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Is carbon suboxide a new candidate as starting material for the synthesis of biomolecules on the primitive earth?
Precambrian Research, 14 (1981) 75--80
75
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
IS C A R B O N S U B O X I D E A NEW C A N D I D A T E AS S T A R T I N G MATERIAL FOR THE SYNTHESIS OF BIOMOLECULES ON THE PRIMITIVE EARTH?
HIROSHI YANAGAWA and FUJIO EGAMI Mitsubishi-Kasei Institute o f Life Sciences, 11 Minamiooya, Machida, T o k y o 194 (Japan)
(Received December 5, 1979; revision accepted May 4, 1980)
ABSTRACT Yanagawa, H. and Egami, F., 1981. Is carbon suboxide a new candidate as starting material for the synthesis of biomolecules on the primitive earth? Precambrian Res., 14: 75--80. Carbon suboxide polymers reacted with hydroxylamine and ammonia under UV irradiation in aqueous medium to form amino acids such as glycine, alanine, serine, threonine, aspartic acid and glutamic acid. This finding suggests that carbon suboxide is a new candidate as starting material for the synthesis of biomolecules on the primitive earth.
INTRODUCTION Two hypotheses have previously been proposed concerning the primitive a t m o s p h e r e o n t h e earth. O n e h y p o t h e s i s can be d e s i g n a t e d t h e r e d u c e d atmosphere hypothesis, the other the oxidized-atmosphere hypothesis. The f o r m e r suggests an a t m o s p h e r e o f CH4, H2, NH3 a n d H 2 0 (Oparin, 1 9 3 8 ; U r e y , 1 9 5 2 ) , t h e l a t t e r an a t m o s p h e r e o f CO2, N2 and H : O ( R u b e y , 1951). Since Miller's ( 1 9 5 3 ) e x p e r i m e n t , t h e r e d u c e d - a t m o s p h e r e h y p o t h e s i s has b e e n p r e d o m i n a n t b e c a u s e t h e e x c e e d i n g l y o x i d i z e d a t m o s p h e r e was s h o w n e x p e r i m e n t a l l y t o be q u i t e i n a d e q u a t e f o r t h e genesis o f a b i o t i c m o l e c u l e s . However, Abelson (1966), Matsuo (1978), and Shimizu (1978) have recently e m p h a s i z e d t h e o x i d i z e d , or less r e d u c e d , a t m o s p h e r e m o d e l o n t h e basis o f c h e m i c a l c o m p o s i t i o n a n d t h e i s o t o p i c r a t i o o f t h e initial a t m o s p h e r e . Moreover, S h i m i z u ( 1 9 7 7 , 1 9 7 9 ) has r e c e n t l y p r o p o s e d a n e w h y p o t h e s i s t h a t a c o n s i d e r a b l e p a r t o f t h e CO in t h e p r i m i t i v e a t m o s p h e r e m i g h t h a v e b e e n c h a n g e d t o a c a r b o n - s u b o x i d e p o l y m e r b y solar u l t r a v i o l e t r a d i a t i o n w h i c h w o u l d h a v e fallen o n or b e e n a b s o r b e d i n t o t h e o c e a n s a n d c o n v e r t e d t o abiotic polymers. C a r b o n s u b o x i d e (C302), d i s c o v e r e d b y O. Diels in 1 9 0 6 , is a v e r y u n u s u a l c o m p o u n d w i t h f o u r c u m u l a t i v e d o u b l e b o n d s . It is a p o i s o n o u s , colorless
0301-9268/81/0000--0000/$02.50
© 1981 Elsevier Scientific Publishing Company
7~ liquid which boils at 6.8°C and melts at 1 0 7 ° C . It is easily converted into its polymers in the presence of acid or base, the colors of which gradually change to pale yellow, orange, reddish-brown, violet, and nearly black with polymerization. C30: reacts well with nucleophiles; for example, it reacts with water and alcohol to afford malonic acid and its ester, respectively. In addition, it reacts extremely readily with amines to form its amides (Dashkevich and Berlin, 1967). Although the reactions of C302 with various nucleophiles in organic solvents have thus been investigated (Kappe and Zieger, 1974}, no synthesis of biomoiecules from C302 or its polymer in aqueous medium has been reported. F. Egami has recently found that a close correlation exists between the concentrations of transition elements in contemporary seawater and their biological behavior and he presumed that transition elements relatively abundant in seawater such as m o l y b d e n u m , iron, and zinc must have played