Viser treff 507-526 av 527

    • Understanding Hyperporphyrin Spectra: TDDFT Calculations on Diprotonated Tetrakis(p-aminophenyl)porphyrin 

      Conradie, Jeanet; Wamser, Carl C.; Ghosh, Abhik (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-29)
      A detailed TDDFT study (with all-electron STO-TZ2P basis sets and the COSMO solvation model) has been carried out on the effect of diprotonation on the UV−vis−NIR spectra of free-base tetraphenylporphyrin and tetrakis(p-aminophenyl)porphyrin. The diprotonated forms have been modeled as their bis-formate complexes, i.e., as so-called porphyrin diacids. The dramatic redshift of the Q-band of ...
    • Understanding the Influence of Lewis Acids on CO2 Hydrogenation: The Critical Effect Is on Formate Rotation 

      Pavlovic, Ljiljana; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-11)
      Lewis acids (LAs) have been shown to accelerate hydrogenation of C0<sub>2</sub>, but the underlying mechanistic details remain to be elucidated. We have employed computational methods to investigate how LAs affect CO<sub>2</sub> hydrogenation with a range of known metal-hydrides (L<sub>n</sub>Ir–H, L<sub>n</sub>Ru–H, L<sub>n</sub>Mn–H, L<sub>n</sub>Co–H). Our results show that LAs can alter the ...
    • Unequivocal structure confirmation of a breitfussin analog by anisotropic NMR measurements 

      Ndukwe, Ikenna E.; Lam, Yu-hong; Pandey, Sunil Kumar; Haug, Bengt Erik; Bayer, Annette; Sherer, Edward C.; Blinov, Kirill A.; Williamson, R. Thomas; Isaksson, Johan; Reibarkh, Mikhail; Liu, Yizhou; Martin, Gary E. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-21)
      Structural features of proton-deficient heteroaromatic natural products, such as the breitfussins, can severely complicate their characterization by NMR spectroscopy. For the breitfussins in particular, the constitution of the five-membered oxazole central ring cannot be unequivocally established via conventional NMR methods when the 4′-position is halogenated. The level of difficulty is exacerbated ...
    • Unexpected Molecular Structure of a Putative Rhenium-Dioxo-Benzocarbaporphyrin Complex. Implications for the Highest Transition Metal Valence in a Porphyrin-Type Ligand Environment 

      Alemayehu, Abraham; Vazquez-Lima, Hugo; Teat, Simon J.; Ghosh, Abhik (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-10-18)
      A combination of quantum chemical calculations and synthetic studies was used to address the possibility of very high (>6) valence states of transition metals in porphyrin‐type complexes. With corrole as a supporting ligand, DFT calculations ruled out Re(VII) and Ir(VII) dioxo complexes as stable species. Attempted rhenium insertion into benzocarbaporphyrin (BCP) ligands on the other hand led to two ...
    • A unique class I polyhydroxyalkanoate synthase (PhaC) from Brevundimonas sp. KH11J01 exists as a functional trimer: A comparative study with PhaC from Cupriavidus necator H16 

      Assefa, Netsanet Gizaw; Hansen, Hilde; Altermark, Bjørn (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-06)
      Polyhydroxyalkanoates (PHAs) are natural biodegradable polyesters that are produced by numerous prokaryotic microorganisms primarily as a carbon- and energy reserve. The PhaC enzyme catalyzes the last step in the PHA biosynthesis pathway and synthesizes PHA polymers from hydroxyalkanoic acids. A type I PhaC from a PHAproducing marine bacterium Brevundimonas sp. KH11J01 (BrPhaC) was identified, ...
    • Unique core genomes of the bacterial family vibrionaceae: insights into niche adaptation and speciation 

      Kahlke, Tim; Goesmann, Alexander; Hjerde, Erik; Willassen, Nils Peder; Haugen, Peik (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      The criteria for defining bacterial species and even the concept of bacterial species itself are under debate, and the discussion is apparently intensifying as more genome sequence data is becoming available. However, it is still unclear how the new advances in genomics should be used most efficiently to address this question. In this study we identify genes that are common to any group of genomes ...
    • Unraveling the Microscopic Origin of Triplet Lasing from Organic Solids 

