| 1. |
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| 2. |
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| 3. |
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| 4. |
- Pfaller, M.A., et al.
(author)
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Twelve years of fluconazole in clinical practice : Global-trends in species distribution and fluconazole susceptibility of bloodstream isolates of Candida
- 2004
-
In: Clinical Microbiology and Infection. - : Elsevier BV. - 1198-743X .- 1469-0691. ; 10:SUPPL. 1, s. 11-23
-
Journal article (peer-reviewed)abstract
- We determined the species distribution and in-vitro susceptibility of 6082 bloodstream infection (BSI) isolates of Candida spp. collected from 250 medical centres in 32 nations over a 10-year period from 1992 through 2001. The species included 3401 C. albicans, 984 C. glabrata, 796 C. parapsilosis, 585 C. tropicalis, 153 C. krusei, 67 C. lusitaniae, 48 C. guilliermondii, 10 C. famata, 10 C. kefyr, six C. pelliculosa, five C. rugosa, four C. lipolytica, three C. dubliniensis, three C. inconspicua, two C. sake and one isolate each of C. lambica, C. norvegensis and C. zeylanoides. Minimum inhibitory concentration determinations were made using the National Committee for Clinical Laboratory Standards reference broth microdilution method. Variation in the rank order and frequency of the different species of Candida was observed over time and by geographic area. The proportion of BSI due to C. albicans and C. glabrata increased and C. parapsilosis decreased over time in Canada, the USA and Europe. C. glabrata was an infrequent cause of BSI in Latin America and the Asia-Pacific region. Very little variation in fluconazole susceptibility was observed among isolates of C. albicans, C. tropicalis and C. parapsilosis. These species accounted for 78% of all BSI and remained highly susceptible (91-100% susceptible) to fluconazole from 1992 to 2001 irrespective of geographic origin. The prevalence of fluconazole resistance among C. glabrata isolates was variable both over time and among the various countries and regions. Resistance to fluconazole among C. glabrata isolates was greatest in the USA and varied by US census region (range 0-23%). These observations are generally encouraging relative to the sustained usefulness of fluconazole as a systemically active antifungal agent for the treatment of candida BSI. © 2004 Copyright by the European Society of Clinical Microbiology and Infectious Diseases.
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| 5. |
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| 6. |
- North, R. L., et al.
(author)
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The state of Lake Simcoe (Ontario, Canada) : the effects of multiple stressors on phosphorus and oxygen dynamics
- 2013
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In: Inland Waters. - 2044-2041 .- 2044-205X. ; 3:1, s. 51-74
-
Journal article (peer-reviewed)abstract
- Lake Simcoe, the largest lake in southern Ontario outside of the Laurentian Great Lakes, is affected by numerous stressors including eutrophication resulting from total phosphorus (TP) loading, climate change, and invasions of exotic species. We synthesized the long-term responses of Lake Simcoe to these stressors by assessing trends in water quality and biological composition over multiple trophic levels. Evidence for climate change included increasing thermal stability of the lake and changes in subfossil diatom communities over time. Although the deep water dissolved oxygen (O-2) minimum has increased significantly since TP load reductions, it is still below estimated historical values and the Lake Simcoe Protection Plan end-of-summer target level of 7 mg O-2 L-1. Low deep water O-2 concentrations corresponded with a decline in coldwater fish abundance. Since 1980, some nutrient concentrations have decreased (spring TP) while others have increased (silica), but many show no obvious changes (ice-free TP, nitrate, ammonium). Increases in water clarity, combined with declines in chlorophyll a and phytoplankton biovolumes in Cook's Bay, were temporally consistent with declines in TP loading and the lake-wide establishment of dreissenid mussels as a major component of the Lake Simcoe ecosystem. Using an investigative tool, we identified 2 periods when abrupt shifts potentially occurred in multiple parameters: 1986 and 1995-1997. Additional ecosystem level changes such as declines in zooplankton, declines in offshore benthic invertebrate abundance, and increased nearshore invertebrate abundance likely reflect the effects of invasive species. The interaction of these multiple stressors have significantly altered the Lake Simcoe ecosystem.
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| 7. |
- Blunden, Jessica, et al.
(author)
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State of the climate in 2013
- 2014
-
In: Bulletin of the American Meteorological Society. - 0003-0007. ; 95
-
Journal article (peer-reviewed)abstract
- © 2014, American Meteorological Society. All rights reserved. In 2013, the vast majority of the monitored climate variables reported here maintained trends established in recent decades. ENSO was in a neutral state during the entire year, remaining mostly on the cool side of neutral with modest impacts on regional weather patterns around the world. This follows several years dominated by the effects of either La Niña or El Niño events. According to several independent analyses, 2013 was again among the 10 warmest years on record at the global scale, both at the Earth’s surface and through the troposphere. Some regions in the Southern Hemisphere had record or near-record high temperatures for the year. Australia observed its hottest year on record, while Argentina and New Zealand reported their second and third hottest years, respectively. In Antarctica, Amundsen-Scott South Pole Station reported its highest annual temperature since records began in 1957. At the opposite pole, the Arctic observed its seventh warmest year since records began in the early 20th century. At 20-m depth, record high temperatures were measured at some permafrost stations on the North Slope of Alaska and in the Brooks Range. In the Northern Hemisphere extratropics, anomalous meridional atmospheric circulation occurred throughout much of the year, leading to marked regional extremes of both temperature and precipitation. Cold temperature anomalies during winter across Eurasia were followed by warm spring temperature anomalies, which were linked to a new record low Eurasian snow cover extent in May. Minimum sea ice extent in the Arctic was the sixth lowest since satellite observations began in 1979. Including 2013, all seven lowest extents on record have occurred in the past seven years. Antarctica, on the other hand, had above-average sea ice extent throughout 2013, with 116 days of new daily high extent records, including a new daily maximum sea ice area of 19.57 million km2 reached on 1 October. ENSO-neutral conditions in the eastern central Pacific Ocean and a negative Pacific decadal oscillation pattern in the North Pacific had the largest impacts on the global sea surface temperature in 2013. The North Pacific reached a historic high temperature in 2013 and on balance the globally-averaged sea surface temperature was among the 10 highest on record. Overall, the salt content in nearsurface ocean waters increased while in intermediate waters it decreased. Global mean sea level continued to rise during 2013, on pace with a trend of 3.2 mm yr-1 over the past two decades. A portion of this trend (0.5 mm yr-1) has been attributed to natural variability associated with the Pacific decadal oscillation as well as to ongoing contributions from the melting of glaciers and ice sheets and ocean warming. Global tropical cyclone frequency during 2013 was slightly above average with a total of 94 storms, although the North Atlantic Basin had its quietest hurricane season since 1994. In the Western North Pacific Basin, Super Typhoon Haiyan, the deadliest tropical cyclone of 2013, had 1-minute sustained winds estimated to be 170 kt (87.5 m s-1) on 7 November, the highest wind speed ever assigned to a tropical cyclone. High storm surge was also associated with Haiyan as it made landfall over the central Philippines, an area where sea level is currently at historic highs, increasing by 200 mm since 1970. In the atmosphere, carbon dioxide, methane, and nitrous oxide all continued to increase in 2013. As in previous years, each of these major greenhouse gases once again reached historic high concentrations. In the Arctic, carbon dioxide and methane increased at the same rate as the global increase. These increases are likely due to export from lower latitudes rather than a consequence of increases in Arctic sources, such as thawing permafrost. At Mauna Loa, Hawaii, for the first time since measurements began in 1958, the daily average mixing ratio of carbon dioxide exceeded 400 ppm on 9 May. The state of these variables, along with dozens of others, and the 2013 climate conditions of regions around the world are discussed in further detail in this 24th edition of the State of the Climate series.
