| 1. |
- Agzenai, Y, et al.
(author)
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In Situ X-ray Polymerization: From Swollen Lamellae to Polymer-Surfactant Complexes
- 2014
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In: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:4, s. 1159-1167
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Journal article (peer-reviewed)abstract
- The influence of the monomer diallyldimethylammonium chloride (D) on the lamellar liquid crystal formed by the anionic surfactant aerosol OT (AOT) and water is investigated, determining the lamellar spacings by SAXS and the quadrupolar splittings by deuterium NMR, as a function of the D or AOT concentrations. The cationic monomer D induces a destabilization of the AOT lamellar structure such that, at a critical concentration higher than 5 wt %, macroscopic phase separation takes place. When the monomer, which is dissolved in the AOT lamellae, is polymerized in situ by X-ray initiation, a new collapsed lamellar phase appears, corresponding to the complexation of the surfactant with the resulting polymer. A theoretical model is employed to analyze the variation of the interactions between the AOT bilayers and the stability of the lamellar structure.
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| 2. |
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| 3. |
- Akesson, Anna, et al.
(author)
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The effect of PAMAM G6 dendrimers on the structure of lipid vesicles
- 2010
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12:38, s. 12267-12272
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Journal article (peer-reviewed)abstract
- Dendrimers are polymers with unique properties that make them promising in a variety of applications such as potential drug and gene delivery systems. PAMAM dendrimers, in particular, have been widely investigated and are efficiently translocated into the cell. The mechanism of translocation, however, is still unknown. Recently it was proposed that PAMAM dendrimers are able to open holes in lipid bilayers by stealing lipid from the bilayer and forming "dendrisomes''. The present work intends to contribute in the clarification of this question: why are dendrimers able to translocate into the cell? We create simple models for cell membranes by using small lipid vesicles that present a single lipid phase at physiologically relevant conditions. We then follow the effect that dendrimers have on the structure of the vesicles by using a combination of various techniques: dynamic light scattering, cryo-TEM and small angle X-ray scattering. We discuss our results with respect to the previous findings and reflect on their possible implications for real translocation in living cells.
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| 4. |
- Alfredsson, Viveka
(author)
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Cryo-TEM studies of DNA and DNA-lipid structures
- 2005
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In: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294. ; 10:5-6, s. 269-273
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Research review (peer-reviewed)abstract
- Studies published between 2001 and 2005 that utilise cryogenic transmission electron microscopy as a tool for investigating solutions containing DNA with or without amphiphiles present are reviewed. DNA or oligonucleotides form complexes with amphiphilic molecules such as lipids, so-called lipoplexes, and the structures and morphologies are excellent objects to study by cryogenic transmission electron microscopy. Recent studies show that this technique is in effective tool for identification of a range of structures such as unilamellar or multilamellar vesicles or dispersed liquid crystalline phases. (c) 2005 Elsevier Ltd. All rights reserved.
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| 5. |
- Alfredsson, Viveka, et al.
(author)
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Formation mechanism of mesoporous silica formed with triblock copolymers; effect of salt addition
- 2005
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In: Studies in Surface Science and Catalysis. - 0167-2991. ; 158, s. 97-104
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Journal article (peer-reviewed)abstract
- SBA-15 was synthesised with Pluronic P104 ((EO)(27)-(PO)(61)-(EO)(27))) its Structure promoter at 45 degrees C, with and without NaCl (1.0 M) added to the Synthesis Mixture. TEOS (tetraethyl orthosilicate) was used as silica source. The formation process was studied by in-situ SAXS/SAXD using synchrotron light. Addition of salt affects the micellar size, initial cell-parameter of the 2-D hexagonal phase (p6mm) as well as the kinetics of the aggregation of the polymer-silica composite. The effects caused by the salt are explained by a general ionic effect. The salt makes the aqueous Solution more polar and hence a worse solvent for the polymer. The ethylene oxide chains of the polymer will be more solvophobic. This leads to a larger aggregation number ofthe micelles as well as to a stronger interaction between them.
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| 6. |
- Alfredsson, Viveka, et al.
(author)
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In-situ studies of the formation mechanism of SBA-15
- 2005
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In: Nanoporous Materials IV, 156. - 0444517480 ; 156, s. 69-74
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Conference paper (peer-reviewed)abstract
- The formation process of SBA-15 has been investigated by time resolved TEM, in-situ SAXS/SAXD and in-situ NMR. The synthesis was done at 35 degrees in acidic solution with tetramethylorthosilicate as the silica source and Pluronic P123 as the structure directing amphiphile. The initially formed silica-polymer composite consists of flocs of spherical micelles in a silica matrix. The micelles then coalesce forming rods that eventually pack into the ordered array of which SBA-15 consists.
