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  • 1.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Borowski, Tomasz
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Oxygen Activation by Rieske Non-Heme Iron Oxygenases, a Theoretical Insight2004Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, nr 34, s. 13031-13041Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The first steps of dioxygen activation in naphthalene 1,2-dioxygenase have been investigated by means of hybrid density functional theory. Reduction of molecular oxygen by this Rieske dioxygenase occurs in the catalytic domain accommodating a mononuclear non-heme iron(II) complex, and it requires two external electrons ultimately delivered by a Rieske [2Fe−2S] cluster hosted in the neighboring domain. Theoretical tools have been applied to gain insight into the O2-binding step and into the first one-electron-transfer process involving the mononuclear and the Rieske centers, and yielding an iron(II)−superoxo intermediate. The reaction, which is mimicked with a model including both metal sites, is found to be a reversible equilibrium. Although the entropic loss associated with the binding of O2 to iron(II) is not canceled by the corresponding enthalpic binding energy, it is, however, balanced by the exothermicity of the electron transfer process from the Rieske cluster to the dioxygen-bound iron(II) complex. The rationalization for the calculated energetics is related to the values of the ionization potential (IP) of the Rieske cluster and the electron affinity (EA) of the mononuclear iron complex: the latter is computed to be higher than the former, when dioxygen is bound to the metal. The possibility that a second external electron is delivered to the mononuclear site before dioxygenation of the substrate has also been examined. It is shown that, if the second electron is available in the Rieske domain, the electron transfer process is energetically favored. The results acquired with the large model comprising the two metal centers are compared to the corresponding information collected from the study of smaller models, where either the mononuclear iron complex or the Rieske cluster is included.

  • 2.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    A Theoretical Study of the Cis-Dihydroxylation Mechanism in Naphthalene 1,2-dioxygenase2004Ingår i: Journal of Biological Inorganic Chemistry, ISSN 0949-8257, E-ISSN 1432-1327, Vol. 9, nr 4, s. 439-452Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The catalytic mechanism of naphthalene 1,2-dioxygenase has been investigated by means of hybrid density functional theory. This Rieske-type enzyme, which contains an active site hosting a mononuclear non-heme iron(II) complex, uses dioxygen and two electrons provided by NADH to carry out the cis-dihydroxylation of naphthalene. Since a (hydro)peroxo-iron(III) moiety has been proposed to be involved in the catalytic cycle, it was probed whether and how this species is capable of cis-dihydroxylation of the aromatic substrate. Different oxidation and protonation states of the Fe–O2 complex were studied on the basis of the crystal structure of the enzyme with oxygen bound side-on to iron. It was found that feasible reaction pathways require a protonated peroxo ligand, FeIII–OOH; the deprotonated species, the peroxo-iron(III) complex, was found to be inert toward naphthalene. Among the different chemical patterns which have been explored, the most accessible one involves an epoxide intermediate, which may subsequently evolve toward an arene cation, and finally to the cis-diol. The possibility that an iron(V)-oxo species is formed prior to substrate hydroxylation was also examined, but found to implicate a rather high energy barrier. In contrast, a reasonably low barrier might lead to a high-valent iron-oxo species [i.e. iron(IV)-oxo] if a second external electron is supplied to the mononuclear iron center before dioxygenation.

  • 3.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mechanism of Aromatic Hydroxylation by an Activated Fe(IV)=O Core in Tetrahydrobiopterin-Dependent Hydroxylases2003Ingår i: Chemistry: a European Journal, ISSN 0947-6539, Vol. 9, nr 17, s. 4055-4067Artikel i tidskrift (Refereegranskat)
  • 4.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mechanism of Dioxygen Cleavage in Tetrahydrobiopterin-Dependent Amino Acid Hydroxylases2003Ingår i: Chemistry: a European Journal, ISSN 0947-6539, Vol. 9, nr 1, s. 106-115Artikel i tidskrift (Refereegranskat)
  • 5.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Que, Jr, Lawrence
    A Density Functional Study of a Biomimetic Non-Heme Iron Catalyst: Insights into Alkane Hydroxylation and Olefin Oxidation by a Formally HO-Fe(V)=O Oxidant2004Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 11, nr 2, s. 692-705Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reactivity of [HO(tpa)FeVO] (TPA=tris(2-pyridylmethyl)amine), derived from OO bond heterolysis of its [H2O(tpa)FeIIIOOH] precursor, was explored by means of hybrid density functional theory. The mechanism for alkane hydroxylation by the high-valent iron–oxo species invoked as an intermediate in Fe(tpa)/H2O2 catalysis was investigated. Hydroxylation of methane and propane by HOFeVO was studied by following the rebound mechanism associated with the heme center of cytochrome P450, and it is demonstrated that this species is capable of stereospecific alkane hydroxylation. The mechanism proposed for alkane hydroxylation by HOFeVO accounts for the experimentally observed incorporation of solvent water into the products. An investigation of the possible hydroxylation of acetonitrile (i.e., the solvent used in the experiments) shows that the activation energy for hydrogen-atom abstraction by HOFeVO is rather high and, in fact, rather similar to that of methane, despite the similarity of the HCH2CN bond strength to that of the secondary CH bond in propane. This result indicates that the kinetics of hydrogen-atom abstraction are strongly affected by the cyano group and rationalizes the lack of experimental evidence for solvent hydroxylation in competition with that of substrates such as cyclohexane.

  • 6.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Que, Jr., Lawrence
    A Density Functional Study of O-O Bond Cleavage for a Biomimetic Non-Heme Iron Complex Demonstrating an Fe(V)-Intermediate2002Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, nr 37, s. 11056-11063Artikel i tidskrift (Refereegranskat)
  • 7.
    Bassan, Arianna
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Que, Jr., Lawrence
    Theoretical Studies on Olefin Oxidation by Biomimetic Non-Heme Iron(III)-Hydroperoxo ComplexesManuskript (Övrigt vetenskapligt)
  • 8.
    Blomberg, L. Mattias
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R.A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E.M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Reduction of Nitric Oxide in Bacterial Nitric Oxide Reductase: A Theoretical Model Study2006Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1757, nr 4, s. 240-252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanism of the nitric oxide reduction in a bacterial nitric oxide reductase (NOR) has been investigated in two model systems of the heme-b3-FeB active site using density functional theory (B3LYP). A model with an octahedral coordination of the non-heme FeB consisting of three histidines, one glutamate and one water molecule gave an energetically feasible reaction mechanism. A tetrahedral coordination of the non-heme iron, corresponding to the one of CuB in cytochrome oxidase, gave several very high barriers which makes this type of coordination unlikely. The first nitric oxide coordinates to heme b3 and is partly reduced to a more nitroxyl anion character, which activates it toward an attack from the second NO. The product in this reaction step is a hyponitrite dianion coordinating in between the two irons. Cleaving an NO bond in this intermediate forms an FeB (IV)O and nitrous oxide, and this is the rate determining step in the reaction mechanism. In the model with an octahedral coordination of FeB the intrinsic barrier of this step is 16.3 kcal/mol, which is in good agreement with the experimental value of 15.9 kcal/mol. However, the total barrier is 21.3 kcal/mol, mainly due to the endergonic reduction of heme b3 taken from experimental reduction potentials. After nitrous oxide has left the active site the ferrylic FeB will form a μ-oxo bridge to heme b3 in a reaction step exergonic by 45.3 kcal/mol. The formation of a quite stable μ-oxo bridge between heme b3 and FeB is in agreement with this intermediate being the experimentally observed resting state in oxidized NOR. The formation of a ferrylic non-heme FeB in the proposed reaction mechanism could be one reason for having an iron as the non-heme metal ion in NOR instead of a Cu as in cytochrome oxidase.

