title: Isotopic probing of molecular oxygen activation at copper(I) sites.
abstract: Copper-dioxygen (CuO2) adducts are frequently proposed as intermediates in enzymes, yet their electronic and vibrational structures have not always been understood. [Cu(eta1-O2)TMG3tren]+ (TMG3tren = 1,1,1-tris{2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl}amine) features end-on (eta1) 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(eta1-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 [triple bond] K(16O16O)/K(16O18O) = 1.0148 +/- 0.0012) is significantly larger than those determined for iron and cobalt eta1-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 O2 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.
authors.affiliation: Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Lanci
authors.forename: Valeriy V
authors.initials: VV
authors.lastname: Smirnov
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Cramer
authors.forename: Ekaterina V
authors.initials: EV
authors.lastname: Gauchenova
authors.forename: Jörg
authors.initials: J
authors.lastname: Sundermeyer
authors.forename: Justine P
authors.initials: JP
authors.lastname: Roth
mesh_terms: D003300:Copper / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000737:chemistry; D013696:Temperature
chemical_list: D010103:Oxygen Isotopes; D003300:Copper; D010100:Oxygen