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| 2. |
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| 3. |
- Agthe, Michael, 1983-
(författare)
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Crystallization on the Mesoscale : Self-Assembly of Iron Oxide Nanocubes into Mesocrystals
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Self-assembly of nanoparticles is a promising route to form complex, nanostructured materials with functional properties. Nanoparticle assemblies characterized by a crystallographic alignment of the nanoparticles on the atomic scale, i.e. mesocrystals, are commonly found in nature with outstanding functional and mechanical properties. This thesis aims to investigate and understand the formation mechanisms of mesocrystals formed by self-assembling iron oxide nanocubes.We have used the thermal decomposition method to synthesize monodisperse, oleate-capped iron oxide nanocubes with average edge lengths between 7 nm and 12 nm and studied the evaporation-induced self-assembly in dilute toluene-based nanocube dispersions. The influence of packing constraints on the alignment of the nanocubes in nanofluidic containers has been investigated with small and wide angle X-ray scattering (SAXS and WAXS, respectively). We found that the nanocubes preferentially orient one of their {100} faces with the confining channel wall and display mesocrystalline alignment irrespective of the channel widths. We manipulated the solvent evaporation rate of drop-cast dispersions on fluorosilane-functionalized silica substrates in a custom-designed cell. The growth stages of the assembly process were investigated using light microscopy and quartz crystal microbalance with dissipation monitoring (QCM-D). We found that particle transport phenomena, e.g. the coffee ring effect and Marangoni flow, result in complex-shaped arrays near the three-phase contact line of a drying colloidal drop when the nitrogen flow rate is high. Diffusion-driven nanoparticle assembly into large mesocrystals with a well-defined morphology dominates at much lower nitrogen flow rates. Analysis of the time-resolved video microscopy data was used to quantify the mesocrystal growth and establish a particle diffusion-based, three-dimensional growth model. The dissipation obtained from the QCM-D signal reached its maximum value when the microscopy-observed lateral growth of the mesocrystals ceased, which we address to the fluid-like behavior of the mesocrystals and their weak binding to the substrate. Analysis of electron microscopy images and diffraction patterns showed that the formed arrays display significant nanoparticle ordering, regardless of the distinctive formation process. We followed the two-stage formation mechanism of mesocrystals in levitating colloidal drops with real-time SAXS. Modelling of the SAXS data with the square-well potential together with calculations of van der Waals interactions suggests that the nanocubes initially form disordered clusters, which quickly transform into an ordered phase.
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| 4. |
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| 5. |
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| 6. |
- Ainalem, Marie-Louise, et al.
(författare)
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DNA Binding to Zwitterionic Model Membranes
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 26:7, s. 4965-4976
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that DNA (linearized plasmid, 4331 base pairs and salmon sperm, 2000 base pairs, respectively) adsorbs to model membranes of zwitterionic liquid crystalline phospholipid bilayers in solutions containing divalent Ca2+ rations, and also in solutions containing monovalent Na+. The interaction between DNA and surface-supported model membranes was followed in situ using null ellipsometry, quartz crystal microbalance with dissipation, as well as neutron reflectometry. In the presence of Na+ (in the absence Of multivalent ions), DNA adopts an extended coil conformation upon adsorption. The solvent content in the adsorbed layer is high, and DNA is positioned on top of the membrane. In the presence of divalent Ca2+. the driving force for the adsorption of DNA is electrostatic, and the adsorbed DNA film is not as dilute its in a solution containing Na+. Cryo-TEM and SANS were further used to investigate the interaction in bulk solution using vesicles as model membrane systems. DNA adsorption could not be identified in the presence of Na+ using SANS, but cryo-TEM indicates the presence of DNA between neighboring unilamellar vesicles. In the presence of Ca2+. DNA induces the formation of multilamellar vesicles in which DNA intercalates the lamellae. Possible electrostatic and hydrophobic mechanisms for the adsorption of DNA in solutions containing monovalent salt are discussed and compared to the observations in divalent salt.
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| 7. |
- Ainalem, Marie-Louise, et al.
(författare)
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DNA compaction induced by a cationic polymer or surfactant impact gene expression and DNA degradation.
- 2014
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in achieving gene regulation in biotechnological and biomedical applications by using synthetic DNA-binding agents. Most studies have so far focused on synthetic sequence-specific DNA-binding agents. Such approaches are relatively complicated and cost intensive and their level of sophistication is not always required, in particular for biotechnological application. Our study is inspired by in vivo data that suggest that DNA compaction might contribute to gene regulation. This study exploits the potential of using synthetic DNA compacting agents that are not sequence-specific to achieve gene regulation for in vitro systems. The semi-synthetic in vitro system we use include common cationic DNA-compacting agents, poly(amido amine) (PAMAM) dendrimers and the surfactant hexadecyltrimethylammonium bromide (CTAB), which we apply to linearized plasmid DNA encoding for the luciferase reporter gene. We show that complexing the DNA with either of the cationic agents leads to gene expression inhibition in a manner that depends on the extent of compaction. This is demonstrated by using a coupled in vitro transcription-translation system. We show that compaction can also protect DNA against degradation in a dose-dependent manner. Furthermore, our study shows that these effects are reversible and DNA can be released from the complexes. Release of DNA leads to restoration of gene expression and makes the DNA susceptible to degradation by Dnase. A highly charged polyelectrolyte, heparin, is needed to release DNA from dendrimers, while DNA complexed with CTAB dissociates with the non-ionic surfactant C12E5. Our results demonstrate the relation between DNA compaction by non-specific DNA-binding agents and gene expression and gene regulation can be achieved in vitro systems in a reliable dose-dependent and reversible manner.
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| 8. |
- Ainalem, Marie-Louise, et al.
(författare)
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DNA condensation using cationic dendrimers-morphology and supramolecular structure of formed aggregates
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:10, s. 4577-4594
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Forskningsöversikt (refereegranskat)abstract
- The control of DNA condensation, i.e. packaging or compaction, is essential for the living cell, but also important in many applications. One example is gene therapy that often utilises vehicles with the ability to condense DNA and thereby protect DNA against degradation, transport DNA across membranes (which act as barriers towards gene delivery), and regulate gene expression. This review discusses the ability of poly(amido amine) dendrimers to condense DNA molecules via attractive electrostatic interactions, which in turn leads to self-assembled structures with a rich variety of morphologies. The process of condensation is cooperative and kinetically controlled, and the structure of the aggregates strongly depends on the size and charge of the dendrimer, and the salt concentration of the aqueous solution. While globular aggregates are formed by large dendrimers, rods and toroids are formed by smaller sized dendrimers with lower total charge per molecule. The globular aggregates appear to be disordered, but the smaller dendrimers give rise to high-ordered packing of the DNA in ordered arrays according to a square or hexagonal unit cell. The high-ordered packing also indicates that the dendrimers deform while inducing the DNA to condense.
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| 9. |
- Ainalem, Marie-Louise, et al.
