is even higher (F¼0.742) and the compound is also sensitive to
NIR light (800–900 nm), which results in bleaching of its
maroon solution and release of NO. These results show that
properly designed manganese nitrosyls can also effectively
deliver NO under light, and their photoactivity can be
modulated by alterations in the ligand frame( 124 ).
In the reaction of a dinuclear Ni(I) complex with NO, one
[Me 2 NN]Ni fragment is trapped as the nickel nitrosyl compound
[Me 2 NN]Ni(NO) ( 31 ).
S-Nitrosothiols undergo a reversible transnitrosation reaction
at zinc tris(pyrazolyl)boratozinc thiolates, iPr2TpZn-SR. These
zinc thiolates are unreactive toward anaerobic NO but rapidly
react with NO in the presence of O 2 or anaerobically with NO 2
to release the S-nitrosothiol RSNO with formation of the
corresponding zinc nitrate( 125 ).
The reactivity of Zn 7 - and Cd 7 -metallothionein (MT) withS-
nitrosopenicillamine (SNAP),S-nitrosoglutathione (GSNO), and
2-(N,N-diethylamino)-diazenolate-2-oxide (DEA/NO) demonstra-
ted that MT is a significant site for cellular reaction of NO or
its compounds. Zn 7 -MT reacts with SNAP or GSNO under aero-
bic conditions and in the presence of light, which stimulates the
decomposition of S-nitrosothiolates to NO and Zn^2 þ, whereas
protein thiols are modified( 126 ).
NOx can also undergo photoredox reactions on solid
photocatalysts modified by coordination compounds, for example,
on TiO 2 modified by H 2 PtCl 6 ( 127 ) or on bismuth tungstate
photocatalysts ( 128 ).
To date, research on light-activated NO donors has almost
exclusively focused on the chemical reactivity of NO in biochemi-
cal systems, but detecting and understanding the role of NO in
the environmental processes is an exciting new field of endeavor
( 129 ). The prerequisites of these operations were presented in this
review, but still new details appear that prove the environmental
importance of cooperation between transition metal ions, natural
ligands, NO, and solar light. A significant example may be found
in the recent report on the role of copper(II) and other divalent
metal ions (zinc, cobalt, and iron) in N 2 O reduction to N 2 in the
presence of sulfides, which is an essential stage of denitrification
processes proceeding both in natural environments (marine
sediments) and industry (activated sludge, methanogenic sludge,
BioDeNOx process) ( 130 ). The photocatalytic release of NO
is accessible also in multiphase systems, as was demonstrated
in case of the encapsulated iron and ruthenium nitrosyl
complexes ( 101 ).
METAL COMPLEXES AS SOLAR PHOTOCATALYSTS 315