| 1. |
- Arnebrant, Thomas, et al.
(författare)
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Protein-surfactant interactions at solid surfaces
- 1995
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Ingår i: Proteins at Interfaces II Fundamentals and Applications. - Washington, DC : American Chemical Society. - 9780841233041 - 9780841215276 ; 602, s. 239-255
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Bokkapitel (refereegranskat)abstract
- Effects of surfactants on protein adsorption are reviewed. Differences between removal of preadsorbed proteins (elutability) and competitive adsorption are discussed and simple models are suggested. It can be concluded that surfactants may interact through solubilization or replacement mechanisms depending on surfactant- surface interactions and surfactant- protein binding. Solubilization requires complex formation between protein and surfactant, and the replacement adsorption of the surfactant to the surface. As for protein adsorption, one of the most important properties affecting the elutability appears to be the conformational stability. Differences between a competitive situation and addition of surfactant after adsorption of the protein are suggested to originate from alteration in surface activity of protein-surfactant complexes formed in solution as compared to pure protein, the difference in diffusivity of surfactants and protein, and time dependent conformational changes of the protein.
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| 2. |
- Cárdenas, Marité, et al.
(författare)
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Human Saliva Forms a Complex Film Structure on Alumina Surfaces
- 2007
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:1, s. 65-69
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Tidskriftsartikel (refereegranskat)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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| 3. |
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| 4. |
- Maric, Selma, et al.
(författare)
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Time-resolved small-angle neutron scattering as a probe for the dynamics of lipid exchange between human lipoproteins and naturally derived membranes
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Atherosclerosis is the main killer in the western world. Today's clinical markers include the total level of cholesterol and high-/low-density lipoproteins, which often fails to accurately predict the disease. The relationship between the lipid exchange capacity and lipoprotein structure should explain the extent by which they release or accept lipid cargo and should relate to the risk for developing atherosclerosis. Here, small-angle neutron scattering and tailored deuteration have been used to follow the molecular lipid exchange between human lipoprotein particles and cellular membrane mimics made of natural, "neutron invisible" phosphatidylcholines. We show that lipid exchange occurs via two different processes that include lipid transfer via collision and upon direct particle tethering to the membrane, and that high-density lipoprotein excels at exchanging the human-like unsaturated phosphatidylcholine. By mapping the specific lipid content and level of glycation/oxidation, the mode of action of specific lipoproteins can now be deciphered. This information can prove important for the development of improved diagnostic tools and in the treatment of atherosclerosis.
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| 5. |
- Yeung, Sing Yee, et al.
(författare)
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Reversible Self-Assembled Monolayers (rSAMs) as Robust and Fluidic Lipid Bilayer Mimics
- 2018
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 34:13, s. 4107-4115
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Tidskriftsartikel (refereegranskat)abstract
- Lipid bilayers, forming the outer barrier of cells, display a wide array of proteins and carbohydrates for modulating interfacial biological interactions. Formed by the spontaneous self-assembly of lipid molecules, these bilayers feature liquid crystalline order, while retaining a high degree of lateral mobility. Studies of these dynamic phenomena have been hampered by the fragility and instability of corresponding biomimetic cell membrane models. Here, we present the construct of a series of oligoethylene glycol-terminated reversible self-assembled monolayers (rSAMs) featuring lipid-bilayer-like fluidity, while retaining air and protein stability and resistance. These robust and ordered layers were prepared by simply immersing a carboxylic acid terminated self-assembled monolayer into 5-50 mu M aqueous omega-(4-ethylene glycol-phenoxy)-alpha-(4-amidinophenoxy)decane solutions. It is anticipated that this new class of robust and fluidic two-dimensional biomimetic surfaces will impact the design of rugged cell surface mimics and high-performance biosensors.
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| 6. |
- Andoralov, Viktor, et al.
(författare)
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Flexible micro(bio)sensors for quantitative analysis of bioanalytes in a nanovolume of human lachrymal liquid
- 2013
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Ingår i: Analytical and Bioanalytical Chemistry. - : Springer. - 1618-2642 .- 1618-2650. ; 405:11, s. 3871-3879
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Tidskriftsartikel (refereegranskat)abstract
- A flexible electrochemical micro(bio)sensor has been designed for determination of several biological compounds, specifically, ascorbate, dopamine, and glucose, in human lachrymal liquid (tears). The microsensor for simultaneous determination of ascorbate and dopamine concentrations was based on a gold microwire modified with the tetrathiafulvalen–7,7,8,8-tetracyanoquinodimethane complex as a catalyst. To monitor glucose concentration in tears, glucose dehydrogenase was immobilized on a gold microwire modified with carbon nanotubes and an osmium redox polymer. A capillary microcell was constructed for sampling tears. The cell had a working volume of 60–100 nL with a sampling deviation of 6.7 %. To check if the microcell was properly filled with buffer or tear sample, a control electrode was introduced into the construction. The electrode was used to measure the electrical resistance of a fully filled nanovolume cell. The mechanical flexibility is one of the most important features of the prototype and allowed direct collection of tears with minimized risk of damage to the eye.
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| 7. |
- Arnebrant, Thomas, et al.
(författare)
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Adsorption of chlorhexidine and black tea onto in vitro salivary pellicles, as studied by ellipsometry
- 2006
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Ingår i: European Journal of Oral Sciences. - : Wiley. - 0909-8836 .- 1600-0722. ; 114, s. 337-342
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption from 0.2% (w/w) chlorhexidine and black tea solutions onto an in vitro pellicle from whole unstimulated saliva on hydroxyapatite discs was studied by ellipsometry. It was found that chlorhexidine adsorbed to the pellicle causing a modification of the pellicle properties, leading to a subsequent increase in adsorption of salivary and black tea components. There was a distinct order of addition effect, whereby chlorhexidine followed by black tea gave an overall greater adsorption of components compared to black tea followed by chlorhexidine. This increase in adsorption gave a concomitant increase in colour or stain as measured by a reflectance chromameter. The increase in adsorbed amounts and stain was modified in part by the adsorption of salivary fractions between the chlorhexidine and black tea treatments. In all cases, the chlorhexidine and black tea modified pellicles were not readily removed by either phosphate or sodium dodecyl sulphate rinses. Thus, following chlorhexidine exposure, the accelerated adsorption of salivary and black tea components can ultimately lead to increased staining of the pellicle.
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| 8. |
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| 9. |
- Arnebrant, Thomas, et al.
(författare)
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Lubricating Properties of the Initial Salivary Pellicle
- 2003
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Ingår i: Biofouling (Print). - : Harwood Academic Publishers. - 0892-7014 .- 1029-2454. ; 19:6, s. 365-369
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Tidskriftsartikel (refereegranskat)abstract
- The role of saliva in the oral cavity is manifold; an important function is to serve as lubricant between hard (enamel) and soft (mucosal) tissues. Intraoral lubrication is of crucial importance in order to maintain functions such as deglutition, mastication and the faculty of speech. A large number of people suffer from impaired salivary functions, displaying symptoms such as 'dry mouth'. This results in a need for methods to assess the lubricating properties of both native saliva and potential artificial saliva formulations. Here, normal as well as lateral forces, acting between adsorbed salivary films, have been measured for the first time by means of colloidal probe atomic force microscopy (AFM). It was found that the presence of salivary pellicles between hard surfaces reduces the friction coefficient by a factor of 20. This reduction of friction is consistent with the long-range purely repulsive nature of the normal forces acting between the salivary films. The lubricating mechanism is presumably based on a full separation of the sliding surfaces by the salivary films. The friction between salivary films has been investigated at normal loads that cover the clinical jaw closing forces, and it can be concluded that the lubricating properties are maintained within this load interval. The present study indicates the usefulness of colloidal probe AFM, which offers a direct and quantitative measure of lubrication at a molecular level, in the study of biotribological phenomena. In particular, the results obtained here may have implications for the development of saliva substitutes.