(författare)
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Dynamic light scattering and fluorescence study of the interaction between double-stranded DNA and poly(amido amine) dendrimers
- 2007
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 8:5, s. 1557-1563
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between a cationic poly(amido amine) (PAMAM) dendrimer of generation 4 and double-stranded salmon sperm DNA in 10 mM NaBr solution has been investigated using dynamic light scattering (DLS) and steady-state fluorescence spectroscopy. The structural parameters of the formed aggregates as well as the complex formation process were studied in dilute solutions. When DNA is mixed with PAMAM dendrimers, it undergoes a transition from a semiflexible coil to a more compact conformation due to the electrostatic interaction present between the cationic dendrimer and the anionic polyelectrolyte. The DLS results reveal that one salmon sperm DNA molecule forms a discrete aggregate in dilute solution with several PAMAM dendrimers with a mean apparent hydrodynamic radius of 50 nm. These discrete complexes coexist with free DNA at low molar ratios of dendrimer to DNA, which shows that cooperativity is present in the complex formation. The formation of the complexes was confirmed by agarose gel electrophoresis measurements. DNA in the complexes was also found to be significantly more protected against DNase catalyzed digestion compared to free DNA. The number of dendrimers per DNA chain in the complexes was found to be approximately 35 as determined by steady-state fluorescence spectroscopy.
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| 10. |
- Ainalem, Marie-Louise, et al.
(författare)
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Interactions between DNA and Poly(amido amine) Dendrimers on Silica Surfaces.
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:11, s. 8625-8635
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Tidskriftsartikel (refereegranskat)abstract
- This study increases the understanding at a molecular level of the interactions between DNA and poly(amido amine) (PAMAM) dendrimers on solid surfaces, which is a subject of potential interest in applications such as gene therapy. We have used in situ null ellipsometry and neutron reflectometry to study the structure of multilayer arrangements formed by PAMAM dendrimers of generation 2 (G2), 4 (G4), and 6 (G6) and DNA on silica surfaces. Specifically, we adsorbed cationic dendrimer layers, then we condensed DNA to form dendrimer-DNA bilayers, and last we exposed further dendrimer molecules to the interface to encapsulate DNA in dendrimer-DNA-dendrimer trilayers. The dendrimer monolayers formed initially result in the deformation of the cationic adsorbates as a result of their strong electrostatic attraction to the hydrophilic silica surface. The highest surface excess and most pronounced deformation occurs for the G6 molecules due to their relatively large size and high surface charge density. G6-functionalized surfaces give rise to the highest surface excess of DNA during the bilayer formation process. This result is explained in terms of the high number of charged binding sites in the G6 monolayer and the low electrostatic repulsion between DNA and exposed patches of silica surface due to the relatively thick G6 monolayer. The binding strengths of the silica-dendrimer and dendrimer-DNA interactions are demonstrated by the high stability of the interfacial bilayers during rinsing. For the formation of trilayers of dendrimers, DNA, and dendrimers, G2 adsorbs as a smooth layer while G4 and G6 induce the formation of less well-defined structures due to more complex DNA layer morphologies.
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| 11. |
- Ainalem, Marie-Louise, et al.
(författare)
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On the Ability of PAMAM Dendrimers and Dendrimer/DNA Aggregates To Penetrate POPC Model Biomembranes
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:21, s. 7229-7244
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Tidskriftsartikel (refereegranskat)abstract
- Poly(amido amine) (PAMAM) dendrimers have previously been shown, as cationic condensing agents of DNA, to have high potential for nonviral gene delivery. This study addresses two key issues for gene delivery: the interaction of the biomembrane with (i) the condensing agent (the cationic PAMAM dendrimer) and (ii) the corresponding dendrimer/DNA aggregate. Using in situ null ellipsometry and neutron reflection, parallel experiments were carried out involving dendrimers or generations 2 (G2), 4 (G4), and 6 (G6). The study demonstrates that free dendrimers of all three generations were able to traverse supported palmitoyloleoylphosphatidylcholine (POPC) bilayers deposited on silica surfaces. The model biomembranes were elevated front the solid surfaces upon dendrimer penetration, which offers a promising new way to generate more realistic model biomembranes where the contact with the supporting surface is reduced and where aqueous cavities are present beneath the bilayer. The largest dendrimer (GO) induced partial bilayer destruction directly upon penetration, whereas the smaller dendrimers (G2 and G4) leave the bilayer intact, so we propose that lower generation dendrimers have greater potential as transfection mediators. In addition to the experimental observations, coarse-grained simulations on the interaction between generation 3 (03) dendrimers and POPC bilayers were performed in the absence and presence of a bilayer-supporting negatively charged surface that emulates the support. The simulations demonstrate that G3 is transported across free-standing POPC bilayers by direct penetration and not by endocytosis. The penetrability was, however, reduced in the presence of a surface, indicating that the membrane transport observed experimentally was not driven solely by the surface. The experimental reflection techniques were also applied to dendrimer/DNA aggregates of charge ratio = 0.5, and while G2/DNA and G4/DNA aggregates interact with POPC bilayers. G6/DNA displays no such interaction. These results indicate that, in contrast to free dendrimer molecules, dendrimer/DNA aggregates of low charge ratios are not able to traverse a membrane by direct penetration.
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| 12. |
- Alexander, Shovsky, 1978-
(författare)
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Polyelectrolyte complexes of bottle brush copolymers : Solution and adsorption properties
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work was to systematically investigate the physico-chemical properties of polyelectrolyte complexes (PECs) formed by bottle brush and linear polyelectrolytes in solution and at solid / liquid interfaces. Electrostatic self-assembly of oppositely charged macromolecules in aqueous solution is a versatile strategy to construction of functional nanostructures with easily controlled properties. Bottle brush architecture, introduced into the PEC, generates a number of distinctive properties of the complexes, related to a broad range of application, such as colloidal stability and protein repellency to name a few. To utilize these materials in a wide range of applications e.g. drug delivery, the understanding of the effects of polymer architecture and solution parameters on the properties of bottle brush PECs is of paramount importance. This thesis constitutes a systematic investigation of PECs formed by a series of cationic bottle-brush polyelectrolytes and a series of anionic linear polyelectrolytes in aqueous solution. The focus of the first part of the thesis was primarily on formation and characterization of PECs in solution, whereas the adsorption properties and adsorption kinetics of bottle-brush polyelectrolytes and their complexes was investigated in the second part of the thesis work. In particular, effects of the side-chain density of the bottlebrush polyelectrolyte, concentration, mixing ratio and molecular weigh of the linearpolyelectrolyte on formation, solution properties, stability and adsorption of PECs were addressed. The pronounced effect of the side-chain density of the bottle-brush polyelectrolyte on the properties of stoichiometric and nonstoichiometric PECs was demonstrated. Formation of PECs by bottle-brush copolymers with high density of side-chains results in small, watersoluble, molecular complexes having nonspherical shape, independent of concentration. Whereas formation of PEC-aggregates was revealed by bottle-brush polyelectrolytes with low side chain density, the level of aggregation in these complexes is controlled by polyelectrolyte concentration. The structure of the PECs formed with low molecular weight polyanions is consistent with the picture that several small linear polyelectrolyte molecules associate with the large bottle-brush. In contrast, when complexation occurs between polyanions of high molecular weigh and the bottle-brush polymers considerably larger PECs are formed, consistent with several bottle-brush polymers associating with one high molecular weight polyanion.
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| 13. |
- Alfredsson, Viveka, et al.
