| 1. |
- Ambrosi, M, et al.
(författare)
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Nanotubes from a vitamin C-based bolaamphiphile
- 2006
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 128:22, s. 7209-7214
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Tidskriftsartikel (refereegranskat)abstract
- A bolaform surfactant, 1,12-diascorbyl dodecanedioate (BOLA12), with ascorbic acid units as the polar headgroups was synthesized for the first time. Once dispersed in water above 0.5% w/w, BOLA12 forms hollow nanotubes as revealed by cryo-TEM experiments. These nanostructures transform into clear micellar solutions on heating. X-ray diffraction and SAXS experiments were performed both on the pure solid and on its aqueous dispersions. The critical aggregation concentration and the phase behavior were determined by conductivity and DSC experiments. The latter technique provided also the amount of strongly bound, solvating water molecules that surround the polar headgroups. BOLA12 shows the same reducing properties of ascorbic acid, as indicated by the antioxidant activity evaluated with the DPPH method. This feature was used for the reduction of Pd(II) ions on the surface of the nanoassemblies, which lead to the formation of large bundles homogeneously coated with palladium as observed in SEM micrographs.
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| 2. |
- Boström, Mathias, et al.
(författare)
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Hofmeister effects in membrane biology : The role of ionic dispersion potentials
- 2003
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 68:4
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Tidskriftsartikel (refereegranskat)abstract
- Membrane biology is notorious for its remarkable, and often strong dependence on the supposedly irrelevant choice of ion pair of background salt solution. While experimentally well known, there has been no progress towards any real theoretical understanding until very recently. We have demonstrated that an important source behind these Hofmeister effects is the ionic excess polarizabilities of ions in solution. Near an interface an ion experiences not only an electrostatic potential, but also a highly specific ionic dispersion potential. At biological concentrations (around 0.1M and higher) when the electrostatic contribution is highly screened this ionic dispersion potential has a dominating influence. We present the result of model calculations for the interfacial tension and surface potential that demonstrates that inclusion of ionic dispersion potentials is an essential step towards predictive theories. Our results are compared with experimental surface and zeta potential measurements on phospholipid bilayers, zirconia, and cationic micelles.
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| 3. |
- Boström, Mathias, et al.
(författare)
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Special ion effects : Why the properties of lysozyme in salt solutions follow a Hofmeister series
- 2003
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Ingår i: Biophysical Journal. - 0006-3495 .- 1542-0086. ; 85:2, s. 686-694
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Tidskriftsartikel (refereegranskat)abstract
- Protein solubility in aqueous solutions depends in a complicated and not well understood way on pH, salt type, and salt concentration. Why for instance does the use of two different monovalent salts, potassium thiocyanate and potassium chloride, produce such different results? One important and previously neglected source of ion specificity is the ionic dispersion potential that acts between each ion and the protein. This attractive potential is found to be much stronger for SCN- than it is for Cl-. We present model calculations, performed within a modified ion-specific double-layer theory, that demonstrate the large effect of including these ionic dispersion potentials. The results are consistent with experiments performed on hen egg-white lysozymes and on neutral black lipid membranes. The calculated surface pH and net lysozyme charge depend strongly on the choice of anion. We demonstrate that the lysozyme net charge is larger, and the corresponding Debye length shorter, in a thiocyanate salt solution than in a chloride salt solution. Recent experiments have suggested that pK(a) values of histidines depend on salt concentration and on ionic species. We finally demonstrate that once ionic dispersion potentials are included in the theory these results can quantitatively be reinterpreted in terms of a highly specific surface pH (and a salt-independent pK(a)).
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| 4. |
- Boström, Mathias, et al.
(författare)
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Why the properties of proteins in salt solutions follow a Hofmeister series
- 2004
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294 .- 1879-0399. ; 9:01-Feb, s. 48-52
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Forskningsöversikt (refereegranskat)abstract
- The physical properties of hen-egg-white lysozyme, and other globular protein, in aqueous solutions depend in a complicated and unexplained way on pH, salt type and salt concentration. One important and previously neglected source of ion specificity is the ionic dispersion potential that acts between each ion and the protein. We present model calculations, performed within a modified ion-specific double layer theory, that demonstrate the large effect of including these ionic dispersion potentials. (C) 2004 Elsevier Ltd. All rights reserved.
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| 5. |
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| 6. |
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| 7. |
- Claesson, PM, et al.
(författare)
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pH-dependent interactions between adsorbed chitosan layers
- 1992
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 8, s. 1406-1412
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Tidskriftsartikel (refereegranskat)abstract
- Chitosan is a cationic polyelectrolyte obtained after N-deacetylation of chitin by alkaline treatment. The adsorption of chitosan and the interaction between chitosan layers have been investigated using a surface force technique. Negatively charged mica surfaces were immersed in a 0.01 wt % acetic acid solution containing 0.01 wt % chitosan. The adsorption of chitosan results in a flat adsorbed layer and a reversal of the sign of the surface charge. The adsorption is essentially irreversible with respect to subsequent dilution. After dilution, the pH dependence of the forces acting between the adsorbed chitosan layers was investigated. The chitosan-mica system is uncharged around pH 6.2 (the pKa of chitosan is around 6.5) At this pH there is a weak attractive interaction between the chitosan-coated surfaces. The minimum in the force vs distance curve is located at a separation of about 20-25 Å. A steric repulsion is observed at smaller separations. At lower and higher pH values the long-range interaction is dominated by a repulsive double-layer force originating from charges on chitosan and on the mica surface, respectively. The information obtained from surface force measurements allows us to suggest a structure of the irreversibly adsorbed layer at various pH values. The pH dependence of the layer structure is rationalized in terms of changes in segment-segment and segment-surface interactions.