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| 10. |
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| 11. |
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| 12. |
- Aroonsang, Watcharapong, et al.
(författare)
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Influence of substratum hydrophobicity on salivary pellicles : organization or composition?
- 2014
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Ingår i: Biofouling (Print). - : Taylor & Francis. - 0892-7014 .- 1029-2454. ; 30:9, s. 1123-1132
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Tidskriftsartikel (refereegranskat)abstract
- Different physico-chemical properties (eg adsorption kinetics, thickness, viscoelasticity, and mechanical stability) of adsorbed salivary pellicles depend on different factors, including the properties (eg charge, roughness, wettability, and surface chemistry) of the substratum. Whether these differences in the physico-chemical properties are a result of differences in the composition or in the organization of the pellicles is not known. In this work, the influence of substratum wettability on the composition of the pellicle was studied. For this purpose, pellicles eluted from substrata of different but well-characterized wettabilities were examined by means of sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that substratum hydrophobicity did not have a major impact on pellicle composition. In all substrata, the major pellicle components were found to be cystatins, amylases and large glycoproteins, presumably mucins. In turn, interpretation of previously reported data based on the present results suggests that variations in substratum wettability mostly affect the organization of the pellicle components.
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| 13. |
- Barrantes, Alejandro, et al.
(författare)
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Characteristics of saliva films adsorbed onto different dental materials studied by QCM-D
- 2014
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Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 442:Special issue: Selected papers from the 26th European Colloid and Interface Society conference (26th ECIS 2012), s. 56-62
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Tidskriftsartikel (refereegranskat)abstract
- The formation of salivary films onto different surfaces relevant in dental research like titania, hydroxyapatite, gold, zirconia, silica, and hydrophobized silica has been studied by means of QCM-D. Human whole saliva (HWS), and sterile filtered HWS (sHWS) both diluted in water to a final concentration of 25% (v/v) were used. Main differences between the salivary films formed from the two saliva types were observed with the help of ΔD vs Δf plots where sHWS samples showed an almost linear adsorption regime for most of the surfaces whereas most of the HWS samples had a marked multi-regime nature indicating that the former ones are homogenous and the later are heterogeneous supporting previous data on a multi-phase adsorption process. The films with highest shear elastic modulus, μ > 105 N m−2, shear viscosity, η ∼ 3 × 10−3 N s m−2, and lowest thickness (∼10 nm) were formed for both types of saliva onto hydroxyapatite and for sHWS on titania. Furthermore, the ratio between the loss, G″, and the storage modulus, G′, indicates that these films have a solid-like behavior (G″/G′ ≤ 0.5). In contrast, for the remaining surfaces the adsorbed films show higher d values and are also characterized by low μ ∼ 104 N m−2, η ∼ 10−3 N s m−2, and by high ratios, G″/G′ > 2, that indicate a fluid like behavior. These observations might be expected to have influence on the lubricating properties of the salivary films. The SDS induced elutability also indicates a different interaction strength and composition of the adsorbed films and is likely associated with the ease by which these surfaces can be cleaned. Our results suggest that, among the relevant materials, zirconia and titania would yield the more lubricious films whereas hydroxyapatite will be the most easily cleaned.
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| 14. |
- Barrantes, Alejandro, et al.
(författare)
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Influence of pH on the build-up of poly-L-lysine/heparin multilayers
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 388:1, s. 191-200
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Tidskriftsartikel (refereegranskat)abstract
- The effect of pH on the build-up-of polyelectrolyte multilayers, PEMs, composed by poly-L-lysine and heparin onto two different substrates, silica and gold, has been studied by means of ellispmetry and quartz crystal microbalance with dissipation, QCM-D. Ellipsometry results indicate that the dry mass grows exponentially with the number of layers, and that this amount is larger as the pH values are raised. From QCM-D data the viscoelastic properties of the multilayered structure have been obtained. These data reflect that PEMs become more viscoelastic as the pH values are increased for silica substrates, while for gold the highest viscoelastic behavior is obtained at neutral pH and the elastic behavior becomes dominant as the pH is further increased or decreased. By combining these two surface techniques it has been also possible to determine the solvent content in the multilayers and reach a deeper understanding of the internal structure.
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| 15. |
- Barrantes, Alejandro, et al.
(författare)
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Poly-L-lysine/heparin multilayer coatings prevent blood protein adsorption
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 485, s. 288-295
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of blood proteins, serum albumin (BSA), immunoglobulin G (IgG) and fibrinogen (FGN), onto model SiO2 planar surfaces coated with poly-L-lysine/heparin multilayers (PLL/HEP) has been investigated by means of ellipsometry and quartz crystal microbalance with dissipation. Aiming at the development of low fouling coatings, this study has been focused on the effects that the number of layers and the type of polyelectrolyte present on the topmost layer have on the adsorption of these proteins. The three proteins interact with PLL-ended coatings whereas HEP-ended coatings prevent the adsorption of both BSA and IgG and induce a decrease in the adsorbed amount of FGN, down to 0.4 mg/m(2) for three bilayers, as the number of PLL/HEP bilayers increases. These results suggest that heparin-ended multilayers prevent protein adsorption, which is an indicative of good blood compatibility. As a consequence we propose that PLL/HEP coatings could be used for the development of vascular medical devices. (C) 2016 Elsevier Inc. All rights reserved.
