Search PubMed⌕ Search

Biomedical subjects

A W Schwartz

Publications and source records attributed to A W Schwartz.

At least 19 recordsLinked to original sources
PubMed2000

Reduction and activation of phosphate on the primitive earth.

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.

Earth, Planet↗
PubMed1999

Chemical reduction of phosphate on the primitive earth.

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.

Apatites↗
PubMed1998

Mineral catalysis of a potentially prebiotic aldol condensation.

Minerals may have played a significant role in chemical evolution. In the course of investigating the chemistry of phosphonoacetaldehyde (PAL), an analogue of glycolaldehyde phosphate, we have observed a striking case of catalysis by the layered hydroxide mineral hydrotalcite ([Mg2Al(OH)6][Cl.nH2O]). In neutral or moderately basic aqueous solutions, PAL is unreactive even at a concentration of 0.1 M. In the presence of a large excess of NaOH (2 M), the compound undergoes aldol condensation to produce a dimer containing a C3-C4 double-bond. In dilute neutral solutions and in the presence of the mineral, however, condensation takes place rapidly, to produce a dimer which is almost exclusively the C2-C3 unsaturated product.

Acetaldehyde↗
PubMed1998

Prebiotic chemistry of phosphonic acids: products derived from phosphonoacetaldehyde in the presence of formaldehyde.

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.

Acetaldehyde↗
PubMed1997

Speculation on the RNA precursor problem.

While no convincing prebiotic synthesis of RNA building blocks has been demonstrated, at least two synthetic analogues of nucleic acids have been described whose properties are remarkably similar to those of RNA. The RNA backbone is thus not the only possible solution to the problem of replicating the information stored in a sequence of purines and pyrmidines. These results indirectly support the suggestion that RNA might have been preceded in evolution by a related molecule which, perhaps, was more easily synthesized than RNA. New results on the prebiotic chemistry of phosphonic acids suggest a possibility that a backbone structure based on ribose-2,4-diphosphonic acid may have formed via some surprisingly simple chemistry.

Animals↗
PubMed1997

Prebiotic evolution: selecting for homochirality before RNA.

Recent results show that the self-assembly of long homochiral oligomers of a nucleotide analogue can be achieved by ligation of short oligomers of chirally mixed composition. Do these results show how the RNA world might have arisen?

Base Sequence↗
PubMed1997

Prebiotic phosphorus chemistry reconsidered.

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.

Atmosphere↗
PubMed1996

Did minerals perform prebiotic combinatorial chemistry?

It has long been suspected that mineral surfaces may have been important in prebiotic chemistry. The recent demonstrations of extended oligomerization of nucleotides, amino acids and carbohydrates on mineral surfaces add support to the potential prebiotic importance of minerals, but leave a number of questions unanswered.

Catalysis↗
PubMed1995

A plausibly prebiotic synthesis of phosphonic acids.

The insolubility of calcium phosphate in water is a significant stumbling block in the chemistry required for the origin of life. The discovery of alkyl phosphonic acids in the Murchison meteorite suggests the possibility of delivery of these water-soluble, phosphorus-containing molecules by meteorites or comets to the early Earth. This could have provided a supply of organic phosphorus for the earliest stages of chemical evolution; although probably not components of early genetic systems, phosphonic acids may have been precursors to the first nucleic acids. Here we report the synthesis of several phosphonic acids, including the most abundant found in the Murchison meteorite, by ultraviolet irradiation of orthophosphorous acid in the presence of formaldehyde, primary alcohols, or acetone. We argue that similar reactions might explain the presence of phosphonic acids in Murchison, and could also have occurred on the prebiotic Earth.

Chromatography, Gas↗
PubMed1992

Selective cleavage of pyrophosphate linkages.

