Cu dmpðÞ 2

 2 þ

þNO^ !Cu dmpðÞ 2

þ

þNOþ ð 19 Þ

NOþþH 2 O!HNO 2 þHþ ð 20 Þ

where dmp¼2,9-dimethyl-1,10-phenanthroline ( 106 ).

iii. The redox reaction between NO and a Cu(II) complex leads to
the production of Cu(I) species and nitrosation of the ligand,
as in the case of a tripodal tetraamine ligand and its
derivatives, which undergo concomitant nitrosation at all
three secondary amine sites( 107 ). A similar effect has been
observed for the fluorescein-derived ligands (Fl):

CuII 2 ðÞFl 2

hi

!

2NO

2CuIþðÞFl 2 ðÞNO 2 ð 21 Þ

The reaction (Eq. 21) is accompanied by fluorescence enhance-
ment and for this reason the copper fluorescein complexes can be
used as NO-sensors ( 108 ).
The reactions of NO with copper proteins as possible NO
targetsin vivoare not as well characterized as those with iron
proteins. Recent studies indicate, however, that redox reactions
can be very fast even at low NO concentrations and in the pres-
ence of oxygen, and therefore the reactions may be of physiologi-
cal relevance. In general, it is assumed that different
spectroscopic types of copper centers react differently with
NO ( 54 ).
The 2-His-1-Glu metal center commonly found in natural non-
heme iron enzymes was engineered into myoglobin, and this new
protein appears capable of binding not only Fe(II) but also Cu(I),
and the sites are active in reducing NO to N 2 O via different
intermediates ( 69 ).
Reaction of the monovalent complex [Me 2 NN]Cu(Z^2 -ONAr)
with NO(g) to give divalent [Me 2 NN]Cu(k^2 -O 2 N 2 Ar) represents
an example of oxidative nitrosylation (where Ar¼3,5-Me 2 C 6 H 3
or Ph). TheC-nitroso adducts reported herein are capable of
incorporating one equivalent of NO into the coordinated ONAr
ligand to form diazeniumdiolates [Cu](k^2 -O 2 N 2 Ar), which
represents oxidative nitrosylation of the formally monovalent
[Me 2 NN]Cu(Z^2 -ONAr). This serves as a well-defined example
that illustrates the possibility of oxidizing a metal center via
functionalization of a bound ligand with NO( 31 ). The liberation
of NO from the copper nitrosyl complexes was not characterized
in detail, but the nitritophenylophosphino complex of Cu(I) was
recently reported to release NO upon protonation ( 109 ).

312 ZOFIA STASICKA