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| 16. |
- Benesch, Johan, 1969-
(författare)
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Null Ellipsometry and Protein Adsorption to Model Biomaterials
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When implants are inserted into the human body cascades of events become started that will determine the outcome of wound healing and ultimately the success of the implantation. The events start with the adsorption of small molecules, and proteins that may be activated (enzymes) or are able to activate cells of the immune defense and the healing process. In the biomaterials research that is conducted in our group we often ask two questions: "How much?" and "What?" proteins adsorb to a specific surface after incubation in serum or plasma. In the first two papers in this thesis I studied how well we are able to determine the answer to the first question. In the latter two works I tried to answer both questions for two model biomaterial surfaces: oligo(ethylene glycol) terminated self assembled monolayers on gold and chitosan coated silicon.In many null ellipsometric studies the protein film refractive, Nfilm, is assumed to be close to 1.5. In the first paper we analyzed if the assumption of Nfilm = 1.465 is satisfactory for the determination of the surface mass density of a submonolayer thin protein film. Human serum albumin (HSA) was labeled with 125I and mixed with non-labeled HSA, and hydrophobic and hydrophilic silicon pieces were incubated in the solutions. The surface mass densities on all pieces determined by both ellipsometry and gamma counter measurements, and was pair-wise compared. The above assumption regarding the value of Nfilm for the agreement between the methods was satisfactory, although precautions have to be made not to overestimate the surface mass density when studying radiolabelled proteins, especially at rough surfaces.Are the assumptions made in Paper I also true for up to 100 nm thick protein films or do we have to use a different protein film refractive index and do the ellipsometric model still hold? Human serum albumin (HSA) and polyclonal anti-HSA were labeled with 125I and mixed with unlabelled proteins. Hydrophobic silicon pieces were alternatingely incubated in the two protein solutions. Again the surface mass density was quantified with null ellipsometry and a gamma counter and the methods compared. The thickest protein layers were also gently scratched and the thickness measured by AFM. It appeared that a protein film refractive index Nfilm = 1.5 was a good choice for the determination of the protein film thickness. However, in order to obtain a good methods agreement for the adsorbed mass density a linear correction term was needed in the Cuypers surface mass density formula for ellipsometry. The physical interpretation of the correction term is presently unclear.Self assembled monolayers (SAMs) containing oligo (ethyleneglycol) end groups (OEG) have been successfully used to minimize protein adsorption from single protein solutions. We investigated the protein resistance in a fibrinogen solution, serum and plasma of OEG-SAMs with an increasing number of OEG units and with different end groups. It turned out that the adsorbed amounts after 10 minutes of plasma incubation and 15 minutes of fibrinogen incubation decreased with an increasing number of EG units. In serum, the total deposition and subsequent deposition of antibodies towards complement proteins (C3c, C3d and properdin) did not depend on the number of EG units. In summary, the investigated OEG-SAMs were not protein resistant in complex solutions, although the adsorbed amounts varied with the number of EG units and the terminal chemical group. Complement deposition was observed at OEG surfaces.For the last 50 odd years different polysaccharides, such as heparin and cellulose have been used for clinical applications and in recent years also chitin and its deacetylated form chitosan have gained increasing attention as potential biomaterials. Previous studies on complement activation by chitosan derivatives have focused on the soluble complement factors and not the surface bound ones that may be important for the binding of cells to surfaces. In our study about 10 nm thick chitosan films were incubated in plasma or serum and subsequently in polyclonal antibodysolutions. The films did not activate complement and the intrinsic pathway of coagulational though fibrinogen was detectable after plasma incubations. When the chitosan film was acetylated it became a strong alternative complement pathway activator in serum and fibrinogen was then no longer antibody detectable after plasma incubations.
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| 17. |
- Boyd, Hannah, 1994-, et al.
(författare)
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A comparison between the structures of reconstituted salivary pellicles and oral mucin (MUC5B) films.
- 2021
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 584, s. 660-668
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Tidskriftsartikel (refereegranskat)abstract
- HYPOTHESIS: Salivary pellicles i.e., thin films formed upon selective adsorption of saliva, protect oral surfaces against chemical and mechanical insults. Pellicles are also excellent aqueous lubricants. It is generally accepted that reconstituted pellicles have a two-layer structure, where the outer layer is mainly composed of MUC5B mucins. We hypothesized that by comparing the effect of ionic strength on reconstituted pellicles and MUC5B films we could gain further insight into the pellicle structure.EXPERIMENTS: Salivary pellicles and MUC5B films reconstituted on solid surfaces were investigated at different ionic strengths by Force Spectroscopy, Quartz Crystal Microbalance with Dissipation, Null Ellipsometry and Neutron Reflectometry.FINDINGS: Our results support the two-layer structure for reconstituted salivary pellicles. The outer layer swelled when ionic strength decreased, indicating a weak polyelectrolyte behavior. While initially the MUC5B films exhibited a similar tendency, this was followed by a drastic collapse indicating an interaction between exposed hydrophobic domains. This suggests that mucins in the pellicle outer layer form complexes with other salivary components that prevent this interaction. Lowering ionic strength below physiological values also led to a partial removal of the pellicle inner layer. Overall, our results highlight the importance that the interactions of mucins with other pellicle components play on their structure.
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| 18. |
- Boyd, Hannah, 1994-, et al.
(författare)
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Effect of nonionic and amphoteric surfactants on salivary pellicles reconstituted in vitro
- 2021
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Surfactants are important components of oral care products. Sodium dodecyl sulfate (SDS) is the most common because of its foaming properties, taste and low cost. However, the use of ionic surfactants, especially SDS, is related to several oral mucosa conditions. Thus, there is a high interest in using non-ionic and amphoteric surfactants as they are less irritant. To better understand the performance of these surfactants in oral care products, we investigated their interaction with salivary pellicles i.e., the proteinaceous films that cover surfaces exposed to saliva. Specifically, we focused on pentaethylene glycol monododecyl ether (C12E5) and cocamidopropyl betaine (CAPB) as model nonionic and amphoteric surfactants respectively, and investigated their interaction with reconstituted salivary pellicles with various surface techniques: Quartz Crystal Microbalance with Dissipation, Ellipsometry, Force Spectroscopy and Neutron Reflectometry. Both C12E5 and CAPB were gentler on pellicles than SDS, removing a lower amount. However, their interaction with pellicles differed. Our work indicates that CAPB would mainly interact with the mucin components of pellicles, leading to collapse and dehydration. In contrast, exposure to C12E5 had a minimal effect on the pellicles, mainly resulting in the replacement/solubilisation of some of the components anchoring pellicles to their substrate.
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| 19. |
- Boyd, Hannah, 1994-
(författare)
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On the structure and mechanical properties of in vitro salivary pellicles
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Salivary pellicles display exceptional hydration and lubrication performance. At present, there are still gaps in the understanding of how this is achieved. The aim of this thesis was therefore to increase our knowledge on the mechanisms underlying these properties and deepen the understanding of how they are related to the composition and structure of pellicles, with a focus on those formed under in vitro conditions. This has applications ranging from the development of artificial saliva and lubricating coatings for biomedical applications to methodological approaches for initial testing of oral healthcare products. For this, we also focused on developing suitable methodological approaches for these studies, centering on atomic force microscopy, quartz crystal microbalance with dissipation monitoring, ellipsometry and neutron reflectometry techniques, to investigate in vitro and model salivary pellicles.First, we confirmed a two-layer structure for in vitro salivary pellicles and showed that the outer layer is mainly composed by the oral mucin MUC5B, but that it also contains other salivary components that enhance swelling and hydration. In the presence of bulk saliva, the outer layer also contains a reversibly and loosely bound fraction. This fraction increases the adhesiveness of the pellicle but unexpectedly has no significant effect on its lubrication performance. We also investigated the effect of mechanical confinement on model salivary pellicles by means of Neutron Reflectometry, revealing that at a pressure of 1 bar they are already completely compressed and dehydrated. Finally, with the aim to advance towards better oral healthcare products, we investigated the effect of nonionic and amphoteric surfactants on salivary pellicles, showing that they have a gentler effect on pellicle structure than the commonly employed anionic surfactants.
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| 20. |
- Cárdenas, Marité, et al.
(författare)
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Interactions of hydroxyapatite surfaces: Conditioning films of human whole saliva
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:14, s. 7262-7268
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Tidskriftsartikel (refereegranskat)abstract
- Hydroxyapatite is a very interesting material given that it is the main component in tooth enamel and because of its uses in bone implant applications. Therefore, not only the characterization of its surface is of high relevance but also designing reliable methods to study the interfacial properties of films adsorbed onto it. In this paper we apply the colloidal probe atomic force microscopy method to investigate the surface properties of commercially available hydroxyapatite surfaces (both microscopic particles and macroscopic discs) in terms of interfacial and frictional forces. In this way, we find that hydroxyapatite surfaces at physiological relevant conditions are slightly negatively charged. The surfaces were then exposed to human whole saliva, and the surface properties were re-evaluated. A thick film was formed that was very resistant to mechanical stress. The frictional measurements demonstrated that the film was indeed highly lubricating, supporting the argument that this system may prove to be a relevant model for evaluating dental and implant systems.