  • 9.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Active Site Midpoint Potentials in Different Cytochrome c Oxidase Families: A Computational Comparison2019Ingår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 58, nr 15, s. 2028-2038Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cytochrome c oxidase (CcO) is the terminal enzyme in the respiratory electron transport chain, reducing molecular oxygen to water. The binuclear active site in CcO comprises a high-spin heme associated with a Cu-B complex and a redox active tyrosine. The electron transport in the respiratory chain is driven by increasing midpoint potentials of the involved cofactors, resulting in a release of free energy, which is stored by coupling the electron transfer to proton translocation across a membrane, building up an electrochemical gradient. In this context, the midpoint potentials of the active site cofactors in the CcOs are of special interest, since they determine the driving forces for the individual oxygen reduction steps and thereby affect the efficiency of the proton pumping. It has been difficult to obtain useful information on some of these midpoint potentials from experiments. However, since each of the reduction steps in the catalytic cycle of oxygen reduction to water corresponds to the formation of an O-H bond, they can be calculated with a reasonably high accuracy using quantum chemical methods. From the calculated O-H bond strengths, the proton-coupled midpoint potentials of the active site cofactors can be estimated. Using models representing the different families of CcO's (A, B, and C), the calculations give midpoint potentials that should be relevant during catalytic turnover. The calculations also suggest possible explanations for why some experimentally measured potentials deviate significantly from the calculated ones, i.e., for Cu-B in all oxidase families, and for heme b(3) in the C family.

  • 10.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Can Reduction of NO to N2O in Cytochrome c Dependent Nitric Oxide Reductase Proceed through a Trans-Mechanism?2017Ingår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 56, nr 1, s. 120-131Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As part of microbial denitrification, NO is reduced to N2O in the membrane bound enzyme nitric oxide reductase, NOR The N N coupling occurs in the diiron binuclear active site, BNC, and different mechanisms for this reaction step have been suggested. Computational studies have supported a so-called cis:b(3)-mechanism, in which the hyponitrite product of the reductive N N bond formation coordinates with one nitrogen to the heme iron and with both oxygens to the non-heme iron in the BNC. In contrast, experimental results have been interpreted to support a so-called trans-mechanism, in which the hyponitrite intermediate coordinates with one nitrogen atom to each of the two iron ions. Hybrid density functional theory is used here to perform an extensive search for possible intermediates of the NO reduction in the cNOR enzyme. It is found that hyponitrite structures coordinating with their negatively charged oxygens to the positively charged iron ions are the most stable ones. The hyponitrite intermediate involved in the suggested trans-mechanism, which only coordinates with the nitrogens to the iron ions, is found to be prohibitively high in energy, leading to a too slow reaction, which should rule out this mechanism. Furthermore, intermediates binding one NO molecule to each iron ion in the BNC, which have been suggested to initiate the trans-mechanism, are found to be too high in energy to be observable, indicating that the experimentally observed electron paramagnetic resonance signals, taken to support such an iron-nitrosyl dimer intermediate, should be reinterpreted.

  • 11.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    How Quantum Chemistry Can Solve Fundamental Problems in Bioenergetics2015Ingår i: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 115, nr 18, s. 1197-1201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three different enzymes are discussed, cytochrome c oxidase, involved in aerobic respiration, cytochrome c dependent nitric oxide reductase, involved in denitrification (anaerobic respiration), and photosystem II, involved in photosynthesis. For all three systems, free energy profiles for the entire catalytic cycle are obtained from quantum mechanical calculations on large cluster models of the active sites, using hybrid density functional theory with the B3LYP* functional. The free energy pro-files are used to solve different fundamental problems concerning energy conservation, enzymatic reaction mechanisms and structure, and also to explain experimental results that seem to be in conflict with each other. Possible future applications to related problems using similar methodology are suggested.

  • 12.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Mechanism of Oxygen Reduction in Cytochrome c Oxidase and the Role of the Active Site Tyrosine2016Ingår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 55, nr 3, s. 489-500Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cytochrome c oxidase, the terminal enzyme in the respiratory chain, reduces molecular oxygen to water and stores the released energy through electrogenic chemistry and proton pumping across the membrane. Apart from the heme-copper binuclear center, there is a conserved tyrosine residue in the active site (BNC). The tyrosine delivers both an electron and a proton during the O-O bond cleavage step, forming a tyrosyl radical. The catalytic cycle then occurs in four reduction steps, each taking up one proton for the chemistry (water formation) and one proton to be pumped. It is here suggested that in three of the reduction steps the chemical proton enters the center of the BNC, leaving the tyrosine unprotonated with radical character. The reproprotonation of the tyrosine occurs first in the final reduction step before binding the next oxygen molecule. It is also suggested that this reduction mechanism and the presence of the tyrosine are essential for the proton pumping. Density functional theory calculations on large cluster models of the active site show that only the intermediates with the proton in the center of the BNC and with an unprotonated tyrosyl radical have a high electron affinity of similar size as the electron donor, which is essential for the ability to take up two protons per electron and thus for the proton pumping. This type of reduction mechanism is also the only one that gives a free energy profile in accordance with experimental observations for the amount of proton pumping in the working enzyme.

  • 13.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    The mechanism for oxygen reduction in the C family cbb(3) cytochrome c oxidases - Implications for the proton pumping stoichiometry2020Ingår i: Journal of Inorganic Biochemistry, ISSN 0162-0134, E-ISSN 1873-3344, Vol. 203, artikel-id 110866Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cytochrome c oxidases (CcOs) couple the exergonic reduction of molecular oxygen to proton pumping across the membrane in which they are embedded, thereby conserving a significant part of the free energy. The A family CcOs are known to pump four protons per oxygen molecule, while there is no consensus regarding the proton pumping stoichiometry for the C family cbb(3) oxidases. Hybrid density functional theory is used here to investigate the catalytic mechanism for oxygen reduction in cbb(3) oxidases. A surprising result is that the barrier for O-O bond cleavage at the mixed valence reduction level seems to be too high compared to the overall reaction rate of the enzyme. It is therefore suggested that the O-O bond is cleaved only after the first proton coupled reduction step, and that this reduction step most likely is not coupled to proton pumping. Furthermore, since the cbb3 oxidases have only one proton channel leading to the active site, it is proposed that the activated E-H intermediate, suggested to be responsible for proton pumping in one of the reduction steps in the A family, cannot be involved in the catalytic cycle for cbb(3), which results in the lack of proton pumping also in the E to R reduction step. In summary, the calculations indicate that only two protons are pumped per oxygen molecule in cbb(3) oxidases. However, more experimental information on this divergent enzyme is needed, e.g. whether the flow of electrons resembles that in the other more well-studied CcO families.

