| 1. |
- Behrens, Manja A, et al.
(författare)
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Temperature-Induced Attractive Interactions of PEO-Containing Block Copolymer Micelles
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:21, s. 6021-6029
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Tidskriftsartikel (refereegranskat)abstract
- Interactions in a temperature sensitive-colloidal model system are investigated over a wide range of temperatures and concentrations to characterize the interparticle interactions within the system. This model system is composed of poly(ethylene oxide) end-capped with an octadecyl chain (C18E100), which by small-angle X-ray scattering (SAXS) have been shown to form spherical micelles in an aqueous salt solution. In the present study a 0.9 M NaF solution is used to shift the cloud point into the experimentally convenient temperature range. Densitometry and SAXS have shown no indication of specific interactions between the salt ions and the micelles. The spherical micelles are found to persist at elevated temperatures and a change in interparticle interaction is observed by viscometry and SAXS. The results are all consistent with the decreased solvent quality of water toward poly(ethylene oxide) with increasing temperature and it is seen that attractive interparticle interactions emerge in the vicinity of the cloud point.
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| 2. |
- Behrens, Manja, et al.
(författare)
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The Shapes of Z-alpha(1)-Antitrypsin Polymers in Solution Support the C-Terminal Domain-Swap Mechanism of Polymerization
- 2014
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Ingår i: Biophysical Journal. - : Elsevier BV. - 1542-0086 .- 0006-3495. ; 107:8, s. 1905-1912
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Tidskriftsartikel (refereegranskat)abstract
- Emphysema and liver cirrhosis can be caused by the Z mutation (Glu342Lys) in the serine protease inhibitor alpha 1-antitrypsin (alpha 1AT), which is found in more than 4% of the Northern European population. Homozygotes experience deficiency in the lung concomitantly with a massive accumulation of polymers within hepatocytes, causing their destruction. Recently, it was proposed that Z-alpha 1AT polymerizes by a C-terminal domain swap. In this study, small-angle x-ray scattering (SAXS) was used to characterize Z-alpha 1AT polymers in solution. The data show that the Z-alpha 1AT trimer, tetramer, and pentamer all form ring-like structures in strong support of a common domain-swap polymerization mechanism that can lead to self-terminating polymers.
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| 3. |
- Dupont, Daniel M, et al.
(författare)
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Protein-binding RNA aptamers affect molecular interactions distantly from their binding sites.
- 2015
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- Nucleic acid aptamer selection is a powerful strategy for the development of regulatory agents for molecular intervention. Accordingly, aptamers have proven their diligence in the intervention with serine protease activities, which play important roles in physiology and pathophysiology. Nonetheless, there are only a few studies on the molecular basis underlying aptamer-protease interactions and the associated mechanisms of inhibition. In the present study, we use site-directed mutagenesis to delineate the binding sites of two 2´-fluoropyrimidine RNA aptamers (upanap-12 and upanap-126) with therapeutic potential, both binding to the serine protease urokinase-type plasminogen activator (uPA). We determine the subsequent impact of aptamer binding on the well-established molecular interactions (plasmin, PAI-1, uPAR, and LRP-1A) controlling uPA activities. One of the aptamers (upanap-126) binds to the area around the C-terminal α-helix in pro-uPA, while the other aptamer (upanap-12) binds to both the β-hairpin of the growth factor domain and the kringle domain of uPA. Based on the mapping studies, combined with data from small-angle X-ray scattering analysis, we construct a model for the upanap-12:pro-uPA complex. The results suggest and highlight that the size and shape of an aptamer as well as the domain organization of a multi-domain protein such as uPA, may provide the basis for extensive sterical interference with protein ligand interactions considered distant from the aptamer binding site.
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| 4. |
- Freeman, Krista G., et al.
