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| 2. |
- Blomberg, Margareta R. A., et al.
(författare)
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O-O bond cleavage in dinuclear peroxo complexes of iron porphyrins : a quantum chemical study
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 46:19, s. 7992-7997
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Tidskriftsartikel (refereegranskat)abstract
- To gain insight into the mechanisms of O-2 activation and cleavage in metalloenzymes, biomimetic metal complexes have been constructed and experimentally characterized. One such model complex is the dinuclear peroxo complex of iron porphyrins observed at low temperature in a noncoordinating solvent. The present theoretical study examines the O-O bond cleavage in these complexes, experimentally observed to occur either at increased temperature or when a strongly coordinating base is added. Using hybrid density functional theory, it is shown that the O-O bond cleavage always occurs in a state where two low-spin irons (S = +/- 1/2) are antiferromagnetically coupled to a diamagnetic state. This state is the ground state when the strong base is present and forms an axial ligand to the free iron positions. In contrast, without the axial ligands, the ground state of the clinuclear peroxo complex has two high-spin irons (S = +/- 5/2) coupled antiferromagnetically. Thus, the activation barrier for O-O bond cleavage is higher without the base because it includes also the promotion energy from the ground state to the reacting state. It is further found that this excitation energy, going from 10 unpaired electrons in the high-spin case to 2 in the low-spin case, is unusually difficult to determine accurately from density functional theory because it is extremely sensitive to the amount of exact exchange included in the functional.
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| 3. |
- Callaghan, Terry V., et al.
(författare)
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A new climate era in the sub-Arctic : Accelerating climate changes and multiple impacts
- 2010
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37:14, s. L14705-
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming in the Swedish sub-Arctic since 2000 has reached a level at which statistical analysis shows for the first time that current warming has exceeded that in the late 1930' s and early 1940' s, and has significantly crossed the 0 degrees C mean annual temperature threshold which causes many cryospheric and ecological impacts. The accelerating temperature increase trend has driven similar trends in the century-long increase in snow thickness, loss of lake ice, increases in active layer thickness, lake water TOC (total organic carbon) concentrations and the assemblages of diatoms, and changes in tree-line location and plant community structure. Some of these impacts were not evident in the first warm period of the 20th Century. Changes in climate are associated with reduced temperature variability, particularly loss of cold winters and cool summers, and an increase in extreme precipitation events that cause mountain slope instability and infrastructure failure. The long term records of multiple, local environmental factors compiled here for the first time provide detailed information for adaptation strategy development while dramatic changes in an environment particularly vulnerable to climate change highlight the need to adopt global mitigation strategies.
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| 4. |
- Johansson, Adam Johannes, 1976-, et al.
(författare)
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Quantifying the Effects of the Self-interaction Error in Density Functional Theory : When do the Delocalized States Appear? II. Iron-oxo Complexes and Closed-shell Substrate Molecules
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129, s. 154301-
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Tidskriftsartikel (refereegranskat)abstract
- Effects of the self-interaction error (SIE) in approximate density functional theory have several times been reported and quantified for the dissociation of charged radicals, charge transfer complexes, polarizabilities, and for transition states of reactions involving main-group molecules. In the present contribution, effects of the SIE in systems composed of a catalytic transition metal complex and a closed-shell substrate molecule are investigated. For this type of system, effects of the SIE have not been reported earlier. It is found that although the best density functionals (e.g., B3LYP) are capable of accurate predictions of structure, thermodynamics, and reactivity of such systems, there are situations and systems for which the magnitude of the SIE can be large, and for which the effects can be severe for the modeling of chemical reactivity. The largest energetic effect reported here is the artificial stabilization of a catalyst-substrate complex by as much as 18 kcal/mol. Also, the disappearance of significant energy barriers for hydrogen atom transfer in certain systems are reported. In line with earlier work, it is found that the magnitude of the SIE is related to the energetics of electron transfer between the metal catalyst and the substrate molecule. It is suggested that these problems might be circumvented by the inclusion of counterions or point charges that would alter the energetics of electron transfer. It is also pointed out that the effects of SIE in the modeling of transition metal reactivity need to be investigated further.
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| 5. |
- Johansson, Adam Johannes, 1976-, et al.
(författare)
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Quantum chemical modeling of the oxidation of dihydroanthracene by the biomimetic nonheme iron catalyst [(TMC)Fe-IV(O)](2+)
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:33, s. 12397-12406
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid density functional theory has been employed to model the oxidation of dihydroanthracene (DHA = C14H12) to anthracene (C14H10) by the biomimetic iron complex [(TMC)Fe-IV(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). Experimentally, the reaction has been studied in a solution of the reactants and the counterion trifluoroacetate (CF3CO2) in the solvent acetonitrile (CH3CN). Depending on the concentration of trifluoroacetate, different coordination situations have been observed by NMR spectroscopy. The complexity of the chemical environment offers a challenging modeling problem, and five different models were initially considered. The effects of the coordination of either a counterion or a solvent molecule were found to be rather small. The reaction was found to be a two-step process in which the first step is rate-limiting. The free energy of activation (Delta G) for the first H-abstraction was found to be between 14.5 and 16.9 kcal mol(-1) depending on the model, in reasonable agreement with experimental data. The second step has a much lower free-energy barrier, found to be completely entropic in origin. In all models, the system is found to have a triplet ground state in the Fe-IV(O) reactant. A spin-crossing of the triplet and quintet potential energy surfaces occurs before the first transition state, and the system is found to end up in the Fe-II quintet state, releasing a water molecule and the anthracene product. Because of the formation of the aromatic anthracene molecule, the reaction is very exothermic.