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| 8. |
- Eskilsson, K, et al.
(författare)
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Effects of adsorption of low-molecular-weight triblock copolymers on interactions between hydrophobic surfaces in water
- 1999
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 15, s. 3242-3249
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report on the interaction forces between hydrophobized silica surfaces immersed in polymer solutions. The polymers studied were a series of polyethylene oxide-polytetrahydrofuran-polyethylene oxide (PEO-PTHF-PEO) triblock copolymers and a polyethylene oxide homopolymer. The interaction forces were measured by the interfacial gauge technique. We show how the interactions depend on the adsorbed state of the copolymers, which in turn depends both on the copolymer concentration and the adsorption time. Above a critical surface coverage, the interaction between approaching surfaces was found to begin with a steric repulsion due to overlap of the adsorbed polymer layers. This repulsion increases as the distance between the surfaces was decreased. The energy-distance curve could, in this regime, be accounted for by the theory of grafted polymer brushes by Alexander-de Gennes. However, the interaction curves did not follow this prediction for small surface-to-surface distances. Instead, the repulsion stabilised at a more or less constant level with decreasing inter-surface separation. Finally, however, hard wall contact was established between the two surfaces. We infer that adsorbed copolymers to a large extent are expelled from the gap between the surfaces in this surface-to-surface distance range. The force needed to expel copolymers from the inter-surface gap was shown to be equal to the surface pressure at the solid-liquid interface. We also studied the influence of the rate of approach and separation of the surfaces on the energy-distance curves. The process of expelling polymers from the surface-to-surface gap was shown to depend on the velocity of the approaching surfaces and the surface coverage. For high approach rates and/or large surface coverage's, the lateral mobility of the polymers was generally observed to restrict the expulsion process of polymers from the gap. However, rapidly repeated force curves measured at constant rate in succession were found to be perfectly reproducible.
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| 9. |
- Eskilsson, K, et al.
(författare)
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Interaction between hydrophilic surfaces in triblock copolymer solution
- 1998
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 14, s. 7287-7291
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Tidskriftsartikel (refereegranskat)abstract
- We report on the interactions between fused quarts surfaces immersed in solutions of low molecular weight nonionic homopolymers and triblock copolymers. The polymers studied were a polyethylene oxide homopolymer and a triblock copolymer of the type polyethylene oxide - polytetrahydrofuran - polyethylene oxide. The surface force measurements were done by the interfacial gauge technique. In water, a strong repulsive force was observed at short surface separations. Similar effects, previously attributed to the presence of hydration water, are due to electro-steric interactions imposed by partial stabilisation and formation of a gel layer on silica. Interestingly, this repulsive interaction was suppressed and not noticed when small amounts of polymers were adsorbed, or when water was substituted for ethanol as medium. Adsorbed polymers induce a long range steric repulsion of a quite different character. However, in solutions of PEO homo polymers, when the distance between the surfaces decreases, the repulsive interaction levels off. It remains more or less constant with decreasing surface-to-surface distance in this region. In this depletion range polymers are partly expelled from the gap between the surfaces. When the surfaces were separated after compression, an adhesive force was observed. This indicates that some adsorbed macromolecules remained in the gap after compression. For the PEO homopolymer the interaction both on approach and separation, showed a weak dependence on polymer concentration over a wide range. For the block copolymers, however, a stronger concentration dependence was observed. For instance, close to the surface aggregation concentration we observed an attractive interaction at some distances. This attraction is caused by bridging of surface micelles. It does not shows up at higher copolymer concentrations where the surface are fully covered by polymers. At low copolymer concentrations the copolymer aggregates are expelled to some extent from the gap between the surfaces at small surface-to surface distances. This depletion leads to a weak distance indifferent region with a small constant repulsion. At higher concentrations the interaction is purely repulsive at all surface-to surface distances, at both approach and separation. We studied also the role of solvent on interaction between surfaces in copolymer solutions. Adsorption of copolymers to silica from ethanol did not show long range interaction patterns but was sufficient to induce adhesion between the surfaces.
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| 10. |
- Herder, CE, et al.
(författare)
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Interactions of hydrocarbon monolayer surfaces across N-alkanes: A steric repulsion
- 1989
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Ingår i: Journal of Chemical Physics. - 0021-9606 .- 1089-7690. ; 90, s. 5801-5805
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Tidskriftsartikel (refereegranskat)abstract
- We present results of force measurements between hydrocarbon monolayer surfaces across n-alkanes (hexane, decane, and tetradecane). The interaction id qualitatively different from that of any previously system and, in particular, bears no resemblance to an oscillatory solvation force. Instead, the force is repulsive from about 2.5 nm, with the exeption of a shallow minimum just outside a force maximum at 0.8-0.9 nm. At smaller separations the force becomes attractive and there is a waek adhesion at contact. We suggest that the force law is due to a steric effect____a repulsive interaction originating in restrictions on chain conformations of the alkanes at small surface separations. This interaction is acessible via simple mean-field theories. The similarity of the liquid-liquid and liquid-surface interactions allows this to dominate over solvation effects. The results are of significance for interaggregate interactions in lamellar liquid crystals, microemulsions, and surfactant- stabilized dispersions.
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