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| 8. |
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| 9. |
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| 10. |
- Ericsson, A., et al.
(author)
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Crystallization of a Zr-based metallic glass produced by laser powder bed fusion and suction casting
- 2021
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In: Journal of Non-Crystalline Solids. - : Elsevier. - 0022-3093 .- 1873-4812. ; 571
-
Journal article (peer-reviewed)abstract
- The crystallization behaviour during low temperature annealing of samples of the Zr59.3Cu28.8Al10.4Nb1.5 (at%) bulk metallic glass produced by suction casting and the laser powder bed fusion (LPBF) process were studied with small angle neutron scattering (SANS), X-ray diffraction and scanning electron microscopy. The in-situ SANS measurements during isothermal annealing reveals that the phase separation in the LPBF processed material proceeds at a smaller characteristic length-scale than the cast material. Quantitative analysis of the SANS data shows that, while the crystallization process in both materials proceed through rapid nucleation followed by diffusion limited growth, the LPBF processed material crystallizes with a smaller cluster size and at a higher rate. The smaller cluster size is attributed to the elevated oxygen content in the LPBF processed material which reduces the nucleation barrier and thus the thermal stability.
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| 11. |
- Hemming, Joanna M., et al.
(author)
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Environmental Pollutant Ozone Causes Damage to Lung Surfactant Protein B (SP-B)
- 2015
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In: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 54:33, s. 5185-5197
-
Journal article (peer-reviewed)abstract
- Lung surfactant protein B (SP-B) is an essential protein found in the surfactant fluid at the air water interface of the lung. Exposure to the air pollutant ozone could potentially damage SP-B and lead to respiratory distress. We have studied two peptides, one consisting of the N-terminus of SP-B [SP-B(1-25)] and the other a construct of the N- and C-termini of SP-B [SP-B-(1-25,B-63-78)], called SMB. Exposure to dilute levels of ozone (similar to 2 ppm) of monolayers of each peptide at the air water interface leads to a rapid reaction, which is evident from an increase in the surface tension. Fluorescence experiments revealed that this increase in surface tension is accompanied by a loss of fluorescence from the tryptophan residue at the interface. Neutron and X-ray reflectivity experiments show that, in contrast to suggestions in the literature, the peptides are not solubilized upon oxidation but rather remain at the interface with little change in their hydration. Analysis of the product material reveals that no cleavage of the peptides occurs, but a more hydrophobic product is slowly formed together with an increased level of oligomerization. We attributed this to partial unfolding of the peptides. Experiments conducted in the presence of phospholipids reveal that the presence of the lipids does not prevent oxidation of the peptides. Our results strongly suggest that exposure to low levels of ozone gas will damage SP-B, leading to a change in its structure. The implication is that the oxidized protein will be impaired in its ability to interact at the air water interface with negatively charged phosphoglycerol lipids, thus compromising what is thought to be its main biological function.
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| 12. |
- Larsen, Simon R., et al.
(author)
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Sample cell for studying liquid interfaces with an in situ electric field using X-ray reflectivity and application to clay particles at oil–oil interfaces
- 2018
-
In: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 25:Part: 3, s. 915-917
-
Journal article (peer-reviewed)abstract
- Commissioning results of a liquid sample cell for X-ray reflectivity studies with an in situ applied electrical field are presented. The cell consists of a Plexiglas container with lateral Kapton windows for air-liquid and liquid-liquid interface studies, and was constructed with grooves to accept plate electrodes on the walls parallel to the direction of the beam. Both copper and ITO plate electrodes have been used, the latter being useful for simultaneous optical studies. Commissioning tests were made at the I07 beamline of the Diamond Light Source.
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| 13. |
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| 14. |
- Thompson, Katherine C., et al.
(author)
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Degradation and Rearrangement of a Lung Surfactant Lipid at the Air-Water Interface during Exposure to the Pollutant Gas Ozone
- 2013
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:14, s. 4594-4602
-
Journal article (peer-reviewed)abstract
- The presence of unsaturated lipids in lung surfactant is important for proper respiratory function. In this work, we have used neutron reflection and surface pressure measurements to study the reaction of the ubiquitous pollutant gas-phase ozone, 03, with pure and mixed phospholipid monolayers at the air-water interface. The results reveal that the reaction of the unsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC, with ozone leads to the rapid loss of the terminal C9 portion of the oleoyl strand of POPC from the air-water interface. The loss of the C9 portion from the interface is accompanied by an increase in the surface pressure (decrease in surface tension) of the film at the air-water interface. The results suggest that the portion of the oxidized oleoyl strand that is still attached to the lipid headgroup rapidly reverses its orientation and penetrates the air-water interface alongside the original headgroup, thus increasing the surface pressure. The reaction of POPC with ozone also leads to a loss of material from the palmitoyl strand, but the loss of palmitoyl material occurs after the loss of the terminal C9 portion from the oleoyl strand of the molecule, suggesting that the palmitoyl material is lost in a secondary reaction step. Further experiments studying the reaction of mixed monolayers composed of unsaturated lipid POPC and saturated lipid dipalmitoyl-sn-glycero-3-phosphocholine, DPPC, revealed that no loss of DPPC from the air-water interface occurs, eliminating the possibility that a reactive species such as an OH radical is formed and is able to attack nearby lipid chains. The reaction of ozone with the mixed films does cause a significant change in the surface pressure of the air-water interface. Thus, the reaction of unsaturated lipids in lung surfactant changes and impairs the physical properties of the film at the air-water interface.
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| 15. |
- Thompson, Katherine C., et al.
