| 1. |
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| 2. |
- Claesson, PM, et al.
(författare)
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Protein interactions at solid surfaces
- 1995
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 57, s. 161-227
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Tidskriftsartikel (refereegranskat)abstract
- In this review article we discuss a large number of the studies of interactions between protein-coated surfaces that has been presented in the literature. We also demonstrate how to relate surface force data to results from other techniques in order to provide a more full picture of protein behaviour at interfaces. One aim of the article is to discuss the experimental procedure and the difficulties with surface force measurements in protein systems. It is particularly important to point out how the sensitivity of this technique differs from that of other techniques, e.g. in determining structural changes in adsorbed proteins and in detecting proteins adsorbed on top of an inner firmly bound layer. It is also important to realize which surface force data that cannot be easily compared with findings from other techniques (one example is the kinetics of adsorption and desorption). We have tried to group proteins into different classes depending on their size and structure, and to try to find results that are common within these classes. It was found that some observations for unordered proteins with amphiphilic character, and for the small compact proteins, appear consistently within the respective class. Hence, for these types of protein common features/principles of the interfacial behaviour are identified. The very large and flexible glycoproteins behave in a similar way to synthetic polymers, but we found it hard to draw any firm conclusions based on the surface force studies presented so far. Perhaps, the most complicated surface behaviour is observed for soft globular proteins that undergo large scale conformational changes upon adsorption and when the layers are held under a high compressive force.
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| 3. |
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| 4. |
- Rippner Blomqvist, B., et al.
(författare)
-
Ellipsometric characterization of ethylene oxide-butylene oxide diblock copolymer adsorption at the air-water interface
- 2005
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 21, s. 5061-5068
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Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry was used to determine the adsorbed layer thickness (d) and the surface excess (adsorbed amount, ¡) of a nonionic diblock copolymer, E106B16, of poly(ethylene oxide) (E) and poly(butylene oxide) (B) at the air-water interface. The results were obtained (i) by the conventional ellipsometric evaluation procedure using the change of both ellipsometric angles and ¢ and (ii) by using the change of ¢ only and assuming values of the layer thickness. It was demonstrated that the calculated surface excesses from the different methods were in close agreement, independent of the evaluation procedure, with a plateau adsorption of about 2.5 mg/m2 (400 Å2/molecule). Furthermore, the amount of E106B16 adsorbed at the air-water interface was found to be almost identical to that adsorbed from aqueous solution onto a hydrophobic solid surface. In addition, the possibility to use combined measurements with H2O or D2O as substrates to calculate values of d and ¡ was investigated and discussed. We also briefly discuss within which limits the Gibbs equation can be used to determine the surface excess of polydisperse block copolymers
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| 5. |
- Auer, F, et al.
(författare)
-
Switchable assembly of stable, ordered molecular layers
- 1999
-
Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 5, s. 1150-1159
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Tidskriftsartikel (refereegranskat)abstract
- Bisamidines can be assembled on self-assembled monolayers of mercaptoalkanoic acids on gold to form stable and ordered but pH-switchable layers (see diagram). At basic pH the layers are stable and charge selective towards charged surfactants and plasma proteins. The system can potentially be used to reversibly introduce new surface properties for given applications that use one single substrate.
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| 6. |
- Berg, I. C. H., et al.
(författare)
-
Lubricating properties of the initial salivary pellicle - an AFM Study
- 2003
-
Ingår i: Biofouling (Print). - : Informa UK Limited. - 0892-7014 .- 1029-2454. ; 19:6, s. 365-369
-
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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| 7. |
- Billsten, Peter, et al.