(författare)
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Portal Stability Controls Dynamics of DNA Ejection from Phage
- 2016
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:26, s. 6421-6429
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Tidskriftsartikel (refereegranskat)abstract
- Through a unique combination of time-resolved single-molecule (cryo-TEM) and bulk measurements (light scattering and small-angle X-ray scattering), we provide a detailed study of the dynamics of stochastic DNA ejection events from phage λ. We reveal that both binding with the specific phage receptor, LamB, and thermo-mechanical destabilization of the portal vertex on the capsid are required for initiation of ejection of the pressurized λ-DNA from the phage. Specifically, we found that a measurable activation energy barrier for initiation of DNA ejection with LamB present, Ea = (1.2 ± 0.1) × 10-19 J/phage (corresponding to ∼28 kTbody/phage at Tbody = 37 °C), results in 15 times increased rate of ejection event dynamics when the temperature is raised from 15 to 45 °C (7.5 min versus 30 s average lag time for initiation of ejection). This suggests that phages have a double fail-safe mechanism for ejection - in addition to receptor binding, phage must also overcome (through thermal energy and internal DNA pressure) an energy barrier for DNA ejection. This energy barrier ensures that viral genome ejection into cells occurs with high efficiency only when the temperature conditions are favorable for genome replication. At lower suboptimal temperatures, the infectious phage titer is preserved over much longer times, since DNA ejection dynamics is strongly inhibited even in the presence of solubilized receptor or susceptible cells. This work also establishes a light scattering based approach to investigate the influence of external solution conditions, mimicking those of the bacterial cytoplasm, on the stability of the viral capsid portal, which is directly linked to dynamics of virion deactivation.
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| 5. |
- Gentile, Luigi, et al.
(författare)
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Dynamic Phase Diagram of a Nonionic Surfactant Lamellar Phase
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:13, s. 3622-3629
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic phase diagram of triethylene glycol dodecyl ether (C12E3) in D2O was determined for 40, 50, and 60 wt % of surfactant. The shear flow effect on the nonionic lamellar phase was investigated as a function of temperature and concentration. The transition from planar lamellae (L-alpha)-to-multilamellar vesicles (MLVs) was characterized by means of rheology, rheo-small-angle neutron and light scattering. New insight into the nature of the transition region between L-alpha and the MLVs state is provided. A disorder-order transition was also observed by SANS. This is attributed to a transition from disordered MLVs to a close-packed array of MLV's with slightly higher order than before. Moreover flow instability was observed in the shear-thickening regime at 40 degrees C.
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| 6. |
- Gentile, Luigi, et al.
(författare)
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Multilamellar Vesicle Formation from a Planar Lamellar Phase under Shear Flow
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:28, s. 8316-8325
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Tidskriftsartikel (refereegranskat)abstract
- The formation of multilamellar vesicles (MLVs) from the lamellar phase of nonionic surfactant system C12E5/D2O under shear flow is studied by time-resolved small angle neutron and light scattering during shear flow. A novel small angle neutron scattering sample environment enables the tracking of the lamellae alignment in the velocity-velocity gradient (1-2) plane during MLV formation, which was tracked independently using flow small angle light scattering commensurate with rheology. During the lamellar-to-multilamellar vesicle transition, the primary Bragg peak from the lamellar ordering was observed to tilt, and this gradually increased with time, leading to an anisotropic pattern with a primary axis oriented at similar to 25 degrees relative to the flow direction. This distorted pattern persists under flow after MLV formation. A critical strain and critical capillary number based on the MLV viscosity are demonstrated for MLV formation, which is shown to be robust for other systems as well. These novel measurements provide fundamentally new information about the flow orientation of lamellae in the plane of flow that cannot be anticipated from the large body of previous literature showing nearly isotropic orientation in the 2,3 and 1,3 planes of flow. These observations are consistent with models for buckling-induced MLV formation but suggest that the instability is three-dimensional, thereby identifying the mechanism of MLV formation in simple shear flow.
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| 7. |
- Gubitosi, Marta, et al.
(författare)
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Stable, metastable and unstable cellulose solutions
- 2017
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Ingår i: Royal Society Open Science. - : The Royal Society. - 2054-5703. ; 4:8
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Tidskriftsartikel (refereegranskat)abstract
- We have characterized the dissolution state of microcrystalline cellulose (MCC) in aqueous tetrabutylammonium hydroxide, TBAH(aq), at different concentrations of TBAH, by means of turbidity and small-angle X-ray scattering. The solubility of cellulose increases with increasing TBAH concentration, which is consistent with solubilization driven by neutralization. When comparing the two polymorphs, the solubility of cellulose I is higher than that of cellulose II. This has the consequence that the dissolution of MCC (cellulose I) may create a supersaturated solution with respect to cellulose II. As for the dissolution state of cellulose, we identify three different regimes. (i) In the stable regime, corresponding to concentrations below the solubility of cellulose II, cellulose is molecularly dissolved and the solutions are thermodynamically stable. (ii) In the metastable regime, corresponding to lower supersaturations with respect to cellulose II, a minor aggregation of cellulose occurs and the solutions are kinetically stable. (iii) In the unstable regime, corresponding to larger supersaturations, there is macroscopic precipitation of cellulose II from solution. Finally, we also discuss strong alkali solvents in general and compare TBAH(aq) with the classical NaOH(aq) solvent.
