Chemistry Letters Vol.33, No.12 (2004)
1545
30 ꢃC. The MVꢂþ concentration was determined by the absorb-
Figure 1. The methanol production was 0.55 mmol dmꢁ3 after
4 h irradiation. The conversion yield of HCO3 to methanol
ꢁ
ance at 605 nm using the molar coefficient 13000 molꢁ1 dm3
18
cmꢁ1
.
was estimated to be 5.5% after 4-h irradiation. In contrast, no
methanol production was observed without irradiation. More-
over, no methanol production was also observed in the absence
of HCO3ꢁ. Thus, the produced methanol is not from the oxidized
TEOA but the origin from HCO3ꢁ reduction with three dehydro-
genases. These results indicate that the photochemical synthesis
When the sample solution was irradiated, the accumulation
of MVꢂþ was observed. The rate of MVꢂþ formation increased
with the concentration of MV2þ. In contrast, the conversion
yield of MV2þ to MVꢂþ increased with the concentration of
MV2þ up to 0.1 mmol dmꢁ3 and then decreased. FDH catalyzes
both the reduction of HCO3ꢁ to formic acid and the oxidation of
formic acid to HCO3ꢁ. The reaction rate of the reduction of
ꢁ
of methanol from HCO3 with FDH, AldDH and ADH via the
photoreduction of MV2þ using ZnTPPS photosensitization.
However, the amount of produced methanol and the turnover
number of ZnTPPS and MV2þ are respectively low values.
The improvement of the methanol production and optimum con-
dition using the reaction system as shown in Scheme 1 is being
studied in detail.
ꢁ
HCO3 to formic acid is 20 times slower than that of the oxida-
ꢁ
tion of formic acid to HCO3 in the system with FDH. At high
MV2þ concentrations, HCO3ꢁ was produced by the oxidation of
formic acid with FDH. The conversion yield of MV2þ to MVꢂþ
is important for formic acid synthesis using the system shown in
Scheme 1. Therefore, the optimum MV2þ concentration is
0.1 mmol dmꢁ3 for methanol synthesis. After 40 min irradiation,
25 mmol dmꢁ3 MVꢂþ was produced. The reduction ratio of
MV2þ to MVꢂþ was about 25% after 40 min irradiation.
In conclusion, photochemical and enzymatic synthesis of
ꢁ
methanol from HCO3 with dehydrogenases FDH, AldDH,
and ADH and MV2þ photoreduction by the visible light photo-
sensitization of ZnTPPS in the presence of TEOA was developed
ꢁ
As the MV2þ photoreduction system with the photosensiti-
zation of ZnTPPS was developed, the photochemical methanol
and the concentration of methanol fromꢁHCO3 was 0.55 mmol
dmꢁ3 and the conversion yield of HCO3 to methanol was esti-
mated to be 5.5% after 4-h irradiation. This system could be de-
veloped to convert CO2 into useful organic compound materials.
ꢁ
synthesis from HCO3 was attempted at above condition with
FDH, AldDH, and ADH. A sample solution containing ZnTPPS
(0.1 mmol dmꢁ3), MV2þ (0.1 mmol dmꢁ3), TEOA (0.3 mol
dmꢁ3) FDH (12.5 units), AldDH (12.5 units) and ADH (12.5
units) was deaerated by freeze-pump-thaw cycles repeated 6
times and then flushed with argon gas for 5 min. NaHCO3
(0.01 mmol dmꢁ3) was added to the sample solution and then ir-
radiated. The produced methanol was measured by gas chroma-
tography using a Sorbitol 25%-Gasport B column (2 m ꢄ 3 mm
i.d., GL Sciences) attached to a Schimadzu GC-8A gas chroma-
tograph (oven temperature, 100 ꢃC; carrier gas, N2; flow rate,
21.8 mL minꢁ1). When the sample solution was irradiated with
a 200-W tungsten lamp, methanol production is shown in
This work was partially supported by The Salt Science
Research Foundation and SANEYOSHI Scholarship
Foundation.
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Published on the web (Advance View) October 30, 2004; DOI 10.1246/cl.2004.1544