| 1. |
- Valle-Delgado, J. J., et al.
(författare)
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Adhesion forces between protein layers studied by means of atomic force microscopy
- 2006
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 22:11, s. 5108-5114
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Tidskriftsartikel (refereegranskat)abstract
- Adhesion forces between different protein layers adsorbed on different substrates in aqueous media have been measured by means of an atomic force microscope using the colloid probe technique. The effects of the loading force, the salt concentration and pH of the medium, and the electrolyte type on the strength, the pull-off distance, and the separation energy of such adhesion forces have been analyzed in depth. Two very different proteins (bovine serum albumin and apoferritin) and two dissimilar substrates (silica and polystyrene) were used in the experiments. The results clearly point out a very important contribution of the electrostatic interactions in the adhesion between protein layers.
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| 2. |
- Valle-Delgado, J. J., et al.
(författare)
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Existence of hydration forces in the interaction between apoferritin molecules adsorbed on silica surfaces
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:21, s. 9544-9554
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Tidskriftsartikel (refereegranskat)abstract
- The atomic force microscope, together with the colloid probe technique, has become a very useful instrument to measure interaction forces between two surfaces. Its potential has been exploited in this work to study the interaction between protein (apoferritin) layers adsorbed on silica surfaces and to analyze the effect of the medium conditions (pH, salt concentration, salt type) on such interactions. It has been observed that the interaction at low salt concentrations is dominated by electrical double layer (at large distances) and steric forces (at short distances), the latter being due to compression of the protein layers. The DLVO theory fits these experimental data quite well. However, a non-DLVO repulsive interaction, prior to contact of the protein layers, is observed at high salt concentration above the isoelectric point of the protein. This behavior could be explained if the presence of hydration forces in the system is assumed. The inclusion of a hydration term in the DLVO theory (extended DLVO theory) gives rise to a better agreement between the theoretical fits and the experimental results. These results seem to suggest that the hydration forces play a very important role in the stability of the proteins in the physiological media.
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| 3. |
- Valle-Delgado, J. J., et al.
(författare)
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Hydration forces between silica surfaces : Experimental data and predictions from different theories
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123, s. 034708-
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Tidskriftsartikel (refereegranskat)abstract
- Silica is a very interesting system that has been thoroughly studied in the last decades. One of the most outstanding characteristics of silica suspensions is their stability in solutions at high salt concentrations. In addition to that, measurements of direct-interaction forces between silica surfaces, obtained by different authors by means of surface force apparatus or atomic force microscope (AFM), reveal the existence of a strong repulsive interaction at short distances (below 2 nm) that decays exponentially. These results cannot be explained in terms of the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, which only considers two types of forces: the electrical double-layer repulsion and the London-van der Waals attraction. Although there is a controversy about the origin of the short-range repulsive force, the existence of a structured layer of water molecules at the silica surface is the most accepted explanation for it. The overlap of structured water layers of different surfaces leads to repulsive forces, which are known as hydration forces. This assumption is based on the very hydrophilic nature of silica. Different theories have been developed in order to reproduce the exponentially decaying behavior (as a function of the separation distance) of the hydration forces. Different mechanisms for the formation of the structured water layer around the silica surfaces are considered by each theory. By the aid of an AFM and the colloid probe technique, the interaction forces between silica surfaces have been measured directly at different pH values and salt concentrations. The results confirm the presence of the short-range repulsion at any experimental condition (even at high salt concentration). A comparison between the experimental data and theoretical fits obtained from different theories has been performed in order to elucidate the nature of this non-DLVO repulsive force.
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| 4. |
- Valle-Delgado, J. J., et al.
(författare)
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Interaction forces between BSA layers adsorbed on silica surfaces measured with an atomic force microscope
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:17, s. 5365-5371
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Tidskriftsartikel (refereegranskat)abstract
- The interaction forces between bovine serum albumin (BSA) layers adsorbed on silica surfaces have been measured using an atomic force microscope (AFM) in Conjunction with the colloid probe technique. Measurements of force-distance curves were made at different pH values and electrolyte concentrations (NaCl and CaCl2). The interaction at long range is dominated by electrical double-layer forces, while at short surface separations an additional repulsion due to the compression of the adsorbed protein layers appears. However, prior to this steric interaction, when the pH is above the isoelectric point of the protein and at high salt concentration, a non-DLVO repulsive interaction is observed. This behavior is explained if the presence of hydration forces in the system is assumed. Theoretical predictions including a hydration term in the DLVO theory fit the experimental results satisfactorily. The results presented in this article provide a direct confirmation that the AFM colloid probe technique can provide a useful way of directly quantifying the interaction of biological macromolecules.
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| 5. |
- Valle-Delgado, J. J., et al.
(författare)
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Interactions between bovine serum albumin layers adsorbed on different substrates measured with an atomic force microscope
- 2004
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 6:7, s. 1482-1486
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Tidskriftsartikel (refereegranskat)abstract
- By the aid of an atomic force microscope (AFM) and the colloid probe technique, the interaction forces between bovine serum albumin (BSA) layers adsorbed on different substrates (silica and polystyrene) have been measured directly as a function of pH and salt concentration. Electrostatic and steric forces dominate the interactions at low salt concentrations. At high salt concentrations, when electrostatic interactions are screened, a very strange behaviour is found as a function of pH. The behaviour around the i.e.p. of the protein is also very striking: the interaction is attractive at low salt concentration, but it is repulsive at high salt concentration. These results could be explained if the presence of hydration forces is assumed. Theoretical predictions including a hydration term in the DLVO theory fit the experimental results satisfactorily.
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| 6. |
- Valle-Delgado, J. J., et al.
(författare)
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Measurement of interactions between protein layers adsorbed on silica by atomic force microscopy
- 2004
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16:26, s. 2383-2392
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Tidskriftsartikel (refereegranskat)abstract
- The present work, using an atomic force microscope and the colloid probe technique, investigates the interaction forces between bovine serum albumin (BSA) layers and between apoferritin layers adsorbed on silica surfaces. The measurements have been carried out in an aqueous medium at different pH values and NaCl concentrations. Similar behaviours have been found with both proteins. Electrostatic and steric forces dominate the interactions between the protein layers at low NaCl concentrations. However, a very strange behaviour is found as a function of pH at high NaCl concentrations. The results obtained under these conditions could be explained if the presence of hydration forces in these systems is assumed.
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