(författare)
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Morphologies and Structure of Brain Lipid Membrane Dispersions
- 2021
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Ingår i: Frontiers in Cell and Developmental Biology. - : Frontiers Media SA. - 2296-634X. ; 9
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Tidskriftsartikel (refereegranskat)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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| 14. |
- Andersson, Tommy, et al.
(författare)
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Effect of Esomeprazole With/Without Acetylsalicylic Acid, Omeprazole and Lansoprazole on Pharmacokinetics and Pharmacodynamics of Clopidogrel in Healthy Volunteers
- 2014
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Ingår i: American Journal of Cardiovascular Drugs. - : Springer Science and Business Media LLC. - 1175-3277 .- 1179-187X. ; 14:3, s. 217-227
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Tidskriftsartikel (refereegranskat)abstract
- The effect of proton pump inhibitors (PPIs) on the pharmacokinetics and pharmacodynamics of clopidogrel was assessed in two healthy volunteer crossover studies. Study 1: subjects received clopidogrel alone (300-mg loading dose, then 75 mg/day for 28 days) and two of three PPIs (omeprazole 80 mg, esomeprazole 40 mg or lansoprazole 60 mg) plus clopidogrel for 29 days in three treatment periods (randomized treatment sequence assignment). Study 2: subjects received clopidogrel alone (75 mg/day for 9 days) and clopidogrel alone for 4 days followed by clopidogrel plus fixed-combination esomeprazole 20 mg/low-dose acetylsalicylic acid (ASA) 81 mg for 5 days in two treatment periods (randomized treatment sequence assignment). Pharmacokinetic effects were estimated by measuring active metabolite of clopidogrel, and pharmacodynamic effects by inhibition of adenosine diphosphate (ADP)-induced platelet aggregation. There was a relative decrease of up to 50 % in exposure to the active metabolite of clopidogrel with the different PPIs (study 1), and close to 40 % with esomeprazole/low-dose ASA (study 2), compared with clopidogrel alone. There was an absolute decrease of up to 17 % in inhibition of ADP-induced platelet aggregation with co-administration of different PPIs, compared with clopidogrel alone; however, no differences in platelet inhibition were observed during co-administration with the esomeprazole/low-dose ASA fixed-dose combination. Omeprazole, esomeprazole and lansoprazole decreased systemic exposure to the active metabolite of clopidogrel in healthy volunteers, leading to modest decreases in its antiplatelet effect. However, no apparent differences in platelet inhibition were observed when esomeprazole was co-administered with low-dose ASA as a fixed-dose combination.
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| 15. |
- Angelescu, Daniel, et al.
(författare)
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Adsorption of Branched-Linear Polyethyleneimine-Ethylene Oxide Conjugate on Hydrophilic Silica Investigated by Ellipsometry and Monte Carlo Simulations
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:16, s. 9961-9971
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of and conformation adopted by a branched-linear polymer conjugate to the hydrophilic silica aqueous solution interface have been studied by in situ null ellipsornetry and Monte Carlo simulations. The conjugate is a highly branched polyethyleneimine structure with ethyleneoxide chains grafted to its primary and secondary amino groups. In situ null ellipsometry demonstrated that the polymer conjugate adsorbs to the silica surface from water and aqueous solution of 1 mM asymmetric divalent salt (calcium and magnesium chloride to emulate hard water) over a large pH range. The adsorbed amount is hardly affected by pH and large charge reversal on the negatively charged silica surface occurred at pH = 4.0, due to the adsorption of the cationic polyelectrolyte. The Monte Carlo simulations using an appropriate coarse-grained model of the polymer in solution predicted a core shell structure with no sharp boundary between the ethyleneimine and ethyleneoxide moieties. The structure at the interface is similar to that in solution when the polymer degree of protonation is low or moderate while at high degree of protonation the strong electrostatic attraction between the ethyleneimine core and oppositely charged silica surface distorts the ethyleneoxide shell so that an "anemone"-like configuration is adopted. The adsorption of alkyl benzene sulfonic acid (LAS) to a preadsorbed polymer layer was also investigated by null ellipsometry. The adsorption data brought additional support for the existence of a strong polymer adsorption and showed the presence of a binding which was further enhanced by the decreased solvency of the surfactant in the salt solution and confirmed the surface charge reversal by the polymer adsorption at pH = 4.0.
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| 16. |
- Arcos-Hernandez, Monica, et al.
(författare)
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Thermoresponsive Glycopolymers Based on Enzymatically Synthesized Oligo-β-Mannosyl Ethyl Methacrylates and N-Isopropylacrylamide
- 2021
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 22:6, s. 2338-2351
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Tidskriftsartikel (refereegranskat)abstract
- We here present a series of thermoresponsive glycopolymers in the form of poly(N-isopropylacrylamide)-co-(2-[β-manno[oligo]syloxy] ethyl methacrylate)s. These copolymers were prepared from oligo-β-mannosyl ethyl methacrylates that were synthesized through enzymatic catalysis, and were subsequently investigated with respect to their aggregation and phase behavior in aqueous solution using a combination of 1H NMR spectroscopy, dynamic light scattering, cryogenic transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The thermoresponsive glycopolymers were prepared by conventional free radical copolymerizations of different mixtures of 2-(β-manno[oligo]syloxy)ethyl methacrylates (with either one or two saccharide units) and N-isopropyl acrylamide (NIPAm). The results showed that below the lower critical solution temperature (LCST) of poly(NIPAm), the glycopolymers readily aggregate into nanoscale structures, partly due to the presence of the saccharide moieties. Above the LCST of poly(NIPAm), the glycopolymers rearrange into a heterogeneous mixture of fractal and disc/globular aggregates. Cryo-TEM and SAXS data demonstrated that the presence of the pendant β-mannosyl moieties in the glycopolymers induces a gradual conformational change over a wide temperature range. Even though the onset of this transition is not different from the LCST of poly(NIPAm), this gradual conformational change offers a variation of the temperature-dependent properties in comparison to poly(NIPAm), which displays a sharp coil-to-globule transition. Importantly, the compacted form of the glycopolymers show a larger colloidal stability compared to the unmodified poly(NIPAm). In addition, the thermoresponsiveness can be conveniently tuned by varying the sugar unit-length and the oligo-β-mannosyl ethyl methacrylate content.
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| 17. |
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| 18. |
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| 19. |
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| 20. |
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| 21. |
- Badell, Maria Valldeperas, et al.
(författare)
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Lipid Sponge-Phase Nanoparticles as Carriers for Enzymes
- 2018
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Ingår i: Biophysical Journal. - : Cell Press. - 0006-3495 .- 1542-0086. ; 114:3, suppl 1, s. 15A-15A
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Immobilization of enzymes into different support materials has been widely studied as means to control their activity and stability. Here we will consider lipid liquid crystalline phases as enzyme carriers, as they have been demonstrated to have a high potential in a range of applications such as drug delivery, protein encapsulation or crystallization thanks to the wide range of self-assembly structures they can form, which have cavities of nano-scale dimensions. Furthermore, such structures have also been observed in a range of living organisms. Although, reverse cubic or hexagonal lipid aqueous phase can be used to entrap smaller biomolecules, it is still challenging to encapsulate bioactive macromolecules, such as proteins. Here, we will present a novel lipid system able to form highly swollen sponge phases (L3), with aqueous pores up to 13 nm of diameter. We will show that this structure is preserved even in excess aqueous solution, where they form sponge-like nanoparticles (L3 NPs) in which two enzymes of different sizes, Aspartic protease and beta-galactosidase (34 KDa and 460 KDa, respectively), could be included. To reveal the nature of the interaction between the enzymes and the lipid matrix, we studied the adsorption of both proteins on the lipid layers formed by the L3 NPs. The results will be discussed in terms of the ability of these nanoparticles to encapsulate and release of the proteins in the lipid matrix.
