THE ROLE PLAYED BY ACID AND BASIC CENTERS
1899
and basic centers as a heterogeneous acidꢀbase carrier.
mol %
40
These centers play an important role in the catalytic
transformation of ethanol. As mentioned, redox
active centers РРFe3+ОН, TPhPFe3+ОН, and perꢀ
TPhPFe3+ОН have structures stabilized by the coordiꢀ
nation of the basic center of the carrier (Al–O:) with
the functional groups of substituted iron porphyrin
catalysts, especially in the axial position with respect
to the central iron ion.
1
2
20
The mechanism of the peroxidase action of biomiꢀ
metics suggested above can be represented in the form
of elementary reactions quite corresponding to modꢀ
ern views on the mechanism of functioning of their
biomimetic analogues in the TsPS theory [12].
The coherent synchronization of hydroxylation
and hydrogen peroxide decomposition with the use of
biomimetic catalysts allows these reactions to be perꢀ
formed under the conditions of mutual strengthening
and weakening (chemical interference) and the rates
of these reactions to be controlled under comparaꢀ
tively mild conditions. This technology nontraditional
for chemical experiments was used to hydroxylate proꢀ
pane into isopropanol with hydrogen peroxide in the
presence of the perꢀFTPhPFe3+ОН/Al2O3 catalyst.
The multistage synthesis of the active center of bioꢀ
mimetic catalyst is most complex. At the initial stage,
Fe(III)tetrapentafluorophenylporphyrin was syntheꢀ
sized. At the final stage, the active mass of iron (III)
perfluorotetraphenylporphyrin was immobilized from
a solution in dimethylformamide (DMFA) on an
acidꢀbase carrier (Al2O3).
0
1
2
τ
, s
Fig. 4. Contact time dependences of reaction product
yields (( and ( ꢀC H OH) at 40°С, Н О
20 wt %, and С Н : Н О = 1 : 2.
1
)
О
2
)
i
[
]
=
2
3
7
2
2
3
8
2 2
both the catalase and monooxigenase reactions. It folꢀ
lows that, over the whole range of contact time variaꢀ
tions, complete consumption of hydrogen peroxide is
observed. According to the kinetics of the catalase and
hydroxylation reactions, hydrogen peroxide conꢀ
sumption is properly distributed between these two
processes.
The dependences of the yields of iꢀC3H7OH and О2
on the concentration of Н2О2 in aqueous solution are
shown in Fig. 5. Before it was supplied into the reacꢀ
tion zone, the solution was transformed into a gas. A
In cytochrome Rꢀ450, the active catalytic center is
iron(III) protoporphyrin complex. Its analogue is the
perꢀFTPhPFe3+ОН/Al2O3 synthesized biomimetic.
Of course, the latter is a mimetic model of the correꢀ
sponding enzyme. If the carrier and conditions are
selected most properly, good results can be obtained
under the conditions more harsh than in living sysꢀ
tems. For instance, it was shown in [3, 4] that gasꢀ
phase monooxigenase mimetics immobilized on variꢀ
ous carriers possess certain advantages characteristic
of usual heterogeneous catalysts.
low yield of iꢀC3H7OH (20.8 mol %) and a high yield
of О2 (42.9 mol %) correspond to a 15% concentration
of hydrogen peroxide. As the concentration of Н2О2
increases, the coherent dependence between the synꢀ
chronous reactions, catalase and monooxigenase,
becomes obvious. At a 20 wt % concentration of
hydrogen peroxide, the yield of iꢀC3H7OH reaches a
maximum (39.3 mol %), and the yield of О2 is miniꢀ
mum (40 mol %). A subsequent insignificant decrease
in the yield of iꢀC3H7OH at a 25 wt % concentration
The dependences of the yields of isopropanol
of hydrogen peroxide (~38 mol %) is accompanied by
a smooth increase in the yield of О2 in the catalase
reaction (42.5 mol %) [13]. It follows from the data
presented in Fig. 5 that the optimum concentration of
hydrogen peroxide for gasꢀphase heterogeneous cataꢀ
lytic hydroxylation of propanol is 20 wt %. In addition,
the conclusion can be drawn that, on the whole, a
strong increase in the concentration of hydrogen perꢀ
oxide decreases the yield of the monooxigenase reacꢀ
(
i
ꢀC3H7OH) and molecular oxygen (О2) in the oxidaꢀ
tion of propane (С3Н8) on contact time are shown in
Fig. 4. At short times ( < 0.6 s), the hydroxylating
τ
τ
τ
activity of the biomimetic remains low. Conversely,
catalase activity predominates, as follows from the
yield of О2. The yield of
conversion of С3Н8 increase at longer
= 1.1 s, it becomes clear that the kinetic curves of the
i
ꢀC3H7OH and, accordingly,
τ
. Starting with
τ
catalase and monooxigenase reactions are synchroꢀ
nized. Changes in the yield of О2 in the catalase reacꢀ
tion show that the almost complete catalytic decomꢀ
position of Н2О2 in the catalase reaction increases the
tion product (
iꢀC3H7OH) and favors the catalase reacꢀ
tion.
The experimental data on the consumption of
= 1.1 s hydrogen peroxide in synchronized reactions are
above 1.1 s preserves the coherꢀ shown in Fig. 6. In reality, the curves shown in Fig. 6
ent synchronized character of product yield curves for are similar to those in Fig. 5, with the difference that
yield of
[13]. An increase in
i
ꢀC3H7OH, which is maximum at
τ
τ
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 84
No. 11
2010
Magerramov
