Przeglądaj {{ collection }} wg Autor "Dybała-Defratyka, Agnieszka"

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  • Pozycja
    Cytochrome P450-catalyzed dealkylation of atrazine by Rhodococcus sp. strain NI86/21 involves hydrogen atom transfer rather than single electron transfer
    (Royal Society of Chemistry, 2014) Meyer, Armin H.; Dybała-Defratyka, Agnieszka; Alaimo, Peter J.; Geronimo, Inacrist; Sanchez, Ariana D.; Cramer, Christopher J.; Elsner, Martin
    Cytochrome P450 enzymes are responsible for a multitude of natural transformation reactions. For oxidative N-dealkylation, single electron (SET) and hydrogen atom abstraction (HAT) have been debated as underlying mechanisms. Combined evidence from (i) product distribution and (ii) isotope effects indicate that HAT, rather than SET, initiates N-dealkylation of atrazine to desethyl- and desisopropylatrazine by the microorganism Rhodococcus sp. strain NI86/21. (i) Product analysis revealed a non-selective oxidation at both the αC and βC-atom of the alkyl chain, which is expected for a radical reaction, but not SET. (ii) Normal 13C and 15N as well as pronounced 2H isotope effects (εcarbon: −4.0‰ ± 0.2‰; εnitrogen: −1.4‰ ± 0.3‰, KIEH: 3.6 ± 0.8) agree qualitatively with calculated values for HAT, whereas inverse 13C and 15N isotope effects are predicted for SET. Analogous results are observed with the Fe(IV)[double bond, length as m-dash]O model system [5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-iron(III)-chloride + NaIO4], but not with permanganate. These results emphasize the relevance of the HAT mechanism for N-dealkylation by P450.
  • Pozycja
    Theoretical predictions of isotope effects versus their experimental values for an example of uncatalyzed hydrolysis of atrazine
    (Royal Society of Chemistry, 2014) Grzybkowska, Anna; Kamiński, Rafał; Dybała-Defratyka, Agnieszka
    Kinetic isotope effects are one of the most powerful experimental techniques for establishing the nature of a chemical process. However their interpretation very often seeks support from electronic structure calculations in order to get detailed information regarding the transition state which is not experimentally available. For an example of atrazine hydrolysis we have shown how the match between experimentally and theoretically determined magnitudes of carbon, nitrogen and chlorine kinetic isotope effects can be used to discuss the mechanism under different reaction conditions. Two different density functionals combined with the explicit presence of solvent molecules and a continuum solvation model revealed that although the reaction proceeds via the same concerted mechanism regardless of the reaction conditions the transition state structure for an acid and base-catalyzed pathway is different.