  • 14.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Borowski, Tomasz
    Himo, Fahmi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Liao, Rong-Zhen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Quantum Chemical Studies of Mechanisms for Metalloenzymes2014Ingår i: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 114, nr 7, s. 3601-3658Artikel, forskningsöversikt (Refereegranskat)
  • 15.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    A quantum chemical study of the mechanism for proton-coupled electron transfer leading to proton pumping in cytochrome c oxidase2010Ingår i: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 108, nr 19-20, s. 2733-2743Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The proton pumping mechanism in cytochrome c oxidase, the terminal enzyme in the respiratory chain, has been investigated using hybrid DFT with large chemical models. In previous studies, a gating mechanism was suggested based on electrostatic interpretations of kinetic experiments. The predictions from that analysis are tested here. The main result is that the suggestion of a positively charged transition state for proton transfer is confirmed, while some other suggestions for the gating are not supported. It is shown that a few critical relative energy values from the earlier studies are reproduced with quite high accuracy using the present model calculations. Examples are the forward barrier for proton transfer from the N-side of the membrane to the pump-loading site when the heme a cofactor is reduced, and the corresponding back leakage barrier when heme a is oxidised. An interesting new finding is an unexpected double-well potential for proton transfer from the N-side to the pump-loading site. In the intermediate between the two transition states found, the proton is bound to PropD on heme a. A possible purpose of this type of potential surface is suggested here. The accuracy of the present values are discussed in terms of their sensitivity to the choice of dielectric constant. Only one energy value, which is not critical for the present mechanism, varies significantly with this choice and is therefore less certain.

  • 16.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    How cytochrome c oxidase can pump four protons per oxygen molecule at high electrochemical gradient2015Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1847, nr 3, s. 364-376Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments have shown that the A-family cytochrome c oxidases pump four protons per oxygen molecule, also at a high electrochemical gradient. This has been considered a puzzle, since two of the reduction potentials involved, Cu(II) and Fe(III), were estimated from experiments to be too low to afford proton pumping at a high gradient The present quantum mechanical study (using hybrid density functional theory) suggests a solution to this puzzle. First, the calculations show that the charge compensated Cu(II) potential for Cu-B is actually much higher than estimated from experiment, of the same order as the reduction potentials for the tyrosyl radical and the ferryl group, which are also involved in the catalytic cycle. The reason for the discrepancy between theory and experiment is the very large uncertainty in the experimental observations used to estimate the equilibrium potentials, mainly caused by the lack of methods for direct determination of reduced Cu-B. Second, the calculations show that a high energy metastable state, labeled E-H, is involved during catalytic turnover. The E-H state mixes the low reduction potential of Fe(III) in heme a(3) with another, higher potential, here suggested to be that of the tyrosyl radical, resulting in enough exergonicity to allow proton pumping at a high gradient In contrast, the corresponding metastable oxidized state, O-H, is not significantly higher in energy than the resting state, O. Finally, to secure the involvement of the high energy E-H state it is suggested that only one proton is taken up via the K-channel during catalytic turnover.

  • 17.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Improved free energy profile for reduction of NO in cytochrome c dependent nitric oxide reductase (cNOR)2016Ingår i: Journal of Computational Chemistry, ISSN 0192-8651, E-ISSN 1096-987X, Vol. 37, nr 19, s. 1810-1818Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantum chemical calculations play an essential role in the elucidation of reaction mechanisms for redox-active metalloenzymes. For example, the cleavage and the formation of covalent bonds can usually not be described only on the basis of experimental information, but can be followed by the calculations. Conversely, there are properties, like reduction potentials, which cannot be accurately calculated. Therefore, computational and experimental data has to be carefully combined to obtain reliable descriptions of entire catalytic cycles involving electron and proton uptake from donors outside the enzyme. Such a procedure is illustrated here, for the reduction of nitric oxide (NO) to nitrous oxide and water in the membrane enzyme, cytochrome c dependent nitric oxide reductase (cNOR). A surprising experimental observation is that this reaction is nonelectrogenic, which means that no energy is conserved. On the basis of hybrid density functional calculations a free energy profile for the entire catalytic cycle is obtained, which agrees much better with experimental information on the active site reduction potentials than previous ones. Most importantly the energy profile shows that the reduction steps are endergonic and that the entire process is rate-limited by high proton uptake barriers during the reduction steps. This result implies that, if the reaction were electrogenic, it would become too slow when the gradient is present across the membrane. This explains why this enzyme does not conserve any of the free energy released.

  • 18.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Siegbahn, Per E. M.
    Mechanism for N2O Generation in Bacterial Nitric Oxide Reductase: A Quantum Chemical Study2012Ingår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 51, nr 25, s. 5173-5186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The catalytic mechanism of reduction of NO to N2O in the bacterial enzyme nitric oxide reductase has been investigated using hybrid density functional theory and a model of the binuclear center (BNC) based on the newly determined crystal structure. The calculations strongly suggest a so-called cis:b(3) mechanism, while the commonly suggested trans mechanism is found to be energetically unfavorable. The mechanism suggested here involves a stable cis-hyponitrite, and it is shown that from this intermediate one N-O bond can be cleaved without the transfer of a proton or an electron into the binuclear active site, in agreement with experimental observations. The fully oxidized intermediate in the catalytic cycle and the resting form of the enzyme are suggested to have an oxo-bridged BNC with two high-spin ferric irons antiferromagnetically coupled. Both steps of reduction of the BNC after N2O formation are found to be pH-dependent, also in agreement with experiment. Finally, it is found that the oxo bridge in the oxidized BNC can react with NO to give nitrite, which explains the experimental observations that the fully oxidized enzyme reacts with NO, and most likely also the observed substrate inhibition at higher NO concentrations.

  • 19.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Proton pumping in cytochrome c oxidase: Energetic requirements and the role of two proton channels2014Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1837, nr 7, s. 1165-1177Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cytochrome c oxidase is a superfamily of membrane bound enzymes catalyzing the exergonic reduction of molecular oxygen to water, producing an electrochemical gradient across the membrane. The gradient is formed both by the electrogenic chemistry, taking electrons and protons from opposite sides of the membrane, and by proton pumping across the entire membrane. In the most efficient subfamily, the A-family of oxidases, one proton is pumped in each reduction step, which is surprising considering the fact that two of the reduction steps most likely are only weakly exergonic. Based on a combination of quantum chemical calculations and experimental information, it is here shown that from both a thermodynamic and a kinetic point of view, it should be possible to pump one proton per electron also with such an uneven distribution of the free energy release over the reduction steps, at least up to half the maximum gradient. A previously suggested pumping mechanism is developed further to suggest a reason for the use of two proton transfer channels in the A-family. Since the rate of proton transfer to the binuclear center through the D-channel is redox dependent, it might become too slow for the steps with low exergonicity. Therefore, a second channel, the K-channel, where the rate is redox-independent is needed. A redox-dependent leakage possibility is also suggested, which might be important for efficient energy conservation at a high gradient. A mechanism for the variation in proton pumping stoichiometry over the different subfamilies of cytochrome oxidase is also suggested. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.

  • 20.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Protonation of the binuclear active site in cytochrome c oxidase decreases the reduction potential of Cu-B2015Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1847, nr 10, s. 1173-1180Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the remaining mysteries regarding the respiratory enzyme cytochrome c oxidase is how proton pumping can occur in all reduction steps in spite of the low reduction potentials observed in equilibrium titration experiments for two of the active site cofactors, CUB(II) and Fe-a3(III). It has been speculated that, at least the copper cofactor can acquire two different states, one metastable activated state occurring during enzyme turnover, and one relaxed state with lower energy, reached only when the supply of electrons stops. The activated state should have a transiently increased Cu-B(II) reduction potential, allowing proton pumping. The relaxed state should have a lower reduction potential, as measured in the titration experiments. However, the structures of these two states are not known. Quantum mechanical calculations show that the proton coupled reduction potential for Cu-B is inherently high in the active site as it appears after reaction with oxygen, which explains the observed proton pumping. It is suggested here that, when the flow of electrons ceases, a relaxed resting state is formed by the uptake of one extra proton, on top of the charge compensating protons delivered in each reduction step. The extra proton in the active site decreases the proton coupled reduction potential for Cu-B by almost half a volt, leading to agreement with titration experiments. Furthermore, the structure for the resting state with an extra proton is found to have a hydroxo-bridge between Cu-B(II) and Fe-a3(III), yielding a magnetic coupling that can explain the experimentally observed EPR silence.

