| 1. |
- Backlund, S, et al.
(författare)
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Partial phase behavior of ionic microemulsions stabilized by sodium dodecylsulfate and alcohol cosurfactants
- 1992
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Ingår i: Progress in Colloid and Polymer Science. - 0340-255X .- 1437-8027. ; 88, s. 36-41
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Tidskriftsartikel (refereegranskat)abstract
- Ionic microemulsions, stabilized by sodium dodecylsulfate and alcohol cosurfactants, have been characterized with respect to phase behavior, particularly the composition of the different phases in Winsor type I, II and III systems. The system containing brine, octane, sodium dodecylsulfate and 1-butanol shows a regular phase behavior, in conformity with the anticipated behavior, i.e., 2-3-2 phases. The phase transitions with increasing 1-butanol concentration are analogous to those occurring with increasing salinity, when compared with previous investigations. For the system containing brine, cyclohexane, sodium dodecylsulfate and benzyl alcohol, the behavior becomes more complex, even at low surfactant contents. The transitions are 2-3-2-3-2 phases over a wide composition range. The compositions of the phases at equilibrium are discussed in relation to structural considerations, as determined by conductivity and NMR self-diffusion measurements.
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| 2. |
- Jonströmer, M, et al.
(författare)
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Aggregation and solvent interaction in nonionic surfactant systems with formamide
- 1990
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 94, s. 7549-7555
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Tidskriftsartikel (refereegranskat)abstract
- The self-association and solvent interaction of some polyethylene glycol alkyl ether surfactants (CxEy) in fornamide have been studied via determinations of phase diagrams and NMR self-diffusion measurements. For C12E3 and C12 E4, small micelles but no liquid chrystalline phases form. Increasing the alkyl chain length to hexadecyl (C16E4, C16E6, and C16E8), mesophase formation occurs analogously to the corresponding aqueous system. No aggregate growth occurs in the micellar phase, neither at high temperatures and high surfactant concentrations nor when approaching the lower consolute temperature. The solvent diffusion was analyzed within the cell diffusion model, and a concentration-independent amount of 1-5 and probably not more than 3 formamide molecules was found to interact with each ethylene oxide group. Furthermore, the calculations indicated a ploymer-like state of the micellar headgroup shell, with a slight decrease of the formamide content therein at a raised temperature. In conclusion, the behaviour of CxEy/formamide systems is qualitatively similar to that of the corresponding aqueous sytem.
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| 3. |
- Sjöberg, M, et al.
(författare)
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A comparison of the counterion binding to ionic micelles in aqueous and nonaqueous systems
- 1992
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 8, s. 409-413
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Tidskriftsartikel (refereegranskat)abstract
- The counterion binding to hexadecyltrimethylammonium fluoride (C16TAF) micelles in three different solvents; water, formamide and ethylene glycol, has been studied both experimentally and theoretically. Self-diffusion measurements by NMR spectroscopy was used as the experimental technique, and the counterion binding was determined for surfactant concentrations up to 20 wt%. The degree of counterion binding was found to be very different in the three solvents; high in water and ethylene glycol but much lower in formamide, with an increase with concentration in the latter system. The Poisson-Boltzman equation was used to calculate how the aggregation number and the dielectrical constant of the solvent affect the counterion binding. A comparison between experimental and calculated values of degrees of counterion binding indicates that the micelles are significally smaller in the non-aqueous systems. The concentration dependence of the counterion binding in formamide was explained as aggregate growth with increasing surfactant concentration.
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| 4. |
- Bratt, Tomas, et al.
(författare)
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Cleavage of the alpha 1-microglobulin-bikunin precursor is localized to the Golgi apparatus of rat liver cells
- 1993
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Ingår i: Biochimica et Biophysica Acta. - 0006-3002. ; 1157:2, s. 54-147
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Tidskriftsartikel (refereegranskat)abstract
- alpha 1-Microglobulin, a plasma protein with immunoregulatory properties, and bikunin, the light chain of the proteinase inhibitors inter-alpha-inhibitor and pre-alpha-inhibitor, are translated as a precursor protein from the same mRNA. The cosynthesis of alpha 1-microglobulin and bikunin is unique compared to other proproteins such as procomplement components and prohormones, since alpha 1-microglobulin and bikunin have no known functional connection. Different forms of intracellular rat liver alpha 1-microglobulin were isolated and characterized by amino acid sequence analysis, lectin binding and glycosidase treatment. Their subcellular distribution was studied by Nycodenz and sucrose gradient centrifugation, pulse-chase experiments, and electrophoresis with subsequent immunoblotting, using pro-C3 and prohaptoglobin as reference proteins. Two alpha 1-microglobulin-bikunin precursors (40 and 42 kDa), containing one and two N-linked oligosaccharides, respectively, were detected in the endoplasmic reticulum. After transport to the Golgi apparatus, the precursors were cleaved, probably C-terminal to the sequence Arg-Ala-Arg-Arg immediately preceding the bikunin part, yielding free sialylated 28 kDa alpha 1-microglobulin, representing the mature protein. The cleavage was almost complete in phosphatidylinositol 4-kinase-enriched membranes, previously identified as a post-Golgi compartment. A fourth intracellular form of alpha 1-microglobulin, 26 kDa, lacked sialic acid. None of the intracellular forms carried the yellow-brown chromophore associated with alpha 1-microglobulin when purified from serum and urine, suggesting that this chromophore becomes linked to the protein after its secretion from the liver cells.