important roles in the chemical evoluation in the primeval sea (Egami, 1974). With this idea as a basis, we have been studying the formation of biomolecules in modified sea medium. The modified sea medium was designed to simulate experimentally chemical evolution in the primeval sea. The concentration of sodium chloride is lower and the concentrations of six transition elements -- iron, m o l y b d e n u m , zinc, copper, cobalt and manganese -are 1000--100,000 times higher than those of contemporary seawater. In the course of this research we have recently found that amino acids such as glycine, alanine, ~-alanine, serine, threonine, aspartic acid, and glutamic acid were produced from formaldehyde (Hatanaka and Egami, 1977; Kamaluddin et al., 1979) and sugars (Yanagawa et al., 1980) in modified sea medium. Based upon these observations, we preliminarily examined the formation of amino acids from C302 in a modified sea medium to search experimentally for a possibility that carbon suboxide was one of the starting materials for the synthesis of biomolecules on the primitive earth. MATERIALS AND METHODS We prepared C302 b y dehydrating 20 g of malonic acid with 200 g o f phosphorus pentoxide in the presence o f 40 g of silica sand at 140--150°C and at 10 -2 Tort for 4 h (Diels and Meyerheim, 1907). The resulting C302 was then purified b y fractional distillation and transferred into a 100-ml pressure bottle equipped with a pressure gauge. Finally 4 ml of purified C302 was obtained. C302 p o l y m e r was prepared b y standing C302 trapped in a pressure bottle at room temperature for 2 days. Modified sea media contained each 0.01 M MgSO4, CaC12 and K2HPO4 and each 0.1 mM Fe(NO3)3, Na2MoO4, ZnC12, Cu(NO3)2, COC12 and MnC12. Each reaction mixture contained 0.06 M of C302 polymer, 0.3 M (as nitrogen) of nitrogen sources ((NH2OH)2"H2SO4, NH4OH and (NH4)2SO4) and modified sea medium. Calcium carbonate (0.5 g) was added to the reaction mixture of Exp. 3 and Exp. 5 to maintain alkaline pH. All reactions were carried o u t
77 under nitrogen gas. Heating and UV irradiation were performed with a silicon oil bath and a high-pressure UV lamp (Ushio Electric model UM-102, 100W). Analysis of amino acids was performed, after 6 N HC1 hydrolysis for 16 h, on a Hitachi KLA-5 amino-acid analyzer. RESULTS AND DISCUSSION Table I shows that C~O2 polymer reacted with hydroxylamine at 105°C in a modified sea medium (pH 6) to form amino acids such as glycine and alanine, but the m o n o m e r did n o t yield any amino acid under the same condition. The m o n o m e r was immediately converted to malonic acid under the condition. The reaction of C302 polymer with hydroxylamine at pH 8 and at 35°C under UV irradiation gave a large a m o u n t of glycine and small amounts of alanine, aspartic acid, serine, glutamic acid and threonine. Furthermore, such amino acids were formed from reactions of C302 polymer and ammonia at pH 8 and pH 12 under UV irradiation. C302 polymer also reacted with ammonia by heating at 105°C to afford glycine, alanine, aspartic acid, serine and glutamic acid. When UV irradiation was used as energy source of the reaction, amino acids were obtainted in higher yields from C302 polymer than that of heating. Especially glycine was formed in the best yield. This may suggest t h a t the C302 polymer does not directly react with hydroxylamine and ammonia but it is at once degraded to certain smaller molecules, for example, formaldehyde or glycolaldehyde under UV irradiation in a modified sea medium, which then react with hydroxylamine and ammonia to afford amino acids. Smith et al. (1963) have demonstrated t h a t C302 polymer was decomposed to CO, CO2, and carbon at 100--500°C in the absence of water. Mullen and Wolf (1962) have reported t h a t C302 was converted to CO and a C20 radical under UV irradiation. Liuti et al. (1966) have found that the system which produced C302 from CO by UV irradiation is very sensitive to impurities; if water is present, it produces methanol and formaldehyde but does