| 1. |
- Axelsson, O., et al.
(författare)
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Reactive evaporation of potassium in CO2 and the formation of bulk intermediates
- 1994
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 12:1, s. 158-160
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Tidskriftsartikel (refereegranskat)abstract
- Potassium vapor condensed in CO2 has been studied by transmission infrared spectroscopy and by total pressure thermal desorption spectroscopy. The results are compared with surface spectroscopic data for CO2 adsorbed on alkali metal overlayers. Both systems show the formation of bulk coordinated oxalate species at cryogenic temperatures and the conversion to carbonate intermediates upon annealing.
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| 2. |
- Chen, W., et al.
(författare)
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Electronic and geometric structure of clean Pt3Ti(111)
- 1994
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Ingår i: Physical Review B. - 0163-1829 .- 1095-3795. ; 50:8, s. 5620-5627
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Tidskriftsartikel (refereegranskat)abstract
- Photoemission spectra and scanning tunneling microscopy (STM) images of the clean Pt3Ti(111) surface are presented. Grazing-emission core-level spectra show that the topmost layer is pure platinum, modified compared with the Pt(111) surface. The Pt 4f levels at the surface are shifted 0.4 eV toward the Fermi level relative to bulk Pt3Ti while the Pt 4f and Ti 2p levels in the bulk are shifted 0.4 and 1.3 eV to higher binding energy relative to pure bulk platinum and titanium, respectively, Tunneling measurements show a surface with only metallic atoms and a small p(2×2) buckling. Our observations of molecularly adsorbed CO are not compatible with metallic titanium atoms at the surface and the STM data thus indirectly confirm that only platinum atoms are present in the topmost layer. Linear muffin-tin-orbital calculations of the bulk band structure and valence-band photoemission spectra reveal highly hybridized electron states between the Pt d and Ti d levels. The calculations give a minor charge transfer from Ti to Pt, 0.37 electrons per Ti atom, but the large core-level shifts reflect the stability of the alloy and the response to the excitation rather than the amount of charge transfer. The observed segregation of platinum to the surface and the altered electronic structure of the topmost layer, due to interaction with the underlying alloy, are in full agreement with earlier conclusions based on low-energy electron-diffraction measurements and on the chemical properties of the surface. © 1994 The American Physical Society.
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| 3. |
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| 4. |
- Hoffmann, F.M., et al.
(författare)
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The activation of CO2 by potassium-promoted Ru(001) I. FT-IRAS and TDMS study of oxalate and carbonate intermediates
- 1994
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 316:3, s. 277-293
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of CO2 with the clean and alkali promoted Ru(001) surface has been studied with time-evolved Fourier transform-infrared reflection absorption spectroscopy (FT-IRAS) and thermal desorption mass spectrometry (TDMS). CO2 adsorbs on the clean Ru(001) surface at 85 K in a physisorbed CO2 monolayer, which desorbs undissociated at 100 K. The interaction of CO2 with a √3 × √3-R30° monolayer of potassium on Ru(001) results in the facile formation of oxalate at 85 K. Oxalate decomposes to carbonate after heating above 150 K, i.e. C2O4 → CO3 + CO. Vibrational spectra suggest, in agreement with theoretical calculations, an ionic carbonate species with D3h symmetry and the molecular plane oriented perpendicular to the surface, although alternate coordinations cannot be completely ruled out. Decomposition of the carbonate starts at 700 K and results in the simultaneous desorption of K and CO2 as major decompositions products, suggesting a reaction pathway of CO3 → CO2 + O and a K:CO3 stoichiometry of ≈1:1. The interaction of CO2 with a multilayer of potassium adsorbed on Ru(001), exhibits similar intermediates as observed for the monolayer, i.e. oxalate and carbonate. However, the overall reaction behavior is more complex and controlled by the penetration of CO2 into the potassium layer, which limits the reaction to only a few (4-5) of the topmost potassium layers. Reaction at 85 K reveals the formation of oxalate, CO2-2 and possibly CO-2 species. Annealing of the multilayer to 425 K results in the formation of carbonate, and the desorption of unreacted potassium. Vibrational spectra characterize an essentially ionic carbonate species with a preferential orientation of the molecular plane perpendicular to the surface, although the vibrational linewidths suggest imperfect ordering of the layer. Further annealing to 550 K results in a well-ordered "bilayer", containing two carbonate species with the molecular plane perpendicular (C2v, first layer) and parallel (C3v, second layer) to the surface, respectively. Decomposition of this layer at 700 K leaves a carbonate monolayer which subsequently decomposes at 750 K. The overall decomposition behavior of the multilayer is complex and is sensitive to the preparation and thickness of the potassium multilayer.
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| 5. |
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| 6. |
- Paul, Jan, et al.
(författare)
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Fast heme release from inactive proteins
- 1991
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - 0167-4838 .- 1879-2588. ; 1079:3, s. 330-334
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Tidskriftsartikel (refereegranskat)abstract
- Kinetics for the release of the prosthetic group from hemoproteins is presented. Heme-protein separation is a biphasic reaction, where an initial phase is significantly faster than the dominant, slow phase. A previous communication concluded that the slow phase represents the active protein. This communication presents data for porphyrin release which shows that the initial fast phase represents an inactive form of the protein. Moreover, we suggest that the fast to slow phase ratio is a sensitive monitor of sample quality for many hemoproteins and that an extrapolation of the slow phase absorbance leads to new estimates for the true physical parameters of unperturbed proteins.
