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- Agback, M, et al.
(författare)
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Theoretical studies of proton transfer reactions in 1-methylindene
- 1998
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Ingår i: ACTA CHEMICA SCANDINAVICA. - 0904-213X. ; 52:5, s. 541-548
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Tidskriftsartikel (refereegranskat)abstract
- The base-catalysed 1,3-proton transfer reactions in 1-methylindene have been studied theoretically in polar (water) and unpolar (cyclohexane) solvents, respectively, for two different choices of bases, namely ammonia and trimethylamine (TMA), using the SM
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- Babcock, Gerald T, et al.
(författare)
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Tyrosyl radicals in enzyme catalysis: Some properties and a focus on photosynthetic water oxidation
- 1997
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Ingår i: Acta Chemica Scandinavica. - 0904-213X. ; 51:5, s. 533-540
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Tidskriftsartikel (refereegranskat)abstract
- Enzymes that require a redox-active amino acid for catalysis or function have emerged as a distinct class of proteins. For the tyrosine-based radical enzymes, we show that the spin-density distribution in the radical follows an odd alternate pattern that is invariant to within 10% across the class. General properties of the radical enzymes are summarized from which we conclude that their essential role in catalysis is to initiate substrate metabolism by hydrogen-atom abstraction. These ideas are extended to the Y-Z and Y-D tyrosines in Photosystem II and a radical-based hydrogen-atom abstraction model for water oxidation is discussed. Differences in rates of oxidation of Y-Z and Y-D by the reaction-center chlorophyll, P680(+), under various conditions, are considered and rationalized on the basis of changes in reorganization energy induced by the local protein structure and by the presence or absence of the (Mn)(4) cluster that binds substrate water.
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- Bugarcic, Zivadin, et al.
(författare)
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cis-Influence and trans-Influence on Bond Distances. Synthesis and Crystal Structures of the Bis(trifluoromethanesulfonates) of Tetrakis(dimethylsulfide)- and Tetrakis(1,4-thioxane)-platinum(II)
- 1991
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Ingår i: Acta Chemica Scandinavica. - : Danish Chemical Society. - 0904-213X. ; 45:4, s. 361-366
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Tidskriftsartikel (refereegranskat)abstract
- Crystals of [Pt{(CH3)2S}4](CF3SO3)2, M(r) = 741.76, and [Pt(C4H8OS)4](CF3SO3)2.H2O, M(r) = 927.93, were prepared by dissolution of platinum(II) hydroxide in solutions of trifluoromethanesulfonic acid in dimethyl sulfide and 1,4-thioxane, respectively. The structures were determined from X-ray intensity data (Mo K-alpha, lambda = 0.7107 angstrom) collected at room temperature with a CAD-4 diffractometer. The space group for the dimethylsulfide compound is P2(1)/c with a = 8.5630(8), b = 8.692(1), c = 16.360(3) angstrom, beta = 97.064(9)-degrees, V = 1208.4(2) angstrom 3, Z = 2, D(x) = 2.038 Mg m-3, F(000) = 720 and mu = 6.43 mm-1. The refinements converged to R = 0.025 for 1922 reflections with I > 3 sigma(I). The 1,4-thioxane compound crystallizes in the space group C2/c with a = 14.438(2), b = 13.016(2), c = 21.696(3) angstrom, beta = 126.32(1)degrees, V = 3285.0(6) angstrom 3, Z = 4, D(x) = 1.876 Mg m-3, F(000) = 1832 and mu = 4.76 mm-1. The refinements converged to R = 0.035 for 2268 reflections with I > 3-sigma(I). The coordination around platinum is square-planar with four sulfur donor ligands in both cases. In the dimethyl sulfide complex the two unique (CH3)2S groups are disordered. The sulfur atoms occupy two different positions with coinciding methyl carbon atoms. The platinum-sulfur distances are between 2.317(3) and 2.321(4) angstrom in the dimethylsulfide and between 2.318(2) and 2.321(2) angstrom in the thioxane complex. Packing forces thus have a negligible influence on these Pt-S distances, and the mean Pt-S distance of 2.319(2) angstrom is a suitable reference distance for calculation of the cis- and trans-influence by other donor atoms on the Pt-S bond in other complexes.
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- Ekman, Pia, et al.
(författare)
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The in vitro modification of phosphorylated pyruvate kinase by a Ca2+-activated protease from rat liver
- 1980
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Ingår i: Acta Chemica Scandinavica. - : Danish Chemical Society. - 0904-213X .- 1902-3103. ; 34:6, s. 419-422
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Tidskriftsartikel (refereegranskat)abstract
- A Ca/+-activated protease from rat liver cell sap was prepared. It was shown to act on rat liver pyruvate kinase that had been phosphorylated by the catalytic subunit of cyclic AMP-dependent protein kinase, the activity being optimum at neutral pH. The modified pyruvate kinase had the same Vmax as the phosphoenzyme but showed a lower affinity for the substrate phosphoenolpyruvate. The possibility that this proteolytic attack is the step that initiates further degradation in the cell is discussed.
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