not produce C302, and if oxygen is present, the only product observed is CO2. Based upon these findings and our result about the formation of amino acids under UV irradiation, we suspected t h a t the photolysis of C302 polymer to smaller molecules in aqueous medium would occur. We actually confirmed that formaldehyde is produced from C302 polymer by UV irradiation in a modified sea medium. We discuss below the genesis of biomolecules from the oxidized atmosphere on the primitive earth. We now support the partially oxidized model t h a t the primitive atmosphere of the earth must have been formed by early catastrophic degassing (Fanale, 1971; Hamano and Ozima, 1978) from the interior and the volcanic gases have contained H20, H2, CO2, CO and N2; but H2 must have quickly dissipated into space (Matsuo, 1978). At an earlier stage of the initial degassing, when CO and H20 were :fully in contact with each other, formaldehyde must have been formed from a part o f CO and H20 by solar ultraviolet radiation (Bar-num and Hartman, 1978). In addi-
78
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
"0
0
~ 0 0 0
0 0 0 0 0 0
0
0 0 ~ 0 0 0
0 0 0 0 0 0
0
0 e~ 0 e~
0
6 0~00~0
~''z N 0
..~ t~
0
~ 0 0 0 0
000000
79
tion, ammonia must have been synthesized simultaneously from N2 and H20 by solar ultraviolet radiation or with gamma:rays (Getoff, 1966). After the ocean was very rapidly formed by cold trapping of water vapor, carbon dioxide and the resulting ammonia and formaldehyde were quickly absorbed in the ocean. Ammonia is unstable to UV irradiation in the atmosphere b u t stable in the marine environment. Therefore, a certain amount of ammonia must have accumulated in the ocean. After a certain period of time after the genesis of the ocean, the most part of the atmosphere changed to less-soluble gases which mainly consisted of CO and N2. At the next stage, when most of the water vapor was condensed by cold trapping, the solar ultraviolet radiation of CO at above the water cloud level easily produced C302 and its polymers (Liuti et al., 1966; Shimizu, 1979). The water vapor concentration above the water cloud level is usually much smaller than that below it. Therefore, water vapor is n o t a barrier to the formation of C302 polymer. A considerable part of the CO in the primitive atmosphere can be expected to have changed to C302 polymer during the early history of the earth because the polymerization rate of C302 m o n o m e r is very rapid. The resulting polymers in the atmosphere might have precipitated in the primeval ocean. The concentration of the p o l y m e r in the oceans (total mass % 1024 g) could have been very high, as much as 0.1%, if CO in the atmosphere (total mass 1021 g) had completely changed to the polymer (Shimizu, 1979). In the primeval ocean the chemically active C302 polymer could convert to many kinds of organic c o m p o u n d s such as formaldehyde and glycolaldehyde under solar ultraviolet radiation. Formaldehyde and glycolaldehyde in the ocean would have been oligomerized to form a mixture of sugar-like substances, formose (Gabel and Ponnamperuma, 1967). At the next step, the formose must have reacted with ammonia to form amino acids, which were gradually changed to polypeptides and a protocell-like structure (Yanagawa and Egami, 1977, 1978a, b) in the ocean. We have confirmed the degradation of C302 polymers to formaldehyde and the formation of amino acids from sugars and ammonia in aqueous medium (Yanagawa et al., 1980a, b). From the point of view described above, we n o w consider that carbon suboxide may have been one of the starting materials for the synthesis of biomolecules on the primitive earth. ACKNOWLEDGEMENTS
We thank Miss Y. Kobayashi for technical assistance and Dr. M. Shimizu for helpful discussions.
REFERENCES Abelson, P.H., 1966. Chemical events on the primitive earth. Proc. Natl. Acad. Sci. U.S., 53:1366. Bar-num, A. and Hartman, H., 1978. Synthesis of organic compounds f r o m c a r b o n monoxide and water by UV photolysis. Origins Life, 9:93.