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| 22. |
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| 23. |
- Bain, C. D., et al.
(författare)
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Complexes of surfactants with oppositely charged polymers at surfaces and in bulk
- 2010
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 155:1-2, s. 32-49
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Tidskriftsartikel (refereegranskat)abstract
- Addition of surfactants to aqueous solutions of polyelectrolytes carrying an opposite charge causes the spontaneous formation of complexes in the bulk phase in certain concentration ranges. Under some conditions, compact monodisperse multichain complexes are obtained in the bulk. The size of these complexes depends on the mixing procedure and it can be varied in a controlled way from nanometers up to micrometers. The complexes exhibit microstructures analoguous to those of the precipitates formed at higher concentrations. In other cases, however, the bulk complexes are large, soft and polydisperse. In most cases, the dispersions are only kinetically stable and exhibit pronounced non-equilibrium features. Association at air-water interfaces readily occurs, even at very small concentrations. When the surfactant concentration is small, the surface complexes are usually made of a surfactant monolayer to which the polymer binds and adsorbs in a flat-like configuration. However, under some conditions, thicker layers can be found, with bulk complexes sticking to the surface. The association at solid-water interfaces is more complex and depends on the specific interactions between surfactants, polymers and the surface. However, the behaviour can be understood if distinctions between hydrophilic surfaces and hydrophobic surfaces are made. Note that the behaviour at air-water interfaces is closer to that of hydrophobic than that of hydrophilic solid surfaces. The relation between bulk and surface complexation will be discussed in this review. The emphasis will be given to the results obtained by the teams of the EC-funded Marie Curie RTN "SOCON".
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| 24. |
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| 25. |
- Barauskas, Justas, et al.
(författare)
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Thermomyces lanuginosus lipase-catalyzed hydrolysis of the lipid cubic liquid crystalline nanoparticles
- 2016
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Ingår i: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 137, s. 50-59
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Tidskriftsartikel (refereegranskat)abstract
- In this study well-ordered glycerol monooleate (GMO)-based cubic liquid crystalline nanoparticles (LCNPs) have been used as substrates for Thermomyces lanuginosus lipase in order to establish the relation between the catalytic activity, measured by pH-stat titration, and the change in morphology and nano-structure determined by cryogenic transmission electron microscopy and synchrotron small angle X-ray diffraction. The initial lipase catalyzed LCNP hydrolysis rate is approximately 25% higher for large 350 nm nanoparticles compared to the small 190 nm particles, which is attributed to the increased number of structural defects on the particle surface. At pH 8.0 and 8.4 bicontinuous Im3m cubic LCNPs transform into "sponge"-like assemblies and disordered multilamellar onion-like structures upon exposure to lipase. At pH 6.5 and 7.5 lipolysis induced phase transitions of the inner core of the particles, following the sequence Im3m cubic -> reversed hexagonal -> reversed micellar Fd3m cubic -> reversed micelles. These transitions to the liquid crystalline phases with higher negative curvature of the lipid/water interface were found to trigger protonation of the oleic acid produced during lipase catalyzed reaction. The increase curvature of the reversed discrete micellar cubic phase was suggested to cause an increase in the oleic acid pK(a) to a larger value observed by pH-stat titration. (C) 2015 Elsevier B.V. All rights reserved.
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| 26. |
- Barauskas, Justas, et al.
(författare)
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Towards redox active liquid crystalline phases of lipids: a monoolein/water system with entrapped derivatives of ferrocene
- 2003
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Ingår i: Chemistry and Physics of Lipids. - 0009-3084. ; 123:1, s. 87-97
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Tidskriftsartikel (refereegranskat)abstract
- The phase and electrochemical behavior of the aqueous mixtures of monoolein (MO) and synthetic ferrocene (Fc) derivatives containing long alkyl chains -(Z)-octadec-9-enoylferrocene (1), (Z)-octadecen-9-ylferrocene (2), and ferrocenylmethyl (Z)-octadec-9-enoate (3)-were studied. At low hydration, the reversed micelles (L-2 phase) and cubic Q(230) phase of MO can accommodate relatively high amounts ( > 6 wt.%) of the Fc-derivative 2, whereas at high hydration, the pseudoternary cubic phase Q(224) is destabilized even at about 2 wt.% of this Fc. Increasing the Fc-derivative content induces L-alpha L-2 and L-alpha --> reversed bicontinuous cubic phase (Q(II)) H-II transitions depending upon hydration. A rough study of the MO system containing compounds I and 3 indicates very similar phase behavior to that of the MO/2/H2O system. Compound 2 apparently has no effect on the lipid monolayer thickness in the pseudoternary L-alpha, H-II and Q(II) liquid crystalline phases of MO. Within a 3D-structure of the Q224 phase, derivatives 1-3 exhibit electrochemical activity on the gold electrode. The one-electron redox conversion processes are electro-chemically quasi-reversible and controlled by diffusion. The values of apparent diffusion coefficient (D-app) and heterogeneous electron-transfer rate constant (k(s)) of Fcs are significantly lo er in the cubic,phase matrix when compared to the acetonitrile solution. By contrast, the MO H-II phase with entrapped Fc-derivatives does not exhibit electrochemical activity on the electrode surface. It is suggested that the diffusional anisotropy and/or localized aggregation of compounds 1-3 within a 2D-structure of the H-II phase account(s) for the latter observation. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.
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| 27. |
- Benjamins, Jan-Willem, et al.
(författare)
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Ellipsometry studies of nonionic surfactant adsorption at the oil-water interface
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:1, s. 149-159
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Tidskriftsartikel (refereegranskat)abstract
- In the presented study we have developed and implemented a methodology for ellipsometry measurements at liquid interfaces that makes it possible to determine the amount adsorbed without assumptions of refractive index or thickness of the adsorbed layer. It was demonstrated that this is possible by combined measurements from different aqueous phases, H2O and D2O, which were shown to have sufficiently different refractive indices. The methodology was tested by studying adsorption of two types of nonionic poly(ethylene glycol) alkyl ether surfactants, CnH2n+1(OC2H4)(m)OH or CnEm at the decane-aqueous interface, where C12E5 was adsorbed from the oil phase and C18E50 from the aqueous phase. The observed plateau values of the adsorbed amounts were 1.38 and 0.93 Mg/M-2 for C12E5 and C18E50, respectively, which is in agreement with the corresponding values of 1.49 and 1.15 Mg/M-2 obtained from applying the Gibbs equation to interfacial tension data for the same systems. We will briefly discuss the adsorption behavior in relation to the molecular structure of the surfactant and the phase behavior of the oil - surfactant- aqueous systems in relation to our experimental results.