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| 21. |
- Cárdenas, Marité, et al.
(författare)
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Solubilization of sphingomyelin vesicles by addition of a bile salt.
- 2008
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Ingår i: Chemistry and Physics of Lipids. - : Elsevier BV. - 0009-3084 .- 1873-2941. ; 151:Sep 25, s. 10-17
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Tidskriftsartikel (refereegranskat)abstract
- The interactions of the bile salt sodium taurocholate (TC) in 50mM Trizma-HCl buffer and 150mM NaCl (pH 9) at 37 degrees C with membranes composed of sphingomyelin (SM) were studied by dynamic light scattering, cryogenic transmission electron microscopy (cryo-TEM) and turbidity measurements. Small unilamellar SM vesicles were prepared by extrusion. Below the CMC of TC, taurocholate addition leads to vesicle growth due to incorporation of the taurocholate molecules into the vesicle bilayer. At around half the CMC of the bile salt, the SM vesicles are transformed into SM/TC mixed worm-like micelles, which are visualized by cryo-TEM for the first time. Further increase in the taurocholate concentration leads to the rupture of these structures into small spherical micelles. Interestingly, large non-spherical micelles were also identified for pure taurocholate solutions. Similar threadlike structures have been reported earlier for the bile salt sodium taurodeoxycholate [Rich, A., Blow, D., 1958. Nature 182, 1777; Blow, D.M., Rich, A., 1960. J. Am. Chem. Soc. 82, 3566-3571; Galantini, L., Giglio, E., La Mesa, C., Viorel-Pavel, N., Punzo, F., 2002. Langmuir 18, 2812] and for mixtures of taurocholate and phosphatidylcholate [Ulmius, J., Lindblom, G., Wennerström, H., Johansson, L.B.-A., Fontel, K., Söderman, O., Ardvisson, G., 1982. Biochemistry 21, 1553; Hjelm, R.P., Thiyagarajan, P., Alkan-Onyuksel, H., 1992. J. Phys. Chem. 96, 8653] as determined by various scattering methods.
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| 22. |
- Carlsson, F, et al.
(författare)
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Lysozyme adsorption to charged surfaces. A Monte Carlo study
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108, s. 9871-
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Tidskriftsartikel (refereegranskat)abstract
- Lysozyme adsorption to charged surfaces was studied by Monte Carlo simulations at different protein concentrations, protein net charges, ionic strengths, and surface charge densities. The lysozyme was represented by a hard sphere with embedded positive and negative surface charges parametrically dependent on the solution pH. A short-range attractive protein-protein potential was included to represent attractive non-Coulomb forces. The charged surface was described by a hard wall with embedded charges representing a mica surface. The protein adsorption was favored by high protein concentration, high protein net charge, low ionic strength, and high surface charge density. Nevertheless, adsorption appeared also for a weakly negatively charged protein to the negatively charged surface as a result of an electrostatically favorable protein orientation at the surface. While a multipole expansion including monopole and dipole moments only was insufficient to explain preferential orientation, an expansion including also quadrupole moments provided a satisfactory picture. Finally, it was found that the short-range attraction between the proteins increased the adsorbed amount, as well as the structure in the adsorbed protein layer. The adsorbed amounts obtained compared favorably with experimental results.
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| 23. |
- Christersson, Cecilia, et al.
(författare)
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Film-forming properties and viscosities of saliva substitutes and human whole saliva
- 2000
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Ingår i: European Journal of Oral Sciences. - : Wiley. - 0909-8836 .- 1600-0722. ; 108:5, s. 418-425
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Tidskriftsartikel (refereegranskat)abstract
- Hypo-salivation, related to medical remedies, is an increasing clinical problem. Studies report a weak correlation between subjective mouth dryness and objective sialometry. This indicates that both quantity and quality of saliva are important for the surface-associated functions of saliva, such as lubrication and hydration, to be expressed. Film-forming properties and viscosities of three saliva substitutes were compared to human saliva. Adsorption to surfaces was measured by ellipsometry, infrared spectroscopy and drop-volume technique. Viscosity measurements were carried out using an oscillating rheometer. Saliva, with the lowest viscosity value and the highest protein content, presented superior film retention on both hydrophilic and hydrophobic surfaces. The carboxymethylcellulose-based MAS 84 showed intermediate values of viscosity, poorest ability to reduce surface tension, and negligible film-forming capacity. The porcine mucin-based Saliva Orthana showed about twice the viscosity of saliva and film-forming capability on preferably hydrophobic substrates. Salinum, a linseed extract, possessed the highest viscosity value and an initial surface tension close to that of saliva. The film retention on hydrophilic surfaces was not as effective as for saliva. The results indicate that the film-forming capacity of saliva substitutes is a property also to be considered in the exploration of clinically effective artificial salivas.
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| 24. |
- Cukkemane, Nivedita, et al.
(författare)
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Anti-adherence and bactericidal activity of sphingolipids against Streptococcus mutans
- 2015
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Ingår i: European Journal of Oral Sciences. - : John Wiley & Sons. - 0909-8836 .- 1600-0722. ; 123:4, s. 221-227
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluated the anti-biofilm activity of sphingosine, phytosphingosine (PHS), and sphinganine for: (i) anti-adherence activity on hydroxyapatite (HA) surfaces; and (ii) bactericidal activity on different Streptococcus mutans phenotypes (i.e. planktonic cells and cells from a disrupted biofilm). For this, HA discs treated with sphingolipids were incubated with S. mutans and the number of adherent cells was evaluated by both culture and confocal microscopy. Sphinganine strongly inhibited bacterial adherence by 1000-fold compared with an untreated surface. Phytosphingosine and sphingosine inhibited bacterial adherence by eight- and five-fold, respectively, compared with an untreated surface. On saliva-coated HA, sphinganine and PHS inhibited bacterial adherence by 10-fold. Bactericidal activity of sphingolipids was evaluated by culture. For biofilms, the strongest bactericidal activity was exhibited by sphingosine compared with PHS and sphinganine. At a concentration of 12.5 μg ml−1, PHS and sphingosine were profoundly effective against planktonic and disrupted biofilms; and sphinganine reduced the number of cells in planktonic form by 100-fold and those derived from a disrupted biofilm by 1000-fold. Atomic force microscopy studies suggested that mechanical stability does not appear to be a factor relevant for anti-fouling activity. The results suggest that sphingolipids may be used to control oral biofilms, especially those loaded with S. mutans.
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| 25. |
- Dagys, Marius, et al.