  • 21.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Quantum chemistry as a tool in bioenergetics2010Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1797, nr 2, s. 129-142Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Recent developments of quantum chemical methods have made it possible to tackle crucial questions in bioenergetics. The most important systems, cytochrome c oxidase in cellular respiration and photosystem II (PSII) in photosynthesis will here be used as examples to illustrate the power of the quantum chemical tools. One main contribution from quantum chemistry is to put mechanistic suggestions onto an energy scale. Accordingly, free energy profiles can be constructed both for reduction of molecular oxygen in cytochrome c oxidase and water oxidation in PSII, including O-O bond cleavage and formation, and also proton pumping in cytochrome c oxidase. For the construction of the energy diagrams, the computational results sometimes have to be combined with experimental information, such as reduction potentials and rate constants for individual steps in the reactions.

  • 22.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    The mechanism for proton pumping in cytochrome c oxidase from an electrostatic and quantum chemical perspective2012Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1817, nr 4, s. 495-505Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The mechanism for proton pumping in cytochrome c oxidase in the respiratory chain, has for decades been one of the main unsolved problems in biochemistry. However, even though several different suggested mechanisms exist, many of the steps in these mechanisms are quite similar and constitute a general consensus framework for discussing proton pumping. When these steps are analyzed, at least three critical gating situations are found, and these points are where the suggested mechanisms in general differ. The requirements for gating are reviewed and analyzed in detail, and a mechanism is suggested, where solutions for all the gating situations are formulated. This mechanism is based on an electrostatic analysis of a kinetic experiment for the O to E transition. The key component of the mechanism is a positively charged transition state. An electron on heme a opens the gate for proton transfer from the N-side to a pump loading site (PLS). When the negative charge of the electron is compensated by a chemical proton, the positive transition state prevents backflow from the PLS to the N-side at the most critical stage of the pumping process. The mechanism has now been tested by large model DFT calculations, and these calculations give strong support for the suggested mechanism. This article is part of a Special Issue entitled: Respiratory Oxidases.

  • 23.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Why is the reduction of NO in cytochrome c dependent nitric oxide reductase (cNOR) not electrogenic?2013Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1827, nr 7, s. 826-833Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The membrane-bound enzyme cNOR (cytochrome c dependent nitric oxide reductase) catalyzes the reduction of NO in a non-electrogenic process. This is in contrast to the reduction of O-2 in cytochrome c oxidase (CcO), the other member of the heme-copper oxidase family, which stores energy by the generation of a membrane gradient. This difference between the two enzymes has not been understood, but it has been speculated to be of kinetic origin, since per electron the NO reduction is more exergonic than the O-2 reduction, and the energy should thus be enough for an electrogenic process. However, it has not been clear how and why electrogenicity, which mainly affects the thermodynamics, would slow down the very exergonic NO reduction. Quantum chemical calculations are used to construct a free energy profile for the catalytic reduction of NO in the active site of cNOR. The energy profile shows that the reduction of the NO molecules by the enzyme and the formation of N2O are very exergonic steps, making the rereduction of the enzyme endergonic and rate-limiting for the entire catalytic cycle. Therefore the NO reduction cannot be electrogenic, i.e. cannot take electrons and protons from the opposite sides of the membrane, since it would increase the endergonicity of the rereduction when the gradient is present, thereby increasing the rate-limiting barrier, and the reaction would become too slow. It also means that proton pumping coupled to electron transfer is not possible in cNOR In CcO the corresponding rereduction of the enzyme is very exergonic.

  • 24.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ädelroth, Pia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mechanisms for enzymatic reduction of nitric oxide to nitrous oxide - A comparison between nitric oxide reductase and cytochrome c oxidase2018Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1859, nr 11, s. 1223-1234Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cytochrome c oxidases (CcO) reduce O-2 to H2O in the respiratory chain of mitochondria and many aerobic bacteria. In addition, some species of CcO can also reduce NO to N2O and water while others cannot. Here, the mechanism for NO-reduction in CcO is investigated using quantum mechanical calculations. Comparison is made to the corresponding reaction in a true cytochrome c-dependent NO reductase (cNOR). The calculations show that in cNOR, where the reduction potentials are low, the toxic NO molecules are rapidly reduced, while the higher reduction potentials in CcO lead to a slower or even impossible reaction, consistent with experimental observations. In both enzymes the reaction is initiated by addition of two NO molecules to the reduced active site, forming a hyponitrite intermediate. In cNOR, N2O can then be formed using only the active-site electrons. In contrast, in CcO, one proton-coupled reduction step most likely has to occur before N2O can be formed, and furthermore, proton transfer is most likely rate-limiting. This can explain why different CcO species with the same heme alpha(3)-Cu active site differ with respect to NO reduction efficiency, since they have a varying number and/or properties of proton channels. Finally, the calculations also indicate that a conserved active site valine plays a role in reducing the rate of NO reduction in CcO.

  • 25.
    Blomberg, Margareta R. A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Ädelroth, Pia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    The mechanism for oxygen reduction in cytochrome c dependent nitric oxide reductase (cNOR) as obtained from a combination of theoretical and experimental results2017Ingår i: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1858, nr 11, s. 884-894Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bacterial NO-reductases (NOR) belong to the heme-copper oxidase (HCuO) superfamily, in which most members are O-2-reducing, proton-pumping enzymes. This study is one in a series aiming to elucidate the reaction mechanisms of the HCuOs, including the mechanisms for cellular energy conservation. One approach towards this goal is to compare the mechanisms for the different types of HCuOs, cytochrome c oxidase (CcO) and NOR, reducing the two substrates O-2 and NO. Specifically in this study, we describe the mechanism for oxygen reduction in cytochrome c dependent NOR (cNOR). Hybrid density functional calculations were performed on large cluster models of the cNOR binuclear active site. Our results are used, together with published experimental information, to construct a free energy profile for the entire catalytic cycle. Although the overall reaction is quite exergonic, we show that during the reduction of molecular oxygen in cNOR, two of the reduction steps are endergonic with high barriers for proton uptake, which is in contrast to oxygen reduction in CcO, where all reduction steps are exergonic. This difference between the two enzymes is suggested to be important for their differing capabilities for energy conservation. An additional result from this study is that at least three of the four reduction steps are initiated by proton transfer to the active site, which is in contrast to CcO, where electrons always arrive before the protons to the active site. The roles of the non-heme metal ion and the redox-active tyrosine in the active site are also discussed.

  • 26.
    Blomkvist, Marita
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL).
    Entrepreneurs and their involvement in producing accounting2005Ingår i: Proceedings of the 28th European Accounting Association (EAA) Annual Congress, Brussels: European Accounting Association , 2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    Entrepreneurs seem to be highly valuable for the firms in which they are involved. However, the knowledge of the role of accounting in a context of entrepreneurship is almost non-existent. Infact, literature in entrepreneurship says that the role of accounting is only about the past and therefore not of interest for entrepreneurs in exploiting opportunities. This paper reports the result of a qualitative study of five entrepreneurs and their involvement in the process of producing the annual report. The study aimed to describe and analyse if and how entrepreneurs are involved in producing accounting information when the annual report was prepared. If the entrepreneur was involved, the purpose was also to explain and the entrepreneurs involvement in the process. In purpose to find entrepreneurs the owner-managers of five small growing companies were asked to participate in semi-structured interviews during which their involvement to produce accounting where discussed. The respondents were also presented the adjustments, the final step in the recording process, and the annual report, in order to assess their involvement and to focus on how the entrepreneurs as producers of annual reports reflect and act in relation to other actors and to the process on the reporting. The study found that the entrepreneurs were certainly involved in producing certain accounting in the annual report. The analysis reveals that the reports were carefully fabricated and consciously managed by the entrepreneurs in the study.

