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M. HAJIMOHAMMADI ET AL.
by a Bruker AMX 300 MHz spectrometer using TMS as
internal standard. Spectral changes were monitored with
a Shimadzu UV-2100 spectrophotometer. Also, Mass
spectra of Hb were carried out by a Bruker autoflex III
smartbeam mass spectrometer.
General procedure for the synthesis of iron(II)-tetrakis-
(4-sulfonatophenyl)porphyrin (FeIIITPPS): FeIIITPPS was
synthesized according to the literature [12].
Scheme 1. Oxidation of aldehydes to carboxylic acids with
heme as an active site of blood
RESULTS AND DISCUSSION
To check the generality of this method, oxidation
of different aldehydes was accomplished by air in the
presence of sheep Hb and water solvent (Table 1). The
reactions were performed in a tube without any par-
ticular precautions. Under these conditions, aldehydes
(Table 1, entries 1–10) were oxidized to the correspond-
ing acids with 77–100% yield. The results of the oxida-
tion reactions in the absence of blood plasma were as
good as those of the reactions in the presence of blood
plasma (Table 1, entry 2). Also, the yield of benzalde-
hyde oxidation in the presence of human blood was as
good as those of the reaction in the presence of sheep
blood (Table 1, entry 3). On the other hand, the reaction
didn’t provide efficient yield in the presence of light,
which is the key factor in photooxygenation reactions
[13] (Table 1, entry 4). In addition, in the presence of N3-,
which is a well-known singlet oxygen scavenger [14],
benzaldehyde was completely converted to benzoic acid
(Table 1, entry 5). These results confirmed that Hb did
not act as a metalloporphyrin to produce singlet oxygen.
It is important to note that oxidation of the substrate does
not continue in the absence of blood or when bubbling of
air is interrupted (Table 1, entries 6 and 7). Therefore, the
presence of blood and O2 are essential for the conversion
of benzaldehyde to benzoic acid.
In the presence of aldehydes with nitrogen or oxygen
atoms on the benzyl substituent, the oxidation process of
aldehydes was blocked (Table 1, entries 11 and 12). This
might be due to strict hindrance of Hb, and it revealed
that the oxidation of different aldehydes was selected
by Hb. Our suggestion for Hbs selectivity is based on
its ring size which is related directly to the size of the
aldehyde to approach the complicated Hb structure.
Throughout aldehyde oxidation, the modified Hb con-
centration was also studied, and high conversion was
observed in 0.565 g/dl sheep Hb (Table 2, entries 1–4).
The rate of benzaldehyde oxidation in neutral conditions
was similar to that in acidic and alkaline pH (Table 2,
entry 2, 5 and 6 ).
oxidation of aldehydes to carboxylic acids using air
(1 atm) in the presence of sheep Hb and water as a sol-
vent (Scheme 1). The reactions proceeded smoothly
under these conditions, with 77–100% conversion and
100% selectivity.
EXPERIMENTAL
General procedure for the synthesis
of carboxylic acids
In the absence of light, 0.5 mmol liquid aldehyde
was added to 0.565 g/dL sheep Hb in pH = 7.0. Air
(1 atm) was bubbled throughout the solution for 7–
150 h. Plasma was separated from blood by centri-
fuging at 6000 rpm for 15 mins. In the light reaction,
0.5 mmol benzaldehyde, 0.565 g/dL sheep Hb and air
(1 atm) were irradiated under visible light (288 power
LED lamps, 1 W, 2.3 V (59660 LUX) for 7 h. After
oxidation of the aldehydes, the solvent was removed
under vacuum and the residue was separated by column
chromatography (silica gel, n-hexane/EtOAc, 13:1) to
obtain the corresponding carboxylic acids (Table 1).
The product structures from entries 1, 8, 9 and 10 in
Table 1 were confirmed by the melting points and by 1H
NMR spectra. The yield and selectivity of the products
were determined by 1H NMR.
Benzoic acid (1): Colorless crystal, mp >120–123°C.
1H NMR (300 MHz, CDCl3) δ 12.88 (brs, 1H, OH), 8.15
(d, J = 7.5 Hz, 2H), 7.47–7.65 (m, 3H) ppm.
Cinnamic acid (8): Colorless crystal, mp >133–
135°C. 1H NMR (300.13 MHz, CDCl3) δ 10.80 (brs, 1H,
OH), 7.78 (d, J = 16.0 Hz, 1H), 7.37–7.59 (m, 5H), 6.44
(d, J = 16.0 Hz, 1H) ppm.
4-chlorobenzoicacid(9):Colorlesscrystal, mp>238–
1
241. H NMR (300.13 MHz, CDCl3) δ 10.28 (brs, 1H,
OH), 8.03 (d, J = 8.3 Hz, 2H), 7.51 (d, J = 8.3 Hz,
2H) ppm.
4-Bromobenzoic acid (10): Colorless crystal, mp>
253–255. 1H NMR (300.13 MHz, CDCl3) δ 8.03 (d, J =
7.94 Hz, 2H), 7.61 (d, J = 8.5 Hz, 2H) ppm, OH not
observed.
The consumption of the starting aldehydes and the for-
mation of the corresponding carboxylic acids monitored
According to the literature, with a change in the oxi-
dation number of iron in none-heme enzymes from +2 or
+3 to +4, one blue shift at the Soret band of hemoglobin
occurs and the intensity of Q band is decreased [15]. The
existence of an axial ligand was confirmed by UV-vis
spectra in the oxidation of 4-bromobenzaldehyde
Copyright © 2018 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2018; 22: 2–7