| 1. |
- Buijs, Jos, et al.
(författare)
-
Localized changes in the structural stability of myoglobin upon adsorption onto silica particles, as studied with hydrogen/deuterium exchange mass spectrometry
- 2003
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 263:2, s. 441-448
-
Tidskriftsartikel (refereegranskat)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).
|
|
| 2. |
|
|
| 3. |
- Lindman, Björn, et al.
(författare)
-
Aggregation, aggregate composition, and dynamics in aqueous sodium cholate solutions
- 1980
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 73:2, s. 556-565
-
Tidskriftsartikel (refereegranskat)abstract
- The translational mobility of aggregates formed in aqueous sodium cholate solutions was obtained from the self-diffusion coefficient of solubilized decanol, which was determined using the capillary tube method with radioactive labeling. Combining these results with the self-diffusion coefficients of cholate ions, sodium ions, and water molecules the following quantities were determined as a function of cholate concentration: the fraction of cholate aggregated, the ratio of counterions and cholate ions in the aggregates, and the hydration number of the aggregates. All the quantities considered differ in their concentration dependences from those of typical micelle forming long chain ionic surfactants. There seems to be no distinctly favored aggregate size but rather the aggregate radius and aggregation number increase progressively with increasing concentration. The aggregation number is much smaller than for typical surfactant micelles. The deduced fraction of aggregated cholate shows that association progresses continuously over a wide concentration range without a well-defined critical micelle concentration. Sodium ion binding to cholate aggregates is highly variable with a rapid increase taking place above 0.1 mole/kg, a conclusion which may also be drawn from 23Na chemical shift and relaxation data. The counterion binding is discussed in relation to the so-called ion condensation model, found to apply with good approximation for simple surfactant aggregates, and in relation to the progressive cholate aggregation. The aggregates are rather strongly hydrated and the hydration number shows a peculiar concentration dependence. Information on the orientation of cholate within the aggregates is deduced by combining deuterium NMR relaxation data of deuterated cholate with the diffusion results. The order parameter is rather insensitive to concentration and points to a packing of cholate in the aggregates which does not change appreciably with concentration and which corresponds to a marked mobility of cholate within the aggregates.
|
|
| 4. |
- Tornberg, Eva, et al.
(författare)
-
A study of the surface enlargement in the drop volume method and its relation to protein adsorption at A/W and O/W interfaces
- 1981
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 79:1, s. 76-84
-
Tidskriftsartikel (refereegranskat)abstract
- In the drop volume method the surface of the drop enlarges throughout the process of the interfacial tension decay. This surface expansion has been measured for drops of various sizes and shapes, where the interfacial tension depression was caused by different proteins such as lysozyme, β-lactoglobulin, bovine serum albumin, sodium caseinate, whey protein concentrate and soy protein isolate at different initial bulk-phase concentrations. The results showed that the surface enlargement could be as large as 33–34% in relation to the initial surface of the drop, and that this surface expansion was mainly dependent on the surface tension decay and the shape of the drop, irrespective of type of protein and protein concentration used. It was found within the limits of error that time of detachment for a drop was not influenced by its surface expansion. These findings make it possible to use the drop volume method for measuring protein adsorption at different interfaces, which has been shown for lysozyme adsorption at the soybean oil-water interface.
|
|
| 5. |
- Tornberg, Eva
(författare)
-
A Surface Tension Apparatus According to the Drop Volume Principle
- 1977
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 60:1, s. 50-53
-
Tidskriftsartikel (refereegranskat)abstract
- A new construction of a drop volume apparatus has proved to be successful in determining the interfacial tension for a variety of pure liquids as well as for solutions having surface tensions, which come to equilibrium quickly. Temperature dependence of the surface tension can easily be recorded even at elevated temperatures, which has been shown for water.
|
|
| 6. |
- Wahlgren, M, et al.
(författare)
-
Adsorption of b-Lactoglobulin onto Silica, Methylated Silica and Polysulphone
- 1990
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 136:1, s. 259-265
-
Tidskriftsartikel (refereegranskat)abstract
- Milk and whey are widely processed by membrane filtration, often using polysulphone membranes. Adsorption of β-lactoglobulin onto polysulphone was studied at protein concn. of 0.1 and 1.0%, as well as 12% to represent concn. encountered during ultrafiltration. Adsorption onto silica and methylated silica surfaces (representing strongly hydrophilic and strongly hydrophobic surfaces resp.) was also studied. Protein was dissolved in 0.01 smallcap˜M phosphate buffer pH 7.0 containing 0.15 smallcap˜M NaC1 and adsorption/desorption was monitored in situ using a Rudolph Thin Film ellipsometer. Polysulphone surfaces adsorbed the greatest amount of β-lactoglobulin and silica the least; methylated silica was intermediate. Differences between methylated silica and polysulphone may reflect differences in surface roughness. Adsorption to polysulphone and methylated silica was not reversed on dilution, whereas adsorption to silica was partially reversible. Pretreatment of polysulphone and methylated silica surfaces with 0.1% β-lactoglobulin markedly reduced subsequent adsorption from 12% β-lactoglobulin (equivalent to adsorption from 0.1% solution alone); preadsorption to silica surfaces had much less effect on subsequent adsorption. Methylated silica was concluded to be a representative model for a polysulphone surface.
|
|
| 7. |
- Wahlgren, Marie C, et al.