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| 6. |
- Johansson, Stefan, et al.
(författare)
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Performance evaluation of complex product development
- 2009
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Ingår i: DS 58-6. - 9781904670100 ; , s. 87-98
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Konferensbidrag (refereegranskat)abstract
- In this paper a conceptual performance evaluation framework is proposed and discussed. The aim of the framework is to present a tool to stakeholders, involved in dynamic complex product development activities, that assists in developing a mutual understanding of performance relevancy. It is argued that a system perspective and the possibility to tailor performance criteria and measures according to contextual circumstances are needed for performance evaluation to improve work in product development. Companies need to consider what metrics that are relevant or applicable to measure or evaluate the product development process in their own business and context. From a performance evaluation perspective, a categorization of activities in product development is made into: Planning, Implementation, and Sales and Delivery. It is argued that the three activity categories have different objectives and need to be evaluated and managed accordingly if the overall development process is to be considered successful. Moreover, each activity category can be modeled using a generic activity model to derive relevant performance criteria, needed for identifying relevant performance indicators. It is argued that this will have implications on how performance, that is, efficiency and effectiveness, in product development is evaluated at a managerial and designer level, since the performance evaluation framework is based on the performed activities. Three different perspectives - integrated, information and learning - are used as basis for the discussion in this paper in order to accomplish an enhanced understanding of the value of the performance evaluation.
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| 7. |
- Kalderén, Christina, et al.
(författare)
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CCL2 mediates anti-fibrotic effects in human fibroblasts independently of CCR2
- 2014
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Ingår i: International Immunopharmacology. - : Elsevier BV. - 1567-5769 .- 1878-1705. ; 20:1, s. 66-73
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Tidskriftsartikel (refereegranskat)abstract
- CCL2 is known for its major role as a chemoattractant of monocytes for immunological surveillance and to site of inflammation. CCL2 acts mainly through the G-protein-coupled receptor CCR2 but has also been described to mediate its effects independently of this receptor in vitro and in vivo. Emerging pieces of evidence indicate that the CCL2/CCR2 axis is involved in fibrotic diseases, such as increased plasma levels of CCL2 and the presence of CCL2-hyperresponsive fibroblasts explanted from patients with systemic sclerosis and idiopathic pulmonary fibrosis. One of the profibrotic key mediators is the myofibroblast characterized by overexpression of alpha-smooth muscle actin and collagen I. However, the correlation between the CCL2/CCR2 axis and the activation of fibroblasts is not yet fully understood. We have screened human fibroblasts of various origins, human pulmonary fibroblasts (HPF), human fetal lung fibroblasts (HFL-1) and primary preadipocytes (SPF-1) in regard to CCL2 stimulated fibrotic responses. Surprisingly we found that CCL2 mediates anti-fibrotic effects independently of CCR2 in human fibroblasts of different origins.
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| 8. |
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| 9. |
- Nilsson, Kerstin, et al.
(författare)
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Vi är oroade över senare ålderspension
- 2017
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Ingår i: Dagens Samhälle. - : Kommunernas och landstingens tidning. - 1652-6511.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Noack, Holger, et al.
(författare)
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Theoretical Insights into Heme-Catalyzed Oxidation of Cyclohexane to Adipic Acid
- 2011
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 50:4, s. 1194-1202
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Tidskriftsartikel (refereegranskat)abstract
- Adipic acid is a key compound in the chemical industry, where it is mainly used in the production of polymers. The conventional process of its generation requires vast amounts of energy and, moreover, produces environmentally deleterious substances. Thus, there is interest in alternative ways to gain adequate amounts of adipic acid. Experimental reports on a one-pot iron-catalyzed conversion of cyclohexane to adipic acid motivated a theoretical investigation based on density functional theory calculations. The process investigated is interesting because it requires less energy than contemporary methods and does not produce environmentally harmful side products. The aim of the present contribution is to gain insight into the mechanism of the iron-catalyzed cyclohexane conversion to provide a basis for the further development of this process. The rate-limiting step of the process is discussed, but considering the accuracy of the calculations, it is difficult to ensure whether the rate-limiting step is in the substrate oxidation or in the generation of the catalytically active species. It is shown that the slowest step in the substrate oxidation is the conversion of cyclohexanol to cyclohexane-1,2-diol. Hydrogen-atom transfer from one of the OH groups of cyclohexane-1,2-diol makes the intradiol cleavage occur spontaneously.
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