGF-I has been suggested to be of importance for cardiovascular structure and function, but the relative role of locally produced and liver-derived endocrine IGF-I remains unclear. Using the Cre-LoxP recombination system, we have previously created transgenic mice with a liver-specific, inducible IGF-I knockout (LI-IGF-I-/-). To examine the role of liver-derived IGF-I in cardiovascular physiology, liver-derived IGF-I was inactivated at 4 wk of age, resulting in a 79% reduction of serum IGF-I levels. At 4 months of age, systolic blood pressure (BP) was increased in LI-IGF-I-/- mice. Echocardiography showed increased posterior wall thickness in combination with decreased stroke volume and cardiac output, whereas other systolic variables were unchanged, suggesting that these cardiac effects were secondary to increased peripheral resistance. Acute nitric oxide-synthase inhibition increased systolic BP more in LI-IGF-I-/- mice than in control mice. LI-IGF-I-/- mice showed impaired acetylcholine-induced vasorelaxation in mesenteric resistance vessels and increased levels of endothelin-1 mRNA in aorta. Thus, the increased peripheral resistance in LI-IGF-I-/- mice might be attributable to endothelial dysfunction associated with increased expression of endothelin-1 and impaired vasorelaxation of resistance vessels. In conclusion, our findings suggest that liver-derived IGF-I is involved in the regulation of BP in mice.
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