Abstract The syntheses of the pyrimidine analogs 5,5-dihydroxymethyl-2,4,6-pyrimidineytrione I, 2... more Abstract The syntheses of the pyrimidine analogs 5,5-dihydroxymethyl-2,4,6-pyrimidineytrione I, 2-amino-5,5-dihydroxymethyl-4,6-pyrimidinedione II, 5,5-di(2-hydroxyethyl)-2,4,6-pyrimidinetrione III, and 2-amino-5,5-di(2-hydroxyethyl)-4,6-pyrimidinedione IV are described.
Fractionation of the H2O-soluble HCN oligomers was performed by means of elution from active char... more Fractionation of the H2O-soluble HCN oligomers was performed by means of elution from active charcoal, chromatography on Sephadex G-15 and ion-exclusion HPLC. In contrast to previously published studies, at least eight different fractions were shown to posess different spectral properties after Sephadex G-15 column chromatography and to yield different sets of products upon hydrolysis. One of these fractions, which gave adenine and hypoxanthine after hydrolysis with 6 M HCl, was purified further by means of cation exclusion HPLC. In this way, a precursor of adenine (and hypoxanthine) has been isolated and is undergoing structural characterization. A tentative structure is suggested and a new reaction scheme leading to the synthesis of adenine from cis-diaminomaleonitrile without isomerization is proposed.
This volume includes chapters on exobiology in space, chemical and early biochemical evolution, l... more This volume includes chapters on exobiology in space, chemical and early biochemical evolution, life without oxygen, potential for chemical evolution in the early environment of Mars, planetary protection issues and sample return missions, and the modulation of biological evolution by astrophysical phenomena. Papers are presented on the results of spaceflight missions, the action of some factors of space medium on the abiogenic synthesis of nucleotides, early peptidic enzymes, microbiology and biochemistry of the methanogenic archaeobacteria, and present-day biogeochemical activities of anaerobic bacteria and their relevance to future exobiological investigations. Consideration is also given to the development of the Alba Patera volcano on Mars, biological nitrogen fixation under primordial Martian partial pressures of dinitrogen, the planetary protection issues in advance of human exploration of Mars, and the difficulty with astronomical explanations of periodic mass extinctions.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 1997
The available evidence indicates that the origin of life on Earth certainly occurred earlier than... more The available evidence indicates that the origin of life on Earth certainly occurred earlier than 3.5 billion years ago and perhaps substantially earlier. The time available for the chemical evolution which must have preceded this event is more difficult to estimate. Both endogenic and exogenic contributions to chemical evolution have been considered; i.e., from chemical reactions in a primitive atmosphere, or by introduction in the interiors of comets and/or meteorites. It is argued, however, that the phosphorus chemistry of Earth's earliest hydrosphere, whether primarily exogenic or endogenic in origin, was most likely dominated by compounds less oxidized than phosphoric acid and its esters. A scenario is presented for the early production of a suite of reactive phosphonic acid derivatives, the properties of which may have foreshadowed the later appearance of biophosphates.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 2000
Electrical discharges in water-saturated N2 containing 1-10% CH4 were shown earlier to reduce pho... more Electrical discharges in water-saturated N2 containing 1-10% CH4 were shown earlier to reduce phosphate to phosphite. This mechanism was suggested as a possible source of water-soluble phosphorus-containing compounds in volcanic environments on the prebiotic Earth. We have now extended our investigations to gas mixtures in which CO2 and N2 are the main components, and studied the effect of introducing small amounts of H2 and CO. We show that surprisingly high conversions to phosphite occur in reducing mixtures and that several percent reduction of apatite occurs even in the presence of as little as 1% each of H2 and CO. We were also able to confirm a previous report of polyphosphate production as a result of heating the mineral apatite in the presence of other minerals.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 1999
If phosphorus played a role in the origin of life, some means of concentrating micromolar levels ... more If phosphorus played a role in the origin of life, some means of concentrating micromolar levels of phosphate (derived from the calcium phosphate mineral apatite), must first have been available. Here we show that simulated (mini)lightning discharges in model prebiotic atmospheres, including only minimally reducing ones, reduce orthophosphates, including apatite, to produce substantial yields of phosphite. Electrical discharges associated with volcanic eruptions could have provided a particularly suitable environment for this process. Production of relatively soluble and reactive phosphite salts could have supplied a pathway by which the first phosphorus atoms were incorporated into (pre)biological systems.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 1998
Phosphonoacetaldehyde (PAL), a phosphonic acid analogue of glycolaldehyde phosphate, reacts in th... more Phosphonoacetaldehyde (PAL), a phosphonic acid analogue of glycolaldehyde phosphate, reacts in the presence of formaldehyde under mildly basic conditions to produce several new products. The reaction proceeds in two stages: a fast aldol condensation of formaldehyde with PAL, and a slower reaction to produce products containing two phosphonic acid groups. We report on the derivatization, isolation by means of HPLC and characterization of these compounds. One of the products is of potential interest as a building block for a prebiotic informational polymer.
