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Sökning: WFRF:(Norrby T)

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  • Abrahamsson, Maria, et al. (författare)
  • Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands.
  • 2008
  • Ingår i: Inorganic Chemistry. - : ACS. - 0020-1669 .- 1520-510X. ; 47:9, s. 3540-3548
  • Tidskriftsartikel (refereegranskat)abstract
    • The structural effect on the metal-to-ligand charge transfer (MLCT) excited-state lifetime has been investigated in bis-tridentate Ru(II)-polypyridyl complexes based on the terpyridine-like ligands [6-(2,2'-bipyridyl)](2-pyridyl)methane (1) and 2-[6-(2,2'-bipyridyl)]-2-(2-pyridyl)propane (2). A homoleptic ([Ru(2)(2)](2+)) and a heteroleptic complex ([Ru(ttpy)(2)](2+)) based on the new ligand 2 have been prepared and their photophysical and structural properties studied experimentally and theoretically and compared to the results for the previously reported [Ru(1)(2)](2+). The excited-state lifetime of the homoleptic Ru-II complex with the isopropylene-bridged ligand 2 was found to be 50 times shorter than that of the corresponding homoleptic Ru-II complex of ligand 1, containing a methylene bridge. A comparison of the ground-state geometries of the two homoleptic complexes shows that steric interactions involving the isopropylene bridges make the coordination to the central Ru-II ion less octahedral in [Ru(2)(2)](2+) than in [Ru(1)(2))(2+). Calculations indicate that the structural differences in these complexes influence their ligand field splittings as well as the relative stabilities of the triplet metal-to-ligand charge transfer ((MLCT)-M-3) and metal-centered ((MC)-M-3) excited states. The large difference in measured excited-state lifetimes for the two homoleptic Ru-II complexes is attributed to a strong influence of steric interactions on the ligand field strength, which in turn affects the activation barriers for thermal conversion from (MLCT)-M-3 states to short-lived (MC)-M-3 states.
  • Bolling-Sternevald, Elisabeth, et al. (författare)
  • Effect of Profound Acid Suppression in Functional Dyspepsia : a Double-Blind, Randomized, Placebo-Controlled Trial
  • 2002
  • Ingår i: Scandinavian Journal of Gastroenterology. - 0036-5521 .- 1502-7708. ; 37:12, s. 1395-1402
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Functional dyspepsia (FD) is defined as persistent or recurrent pain/discomfort centred in the upper abdomen, where no structural explanation for the symptoms is found. The role of drug treatment remains controversial. The aim in this study was to evaluate the effect of omeprazole 20 mg twice daily (b.i.d) and to test methods for symptom assessment.Methods: 197 patients fulfilling the criteria for FD were randomly allocated to double-blind treatment with omeprazole 20 mg b.i.d ( n = 100) or placebo ( n = 97) for 14 days. Patients with a known gastrointestinal disorder or with main symptoms indicating gastro-oesophageal reflux disease or irritable bowel syndrome were excluded. Helicobacter pylori testing and 24-h intra-oesophageal 24-h pH-metry were performed before randomization. The patients recorded dyspeptic symptoms on diary cards.Results: A stringent endpoint, 'complete symptom relief on the last day of treatment', was the primary efficacy variable. For the APT cohort, this was achieved in 29.0% and 17.7% on omeprazole and placebo, respectively (95% CI of difference (11.3%): -0.4%-23.0%, P = 0.057). Similar figures in the PP cohort were 31.0% and 15.5%, respectively (95% CI of difference (15.5%): 3.2%-27.7%, P = 0.018). The benefit of omeprazole in the PP cohort was confirmed by secondary endpoints such as, no dyspeptic symptoms on the last 2 days of treatment and overall treatment response. H. pylori status and the level of oesophageal acid exposure did not significantly influence the response to therapy.Conclusion: A subset of patients with FD will respond to therapy with omeprazole.
  • Brink, A., et al. (författare)
  • Fast and reversible insertion of carbon dioxide into zirconocene-alkoxide bonds. A mechanistic study
  • 2014
  • Ingår i: Dalton Transactions. - : Royal Society of Chemistry. - 1477-9226 .- 1477-9234. ; 43:23, s. 8894-8898
  • Tidskriftsartikel (refereegranskat)abstract
    • In two consecutive equilibria the compound (Cp*)(2)Zr(OMe)(2) undergoes insertion of CO2 to form the mono- and bis-hemicarbonates. Both equilibria are exothermic but entropically disfavoured. Magnetisation transfer experiments gave kinetic data for the first equilibrium showing that the rate of insertion is overall second order with a rate constant of 3.20 +/- 0.12 M-1 s(-1), which is substantially higher than those reported for other early transition metal alkoxides, which are currently the best homogeneous catalysts for dimethyl carbonate formation from methanol and CO2. Activation parameters for the insertion reaction point to a highly ordered transition state and we interpret that as there being a substantial interaction between the CO2 and the metal during the C-O bond formation. This is supported by DFT calculations showing the lateral attack by CO2 to have the lowest energy transition state.
  • Ahlquist, Mårten, et al. (författare)
  • An experimental and theoretical study of the mechanism of stannylcupration of alpha, beta-acetylenic ketones and esters
  • 2006
  • Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 12:10, s. 2866-2873
  • Tidskriftsartikel (refereegranskat)abstract
    • The title reaction has been investigated by experimental and computational (DFT) techniques, and subsequently compared to the corresponding carbocupration reaction, with particular emphasis oil the stereoselectivity. For stannylcupration of an ynone substrate, only the anti-addition product is observed, whereas for the corresponding ynoate substrate, the stereoselectivity can be affected by the reaction conditions: in the presence of methanol as proton donor, the initial syn-addition product can be trapped, whereas a syn/anti mixture is obtained in a non-protic solvent. This is in sharp contrast to the carbocupration of the same ynone substrate with a cyanocuprate (RCu(CN)Li), which is highly selective for syn-addition. The product selectivities can be understood from a detailed computational characterization of the reaction paths, and in particular from the relative stabilities of the vinyl cuprate and allenolate intermediates. It is suggested that the stereodetermining step is protonation of vinyl cuprate intermediates.
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  • Resultat 1-10 av 36
  • [1]234Nästa

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