The study of model compounds continues to significantly contribute to our u
nderstanding of the role of transition metals at the active sites of enzyme
s. Recent advances in the field include the use of mimics for enzymes that
activate dioxygen, as dioxygen is not only manipulated in nature but also h
as industrial significance in metal-catalyzed oxidations of organics. Coppe
r, nonheme and heme iron coordination complexes have been used to mimic rev
ersible dioxygen-binding by the three classes of blood-oxygen carriers - he
mocyanin, hemerythrin and hemoglobin/myoglobin - while functional mimics of
oxygenases and oxidases with copper and iron have also provided key insigh
ts into important dioxygen activation processes.