(författare)
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Structural Changes of T4 Lysozyme upon Adsorption to Silica Nanoparticles Measured by Circular Dichroism
- 1995
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 175:1, s. 77-82
-
Tidskriftsartikel (refereegranskat)abstract
- The change in the secondary structure of T4 lysozyme upon adsorption to silica particles was studied with circular dichroism. Two different mutants of the protein along with the wild type were investigated. The mutants differ from wild type by substitution of isoleucine for cysteine or tryptophan at position 3 and were chosen to represent a range of stability as quantified by their energies of thermal unfolding. The mutants differ in ΔG, at 65°C and pH 6.5, compared to the wild-type enzyme with -2.8 and 1.2 kcal/mol for the tryptophan and cysteine mutants, respectively. After adsorption to 9-nm silica nanoparticles for 90 min, a large change in the spectrum was observed for the less stable tryptophan mutant, while the changes were smaller for the wild type and the cysteine mutant. The spectral changes before and after adsorption corresponded to a calculated loss of α-helix of 12% for the wild type, 9% for the cysteine mutant, and 29% for the tryptophan mutant. Structural changes during adsorption of the proteins were also followed kinetically at 222 nm. The rate of conformational change differed among the three proteins and was fastest for the tryptophan mutant. In the case of the tryptophan mutant the time required for half of the measured change to occur was approximately 5 min, while for the cysteine mutant and the wild-type T4 lysozyme more than 10 min was required.
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| 8. |
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| 9. |
- Carlsson, F, et al.
(författare)
-
Interactions between local anaesthetic agents and poly(N-isopropyl acrylamide) through phase behavior, surface tension, and adsorption measurements
- 2001
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 233, s. 320-328
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Tidskriftsartikel (refereegranskat)abstract
- he interaction between the local anaesthetic agents prilocaine and lidocaine, on one hand, and poly(N-isopropyl acrylamide) (pNIPAM), on the other, is investigated through studies of the polymer phase behavior and through surface tension and adsorption measurements. In particular, the cloud points (CP) for pNIPAM in the presence of lidocaine and prilocaine under different conditions were compared to the effects of electrolytes and alcohols. It was found that the electrolytes affect the CP of pNIPAM in a lyotropic manner, whereas alcohols depress the CP of pNIPAM in an alkyl chain length dependent way; i.e., the longer the chain, the larger the decrease in CP. Lidocaine and prilocaine affect the CP of pNIPAM in a pH-dependent manner. Below the p Ka of lidocaine and prilocaine, these cosolutes do not substantially affect the CP in the concentration range investigated, but rather behave analogous to simpler electrolytes. Above the p Ka, on the other hand, they strongly depress the CP already at low concentrations. In parallel, at low pH, the surface tension reduction due to lidocaine or prilocaine is marginal, whereas at high pH the surface tension is reduced considerably. Thus, the poor solubility of prilocaine and lidocaine at high pH causes these to become more surface active and simultaneously interact in a more pronounced way with pNIPAM. Furthermore, it was found from ellipsometry that an adsorbed pNIPAM layer contracts when lidocaine is added, presumably due to a lidocaine-pNIPAM interaction similar to that causing pNIPAM to phase separate. Analogous to this, it was demonstrated that an adsorbed pNIPAM layer shrinks and swells reversibly when the temperature is cycled above and beneath the CP.
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| 10. |
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| 11. |
- Fröberg, JC, et al.
(författare)
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Effect of structural stability on the characteristics of adsorbed layers of T4
- 1998
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 14, s. 456-462
-
Tidskriftsartikel (refereegranskat)abstract
- The interferometric surface force technique has been employed to determine how the structural stability of globular proteins affects their adsorption and the interactions between adsorbed protein layers. The system consisted of positively charged bacteriophage T4 lysozyme and negatively charged mica surfaces. The wild type and one synthetic mutant of the protein, Ile3->Trp, differing in structural stability while the total charge and tertiary structure are the same, were studied. The adsorption leads to a nearly complete neutralization of the negative surface charge of mica, reducing the long-range electrostatic double-layer interaction acting between mica surfaces. The thickness of the adsorbed layer is for the wild type consistent with the dimensions of the protein, while the Ile3->Trp mutant gives a layer with a thickness smaller than any of its native dimensions. Another consequence of the difference in structural stability is that the short range attraction between one protein layer and one bare mica surface is an order of magnitude larger for the Ile3->Trp mutant than for the wild type. The results demonstrate that the less stable mutant loses its tertiary structure upon adsorption, whereas the wild type retains its globular shape. These differences provide an understanding for the differences in adsorbed amount and complements the information about changes in secondary structure upon adsorption observed with other methods.