Pyrophosphate linkages have a number of important roles in biology and are also formed chemically with great ease. They often are unwanted products, such as in the nonenzymatic oligomerization of mononucleotides. We have found that Zr(4+)- and Th(4+)-ions catalyze the symmetrical hydrolysis of pyrophosphate linkages. Oligonucleotide analogs linked by pyrophosphate bonds are substantially degraded in the presence of these metals, even at 0 degrees C. Conditions are described which permit the decapping of a pyrophosphate capped oligonucleotide. Oligodeoxynucleotides can be decapped by this procedure without cleavage of phosphodiester linkages. Oligoribonucleotides are susceptible to partial hydrolysis and require purification by HPLC after decapping.

Chromatography, High Pressure Liquid↗
PubMed1990

Oligomerizations of deoxyadenosine bis-phosphates and of their 3'-5', 3'-3', and 5'-5' dimers: effects of a pyrophosphate-linked, poly(T) analog.

A pyrophosphate-linked polynucleotide analog based on thymidine 3',5' bis-phosphate (pTp) catalyzes the oligomerization of activated dimers of pdAp in the presence of MgCl2. Although no catalysis of the oligomerization of the activated monomer (ImpdAplm) was observed in the presence of MgCl2, there was a significant stimulation of oligomerization by the template in the presence of MnCl2.

Deoxyadenine Nucleotides↗
PubMed1990

Oligomerization of cytosine-containing nucleotide analogs in aqueous solution.

Bisphosphoimidazolides of 2'-deoxycytidine and of its acyclic analog C can be oligomerized in aqueous solution in the presence of Mn(II). Under certain conditions, a range of products extending to at least the 20mer can be obtained. These products are of interest as possible templates for oligomerization of the complementary monomers.

Biological Evolution↗
PubMed1989

Was adenine the first purine?

Oligomerization of HCN (1 molar) in the presence of added formaldehyde (0.5 molar) produced an order of magnitude more 8-hydroxymethyladenine than adenine or any other biologically significant purine. This result suggests that on the prebiotic Earth, nucleoside analogs may have been synthesized directly in more complex mixtures of HCN with other aldehydes.

Adenine↗
PubMed1989

Template-directed oligomerization catalyzed by a polynucleotide analog.

A pyrophosphate-linked analog of polycytidylic acid has been synthesized and shown to catalyze the oligomerization of the complementary monomer 2'-deoxyguanosine 3',5'-bisphosphoimidazolide. Analogs of polynucleotides are of interest in studies of the origins of life as possible precursors of the first RNA molecules. These results demonstrate that such molecules are capable of serving as templates for further synthesis.

Catalysis↗
PubMed1989

Oligomerization of deoxynucleoside-bisphosphate dimers: template and linkage specificity.

Evidence is presented that a poly(U) template selectively favors the oligomerization of the activated, 3'-5' pyrophosphate-linked dimer pdAppdAp, in comparison with the 3'-3' and 5'-5' linked dimers. In the absence of poly(U), the 5'-5' linked dimer is the most reactive, and chains are formed which are more than 60 monomer units in length.

Deoxyribonucleosides↗
PubMed1989

Nucleic acid analogues and the origins of replication.

Recent interest in the properties of "nucleic acid-like structures" has been stimulated by difficulties encountered in the synthesis and nonenzymatic oligomerization of nucleotides. However, none of the newly proposed monomers has yet been synthesized in a plausibly prebiotic manner. Arguments are presented that analogues based on 8-hydroxymethyladenine and 5-hydroxymethyluracil are promising candidates for primitive nucleotide precursors.

Adenine↗
PubMed1987

Nucleic acid-like structures. III. Oligomerization of 3'-deoxyadenosine 2',5'-diphosphoimidazolide.

The activated dimonophosphate of 3'-deoxyadenosine (cordycepin) undergoes oligomerization to produce a new family of pyrophosphate-linked oligomers in which the average repeating unit involves a nine-atom structural group. The presence of a poly(U) template increases the relative yields of higher oligomers, although the template-free reaction is itself extremely efficient.

Deoxyadenine Nucleotides↗