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| 28. |
- Benjamins, Jan-Willem, et al.
(författare)
-
Formation of a liquid crystalline phase from phosphatidylcholine at the oil-aqueous interface
- 2005
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:7, s. 2804-2810
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption of phospholipid (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) and formation of a surface phase at the oil-water interface has been followed by using ellipsometry. The properties of the interfacial phase were found to depend strongly on whether phospholipid was added to the oil phase or to the aqueous phase as liposomal structures. In the latter case a monolayer formed, while if the phospholipid was supplied from the oil phase a lamellar phase appeared at the interface. The effect on the stabilizing surface phase of a surface-active protein (P-lactoglobulin) was also investigated. The observations are important for understanding stabilizing properties of surface-active compounds commonly used to stabilize emulsions. In addition it has been demonstrated that ellipsometry can be used to study the initial process when a two-phase system consisting of a water and an oil phase is transformed into a three phase system or eventually to a one-phase system.
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| 29. |
- Benjamins, Jan-Willem, et al.
(författare)
-
New experimental setup to use ellipsometry to study liquid-liquid and liquid-solid interfaces
- 2002
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:16, s. 6437-6444
-
Tidskriftsartikel (refereegranskat)abstract
- Different types of optical light guides were constructed and tested to enable convenient multiple angle of incidence ellipsometry, on solid and liquid interfaces in liquid solutions. Two light guides are needed on an ellipsometer, one to guide the incoming light and one to guide the light that is reflected at the test surface, and therefore one light guide was mounted on the laser arm and one on the detector arm of the ellipsometer. With this arrangement the optical windows automatically adjust to always be perpendicular to the direction of the light independent of the angle of incidence. The purpose with these light guides is to facilitate the passage of light through the air/solution interface. A thorough theoretical and experimental analysis of optical errors introduced by such light guides is presented. This discussion includes the effect of multiple reflections between and within the windows of the light guides' On the basis of this analysis a new ellipsometry setup with light guides, consisting of glass tube's with glued end windows, was developed. This setup makes it possible to perform accurate measurements in almost any type of measuring cell at any angle of incidence.
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| 30. |
- Black, Camilla F, et al.
(författare)
-
Linear dsDNA Partitions Spontaneously into the Inverse Hexagonal Lyotropic Liquid Crystalline Phases of Phospholipids.
- 2010
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 132:28, s. 9728-9732
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, we reported that DNA associated with inverse hexagonal (H(II)) lyotropic liquid crystal phases of the lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) was actively transcribed by T7 RNA polymerase. (1) Our findings suggested that key components of the transcription process, probably the T7 RNA polymerase and the DNA, remained associated with the monolithic H(II) phase throughout transcription. Here, we investigate the partitioning of DNA between an H(II) lyotropic liquid crystal phase and an isotropic supernatant phase in order to develop insights into the localization of DNA in liquid crystalline environments. Our results show that linear double stranded DNA (dsDNA) molecules partition spontaneously into monolithic preformed H(II) liquid crystal phases of DOPE. We propose that this process is driven by the increase in entropy due to the release of counterions from the DNA when it inserts into the aqueous pores of the H(II) phase.
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| 31. |
- Borné, Johanna, et al.
(författare)
-
Effect of lipase on different lipid liquid crystalline phases formed by oleic acid based acylglycerols in aqueous systems
- 2002
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:23, s. 8972-8981
-
Tidskriftsartikel (refereegranskat)abstract
- This study deals with the interplay between the interfacial structure of lipid liquid crystalline (1c) substrates and the lipolysis rate. Thermomyces (formerly Humicola) lanuginosa lipase (TLL) was added to lamellar (L-alpha), reversed bicontinuous cubic (C), and reversed hexagonal (H-II)1c phases, based on monoolein (MO), MO-sodium oleate (NaO), MO-oleic acid (OA), and MO-diolein (DO) with water. The changes in self-assembled structure and lipid composition during lipolytic processes were followed by polarizing microscopy, small-angle X-ray diffraction, and high-performance liquid chromatography (HPLC). Indeed, the observed changes in self-assembled structures could be predicted from either the MO-OA-(H2O)-H-2 ternary phase diagram, where the lipolysis gives rise to a transition of C --> H-II --> micellar cubic (C-mic) --> reversed micellar phase + dispersion, or the MO-NaO-(H2O)-H-2 ternary phase-diagram, where the corresponding sequence is L-alpha --> H-I. These observations are discussed in terms of the degree of protonation of the fatty acid. The specific activity of TLL on the C-D and OA-H-II samples as determined from the lipolysis rate was found to be the similar under. the employed experimental conditions. The HPLC data showed that the ratio between the substrate (MO/DO) and final product (OA) approached about the same values regardless of the initial substrate composition and structure.
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| 32. |
- Borné, Johanna, et al.
(författare)
-
Effect of lipase on monoolein-based cubic phase dispersion (cubosomes) and vesicles
- 2002
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:40, s. 10492-10500
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of adding a Thermomyces (formerly Humicola) lanuginosa lipase (TLL) to a cubic dispersion of the binary monoolein (MO)-(H2O)-H-2 system and to vesicles formed by the ternary MO-sodium oleate (NaO)(H2O)-H-2 system at high water content has been studied. The change in lipid aggregate structure during the lipolytic process was observed by light microscopy, cryo-TEM, and dynamic light scattering, and the lipid composition was determined with HPLC. The sequence of lipid aggregate structures observed upon lipase addition to the cubic dispersion is cubic dispersion --> reversed cubic, hexagonal, and lamellar structures --> large polygonal structures --> dispersed oil droplets. The addition of lipase to MO/NaO aqueous-based vesicles did not change the morphology significantly. However, close to steady state, the vesicles changed from having smooth interfaces to irregular ones. When lipolysis reached steady state, the MO/(OA+NaO) ratio was similar in the two systems studied, although the morphology of the structures formed during lipolysis differed significantly. These differences are discussed in relation to the degree of dissociation of the fatty acid.
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| 33. |
- Borné, Johanna, et al.
(författare)
-
Microscopy, SAXD, and NMR studies of phase behavior of the monoolein-diolein-water system
- 2000
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 16:26, s. 10044-10054
-
Tidskriftsartikel (refereegranskat)abstract
- The phase behavior of the ternary monoolein (MO)-diolein (DO)-water ((H2O)-H-2) system is presented. The experimental phase behavior and microstructure are studied by a combination of polarizing microscopy, small-angle X-ray diffraction, and NMR methods. Monoolein forms extensive reversed bicontinuous cubic liquid crystalline phases (C) that are in equilibrium with a lamellar liquid crystalline phase (L-alpha) on the water-poor side and with excess water on the other side. The presence of small amounts of DO in the MO-water system is sufficient to destabilize the C and L-alpha liquid crystalline phases. Formation of a reversed hexagonal (HII) phase from the cubic phase occurs at a lower transition temperature than that reported for the MO-water system. Within the cubic region, the diamond cubic phase, CD, is less stable than the gyroid type, C-G. The solubility of DO increases within this phase when the MO content increases, and the phase reaches its maximum stability at 4 wt % DO. The large HII-phase formed in the ternary system is in equilibrium with water, and it solubilizes about 30 wt % DO within its stability range. A stable dispersion is formed at even higher DO concentrations. An ideal swelling of the HII-phase with increasing polar volume fraction is observed, whereas the length of the hydrocarbon chains along the hexagonal faces is constant. We measure a slight change of the average area per molecule in the H-II-phase with DO concentration. The formation and stability of the liquid crystalline phases can be qualitatively understood from the self-aggregation model, using the geometrical packing parameter of the lipids.