80 Dashkevich, L.B. and Beilin,V.G., 1967. Carbon suboxide in organic synthesis. Russ. Chem. Rev., 36:391. Diels, O. and Meyerheim, G., 1907. IJber das Kohlensuboxyd (II).Bet. Dtsch. Chem. Ges., 40:355. Egami, F., 1974. Minor elements and evolution. J. Mol. Evol., 4:113. Fanale, F.O., 1971. A case for catastrophic early degassing of the earth. Chem. Geol., 8:79. Gabel, N.W. and Ponnamperuma, C., 1967. Model for origin of monosaccharides. Nature, 216:453. Getoff, N., 1966. Radiation-induced synthesis of ammonia from nitrogen and water. Nature, 210:940. Hamano, Y. and Ozima, M., 1978. Rare-gas regime and the evolution of planetary atmosphere. In : Origin of Life--Proc. 5th Int. Conf. Origin of Life. Center for Acad. Publ. Japan, Tokyo. p.35. Hatanaka, H. and Egami, F., 1977. The formation of amino acids and related oligomers from formaldehyde and hydroxylamine in modified sea mediums related to prebiotic conditions. Bull. Chem. Soc. Jpn., 50:1147. Kamaluddin, Yanagawa, H. and Egami, F., 1979. Formation of molecules of biological interest from formaldehyde and hydroxylamine in a modified sea medium. J. Biochem., 85 :1503. Kappe, V.R. and Zieger, E., 1974. Kohlensuboxid in der pr~iparativenorganischen Chemie. Angew. Chem., 86:529. Liuti, G., Dondes, S. and Harteck, P., 1966. Photochemical production of C30: from CO. J. Chem. Phys., 44: 4051. Matsuo, S., 1978. The oxidation state of the primordial atmosphere. In: Origin of Life-Proc. 5th Int. Conf. Origin of Life. Center for Acad. Publ. Japan, Tokyo, p.21. Miller, S.L., 1953. A production of amino acids under possible primitive earth conditions. Science, 117:528. Mullen, R.T. and Wolf, A.P., 1962. Photolysis of carbon-2-14C~suboxide in ethylene. J. Am. Chem. Soc., 84:3214. Oparin, A.I., 1938. The Origin of Life. (Translated by S. Margulis). Macmillan, New York. Rubey, W.W., 1951. Geological history of sea water. Geol. Soc. Am. Bull.,62:1111. Shimizu, M., 1977. A n evolutional model of the terrestrialatmosphere from a comparative planetological view. Inst. Space Aeronaut. Sci.,Univ. Tokyo, Note, 45. Shimizu, M., 1978. Evolution of atmosphere: comparative planetology. In: Origin of Life--Proc. 5th Int. Conf. Origin of Life, Center for Acad. Publ. Japan, Tokyo, p.35. Shimizu, M., 1979. A n evolutional model of the terrestrialatmosphere from a comparative planetological view. Precambrian Res,, 9:311. Smith, R.N., Young, D.A., Smith, E.N. and Carter, C.C., 1963. The structure and properties of carbon suboxide polymer. Inorg. Chem., 2:829. Urey, H.C., 1952. O n the early chemical history of the earth and the origin of life.Proc. Natl. Acad. Sci. U.S.A., 38:351. Yanagawa, H. and Egami, F., 1977. Formation of protocell-likestructures from glycine and formaldehyde in a modified sea medium. Proc. Jpn. Acad., 53:42. Yanagawa, H. and Egami, F., 1978a. Marigranules from glycine and acidic,basic, and aromatic amino acids in a modified sea medium. Proc. Jpn. Acad., 54:10. Yanagawa, H. and Egami, F., 1978b. Marisome from glycine and acidic,basic, and aromatic amino acids in a modified sea medium. Proc. Jpn. Acad., 54:331. Yanagawa, H., Kobayashi, Y. and Egami, F., 1980a. Characterization of marigranules and marisomes, organized particleswith elastin-likestructures. J. Biochem., 87:855. Yanagawa, H., Kobayashi, Y. and Egami, F., 1980b. Genesis of amino acids in the primeval sea: formation of amino acids from sugars and ammonia in a modified sea medium. J. Biochem., 87:359.
