Isotopic probing of molecular oxygen activation at copper(I) sites

Michael P. Lanci, Valeriy V. Smirnov, Chris Cramer, Ekaterina V. Gauchenova, Jörg Sundermeyer, Justine P. Roth

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Abstract

Copper-dioxygen (CuO2) adducts are frequently proposed as intermediates in enzymes, yet their electronic and vibrational structures have not always been understood. [Cu(η1-O2)TMG 3tren]+ (TMG3-tren = 1,1,1-tris{2-[N 2-(1,1,3,3-tetramethylguanidino)]ethyl}amine) features end-on (η1) O2 coordination in the solid state. Described here is an investigation of the compound's solution properties by nuclear magnetic resonance spectroscopy, density functional calculations, and oxygen isotope effects. The study yields two major findings. First, [Cu(η1-O2)TMG3tren]+ is paramagnetic due to a triplet electronic structure; this is in contrast to other copper compounds where O2 is bound in a side-on manner. Second, the oxygen equilibrium isotope effect upon O2 binding to copper(I) ( 18O EIE = K(16O16O)/K(16O 18O) = 1.0148 ± 0.0012) is significantly larger than those determined for iron and cobalt η1-O2 adducts. This result is suggested to reflect greater ionic (CuII-O2 -I) character within the valence bond description. A revised interpretation of the physical origins of the 18O EIEs upon O 2 binding to redox metals is also advanced along with experimental data that should be used as benchmarks for interpreting 18O kinetic isotope effects upon enzyme reactions.

Original languageEnglish (US)
Pages (from-to)14697-14709
Number of pages13
JournalJournal of the American Chemical Society
Volume129
Issue number47
DOIs
StatePublished - Nov 28 2007

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    Lanci, M. P., Smirnov, V. V., Cramer, C., Gauchenova, E. V., Sundermeyer, J., & Roth, J. P. (2007). Isotopic probing of molecular oxygen activation at copper(I) sites. Journal of the American Chemical Society, 129(47), 14697-14709. https://doi.org/10.1021/ja074620c