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| 12. |
- Hahn Berg, IC, et al.
(författare)
-
Ellipsometry and TIRF studies of enzymatic degradation of interfacial proteinaceous layers
- 2001
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 17, s. 1641-1652
-
Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry and total internal reflectance fluorescence spectroscopy (TIRF) have been employed to investigate the layer structure of gelatin adsorbed from aqueous solutions onto silica/glass and methylated silica/glass, as well as the effects of addition of the proteolytic enzymes krillase and trypsin, in relation to temperature, enzyme concentration and enzymatic activity. The results for the hydrophilic substrates show that homogeneous and heterogeneous exchange occurs readily, as does autolysis of trypsin at the interface. At the hydrophobic substrates, the effect of exchange is limited and a residual gelatin fraction is present at the interface throughout. The interfacial behavior of gelatin above and below the helix formation temperature (Thelix) shows that more extended surface layers are formed at both substrates below Thelix . At the hydrophilic substrates, the higher adsorbed layer thickness below Thelix is mainly due to the adsorption of more gelatin than at the higher temperature, whereas, at the hydrophobic substrates, the increase in layer thickness below Thelix is due to a decrease in packing density. Enzyme addition to preadsorbed gelatin at methylated silica results in the transition to a thinner and denser layer, that contains both residual gelatin and proteolytic enzymes (i.e., krillase or trypsin). At hydrophobic surfaces, a faster and more extensive degradation of the gelatin layer is observed with increasing krillase concentration, the effect of which is similar above and below Thelix . The effect of trypsin addition to preadsorbed gelatin is enhanced at TThelix . Finally, the exposure of preadsorbed gelatin to inactivated krillase showed a nearly complete elimination in the effects observed upon addition of intact krillase. This indicated that the enzymatic activity of krillase in its native form plays a major role for the interaction between krillase and preadsorbed gelatin.
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| 13. |
- Hahn Berg, IC, et al.
(författare)
-
Intraoral lubrication of PRP-1, statherin and mucin as studied by AFM
- 2004
-
Ingår i: Biofouling (Print). - 0892-7014 .- 1029-2454. ; 20, 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 pellicle key components (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 behavior. To various extent, the investigated proteins 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. We conclude that PRP-1 has the highest lubricating capacity as a pure fraction among the investigated preparations, 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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| 14. |
- Hahn Berg, IC, et al.
(författare)
-
Lubricating properties of the initial salivary pellicle – an AFM study
- 2003
-
Ingår i: Biofouling (Print). - 0892-7014 .- 1029-2454. ; 19, s. 365-369
-
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 as well as potential artificial saliva formulations. Here we measure normal as well as lateral forces, acting between adsorbed salivary films, for the first time by means of colloidal probe atomic force microscopy. We find 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 well 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 atomic force microscopy, which offers a direct and quantitative measure of the lubrication on 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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| 15. |
- Hahn Berg, IC, et al.
(författare)
-
Proteolytic degradation of oral biofilms in vitro and in vivo: potential of proteases originating from Euphausia superba for plaque control
- 2001
-
Ingår i: European Journal of Oral Sciences. - 0909-8836 .- 1600-0722. ; 109, s. 316-324
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with enzymatic removal of dental plaque, in vitro as well as in vivo, using proteases from the Antarctic krill shrimp (Euphausia superba), referred to as Krillase®. Krillase exhibits both endo- and exopeptidase activity but has no microbicidal effect. In model systems with pure cultures of oral microorganisms, Krillase demonstrated inhibition of microbial adhesion to saliva-coated hydroxyapatite. Furthermore, a protocol for the growth of reproducible in vitro plaque films has been developed, and effects of Krillase on the plaque film were investigated by means of scanning electron microscopy (SEM). The results showed that Krillase efficiently released microorganisms from plaque in vitro, the effect being dependent on the enzymatic activity. The surface energy of the substratum had a minor influence on the formation and removal of plaque in vitro. Ellipsometric studies on the formation and enzymatic removal of a salivary pellicle indicated that the enzymatic effect on plaque may partly depend on degradation of the salivary pellicle. Krillase was also able to remove plaque accumulated on dentures in vivo. Our results demonstrate the potential of Krillase for plaque control, and that these enzymes are worthy of further investigations including clinical studies and work to find a suitable vehicle
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| 16. |
- Hahn Berg, IC, et al.
