A series of
Cu
II and Zn
IIcomplexes with new ligands having either one or two substitutedphenolatesappended to the 1,4,7-triaza
cy
clononane frame were prepared and
chara
cterized by opti
cal absorption, EPR, NMR,and/or resonan
ce Raman spe
ctros
copy,
cy
cli
c voltammetry, and, in eight
cases, X-ray
crystallography. Features ofthe a
ctive site geometries of the Cu
II-tyrosinate formsof gala
ctose and glyoxal oxidases (GAO and GLO) weremodeled by these
complexes, in
cluding the binding of a redox-a
ctivephenolate and an exogenous ligand (Cl
-,CH
3CO
2-, orCH
3CN) in a
cis-equatorial position of asquare pyramidal metal ion. The role of the unique
orthoS
-C
covalent bond between a
cysteine (C228) and theequatorial tyrosinate (Y272) in the proteins was probedthrough an examination of the opti
cal absorption and ele
ctro
chemi
calproperties of sets of similar
complexes
comprisedof phenolate ligands with differing
ortho substituents,in
cluding thioether groups. The
o-alkylthio unitinfluen
cesthe PhO
- ![](/images/entities/rarr.gif)
Cu
II LMCT transition and theM
II-phenolate/M
II-phenoxyl radi
cal redoxpotential, but to a relativelysmall degree. Ele
ctro
chemi
cal and
chemi
cal one-ele
ctron oxidationsof the Cu
II and Zn
II complexes of ligandshaving
tert-butyl prote
cting groups on the phenolates yielded newspe
cies that were identified as novel M
II-phenoxylradi
cal
compounds analogous to the a
ctive Cu
II-tyrosyl radi
calforms of GAO and GLO. The M
II-phenoxyl radi
calspe
cieswere
chara
cterized by opti
cal absorption, EPR, and resonan
ce Ramanspe
ctros
copy, as well as by their stoi
chiometryof formation and
chemi
cal redu
ction. Notable features of theCu
II-phenoxyl radi
cal
compounds that are similartotheir protein
counterparts in
clude EPR silen
ce indi
cative of magneti
ccoupling between the Cu
II ion and the boundradi
cal, a band with
![](/images/gif<font color=)
chars/lambda.gif" BORDER=0 >
max ![](/images/entities/ap.gif)
410 nm (
![](/images/gif<font color=)
chars/epsilon.gif" BORDER=0 >
![](/images/entities/ap.gif)
3900M
-1 cm
-1) inUV-vis spe
ctra diagnosti
c for the phenoxyl radi
cal,and a feature attributable to the phenoxyl radi
cal C-O vibration(
![](/images/gif<font color=)
chars/nu.gif" BORDER=0 >
7a) in resonan
ce Raman spe
ctra. SimilarRamanspe
ctra and ele
ctro
chemi
cal behavior for the Zn
II analogs,as well as an isotropi
c signal at
g = 2.00 in theirX-bandEPR spe
ctra, further
corroborate the formulations of theM
II-phenoxyl radi
cal spe
cies.