| 1. |
- Campos, J, et al.
(författare)
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On the interaction between adsorbed layers of monoolein and the lipase action on the formed layers
- 2002
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Ingår i: Colloids and Surfaces B: Biointerfaces. - 1873-4367 .- 0927-7765. ; 26:1-2, s. 172-182
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Tidskriftsartikel (refereegranskat)abstract
- We used the Surface Force Apparatus (SFA) and ellipsometry techniques to study the interaction forces and the adsorption behavior of monoolein (MO), respectively. MO was adsorbed from water to a hydrophobised mica or silica surface. In addition the effect of added lipase, Thermomyces (Humicula) lanuginosa lipase (TLL), to an adsorbed layer of MO was investigated. The force versus distance curves between two MO covered surfaces feature a strong repulsive interaction beneath 400 A. The range of the repulsive force decreases, however, with the number of approaches. No adhesion was observed, provided that the surfaces were not taken to hydrophobic contact. The surface separation at MO-MO contact was determined to about 55 Angstrom This means a layer thickness of about 27 Angstrom, which is comparable to the thickness (25 Angstrom) determined by ellipsometry. The repulsive force may arise from compression of a cubic phase of MO. This phase are suggested to form between the surfaces when they approach close contact due to capillary induced phase separation (CIPS) from the saturated MO solution. The repulsive force changes significantly with time after addition of TLL (concentration of about 1 x 10(-8) M). In contrast to the force curves recorded before adding TLL, the surfaces do not seem to be completely covered with MO as we always observed an attractive force (inward jump) of similar range as was observed between pure OTE surfaces. Ellipsometry measurement of TLL action on MO covered hydrophobic surface reveals a significant and sharp decrease of the amounts adsorbed. Furthermore, the rate of decrease and reduction in adsorbed amount increased with TLL concentration. (C) 2002 Elsevier Science B.V. All rights. reserved.
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| 2. |
- Lindh, Liselott, et al.
(författare)
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Adsorption of MUC5B and the role of mucins in early salivary film formation
- 2002
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Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier. - 1873-4367 .- 0927-7765. ; 25:2, s. 139-146
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Tidskriftsartikel (refereegranskat)abstract
- Salivary mucins are known to play important roles in the formation of oral salivary films. The aims of the present study were to investigate the behaviour of salivary mucins at solid surfaces with different wettabilities, as well as the influence of electrolyte on the adsorption behaviour. A pure preparation of human salivary MUC5B was used together with a commercial one of bovine submaxillary mucin (BSM). Amounts adsorbed from freshly prepared solutions onto hydrophilic and hydrophobic surfaces versus time were measured in situ by ellipsometry. At low concentrations, larger amounts were adsorbed onto hydrophobic than onto hydrophilic silica indicating a higher affinity for the former surfaces. Furthermore, on hydrophilic surfaces adsorbed amounts of MUC5B and BSM show good agreement at low concentrations (< 0. 10 mg ml(-1)). However, at higher concentrations MUM adsorbed to a lower extent than BSM. At hydrophobic surfaces, isotherm shapes were similar for the two preparations, but the amounts were shifted to higher values for MUC5B. Finally, the presence of electrolyte increased adsorption and the increase was more pronounced on hydrophilic surfaces. The increased adsorption at a higher ionic strength indicates a more compact structure of the mucin due to electrostatic screening and the fact that the effect was more pronounced on the hydrophilic surfaces points to a higher relative importance of electrostatic interactions in this case. We conclude that the two mucins investigated behave in a qualitatively similar manner and show the highest affinity for hydrophobic surfaces.
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| 3. |
- Wannerberger, Kristin, et al.
(författare)
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Adsorption from lipase-surfactant solutions onto methylated silica surfaces
- 1996
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Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 1873-4367 .- 0927-7765. ; 6:1, s. 27-36
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Tidskriftsartikel (refereegranskat)abstract
- In situ ellipsometry was used to study the adsorption/desorption of highly purified lipase from Humicola lanuginosa in mixtures with surfactants, at the solid/liquid interface. The effect of the surfactant was studied both when it was allowed to adsorb in mixture with lipase and when added after lipase adsorption. Silica surfaces, totally or partially methylated, were used and the surfactants were SDS (anionic), C12E5 and a commercial alcohol ethoxylate (AE) (both nonionic). The experiments were carried out so as to simulate a laundry process and the pH throughout the study was kept at 9 by means of Tris-HCl buffer.From the results it was shown that the lipase did not adsorb until the diluted, that is during the rinsing period. This was found for all the lipase-surfactant mixtures in the study. However, the amount of lipase adsorbed was larger after rinsing in mixture with SDS, compared with C12E5. The results from addition of surfactant after lipase adsorption indicated that the lipase was replaced by surfactant. This was found for SDS and C12E5 at both the hydrophobic surface and the surface with intermediate hydrophobicity.
