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Organic synthesis by quench reactions.

The effects of chemical quench reactions on the formation of organic compounds at a water surface under simulated primordial earth conditions were investigated for the study of chemical evolution. A mixture of gaseous methane and ammonia over a water surface was exposed to an arc discharge between an electrode and the water surface. This discharge served as a source of dissociated, ionized and excited atomic and molecular species. Various organic molecules were formed in the gaseous, aqueous, and solid states by a subsequent quenching of these reactive species on the water surface. The effects of these water-surface quench reactions were assessed by comparing the amounts of synthesized molecules to the amounts which formed during the discharge of an arc above the water level. The results showed that: (1) the water-surface quench reaction permitted faster rates of formation of an insoluble solid and (2) the quench discharge yielded twice as much amino acids and 17 times more insoluble solids by weight than the other discharge. The highest yield of amino acids with the quench reaction was 9 x 10-7 molecules per erg of input energy. These observations indicate that quench reactions on the oceans, rain, and clouds that would have followed excitation by lightning and shock waves may have played an important role in the prebiotic milieu. Furthermore, the possibility exists that quench reactions can be exploited for the synthesis of organic compounds on a larger scale from simple starting materials.

Amino Acids↗

PubMed1995

Binding of adenine and adenine-related compounds to the clay montmorillonite and the mineral hydroxylapatite.

The first living things may have consisted of no more than RNA or RNA-like molecules bound to the surfaces of mineral particles. A key aspect of this theory is that these mineral particles have binding sites for RNA and its prebiotic precursors. The object of this study is to explore the binding properties of two of the best studied minerals, montmorillonite and hydroxylapatite, for possible precursors of RNA. The list of compounds investigated includes purines, pyrimidines, nucleosides, nucleotides, nucleotide coenzymes, diaminomaleonitrile and aminoimidazole carboxamide. Affinities for hydroxylapatite are dominated by ionic interactions between negatively charged small molecules and positively charged sites in the mineral. Binding to montmorillonite presents a more complex picture. These clay particles have a high affinity for organic ring structures which is augmented if they are positively charged. This binding probably takes place on the negatively charged faces of these sheet-like clay particles. Additional binding sites on the edges of these sheets have a moderate affinity for negatively charged molecules. Small molecules that bind to these minerals sometimes bind independently to sites on the minerals and sometimes bind cooperatively with favorable interactions between the bound molecules.

Adenine↗

PubMed1995

Chirality and life.

The crucial role of homochirality and chiral homogeneity in the self-replication of contemporary biopolymers is emphasized, and the experimentally demonstrated advantages of these chirality attributes in simpler polymeric systems are summarized. The implausibility of life without chirality and hence of a biogenic scenario for the origin of chiral molecules is stressed, and chance and determinate abiotic mechanisms for the origin of chirality are reviewed briefly in the context of their potential viability on the primitive Earth. It is concluded that all such mechanisms would be nonviable, and that the turbulent prebiotic environment would require an ongoing extraterrestrial source for the accumulation of chiral molecules on the primitive Earth. A scenario is described wherein the circularly polarized ultraviolet synchrotron radiation from the neutron star remnants of supernovae engenders asymmetric photolysis of the racemic constituents in the organic mantles on interstellar dust grains, whereupon these chiral constituents are transported repetitively to the primitive Earth by direct accretion of the interstellar dust or through impacts of comets and asteroids.

Adsorption↗

PubMed1995

Electroweak enantioselection and the origin of life.

All biomolecules are of one hand--but what determines which hand? Why is life based on L-amino acids and D-sugars rather than D-amino acids and L-sugars? We believe the symmetry-breaker could be the weak force, which causes enantiomers to differ very slightly in energy. In this paper we present our calculations of this parity-violating energy difference (PVED) for a range of important biomolecules, and in nearly all cases it is indeed the 'natural' enantiomer which is the more stable.

Amino Acids↗

PubMed1995

The role of accuracy for early stages of the origin of life.

