Social event to take place from 12:30pm-12:45pm in the breezeway.
Abstract:
Copper ion is a vital constituent of metalloprotein active sites, those required to support the life of aerobic organisms. The biological roles of copper proteins include electron shuttling/trafficking and the processing of the critical small molecule nitrogen oxides NO (nitric oxide; nitrogen monoxide), nitrite (NO2–) and nitrous oxide (N2O). In the processing of O2 (molecular oxygen; dioxygen), copper proteins participate in hemolymph O2-transport, oxygenase activity (i.e., O-atom(s) insertion into organic substrates) and O2-reduction to hydrogen peroxide or water accompanied by substrate dehydrogenation/oxidation. Functions include pigment production, generation of neurotransmitters and hormones, conversion of methane to methanol, oxidative cleavage of recalcitrant polysaccharides as well as production and scavenging of reactive oxygen species (ROS). Much of the biochemistry of copper surrounds the rich one-electron (e−) redox chemistry of copper shuttling within the CuII/CuI oxidation states. Brief overviews of relevant copper-protein biochemistry will be woven into the presentation of relevant coordination chemistry.
Our long-term research program on copper-dioxygen chemistry has focused on ligand design, systematic ligand variation and the use of cryogenic solution handling, enabling the generation and investigation of new coordination complexes, ligand-bound CuIn/O2(g) (n = 1, 2) derived species. Through this approach, one may identify factors such as donor atom type or number, coordination geometry, metal complex redox potential, and second coordination sphere composition, those which significantly contribute to the unique reactivity properties of Cu-metalloprotein active sites, the nature/structure of reactive intermediates and details concerning reaction mechanism(s) involved.
Prior to our research efforts, no synthetically derived well-characterized CuIn-(O2(g)) species existed. Success in this area has come from carefully considered ligand design and application of cryogenic solution handling. Use of tripodal tetradentate N4 ligands leads to the generation of superoxo-copper(II) {(ligand)CuII(O2•–)} complexes and/or peroxo-dicopper(II) analogs which have been characterized structurally/spectroscopically and have been examined with respect to a variety of reaction types. Binucleating ligands of several types hold two copper(I) ions and exhibit various reactivities, including reversible O2(g)-binding and/or ‘activation’ of the bound peroxo (O22–) ligand leading to hydroxylation of unactivated arene C–H bonds, chemistry which has relevance to Tyrosinase enzyme reaction mechanism. Use of derived (by arene hydroxylation) binucleating ligand containing phenolato-bridged dicopper complexes leads to new kinds of superoxo, peroxo or hydroperoxo dicopper(II) complexes. We show that these species can be reversibly interconverted with oxidants/reductants and/or acids-bases, thus leading us to elucidate thermodynamic interrelationships; these reveal how differences in ligand properties influence the nature (i.e., reactivity) of the O2(g)-derived species bound to copper ion(s). Time permitting, presentation of a recently described peroxo-dicopper(II) complex nucleophilic oxidative aldehyde deformylation reaction, that involving dioxygenase chemistry, will be presented.
Results obtained from the present research presented provides insights into biological copper ion mediated O2-processing and thus also possibly can apply to practical organic oxidation chemistry and/or energy related fuel-cell technologies.