(author)
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Reaction of a Phospholipid Monolayer with Gas-Phase Ozone at the Air-Water Interface : Measurement of Surface Excess and Surface Pressure in Real Time
- 2010
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:22, s. 17295-17303
-
Journal article (peer-reviewed)abstract
- The reaction between gas-phase ozone and monolayers of the unsaturated lipid 1-palmitoy1-2-oleoyl-sn-glycero-3-phosphocholine, POPC, on aqueous solutions has been studied in real time using neutron reflection and surface pressure measurements. The reaction between ozone and lung surfactant, which contains POPC, leads to decreased pulmonary function, but little is known shout the changes that occur to the interfacial material as a result of oxidation. The results reveal that the initial reaction of ozone with POPC leads to a rapid increase in surface pressure followed by a slow decrease to very low values. The neutron reflection measurements, performed on an isotopologue of POPC with a selectively deuterated palmitoyl strand, reveal that the reaction leads to loss of this strand from the air-water interface. suggesting either solubilization of the product lipid or degradation of the palmitoyl strand by a reactive species. Reactions of H-1-POPC on D2O reveal that the headgroup region of the lipids in aqueous solution is not dramatically perturbed by the reaction of POPC monolayers with ozone supporting degradation of the palmitoyl strand rather than solubilization. The results are consistent with the reaction of ozone with the oleoyl strand of POPC at the air water interface leading to the formation of OH radicals. the highly reactive OH radicals produced can then go on to react with the saturated palmitoyl strands leading to the formation or oxidized lipids with shorter alkyl tails.
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| 16. |
- Ainalem, Marie-Louise, et al.
(author)
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On the Ability of PAMAM Dendrimers and Dendrimer/DNA Aggregates To Penetrate POPC Model Biomembranes
- 2010
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:21, s. 7229-7244
-
Journal article (peer-reviewed)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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| 17. |
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| 18. |
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| 19. |
- Berts, Ida, 1984-, et al.
(author)
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Controlling adsorption of albumin with hyaluronan on silica surfaces and sulfonated latex particles
- 2017
-
In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 504, s. 315-324
-
Journal article (peer-reviewed)abstract
- Polysaccharides are known to modify binding of proteins at interfaces and this paper describes studies of these interactions and how they are modified by pH. Specifically, the adsorption of human serum albumin on to polystyrene latex and to silica is described, focusing on how this is affected by hyaluronan. Experiments were designed to test how such binding might be modified under relevant physiological conditions. Changes in adsorption of albumin alone and the co-adsorption of albumin and hyaluronan are driven by electrostatic interactions. Multilayer binding is found to be regulated by the pH of the solution and the molecular mass and concentration of hyaluronan. Highest adsorption was observed at pH below 4.8 and for low molecular mass hyaluronan (<= 150 kDa) at concentrations above 2 mg ml(-1). On silica with grafted hyaluronan, albumin absorption is reversed by changes in solvent pH due to their strong electrostatic attraction. Albumin physisorbed on silica surfaces is also rinsed away with dilute hyaluronan solution at pH 4.8. The results demonstrate that the protein adsorption can be controlled both by changes of pH and by interaction with other biological macromolecules.
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| 20. |
- Berts, Ida, et al.
(author)
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Polymeric Smart Coating Strategy for Titanium Implants
- 2014
-
In: Advanced Engineering Materials. - : Wiley. - 1438-1656 .- 1527-2648. ; 16:11, s. 1340-1350
-
Journal article (peer-reviewed)abstract
- Hyaluronan based hydrogel coatings can mimic extracellular matrix components and incorporate growth factors that can be released during a progressive degradation while new tissue regenerates. This paper describes a structural characterization of a hydrogel coating made of modified hyaluronan polymers and how these coatings interact with bone morphogenetic protein-2 (BMP-2). Quartz crystal microbalance and neutron reflectivity measurements were used for in-situ, real-time measurements of the adsorption properties of polymers and proteins on smooth titanium oxide surfaces that mimic implant products in orthopedics. The adsorption of BMP-2 on a bare titanium oxide surface is compared to that on titanium oxide coated with different chemically modified hyaluronan, the most important being hyaluronan with bisphosphonate groups (HA-BP). The subsequent release of the BMP-2 from these hydrogel coatings could be triggered by calcium ions. The amount of adsorbed protein on the surfaces as well as the amount of released protein both depend on the type of hyaluronan coating. We conclude that HA-BP coated titanium oxide surfaces provide an excellent material for growth factor delivery in-vivo.
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| 21. |
- Berts, Ida, 1984-
(author)
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Relating the Bulk and Interface Structure of Hyaluronan to Physical Properties of Future Biomaterials
- 2013
-
Doctoral thesis (other academic/artistic)abstract
- This dissertation describes a structural investigation of hyaluronan (HA) with neutron scattering techniques. HA is a natural biopolymer and one of the major components of the extracellular matrix, synovial fluid, and vitreous humor. It is used in several biomedical applications like tissue engineering, drug delivery, and treatment of osteoarthritis. Although HA is extensively studied, very little is known about its three-dimensional conformation and how it interacts with ions and other molecules. The study aims to understand the bulk structure of a cross-linked HA hydrogel, as well as the conformational arrangement of HA at solid-liquid interfaces. In addition, the structural changes of HA are investigated by simulation of physiological environments, such as changes in ions, interactions with nanoparticles, and proteins etc. Small-angle neutron scattering and neutron reflectivity are the two main techniques applied to investigate the nanostructure of hyaluronan in its original, hydrated state.The present study on hydrogels shows that they possess inhomogeneous structures best described with two correlation lengths, one of the order of a few nanometers and the other in the order of few hundred nanometers. These gels are made up of dense polymer-rich clusters linked to each other. The polymer concentration and mixing governs the connectivity between these clusters, which in turn determines the viscoelastic properties of the gels. Surface-tethered HA at a solid-liquid interface is best described with a smooth varying density profile. The shape of this profile depends on the immobilization chemistry, the deposition protocol, and the ionic interactions. HA could be suitably modified to enhance adherence to metal surfaces, as well as incorporation of proteins like growth factors with tunable release properties. This could be exploited for surface coating of implants with bioactive molecules. The knowledge gained from this work would significantly help to develop future biomaterials and surface coatings of implants and biomedical devices.
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| 22. |
- Berts, Ida, et al.
(author)
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Structure of polymer and particle aggregates in hydrogel composites
- 2013
-
In: Journal of Polymer Science Part B. - : Wiley. - 0887-6266 .- 1099-0488. ; 51:6, s. 421-429
-
Journal article (peer-reviewed)abstract
- Knowledge of the structure of a biomaterial is usually vital to control its function. This article provides a structural characterization of a hyaluronan scaffold that has demonstrated good biocompatibility and is used to induce bone regeneration. Hyaluronan hydrogels are appealing materials that can function as a matrix to incorporate both organic and inorganic substances to enhance tissue growth. Because of the intrinsic properties of this swollen matrix, one needs a very sensitive technique that can be applied in situ to determine the organization of the polymers in a gel. Small-angle neutron scattering is used to determine the characteristics of the inhomogeneous structure of the hydrogel both with and without added particles. The results are interpreted using models of structure with two length scales that are beyond the traditional picture of homogeneous gels. The observed structure and the dimensions can explain the previously reported rheological properties of gels containing different amount of polymers. Hydroxyapatite nanoparticles added to the gel are frozen in the gel matrix. We are able to determine the distribution and shape of these particles as they aggregate around the polymer chains. We have also concluded, in this case, that the particle structure is concentration independent. Information about the nanostructure for an applicable biomaterial guides the formulation, preparation, and use that should lead to further understanding of its exploitation.