(författare)
-
Salivary protein adsorption onto hydroxyapatite and SDS-mediated elution studied by in situ ellipsometry
- 2001
-
Ingår i: Biofouling (Print). - 0892-7014 .- 1029-2454. ; 17, s. 173-187
-
Tidskriftsartikel (refereegranskat)abstract
- Whole unstimulated saliva from two donors was investigated both with respect to adsorption characteristics and SDS-induced elutability. Salivary protein adsorption onto hydroxyapatite (HA) discs was studied by means of in situ ellipsometry in the concentration range 0.1-20% saliva. The adsorbed amounts on HA were found to be similar to those on silica, but the rates of adsorption were lower. Protein adsorption was virtually unaffected by the presence of Na+, whereas Ca2+ induced nucleation of calcium phosphate at the surface, the deposition rate being influenced by the pellicle age but not by the presence of saliva in bulk solution. The SDS elutability of adsorbed pellicles was determined on HA as well as on silica surfaces. Desorption from both surfaces was found to occur in the same SDS concentration range, although a residual layer was observed on HA. The slight net positive charge and lower charge density of HA as compared to the strongly negatively charged silica, may, at least partly, account for this observation by causing a reduction in the repulsive force between protein-surfactant complexes and the surface. Interindividual differences, observed in the adsorption as well as elution experiments, are thought to relate to the compositional differences observed by SDS-PAGE
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| 17. |
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| 18. |
- Hansen, PHF, et al.
(författare)
-
Shear induced aggregation of a pectin stabilised emulsion in two dimensions
- 2001
-
Ingår i: Colloid and Polymer Science. - 0303-402X .- 1435-1536. ; 279, s. 153-160
-
Tidskriftsartikel (refereegranskat)abstract
- Shear induced aggregation of a Pectin stabilised emulsion trapped at the air-liquid interface was studied in a Couette system by video enhanced microscopy. From dimension analysis, Brownian motion was identified to enhance the probability of bond formation. The characteristic time scale of aggregation was found to scale as tc \sim / rather than tc \sim 1/˙ as expected for orthokinetic aggregation. The structure of very large clusters showed strongly rearranged strands and fractal scaling for low ˙ and , analysed by density auto-correlation. At high ˙ and , the cluster was dominated by larger drops and no fractal scaling could be determined for the accessible length scales.
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| 19. |
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| 20. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Lysozyme-water interactions studied by sorption calorimetry
- 2004
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 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 50degreesC. Desorption calorimetric measurements were performed at 25 and 40degreesC. 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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| 21. |
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| 22. |
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| 23. |
- McGuire, J, et al.
(författare)
-
Comparative Adsorption Studies with Synthetic, Structural Stability and Charge Mutants of Bacteriophage T4 Lysozyme.
- 1995
-
Ingår i: Proteins at Interfaces II. - Washington, DC : American Chemical Society. - 9780841233041 - 9780841215276 ; 602, s. 52-65
-
Bokkapitel (refereegranskat)abstract
- We have purified wild type, three structural stability mutants and four charge mutants of bacteriophage T4 lysozyme from E. coli strains harboring desired expression vectors. Structural stability mutants were produced by substitution of the isoleucine at amino acid position three, yielding a set of proteins with stabilities ranging from 1.2 kcal/mol greater, to 2.8 kcal/mol less, than that of the wild type. Charge mutants were produced by replacement of positively charged lysine residues with glutamic acid, yielding a set of molecules with formal charges ranging from +5 to +9 units. Adsorption kinetic data, along with the dodecyltrimethylammonium bromide-mediated elutability of each protein, has been monitored with in situ ellipsometry at hydrophobic and hydrophilic silica surfaces. A simple mechanism that allows adsorbing protein to adopt one of two states, each associated with a different resistance to elution and a different interfacial area occupied per molecule, has been used to assist interpretation of the adsorption data. Conditions implicit in the model have been used to estimate the fraction of molecules present on the surface just prior to surfactant addition that had adopted the more resistant state, and this fraction has been observed to correlate positively with resistance to elution. For the stability mutants, these properties were clearly related to protein stability as well. Concerning the charge mutants, results have not been clearly explainable in terms of protein net charge, but rather in terms of the probable influence of the location of each substitution relative to other mobile, solvent-exposed, charged side chains of the molecule.