  • 27.
    Blomkvist, Marita
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL).
    Entrepreneurs as accountants - the year -end procedures in Gazelle firms2009Ingår i: Proceedings of the 32nd European Accounting Association (EAA) Annual Congress, Brussels: European Accounting Association , 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Entrepreneurs seem to be highly valuable for the firms in which they are involved. However, the knowledge of the role of accounting in a context of entrepreneurship is limited. In fact, some literature on entrepreneurship indicates that the role of accounting is only about the past and therefore not of interest for entrepreneurs in the entrepreneurial process.

    This paper reports the results of one empirical study. The study aimed to explore how and why entrepreneurs in successful fast growing firms, i.e. Gazelle firms, participate in the year end procedures. In order to find entrepreneurs a survey was sent to a sample of 257 managers of Gazelle firms and to a control group of 227 managers in not growing firms. The responding rate was more than 50% from both groups. Entrepreneurs in Gazelle firms produce formal financial accounting information and the spent more time compared with managers in not growing firms in this process. Further, the results indicate that that there is a negative relationship between the size and the firm and participation in the year-end procedures.

  • 28.
    Blomkvist, Marita
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Entreprenörer som redovisare: Bokslutsprocessen i Gasellföretag2011Bok (Övrig (populärvetenskap, debatt, mm))
  • 29.
    Blomkvist, Marita
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Entreprenörer som redovisare: bokslutsprocessen i Gasellföretag2008Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Entrepreneurs seem to be highly valuable for the firms in which they are involved. However, the knowledge of the role of accounting in a context of entrepreneurship is limited. In fact, some literature on entrepreneurship indicates that the role of accounting is only about the past and therefore not of interest for entrepreneurs in the entrepreneurial process.

    This dissertation reports the results of two empirical studies. The first study is a qualitative pilot study of five entrepreneurs in fast growing firms and their participation in the year-end procedure. The respondents were presented the adjustments in the final step of the recording process and the annual report in order to assess their participation and to focus on how the entrepreneurs as producers of accounting reflect and act in relation to other actors and to the process of reporting. The pilot study found that the entrepreneurs were certainly involved in use and produce of certain accounting in the year-end procedures. The second study is based on the result from the pilot study and on agency theory the study aimed to describe and explain how and why entrepreneurs in successful fast growing firms, i.e. Gazelle firms, compared with a control group of managers in not growing firms, are participating in the year-end procedures. Also, the study aimed to analyse differences between entrepreneurs´ participation and other managers´ participation in this process. The study focused on the activities in the year-end procedures concerned with the values of R&D, stock and work-in-progress and accounts receivables. In order to find entrepreneurs the survey was sent to a sample of 257 managers of Gazelle firms and to a sample of 227 managers in not growing firms. Also, the annual report from the firms where the respondents where involved were collected. This data was also included in the study. The responding rate was 50% from both groups. The most notable finding is, in contradiction to literature on entrepreneurship, that entrepreneurs in Gazelle firms use and produce formal financial accounting information. Entrepreneurs in Gazelle firms spend more time and they are also involved in discussions with more actors compared with managers in not growing firms. Further, the results indicate that entrepreneurs in Gazelle firms will participate to a larger extent when the profitability in the firm decreases compared to managers in not growing firms. Finally, the dissertation gives insight in the role of formal financial accounting in the context of entrepreneurship, a research area we know little about.

  • 30.
    Blomkvist, Marita
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Entreprenörers delaktighet i att producera redovisning2004Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Entrepreneurs seem to be highly valuable for the firms in which they are involved. However, the knowledge of the role of accounting in a context of entrepreneurship is almost non-existent.  Infact, literature in entrepreneurship says that the role of accounting is only about the past and therefore not of interest for the entrepreneur in exploiting opportunities. This paper reports the result of a qualitative study of five entrepreneurs and their involvement in the process of financial reporting. The study aimed to describe and analyse if and how entrepreneurs are involved in producing accounting information when the annual report were prepared. If the entrepreneurs were involved, the purpose was also to explain why the entrepreneurs were involved in the process. In purpose to find entrepreneurs the owner-managers of five small growing companies were asked to participate in semi-structured interviews during which their involvement to produce accounting where discussed. The respondents were also presented the adjustments, the final step in the recording process, and the annual report, in order to assess their involvement and to focus on how the entrepreneurs as producers of annual reports reflect and act in relation to other actors and to the process on the reporting.

    The study found that the entrepreneurs were certainly involved in producing the annual report. The analysis reveals that the reports were carefully fabricated and consciously managed by the entrepreneurs in the study. The entrepreneurs where involved in the process when certain values of the assets were established and they wrote the directors annual report.

    The study concludes that it appears to be important for entrepreneurs in small growing firms to discuss and produce accounting together with other actors, primarily the accountant, to improve their understanding and to identify how the audience of the annual reports may read and interpret the annual reports.

  • 31.
    Blomkvist, Marita
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL).
    Gasellentreprenörer och delaktighet i bokslutsprocessen - vad skiljer dem från andra företagsledare?2007Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Entrepreneurs seem to be highly valuable for the firms in which they are involved. However, the knowledge of the role of accounting in a context of entrepreneurship is limited. In fact, some literature on entrepreneurship indicates that the role of accounting is only about the past and therefore not of interest for entrepreneurs in exploiting opportunities. In contrast, recent studies in accounting and the context of entrepreneurship reveal that entrepreneurs use and construct accounting information with diverse characteristics.

     

    This paper reports the preliminary results of a survey and archival study. The study aimed to describe and explain how successful entrepreneurs and other managers are participating in the year-end procedures. Also, the study aimed to analyse differences between successful entrepreneurs´ participation and other manager’s participation in this process. The study focused on the activities in the year-end procedures concerned with the values of R&D, stock and work-in-progress and accounts receivables. In order to find successful entrepreneurs the survey was send to a sample of 257 managers of profitable, continuously growing companies. In order to find other managers, who not where successfully entrepreneurial, the survey was send to a sample of 227 managers in not growing companies. Also, the annual report from the companies where the respondents where involved in was collected. This data was also included in the study. The responding rate was about 50% from both groups. The most notable finding is, in contradiction to literature on entrepreneurship, that successful entrepreneurs use financial accounting information. Further, a preliminary result shows that successful entrepreneurs participate more than other managers in producing financial accounting. Ownership structure, degree of growth and individual motives related to stakeholders seems to be some factors that influence the degree of participation.

  • 32.
    Blomkvist, Marita
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL).
    The demand for external accounting services by small and medium siced firms (SMEs) in Sweden - the role of fast growth2010Ingår i: Proceedings of the 33rd European Accounting Association (EAA) Annual Congress, Brussels: European Accounting Association , 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to stimulate growth economy, discussions about how to simplicity accounting regulation for SMEs have been highlighted during the past decades.

    From previous research we know that the demand for accounting and advisory service vary with size. Also, the quality of advice from accountants plays an important role besides accounting service. However, some firms find accounting as a burden and in an entrepreneurial context external accounting seems not to be useful.