      Paul, Lopa; Banerjee, Ambar; Paul, Ankan; Ruud, Kenneth; Chakrabarti, Swapan (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-16)
      We present a heuristic mechanism for the origin of the unusual triplet lasing from (E)-3-(((4-nitrophenyl)imino)methyl)-2H-thiochroman-4-olate·BF<sub>2</sub>. We demonstrate that whereas the moderate lifetime (1.03 μs) of the first triplet state (T<sub>1</sub>) prohibits triplet–triplet annihilation, the relatively faster S<sub>1</sub> → T<sub>1</sub> intersystem crossing and the 10<sup>4</sup> times ...
    • Vibrational Corrections to NMR Spin-Spin Coupling Constants from Relativistic Four-Component DFT Calculations 

      Jakubowska, Katarzyna; Pecul, Magdalena; Ruud, Kenneth (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-09-22)
      Zero-point vibrational (ZPV) corrections to the nuclear spin–spin coupling constants have been calculated using four-component Dirac–Kohn–Sham DFT for H<sub>2</sub>X (where X = O, S, Se, Te, Po), XH<sub>3</sub> (where X = N, P, As, Sb, Bi), and XH<sub>4</sub> (where X = C, Si, Ge, Sn, and Pb) molecules and for HC≡CPbH<sub>3</sub>. The main goal was to study the influence of relativistic effects on ...
    • Vibrionaceae core, shell and cloud genes are non-randomly distributed on Chr 1: An hypothesis that links the genomic location of genes with their intracellular placement 

      Sonnenberg, Cecilie Bækkedal; Kahlke, Tim; Haugen, Peik (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-10-06)
      <i>Background</i> - The genome of <i>Vibrionaceae</i> bacteria, which consists of two circular chromosomes, is replicated in a highly ordered fashion. In fast-growing bacteria, multifork replication results in higher gene copy numbers and increased expression of genes located close to the origin of replication of Chr 1 (<i>ori1</i>). This is believed to be a growth optimization strategy to satisfy ...
    • Vinyl Sulfoxonium Ylide: A New Vinyl Carbenoid Transfer Reagent for the Synthesis of Heterocycles 

      Vaitla, Janakiram; Bayer, Annette; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-04-10)
      Sulfoxonium ylides have recently gained prominence as safe carbenoid precursors in metal-catalyzed reactions. The stability and reactivity of sulfoxonium ylides depend on the substitution of the ylide carbon. The reactivity of vinyl-substituted sulfoxonium ylides is different and offers several advantages over known stabilized sulfoxonium ylides in the case of carbenoid transfer reactions. Herein, ...
    • Visible light-exposed lignin facilitates cellulose solubilization by lytic polysaccharide monooxygenases 

      Kommedal, Eirik; Angeltveit, Camilla Fløien; Klau, Leesa Jane; Ayuso-Fernandez, Ivan; Arstad, Bjørnar; Antonsen, Simen; Stenstrøm, Yngve; Ekeberg, Dag; Gírio, Francisco; Carvalheiro, Florbela; Horn, Svein Jarle; Aachmann, Finn Lillelund; Eijsink, Vincent (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-02-24)
      Lytic polysaccharide monooxygenases (LPMOs) catalyze oxidative cleavage of crystalline polysaccharides such as cellulose and are crucial for the conversion of plant biomass in Nature and in industrial applications. Sunlight promotes microbial conversion of plant litter; this effect has been attributed to photochemical degradation of lignin, a major redox-active component of secondary plant cell walls ...
    • Visible-light photocatalytic double C–H Functionalization of indoles: a synergistic experimental and computational study 

      Erdenebileg, Uranbaatar; Demissie, Taye Beyene; Hansen, Jørn H (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-21)
      Herein is disclosed a novel visible-light photocatalytic double C–H functionalization of indoles. The reaction affords 2,3-difunctional- ized indoles in up to 84% yield, but the reaction rate depends strongly on electronic substituent effects. Mechanistic DFT studies and control experiments suggest that the secondary functionalization occurs through an independent photocatalytic oxidation ...
    • Wavelet formulation of the polarizable continuum model. II. Use of piecewise bilinear boundary elements 

      Bugeanu, Monica; Di Remigio, Roberto; Mozgawa, Krzysztof; Reine, Simen Sommerfelt; Harbrecht, Helmut; Frediani, Luca (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-27)
      The simplicity of dielectric continuum models has made them a standard tool in almost any Quantum Chemistry (QC) package. Despite being intuitive from a physical point of view, the actual electrostatic problem at the cavity boundary is challenging: the underlying boundary integral equations depend on singular, long-range operators. The parametrization of the cavity boundary should be molecular- ...
    • A weighted minimum distance using hybridization of particle swarm optimization and Bacterial Foraging 