75
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
IS C A R B O N S U B O X I D E A NEW C A N D I D A T E AS S T A R T I N G MATERIAL FOR THE SYNTHESIS OF BIOMOLECULES ON THE PRIMITIVE EARTH?
HIROSHI YANAGAWA and FUJIO EGAMI Mitsubishi-Kasei Institute o f Life Sciences, 11 Minamiooya, Machida, T o k y o 194 (Japan)
(Received December 5, 1979; revision accepted May 4, 1980)
ABSTRACT Yanagawa, H. and Egami, F., 1981. Is carbon suboxide a new candidate as starting material for the synthesis of biomolecules on the primitive earth? Precambrian Res., 14: 75--80. Carbon suboxide polymers reacted with hydroxylamine and ammonia under UV irradiation in aqueous medium to form amino acids such as glycine, alanine, serine, threonine, aspartic acid and glutamic acid. This finding suggests that carbon suboxide is a new candidate as starting material for the synthesis of biomolecules on the primitive earth.
INTRODUCTION Two hypotheses have previously been proposed concerning the primitive a t m o s p h e r e o n t h e earth. O n e h y p o t h e s i s can be d e s i g n a t e d t h e r e d u c e d atmosphere hypothesis, the other the oxidized-atmosphere hypothesis. The f o r m e r suggests an a t m o s p h e r e o f CH4, H2, NH3 a n d H 2 0 (Oparin, 1 9 3 8 ; U r e y , 1 9 5 2 ) , t h e l a t t e r an a t m o s p h e r e o f CO2, N2 and H : O ( R u b e y , 1951). Since Miller's ( 1 9 5 3 ) e x p e r i m e n t , t h e r e d u c e d - a t m o s p h e r e h y p o t h e s i s has b e e n p r e d o m i n a n t b e c a u s e t h e e x c e e d i n g l y o x i d i z e d a t m o s p h e r e was s h o w n e x p e r i m e n t a l l y t o be q u i t e i n a d e q u a t e f o r t h e genesis o f a b i o t i c m o l e c u l e s . However, Abelson (1966), Matsuo (1978), and Shimizu (1978) have recently e m p h a s i z e d t h e o x i d i z e d , or less r e d u c e d , a t m o s p h e r e m o d e l o n t h e basis o f c h e m i c a l c o m p o s i t i o n a n d t h e i s o t o p i c r a t i o o f t h e initial a t m o s p h e r e . Moreover, S h i m i z u ( 1 9 7 7 , 1 9 7 9 ) has r e c e n t l y p r o p o s e d a n e w h y p o t h e s i s t h a t a c o n s i d e r a b l e p a r t o f t h e CO in t h e p r i m i t i v e a t m o s p h e r e m i g h t h a v e b e e n c h a n g e d t o a c a r b o n - s u b o x i d e p o l y m e r b y solar u l t r a v i o l e t r a d i a t i o n w h i c h w o u l d h a v e fallen o n or b e e n a b s o r b e d i n t o t h e o c e a n s a n d c o n v e r t e d t o abiotic polymers. C a r b o n s u b o x i d e (C302), d i s c o v e r e d b y O. Diels in 1 9 0 6 , is a v e r y u n u s u a l c o m p o u n d w i t h f o u r c u m u l a t i v e d o u b l e b o n d s . It is a p o i s o n o u s , colorless
0301-9268/81/0000--0000/$02.50
© 1981 Elsevier Scientific Publishing Company
7~ liquid which boils at 6.8°C and melts at 1 0 7 ° C . It is easily converted into its polymers in the presence of acid or base, the colors of which gradually change to pale yellow, orange, reddish-brown, violet, and nearly black with polymerization. C30: reacts well with nucleophiles; for example, it reacts with water and alcohol to afford malonic acid and its ester, respectively. In addition, it reacts extremely readily with amines to form its amides (Dashkevich and Berlin, 1967). Although the reactions of C302 with various nucleophiles in organic solvents have thus been investigated (Kappe and Zieger, 1974}, no synthesis of biomoiecules from C302 or its polymer in aqueous medium has been reported. F. Egami has recently found that a close correlation exists between the concentrations of transition elements in contemporary seawater and their biological behavior and he presumed that transition elements relatively abundant in seawater such as m o l y b d e n u m , iron, and zinc must have played important roles in the chemical evoluation in the primeval sea (Egami, 1974). With this idea as a basis, we have been studying the formation of biomolecules in