(författare)
-
Comparison of bioelectrocatalysis at Trichaptum abietinum and Trametes hirsuta laccase modified electrodes
- 2014
-
Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 130, s. 141-147
-
Tidskriftsartikel (refereegranskat)abstract
- Bioelectrocatalytic reduction of oxygen to water at electrodes modified with gold nanoparticles and a new laccase from Trichaptum abietinum (TaLc) was studied. The bioelectrocatalytic current was found to be much higher at TaLc modified electrodes than at similarly prepared electrodes modified with a broadly used laccase from Trametes hirsuta (ThLc). To explain this difference the bioelectrocatalysis was described in terms of kinetic rate constants based on simultaneous cyclic voltammetry and quartz crystal microbalance measurements. From analysis of the rate constants both laccases appeared to possess similar rates (k(0)) of direct electron transfer. However, the enzyme turnover (k(cat)) was about three-fold higher for gold nanoparticle bound TaLc than for ThLc, calculated using surface concentration of enzyme established by QCM-D. Near reversible potential-induced reorientation of adsorbed proteins was observed by surface enhanced Raman spectroscopy. (C) 2014 Elsevier Ltd. All rights reserved.
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| 26. |
- Dagys, Marius, et al.
(författare)
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Laccase-gold nanoparticle assisted bioelectrocatalytic reduction of oxygen
- 2010
-
Ingår i: Electrochemistry communications. - : ScienceDirect. - 1388-2481 .- 1873-1902. ; 12:7, s. 933-935
-
Tidskriftsartikel (refereegranskat)abstract
- It was found that homogeneous activity of Trametes hirsuta laccase is considerably diminished in the presence of gold nanoparticles (Au-NPs). Heterogeneous electron transfer studies revealed that Au-NPs facilitate direct electron transfer (DET) between the T1 copper site of the laccase and the surface of Au-NP modified electrodes. DET was characterized by the standard heterogeneous ET constant of 0.5 +/- 0.6 s(-1) at Au-NPs with an average diameter of 50 nm. As a consequence of this a well pronounced DET based bioelectrocatalytic oxygen reduction with current densities of 5-30 mu A cm(-2) has been achieved at the laccase-Au-NP modified electrodes.
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| 27. |
- Dahlstrom, M., et al.
(författare)
-
Affinity states of biocides determine bioavailability and release rates in marine paints
- 2015
-
Ingår i: Biofouling. - : Informa UK Limited. - 0892-7014 .- 1029-2454. ; 31:2, s. 201-210
-
Tidskriftsartikel (refereegranskat)abstract
- A challenge for the next generation marine antifouling (AF) paints is to deliver minimum amounts of biocides to the environment. The candidate AF compound medetomidine is here shown to be released at very low concentrations, ie ng ml(-1) day(-1). Moreover, the release rate of medetomidine differs substantially depending on the formulation of the paint, while inhibition of barnacle settlement is independent of release to the ambient water, ie the paint with the lowest release rate was the most effective in impeding barnacle colonisation. This highlights the critical role of chemical interactions between biocide, paint carrier and the solid/aqueous interface for release rate and AF performance. The results are discussed in the light of differential affinity states of the biocide, predicting AF activity in terms of a high surface affinity and preserved bioavailability. This may offer a general framework for the design of low-release paint systems using biocides for protection against biofouling on marine surfaces.
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| 28. |
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| 29. |
- Delvar, Alice, et al.
(författare)
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Interaction of polyelectrolytes with salivary pellicles on hydroxyapatite surfaces under erosive acidic conditions
- 2015
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 38:7, s. 21610-21618
-
Tidskriftsartikel (refereegranskat)abstract
- The modification of acidic beverage formulations with food-approved, nonhazardous substances with antierosive properties has been identified as a key strategy for counteracting the prevalence of dental erosion, i.e., the acid-induced dissolution of hydroxyapatite (HA, the main mineral component of tooth surfaces). While many of such substances have been reported, very little is known on how they interact with teeth and inhibit their acid-induced dissolution. With the aim of filling this gap in knowledge, we have studied under acidic conditions the interaction between two polyelectrolytes of differing ionic character, carboxymethyl cellulose (CMC) and chitosan, and saliva-coated hydroxyapatite, i.e., a model for the outer surface of teeth. These studies were performed by means of ellipsometry, quartz crystal microbalance with dissipation monitoring, and atomic force microscopy. We also studied, by means of pH variations, how dissolution of saliva-coated HA is affected by including these polyelectrolytes in the erosive solutions. Our results confirm that salivary films protect HA from acid-induced dissolution, but only for a limited time. If the acid is modified with CMC, this polyelectrolyte incorporates into the salivary films prolonging in time their protective function. Eventually, the CMC-modified salivary films are removed from the HA surfaces. From this moment, HA is continuously coated with CMC, but this offers only a weak protection against erosion. When the acid is modified with the cationic chitosan, the polyelectrolyte adsorbs on top of the salivary films. Chitosan-modified salivary films are also eventually replaced by bare chitosan films. In this case both coatings offer a similar protection against HA dissolution, which is nevertheless notably higher than that offered by CMC.
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| 30. |
- Fagerström, Anton, et al.
(författare)
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Surfactant softening of plant leaf cuticle model wax : a Differential Scanning Calorimetry (DSC) and Quartz Crystal Microbalance with Dissipation (QCM-D) study
- 2014
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 426, s. 22-30
-
Tidskriftsartikel (refereegranskat)abstract
- The aim was to quantify the softening effect that two surfactants (C10EO7 and C8G1.6) have on a plant leaf cuticle model wax. Effects on the thermotropic phase behavior and fluidity of the wax (C22H45OH/C32H66/H2O) were determined. The model wax is crystalline at ambient conditions, yet it is clearly softened by the surfactants. Both surfactants decreased the transition temperatures in the wax and the G″/G' ratio of the wax film increased in irreversible steps following surfactant exposure. C10EO7 has a stronger fluidizing effect than C8G1.6 due to stronger interaction with the hydrophobic waxes. Intracuticular waxes (IW) comprise both crystalline and amorphous domains and it has previously been proposed that the fluidizing effects of surfactants are due to interactions with the amorphous parts. New data suggests that this may be a simplification. Surfactants may also absorb in crevices between crystalline domains. This causes an irreversible effect and a softer cuticle wax.
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| 31. |
- Falk, Magnus, et al.
(författare)
-
Biofuel cell as a power source for electronic contact lenses
- 2012
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Ingår i: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 37:1, s. 38-45
-
Tidskriftsartikel (refereegranskat)abstract
- Here we present unequivocal exptl. proof that microscale cofactor- and membrane-less, direct electron transfer based enzymic fuel cells do produce significant amts. of elec. energy in human lachrymal liq. (tears). 100 μm diam. gold wires, covered with 17 nm gold nanoparticles, were used to fashion three-dimensional nanostructured microelectrodes, which were biomodified with Corynascus thermophilus cellobiose dehydrogenase and Myrothecium verrucaria bilirubin oxidase as anodic and cathodic bioelements, resp. The following characteristics of miniature glucose/oxygen biodevices operating in human tears were registered: 0.57 V open-circuit voltage, about 1 μW cm-2 max. power d. at a cell voltage of 0.5 V, and more than 20 h operational half-life. Theor. calcns. regarding the max. recoverable elec. energy can be extd. from the biofuel and the biooxidant, glucose and mol. oxygen, each readily available in human lachrymal liq., fully support our belief that biofuel cells can be used as elec. power sources for so called smart contact lenses.
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| 32. |
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| 33. |
- Falk, Magnus, et al.