      Muhammad Fuad, Muhammad Marwan (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
    • When Optimization Is Just an Illusion 

      Muhammad Fuad, Muhammad Marwan (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Bio-inspired optimization algorithms have been successfully applied to solve many problems in engineering, science, and economics. In computer science bio-inspired optimization has different applications in different domains such as software engineering, networks, data mining, and many others. However, some applications may not be appropriate or even correct. In this paper we study this phenomenon ...
    • X-ray absorption resonances near L2,3-edges from real-time propagation of the Dirac–Kohn–Sham density matrix 

      Kadek, Marius; Konecny, Lukas; Gao, Bin; Repisky, Michal; Ruud, Kenneth (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-07)
      The solution of the Liouville–von Neumann equation in the relativistic Dirac–Kohn–Sham density matrix formalism is presented and used to calculate X-ray absorption cross sections. Both dynamical relaxation effects and spin–orbit corrections are included, as demonstrated by calculations of the X-ray absorption of SF6 near the sulfur L2,3-edges. We also propose an analysis facilitating the interpretation ...
    • X-ray Absorption Spectroscopy as a Probe of Ligand Noninnocence in Metallocorroles: The Case of Copper Corroles 

      Lim, Hyeongtaek; Kolle, Ekaney Thomas; Hedman, Britt; Hodgson, Keith O; Ghosh, Abhik; Solomon, Edward I. (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-05-02)
      The question of ligand noninnocence in Cu corroles has long been a topic of discussion. Presented herein is a Cu K-edge X-ray absorption spectroscopy (XAS) study, which provides a direct probe of the metal oxidation state, of three Cu corroles, Cu[TPC], Cu[Br8TPC], and Cu[(CF3)8TPC] (TPC = meso-triphenylcorrole), and the analogous Cu(II) porphyrins, Cu[TPP], Cu[Br8TPP], and Cu[(CF3)8TPP] (TPP = ...
    • X-ray absorption spectroscopy of archetypal chromium porphyrin and corrole derivatives 

      Cao, Rui; Thomas, Kolle E.; Ghosh, Abhik; Sarangi, Ritimukta (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-29)
      A combination of Cr K-edge XAS and DFT calculations have been performed on archetypal chromium porphyrinoid complexes Cr<sup>IV</sup>[TMP]O (<b>2</b>) and Cr<sup>V</sup>[TPC]O (<b>3</b>), and the results have been compared to the reference compound Cr<sup>III</sup>[TPP]Cl (<b>1</b>), where TPP<sup>2−</sup>, TMP<sup>2−</sup>, and TPC<sup>3−</sup> are the anions of <i>meso</i>-tetraphenylporphyrin, ...
    • X-ray absorption spectroscopy of exemplary platinum porphyrin and corrole derivatives: metal- versus ligand-centered oxidation 

      Ghosh, Abhik (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-30)
      A combination of Pt L<sub>3</sub>-edge X-ray absorption spectroscopy (EXAFS and XANES) and DFT (TPSS) calculations have been performed on powder samples of the archetypal platinum porphyrinoid complexes Pt<sup>II</sup>[TpCF<sub>3</sub>PP], Pt<sup>IV</sup>[TpCF<sub>3</sub>PP]Cl<sub>2</sub>, and Pt<sup>IV</sup>[TpCF<sub>3</sub>PC](Ar)(py), where TpCF<sub>3</sub>PP<sup>2-</sup> = meso-tetrakis(p-tr ...
    • X-ray crystal structure of Vibrio alkaline phosphatase with the non-competitive inhibitor cyclohexylamine 

      Ásgeirsson, Bjarni; Markússon, Sigurbjörn; Hlynsdóttir, Sigríður S.; Helland, Ronny; Hjörleifsson, Jens G. (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-10-15)
      <i>Background</i> - <i>Para</i>-nitrophenyl phosphate, the common substrate for alkaline phosphatase (AP), is available as a cyclohexylamine salt. Here, we report that cyclohexylamine is a non-competitive inhibitor of APs.<br><br> <i>Methods</i> - Cyclohexylamine inhibited four different APs. Co-crystallization with the cold-active <i>Vibrio</i> AP (VAP) was performed and the structure solved.<br><br> ...