Sökning: "Tim Clark"

Hittade 3 avhandlingar innehållade orden Tim Clark.

  1. 1. Quantum Chemical Studies of Protein-Bound Chromophores, UV-Light Induced DNA Damages, and Lignin Formation

    Författare :Bo Durbeej; Leif Eriksson; Tim Clark; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Quantum chemistry; quantum chemistry; calculations; density functional theory; excited states; photochemistry; chromophores; absorption spectra; bathochromic shift; isomerization; UV radiation; DNA damages; cycloaddition reactions; photoenzymic repair; electron transfer; lignin; polymerization; phenoxy radicals; dilignols; Kvantkemi; Quantum chemistry; Kvantkemi;

    Sammanfattning : Quantum chemical methods have been used to provide a better understanding of the photochemistry of astaxanthin and phytochromobilin; the photoenzymic repair of UV-light induced DNA damages; and the formation of lignin. The carotenoid astaxanthin (AXT) is responsible for the colouration of lobster shell. LÄS MER

  3. 2. Quantum Chemical Studies of Radical Cation Rearrangement, Radical Carbonylation, and Homolytic Substitution Reactions

    Författare :Daniel Norberg; Nessima Salhi-Benachenhou; Sten Lunell; Tim Clark; Uppsala universitet; []
    Nyckelord :Quantum chemistry; quantum chemistry; coupled-cluster; density functional theory; meta-GGA; reaction mechanism; potential energy surface; isomerization; fragmentation; dissociation; condensation; addition; SH2; hydrogen abstraction; iodine atom transfer; complex; weakly interacting system; hyperfine coupling constant; Kvantkemi;

    Sammanfattning : Quantum chemical calculations have been performed to investigate radical cation rearrangement, radical carbonylation, and homolytic substitution reactions of organic molecules. The rearrangement of the bicyclopropylidiene radical cation to the tetramethyleneethane radical cation is predicted to proceed with stepwise disrotatory opening of the two rings. LÄS MER

  4. 3. Theoretical Modeling of Enzyme Catalysis with Focus on Radical Chemistry

    Författare :Vladimir Pelmenschikov; Per E. M. Siegbahn; Tim Clark; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; density functional theory; enzyme catalysis; radical chemistry; zinc-containing peptidase; methyl-coenzyme M reductase; ribonucleotide reductase; superoxide dismutase; Quantum chemistry; Kvantkemi;

    Sammanfattning : Hybrid density functional theory (DFT) B3LYP method is applied to study the four diverse enzyme systems: zinc-containing peptidases (thermolysin and stromelysin), methyl-coenzyme M reductase, ribonucleotide reductases (classes I and III), and superoxide dismutases (Cu,Zn- and Ni-dependent enzymes). Powerfull tools of modern quantum chemistry are used to address the questions of biological pathways at their molecular level, proposing a novel mechanism for methane production by methyl-coenzyme M reductase and providing additional insights into hydrolysis by zinc peptidases, substrate conversion by ribonucleotide reductases, and biological superoxide dismutation. LÄS MER