Spin transition during H2O2 formation in the oxidative half-reaction of copper amine oxidases
2004 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 36, 13882-13892 p.Article in journal (Refereed) Published
Dioxygen reduction in the oxidative half-reaction of copper amine oxidases (CAOs) has been studied quantum chemically using the hybrid density functional theory (B3LYP). The reductive activation of dioxygen is a spin-forbidden process for which substantial kinetic O-18 (but no deuterium) isotope effects have been found experimentally. The proposed mechanism was divided into three steps, and the last step was studied for two different potential energy surfaces: the quartet and the doublet surfaces. It is suggested that dioxygen reduction occurs through a spin transition that is induced by the exchange interaction between the impaired spins of the Cu(II) ion and the O-2(-) anion. The step involving this spin transition is suggested to be rate-limiting, which gives a rationalization for the puzzling experimental results when copper is substituted for other metals. The spin transition is triggered by the calculated vibronic perturbation of 5.4 (kcal/mol) Angstrom(-1), which leads to a very fast rate of 8 x 10(10) s(-1) for the spin transition. However, since the spin transition occurs at a calculated energy that is 18-20 kcal/mol higher than that of the reactant, this step could still be rate-limiting. The difference in the O-O bond distance between the resting state (free dioxygen) and the point of the spin transition provides an explanation for the oxygen isotope effect.
Place, publisher, year, edition, pages
2004. Vol. 108, no 36, 13882-13892 p.
continuum dielectric theory, self-consistent-field, crystal-structure, hansenula-polymorpha, enzyme catalysis, mechanism, topaquinone, biogenesis, activation, dioxygen
IdentifiersURN: urn:nbn:se:kth:diva-23702DOI: 10.1021/jp0478312ISI: 000223703900045ScopusID: 2-s2.0-4544299447OAI: oai:DiVA.org:kth-23702DiVA: diva2:342401
QC 20100525 QC 201109162010-08-102010-08-102011-09-16Bibliographically approved