(författare)
-
Miniature direct electron transfer based enzymatic fuel cell operating in human sweat and saliva
- 2014
-
Ingår i: Fuel Cells. - : John Wiley & Sons. - 1615-6846 .- 1615-6854. ; 14:6, s. 1050-1056
-
Tidskriftsartikel (refereegranskat)abstract
- We present data on operation of a miniature membrane-less, direct electron transfer based enzymatic fuel cell in human sweat and saliva. The enzymatic fuel cell was fabricated following our previous reports on miniature biofuel cells, utilizing gold nanoparticle modified gold microwires with immobilized cellobiose dehydrogenase and bilirubin oxidase. The following average characteristics of miniature glucose/oxygen biodevices operating in human sweat and saliva, respectively, were registered: 580 and 560 mV open-circuit voltage, 0.26 and 0.1 μW cm–2 power density at a cell voltage of 0.5 V, with up to ten times higher power output at 0.2 V. When saliva collected after meal ingestion was used, roughly a two-fold increase in power output was obtained, with a further two-fold increase by addition of 500 μM glucose. Likewise, the power generated in sweat at 0.5 V increased two-fold by addition of 500 μM glucose.
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| 34. |
- Falk, Yana Znamenskaya, et al.
(författare)
-
Effects of Hydration on Structure and Phase Behavior of Pig Gastric Mucin Elucidated by SAXS
- 2018
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 122:30, s. 7539-7546
-
Tidskriftsartikel (refereegranskat)abstract
- In this work small-angle X-ray scattering (SAXS) was used to study hydration and temperature-induced changes of pig gastric mucin (PGM) within the entire concentration range. The scattering is interpreted as originating from PGM fiber-like structures that adopt rod-like bottle-brush conformation in dilute solutions. On the basis of the knowledge about molecular structure of mucins and SAXS data for dilute solutions, we propose a theoretical model for predicting mucin conformation in solution and calculate the corresponding scattering profile. This bottle-brush model comprises a protein backbone with carbohydrate side chains and corresponding structural parameters, such as grafting distance and lengths of the backbone and side chains. It describes the experimental PGM data from dilute solutions in the full q range very well. It furthermore suggests that the carbohydrate side chains are grafted with a regular separation of around 5 nm and a length of 14 nm. The cross-section size with a radius of about 1 nm is also in accordance with the size of the carbohydrate units. Structuring of PGM solutions at higher concentrations was investigated by analyzing semidilute and concentrated PGM samples. Starting at about 20 wt %, Bragg peaks become clearly visible indicating a more ordered mucin system. In very dehydrated and fully dry mucin samples these peaks are not present indicating lack of long-range order. The SAXS data show that the structural change occurring at about 80 wt % mucin and 25 degrees C corresponds to a glass transition in agreement with our previous calorimetric results. Temperature also has an effect on the phase behavior of mucin. At intermediate levels of hydration, a phase transition is observed at about 60-70 degrees C. The main Bragg peak appears to split in two, indicating formation of a different structure at elevated temperatures. These findings are used to improve the PGM water phase diagram.
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| 35. |
- Gonzalez-Martinez, Juan F, et al.
(författare)
-
MUC5B mucin films under mechanical confinement : A combined neutron reflectometry and atomic force microscopy study.
- 2022
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 614, s. 120-129
-
Tidskriftsartikel (refereegranskat)abstract
- HYPOTHESIS: Among other functions, mucins hydrate and protect biological interfaces from mechanical challenges. Mucins also attract interest as biocompatible coatings with excellent lubrication performance. Therefore, it is of high interest to understand the structural response of mucin films to mechanical challenges. We hypothesized that this could be done with Neutron Reflectometry using a novel sample environment where mechanical confinement is achieved by inflating a membrane against the films.EXPERIMENTS: Oral MUC5B mucin films were investigated by Force Microscopy/Spectroscopy and Neutron Reflectometry both at solid-liquid interfaces and under mechanical confinement.FINDINGS: NR indicated that MUC5B films were almost completely compressed and dehydrated when confined at 1 bar. This was supported by Force Microscopy/Spectroscopy investigations. Force Spectroscopy also indicated that MUC5B films could withstand mechanical confinement by means of steric interactions for pressures lower than ∼ 0.5 bar i.e., mucins could protect interfaces from mechanical challenges of this magnitude while keeping them hydrated. To investigate mucin films under these pressures by means of the employed sample environment for NR, further technological developments are needed. The most critical would be identifying or developing more flexible membranes that would still meet certain requirements like chemical homogeneity and very low roughness.
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| 36. |
- Haberska, Karolina, et al.
(författare)
-
Activity of lactoperoxidase when adsorbed on protein layers
- 2008
-
Ingår i: Talanta. - : Elsevier. - 0039-9140 .- 1873-3573. ; 76:5, s. 1159-1164
-
Tidskriftsartikel (refereegranskat)abstract
- Lactoperoxidase (LPO) is an enzyme, which is used as an antimicrobial agent in a number of applications, e.g., food technology. In the majority of applications LPO is added to a homogeneous product phase or immobilised on product surface. In the latter case, however, the measurements of LPO activity are seldom reported. In this paper we have assessed LPO enzymatic activity on bare and protein modified gold surfaces by means of electrochemistry. It was found that LPO rapidly adsorbs to bare gold surfaces resulting in an amount of LPO adsorbed of 2.9 mg/m2. A lower amount of adsorbed LPO is obtained if the gold surface is exposed to bovine serum albumin, bovine or human mucin prior to LPO adsorption. The enzymatic activity of the adsorbed enzyme is in general preserved at the experimental conditions and varies only moderately when comparing bare gold and gold surface pretreated with the selected proteins. The measurement of LPO specific activity, however, indicate that it is about 1.5 times higher if LPO is adsorbed on gold surfaces containing a small amount of preadsorbed mucin in comparison to the LPO directly adsorbed on bare gold.
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| 37. |
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| 38. |
- Hahn Berg, Cecilia I, et al.
(författare)
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Intraoral Lubrication of PRP-1, Statherin and Mucin as Studied by AFM
- 2004
-
Ingår i: Biofouling (Print). - : Taylor & Francis. - 0892-7014 .- 1029-2454. ; 20:1, s. 65-70
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper was to elucidate the mechanisms behind salivary lubrication with special emphasis on the lubricity of three key components of the pellicle, viz human acidic proline-rich protein 1 (PRP-1), human statherin and bovine submaxillary mucin (BSM). The lubricating properties of the proteins have been assessed by means of colloidal probe atomic force microscopy, and are discussed in relation to their adsorption behaviour. To various extents, the proteins investigated all showed a lubricating effect when adsorbed to silica surfaces. For comparable concentrations, PRP-1 was found to have a more pronounced lubricating effect than BSM, which in turn showed a higher lubricity than statherin. The relative lubricity is in accordance with previously reported relative adsorbed amounts of the three proteins, within the investigated concentration interval. It is concluded that PRP-1 has the highest lubricating capacity as a pure fraction among the preparations investigated, and that the lubricating effect of PRP-1 as a pure fraction is notably large as compared to the lubricity of human whole saliva.
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| 39. |
- Halthur, Tobias J, et al.