    The question in this study is whether fast growing SMEs demand more external accounting service compared to stable firms. Fast growing firms in this study is defined as firms who just have doubled turnover during the last three years and at the end of this period have more than 10 employees and less than 250 employees. The empirical data is based of information from a survey answered by 131 managers of fast growing firms and 98 managers of stable firms Sweden. Also archival data from the annual report is included.

    The findings give support to the hypothesis that fast growing SMEs demand more external accounting service when it comes to preparation of annual account and annual report. The result shows no differences between the two groups when demand of external book keeping service is analysed.

  • 33.
    Blomkvist, Marita
    et al.
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Hansson, Agneta
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Ulvenblad, Pia
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Lindholm Dahlstrand, Åsa
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Gendered structures in academic entrepreneurship and innovation – A development towards world-class standard in educational programmes in Sweden2010Ingår i: VIII Triple Helix International Conference on University, Industry and Government Linkages: Book of abstracts / [ed] Marcelo Amaral, Ilana Sender, Manuel Cendoya, Rafael Zaballa, 2010, s. 35-35Konferensbidrag (Refereegranskat)
    Abstract [en]

    An integration of activities such as incubators, technology transfer, student and alumni organisations etc related to entrepreneurship education is seen as promoting economic development and innovativeness in many parts of the world. This way of creating systems for entrepreneurship development has also recently been focused in Sweden. As a result of Swedish Government's ambition to stimulate growth economy, university entrepreneurship education program spring up all over the country in order to promote students' entrepreneurship.From previous research we know that the infrastructure has an impact for entrepreneurship (Delatte & Baytos, 1993; Hannon, 2003; Rosa & Dawson, 2006, Xu, 2010). The structure relates to the number of individuals in the management structure and the role the individual has in the management structure such as member of the board or manager. It also refers to characteristics of the individuals involved in the management such as diversity, gender, age, education competence and previous experience (Rosa & Dawson, 2006). Further, it has been shown that managers are important since a lack of role models have been shown to have an impact for both female entrepreneurs and female managers in decisions of starting and/or managing a business (Crampton & Mishra, 1999; Mattis, 2004). However, public and private initiatives aimed to support business development usually are following a gender blind norm both in the way it is presented, for example regarding language and psychological accessibility, and considering the fields pointed out. Research shows that women don't feel themselves addressed by these initiatives or that it concerns them (NUTEK, 2001; NUTEK, R 2007:34).Swedish Government recently challenged to higher education institutions to apply for finance to a development towards world- class standard in educational programmes in entrepreneurship and innovation (Prop. 2008/2009:1/16). The invitation was directed to higher education institutions that already run advanced studies in entrepreneurship and innovation and that also have a strong connection to research in the same area. Swedish National Agency for Higher Education was commissioned by the Government to examine the applications and invited a panel of international academic experts to asses the applications. Eleven applications were submitted from higher education institutions in the field of entrepreneurship and innovation. Four of the eleven institutions which applied where recommended by the panel of experts and these institutions were further ranked and recommended by Swedish National Agency for Higher Education to the University Chancellor. Two of these institutions were finally selected to be financed by the Swedish Government.This paper focuses on these eleven applications and the review process. The aim of the paper is to analyze and illustrate in what way the applications as well as the review process is gendered for example in terms of discourse and symbols in relation to educational setting, organizational structure, infrastructure, education management, education team assigned and branches of industry (Acker, 1992; Bruni, Gherardi & Poggio, 2005; Gunnarsson, Westberg, Andersson & Balkmar, 2007). We expect to find how gender is mirrored in these highly ranked applications and what impact the presence or absence of a gender focus will have for entrepreneurship and innovation education.

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  • 34.
    Blomkvist, Marita
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Johansson, Jeaneth
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN). Luleå University of Technology, Luleå, Sweden.
    Malmström, Malin
    Luleå University of Technology, Luleå, Sweden.
    Accounting Knowledge in Innovative Firms – Direct Contacts with Auditors for Strategic Actions2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Managers’ use of auditors in decision processes are well known in the accounting literature but little is known on managers in innovative firms and their acquisition of accounting knowledge through direct contacts with auditors. We conducted a multiple embedded study of exploratory character based on 19 interviews with managers and auditors connected to six innovative firms. We show that managers in innovative firms apply informal management control in early phases and thus also rely to a high extent on external auditors for such purposes. Management acquisition of accounting knowledge may however stepwise contribute to a more formalized control system as management competence increase. This study suggests that competence based view may be useful for understanding the role of accounting and auditors.

  • 35.
    Blomkvist, Marita
    et al.
    University of Gothenburg, Gothenburg, Sweden.
    Johansson, Jeaneth
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL). Luleå University of Technology, Luleå, Sweden.
    Malmström, Malin
    Luleå University of Technology, Luleå, Sweden.
    Accounting knowledge in innovative firms - Direct contacts with external auditors for strategic actions2016Ingår i: International Journal of Managerial and Financial Accounting, ISSN 1753-6715, E-ISSN 1753-6723, Vol. 8, nr 3-4, s. 209-229Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Managers’ use of auditors in decision processes is well known in the accounting literature, but little is known about owner-managers in innovative firms and their acquisition of accounting knowledge through direct contacts with external auditors. We conducted a multiple embedded study of exploratory character based on 21 interviews with owner-managers and external auditors connected to six innovative firms. We show that owner-managers in innovative firms apply informal management control in early phases of the innovation process and thus also rely heavily on external auditors for such purposes. However, management’s acquisition of accounting knowledge may contribute over time to the development of a more formalised control system as their competence increases. This study suggests that a competence-based view may be useful for understanding the role of accounting and external auditors in innovative firms’ management control systems. Copyright © 2016 Inderscience Enterprises Ltd.

  • 36.
    Blomkvist, Marita
    et al.
    University of Gothenburg, Gothenburg, Sweden.
    Johansson, Jeaneth
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL).
    Rodgers, Waymond
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL). University of Texas el Paso, El Paso, Texas, United States.
    Examining Entrepreneurs' Knowledge Based View of the Firm: lnfluencing financial information in innovative activities2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    This study focuses on knowledge management and entrepreneurs’ perceptions in terms of knowledge sharing, the use of financial statement information and how these impact on their strategic business judgments and decision choices in innovative SME firms. Using a strategic decision making process model we test our assumptions regarding entrepreneurs´ knowledge routines implemented by non-Gazelle companies in strategic business decision. Combining survey data and financial data from a unique archival database we test our propositions on Swedish SMEs. The results of the structural equation analysis implied that non-Gazelle companies are propelled primarily by non-financial information captured by the expertise of managers and investors. Traditional financial information does not include entrepreneurs´ decision making however, the results indicate that entrepreneurs risk awareness is reported as a part of the frame why entrepreneurs´ make decisions.

  • 37.
    Blomkvist, Marita
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Paananen, Mari
    Brunel University, London, United Kingdom.
    The cost of debt implications of financial reporting quality among privately owned Swedish SMEs2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Using a unique database and manually collected data we analyse and document accounting choices made by Swedish SMEs between 2005 and 2008. We find that given an option to report under Swedish GAAP or a translation of IFRS (SFASC/IFRS), only 5 firms out of 1,500 opted to do so. Further analysis of choices of picking individual standards of SFASC/IFRS shows no significant difference across Gazelles and Non-Gazelles. Among firms that select individual SFASC/IFRS standards most opt to use the percentage-of-completion method for long-term contracts. We also investigate differences in quality of financial reporting across Gazelles and Non-Gazelles and find that the financial reporting quality is consistently higher among Gazelles compared to Non-Gazelles. Test of cost of debt implications show that creditors find Gazelles’ financial reporting more useful to assess the credit risk resulting in lower cost of debt for this group of firms. Thus, SMEs seem to have little incentive to switch to SFASC/IFRS, which may be an indication of their attitude to future adoption of IFRS for SMEs as well. Furthermore, the results suggest that SMEs with an incentive to produce high quality financial reporting to raise capital, Gazelles, are able to do so using Swedish GAAP. These findings raise the question whether the IFRS for SMEs project is worthwhile.