modified sea medium. The modified sea medium was designed to simulate experimentally chemical evolution in the primeval sea. The concentration of sodium chloride is lower and the concentrations of six transition elements -- iron, m o l y b d e n u m , zinc, copper, cobalt and manganese -are 1000--100,000 times higher than those of contemporary seawater. In the course of this research we have recently found that amino acids such as glycine, alanine, ~-alanine, serine, threonine, aspartic acid, and glutamic acid were produced from formaldehyde (Hatanaka and Egami, 1977; Kamaluddin et al., 1979) and sugars (Yanagawa et al., 1980) in modified sea medium. Based upon these observations, we preliminarily examined the formation of amino acids from C302 in a modified sea medium to search experimentally for a possibility that carbon suboxide was one of the starting materials for the synthesis of biomolecules on the primitive earth. MATERIALS AND METHODS We prepared C302 b y dehydrating 20 g of malonic acid with 200 g o f phosphorus pentoxide in the presence o f 40 g of silica sand at 140--150°C and at 10 -2 Tort for 4 h (Diels and Meyerheim, 1907). The resulting C302 was then purified b y fractional distillation and transferred into a 100-ml pressure bottle equipped with a pressure gauge. Finally 4 ml of purified C302 was obtained. C302 p o l y m e r was prepared b y standing C302 trapped in a pressure bottle at room temperature for 2 days. Modified sea media contained each 0.01 M MgSO4, CaC12 and K2HPO4 and each 0.1 mM Fe(NO3)3, Na2MoO4, ZnC12, Cu(NO3)2, COC12 and MnC12. Each reaction mixture contained 0.06 M of C302 polymer, 0.3 M (as nitrogen) of nitrogen sources ((NH2OH)2"H2SO4, NH4OH and (NH4)2SO4) and modified sea medium. Calcium carbonate (0.5 g) was added to the reaction mixture of Exp. 3 and Exp. 5 to maintain alkaline pH. All reactions were carried o u t
77 under nitrogen gas. Heating and UV irradiation were performed with a silicon oil bath and a high-pressure UV lamp (Ushio Electric model UM-102, 100W). Analysis of amino acids was performed, after 6 N HC1 hydrolysis for 16 h, on a Hitachi KLA-5 amino-acid analyzer. RESULTS AND DISCUSSION Table I shows that C~O2 polymer reacted with hydroxylamine at 105°C in a modified sea medium (pH 6) to form amino acids such as glycine and alanine, but the m o n o m e r did n o t yield any amino acid under the same condition. The m o n o m e r was immediately converted to malonic acid under the condition. The reaction of C302 polymer with hydroxylamine at pH 8 and at 35°C under UV irradiation gave a large a m o u n t of glycine and small amounts of alanine, aspartic acid, serine, glutamic acid and threonine. Furthermore, such amino acids were formed from reactions of C302 polymer and ammonia at pH 8 and pH 12 under UV irradiation. C302 polymer also reacted with ammonia by heating at 105°C to afford glycine, alanine, aspartic acid, serine and glutamic acid. When UV irradiation was used as energy source of the reaction, amino acids were obtainted in higher yields from C302 polymer than that of heating. Especially glycine was formed in the best yield. This may suggest t h a t the C302 polymer does not directly react with hydroxylamine and ammonia but it is at once degraded to certain smaller molecules, for example, formaldehyde or glycolaldehyde under UV irradiation in a modified sea medium, which then react with hydroxylamine and ammonia to afford amino acids. Smith et al. (1963) have demonstrated t h a t C302 polymer was decomposed to CO, CO2, and carbon at 100--500°C in the absence of water. Mullen and Wolf (1962) have reported t h a t C302 was converted to CO and a C20 radical under UV irradiation. Liuti et al. (1966) have found that the system which produced C302 from CO by UV irradiation is very sensitive to impurities; if water is present, it produces methanol and formaldehyde but does not produce C302, and if oxygen is present, the only product observed is CO2. Based upon these findings