BIOINORGANIC CHEMISTRY A Short Course Second Edition

CYTOCHROME c OX IDASE 441

Chemical Reviews paper.^138 We can only discuss a small number of these here,
but some important categories are (1) synthetic Fe(II) – Cu(I) complexes and
their reactions with O 2 , (2) oxidized heme – copper models (Fe(III) – X – Cu(II)
complexes, where X equals oxo - and hydroxo - bridged complexes, cyanide -
bridged complexes, or other X - bridged complexes), (3) crosslinked histidine –
tyrosine residues at the heme – copper center, and (4) Cu A site synthetic
models.
In category (1) above, the earliest synthetic Fe(II) – Cu(I) complexes, pre-
pared beginning in 1981,^149 were adapted from the “ picket - fence porphyrin ”
concept pioneered by the J. P. Collman laboratory.^150 The Gunter and Mander
complexes^149 reacted with dioxygen at room temperature to yield oxidized
compounds such as [(P)Fe III – OH – Cu II (N 4 )], P = porphyrin ligand, N 4 = copper
ion ligand system. (See Figure 7.43 .)
Research on Fe(II) – Cu(I) complexes has continued through the years in
research groups headed by J. P. Collman, Y. Naruta, B. Boitrel, and Kenneth
Karlin. One system that has been thoroughly characterized by Karlin and co -
workers involves the reaction of a [(TMPA)Cu(I)(RCN)] + complex with a
[(F 8 TPP)Fe(II)] complex. The TMPA ligand is tris (2 - pyridylmethyl)amine,
RCN = MeCN = acetonitrile, and F 8 TPP = tetrakis (2,6 - difl uorophenyl)porphy-
rinate ( − 2 charge).^151 These researchers found that reaction with dioxygen in
acetonitrile at− 40 ° C resulted in formation of the heterobinuclear peroxo
complex [( 82 ) III−−(^2 −+) II( )] F TPP Fe rather than homobinuclear O Cu TMPA
heme – peroxo or a binuclear copper – peroxo complexes. The reaction is shown
in Figure 7.44.
The product was identifi ed by a number of spectroscopic methods. Dioxy-
gen uptake was measured by spectrophotometric titration. MALDI – TOF – MS
(matrix - assisted laser desorption/ionization – time of fl ight – mass spectrome-
try), an MS method particularly suited to determining molecular masses of
biopolymers and synthetic materials with relative masses up to several hundred
kilodaltons, determined that the product contained stoichiometric amounts of
the heme starting material, the copper complex, and dioxygen in a 1 : 1 : 1 ratio.

Figure 7.43 Cytochrome c oxidase model complexes, [(Porphyrin)Fe III – OH – Cu II (N 4 )],
as synthesized in reference 149.

N

N

N FeII N

HN

O

N

N

NH

O N

HN

O

NH

O

CuI N

N

N

N FeIII N

HN

O

N

N

NH

O

NH

O

N

N

HN

O

CuII

(OH)

RT, O 2