In studying the origins of life, it is important to examine reactions of substrate mixtures that ... more In studying the origins of life, it is important to examine reactions of substrate mixtures that could plausibly have accumulated on the primitive earth. Nucleoside diphosphates would probably have been synthesized along with the standard nucleotides under prebiotic conditions. For these reasons, the template-directed reactions of activated derivatives of these diphosphates, alone or mixed with activated nucleotides, were investigated. An activated derivative of deoxyguanosine 3',5'-diphosphate condensed efficiently on a polycytidylate template to give oligonucleotide analogues in which each 3',5'-phosphodiester bond was replaced by a pyrophosphate linkage. Oligomers were formed even in the absence of a template, but much more slowly. Template-directed condensation occurred also with an analogous deoxyadenosine derivative on polyuridylic acid and with an analogous acycloguanosine derivative on polycytidylic acid.
The theory of the "RNA World" states that the first molecular systems to displa... more The theory of the "RNA World" states that the first molecular systems to display the properties of self-replication and evolution were RNA molecules. The origin of life not only depended crucially upon this event, but RNA molecules can even be viewed as the first "living" things. In recent years this theory has gained ascendancy over competing ideas and is now largely accepted by biologists as the most satisfactory explanation for the origin of life. The reasons for this development will be reviewed and the problem of the origin of the first RNA molecules will be discussed.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2006
The prebiotic synthesis of phosphorus-containing compounds—such as nucleotides and polynucleotide... more The prebiotic synthesis of phosphorus-containing compounds—such as nucleotides and polynucleotides—would require both a geologically plausible source of the element and pathways for its incorporation into chemical systems on the primitive Earth. The mineral apatite, which is the only significant source of phosphate on Earth, has long been thought to be problematical in this respect due to its low solubility and reactivity. However, in the last decade or so, at least two pathways have been demonstrated which would circumvent these perceived problems. In addition, recent results would seem to suggest an additional, extraterrestrial source of reactive phosphorus. It appears that the ‘phosphorus problem’ is no longer the stumbling block which it was once thought to be.
Abstract The syntheses of the pyrimidine analogs 5,5-dihydroxymethyl-2,4,6-pyrimidineytrione I, 2... more Abstract The syntheses of the pyrimidine analogs 5,5-dihydroxymethyl-2,4,6-pyrimidineytrione I, 2-amino-5,5-dihydroxymethyl-4,6-pyrimidinedione II, 5,5-di(2-hydroxyethyl)-2,4,6-pyrimidinetrione III, and 2-amino-5,5-di(2-hydroxyethyl)-4,6-pyrimidinedione IV are described.
Fractionation of the H2O-soluble HCN oligomers was performed by means of elution from active char... more Fractionation of the H2O-soluble HCN oligomers was performed by means of elution from active charcoal, chromatography on Sephadex G-15 and ion-exclusion HPLC. In contrast to previously published studies, at least eight different fractions were shown to posess different spectral properties after Sephadex G-15 column chromatography and to yield different sets of products upon hydrolysis. One of these fractions, which gave adenine and hypoxanthine after hydrolysis with 6 M HCl, was purified further by means of cation exclusion HPLC. In this way, a precursor of adenine (and hypoxanthine) has been isolated and is undergoing structural characterization. A tentative structure is suggested and a new reaction scheme leading to the synthesis of adenine from cis-diaminomaleonitrile without isomerization is proposed.