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| 8. |
- Hagman, Joel, et al.
(författare)
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On the dissolution state of cellulose in cold alkali solutions
- 2017
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; , s. 2003-2015
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Tidskriftsartikel (refereegranskat)abstract
- We have characterized the dissolved state of microcrystalline cellulose (MCC) in cold alkali [2.0 M NaOH(aq)] solutions using a combination of small angle X-ray (SAXS) and static light scattering (SLS), (Formula presented.)H NMR, NMR self-diffusion, and rheology experiments. NMR and SAXS data demonstrate that the cellulose is fully molecularly dissolved. SLS, however, shows the presence of large concentration fluctuations in the solution, consistent with significant attractive cellulose-cellulose interactions. The scattering data are consistent with fractal cellulose aggregates of micrometre size having a mass fractal dimension (Formula presented.). At 25(Formula presented.) the solution structure remains unchanged on the time scale of weeks. However, upon heating the solutions above 35(Formula presented.) additional aggregation occurs on the time scale of minutes. Decreasing or increasing the NaOH concentration away from the “optimum” 2 M also leads to additional aggregation. This is seen as an increase of the SAXS intensity at lower q values. Addition of urea (1.8 and 3.6 M, respectively) does not significantly influence the solution structure. With these examples, we will discuss how scattering methods can be used to assess the quality of solvents for cellulose.
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| 9. |
- Ishikawa, Kazuhiro, et al.
(författare)
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Microemulsions of Record Low Amphiphile Concentrations Are Affected by the Ambient Gravitational Field
- 2016
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:26, s. 6074-6079
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that the ternary system heavy water-heptane-hexadecyl hexaethylene oxide (C16E6) has a stable bicontinuous microemulsion phase down to an exceptionally low concentration at the balanced temperature of 26.8 °C. It is further demonstrated that the ambient gravitational field has an influence on the observed phase equilibria for typical sample sizes (∼1 cm). Direct measurements using a nuclear magnetic resonance imaging technique demonstrate that sample compositions vary with the height in the vials. It is furthermore found that some samples show four phases at equilibrium in apparent violation of Gibbs' phase rule. It is pointed out that Gibbs' phase rule strictly applies only when effects of gravity are negligible. A further consequence of the ambient gravitational field is that, for the system studied, the microemulsion one-phase samples are not observed, when using standard size vials, that is, sample heights on the order of a centimeter. Quantitative determinations of concentration profiles can be used to determine parameters of the free-energy density for the system.
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| 10. |
- Johans, Christoffer, et al.
(författare)
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Potential Determining Salts in Microemulsions: Interfacial Distribution and Effect on the Phase Behavior
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:51, s. 15738-15746
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Tidskriftsartikel (refereegranskat)abstract
- In this work we consider potential determining salts, also referred to as phase transfer agents for a future objective of electrochemistry at the oil-water interface in microemulsions. We have studied these salts, composed of a hydrophilic and a hydrophobic ion, in microemulsion stabilized by nonionic surfactants with an oligo ethylene oxide headgroup. NMR measurements show that the salts preferentially dissociate across the surfactant interface between the oil and water domains, and hence create a potential drop across the surfactant film, and back to back diffuse double layers in the oil and water phases. These observations are also supported by Poisson-Boltzmann calculations. This adsorption like event stabilizes the microemulsion. Repulsive long-range interactions between thin lamellae of surfactant and water lamellae in oil were observed using SAXS, thus confirming the presence of electrostatic forces mediated through the oil domain. We also observed that reversing the charges on the potential determining salts had opposite effects on the phase inversion temperature.
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