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| 23. |
- Berts, Ida, et al.
(author)
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Tuning the density profile of surface-grafted hyaluronan and the effect of counter-ions
- 2013
-
In: European Physical Journal E. - : Springer Science and Business Media LLC. - 1292-8941 .- 1292-895X. ; 36:7, s. 70-
-
Journal article (peer-reviewed)abstract
- The present paper investigates the structure and composition of grafted sodium hyaluronanat a solid-liquid interface using neutron reflection. The solvated polymer at the surface could be described with a density profile that decays exponentially towards the bulk solution. The density profileof the polymer varied depending on the deposition protocol. A single-stage deposition resulted in denser polymer layers, while layers created with a two-stage deposition process were more diffuse and had an overall lower density. Despite the diffuse density profile, two-stage deposition leads to a highersurface excess. Addition of calcium ions causes a strong collapse of the sodium hyaluronan chains, increasing the polymer density near the surface. This effect is more pronounced on the sample prepared by two-stage deposition due to the initial less dense profile. This study provides an understanding at a molecular level of how surface functionalization alters the structure and howsurface layers respond to changes in calcium ions in the solvent.
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| 24. |
- Cárdenas, Marité, et al.
(author)
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Human Saliva Forms a Complex Film Structure on Alumina Surfaces
- 2007
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:1, s. 65-69
-
Journal article (peer-reviewed)abstract
- Films formed from saliva on surfaces are important for the maintenance of oral health and integrity by protection against chemical and/or biological agents. The aim of the present study was to investigate adsorbed amounts, thickness, and structure of films formed from human whole saliva on alumina surfaces by means of in situ ellipsometry, neutron reflectivity, and atomic force microscopy. Alumina (Al2O3, synthetic sapphire) is a relevant and interesting substrate for saliva adsorption studies as it has an isoelectric point close to that of tooth enamel. The results showed that saliva adsorbs rapidly on alumina. The film could be modeled in two layers: an inner and dense thin region that forms a uniform layer and an outer, more diffuse and thicker region that protrudes toward the bulk of the solution. The film morphology described a uniformly covering dense layer and a second outer layer containing polydisperse adsorbed macromolecules or aggregates.
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| 25. |
- Chien, Yu-Chuan, 1990-, et al.
(author)
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Correlations between precipitation reactions and electrochemical performance of lithium-sulfur batteries probed by operando scattering techniques
- 2022
-
In: Chem. - : Elsevier. - 2451-9294. ; 8:5
-
Journal article (peer-reviewed)abstract
- A comprehensive description of electrochemical processes in the positive electrode of lithium-sulfur batteries is crucial for the utilization of active material. However, the discharge mechanisms are complicated due to various reactions in multiple phases and the tortuosity of the highly porous carbon matrix. In this work, simultaneous measurements of small-angle and wide-angle scattering and cell resistance are performed on operating lithium-sulfur cells. Results indicate that precipitates grow mostly in number, not in size, and that the structure of the carbon matrix is not affected. The comparison of the small-angle and wide-angle scattering reveals the amorphous discharge products found at a low discharge rate. Further analysis demonstrates the correlation between the diffusion resistance and the compositional change of electrolyte in the mesopores at the end of discharge, which suggests that Li-ion deficiency is the limiting factor for sulfur utilization at a medium discharge rate.
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| 26. |
- Chien, Yu-Chuan, 1990-, et al.
(author)
-
Mechanistic Insights on the Mesoscale in the Positive Electrode of Lithium–Sulfur Batteries
-
Other publication (other academic/artistic)abstract
- A comprehensive description of the electrochemical processes in the positive electrodeof lithium–sulfur batteries is critical to the enhancement of sulfur utilization. However,the discharge mechanisms are complicated due to the various reactions in multiplephases and the tortuosity of the highly porous carbon matrix. While previous studieshave focused on the precipitation of Li2S, the effect of the limited mass transport insidethe micro-/mesopores of an electrode with optimized surface area have largely beenneglected. In this work, operando small-angle scattering with three different contrasts,and wide-angle scattering, has been performed with simultaneous resistance measure-ment of internal and diffusion. The results indicate that both electrode passivation andcomplete pore blockage are unlikely since the precipitates are surrounded by the elec-trolyte and grow mostly in number, not in size. The difference between the small- andwide-angle scattering reveals the amorphous discharge products at a low C-rate. Furtheranalyses demonstrate the correlation between the diffusion resistance and the contrastin the mesopores at the end of discharge, which suggests that Li-ion deficiency is thelimiting factor of sulfur utilization at a medium C-rate.
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| 27. |
- Cockcroft, Jeremy K., et al.
(author)
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Understanding the structure and dynamics of cationic surfactants from studies of pure solid phases
- 2019
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:47, s. 25945-25951
-
Journal article (peer-reviewed)abstract
- A homologous series of n-alkyl trimethylammonium bromide surfactants, H(CH2)(n)N+(CH3)(3) Br-, from C(10)TAB to C(18)TAB have been studied systematically in the bulk over a wide range of temperatures. Common features in the structures are identified, with packing dominated by the co-ordination of the cationic head groups with bromide anions and interdigitation of the hydrocarbon chains. This arrangement provides an explanation for the thin adsorbed bilayers that have been observed at various hydrophilic surfaces from aqueous solutions in previous studies. The molecular volumes and arrangement are comparable with structures of a number of different self-assembled amphiphiles. For these surfactants with bromide counter-ions, formation of crystal hydrates was not observed. The alkyl chains are highly mobile and at high temperatures a plastic phase is found for all materials with a transition enthalpy that is similar to the melting enthalpy of many long alkyl chains. Other unexpected phase transitions depend more markedly on the hydrocarbon chain length and evidently depend on delicate balances of the various contributions to the free energy.
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| 28. |
- Dicko, Cedric, et al.
(author)
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NUrF-Optimization of in situ UV-vis and fluorescence and autonomous characterization techniques with small-angle neutron scattering instrumentation
- 2020
-
In: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 91:7
-
Journal article (peer-reviewed)abstract
- We have designed, built, and validated a (quasi)-simultaneous measurement platform called NUrF, which consists of neutron small-angle scattering, UV-visible, fluorescence, and densitometry techniques. In this contribution, we illustrate the concept and benefits of the NUrF setup combined with high-performance liquid chromatography pumps to automate the preparation and measurement of a mixture series of Brij35 nonionic surfactants with perfluorononanoic acid in the presence of a reporter fluorophore (pyrene).