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| 24. |
- McGuire, J, et al.
(författare)
-
Structural Stability Effects on Adsorption and Dodecyltrimethylammonium Bromide-Mediated Elutability of Bacteriophage T4 Lysozyme at Silica Surfaces
- 1995
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 170, s. 182-192
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of structural stability on the adsorption and dodecyltrimethylammonium bromide (DTAB)-mediated elutability of bacteriophage T4 lysozyme was monitored at hydrophilic and hydrophobic silica surfaces with in situ ellipsometry. Mutant lysozymes were produced by substitution of the isoleucine at amino acid position three, yielding a set of proteins with values of ΔGunfolding ranging from 1.2 kcal/mol greater to 2.8 kcal/mol less than that of the wild type. Three structural stability mutants along with the wild type protein were purified from Escherichia coli strains harboring the desired expression vectors. Differences in interfacial behavior among the proteins were observed to be substantial with respect to both the adsorption kinetic behavior and the DTAB-mediated elutability exhibited by each. A positive correlation was observed to exist between elutability and protein stability. A simple mechanism that allows absorbing protein to adopt one of two states, each associated with a different resistance to elution and a different interfacial area occupied per molecule, was used to assist interpretation of the adsorption data recorded prior to surfactant addition. Conditions implicit in the model allowed estimation of the mass of molecules present on the surface just prior to surfactant addition, that were in the more resistant state in each test. The calculated fraction of adsorbed protein in the more tightly bound state correlated positively with resistance to elution.
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| 25. |
- McGuire, J, et al.
(författare)
-
The Influence of Net Charge and Charge Location on Adsorption and Dodecyltrimethylammonium Bromide-Mediated Elutability of Bacteriophage T4 Lysozyme at Silica Surfaces
- 1995
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 170:1, s. 193-202
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of net charge and charge location on the adsorption and dodecyltrimethylammonium bromide (DTAB)-mediated elutability of bacteriophage T4 lysozyme was monitored at hydrophilic and hydrophobic silica surfaces with in situ ellipsometry. Mutant lysozymes were produced by substitution of selected lysine residues with glutamic acid, each substitution thus decreasing the net charge of the protein by 2 units. The wild-type protein (net charge +9) and four mutant proteins, each of net charge +7 or +5, were purified from Escherichia coli strains harboring the desired expression vectors. Differences in interfacial behavior among the proteins were observed with respect to both the adsorption kinetics and the DTAB-mediated elutability exhibited by each. No simple relationship between protein net charge and surface behavior was observed, indicating that the location of the charge replacements had the major effect on surface behavior. At hydrophilic surfaces, mutations allowing the most mobile regions of positive charge to more readily orient toward the interface increased that protein's resistance to elutability; at hydrophobic surfaces, mutations favoring or otherwise not inhibiting hydrophobic association between the protein and the surface increased the resistance to elutability. This was not related to protein net charge, but to the probable influence of the location of each substitution relative to the other mobile, solvent-exposed, charged side chains of the molecule.
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| 26. |
- Skepö, Marie, et al.