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| 34. |
- Borné, Johanna, et al.
(författare)
-
Vesicle formation and other structures in aqueous dispersios of monoolein and sodium oleate
- 2003
-
Ingår i: Journal of Colloid and Interface Science. - 1095-7103. ; 257:2, s. 310-320
-
Tidskriftsartikel (refereegranskat)abstract
- The macroscopic appearance and microstructure in the dilute corner of the ternary monoolein (MO)-sodium oleate (NaO)-water ((H2O)-H-2) system have been investigated by visual inspection and by using direct structural imaging with light microscopy and cryogenic transmission electron microscopy. The microstructural transformations that take place between the micellar phase (binary NaO-(H2O)-H-2 axis) and the dispersed cubic phase (binary MO-(H2O)-H-2 axis) upon increasing the ratio of MO to NaO are micelles, ruptured multilamellar vesicles together with flexible threads, various vesicle structures, vesicles in equilibrium with densely packed layers that either represent bilayers or domains of H- I tubes visible from the side, and finally a pattern that may be either a cubic phase or domains of HII tubes visible in a cross section. Spontaneously formed uni- and multilamellar vesicles that show long-term stability are found to be the dominant structure for mixed dispersions over almost the entire concentration range. The addition of NaOH to the non-bilayer-forming system, the ternary MO-OA (oleic acid)-(H2O)-H-2 system, leads to the fort-nation of vesicles. Vesicles were also observed in other ternary MO-aqueous-based systems with potassium oleate, cetyltrimethylammonium bromide, sodium taurodeoxycholate, or dipalmitoylphosphatidylcholine instead of NaO. (C) 2003 Elsevier Science (USA). All rights reserved.
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| 35. |
- Boysen, Anders T., et al.
(författare)
-
Fluorescent labeling of helminth extracellular vesicles using an in vivo whole organism approach
- 2020
-
Ingår i: Biomedicines. - 2227-9059. ; 8:7
-
Tidskriftsartikel (refereegranskat)abstract
- In the last two decades, extracellular vesicles (EVs) from the three domains of life, Archaea, Bacteria and Eukaryotes, have gained increasing scientific attention. As such, the role of EVs in host-pathogen communication and immune modulation are being intensely investigated. Pivotal to EV research is the determination of how and where EVs are taken up by recipient cells and organs in vivo, which requires suitable tracking strategies including labelling. Labelling of EVs is often performed post-isolation which increases risks of non-specific labelling and the introduction of labelling artefacts. Here we exploited the inability of helminths to de novo synthesise fatty acids to enable labelling of EVs by whole organism uptake of fluorescent lipid analogues and the subsequent incorporation in EVs. We showed uptake of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) (DOPE-Rho) in Anisakis spp. and Trichuris suis larvae. EVs isolated from the supernatant of Anisakis spp. labelled with DOPE-Rho were characterised to assess the effects of labelling on size, structure and fluorescence of EVs. Fluorescent EVs were successfully taken up by the human macrophage cell line THP-1. This study, therefore, presents a novel staining method that can be utilized by the EV field in parasitology and potentially across multiple species.
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| 36. |
- Brennan, Jennifer L., et al.
(författare)
-
Enzymatic Activity of Lipase-Nanoparticle Conjugates and the Digestion of Lipid Liquid Crystalline Assemblies
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:16, s. 13590-13599
-
Tidskriftsartikel (refereegranskat)abstract
- Variants of lipase were attached to gold nanoparticles (NPs) and their enzymatic activity was studied. The two bioengineered lipase variants have been prepared with biotin groups attached to different residues on the protein outer surface. The biotinylation was evidenced by denaturing polyacrylamide gel electrophoresis and quantified by the ([2-(4'-hydroxyazobenzene)]benzoic acid spectrophotometric test. NPs of 14 +/- 1 nm diameter coated with thiolated-polyethylene glycol ligands containing controlled proportions of biotin moieties have been prepared and characterized by transmission electron microscopy, UV-vis spectroscopy, small angle neutron scattering, and elemental analysis. These biotin-functionalized NPs were conjugated to lipase using streptavidin as a linker molecule. Enzyme activity assays on the lipase-nanoparticle conjugates show that the lipase loading and activity of the NPs can be controlled by varying the percentage of biotin groups in the particle protecting coat. The lipase-NP conjugates prepared using one variant display higher activity than those prepared using the other variant, demonstrating orientation-dependent enzyme activity. Cryogenic transmission electron microscopy was used to visualize the enzymatic activity of lipase-NP on well-defined lipid substrates. It was found that lipase-coated NPs are able to digest the substrates in a different manner in comparison to the free lipase.
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| 37. |
- Burrell, Jamie, et al.
(författare)
-
Using Curvature Power to Map the Domain of Inverse Micellar Cubic Phases : The Case of Aliphatic Aldehydes in 1,2-Dioleoyl-sn-glycero-3-phosphoethanolamine
- 2017
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 33:44, s. 12804-12813
-
Tidskriftsartikel (refereegranskat)abstract
- Oxylipins, or fatty aldehydes, are a class of molecules produced from membrane lipids as a result of oxidative stress or enzyme-mediated peroxidation. Here we report the effects of two biologically important fatty aldehydes, trans,trans-2,4-decanedienal (DD) and cis-11-hexadecenal (HD), on the phase behavior of the lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) in water. We compare the phase behavior of DD/DOPE and HD/DOPE mixtures to the phase behavior of oleic acid/DOPE mixtures and show that DD, HD, and oleic acid have similar effects on the phase diagrams of DOPE. Notably, both DD and HD, like oleic acid, induce the formation of Fd3m inverse micellar cubic phases in DOPE/water mixtures. This is the first time that Fd3m phases in fatty aldehyde-containing mixtures have been reported. We assess the effects of DD, HD, and oleic acid on DOPE in terms of lipid spontaneous curvatures and propose a method to predict the formation of Fd3m phases from the curvature power of amphiphiles. This methodology predicts that Fd3m phases will become stable if the spontaneous curvature of a lipid mixture is -0.48 ± 0.05 nm-1 or less.
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| 38. |
- Caboi, F, et al.
(författare)
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Lipase action on a monoolein/sodium oleate aqueous cubic liquid crystalline phase - a NMR and X-ray diffraction study
- 2002
-
Ingår i: Colloids and Surfaces B: Biointerfaces. - 1873-4367. ; 26:1-2, s. 159-171
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of adding Thermomyces (formerly Humicola) lanuginosa lipase (TLL) to a monoolein (MO)/sodium oleate (NaO) aqueous cubic liquid crystalline phase has been studied. H-1-NMR, C-13-NMR, H-1-PGSE (Pulsed-magnetic field Gradient Spin-Echo) self-diffusion measurements, and Small Angle X-ray Diffraction were used to follow the degradation of the cubic phase. The reaction sequence in terms of phase transitions follows the order bicontinuous cubic --> reverse hexagonal --> micellar cubic --> micellar phase and corresponds to the previously determined phase diagrams. These changes correlate with changes in the lipid composition observed by C-13-NMR and confirmed by HPLC analysis. The initial decrease of the diffusion coefficients of water and lipid can be related to the transformation of the bicontinuous cubic phase to a reverse hexagonal structure. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 39. |
- Caltagirone, Claudia, et al.