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| 29. |
- Gelli, Rita, et al.
(author)
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Modifying the crystallization of amorphous magnesium-calcium phosphate nanoparticles with proteins from Moringa oleifera seeds
- 2021
-
In: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 589, s. 367-377
-
Journal article (peer-reviewed)abstract
- Hypothesis: Endogenous Amorphous Magnesium-Calcium Phosphates (AMCPs) form in the human body and, besides their biomedical implications, the development of effective stabilization strategies is an open challenge. An interesting approach consists of stabilizing amorphous phosphates with macromolecules that have beneficial effects from a nutritional/medical point of view, for a potential application of the hybrid particles in nutraceutics or drug delivery.Experimental: We investigated the effect of proteins extracted from Moringa oleifera seeds (MO) on the features of synthetic analogs of AMCPs and on their crystallization pathway. The stability of the amorphous phase was studied using infrared spectroscopy and X-ray diffraction. To unravel the effect of the protein on the nano-scale structure of the inorganic particles, we also studied how MO affects the features of the amorphous phase using thermal analysis, small angle X-ray scattering and confocal Raman microscopy.Findings: We observed that MO markedly delays the transition from amorphous to crystalline phosphate in a concentration-dependent fashion. Interestingly, MO not only enhances the lifetime of the amorphous phase, but also influences the type and amount of crystalline material formed. The results are relevant from both a fundamental and an applied perspective, paving the way for the use of these hybrids in the field of nutraceutics and drug delivery.
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| 30. |
- Gustafsson, Emil, et al.
(author)
-
Interactions of amphiphiles with plasticisers used in polymers : Understanding the basis of health and environmental challenges
- 2020
-
In: Advances in Colloid and Interface Science. - : ELSEVIER. - 0001-8686 .- 1873-3727. ; 277
-
Journal article (peer-reviewed)abstract
- Plasticisers are widely used to provide desirable mechanical properties of many polymeric materials. These small molecule additives are also known to leach from the finished products, and this not only may modify the physical properties but the distribution of these materials in the environment and in the human body can cause long-term health concerns and environmental challenges. Many of these plasticisers are esters of polyvalent acids and phthalic acid has previously been predominant but various alternatives are now being more widely explored. The eventual distribution of these compounds depends not just on solubility in aqueous media and on vapour pressure but also on their interaction with other materials, particularly lipids and amphiphiles. This review provides an overview of both the basic physical data (solubility, partition coefficients, surface tension, vapour pressure) that is available in the literature and summarises what has been learnt about the molecular interactions of various plasticisers with surfactants and lipids.
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| 31. |
- Gustafsson, Emil, et al.
(author)
-
Understanding interactions of plasticisers with a phospholipid monolayer
- 2024
-
In: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 20:13, s. 2892-2899
-
Journal article (peer-reviewed)abstract
- The use of DEHP (diethylhexyl phthalate) is now banned for most applications in Europe; the exception is for blood bags, where its toxicity is overshadowed by its ability to extend the storage life of red blood cells. Another plasticiser, BTHC (butanoyl trihexyl citrate), is used in paediatric blood bags but does not stabilise blood cells as effectively. Interactions between plasticisers and lipids are investigated with a phospholipid, DMPC, to understand the increased stability of blood cells in the presence of DEHP as well as bioaccumulation and identify differences with BTHC. Mixed monolayers of DMPC and DEHP or BTHC were studied on Langmuir troughs where surface pressure/area isotherms can be measured. Neutron reflection measurements were made to determine the composition and structure of these mixed layers. A large amount of plasticiser can be incorporated into a DMPC monolayer but once an upper limit is reached, plasticiser is selectively removed from the interface at high surface pressures. The upper limit is found to occur between 40–60 mol% for DEHP and 20–40 mol% for BTHC. The areas per molecule are also different with DEHP being in the range of 50–100 Å2 and BTHC being 65–120 Å2. Results indicate that BTHC does not fit as well as DEHP in DMPC monolayers which could help explain the differences observed with regards to the stability of blood cells.
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| 32. |
- Gustafsson, Emil, et al.
(author)
-
Understanding interactions of plasticisers with a phospholipid monolayer
- 2024
-
In: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 20:13, s. 2892-2899
-
Journal article (peer-reviewed)abstract
- The use of DEHP (diethylhexyl phthalate) is now banned for most applications in Europe; the exception is for blood bags, where its toxicity is overshadowed by its ability to extend the storage life of red blood cells. Another plasticiser, BTHC (butanoyl trihexyl citrate), is used in paediatric blood bags but does not stabilise blood cells as effectively. Interactions between plasticisers and lipids are investigated with a phospholipid, DMPC, to understand the increased stability of blood cells in the presence of DEHP as well as bioaccumulation and identify differences with BTHC. Mixed monolayers of DMPC and DEHP or BTHC were studied on Langmuir troughs where surface pressure/area isotherms can be measured. Neutron reflection measurements were made to determine the composition and structure of these mixed layers. A large amount of plasticiser can be incorporated into a DMPC monolayer but once an upper limit is reached, plasticiser is selectively removed from the interface at high surface pressures. The upper limit is found to occur between 40-60 mol% for DEHP and 20-40 mol% for BTHC. The areas per molecule are also different with DEHP being in the range of 50-100 Å2 and BTHC being 65-120 Å2. Results indicate that BTHC does not fit as well as DEHP in DMPC monolayers which could help explain the differences observed with regards to the stability of blood cells.
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| 33. |
- Hellsing, Maja, et al.
(author)
-
Charged Polystyrene Nanoparticles Near a SiO2/Water Interface
- 2019
-
In: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 35:1, s. 222-228
-
Journal article (peer-reviewed)abstract
- Quartz crystal microbalance with dissipation (QCM-D) monitoring is used to investigate the adsorption processes at liquid-solid interfaces and applied increasingly to characterize viscoelastic properties of complex liquids. Here, we contribute new insights into the latter field by using QCM-D to investigate the structure near the interface and the high-frequency viscoelastic properties of charge-stabilized polystyrene particles (radius 37 nm) dispersed in water. The study reveals changes with increasing ionic strength and particle concentration. Replacing water with a dispersion is usually expected to give rise to a decrease in frequency, f. Increases in both f and dissipation, D, were observed on exchanging pure water for particle dispersions at a low ionic strength. The QCM-D data are well-represented by a viscoelastic model, with viscosity increasing from 1.0 to 1.3 mPa s as the particle volume fraction changes from 0.005 to 0.07. This increase, higher than that predicted for noninteracting dispersions, can be explained by the charge repulsion between the particles giving rise to a higher effective volume fraction. It is concluded that the polystyrene particles did not adhere to the solid surface but rather were separated by a layer of pure dispersion medium. The QCM-D response was successfully represented using a viscoelastic Kelvin-Voigt model, from which it was concluded that the thickness of the dispersion medium layer was of the order of the particle-particle bulk separation, in the range of 50-250 nm, and observed to decrease with both particle concentration and addition of salt. Similar anomalous frequency and dissipation responses have been seen previously for systems containing weakly adherent colloidal particles and bacteria and understood in terms of coupled resonators. We demonstrate that surface attachment is not required for such phenomena to occur, but that a viscoelastic liquid separated from the oscillating surface by a thin Newtonian layer gives rise to similar responses.