  • 38.
    Blomkvist, Marita
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Paananen, Mari
    Business School University of Exeter, Exeter, United Kingdom.
    The Cost of Debt Implications of Information Environment Choices Among Privately Owned Swedish Small and Mid-Sized Companies2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    We investigate improvements of the information environment and cost of debt implications. Capturing choices of accounting standards, auditor quality, and board size reflecting improvements of the information environment we find that the need of financing triggers an improvement, the most common actions are to switch to more qualified accountants and add board members. Improvements of the environment result in a reduction of cost of debt. Tests show that increasing audit quality decrease cost of debt. This is relevant to the discussion on accounting regulation for private firms among U.S. and European policy-makers showing that stakeholders do not demand valuation-oriented accounting.

  • 39.
    Blomkvist, Marita
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Paananen, Mari
    University of Exeter, Exeter, United Kingdom.
    The impact of managers´participating in the year-end accounting process on accounting quality and cost of debt among Swedish privately owned Gazelles2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Using a combination of survey data and unique archival databases we investigate the impact of managers´ participation in the year-end accounting process on the quality of financial reporting and cost of debt among Swedish privately owned Gazelles (rapidly growing firms) compared to Non-Gazelles. We find that managers of Gazelles are more prone to participate in the year-end accounting process compared to Non-Gazelles. Further, we find weak evidence that Gazelles produce higher quality financial reports (in terms of conservatism). Further, our results indicate that Gazelles experience lower cost of debt, though this is not statistically significant. We also find that private firms manage earnings to a greater extent the smaller they are and that the cost of debt systematically decreases with size for groups of firms.

  • 40.
    Blomkvist, Marita
    et al.
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Ulvenblad, Pia
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Hansson, Agneta
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Is there a structural “glass ceiling” hindering women on the business incubator arena? – A study of Swedish business incubators web sites2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper seeks to explore if there is an indication of a structural “glass ceiling” hindering women within business support environments. By analyzing 44 Swedish incubators’ web sites from four different perspectives, the study wants to describe and discuss the particular way gender seem to be structured in incubators’ organisations. The results reveal that there is a male dominance in the incubators’ organisations. The criteria for becoming an entrepreneur in the incubator such as characteristics are subtle. It can be assumed that hidden gender structures can prevent female entrepreneurs from entering the incubator.

  • 41. Borowski, Tomasz
    et al.
    Wojcik, Anna
    Milaczewska, Anna
    Georgiev, Valentin
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik. Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    The alkenyl migration mechanism catalyzed by extradiol dioxygenases: a hybrid dft study2012Ingår i: Journal of Biological Inorganic Chemistry, ISSN 0949-8257, E-ISSN 1432-1327, Vol. 17, nr 6, s. 881-890Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    6-Hydroxymethyl-6-methylcyclohexa-2,4-dienone is a mechanistic probe which when incubated with an extradiol dioxygenase yields a 2-tropolone product. This observation was originally interpreted as evidence supporting a direct heterolytic 1,2-alkenyl migration mechanism for a ring expansion reaction catalyzed by this class of Fe(II)-dependent nonheme enzymes (Xin and Bugg in J Am Chem Soc 130:10422-10430, 2008). In the work reported in this contribution we used quantum chemical methods to test whether such a mechanism is energetically possible and we found that it is not, neither for the mechanistic probe nor for the native catalytic cycle intermediate. Models of increasing complexity were used to calculate energy barriers to the heterolytic 1,2-alkenyl migration and alternative radical mechanisms. It was found that the former involves substantially higher barriers than the latter. A tentative radical mechanism that accounts for the transformation of the probe substrate to 2-tropolone was also proposed, and it involves acceptable barriers.

  • 42. Chen, Shi-Lu
    et al.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    An investigation of possible competing mechanisms for Ni-containing methyl-coenzyme M reductase2014Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 27, s. 14029-14035Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ni-containing methyl-coenzyme M reductase (MCR) is capable of catalyzing methane formation from methyl-coenzyme M (CH3-SCoM) and coenzyme B (CoB-SH), and also its reverse reaction (methane oxidation). Based on extensive experimental and theoretical investigations, it has turned out that a mechanism including an organometallic methyl-Ni(III)F-430 intermediate is inaccessible, while another mechanism involving a methyl radical and a Ni(II)-SCoM species currently appears to be the most acceptable one for MCR. In the present paper, using hybrid density functional theory and an active-site model based on the X-ray crystal structure, two other mechanisms were studied and finally also ruled out. One of them, involving proton binding on the CH3-SCoM substrate, which should facilitate methyl-Ni(III)F-430 formation, is demonstrated to be quite unfavorable since the substrate has a much smaller proton affinity than the F-430 cofactor. Another one (oxidative addition mechanism) is also shown to be unfavorable for the MCR reaction, due to the large endothermicity for the formation of the ternary intermediate with side-on C-S (for CH3-SCoM) or C-H (for methane) coordination to Ni.

  • 43.
    Chen, Shi-Lu
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    How Is a Co-Methyl Intermediate Formed in the Reaction of Cobalamin-Dependent Methionine Synthase?: Theoretical Evidence for a Two-Step Methyl Cation Transfer Mechanism2011Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 115, nr 14, s. 4066-4077Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A methyl-Co(cobalamin) species has been characterized to be a crucial intermediate in the last step of the de novo biosynthesis of methionine catalyzed by cobalamin-dependent methionine synthase (MetH). However, exactly how it is formed is still an open question. In the present article, the formation of the methyl-Co(cobalamin) species in MetH has been investigated with B3LYP* hybrid DFT including van der Waals (vdW) interactions (i.e., dispersion) and using a chemical model built on X-ray crystal structures. The methyl cation and radical transfer mechanisms have been examined in various protonation states. The calculations reveal that the CH(3)-Co(III)(cobalamin) formation in MetH proceeds along a stepwise pathway, where the first step is a methyl cation transfer from the protonated methyltetrahydrofolate (CH(3)-THF) substrate to the Co(I)cobalamin. The second step is a binding of His759 to the other side (a-face) of Co. The former methyl transfer is computed to be the rate-limiting step with a barrier of 18 kcal/mol, which is reduced to 13 kcal/mol when dispersion is included. For the first step, the protonation at the methyl-bound nitrogen of CH(3)-THF is very important. The methyl transfer is otherwise unreachable with a very high barrier of similar to 38 kcal/mol. The deprotonation of the alpha-face His759-Asp757-Ser810 triad is found to be much less significant but slightly facilitates the CH(3)-Co(III)Cbl formation. There has been a long-standing discrepancy of 10-20 kcal/mol between theory and experiment in previous B3LYP computations of the Co C bond dissociation energy for the methyl-Co(cobalamin) species. The calculations indicate that the lack of dispersion (similar to 11 kcal/mol) is the main origin of this puzzling problem. With these effects, B3LYP* gives a bond strength of 32 kcal/mol compared to the experimental value of 37 +/- 3 kcal/mol. Overall, the present calculations give many examples of dispersion that makes non-negligible contributions to the energetics of enzyme reactions, especially for systems involving at least one large reacting fragment approaching or departing.

