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| 2. |
- Hook, F.F, et al.
(författare)
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A comparative study of protein adsorption on titanium oxide surfaces using in situ ellipsometry, optical waveguide lightmode spectroscopy, and quartz crystal microbalance/dissipation
- 2002
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 24:2, s. 155-170
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption kinetics of three model proteins - human serum albumin, fibrinogen and hemoglobin - has been measured and compared using three different experimental techniques: optical waveguide lightmode spectroscopy (OWLS), ellipsometry (ELM) and quartz crystal microbalance (QCM-D). The studies were complemented by also monitoring the corresponding antibody interactions with the pre-adsorbed protein layer. All measurements were performed with identically prepared titanium oxide coated substrates. All three techniques are suitable to follow in-situ kinetics of protein-surface and protein-antibody interactions, and provide quantitative values of the adsorbed adlayer mass. The results have, however, different physical contents. The optical techniques OWLS and ELM provide in most cases consistent and comparable results, which can be straightforwardly converted to adsorbed protein molar ('dry') mass. QCM-D, on the other hand, produces measured values that are generally higher in terms of mass. This, in turn, provides valuable, complementary information in two respects: (i) the mass calculated from the resonance frequency shift includes both protein mass and water that binds or hydrodynamically couples to the protein adlayer, and (ii) analysis of the energy dissipation in the adlayer and its magnitude in relation to the frequency shift (c.f. adsorbed mass) provides insight about the mechanical/structural properties such as viscoelasticity. © 2002 Elsevier Science B.V. All rights reserved.
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| 3. |
- Rotsaert, F. A. J., et al.
(författare)
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Biophysical and structural analysis of a novel heme b iron ligation in the flavocytochrome cellobiose dehydrogenase
- 2003
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 278:35, s. 33224-33231
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Tidskriftsartikel (refereegranskat)abstract
- The fungal extracellular flavocytochrome cellobiose dehydrogenase (CDH) participates in lignocellulose degradation. The enzyme has a cytochrome domain connected to a flavin-binding domain by a peptide linker. The cytochrome domain contains a 6-coordinate low spin b-type heme with unusual iron ligands and coordination geometry. Wild type CDH is only the second example of a b-type heme with Met-His ligation, and it is the first example of a Met-His ligation of heme b where the ligands are arranged in a nearly perpendicular orientation. To investigate the ligation further, Met(65) was replaced with a histidine to create a bis-histidyl ligated iron typical of b-type cytochromes. The variant is expressed as a stable 90-kDa protein that retains the flavin domain catalytic reactivity. However, the ability of the mutant to reduce external one-electron acceptors such as cytochrome c is impaired. Electrochemical measurements demonstrate a decrease in the redox midpoint potential of the heme by 210 mV. In contrast to the wild type enzyme, the ferric state of the protoheme displays a mixed low spin/high spin state at room temperature and low spin character at 90 K, as determined by resonance Raman spectroscopy. The wild type cytochrome does not bind CO, but the ferrous state of the variant forms a CO complex, although the association rate is very low. The crystal structure of the M65H cytochrome domain has been determined at 1.9 Angstrom resolution. The variant structure confirms a bis-histidyl ligation but reveals unusual features. As for the wild type enzyme, the ligands have a nearly perpendicular arrangement. Furthermore, the iron is bound by imidazole N-delta1 and N-epsilon2 nitrogen atoms, rather than the typical N-epsilon2/N-epsilon2 coordination encountered in bis-histidyl ligated heme proteins. To our knowledge, this is the first example of a bis-histidyl N-delta1/N-epsilon2-coordinated protoporphyrin IX iron.
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| 4. |
- Friese, M. E. J., et al.
(författare)
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Optically driven micromachine elements
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:4, s. 547-549
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Tidskriftsartikel (refereegranskat)abstract
- We report on a proof of principle demonstration of an optically driven micromachine element. Optical angular momentum is transferred from a circularly polarized laser beam to a birefringent particle confined in an optical tweezers trap. The optical torque causes the particle to spin at up to 350 Hz, and this torque is harnessed to drive an optically trapped microfabricated structure. We describe a photolithographic method for producing the microstructures and show how a light driven motor could be used in a micromachine system.
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| 7. |
- Nilsson, P, et al.
(författare)
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Microwave-assisted enantioselective Heck reactions : Expediting high reaction speed and preparative convenience
- 2002
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Ingår i: Synthesis (Stuttgart). - Univ Uppsala, Ctr Biomed, Dept Organ Pharmaceut Chem, S-75123 Uppsala, Sweden.. - 0039-7881 .- 1437-210X. ; :11, s. 1611-1614
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Tidskriftsartikel (refereegranskat)abstract
- Palladium-catalyzed asymmetric Heck reactions have been per-formed using high temperature conditions with the aid of controlled microwave dielectric heating. Significant enantioselectivities of up to 92% ee were obtained under non-inert conditions utilizing the previously reported thermostable palladium-phosphineoxazoline catalytic system. With microwave irradiation. reaction times of hours instead of days were obtained. Enantiomeric purities and conversions were found to be strongly dependent on both the choice of the aryl triflate, the reaction temperature, the solvent and the base. Examples of asymmetric arylations of electron-rich as well as neutral cyclic alkenes are presented.
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| 8. |
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