Summary of Current Research Projects in the Tolman Group
Current Projects (select to go to description)
Synthetic Modeling of Copper
Protein Active Sites: Dioxygen
Activation
Synthetic Modeling of Copper Protein
Active Sites: Cu-Sulfur Centers
New Catalysts for the Synthesis of Polymers From Renewable Resources
![]() Figure 1. Equilibrium between peroxo- and bisoxodicopper complexes. Figure 2. 1:1 Cu-dioxygen adducts.
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Numerous copper-containing proteins use the oxidizing power of dioxygen to perform chemically interesting and important transformations, including the selective hydroxylation of hydrocarbons. A goal of our research is to understand on a fundamental chemical level how these processes occur through the detailed study of small molecule analogs of the metalloprotein active sites using a combination of experimental and theoretical methods. The specific questions we ask include: What are the structures, physicochemical properties, and reactivities of species resulting from the interaction of Cu(I) complexes with dioxygen? How do supporting ligand electronic and structural features influence the course of the Cu(I)/dioxygen reactions, as well as the interconversions among the various types of resulting reactive species? In previous work, we characterized a new type of
Cu/dioxygen
intermediate that contains a bis(oxo)dicopper(III,III) core, and showed
that it can equlibrate with a side-on (peroxo)dicopper(II,II) isomer in
a process that models how the dioxygen O-O bond may be broken and
formed at dimetal active sites in biology and catalysis (Figure 1).
More recently, we characterized
monomeric 1:1 species (Figure 2)
that model
reactive
intermediates postulated to be involved in dioxygen activation at
single
copper sites in proteins (e.g. dopamine beta-monooxygenase). Current work focuses on evaluating ligand effects on copper-oxygen reactivity and on targeting putative copper-oxo species proposed as reaction intermediates (Figure 3). Funding: National Institutes of Health |
Figure 4. Models of (left) type 1
and (right) CuA electron transfer
sites. Figure 5. Copper-sulfur complexes supported by N-donor ligands. |
Copper-sulfur centers in biology include
the binuclear, delocalized mixed-valence "CuA" and monocopper
"Type 1" electron transfer sites, as well as a novel
tetracopper-sulfide cluster in nitrous oxide reductase. The Type 1 and
CuA sites shuttle electrons via redox reactions that
occur rapidly, often over long distances, and at
widely varying
potentials. As a consequence of their unusual
structural
and spectroscopic properties and their importance in biological
electron
transfer, we have been interested in preparing synthetic
analogs in order to assess
how
their structures, spectral properties, and ET function are related. We
are also actively probing N-donor ligand supported copper-sulfur
chemistry, with the ultimate goal of understanding the role of sulfide
in the structure and function of the nitrous oxide reductase. We have prepared accurate models of the CuA center and
several key
members of the type 1 class of active sites (Figure 4). Detailed
spectroscopic studies performed in collaboration with the Solomon group
(Stanford) have provided new insights into the electronic structures of
these molecules and their protein counterparts. We have prepared
several new copper-sulfur complexes, including those with S-S bonds and
a novel delocalized mixed valent tricopper-sulfide that reacts with nitrous oxide (Figure 5). Current work is focused
on further exploring copper-sulfur chemistry with a wide variety of
N-donor ligands. Funding: National Institutes of Health |