This volume includes chapters on exobiology in space, chemical and early biochemical evolution, l... more This volume includes chapters on exobiology in space, chemical and early biochemical evolution, life without oxygen, potential for chemical evolution in the early environment of Mars, planetary protection issues and sample return missions, and the modulation of biological evolution by astrophysical phenomena. Papers are presented on the results of spaceflight missions, the action of some factors of space medium on the abiogenic synthesis of nucleotides, early peptidic enzymes, microbiology and biochemistry of the methanogenic archaeobacteria, and present-day biogeochemical activities of anaerobic bacteria and their relevance to future exobiological investigations. Consideration is also given to the development of the Alba Patera volcano on Mars, biological nitrogen fixation under primordial Martian partial pressures of dinitrogen, the planetary protection issues in advance of human exploration of Mars, and the difficulty with astronomical explanations of periodic mass extinctions.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 1997
The available evidence indicates that the origin of life on Earth certainly occurred earlier than... more The available evidence indicates that the origin of life on Earth certainly occurred earlier than 3.5 billion years ago and perhaps substantially earlier. The time available for the chemical evolution which must have preceded this event is more difficult to estimate. Both endogenic and exogenic contributions to chemical evolution have been considered; i.e., from chemical reactions in a primitive atmosphere, or by introduction in the interiors of comets and/or meteorites. It is argued, however, that the phosphorus chemistry of Earth's earliest hydrosphere, whether primarily exogenic or endogenic in origin, was most likely dominated by compounds less oxidized than phosphoric acid and its esters. A scenario is presented for the early production of a suite of reactive phosphonic acid derivatives, the properties of which may have foreshadowed the later appearance of biophosphates.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 2000
Electrical discharges in water-saturated N2 containing 1-10% CH4 were shown earlier to reduce pho... more Electrical discharges in water-saturated N2 containing 1-10% CH4 were shown earlier to reduce phosphate to phosphite. This mechanism was suggested as a possible source of water-soluble phosphorus-containing compounds in volcanic environments on the prebiotic Earth. We have now extended our investigations to gas mixtures in which CO2 and N2 are the main components, and studied the effect of introducing small amounts of H2 and CO. We show that surprisingly high conversions to phosphite occur in reducing mixtures and that several percent reduction of apatite occurs even in the presence of as little as 1% each of H2 and CO. We were also able to confirm a previous report of polyphosphate production as a result of heating the mineral apatite in the presence of other minerals.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 1999
If phosphorus played a role in the origin of life, some means of concentrating micromolar levels ... more If phosphorus played a role in the origin of life, some means of concentrating micromolar levels of phosphate (derived from the calcium phosphate mineral apatite), must first have been available. Here we show that simulated (mini)lightning discharges in model prebiotic atmospheres, including only minimally reducing ones, reduce orthophosphates, including apatite, to produce substantial yields of phosphite. Electrical discharges associated with volcanic eruptions could have provided a particularly suitable environment for this process. Production of relatively soluble and reactive phosphite salts could have supplied a pathway by which the first phosphorus atoms were incorporated into (pre)biological systems.
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 1998
Phosphonoacetaldehyde (PAL), a phosphonic acid analogue of glycolaldehyde phosphate, reacts in th... more Phosphonoacetaldehyde (PAL), a phosphonic acid analogue of glycolaldehyde phosphate, reacts in the presence of formaldehyde under mildly basic conditions to produce several new products. The reaction proceeds in two stages: a fast aldol condensation of formaldehyde with PAL, and a slower reaction to produce products containing two phosphonic acid groups. We report on the derivatization, isolation by means of HPLC and characterization of these compounds. One of the products is of potential interest as a building block for a prebiotic informational polymer.
In studying the origins of life, it is important to examine reactions of substrate mixtures that ... more In studying the origins of life, it is important to examine reactions of substrate mixtures that could plausibly have accumulated on the primitive earth. Nucleoside diphosphates would probably have been synthesized along with the standard nucleotides under prebiotic conditions. For these reasons, the template-directed reactions of activated derivatives of these diphosphates, alone or mixed with activated nucleotides, were investigated. An activated derivative of deoxyguanosine 3',5'-diphosphate condensed efficiently on a polycytidylate template to give oligonucleotide analogues in which each 3',5'-phosphodiester bond was replaced by a pyrophosphate linkage. Oligomers were formed even in the absence of a template, but much more slowly. Template-directed condensation occurred also with an analogous deoxyadenosine derivative on polyuridylic acid and with an analogous acycloguanosine derivative on polycytidylic acid.
The theory of the "RNA World" states that the first molecular systems to displa... more The theory of the "RNA World" states that the first molecular systems to display the properties of self-replication and evolution were RNA molecules. The origin of life not only depended crucially upon this event, but RNA molecules can even be viewed as the first "living" things. In recent years this theory has gained ascendancy over competing ideas and is now largely accepted by biologists as the most satisfactory explanation for the origin of life. The reasons for this development will be reviewed and the problem of the origin of the first RNA molecules will be discussed.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2006
The prebiotic synthesis of phosphorus-containing compounds—such as nucleotides and polynucleotide... more The prebiotic synthesis of phosphorus-containing compounds—such as nucleotides and polynucleotides—would require both a geologically plausible source of the element and pathways for its incorporation into chemical systems on the primitive Earth. The mineral apatite, which is the only significant source of phosphate on Earth, has long been thought to be problematical in this respect due to its low solubility and reactivity. However, in the last decade or so, at least two pathways have been demonstrated which would circumvent these perceived problems. In addition, recent results would seem to suggest an additional, extraterrestrial source of reactive phosphorus. It appears that the ‘phosphorus problem’ is no longer the stumbling block which it was once thought to be.
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Papers by Alan W Schwartz