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| 34. |
- Hellsing, Maja S., 1975-
(author)
-
Adsorption and Ordering of Surface Active Molecules and Particles at Solid Interfaces and in the Bulk
- 2012
-
Doctoral thesis (other academic/artistic)abstract
- Factors that influence the process of adsorption and order of dilute and concentrated systems of molecules and particles are explored in this thesis. The results are based largely on neutron scattering techniques. Study of the adsorption from dilute solutions of a common surfactant, AOT (sodium bis (2-ethylhexyl) sulfosuccinate), at a solid/liquid interface showed that AOT molecules adsorbed to the interface in a bilayer structure, with the hydrocarbon tails at maximum packing density even at very low concentrations. At higher AOT concentrations, a stack of fluctuating layers each separated by large amounts of water next to the dense bilayer was seen. The driving force for adsorption is dominated by self-assembly of AOT. It was found that an oriented lamellar phase wets the interface below the bulk concentration for formation of this phase.Proteins can be viewed as polymeric surfactants. The adsorption of proteins from seeds of the Moringa oleifera tree to a silicon oxide surface was studied to elucidate the mechanism of the protein as a flocculent in water treatment processes. The protein was found to adsorb at the interface as dense layers with a thickness suggestive of co-adsorption rather than single isolated molecules. The strong adsorption and tendency to associate in solution suggest mechanisms for flocculating particulate impurities in water.As with surfactants, dispersions of colloidal particles can assemble in regular structures by self-assembly. Polystyrene latex particles were studied and could form large three-dimensional crystals of about 1×1 cm2 in a 2 mm path cell. The diffraction pattern indicated a close packed structure with the 110 axis perpendicular to the container wall. The crystal was well-aligned and oriented by the direction of flow. At the solid interface large two-dimensional domains of about 20 cm2 of highly oriented particles were formed. The particle-particle separation at the surface and in the bulk was determined by the charge repulsion of the particles.
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| 35. |
- Hellsing, Maja S., et al.
(author)
-
Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces
- 2012
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:22, s. 221601-
-
Journal article (peer-reviewed)abstract
- We report on the formation of large two-dimensional domains (about 20 cm2) of oriented and ordered structures of polystyrene particles dispersed in water at a solid/liquid interface. Gentle flow of the dispersed sample into the holder at a shear strain rate of about 0.1 s−1 caused particles at the air/latex meniscus to self-assemble in a regular structure on both solid silica or alumina surfaces. Scattering experiments show that the particle separation at the surface was the same as in the bulk and determined by repulsion arising from the charges on the particles. Close-packed planes formed parallel to the interface.
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| 36. |
- Hellsing, Maja S., et al.
(author)
-
Effect of Concentration and Addition of Ions on the Adsorption of Aerosol-OT to Sapphire
- 2010
-
In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:18, s. 14567-14573
-
Journal article (peer-reviewed)abstract
- Aerosol-OT (sodium bis 2-ethylhexyl sulfosuccinate or NaAOT) adsorbs to hydrophilic sapphire solid surfaces The structure of the formed bilayer has been determined over the concentration range 0 2-7 4mM NaAOT It was found that the hydrocarbon tails pack at maximum packing limit at very low concentrations, and that the thickness of the bilayer was concentration-independent The adsorption was found to increase with concentration, with the surfactant molecules packing closer laterally The area per molecule was found to change from 138 +/- 25 to 51 +/- 4 angstrom(2) over the concentration range studied, with the thickness of the layer being constant at 33 2 A Addition of small amounts of salt was found to increase the surface excess, with the bilayer being thinner with a slightly larger area per molecule Addition of different salts of the same valency was found to have a very similiar effect, as had the addition of NaOH and HCl Hence, the effects of adding acid or base should be considered an effect of ionic strength rather than an effect of pH Adsorption of NaAOT to the sapphire surface that carries an opposite charge to the anionic surfactant is similar in many respects to the adsorption reported previously for hydrophilic and hydrophobic silica surfaces This suggests that the adsorption of NaAOT to a sui face is driven primarily by NaAOT self-assembly rather than effects of electrostatic at to the interface
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| 37. |
- Hellsing, Maja S., et al.
(author)
-
Scattering from Dilute and Lamellar Phase Solutions of Aerosol-OT Simultaneous Probe of Surface Structures and Bulk
- 2011
-
In: Trends in colloid andinterface science XXIV. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642190377 ; , s. 139-142
-
Conference paper (peer-reviewed)abstract
- The benefits of simultaneous studies of adsorbed layers and bulk structures are shown for solutions of the surfactant Aerosol-OT. Above the critical micelle concentration, Aerosol-OT forms an aligned lamellar phase at the sapphire/solution interface which is in equilibrium with a bulk phase that consists of coexisting micellar solution and dispersed lamellar phase. Measurements of the aligned surface layers and the bulk scattering from a 2% wt solution by grazing incidence and small-angle neutron scattering show that the bulk consist of lamellar structures with the same d-spacing as seen at the surface but without the surface induced alignment. The surface lamellar structure corresponds to a 10% volume fraction for a 2% wt bulk which implies that there must be coexistence of regions of different concentration. Scattering patterns measured in grazing incidence geometry clearly show the relative contributions from small-angle scattering and specular reflectivity.
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| 38. |
- Hellsing, Maja S., et al.
(author)
-
Structure of a large colloidal crystal : controlling orientation and three-dimensional order
- 2012
-
In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 2:18, s. 7091-7098
-
Journal article (peer-reviewed)abstract
- The three-dimensional crystal structure of charge stabilised polystyrene latex in deionised water was investigated by small-angle neutron diffraction. Crystallisation with a grain size of approximately 1 x 1 cm(2) was observed when the sample was flowed gently in to a 2 mm path cell. Bragg scattering peaks arising from the structure were observed under rotation about three perpendicular axes of the sample. The diffraction patterns indicate clearly that there is a cubic close packed structure with a 110 axis perpendicular to the cell wall. Rotations in small steps show large changes and indicate that the crystal is well oriented and has three-dimensional order. The crystal orientation was controlled by the meniscus and direction of flow when filling the cell.
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| 39. |
- Hellsing, Maja S., et al.