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| 5. |
- Sjöberg, Göran, 1951-
(författare)
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Nesting and migration in the introduced Canada goose in Sweden
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the thesis was to document patterns in breeding and migration in Swedish Canada geese Branta canadensis, to explain these against the genetic and historical background of the population, and to test predictions of hypotheses pertaining to parental investment.The Canada goose population in Sweden was founded by the introduction of a few individuals in the 1930's. DNA fingerprint similarity between geese breeding in Sweden was on average at the same level as between inbred close relatives in other wild bird species. The genetic variability of the population appeared to be considerably reduced in comparison to that of Canada geese breeding in North America.Dispersal and migration patterns were studied using plastic neck-bands that could be identified at long distance. Most Canada goose females nested at the lake where they grew up. Males were more prone to disperse than females, although most of them still returned to breed close to their area of origin.Geese from three breeding areas in Sweden had different winter distributions, although wintering areas overlapped considerably. Individual geese tended to return to the same wintering area as they had used in previous years.The females' investment in the egg clutch was related to the migration distance from spring foraging areas to the nesting area, suggesting an energetic cost of migration for egg production. Within breeding seasons, clutch size decreased with later initiation of nesting, but only in years with early breeding. A probable reason for this decrease was that body reserves available for egg production were larger in early layers. In years with late breeding, clutch size did not decrease, most likely because late-nesting females could supplement their body reserves by foraging on fresh vegetation.Nest defence intensity was studied by recording the behaviour of the female geese when a human approached the nest. The results largely confirmed predictions for nest defence intensity extracted from parental investment theory.
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| 6. |
- Sjöberg, M, et al.
(författare)
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2H Nuclear magnetic relaxation of 1.1-2H hexadecyltrimethylammonium bromide in micellar solutions of nonaqueous polar solvents and their mixtures with water
- 1990
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 6, s. 1205-1211
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Tidskriftsartikel (refereegranskat)abstract
- The 2H spin-lattice and spin-spin nuclear magnetic relaxtion rates were measured at different frequencies for α-deuterated hexadecyltrimethylammonium bromide in micellar solutions of nonaqueous and mixed solvent systems. Three nonaqueous polar solvents, viz., formamide, ethylene glycol, and N-methylformamide, and their mixtures with water were used. The two-step model for magnetic relaxation of surfactant aggregates was fitted to the frequency-dependent relaxation rates for the surfactant, yielding a local order parameter and correlation times for a fast local motion and for a slow aggregate motion. The measurements show that the surfactant aggregates in formamide, ethylene glycol, and their mixtures with water. No aggregation occurs in N-methylformamide at water contents lower than 50 wt%. Approximate aggregate radii, obtained from the slow correlation times, show that the aggregates formed in formamide and in ethylene glycol are smaller than in water. The local order parameter, obtained from the relaxation measurements as well as from the quadrupolar splittings in the hexagonal phases, increases with increasing water content both in the formamide and in the ethylene glycol systems.
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| 7. |
- Sjöberg, M, et al.
(författare)
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A thermodynamic study of the solvophobic effect in formamide solutions of nonpolar molecules
- 1993
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 9, s. 973-979
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamics associated with the solvophobic effect in solutions of nonpolar molecules in formamide were esamined using high performance liquid chromatography (HPLC). The transfer of a serie of alkylbenzenes from forma mide to hydrocarbon environ ment was studied in the temperature range S80 °C in order to obtain the molar free energy, entropy, and enthalpy of transfer. The HPLC system consisted of poly(dimethylsilosane), PDMS, coated glass beads as the stationary phase and formamide as the mobile phase. The free energy and the enthalpy of transfer were found to be negative, while the entropy of transfer was positive. In general, the thermodynamic transfer quantities for formamide are both smaller in magnitude and les s tempe rature depe n de nt than those previou sly dete rm ined with water as the mobile phase. The relatively small ZxCp of transfer in the case of formamide indicates that there is negligible structuring of the formamide molecules around the nonpolar molecules, in contrast to the water case. The positive entropy of transfer in the case of formamide is attributed to comples formation between the alkylbenzenes and formamide. The driving force for the solvophobic effect seems to arise from the same source as the hydrophobic effect, namely the large cohesive energy of the solvent. This interpretation was used to explain differences in surfactant aggregation in formamide and water.
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| 8. |
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| 9. |
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| 10. |
- Waltermo, Å, et al.
(författare)
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Adsorption of an ethoxylated amine surfactant on mica and its effect on the surface forces
- 1993
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 156, s. 365-376
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of tetraoxyethylene dodecylamine (C12NHE4) on mica and its effect on the interparticle forces between negatively charged muscovite mica surfaces has been studied employing the surface force technique. The pH of the solution has a decisive influence on the amount adsorbed, the structure of the adsorbed layer, and the interparticle forces. The main parameters which determine the structure of the adsorbed C12NHE4 -- layer are the area per lattice charge compared to the size of the molecule, the affinity between the polar group and the surface, and the affinity between the polar group and water. Below a pH of about 8 the positively charged ammonium group binds electrostatically and a surfactant monolayer is formed on each surface. At a surfactant concentration of 10-4 M, (a factor of 4 below the cmc) the surfaces are nearly uncharged. The attractive force between the monolayer coated surfaces is of a similar magnitude as the expected van der Waals force. At a pH value of 9-10 the majority of the surfactants are uncharged. Consequently, the head-group repulsion decreases, and, at a surfactant concentration of 10-4 M, an uncharged bilayer builds up on each surface. At short separations a steric force/hydration force arises from compression and dehydration of the polar groups that are directed towards the solution. At even higher pH values the affinity between the polar group and the surface decreases resulting in a disordered adsorbed layer. A repulsive electrostatic double-layer force dominates at large distances, and a steric force/hydration force is present at short surface separations. As the pH is lowered again the outer layer desorbs, which results in a reappearance of a strong attractive force at short separations.
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