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| 7. |
- Smith, M.L., et al.
(författare)
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Heme-protein fission under non-denaturing conditions
- 1991
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 88:3, s. 882-886
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Tidskriftsartikel (refereegranskat)abstract
- Slow heme transfer from horseradish peroxidases C2 and A2, cytochrome c peroxidase, chloroperoxidase, and leghemoglobins to a heme acceptor protein, apomyoglobin, has been studied under mild conditions. The reaction is best described as heme release into water followed by quick engulfment by apomyoglobin. The energetics of the activated process are large and interpreted as connected to both polypeptide motions during release and the ordering of water around the heme during solvation. The free energy required to break the iron(III)-ligand 5 (L5) bond is a minor but crucial portion of the activation free energy. Donor-acceptor protein interactions are not involved in the transfer. Fast heme release from inactive protein has also been observed. Apoprotein recombination with porphyrins and hemes suggest that this lack of activity is a result of Fe-L5 bond breaking.
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| 8. |
- Axelsson, Paul, et al.
(författare)
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Posterolateral lumbar fusion. Outcome of 71 consecutive operations after 4 (2-7) years
- 1994
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Ingår i: Acta Orthopaedica Scandinavica. - 0001-6470. ; 65:3, s. 14-309
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Tidskriftsartikel (refereegranskat)abstract
- We report the outcome of 71 consecutive posterolateral lumbar fusions without spinal instrumentation. The indication for the operation was spondylolysis-olisthesis, degenerative disc disease/facet joint arthrosis, or pain after prior laminectomy. Concerning pain relief, 29/43 patients with spondylolysis-olisthesis were classified as good. The corresponding figures in the group with degenerative disc disease and/or facet joint arthrosis were 8/16 patients and in the group with pain post-laminectomy, 6/12 patients. No surgical complications were noted. In the total material 54 patients had a solid fusion, as defined by radiographic osseous trabecular bridging at all intended levels. One-level fusions tended to heal solidly in a higher frequency than two-level fusions. For the spondylolysis-olisthesis group, healed fusion correlated with a good clinical result. Such a correlation could not be verified for the other diagnostic groups. We conclude that non-instrumented posterolateral lumbar fusion is a valid method for treating low-grade spondylolysis-olisthesis, especially when the aim is to fuse a single level. Improved patient selection methods are required in fusion for degenerative disc disease and pain after laminectomy.
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| 9. |
- Chen, W., et al.
(författare)
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Structure determination of Pt3Ti(111) by automated tensor LEED
- 1993
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 5, s. 4585-4594
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Tidskriftsartikel (refereegranskat)abstract
- An analysis of low-energy electron diffraction (LEED) I-V spectra from the clean Pt3Ti(111) surface was performed by comparing measured intensities with data calculated using an automated tensor LEED program, which employs a directed search optimization procedure. It was found that the topmost layer is pure Pt and that the other layers have the bulk composition. The first and second interlayer spacings are 2.23+or-0.03 AA and 2.21+or-0.03 AA respectively, corresponding to a contraction of 0.9% and 1.8% of the bulk value. The perpendicular buckling is 0.04 AA +or-0.05 AA in the top layer and 0.15 AA +or-0.04 AA in the second layer. The results are in full accordance with previous investigations of the physical and chemical properties of this surface.
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| 10. |
- Christakopoulos, Paul, et al.
(författare)
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Purification and Characterisation of an Extracellular β-Glucosidase with Transglycosylation and Exo-glucosidase Activities from Fusarium oxysporum
- 1994
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956 .- 1432-1033. ; 224:2, s. 379-385
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Tidskriftsartikel (refereegranskat)abstract
- An extracellular β-glucosidase from Fusarium oxysporum was purified to homogeneity by gel-filtration and ion-exchange chromatographies. The enzyme, a monomeric protein of 110 kDa, was maximally active at pH 5.0–6.0 and at 60°C. It hydrolysed 1→4-linked aryl-β-glucosides and 1→4-linked, 1→3-linked and 1→6–linked β-glucosides. The apparent Km and kcat values for p -nitrophenyl β-d-glucopyranoside (4-NpGlcp) and cellobiose were 0.093 (Km), 1.07 mM (kcat) and 1802 (Km), 461.5 min-1 (kcat), respectively. Glucose and gluconolactone inhibited the enzyme competitively with Ki values of 2.05 mM and 3.03 μM, respectively. Alcohols activated the enzyme; butanol showed maximum effect (2.2-fold at 0.5 M) while methanol increased the activity by 1.4-fold at 1 M. The enzyme catalysed the synthesis of methylglucosides, ethylglucoside and propylglucosides, as well as trisaccharides in the presence of different alcohols and disaccharides, respectively. In addition, the enzyme hydrolysed the unsubstituted and methylumbelliferyl cello-oligosaccharides [MeUmb(Glc)n] but the rate of hydrolysis decreased with increasing chain length. Analysis of products released from MeUmb(Glc)n as a function of time revealed that the enzyme attacked these substrates in a stepwise manner and from both ends. Thus, β-glucosidase from F. oxysporum, with the above interesting properties, could be of commercial interest.
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