  • 44. Chen, Shi-Lu
    et al.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    How Is Methane Formed and Oxidized Reversibly When Catalyzed by Ni-Containing Methyl-Coenzyme M Reductase?2012Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 18, nr 20, s. 6309-6315Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ni-containing methyl-coenzyme M reductase (MCR) is capable of catalyzing methane formation and has recently been observed to also be able to catalyze the reverse reaction, the anaerobic oxidation of methane. The forward reaction has been extensively studied theoretically before and was found to consist of two steps. The first step is rate-limiting and the second step was therefore treated at a lower level. For an accurate treatment of the reverse reaction, both steps have to be studied at the same level. In the present paper, the mechanisms for the reversible formation and oxidation of methane catalyzed by MCR have been investigated using hybrid density functional theory with recent developments, in particular including dispersion effects. An active-site model was constructed based on the X-ray crystal structure. The calculations indicate that the MCR reaction is indeed reversible and proceeds via a methyl radical and a Ni-S(CoM) intermediate with reasonable reaction barriers in both directions. In a competing mechanism, the formation of the crucial Ni-methyl intermediate, was found to be strongly endergonic by over 20 kcal?mol-1 (including a barrier) with dispersion and entropy effects considered, and thus would not be reachable in a reasonable time under natural conditions.

  • 45.
    Chen, Shi-Lu
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pelmenschikov, Vladimir
    Blomberg, Margareta R.A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per .E.M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Is There a Ni-Methyl Intermediate in the Mechanism of Methyl-Coenzyme M Reductase (MCR)?2009Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, s. 9912-9913Artikel i tidskrift (Refereegranskat)
  • 46.
    Georgiev, Valentin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Borowski, Tomasz
    Polish Academy of Sciences.
    Blomberg, Margareta R.A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E.M.
    A comparison of the reaction mechanisms of iron- and manganese-containing 2,3-HPCD: an important spin transition for manganese2008Ingår i: Journal of Biological Inorganic Chemistry, ISSN 0949-8257, E-ISSN 1432-1327, Vol. 13, nr 6, s. 929-40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Homoprotocatechuate (HPCA) dioxygenases are enzymes that take part in the catabolism of aromatic compounds in the environment. They use molecular oxygen to perform the ring cleavage of ortho-dihydroxylated aromatic compounds. A theoretical investigation of the catalytic cycle for HPCA 2,3-dioxygenase isolated from Brevibacterium fuscum (Bf 2,3-HPCD) was performed using hybrid DFT with the B3LYP functional, and a reaction mechanism is suggested. Models of different sizes were built from the crystal structure of the enzyme and were used in the search for intermediates and transition states. It was found that the enzyme follows a reaction pathway similar to that for other non-heme iron dioxygenases, and for the manganese-dependent analog MndD, although with different energetics. The computational results suggest that the rate-limiting step for the whole reaction of Bf 2,3-HPCD is the protonation of the activated oxygen, with an energy barrier of 17.4 kcal/mol, in good agreement with the experimental value of 16 kcal/mol obtained from the overall rate of the reaction. Surprisingly, a very low barrier was found for the O-O bond cleavage step, 11.3 kcal/mol, as compared to 21.8 kcal/mol for MndD (sextet spin state). This result motivated additional studies of the manganese-dependent enzyme. Different spin coupling between the unpaired electrons on the metal and on the evolving substrate radical was observed for the two enzymes, and therefore the quartet spin state potential energy surface of the MndD reaction was studied. The calculations show a crossing between the sextet and the quartet surfaces, and it was concluded that a spin transition occurs and determines a barrier of 14.4 kcal/mol for the O-O bond cleavage, which is found to be the rate-limiting step in MndD. Thus the two 83% identical enzymes, using different metal ions as co-factors, were found to have similar activation energies (in agreement with experiment), but different rate-limiting steps.

  • 47.
    Georgiev, Valentin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Noack, Holger
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R.A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per E.M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    A DFT Study on the Catalytic Reactivity of a Functional Model Complex for  Intradiol-Cleaving Dioxygenases2010Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, nr 17, s. 5878-5885Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The enzymatic ring cleavage of catechol derivatives is catalyzed by two groups of dioxygenases: extradiol- and intradiol-cleaving dioxygenases. Although having different oxidation state of their nonheme iron sites and different ligand coordinations, both groups of enzymes involve a common peroxy intermediate in their catalytic cycles. The factors that lead to either extradiol cleavage resulting in 2-hydroxymuconaldehyde or intradiol cleavage resulting in muconic acid are not fully understood. Well-characterized model compounds that mimic the functionality of these enzymes offer a basis for direct comparison to theoretical results. In this study the mechanism of a biomimetic iron complex is investigated with density functional theory (DFT). This complex catalyzes the ring opening of catecholate with exclusive formation of the intradiol cleaved product. Several spin states are possible for the transition metal system, with the quartet state found to be of main importance during the reaction course. The mechanism investigated provides an explanation for the observed selectivity of the complex. First, a bridging peroxide is formed, which decomposes to an alkoxy radical by O−O homolysis. In contrast to the subsequent barrier-free intradiol C−C bond cleavage, the extradiol pathway proceeds via the formation of an epoxide, which requires an additional activation barrier.

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    FULLTEXT02
  • 48.
    Hansson, Agneta
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Blomkvist, Marita
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Ulvenblad, Pia
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Akademiskt nyföretagande2011Ingår i: Kvinnors företagande - Mål eller medel? / [ed] Eva Blomberg, Gun Hedlund & Martin Wottle, Stockholm: SNS förlag, 2011, s. 215-243Kapitel i bok, del av antologi (Refereegranskat)
  • 49.
    Hansson, Agneta
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Stridh, Kicki
    Internationell Kompetens AB, Ljungbyhed.
    Blomkvist, Marita
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    Ulvenblad, Pia
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Centrum för innovations-, entreprenörskaps- och lärandeforskning (CIEL), Knowledge Entrepreneurship and Enterprise Research (KEEN).
    A gender perspective on national measures promoting innovation and entrepreneurship2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Public programs and measures aimed to support business, innovation and entrepreneurship in Sweden are by tradition targeted manufacturing companies in order to develop technology and to make industry more competitive. Such initiatives are following a gender blind norm, in the way they define their fields of action, and also in how they are presented, for example regarding language and psychological accessibility. Research shows that women don‟t feel themselves addressed by these initiatives or that it concerns their companies.

    We think that a deeper understanding about why women are not reached, or attracted, by official measures taken to support business growth, can guide us in developing new models, methods and tools to stimulate and facilitate a climate for growth of women‟s entrepreneurship and long-term improve the conditions for women to create, run and develop their enterprises. We exemplify this through cases from three national R&D programmes financed by VINNOVA (The Swedish Governmental Agency for Innovation Systems) and KK-Stiftelsen (the Swedish Knowledge Foundation), both governmental authorities and research funders that aims to promote growth and prosperity throughout Sweden.

    In the paper we discuss official efforts aimed to support business development and growth. In what way are they gender marked? What structures are active on different levels? What is the consistence between ambitions from the program managers and how presentation of the programs is received by the target groups? Who are reached and who participates? 

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    fulltext
  • 50.
    Johansson, Adam Johannes
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Blomberg, Margareta R. A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Siegbahn, Per. E. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    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 Molecules2008Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, s. 154301-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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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