(author)
-
Structure of flocs of latex particles formed by addition of protein from Moringa seeds
- 2014
-
In: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 460, s. 460-467
-
Journal article (peer-reviewed)abstract
- Proteins extracted from the seeds of Moringa trees are effective flocculents for particles dispersed in water and are attractive as a natural and sustainable product for use in water purification. Studies with a model system consisting of polystyrene latex particles have shown that the protein adsorbs to the surface and causes flocculation as unusually dense aggregates. Small-angle neutron scattering that exploits contrast matching of deuterated latex particles dispersed in D2O to highlight bound protein has shown that the adsorbed amount reaches about 3 mg m(-2). The particles form very compact flocs that are characterized by fractal dimensions that approach the theoretical maximum of 3. Ultra small-angle neutron scattering allows these flocs to be characterized for a range of particle and protein concentrations. Proteins from two species of Moringa trees were investigated. The protein from Moringa stenopetala seeds gave rise to slightly lower fractal dimensions compared to Moringa oleifera, but still much larger than values observed for conventional ionic or polymeric flocculents that are in the range 1.75-2.3. Compact flocs are desirable for efficient separation of impurities and dewatering of sludge as well as other applications. A trend of increasing fractal dimension with particle concentration was observed when M. stenopetala seed protein was used and this resembles the behaviour predicted in Brownian dynamics simulation of flocculation. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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| 40. |
- Hemming, Joanna M., et al.
(author)
-
Changes to lung surfactant monolayers upon exposure to gas phase ozone observed using X-ray and neutron reflectivity
- 2022
-
In: Environmental Science. - : Royal Society of Chemistry. - 2634-3606. ; 2:4, s. 753-760
-
Journal article (peer-reviewed)abstract
- Exposure to the secondary pollutant ozone in ambient air is associated with adverse health effects when inhaled. In this work we use surface pressure measurements, combined with X-ray and neutron reflection, to observe changes in a layer of lung surfactant at the air water interface when exposed to gas phase ozone. The results demonstrate that the layer reacts with ozone changing its physical characteristics. A slight loss of material, a significant thinning of the layer and increased hydration of the surfactant material is observed. The results support the hypothesis that unsaturated lipids present in lung surfactant are still susceptible to rapid reaction with ozone and the reaction changes the properties of the interfacial layer.
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| 41. |
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| 42. |
- Jones, Stephanie H., et al.
(author)
-
Aqueous Radical Initiated Oxidation of an Organic Monolayer at the Air-Water Interface as a Proxy for Thin Films on Atmospheric Aerosol Studied with Neutron Reflectometry
- 2023
-
In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:42, s. 8922-8934
-
Journal article (peer-reviewed)abstract
- Neutron reflectometry has been used to study the radical initiated oxidation of a monolayer of the lipid 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) at the air–solution interface by aqueous-phase hydroxyl, sulfate, and nitrate radicals. The oxidation of organic films at the surface of atmospheric aqueous aerosols can influence the optical properties of the aerosol and consequently can impact Earth’s radiative balance and contribute to modern climate change. The amount of material at the air–solution interface was found to decrease on exposure to aqueous-phase radicals which was consistent with a multistep degradation mechanism, i.e., the products of reaction of the DSPC film with aqueous radicals were also surface active. The multistep degradation mechanism suggests that lipid molecules in the thin film degrade to form progressively shorter chain surface active products and several reactive steps are required to remove the film from the air–solution interface. Bimolecular rate constants for oxidation via the aqueous phase OH radical cluster around 1010 dm3 mol–1 s–1. Calculations to determine the film lifetime indicate that it will take ∼4–5 days for the film to degrade to 50% of its initial amount in the atmosphere, and therefore attack by aqueous radicals on organic films could be atmospherically important relative to typical atmospheric aerosol lifetimes.
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| 43. |
- Jones, Stephanie H., et al.
(author)
-
Are organic films from atmospheric aerosol and sea water inert to oxidation by ozone at the air-water interface?
- 2017
-
In: Atmospheric Environment. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1352-2310 .- 1873-2844. ; 161, s. 274-287
-
Journal article (peer-reviewed)abstract
- The heterogeneous oxidation of thin films of organic material extracted from real aerosol and sea-water samples was studied at the air-water interface using X-ray reflectivity. Oxidation of thin films of organic material extracted from real aerosol and sea-water is important in further understanding the impact of coated aerosols on the climate of the Earth. Surface active insoluble organic material extracted from the atmosphere was found to form stable films at the air-water interface (thickness measured as 10-14 nm). On exposure of the films to gas-phase ozone, no reaction (or change in the relative scattering length of the interface) was observed, indicating a potential lack of unsaturated organic material in the samples. Gas chromatography and electrospray ionization mass spectrometry showed the presence of saturated compounds in the samples. It is therefore proposed that the amount of unsaturated compounds as compared to saturated compounds in the atmospheric material is so low that the mass spectrometry analyses, as well as gas-phase oxidation are dominated by saturated material. A reaction was observed on exposure of the same films to aqueous phase hydroxyl and nitrate radicals and a film thinning mechanism is proposed to explain the change in scattering length of the film at the air-water interface. It can be suggested tentatively that oxidation by gas-phase ozone is not important in the atmosphere for organic films on aqueous atmospheric aerosol and that further studies should focus on radical induced oxidation of saturated organic material instead of unsaturated proxies that are typically studied.
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| 44. |
- Kasper, S, et al.
(author)
-
Selective activation of the probasin androgen-responsive region by steroid hormones
- 1999
-
In: Journal of molecular endocrinology. - : Bioscientifica. - 0952-5041 .- 1479-6813. ; 22:3, s. 313-325
-
Journal article (peer-reviewed)abstract
- Glucocorticoid and androgen receptors have been shown to function through the same palindromic glucocorticoid response element (GRE) and yet have differential effects on gene transcription. In this study, we examined the functional and structural relationship of the androgen and glucocorticoid receptors with the androgen responsive region (ARR) of the probasin (PB) gene containing two androgen receptor binding sites, ARBS-1 and ARBS-2. Transfection studies indicated that one copy of each cis-acting DNA element was essential for maximal androgen-induced chloramphenicol acetyltransferase (CAT) activity and that androgen selectivity was maintained when multiple copies of the minimal wild type (wt) androgen responsive region containing both ARBS-1 and ARBS-2 (-244 to -96) were subcloned in front of the thymidine kinase promoter. Furthermore, replacing the androgen response region with 1, 2 or 3 copies of either ARBS-1 or ARBS-2 restored less than 4% of the biological activity seen with the wt PB ARR. Multiple copies of either ARBS-1 or ARBS-2 did not result in glucocorticoid-induced CAT gene activity. By comparison, 1 or 2 copies of the tyrosine aminotransferase (TAT) GRE, as well as the mouse mammary tumour virus GRE, were strong inducers of CAT activity in response to both androgen and glucocorticoid treatment. In addition, band shift assays demonstrated that although the synthetic glucocorticoid receptor, GR-DNA binding domain (GR-DBD), and the synthetic androgen receptor, AR2, could interact with the TAT GRE (dissociation constants Kd of 63.9 and 14.1 respectively), only AR2 but not GR-DBD binding could be detected on ARBS-1 and ARBS-2. Our findings provide further evidence that androgen-induced regulation of gene transcription can occur through androgen-specific DNA binding sites that are distinct from the common GRE.