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| 7. |
- Alfredsson, Viveka, et al.
(author)
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Morphologies and Structure of Brain Lipid Membrane Dispersions
- 2021
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In: Frontiers in Cell and Developmental Biology. - : Frontiers Media SA. - 2296-634X. ; 9
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Journal article (peer-reviewed)abstract
- This study aims to explore the variety of previously unknown morphologies that brain lipids form in aqueous solutions. We study how these structures are dependent on cholesterol content, salt solution composition, and temperature. For this purpose, dispersions of porcine sphingomyelin with varying amounts of cholesterol as well as dispersions of porcine brain lipid extracts were investigated. We used cryo-TEM to investigate the dispersions at high-salt solution content together with small-angle (SAXD) and wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) for dispersions in the corresponding salt solution at high lipid content. Sphingomyelin forms multilamellar vesicles in large excess of aqueous salt solution. These vesicles appear as double rippled bilayers in the images and as split Bragg peaks in SAXD together with a very distinct lamellar phase pattern. These features disappear with increasing temperature, and addition of cholesterol as the WAXD data shows that the peak corresponding to the chain crystallinity disappears. The dispersions of sphingomyelin at high cholesterol content form large vesicular type of structures with smooth bilayers. The repeat distance of the lamellar phase depends on temperature, salt solution composition, and slightly with cholesterol content. The brain lipid extracts form large multilamellar vesicles often attached to assemblies of higher electron density. We think that this is probably an example of supra self-assembly with a multiple-layered vesicle surrounding an interior cubic microphase. This is challenging to resolve. DSC shows the presence of different kinds of water bound to the lipid aggregates as a function of the lipid content. Comparison with the effect of lithium, sodium, and calcium salts on the structural parameters of the sphingomyelin and the morphologies of brain lipid extract morphologies demonstrate that lithium has remarkable effects also at low content.
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| 8. |
- Alfredsson, Viveka, et al.
(author)
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The Dynamic Association Processes Leading from a Silica Precursor to a Mesoporous SBA-15 Material.
- 2015
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In: Accounts of Chemical Research. - : American Chemical Society (ACS). - 1520-4898 .- 0001-4842. ; 48:7, s. 1891-1900
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Research review (peer-reviewed)abstract
- During the last two decades, the synthesis of silica with an ordered mesoporous structure has been thoroughly explored. The basis of the synthesis is to let silica monomers polymerize in the presence of an amphiphilic template component. In the first studies, cationic surfactants were used as structure inducer. Later it was shown that pluronic copolymers also could have the role. One advantage with the pluronics copolymers is that they allow for a wider variation in the radius of pores in the resulting silica material. Another advantage lies in the higher stability resulting from the thicker walls between the pores. Mesoporous silica has a very high area to volume ratio, and the ordered structure ensures surface homogeneity. There are a number of applications of this type of material. It can be used as support for catalysts, as templates to produces other mesoporous inorganic materials, or in controlled release applications. The synthesis of mesoporous silica is, from a practical point of view, simple, but there are significant possibilities to vary synthesis conditions with a concomitant effect on the properties of the resulting material. It is clear that the structural properties on the nanometer scale are determined by the self-assembly properties of the amphiphile, and this knowledge has been used to optimize pore geometry and pore size. To have a practical functional material it is desirable to also control the structure on a micrometer scale and larger. In practice, one has largely taken an empirical approach in optimizing reaction conditions, paying less attention to underlying chemical and physicochemical mechanisms that lead from starting conditions to the final product. In this Account, we present our systematic studies of the processes involved not only in the formation of the mesoporous structure as such, but also of the formation of structures on the micrometer scale. The main point is to show how the ongoing silica polymerization triggers a sequence of structural changes through the action of colloidal interactions. Our approach is to use a multitude of experimental methods to characterize the time evolution of the same highly reproducible synthesis process. It is the silica polymerization reactions that set the time scale, and the block copolymer self-assembly responds to the progress of the polymerization through a basically hydrophobic interaction between silica and ethylene oxide units. The progression of the silica polymerization leads to an increased hydrophobicity triggering an aggregation process resulting in the formation of silica-copolymer composite particles of increasing size. The particle growth occurs in a stepwise way caused by intricate shifts between colloidal stability and instability. By tuning reaction conditions one can have an end product of hexagonal prism composite particles with single crystal 2D hexagonal order.
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| 9. |
- Ambrosi, M, et al.
(author)
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Nanotubes from a vitamin C-based bolaamphiphile
- 2006
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 128:22, s. 7209-7214
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Journal article (peer-reviewed)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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| 10. |
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