Investigations of the Efficient Electrocatalytic Interconversions of Carbon Dioxide and Carbon Monoxide by Nickel-Containing Carbon Monoxide Dehydrogenases - The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment - page 88

CN , but instead reacts to stabilize an inactive state at a higher oxidation level
(Figure 9 ). This state must be analogous to but not identical with C ox because the
reactivation potential of the -sulfido product is much more negative. It is therefore

unlikely that sulfide can be an activator of CODH catalysis, as was suggested by
earlier work [ 33 , 40 ]. An interesting observation is made when thiocyanate, NCS ,
is introduced. In marked contrast to cyanate, NCO , NCS does not inhibit CO 2
reduction; instead there is partial inhibition of CO oxidation and an oxidized
inactive state is formed that does not activate at the same potential as C ox
(in CODH I), but at a more negative potential, closer to that observed when sulfide
is present. One possibility is that NCS also reacts to stabilize an inactive oxidized
state by leaving a bridging sulfur, either as sulfide or an intact S-bound NCS .

μ

Figure 9 Reactions of
CODH with sulfide and
thiocyanate. Upper Panel:
Cyclic voltammograms
showing the reaction of
CODH I Ch and CODH II Ch
with sulfide: An aliquot of
Na 2 S stock solution (giving
1 mM final concentration)
was injected into the
electrochemical cell. The
panel is reconstructed using
data from [ 18 ] and
[ 19 ]. Lower Panel: Cyclic
voltammograms showing
the inhibition of CODH I Ch
by thiocyanate: An aliquot
of KSCN stock solution
(giving 6.6 mM final
concentration) was injected
into the electrochemical
cell. Experimental
conditions: 25 C, 0.2 M
MES buffer (pH 7.0),
rotation rate 3500 rpm, scan
rate: 1 mV s 1 .