| 1. |
- Buijs, Jos, et al.
(author)
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Localized changes in the structural stability of myoglobin upon adsorption onto silica particles, as studied with hydrogen/deuterium exchange mass spectrometry
- 2003
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 263:2, s. 441-448
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Journal article (peer-reviewed)abstract
- A new method is presented for monitoring the conformational stability of various parts of a protein that is physically adsorbed onto nanometer-sized silica particles. The method employs hydrogen/deuterium (H/D) exchange of amide hydrogens, a process that is extremely sensitive to structural features of proteins. The resulting mass increase is analyzed with Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Higher structural specificity is obtained by enzymatically cleaving the adsorbed proteins prior to mass spectrometric analysis. The mass increases of four peptic fragments of myoglobin are followed as a function of the H/D exchange time. The four peptic fragments cover 90% of the myoglobin structure. Two of the peptic fragments, located in the middle of the myoglobin sequence and close to the heme group, do not show any adsorption-induced changes in their structural stability, whereas the more stable C- and N-terminal fragments are destabilized. Interestingly, for the N-terminal fragment, comprising residues 1–29, two distinct and equally large conformational populations are observed. One of these populations has a stability similar to that in solution (−23 kJ/mol), whereas the other population is highly destabilized upon adsorption (−11 kJ/mol).
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| 2. |
- Bydén Sjöbom, Malin, et al.
(author)
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Binary Phase Equilibria of Three alfa-Methylsubstituted Sodium Alkanoate Surfactant Systems.
- 2003
-
In: Journal of Colloid and Interface Science. - 0021-9797. ; 257:2, s. 333-336
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Journal article (peer-reviewed)abstract
- In this work, we continue our study of methyl -substituted surfactants and present the aqueous binary phase diagrams of racemic sodium 2-methyloctanoate, -nonanoate, and -dodecanoate, respectively. All systems have very low Krafft temperatures within the solution phase, between 1 and 4 degreesC. The phase sequences of the two shorter surfactants are very similar to those of the unsubstituted sodium octanoate, although with somewhat different range of existence for the phases formed. The sodium 2-methyldodecanoate system is different from the unsubstituted sodium dodecanoate system, as the former seems to lack a hexagonal phase. The surfactant systems were delineated using H-2 NMR splittings and crossed polarizers, and combined with SAXS for determination of phase structure.
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| 3. |
- Karlsson, L M, et al.
(author)
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Penetration and loading of human serum albumin in porous silicon layers with different pore sizes and thicknesses
- 2003
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 266:1, s. 40-47
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Journal article (peer-reviewed)abstract
- Human serum albumin was adsorbed into porous silicon layers with thickness up to 3 µm and with different mean pore radius in the range 4.5-10 nm. The adsorbed amount of protein was quantified by I125 radioactive labeling techniques and ellipsometry. The results show that albumin penetrated into the pores when the mean pore radius was larger than 5.5 nm, but could not totally occupy the available surface area when the layer thickness was larger than 1 µm. Loading of albumin both into porous layers and onto plane silicon as a function of albumin concentration was also investigated. These measurements show that loading of protein increased with protein concentration at least up to 10 mg/ml for porous silicon and up to 1 mg/ml for plane silicon. The maximum deposition into the type of porous layers used here was 28 µg/cm2, compared to 0.36 µg/cm2 for plane silicon. © 2003 Elsevier Inc. All rights reserved.
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| 4. |
- Persson, C. M., et al.
(author)
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Testing the Gouy-Chapman theory by means of surface tension measurements for SDS-NaCl-H2O mixtures
- 2003
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 267:1, s. 151-154
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Journal article (peer-reviewed)abstract
- Surface tension isotherms were measured for sodium dodecyl sulfate (SDS) at different concentrations of added salt (NaCl). The free energy of the surfactant monolayer was assessed by invoking the Gouy-Chapman theory for the charged head groups, the hydrophobic (Tanford) free energy of transfer of the hydrocarbon chain, and the hydrocarbon chain configurational free energy according to Gruen's calculations and finally macroscopic contact terms. In particular, the effect of an increased salt concentration in bulk was examined. Theoretical predictions compare well with the experimental findings, and good agreement was found with respect to both the variation of free energy of the monolayer and the surface pressure behavior. Thus, at least for a liquid-expanded monolayer of SDS, the Gouy-Chapman model yields a satisfactory account of the electrostatic contribution to the thermodynamic properties at different salt concentrations of NaCl.
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| 5. |
- Theander, Katarina, et al.
(author)
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Synergism and Foaming Properties in Mixed Nonionic/Fatty Acid Surfactant Systems
- 2003
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 267, s. 9-17
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Journal article (peer-reviewed)abstract
- The synergism and foaming behavior of a mixed surfactant system consisting of a nonionic surfactant (polyethoxylated alkyl ether CnEm) and a fatty acid soap (sodium oleate) were studied. The micellar interaction parameter (the beta-parameter) was determined from the cmc following the approach of Rubingh's regular solution theory. For both the C12E6/sodium oleate and the C14E6/sodium oleate mixtures, the results indicate a fairly strong attractive interaction (negative beta-values), which were in agreement with previous data reported for other nonionic/anionic surfactant systems. The characteristics of the foam produced from the surfactants were evaluated using a glass column equipped with a series of electrodes measuring the conductance of the foam, which enabled the water content of the foam to be determined. From these measurements. since the total foam volume was almost the same for all concentrations and surfactants, we compared the amount of liquid in the foam produced under dynamic foaming and the ability of the foam to entrain the liquid after the airflow was switched-off (static foam stability). The amount of liquid in the foam 100 s after the air was switched-off followed the order NaOl > C12E6 > C14E6. Also, the mixtures had the same foam volumes as the pure surfactants at the same concentration. However, both mixtures had higher concentrations of liquid in the foam when the mole fraction of the nonionic surfactant in the mixed surfactant system was greater than about >0.3 in the solution.