(författare)
-
Sequential adsorption of bovine mucin and lactoperoxidase to various substrates studied with quartz crystal microbalance with dissipation
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:7, s. 4901-4908
-
Tidskriftsartikel (refereegranskat)abstract
- Mucin and lactoperoxidase are both natively present in the human saliva. Mucin provides lubricating and antiadhesive function, while lactoperoxidase has antimicrobial activity. We propose that combined Films of the two proteins can be used as a strategy for surface modification in biomedical applications such as implants or biosensors. In order to design and ultilize mixed protein films, it is necessary to understand the variation in adsorption behavior of the proteins onto different surfaces and how it affects their interaction. The quartz crystal microbalance with dissipation (QCM-D) technique hats been used to extract information of the adsorption properties of bovine mucin (BSM) and lactoperoxidase (LPO) to gold, silica. and hydrophobized silica surfaces. The information has further been used to retrieve information of the viscoelastic properties of the adsorbed film. The adsorption and compaction of BSM were found to vary depending on the nature of the underlying bare surface, adsorbing as at thick highly hydrated film with loops and tails extending out in the bulk on gold and as a thinner film with much lower adsorbed amount on silica; and on hydrophobic surfaces, BSM adsorbs as a flat and much more compact layer. On gold and silica, the highly hydrated BSM film is cross-linked and compacted by the addition of LPO, whereas the compaction is not as pronounced on the already more compact film formed on hydrophobic surfaces. The adsorption of LPO to bare surfaces also varied depending on the type of surface. The adsorption profile of BSM onto LPO-coated surfaces mimicked the adsorption to the underlying surface, implying little interaction between the LPO and BSM. The interaction between the protein layers was interpreted as a combination of electrostatic and hydrophobic interactions, which was in turn influenced by the interaction of the proteins with the different substrates.
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| 40. |
- Hamit-Eminovski, Jildiz, et al.
(författare)
-
An ellipsometry study on the effect of aluminium chloride and ferric chloride formulations on mucin layers adsorbed at hydrophobic surfaces
- 2010
-
Ingår i: Biofouling (Print). - : Taylor & Francis. - 0892-7014 .- 1029-2454. ; 26:5, s. 511-518
-
Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry was used to investigate the effect of polyaluminium chloride (PAC) formulations of different degrees of hydrolysation on an adsorbed mucin film. The results were compared to the effect of aluminium chloride (AlCl3) and ferric chloride. A compaction of the mucin film took place upon addition of the formulations and this occurred to different extents and at different concentrations for the different formulations. The compaction of PAC of a low degree of hydrolysis behaved similarly to AlCl3. PAC of a high degree of hydrolysis showed a greater compaction effect than the other aluminium formulations. The initial compaction concentration was found to be 0.001 mM which is less than previously found for aluminium–mucin complex formation in bulk. The reversibility of the compaction was also investigated. The compaction of the mucin film was found to be partly reversible for AlCl3 and PAC of low degree of hydrolysis. No reversibility was observed for the formulations of PAC of high hydrolysis grade or for ferric chloride. The results are consistent with previously observed effects of PAC of a low degree of hydrolysis on bacterial surfaces where a compaction of surface polymers was indicated by the reduced range of repulsive steric interactions.
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| 41. |
- Hamit, Jildiz, et al.
(författare)
-
Change in surface properties of Microthrix parvicella upon addition of polyaluminium chloride as characterized by atomic force microscopy
- 2010
-
Ingår i: Biofouling (Print). - : Taylor & Francis. - 0892-7014 .- 1029-2454. ; 26:3, s. 323-331
-
Tidskriftsartikel (refereegranskat)abstract
- The filamentous bacterium Microthrix parvicella causes severe separation and foaming problems at wastewater treatment plants (WWTPs). An effective control of the bacterium in activated sludge WWTPs can be accomplished by dosage with polyaluminium chloride (PAX-14). The purpose of this study was to investigate whether addition of PAX-14 affects surface properties such as the hydrophobicity of the bacterium and to study the exopolymers of M. parvicella that host surface-associated enzymes. To this end, force measurements by atomic force microscopy were carried out to measure the interactions between hydrophilic and hydrophobized tips and the bacterium surface. Addition of PAX-14 caused no changes in the hydrophobicity of the bacterium surface but the data indicate that it collapsed the polymeric layer likely due to electrostatic screening. It is concluded that the collapse of the polymeric layer may affect the transport of substrates (eg free fatty acids) to the bacterium and hence the competitiveness of M. parvicella compared to the other bacteria present in activated sludge.
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| 42. |
- Joiner, A, et al.
(författare)
-
Adsorption from black tea and red wine onto in vitro salivary pellicles studied by ellipsometry
- 2003
-
Ingår i: European Journal of Oral Sciences. - : Blackwell Munksgaard. - 0909-8836 .- 1600-0722. ; 111, s. 417-422
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of black tea and red wine components onto a pellicle-like protein layer formed in vitro by adsorption from whole unstimulated saliva on hydroxyapatite discs were studied by in situ ellipsometry. It was found that components from black tea readily adsorbed to the pellicle. Subsequent exposure to saliva led to further adsorption of salivary components to give an overall increase in the amounts adsorbed. The amounts adsorbed increased still further following a third tea and saliva exposure. Components of red wine gave significantly greater amounts of adsorption to the pellicle than black tea. The adsorption of components of black tea gave a concomitant increase in colour or stain as measured by a reflectance chromameter. In all cases, the black tea- and red wine-modified pellicles were not eluted by either phosphate buffer or sodium dodecyl sulphate (SDS) rinses. Thus, black tea and red wine components have been shown to have a profound effect on in vitro pellicle maturation, causing thickened layers of stained material to build up, which are not readily removed.
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| 43. |
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| 44. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Hydration of a natural polyelectrolyte xanthan gum : Comparison with non-ionic carbohydrates
- 2010
-
Ingår i: Carbohydrate Polymers. - : Elsevier. - 0144-8617 .- 1879-1344. ; 82:2, s. 284-290
-
Tidskriftsartikel (refereegranskat)abstract
- In dilute solutions, polyelectrolytes exhibit more hydrophilic properties than non-charged polymers do. However, extension of this statement on almost dry systems is questionable. In this study we present sorption calorimetric data on hydration of a natural carbohydrate polyelectrolyte xanthan gum and make comparison with analogous data of three types of cellulose which is a non-charged carbohydrate polymer. An analysis of the sorption isotherm shows that at given relative humidities xanthan gum absorbs greater amount of water than non-charged cellulose does. Nonetheless, the enthalpies of hydration of xanthan gum and of all three considered types of cellulose at zero water content are equal to −18 kJ/mol. Thus, entropy of hydration plays an important role in water sorption behaviour of xanthan gum. The apparent absence of an ion effect on polymer–water interactions can be explained by solvation of ions by OH-groups of the dry xanthan gum. Ab initio calculations presented here show that solvation of an ionic group of xanthan gum by a carbohydrate hydroxyl is as strong as hydration of the same group by water. The exothermic heat effect of hydration arises from the loss of the mobility of water on the rigid glassy environment of the polymer. For the first time, the glass transition temperature of dry xanthan gum is reported to be 60 °C.