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| 45. |
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| 46. |
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| 47. |
- King, Martin D., et al.
(author)
-
Oxidation of oleic acid at the air-water interface and its potential effects on cloud critical supersaturations
- 2009
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:35, s. 7699-7707
-
Journal article (peer-reviewed)abstract
- The oxidation of organic films on cloud condensation nuclei has the potential to affect climate and precipitation events. In this work we present a study of the oxidation of a monolayer of deuterated oleic acid (cis-9-octadecenoic acid) at the air-water interface by ozone to determine if oxidation removes the organic film or replaces it with a product film. A range of different aqueous sub-phases were studied. The surface excess of deuterated material was followed by neutron reflection whilst the surface pressure was followed using a Wilhelmy plate. The neutron reflection data reveal that approximately half the organic material remains at the air-water interface following the oxidation of oleic acid by ozone, thus cleavage of the double bond by ozone creates one surface active species and one species that partitions to the bulk (or gas) phase. The most probable products, produced with a yield of similar to(87 +/- 14)%, are nonanoic acid, which remains at the interface, and azelaic acid (nonanedioic acid), which dissolves into the bulk solution. We also report a surface bimolecular rate constant for the reaction between ozone and oleic acid of (7.3 +/- 0.9) x 10(-11) cm(2) molecule s(-1). The rate constant and product yield are not affected by the solution sub-phase. An uptake coefficient of ozone on the oleic acid monolayer of similar to 4 x 10(-6) is estimated from our results. A simple Kohler analysis demonstrates that the oxidation of oleic acid by ozone on an atmospheric aerosol will lower the critical supersaturation needed for cloud droplet formation. We calculate an atmospheric chemical lifetime of oleic acid of 1.3 hours, significantly longer than laboratory studies on pure oleic acid particles suggest, but more consistent with field studies reporting oleic acid present in aged atmospheric aerosol.
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| 48. |
- King, Martin D., et al.
(author)
-
The reaction of oleic acid monolayers with gas-phase ozone at the air water interface : the effect of sub-phase viscosity, and inert secondary components
- 2020
-
In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 22:48, s. 28032-28044
-
Journal article (peer-reviewed)abstract
- Organic films that form on atmospheric particulate matter change the optical and cloud condensation nucleation properties of the particulate matter and consequently have implications for modern climate and climate models. The organic films are subject to attack from gas-phase oxidants present in ambient air. Here we revisit in greater detail the oxidation of a monolayer of oleic acid by gas-phase ozone at the air-water interface as this provides a model system for the oxidation reactions that occur at the air-water interface of aqueous atmospheric aerosol. Experiments were performed on monolayers of oleic acid at the air-liquid interface at atmospherically relevant ozone concentrations to investigate if the viscosity of the sub-phase influences the rate of the reaction and to determine the effect of the presence of a second component within the monolayer, stearic acid, which is generally considered to be non-reactive towards ozone, on the reaction kinetics as determined by neutron reflectometry measurements. Atmospheric aerosol can be extremely viscous. The kinetics of the reaction were found to be independent of the viscosity of the sub-phase below the monolayer over a range of moderate viscosities, eta/eta water = 1.0-7.2, demonstrating no involvement of aqueous sub-phase oxidants in the rate determining step. The kinetics of oxidation of monolayers of pure oleic acid were found to depend on the surface coverage with different behaviour observed above and below a surface coverage of oleic acid of similar to 1 x 10(18) molecule m(-2). Atmospheric aerosol are typically complex mixtures, and the presence of an additional compound in the monolayer that is inert to direct ozone oxidation, stearic acid, did not significantly change the reaction kinetics. It is demonstrated that oleic acid monolayers at the air-water interface do not leave any detectable material at the air-water interface, contradicting the previous work published in this journal which the authors now believe to be erroneous. The combined results presented here indicate that the kinetics, and thus the atmospheric chemical lifetime for unsaturated surface active materials at the air-water interface to loss by reaction with gas-phase ozone, can be considered to be independent of other materials present at either the air-water interface or in the aqueous sub-phase.
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| 49. |
- Kwaambwa, Habauka M., et al.
(author)
-
Interaction of Moringa oleifera seed protein with a mineral surface and the influence of surfactants
- 2015
-
In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 448, s. 339-346
-
Journal article (peer-reviewed)abstract
- The paper describes the adsorption of purified protein from seeds of Moringa olelfera to a sapphire interface and the effects of addition of the anionic surfactant sodium dodecylsulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB). Neutron reflection was used to determine the structure and composition of interfacial layers adsorbed at the solid/solution interface. The maximum surface excess of protein was found to be about 5.3 mg m(-2). The protein does not desorb from the solid/liquid interface when rinsed with water. Addition of SDS increases the reflectivity indicating co-adsorption. It was observed that CTAB is able to remove the protein from the interface. The distinct differences to the behavior observed previously for the protein at the silica/water interface are identified. The adsorption of the protein to alumina in addition to other surfaces has shown why it is an effective flocculating agent for the range of impurities found in water supplies. The ability to tailor different surface layers in combination with various surfactants also offers the potential for adsorbed protein to be used in separation technologies.
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| 50. |
- Kwaambwa, Habauka M., et al.
(author)
-
Interactions of surfactants with a water treatment protein from Moringa oleifera seeds in solution studied by zeta-potential and light scattering measurements
- 2012
-
In: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 97:4, s. 209-218
-
Journal article (peer-reviewed)abstract
- Protein extracted from Moringa oleifera (MO) seeds has been advocated as a cheap and environmental friendly alternative to ionic flocculants for water purification. However, the nature and mechanism of its interaction with particles in water, as well as with dissolved surface-active molecules, are not well understood. In this article, we report studies of the protein and its interaction with four surfactants using dynamic light scattering (DLS), zeta-potential and turbidity measurements. Zeta-potential measurements identified points of charge reversal and the turbidity and DLS measurements were used to characterize the microstructure and size of protein-surfactant complexes. From the points of charge reversal, it was estimated that 7 anions are required to neutralize the positive charges of each protein molecule at pH 7. For protein mixtures with sodium dodecyl sulfate and dodecyl di-acid sodium salt, the peak in turbidity corresponds to concentrations with a large change in zeta-potential. No turbidity was observed for protein mixtures with either the nonionic surfactant Triton X-100 or the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate. Changes of pH in the range 410 have little effect on the zeta-potential, turbidity, and the hydrodynamic radius reflecting the high isoelectric point of the protein. Addition of small amounts of salt has little effect on the size of protein in solution. These results are discussed in the context of the use of the MO protein in water treatment.
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