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| 4. |
- Benesch, Johan, et al.
(författare)
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Quantification of adsorbed human serum albumin at solid interfaces : A comparison between radioimmunoassay (RIA) and simple null ellipsometry
- 2000
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 18:2, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- Radioimmunoassay (RIA) and null ellipsometry are two common methods to quantify adsorbed proteins. However, the accuracy of null ellipsometry with a constant protein refractive index (n=1.465, k=0) at ?=632.8 nm has this far not been explored. The present study compared the methods, and the degree of agreement between the simplified single wavelength null ellipsometry and RIA to quantify adsorbed proteins was explored on different surfaces. The quantification methods agreed well when Angstrom smooth hydrophilic or hydrophobic silicon surfaces, and freshly radio-labelled proteins were used. Some discrepancies were noted when either rough surface or stored and aged labelled proteins were used. The differences decreased when the aged protein solution was equilibrated with freshly dissolved proteins at room temperature (RT) for a few hours prior to the surface incubations. Significant differences were also noted between the methods when albumin was adsorbed at it's iso-electric point (pH 4.8). Copyright (C) 2000 Elsevier Science B.V.
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| 5. |
- Bogdanovic, G., et al.
(författare)
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Tip friction - torsional spring constant determination
- 2000
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 19:4, s. 397-405
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Tidskriftsartikel (refereegranskat)abstract
- A non-destructive technique is presented for verifying torsional spring constants used in lateral force microscopy. Various calibrations of the microscope are required and these are detailed. The technique produces reasonable values which tend to be larger than those predicted from considerations of the cantilever dimensions. The differences are discussed in terms of length corrections and particularly the uncertainty in the thickness of the cantilevers, which has an enormous effect on the values obtained through a priori calculations. Methods for inferring the thickness are discussed. Further, artefacts in conventional force measurements related to the experiments performed here are discussed.
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| 6. |
- Evertsson, H., et al.
(författare)
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NMR self diffusion measurements of the monooleoylglycerol/poly ethylene glycol/water L-3 phase
- 2002
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 26:02-jan, s. 21-29
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Tidskriftsartikel (refereegranskat)abstract
- The monooleoylglycerol (GMO)/poly ethylene oxide (PEG)/water sponge (L-3) phase has been investigated by pulsed-gradient spin-echo NMR self-diffusion. The data allow the L-3 phase to be modeled as a bicontinuous system with respect to the lipid and water domains. It is proposed by using the interconnected rod model that the solvent PEG mainly distributes to the water domain, but has a higher weight fraction partition to the lipid head groups of the local GMO bilayer than water. The data is put in relation to earlier self-diffusion measurements on the binary GMO/water cubic phase, as well as earlier conductivity and X-ray diffraction measurements on the very same L-3 phase.
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| 7. |
- Hook, F.F, et al.
(författare)
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A comparative study of protein adsorption on titanium oxide surfaces using in situ ellipsometry, optical waveguide lightmode spectroscopy, and quartz crystal microbalance/dissipation
- 2002
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 24:2, s. 155-170
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption kinetics of three model proteins - human serum albumin, fibrinogen and hemoglobin - has been measured and compared using three different experimental techniques: optical waveguide lightmode spectroscopy (OWLS), ellipsometry (ELM) and quartz crystal microbalance (QCM-D). The studies were complemented by also monitoring the corresponding antibody interactions with the pre-adsorbed protein layer. All measurements were performed with identically prepared titanium oxide coated substrates. All three techniques are suitable to follow in-situ kinetics of protein-surface and protein-antibody interactions, and provide quantitative values of the adsorbed adlayer mass. The results have, however, different physical contents. The optical techniques OWLS and ELM provide in most cases consistent and comparable results, which can be straightforwardly converted to adsorbed protein molar ('dry') mass. QCM-D, on the other hand, produces measured values that are generally higher in terms of mass. This, in turn, provides valuable, complementary information in two respects: (i) the mass calculated from the resonance frequency shift includes both protein mass and water that binds or hydrodynamically couples to the protein adlayer, and (ii) analysis of the energy dissipation in the adlayer and its magnitude in relation to the frequency shift (c.f. adsorbed mass) provides insight about the mechanical/structural properties such as viscoelasticity. © 2002 Elsevier Science B.V. All rights reserved.