(författare)
-
The concentration dependence of adsorption from a mixture of β-lactoglobulin and sodium dodecyl sulfate onto methylated silica surfaces
- 1992
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 148:1, s. 201-206
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption from a mixture of SDS and β-Lactoglobulin, 1:5 (), onto a methylated silica surface was studied in situ by ellipsometry. The amounts adsorbed from different concentrations of the mixture, at pH 7, were compared with those adsorbed from the corresponding pure SDS and β-lactoglobulin solutions. At high concentrations of the mixture, where the CMC of SDS is approached or exceeded, the adsorbate was probably dominated by SDS, indicated by similar kinetics and amounts adsorbed as for SDS solution alone. The amount adsorbed increased, in this concentration range, when the system was rinsed with buffer solution. This was probably due to an exchange between SDS and β-lactoglobulin when the system was diluted. At intermediate concentrations of SDS and β-lactoglobulin, the amounts adsorbed from the mixtures increased and reached a maximum. This maximum was observed both before and after rinsing. Before rinsing the adsorbate might have been a mixture of SDS and β-lactoglobulin while after rinsing probably only β-lactoglobulin remained. At low concentrations, larger amounts were adsorbed from the mixture than from β-lactoglobulin solution alone. In this concentration range rinsing caused minor desorption, indicating that SDS is co-adsorbed with the protein, even in those cases were no adsorption from a pure SDS solution was seen. This indicated that the binding of SDS to β-lactoglobulin at low concentrations is stronger than to the silica surface and that this binding facilitated the adsorption of protein.
|
|
| 8. |
- Bohlin, Leif, et al.
(författare)
-
Cone-plate instrument for stress relaxation measurements
- 1980
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 73:1, s. 61-65
-
Tidskriftsartikel (refereegranskat)abstract
- An instrument for the measurement of stress relaxation in shear is described. The force is detected by a sensitive piezoresistive pressure transducer. The requirement of constant strain can be fulfilled within less than 1%. Preset values of shear strain can be imposed on the sample within 0.1 sec. This instrument is suitable for soft solids and elastic liquids with a lower limit of ∼ 1 sec for the relaxation time. Results are given for wheat flour dough, a gelatinous deoxycholate complex and a gelatin gel. The instrument is simple, robust, and reliable, as well as inexpensive.
|
|
| 9. |
- Bydén Sjöbom, Malin, et al.
(författare)
-
Binary Phase Equilibria of Three alfa-Methylsubstituted Sodium Alkanoate Surfactant Systems.
- 2003
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797. ; 257:2, s. 333-336
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 10. |
- Hermansson, Ann-Marie, et al.
(författare)
-
Characterization of protein gels by scanning and transmission electron microscopy : A methodology study of soy protein gels
- 1981
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 81:2, s. 519-530
-
Tidskriftsartikel (refereegranskat)abstract
- Different preparation techniques for scanning (SEM) and for transmission electron microscopy (TEM) were compared in order to characterize the structure of protein gels. SEM specimens were prepared by chemical fixation, dehydration, and critical-point drying. TEM specimens were prepared by using techniques of thin-sectioning and freeze-fracturing/etching. Thin sections were made after varying fixation and staining conditions. For freeze-fracturing/etching, the standard freezing procedure both using and omitting cryoprotectants (glycerol), as well as a particular modification of the "soil-emulsion" freezing technique without cryoprotective pretreatment were used. Finally, critical-point dried specimens (produced for SEM) were freeze-etched after infiltration with dioxane. The various techniques of preparation were applied to soy protein gels made in distilled water and in 0.2M NaCl under well defined conditions. The gel structures differed with regard to the state of aggregation which depended on the presence or absence of NaCl. The network structure was found to be of two levels. First, there was an orientation on the molecular level in the form of strands and fine ring structures. Second, there was a coarser network with voids of the magnitude of ?0.2 ?m. The pore size distribution of the latter network was found to be very sensitive to environmental factors such as low ionic strength and presence of cryoprotectants mainly due to swelling. The information obtained by the various techniques generally showed good agreement and were complementary. Distinct preparation artifacts caused by improper freezing or critical-point drying were also revealed. © 1981 Academic Press, Inc. All rights of reproduction in any form reserved.
|
|