(författare)
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Solvatochromic fluorescent BODIPY derivative as imaging agent in camptothecin loaded hexosomes for possible theranostic applications
- 2015
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:30, s. 23443-23449
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Tidskriftsartikel (refereegranskat)abstract
- We here discuss the potential theranostic nanomedicine application of an innovative formulation consisting of monoolein-based nanoparticles with a two-dimensional hexagonal inner structure stabilized in water using a mixture of PEO132-PPO50-PEO132 block copolymers with and without conjugated folate for targeting. The proposed tumor-cell targeted formulation was shown to be able to simultaneously host the model anticancer drug camptothecin and a pyrene-modified BODIPY fluorophore, based on dynamic light scattering, small-angle X-ray scattering, and cryogenic transmission electron microscopy. The photophysical properties of the fluorophore were studied in solution in various solvents. A marked fluorescent solvatochromism, whose origin was explained by time-dependent density functional theory theoretical calculations, was observed. Fluorescence microscopy showed that HeLa cells readily internalize these nanoparticles, and that the fluorophore localizes within the lipid droplets. In addition, cytotoxicity test revealed that these nanoparticles are not toxic at the concentration used for the imaging analysis.
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| 40. |
- Campbell, Richard A., et al.
(författare)
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Direct Impact of Nonequilibrium Aggregates on the Structure and Morphology of Pdadmac/SDS Layers at the Air/Water Interface
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:29, s. 8664-8674
-
Tidskriftsartikel (refereegranskat)abstract
- We discuss different nonequilibrium mechanisms by which bulk aggregates directly modify, and can even control, the interfacial structure and morphology of an oppositely charged polyelectrolyte/surfactant (P/S) mixture. Samples are categorized at the air/water interface with respect to the dynamic changes in the bulk phase behavior, the bulk composition, and the sample history using complementary surface-sensitive techniques. First, we show that bulk aggregates can spontaneously interact with the adsorption layer and are retained in it and that this process occurs most readily for positively charged aggregates with an expanded structure. In this case, key nonequilibrium issues of aggregate dissociation and spreading of surface-active material at the interface have a marked influence on the macroscopic interfacial properties. In a second distinct mechanism, aggregates inherently become trapped at the interface during its creation and lateral flocculation occurs. This irreversible process is most pronounced for aggregates with the lowest charge. A third mechanism involves the deposition of aggregates at interfaces due to their transport under gravity. The specificity of this process at an interface depends on its location and is mediated by density effects in the bulk. The prevalence of each mechanism critically depends on a number of different factors, which are outlined systematically here for the first time. This study highlights the sheer complexity by which aggregates can directly impact the interfacial properties of a P/S mixture. Our findings offer scope for understanding seemingly mysterious irreproducible effects which can compromise the performance of formulations in wide-ranging applications from foams to emulsions and lubricants.
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| 41. |
- Campbell, Richard A., et al.
(författare)
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Effects of Bulk Colloidal Stability on Adsorption Layers of Poly(diallyldimethylammonium Chloride)/Sodium Dodecyl Sulfate at the Air-Water Interface Studied by Neutron Reflectometry
- 2011
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:51, s. 15202-15213
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Tidskriftsartikel (refereegranskat)abstract
- We show for the oppositely charged system poly(diallyldimethylammonium chloride)/sodium dodecyl sulfate that the cliff edge peak in its surface tension isotherm results from the comprehensive precipitation of bulk complexes into sediment, leaving a supernatant that is virtually transparent and a depleted adsorption layer at the air/water interface. The aggregation and settling processes take about 3 days to reach completion and occur at bulk compositions around charge neutrality of the complexes which lack long-term colloidal stability. We demonstrate excellent quantitative agreement between the measured surface tension values and a peak calculated from the surface excess of surfactant in the precipitation region measured by neutron reflectometry, using the approximation that there is no polymer left in the liquid phase. The nonequilibrium nature of the system is emphasized by the production of very different interfacial properties from equivalent aged samples that are handled differently. We go on to outline our perspective on the "true equilibrium" state of this intriguing system and conclude with a comment on its practical relevance given that the interfacial properties can be so readily influenced by the handling of kinetically trapped bulk aggregates.
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| 42. |
- Campbell, Richard A., et al.
(författare)
-
Multilayers at Interfaces of an Oppositely Charged Polyelectrolyte/Surfactant System Resulting from the Transport of Bulk Aggregates under Gravity
- 2012
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 116:27, s. 7981-7990
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Tidskriftsartikel (refereegranskat)abstract
- We show conclusively that multilayers at interfaces of an oppositely charged polyelectrolyte/surfactant system can result from the transport under gravity of bulk aggregates with internal molecular structure. This process was demonstrated by measurements of poly-(diallyldimethylammonium chloride)/sodium dodecyl sulfate solutions at the air/liquid and solid/liquid interfaces using neutron reflectometry. In the latter case a novel approach involving the comparison of reflection up versus down measurements provided key evidence. Interfacial multilayers indicated by a strong Bragg peak and clear off-specular scattering are exhibited under three conditions: (1) only for samples in the phase separation region, (2) only for fresh samples where a suspension of bulk aggregates remains in solution, and (3) only when the creaming or sedimentation process occurs in the direction of the interface under examination. This bulk transport mechanism is an alternative route of formation of interfacial multilayers to surface induced self assembly The two processes evidently give rise to interfaces with very different structural and rheological properties. Such directionality effects in the formation of nanostructured liquid interfaces may have implications for a broad range of soft matter and biophysical systems containing macromolecules such as synthetic polymers, proteins, or DNA.
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| 43. |
- Campbell, Richard A., et al.
(författare)
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New Perspective on the Cliff Edge Peak in the Surface Tension of Oppositely Charged Polyelectrolyte/Surfactant Mixtures
- 2010
-
Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:20, s. 3021-3026
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Tidskriftsartikel (refereegranskat)abstract
- We present how dramatically the nonequilibrium nature of an oppsitely charged polyelectrolyte/surfactant mixture can affect the interfacial properties. We show for the first time that the cliff edge peak in the surface tension of the poly(diallydimethylammonium chloride)/sodium dodecyl surfate system is produced as a direct result of depletion of surface-active material from the bulk solution due to a show precipitation process in the phase separation region. Simple illustrations are given of how to control the production of the peak, to eliminate the feature for equivalent aged solutions through the use of different sample handling methods, and even to change its characteristics at short surface ages. The potential to tune nonequilibrium, steady-state interfacial properties for such strongly associating system is clearly demonstrated. We propose that our findings in general may be applicable to a broad range of mixture containing surfactants and oppositely charged macromolecules such as polymers proteins and DNA.
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| 44. |
- Campos, J, et al.