(författare)
-
Coarse-grained modeling of proline rich protein 1 (PRP-1) in bulk solution and adsorbed to a negatively charged surface
- 2006
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110:24, s. 12141-12148
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Tidskriftsartikel (refereegranskat)abstract
- Structural properties of the acidic proline rich protein PRP-1 of salivary origin in bulk solution and adsorbed onto a negatively charged surface have been studied by Monte Carlo simulations. A simple model system with focus on electrostatic interactions and short-ranged attractions among the uncharged amino acids has been used. In addition to PRP-1, some mutants were considered to assess the role of the interactions in the systems. Contrary to polyelectrolytes, the protein has a compact structure in salt-free bulk solutions, whereas at high salt concentration the protein becomes more extended. The protein adsorbs to a negatively charged surface, although its net charge is negative. The adsorbed protein displays an extended structure, which becomes more compact upon addition of salt. Hence, the conformational response upon salt addition in the adsorbed state is the opposite as compared to that in bulk solution. The conformational behavior of PRP-1 in bulk solution and at charged surfaces as well as its propensity to adsorb to surfaces with the same net charge are rationalized by the block polyampholytic character of the protein. The presence of a triad of positively charged amino acids in the C-terminal was found to be important for the adsorption of the protein.
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| 27. |
- Valentijn-Benz, Marianne, et al.
(författare)
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Sphingoid Bases Inhibit Acid-Induced Demineralization of Hydroxyapatite
- 2015
-
Ingår i: Caries Research. - : S. Karger. - 0008-6568 .- 1421-976X. ; 49:1, s. 9-17
-
Tidskriftsartikel (refereegranskat)abstract
- Calcium hydroxyapatite (HAp), the main constituent of dental enamel, is inherently susceptible to the etching and dissolving action of acids, resulting in tooth decay such as dental caries and dental erosion. Since the prevalence of erosive wear is gradually increasing, there is urgent need for agents that protect the enamel against erosive attacks. In the present study we studied in vitro the anti-erosive effects of a number of sphingolipids and sphingoid bases, which form the backbone of sphingolipids. Pretreatment of HAp discs with sphingosine, phytosphingosine (PHS), PHS phosphate and sphinganine significantly protected these against acid-induced demineralization by 80 ± 17%, 78 ± 17%, 78 ± 7% and 81 ± 8%, respectively (p < 0.001). On the other hand, sphingomyelin, acetyl PHS, octanoyl PHS and stearoyl PHS had no anti-erosive effects. Atomic force measurement revealed that HAp discs treated with PHS were almost completely and homogeneously covered by patches of PHS. This suggests that PHS and other sphingoid bases form layers on the surface of HAp, which act as diffusion barriers against H+ ions. In principle, these anti-erosive properties make PHS and related sphingosines promising and attractive candidates as ingredients in oral care products.
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| 28. |
- Wahlgren, M, et al.
(författare)
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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
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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.
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| 29. |
- Wahlgren, M, et al.
(författare)
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Adsorption of Lysozyme
- 1994
-
Ingår i: ACS National Meeting Book of Abstracts. - 0065-7727. ; 207:1, s. 74-74
-
Konferensbidrag (refereegranskat)
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| 30. |
- Wahlgren, M, et al.
(författare)
-
Competition Between Fibrinogen and a Nonionic Surfactant at Adsorption to a Wettability Gradient Surface
- 1995
-
Ingår i: Colloids and Surfaces B: Biointerfaces. - 0927-7765. ; 4:1, s. 23-31
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Tidskriftsartikel (refereegranskat)abstract
- The competition between mixtures of fibrinogen and a non-ionic surfactant (C12E5) with respect to adsorption onto a wettability gradient solid surface was studied by the use of ellipsometry. The effects of surface hydrophobicity and surfactant association were investigated. Furthermore the effect of clouding of the surfactant was studied by performing measurements at temperatures above and below the cloud point. At all concentrations, the fibrinogen (0.02–0.40 mg ml−1) was preferentially adsorbed onto the hydrophilic part of the gradient surface. At surfactant concentrations above and around the CMC, the protein was inhibited from adsorbing by the surfactant at the hydrophobic as well as in the intermediate part (50° ⩽ contact angle ⩽ 80°) of the gradient. As the surfactant concentrations was further reduced the protein was able to compete and adsorb onto the whole or parts of the gradient surface. In the case of a surfactant concentration of two-fifths of the CMC, the competitive power of the surfactant increased with temperature and the surfactant could hinder protein adsorption over a larger interval of the gradient surface. These observations were also verified by in situ measurements on non-gradient surfaces. The competition can be explained by considering the main interactions between protein and surfactant with the surface. In this respect cooperation in the self-association of the surfactant seems to be of great importance. The use of gradient surfaces makes it possible to observe subtle changes in these interactions.