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| 8. |
- Lestelius, Magnus, et al.
(författare)
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Order/disorder gradients of n-alkanethiols on gold
- 1999
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Ingår i: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 15:1, s. 57-70
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the interfacial properties of one-dimensional molecular gradients of alkanethiols (HS-(CH2)(n)- X) on gold. The kinetics and thermodynamics of monolayer formation are important issues for these types of mixed molecular assemblies. The influence of chain length difference on the contact angles with hexadecane (HD), theta(a) and theta(r), and the hysteresis, has been studied by employing alkanethiols HS-(CH2)(n)-CH3, with n = 9, 11, 13, 15 and 17, in the preparation of the self-assembled monolayers (SAM) gradients. The contact angles with hexadecane, at the very extreme ends of the gradients, show characteristic values of a highly ordered CH3-like assembly: theta(a) = 45-50 degrees. In the middle of the gradients theta(a) drops noticeably and exhibits values representative for CH2-like polymethylenes, theta(a) = 20-30 degrees, indicating a substantial disordering of the protruding chains of the longer component in the gradient assembly. As expected, the exposure of CH2-groups to the probing liquid increases with increasing differential chain length of the two n-alkanethiol used, in this case eight methylene units. However, the contact angles always display a non-zero value which means that even at a chain length difference of eight methylene units there is a substantial exposure of methyl (CH3) groups to the probing liquid. With infrared reflection-absorption spectroscopy (IRAS) we have monitored the structural behavior of the polymethylene chains along the gradient. We find complementary evidence for disordered chains in the gradient region, and the IRAS results correlate well with the contact angle measurements. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 9. |
- Petoral, Rodrigo Jr, 1975-, et al.
(författare)
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Arg–Cys and Arg–cysteamine adsorbed on gold and the G-protein–adsorbate interaction
- 2002
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 25:4, s. 335-346
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Tidskriftsartikel (refereegranskat)abstract
- The dipeptide, Arg–Cys, and the related molecule, Arg–cysteamine, are adsorbed to gold surfaces and the monolayers are characterized. Chemical binding and electronic structure of the monolayers are obtained by X-ray photoelectron spectroscopy (XPS). Strong molecular binding of the adsorbates to gold surface through the sulfur atom is attained. Orientation of the adsorbates on gold is studied using infrared reflection absorption spectroscopy (IRAS). Arg–Cys is interpreted to be adsorbed on gold in a compact configuration. The Arg–cysteamine molecule is adsorbed on gold with the main molecular axis perpendicular to the surface. Interaction of G-protein with the adsorbates was studied using the surface plasmon resonance (SPR) technique. It is believed that arginine has a major role in G-protein recognition since the G-protein-coupled receptor (GPCR) α2A has an arginine-rich region in the G-protein-binding part of the third intracellular loop.
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| 10. |
- Sharma, P.K., et al.
(författare)
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Adhesion of Paenibacillus polymyxa on chalcopyrite and pyrite : Surface thermodynamics and extended DLVO theory
- 2003
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 29:1, s. 21-38
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Tidskriftsartikel (refereegranskat)abstract
- The adhesion behaviour of Paenibacillus polymyxa bacteria on pyrite and chalcopyrite is examined by the surface thermodynamics and the extended DLVO theory approaches. In addition, the bacteria are adapted to pyrite and chalcopyrite minerals, and the adhesion behaviour of these bacteria is also investigated. The significance of acid-base interactions in adhesion is assessed. The essential parameters needed for the calculations of interaction energy between bacteria and mineral are experimentally determined. The results illustrate that the bacterial surfaces are more energetic than the mineral surfaces and the bacteria acquired acid-base surface energy component during their adaptation to mineral. The extended DLVO approach is found to be more effective in predicting the adhesion behaviour than the expectations from thermodynamic approach. The thermodynamic approach yields no bacterial adhesion on minerals and this discrepancy is the result of inadequate description of electrostatic interactions. The adhesion predictions by the DLVO approach are able to partially explain the bioflotation results of pyrite and chalcopyrite. Extended DLVO shows that on account of high bacterial surface energy, their aggregation is not feasible. But due to the hydrophobicity of pyrite and chalcopyrite, their aggregation is possible.
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