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| 6. |
- Uvdal, Kajsa, et al.
(author)
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Tyrosine derivatives assembled on gold
- 2003
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 260:2, s. 361-366
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Journal article (peer-reviewed)abstract
- Two different tyrosine derivatives, one with the OH group free and one with the OH group phosphorylated, linked to 3-mercaptopropionic acid through an amide bond are adsorbed to gold surfaces. The adsorbates are studied by means of X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IRAS). The techniques are used to investigate the coordination to the surface and the molecular orientation of adsorbates relative to the surface. Molecular surface interactions, causing chemical shifts in the core level XPS spectra of the adsorbates on gold, are investigated using multilayer films as references. Angle-dependent XPS, XPS(T), and IRAS are used to estimate molecular orientation relative to the surface. The tyrosine derivatives adsorb chemically to the surface through the sulfur atoms and highly organized monolayers are formed with the OH and the PO32- exposed to the air/vacuum interface. © 2003 Elsevier Science (USA). All rights reserved.
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| 7. |
- Ahualli, S., et al.
(author)
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Use of a cell model for the evaluation of the dynamic mobility of spherical silica suspensions
- 2007
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 309:2, s. 342-349
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Journal article (peer-reviewed)abstract
- In this paper we evaluate the validity of a cell model for the calculation of the dynamic mobility of concentrated suspensions of spheres. The key point is the consideration of the boundary conditions (electrical and hydrodynamic) at the boundary of the fluid cell surrounding a single probe particle. The model proposed is based on a universal criterion for the averages of fluid velocity, electric potential, pressure field or electrochemical properties in the cell. The calculations are checked against a wide set of experimental data on the dynamic mobility of silica suspensions with two different radii, several ionic strengths, and two particle concentrations. The comparison reveals an excellent agreement between theory and experiment, and the model appears to be extremely suitable for correctly predicting the behavior of the dynamic mobility, including the changes in the zeta potential, ?, with ionic strength, the frequency and amplitude of the Maxwell-Wagner-O'Konski relaxation, and the inertial relaxation occurring at the top of the frequency range accessible to our experimental device. © 2007 Elsevier Inc. All rights reserved.
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| 8. |
- Andersson, KM, et al.
(author)
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DLVO interactions of tungsten oxide and cobalt oxide surfaces measured with the colloidal probe technique
- 2002
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 246, s. 309-315
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Journal article (peer-reviewed)abstract
- We have investigated the DLVO surface forces of oxidised tungsten and cobalt surfaces using the atomic force microscope (AFM) colloidal probe technique. It was shown by X-ray Photoelectron Spectroscopy (XPS), and electrokinetic measurements that this model system is representative for industrial WC and Co powders used in the production of hard metals. We found that the attractive van der Waals forces are well described by Hamaker constants, calculated from optical data for WO3 and CoOOH. The repulsive electrostatic double layer forces between WO3 surfaces increase with increasing pH due to an increasingly negative surface potential. This surface potential decreases with increasing ionic strength at pH 7.5. The electrostatic interaction between WO3 and CoOOH is attractive at pH 10, suggesting a positively charged CoOOH surface.
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| 9. |
- Aramaki, Kenji, et al.
(author)
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Self-diffusion study of micelles in poly(oxyethylene)-polydimethylsiloxane diblock copolymer and poly(oxyethylene) alkyl ether systems
- 2006
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 300:1, s. 354-360
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Journal article (peer-reviewed)abstract
- Self-diffusion constants of amphiphilic molecules in D2O solutions of mixed poly(oxyethylene)-polydimethylsiloxane diblock copolymer (POE-PDMS, SimC3EOn) and poly(oxyethylene) dodecyl ether (C12EOn) were measured by pulsed-field-gradient NMR method. In the D2O/Si25C3EO51.6/C12EO8 or D2O/Si52C3EO51.6/Cl2EO8 systems, small and large micelles coexist in a wide range of SimC3EO51.6 fraction in total amphiphiles, whereas such a coexisting phenomenon does not take place in the D2O/Si5.8C3EO51.6/Cl2EO8 system. The coexisting phenomenon also takes place in the D2O/Si25C3EO51.6/Cl2EO5 system although the range of mixing fraction is limited. By obtaining each contribution of surfactant and copolymer molecules to the attenuation decay of the echo signal from the proton of the poly(oxyethylene) chain, we could evaluate the composition of the mixed micelles in the D2O/Si25C3EO51.6/Cl2EO8 system. The copolymer content in the mixed micelle increases proportionally to the copolymer mole fraction in the aqueous solution. From the series of self-diffusion measurements, we can conclude that the miscibility Of SimC3EOn and C12EOn in aqueous micelles becomes poor and the coexisting phenomenon takes place when the PDMS chain becomes much longer than the dodecyl chain of C12EOn or the POE chain of C12EOn becomes long. Furthermore it is also revealed that very few silicone copolymer molecules can be incorporated in small surfactant micelles. (c) 2006 Elsevier Inc. All rights reserved.
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| 10. |
- Attard, Phil, et al.
(author)
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Effective spring description of a bubble or a droplet interacting with a particle
- 2002
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In: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 247:1, s. 255-257
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Journal article (other academic/artistic)abstract
- It is shown that the interaction of a particle with a liquid drop or a gas bubble may be quantitatively described over the whole distance regime by treating the fluid interface as a Hookean spring. An algorithm suitable for analyzing atomic force microscopy data suitable for a calculator or a spread-sheet is given and applied to data for oil drops. (C) 2002 Elsevier Science (USA).
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