and our result about the formation of amino acids under UV irradiation, we suspected t h a t the photolysis of C302 polymer to smaller molecules in aqueous medium would occur. We actually confirmed that formaldehyde is produced from C302 polymer by UV irradiation in a modified sea medium. We discuss below the genesis of biomolecules from the oxidized atmosphere on the primitive earth. We now support the partially oxidized model t h a t the primitive atmosphere of the earth must have been formed by early catastrophic degassing (Fanale, 1971; Hamano and Ozima, 1978) from the interior and the volcanic gases have contained H20, H2, CO2, CO and N2; but H2 must have quickly dissipated into space (Matsuo, 1978). At an earlier stage of the initial degassing, when CO and H20 were :fully in contact with each other, formaldehyde must have been formed from a part o f CO and H20 by solar ultraviolet radiation (Bar-num and Hartman, 1978). In addi-
78
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
"0
0
~ 0 0 0
0 0 0 0 0 0
0
0 0 ~ 0 0 0
0 0 0 0 0 0
0
0 e~ 0 e~
0
6 0~00~0
~''z N 0
..~ t~
0
~ 0 0 0 0
000000
79
tion, ammonia must have been synthesized simultaneously from N2 and H20 by solar ultraviolet radiation or with gamma:rays (Getoff, 1966). After the ocean was very rapidly formed by cold trapping of water vapor, carbon dioxide and the resulting ammonia and formaldehyde were quickly absorbed in the ocean. Ammonia is unstable to UV irradiation in the atmosphere b u t stable in the marine environment. Therefore, a certain amount of ammonia must have accumulated in the ocean. After a certain period of time after the genesis of the ocean, the most part of the atmosphere changed to less-soluble gases which mainly consisted of CO and N2. At the next stage, when most of the water vapor was condensed by cold trapping, the solar ultraviolet radiation of CO at above the water cloud level easily produced C302 and its polymers (Liuti et al., 1966; Shimizu, 1979). The water vapor concentration above the water cloud level is usually much smaller than that below it. Therefore, water vapor is n o t a barrier to the formation of C302 polymer. A considerable part of the CO in the primitive atmosphere can be expected to have changed to C302 polymer during the early history of the earth because the polymerization rate of C302 m o n o m e r is very rapid. The resulting polymers in the atmosphere might have precipitated in the primeval ocean. The concentration of the p o l y m e r in the oceans (total mass % 1024 g) could have been very high, as much as 0.1%, if CO in the atmosphere (total mass 1021 g) had completely changed to the polymer (Shimizu, 1979). In the primeval ocean the chemically active C302 polymer could convert to many kinds of organic c o m p o u n d s such as formaldehyde and glycolaldehyde under solar ultraviolet radiation. Formaldehyde and glycolaldehyde in the ocean would have been oligomerized to form a mixture of sugar-like substances, formose (Gabel and Ponnamperuma, 1967). At the next step, the formose must have reacted with ammonia to form amino acids, which were gradually changed to polypeptides and a protocell-like structure (Yanagawa and Egami, 1977, 1978a, b) in the ocean. We have confirmed the degradation of C302 polymers to formaldehyde and the formation of amino acids from sugars and ammonia in aqueous medium (Yanagawa et al., 1980a, b). From the point of view described above, we n o w consider that carbon suboxide may have been one of the starting materials for the synthesis of biomolecules on the primitive earth. ACKNOWLEDGEMENTS
We thank Miss Y. Kobayashi for technical assistance and Dr. M. Shimizu for helpful discussions.
REFERENCES Abelson, P.H., 1966. Chemical events on the primitive earth. Proc. Natl. Acad. Sci. U.S., 53:1366. Bar-num, A. and Hartman, H., 1978. Synthesis of organic compounds f r o m c a r b o n monoxide and water by UV photolysis. Origins Life, 9:93.
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