| 1. |
- Bergkvist, Magnus, et al.
(författare)
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TM-AFM Threshold Analysis of Macromolecular Orientation : A Study of the Orientation of IgG and IgE on Mica Surfaces
- 1998
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 206:2, s. 475-481
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption and orientation properties of two different types of immunoglobulin molecules on derivatized and native mica surfaces were investigated using TM-AFM. The analyses included height measurements at two different pH values and a new technique, presented here as threshold analysis, which displays the outer mantle shape of an adsorbed protein. A major difference in preferential orientation is observed upon comparing the adsorption of the two proteins onto the different surfaces. The characteristics of both the adsorbed immunoglobulin and the surface are important for any preferential orientation of the adsorbed protein.
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| 2. |
- Berner, Simon, et al.
(författare)
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Electronic and structural studies of immobilized thiol-derivatized cobalt porphyrins on gold surfaces
- 2007
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 253:18, s. 7540-7548
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Tidskriftsartikel (refereegranskat)abstract
- The immobilisation of thiol-derivatized cobalt porphyrins on gold surfaces has been studied in detail by means of combined scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). S-thioacetyl has been used as a protective group for the thiol. Different routes for deprotection of the acetyl groups were performed in acidic and in basic conditions. The results show the formation of monolayer films for the different preparation schemes. The immobilisation of the molecules on the gold surface takes place through the thiol-linkers by the formation of multiple thiolate bonds. In the case of layers formed with protected porphyrins approximately 60% of the linkers are bonded to the gold surface whereas for deprotected layers the amount of bonded linkers is increased up to about 80%. STM measurements revealed that the molecules arrange in a disordered overlayer and do not exhibit mobility on the gold surface. Annealing experiments have been performed in order to test the stability of the porphyrin layers. Disordered patterns have been observed in the STM images after annealing at T = 400 °C. XPS revealed that the sulphur content disappeared completely after annealing at T = 180 °C and that the molecules did undergo significant modifications.
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| 3. |
- Buijs, Jos, et al.
(författare)
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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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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 263:2, s. 441-448
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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).
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| 4. |
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| 5. |
- Johansson, LarsErik, et al.
(författare)
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A magnetic microchip for controlled transport of attomole levels of proteins
- 2010
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Ingår i: Lab on a Chip. - : Royal Society of Chemistry (RSC). - 1473-0197 .- 1473-0189. ; 10:5, s. 654-661
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Tidskriftsartikel (refereegranskat)abstract
- A novel method of controlled transport of proteins immobilized on micrometre-sized magnetic beads in a lab-on-a-chip environment is presented. Bead motion is controlled by lithographically made magnetic elements forming transportation lines in combination with an applied in-plane rotating magnetic field. In this way, transport of attomole amounts of proteins is controlled with micrometre precision. Also, the activity of proteins immobilized on the beads is demonstrated by injecting antibodies into the system. A critical step in developing the method was to reduce sticking forces between beads and substrate during transportation of proteins. Charge interaction was found to be of minor importance compared to hydrophobic forces. To achieve a reliable transport of biologically active proteins, both substrate and beads were coated with polyethylene glycol (PEG) and the protein covered beads were suspended in buffer with surfactants. The described system fulfils all the important unit operations of a microfluidic platform and, as a further advantage, presents less need for microchannels and electric wiring.
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| 6. |
- Larsericsdotter, Helén, et al.
(författare)
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Structure, stability, and orientation of BSA adsorbed to silica
- 2005
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. ; 289:1, s. 26-35
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, the structure, stability, and orientation of bovine serum albumin (BSA) adsorbed onto silica particles were studiedusing differential scanning calorimetry (DSC) and limited proteolysis in combination with mass spectrometry (MS). DSC gave informationon the overall structural stability of BSA while limited proteolysis was used to probe the accessibility of enzymatic cleavage sites, therebyyielding information on the orientation and structure of BSA adsorbed to silica surfaces. Thermal investigation of BSA in various buffers,both free in solution and in the adsorbed state, showed that solutes that surround the protein played an important role with respect to theoverall structural stability and the structural heterogeneity of BSA. Limited proteolysis with trypsin and chymotrypsin indicated that BSA inthe adsorbed state is oriented with domain 2 facing the silica surface. Also, upon adsorption, no additional cleavage sites were exposed. Thecombination of the results presented in this study implied that BSA molecules adsorbed onto silica particles were significantly reduced intheir structural stability, but not to an extent that internal residues within the native structure became fully exposed to the solution. 2005 Elsevier Inc. All rights reserved.
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| 7. |
- Larsericsdotter, Helén, et al.
(författare)
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Thermodynamic analysis of lysozyme adsorbed to silica
- 2004
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. ; 276:2, s. 261-268
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Tidskriftsartikel (refereegranskat)abstract
- The structural stability of hen egg white lysozyme in solution and adsorbed to small colloidal silica particles at various surface concentrations was investigated using hydrogen–deuterium (H/D) exchange in combination with mass spectrometry (HDX-MS) and differential scanning calorimetry (DSC). The combination of HDX-MS and DSC allows a full thermodynamic analysis of the lysozyme structure as both the enthalpy and the Gibbs free energy can be derived from the various measurements. Moreover, both HDX-MS and DSC provide information on the relative structural heterogeneity of lysozyme in the adsorbed state compared to that in solution. Results demonstrated that at high surface coverage, the structural stability of lysozyme was only marginally affected by adsorption to silica particles whereas the unfolding enthalpy decreased by more than 10%, meaning that the entropy of lysozyme increased with a similar value upon adsorption. Furthermore, the structural heterogeneity increased considerably. At lower surface concentrations, the structural heterogeneity increased further whereas the enthalpy of unfolding decreased. Further analyses of the HDX-MS experiments clearly indicated that folding/unfolding of lysozyme occurs through a two-domain process. These two domains had a similar amount of structural elements and a difference in stabilization energy of 8 kJ/mol, regardless if lysozyme was in solution or adsorbed to silica.
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