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| 32. |
- Wahlgren, M, et al.
(författare)
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Removal of Lysozyme from Methylated Silica Surfaces by a Nonionic Surfactant Pentaethyleneglycol Mono n-Dodecyl Ether (C12E5)
- 1996
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Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765. ; 6:2, s. 63-69
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Tidskriftsartikel (refereegranskat)abstract
- The removal of lysozyme adsorbed to a hydrophobic surface by a non-ionic surfactant, C12E5, was investigated using in situ ellipsometry. Both the adsorption and removal of protein were studied at different protein and surfactant concentrations. The surfaces used were methylated silica surfaces and the experiments were carried out at pH 5.6 in 0.01 M NaCl solution. The adsorption isotherm of lysozyme did not reach a plateau level within the concentration range investigated and judging from the adsorbed amount at high protein concentrations the protein adsorbs at least in a bilayer. The adsorbed protein was only to a minor extent removed upon rinsing with buffer and addition of surfactant gave partial removal which was dependent on surfactant concentration and the amount of protein adsorbed. An increase in the surface concentration of protein led to a decrease in the fraction of the adsorbate that was removed due to surfactants. However, the absolute amount removed did not decrease but levelled off at 1.3 mg m−2. The removal of adsorbed lysozyme started at about the same surfactant concentration as that required for the surfactant to adsorb at the interface and the amount removed by surfactant increased with surfactant concentration up to half its cmc.
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| 33. |
- Wahlgren, M, et al.
(författare)
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The Elutability of Fibrinogen by Sodium Dodecyl Sulphate and Akyltrimethylammonium Bromides.
- 1993
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 70:2, s. 151-158
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Tidskriftsartikel (refereegranskat)abstract
- The elutability of adsorbed fibrinogen by cationic surfactants of different chain lengths (dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, cetyltrimethylammonium bromide), and an anionic surfactant (sodium dodecyl sulphate (SDS)) was studied using in situ ellipsometry. The concentrations of the surfactants were twice the CMC in water and for fibrinogen, 0.4 mg ml−1. The investigation was carried out for two model surfaces: methylated silica (hydrophobic) and silica (hydrophilic and negatively charged, at pH 7). As a complement, a surface with a gradient in surface hydrophobicity was used. The end points of the gradient are similar to the methylated silica and silica surfaces with respect to hydrophobicity. All the surfactants adsorbed on the methylated silica surfaces, whereas only the cationic surfactants adsorbed on the silica surface. The adsorption of fibrinogen was 0.64 ± 0.03 μg cm−1 and 0.35 ± 0.03 μg cm−2 on the methylated silica and silica surfaces, respectively. Addition of surfactant led to a decrease in the amount of fibrinogen adsorbed on the methylated silica surface for all the surfactants, but only SDS affected the amounts adsorbed on the silica surfaces to any great extent. Despite the fact that the cationic surfactants adsorbed onto the silica surface, they did not affect the amount of fibrinogen adsorbed. The removal of protein decreased for the alkyltrimethylammonium bromides with increasing hydrophilicity of the gradient surfaces, and the amount of fibrinogen remaining after surfactant treatment decreased slightly for SDS. The effect of the chain length of the surfactant on elutability was small. The rate of removal of fibrinogen by the surfactants was found to be slower for SDS compared with the alkyltrimethylammonium bromides at the methylated silica surface, and at the hydrophobic end and in the intermediate part of the gradient.Adsorption from mixtures of surfactant and fibrinogen was also studied and the effects of cationic and anionic surfactants were quite different. The adsorption of fibrinogen was increased in the presence of the cationic surfactants, especially on the silica surface, but decreased in the presence of SDS. As surfactant adsorption onto clean surfaces is reversible with respect to dilution it might be assumed that the adsorbate mainly consists of fibrinogen. A trend was observed for the amounts of fibrinogen remaining after rinsing with buffer; the amounts increased with decreasing length of the surfactant hydrocarbon chain.
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| 34. |
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| 35. |
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