(författare)
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On the interaction between adsorbed layers of monoolein and the lipase action on the formed layers
- 2002
-
Ingår i: Colloids and Surfaces B: Biointerfaces. - 1873-4367 .- 0927-7765. ; 26:1-2, s. 172-182
-
Tidskriftsartikel (refereegranskat)abstract
- We used the Surface Force Apparatus (SFA) and ellipsometry techniques to study the interaction forces and the adsorption behavior of monoolein (MO), respectively. MO was adsorbed from water to a hydrophobised mica or silica surface. In addition the effect of added lipase, Thermomyces (Humicula) lanuginosa lipase (TLL), to an adsorbed layer of MO was investigated. The force versus distance curves between two MO covered surfaces feature a strong repulsive interaction beneath 400 A. The range of the repulsive force decreases, however, with the number of approaches. No adhesion was observed, provided that the surfaces were not taken to hydrophobic contact. The surface separation at MO-MO contact was determined to about 55 Angstrom This means a layer thickness of about 27 Angstrom, which is comparable to the thickness (25 Angstrom) determined by ellipsometry. The repulsive force may arise from compression of a cubic phase of MO. This phase are suggested to form between the surfaces when they approach close contact due to capillary induced phase separation (CIPS) from the saturated MO solution. The repulsive force changes significantly with time after addition of TLL (concentration of about 1 x 10(-8) M). In contrast to the force curves recorded before adding TLL, the surfaces do not seem to be completely covered with MO as we always observed an attractive force (inward jump) of similar range as was observed between pure OTE surfaces. Ellipsometry measurement of TLL action on MO covered hydrophobic surface reveals a significant and sharp decrease of the amounts adsorbed. Furthermore, the rate of decrease and reduction in adsorbed amount increased with TLL concentration. (C) 2002 Elsevier Science B.V. All rights. reserved.
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| 45. |
- Cárdenas, Marité, et al.
(författare)
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DNA and cationic surfactant complexes at hydrophilic surfaces. An ellipsometry and surface force study
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:20, s. 8597-8603
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption and formation of DNA and cationic surfactant complexes at the silica-aqueous interface have been studied by ellipsometry. The interaction between the DNA-surfactant complexes at the mica-aqueous interface has been determined by the interferometric surface force apparatus. Adsorption was as expected not observed on negatively charged hydrophilic surfaces for DNA and when DNA-cationic surfactant complexes were negatively charged. However, adsorption was observed when there is an excess of cationic surfactant, just below the point of phase separation. The adsorption process requires hours to reach steady state. The adsorbed layer thickness is large at low surface coverage but becomes more compact and thinner at high coverage. A long-range repulsive force was observed between adsorbed layers of DNA-cationic surfactant complexes, which was suggested to be of both electrostatic and steric origin. The forces were found to be dependent on the equilibration time and the experimental pathway.
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| 46. |
- Cárdenas, Marité, et al.
(författare)
-
DNA and cationic surfactants at solid surfaces
- 2005
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 270-271, s. 33-43
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of DNA at different types of interfaces and how the formed structures DNA at an interface could be affected by cationic surfactant has been studied. Particular attention was paid to how the type of cationic surfactant and DNA (single or double stranded and length) affects the compaction/decompaction of DNA. Adsorption of DNA-cationic surfactant complexes is determined by a delicate balance of DNA-surface, cationic surfactant-surface, and cationic surfactant-DNA interactions. DNA do not adsorb on hydrophilic negatively charged surfaces due to effective electrostatic repulsion between DNA and the surfacs. However, the interaction between DNA cationic surfactant ions leads to a substantial adsorption of the formed DNA-cationic surfactant complex once the charge density of both the DNA macromolecule and the surface is sufficiently decreased. On hydrophobic surfaces, where both DNA and cationic surfactant interact with the surface, the presence of the cationic surfactant leads to a considerable increase in adsorbed amount and a significant layer compaction of DNA. The stability of the mixed adsorbed layer largely depends on the strength of the interactions between DNA and the cationic surfactant, as well as between the surface and the cationic surfactant. DNA interacts with small latex particles in a similar way as to the macroscopic hydrophobic flat surfaces. (c) 2005 Elsevier B.V All rights reserved.
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| 47. |
- Cárdenas, Marité, et al.
(författare)
-
DNA compaction at hydrophobic surfaces induced by a cationic amphiphile
- 2003
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:19, s. 7712-7718
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Tidskriftsartikel (refereegranskat)abstract
- Cetyltrimethylammonium bromide (CTAB) induces partially irreversible compaction of DNA-adsorbed layers on hydrophobic silica. Additionally, there is a synergistic increase in the adsorbed amount when both CTAB and DNA are present as compared to the surface excess concentration of either of the individual components. In this study of the DNA adsorption and DNA-CTAB coadsorption by ellipsometry, emphasis has been placed on the DNA molecular weight as well as its conformation (single and double stranded). The DNA molecular weight and conformation have a large effect on the surfactant-free DNA adsorption behavior but not on he mixed DNA-CTAB adsorption behavior. Comparison between interfacial and bulk complexation has been made where possible. The DNA-CTAB complexes at the interface are neutral despite the large excess of DNA in the bulk. The final structure of the adsorbed layer was found to be dependent on the history of complex formation and DNA size.
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| 48. |
- 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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| 49. |
- Cárdenas, Marité, et al.
(författare)
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DNA compaction onto hydrophobic surfaces by different cationic surfactants
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:14, s. 6495-6502
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Tidskriftsartikel (refereegranskat)abstract
- DNA compaction by alkyltrimethylammonium surfactants at hydrophobized silica surfaces and the effect of the counterion, as well as the hydrocarbon chain length, was investigated by in situ null-ellipsometry. In addition, DNA compaction in the presence of a gemini surfactant, hexyl-alpha,omega-bis(dodecyldimethylammonium bromide), was studied. The type of cationic amphiphile used was found not to have a pronounced effect on the mixed DNA-cationic surfactant adsorbed layer thickness, although the surface concentration excess for the mixed layers seemed to follow the same trend as that for DNA-free surfactant layers. Interestingly, it was also found that the stability of the mixed adsorbed layer largely depends on the cationic surfactant used.
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| 50. |
- Cárdenas, Marité, et al.
(författare)
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Interaction between DNA and charged colloids could be hydrophobically driven
- 2005
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 6:2, s. 832-837
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of DNA with amino-functionalized polystyrene particles has been studied by using a dynamic light scattering (DLS) technique. In 10 mM NaBr solution the particles have a hydrodynamic radius of 76 nm and the DNA macromolecule investigated (double stranded) has a hydrodynamic radius of 107 nm. At very low DNA concentrations, DNA adopts a flat conformation on the particle surface. If the DNA concentration is increased above 0.1 mu g/mL, the thickness of the DNA layer increases, suggesting the presence of large loops and tails. Although the particles contain primary amino groups, they have a negative net charge under the conditions used in this work. Thus, the driving force for DNA adsorption is not of electrostatic origin but rather due to a hydrophobic effect. Addition of cationic surfactant to the DNA-precoated amino functionalized particles induces changes in the adsorbed layer conformation, in agreement with the coadsorption of cationic surfactant.
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