5:15 PM - 6:45 PM
[U11-P06] Synthesis of metabolic-hub compounds starting from CO2 as a reaction substrate
For the emergence of life, expression of proto-metabolism is inevitable. On the primitive earth, only simple molecules like carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4) are considered to be available. Thus, key question is how biologically important substances (metabolic-hub compounds) had been synthesized from simple inorganic compounds. To get insight concerning this issue, many researchers have attempted to reproduce metabolic cycle in laboratory scale and opened individual pathways to synthesize metabolic-hub compounds. Since each experimental condition is different, however, it is questionable whether metabolic-hub compounds can actually be synthesized from CO2 through a series of reactions.
Here in this work, we set our goal to one pot synthesis of metabolic-hub compounds starting from CO2. The target reactions are photochemical reduction of CO2 to oxalate ((COO-)2) and subsequent electrochemical reduction to glycolate (C2H3O32–) and glyoxylate (C2HO3–). Each step have been already demonstrated by our group and others (Z. Liu et al., Nat. Chem., 2021, 13, 1126), but pH condition is different. Namely, reported CO2 reduction to oxalate was demonstrated under alkaline condition (pH=9), while electrochemical reduction of oxalate to glycolate/glyoxylate proceeded only under acidic condition (pH=1). In order to bridge these two differences, we focused on metal sulfide minerals with the expectation that mineral surface acts as catalytic site to promote photochemical CO2 reduction under acidic condition.
Photochemical CO2 reduction was conducted in the presence of 5 mM NaHCO3 (CO2 source), SO32- (electron source), and each metal sulfide mineral (MoS2, PbS, ZnS, CoS2, CuS, CuFeS2, FeS2) with the illumination of 254 nm Ultraviolet light.
After light irradiation, we detected several organic compounds including oxalate, formate (HCOO-), and tartronic acid (C3H2O52-). Remarkably, in the presence of MoS2, oxalate production proceeded even under pH =3, in which no oxalate was detected in the absence of metal sulfide minerals. X-ray diffraction patterns for metal sulfide samples after photochemical reaction exhibited they retained their original crystal structure (except for PbS), indicating those minerals worked as catalysts.
In summary, to achieve sequential synthesis of metabolic-hub substance from CO2, CO2 reduction to oxalate under acidic / neutral condition is one of the key steps. Although photochemical reduction of CO2 to oxalate in the presence of SO32- proceeded only under alkaline condition, MoS2 addition triggered the reaction under neutral / acidic pH. The result indicates the possibility to pave the way to one pot-synthesis of glycolate/glyoxylate combining photochemical reduction of CO2 and subsequent electrochemical reduction of produced oxalate in the presence of metal sulfide.
Here in this work, we set our goal to one pot synthesis of metabolic-hub compounds starting from CO2. The target reactions are photochemical reduction of CO2 to oxalate ((COO-)2) and subsequent electrochemical reduction to glycolate (C2H3O32–) and glyoxylate (C2HO3–). Each step have been already demonstrated by our group and others (Z. Liu et al., Nat. Chem., 2021, 13, 1126), but pH condition is different. Namely, reported CO2 reduction to oxalate was demonstrated under alkaline condition (pH=9), while electrochemical reduction of oxalate to glycolate/glyoxylate proceeded only under acidic condition (pH=1). In order to bridge these two differences, we focused on metal sulfide minerals with the expectation that mineral surface acts as catalytic site to promote photochemical CO2 reduction under acidic condition.
Photochemical CO2 reduction was conducted in the presence of 5 mM NaHCO3 (CO2 source), SO32- (electron source), and each metal sulfide mineral (MoS2, PbS, ZnS, CoS2, CuS, CuFeS2, FeS2) with the illumination of 254 nm Ultraviolet light.
After light irradiation, we detected several organic compounds including oxalate, formate (HCOO-), and tartronic acid (C3H2O52-). Remarkably, in the presence of MoS2, oxalate production proceeded even under pH =3, in which no oxalate was detected in the absence of metal sulfide minerals. X-ray diffraction patterns for metal sulfide samples after photochemical reaction exhibited they retained their original crystal structure (except for PbS), indicating those minerals worked as catalysts.
In summary, to achieve sequential synthesis of metabolic-hub substance from CO2, CO2 reduction to oxalate under acidic / neutral condition is one of the key steps. Although photochemical reduction of CO2 to oxalate in the presence of SO32- proceeded only under alkaline condition, MoS2 addition triggered the reaction under neutral / acidic pH. The result indicates the possibility to pave the way to one pot-synthesis of glycolate/glyoxylate combining photochemical reduction of CO2 and subsequent electrochemical reduction of produced oxalate in the presence of metal sulfide.