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| 45. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Hydration of lysozyme : the protein-protein interface and the enthalpy-entropy compensation
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:6, s. 3918-3922
-
Tidskriftsartikel (refereegranskat)abstract
- Water sorption isotherms of proteins are usually interpreted with such models as BET or GAB that imply the formation of multilayers at solid-gas interface. However, this approach is not applicable to globular proteins such as humid lysozyme where a solid-gas interface does not exist. Another popular approach is the D’Arcy-Watt model, where besides the formation of multilayers the heterogeneity of energies of sorption sites of proteins is taken into account. Here we present sorption calorimetric data on the hydration of lysozyme that confirms the existence of the heterogeneity. The magnitude of the heterogeneity is, however, lower than one can expect on the basis of the existence of a solid-gas interface. Moreover, the calorimetric data show a strong enthalpy-entropy compensation that leads to almost constant effective free energy of hydration in the activity range normally used for fitting the data to sorption models. This allows the use of the Langmuir equation for the fitting of the initial part of the sorption isotherm of lysozyme. Assuming the formation of a monolayer of water at the protein-protein interface, one can estimate the size of the lysozyme molecules from the sorption isotherm. The result of this estimation is in good agreement with the structural data on lysozyme, which supports the presented approach.
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| 46. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Hydration of microcrystalline cellulose and milled cellulose studied by sorption calorimetry.
- 2008
-
Ingår i: Phys. Chem. B.. - : American Chemical Society (ACS). ; 112:12, s. 3728-3734
-
Tidskriftsartikel (refereegranskat)abstract
- The hydration of two different polymorphs of microcrystalline cellulose (cellulose I and II), as well as the hydration of amorphous cellulose was studied using water sorption calorimetry, gravimetric water vapor sorption, nitrogen sorption, and X-ray powder diffraction. Amorphous cellulose was prepared by means of ball-milling of microcrystalline cellulose (MCC). Whereas X-ray data showed the untreated MCC to consist of cellulose I, the amorphous cellulose was found to recrystallize into cellulose II after contact with water or water vapor at relative humidities (RHs) above 90%. Sorption isotherms show an increase of water sorption in the sequence cellulose I < cellulose II < amorphous cellulose. The enthalpy of water sorption becomes more exothermic in the same sequence. The specific area of cellulose is dramatically higher when calculated from the water adsorption than when calculated from nitrogen adsorption. A proposed mechanism of water sorption by MCC implies the adsorption of water molecules at solid-solid interfaces, i.e., between neighboring microfibrils, which explains the observed difference between water and nitrogen. The Brunauer-Emmett- Teller (BET) model is therefore not appropriate for the description of the hydration of cellulose. Rather, the Langmuir model represents a more accurate description of water sorption by MCC at low RH. At higher RH, the water adsorption competes with capillary condensation. The thickness of microfibrils, as calculated using the fitting of the sorption isotherm of MCC with the Langmuir equation, is about 4 nm. This value compares favorably with literature data.
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| 47. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Hydration of Thermally Denatured Lysozyme Studied by Sorption Calorimetry and Differential Scanning Calorimetry
- 2006
-
Ingår i: J.Phys.Chem.B.. - : American Chemical Society (ACS). ; 110, s. 10144-10150
-
Tidskriftsartikel (refereegranskat)abstract
- We have studied hydration (and dehydration) of thermally denatured hen egg lysozyme using sorption calorimetry. Two different procedures of thermal denaturation of lysozyme were used. In the first procedure the protein was denatured in an aqueous solution at 90 °C, in the other procedure a sample that contained 20% of water was denatured at 150 °C. The protein denatured at 90 °C showed very similar sorption behavior to that of the native protein. The lysozyme samples denatured at 150 °C were studied at several temperatures in the range of 25-60 °C. In the beginning of sorption, the sorption isotherms of native and denatured lysozyme are almost identical. At higher water contents, however, the denatured lysozyme can absorb a greater amount of water than the native protein due to the larger number of available sorption sites. Desorption experiments did not reveal a pronounced hysteresis in the sorption isotherm of denatured lysozyme (such hysteresis is typical for native lysozyme). Despite the unfolded structure, the denatured lysozyme binds less water than does the native lysozyme in the desorption experiments at water contents up to 34 wt %. Glass transitions in the denatured lysozyme were observed using both differential scanning calorimetry and sorption calorimetry. Partial molar enthalpy of mixing of water in the glassy state is strongly exothermic, which gives rise to a positive temperature dependence of the water activity. The changes of the free energy of the protein induced by the hydration stabilize the denatured form of lysozyme with respect to the native form.
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| 48. |
- Kocherbitov, V, et al.
(författare)
-
Lysozyme-Water Interactions Studied by Sorption Calorimetry
- 2004
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:49, s. 19036-19042
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Tidskriftsartikel (refereegranskat)abstract
- Hydration of hen egg white lysozyme was studied by using the method of sorption calorimetry at 25, 40, and 50 °C. Desorption calorimetric measurements were performed at 25 and 40 °C. The activity of water and partial molar enthalpy of mixing of water were determined as functions of water content. Hydration of lysozyme occurs in four steps: slow penetration of water into the protein−protein interface; gradual glass transition, which occurs in every protein molecule independently of other molecules; further water uptake with disaggregation of protein aggregates and formation of a monolayer of water; and accumulation of free water. The amount of bound water found in desorption experiments is 420 water molecules per lysozyme molecule. Two hysteresis loops were found in the sorption isotherm of lysozyme. The small loop is caused by the slow penetration of water molecules into the protein−protein interface at very low water contents, while the large loop is due to the slow kinetics of aggregation of protein molecules upon desorption. The phase diagram of the lysozyme−water system is presented.
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| 49. |
- Krikstolaityte, Vida, et al.
(författare)
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Bioelectrocatalytic reduction of oxygen at gold nanoparticles modified with laccase
- 2014
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Ingår i: Bioelectrochemistry. - : Elsevier. - 1567-5394 .- 1878-562X. ; 95, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- To characterise bioelectrocatalytic oxygen reduction at gold nanoparticles (AuNPs) modified with Trametes hirsuta laccase (ThLc) combined electrochemical and quartz crystal microbalance measurements have been used. The electrodes with different degrees of AuNP-monolayer coverage, theta, have been studied. In every case of theta close to theoretically possible 44 ThLc molecules adsorbed at 22 nm diameter AuNP. The bioelectrocatalytic current was recalculated down to the current at a single AuNR Unexpectedly, the current at a single AuNP was higher when theta was higher. The maximum current reached at a single AuNP was 31.10(-18) A which corresponds to the enzyme turnover (k(cat)) 13 s(-1). This rate is lower than the homogeneous ThLc turnover (190 s(-1)) suggesting partial denaturation of ThLc upon adsorption or that some ThLc are not in DET contact with the electrode surface
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| 50. |
- Krikstolaityte, Vida, et al.
(författare)
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Development of a plastic membrane containing micro-hole(s) for a potential bio-sensing application
- 2017
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Ingår i: Procedia Technology. - : Elsevier. - 2212-0173. ; 27:Special Issue Biosensors 2016, s. 252-253
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a poly (methyl methacrylate) membrane containing micro-holes (MHs) as a prototype of a simple sensing platform of a lab-on-a-chip device has been developed for a potential analysis of clinical fluidic samples. A four probe electrochemical impedance spectroscopy (EIS) setup, with two electrodes placed on each side of the membrane, was adopted for monitoring the MH impedance (Fig. 1a). The setup was used to investigate, if EIS is suitable to sense the trapping of an analyte inside the MHs. Latex micro-beads with a diameter of 10 mu m were used to test clogging of the MHs. Additionally, finite element model simulations were performed using Comsol Multiphysics software to theoretically evaluate the sensitivity field of the EIS measurement along the MHs. (C) 2017 The Authors. Published by Elsevier Ltd.
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