The role of accuracy in developing stages in the origin of life is investigated by mathematical models. Errors yield difficult stability problems in a description of a cooperative system with information-carriers (genes) and catalytic polymers (enzymes) that are related to each other. This problem is highly relevant for a proper understanding of the RNA world. The model that is treated takes two relevant error effects, which can be coupled, into account. One is the occurrence of parasites, inactive genes that are efficiently reproduced by the catalytic support of other polymers but which do not give rise to any catalytic activity. The other is an error propagation due to the fact that erroneous catalysts will provide an increased error level and thus more erroneous catalysts which may lead to still increasing error levels, eventually an error catastrophe.

Evolution, Chemical↗

PubMed1993

Evaporation cycle experiments--a simulation of salt-induced peptide synthesis under possible prebiotic conditions.

Evaporation cycles applied to dilute solutions of amino acids, Cu(II) and NaCl lead to peptides within 1-3 days. This simulation of possible coastal or laguna processes in a primitive earth environment gives further indications towards the relevance of the salt-induced peptide formation reaction in chemical evolution. The experiments were successfully applied to glycine, alanine, aspartic and glutamic acid. Besides isolated amino acids, also their mixtures with glycine as reaction partner were studied, leading to peptides for all of the aforementioned substances, as well as for valine and proline, which do not dimerize alone. Sequence preferences and some conservation of optical purity were observed.

Amino Acids↗

PubMed1995

Confined-pyrolysis as an experimental method for hydrothermal organic synthesis.

A closed pyrolysis system has been developed as a tool for studying the reactions of organic compounds under extreme hydrothermal conditions. Small high pressure stainless steel vessels in which the ratio of sediment or sample to water has been adjusted to eliminate the headspace at peak experimental conditions confines the organic components to the bulk solid matrix and eliminates the partitioning of the organic compounds away from the inorganic components during the experiment. Confined pyrolysis experiments were performed to simulate thermally driven catagenetic changes in sedimentary organic matter using a solids to water ratio of 3.4 to 1. The extent of alteration was measured by monitoring the steroid and triterpenoid biomarkers and polycyclic aromatic hydrocarbon distributions. These pyrolysis experiments duplicated the hydrothermal transformations observed in nature. Molecular probe experiments using alkadienes, alkenes and alkanes in H2O and D2O elucidated the isomerization and hydrogenation reactions of aliphatic compounds and competing oxidative reactions occurring under hydrothermal conditions. This confined pyrolysis technique is being applied to test experiments on organic synthesis of relevance to chemical evolution for the origin of life.

Alkanes↗

PubMed1980

A theory for the origin of a self-replicating chemical system. I: Natural selection of the autogen from short, random oligomers.

A theory is described for the origin of a simple chemical system named an autogen, consisting of two short oligonucleotide sequences coding for two simple catalytic peptides. If the theory is valid, under appropriate conditions the autogen would be capable of self-reproduction in a truly genetic process involving both replication and translation. Limited catalytic ability, short oligomer sequences, and low selectivities leading to sloppy information transfer processes are shown to be adequate for the origin of the autogen from random background oligomers. A series of discrete steps, each highly probable if certain minimum requirements and boundary conditions are satisfied, lead to exponential increase in population of all components in the system due to autocatalysis and hypercyclic organization. Nucleation of the components and exponential increase to macroscopic amounts could occur in times on the order of weeks. The feasibility of the theory depends on a number of factors, including the capability of simple protoenzymes to provide moderate enhancements of the accuracies of replication and translation and the likelihood of finding an environment where all of the required processes can occur simultaneously. Regardless of whether or not the specific form proposed for the autogen proves to be feasible, the theory suggests that the first self-replicating chemical systems may have been extremely simple, and that the period of time required for chemical evolution prior to Darwinian natural selection may have been far shorter than generally assumed. Due to the short time required, this theory, unlike others on the origin of genetic processes, is potentially capable of direct experimental verification. A number of prerequisites leading up to such an experiment are suggested, and some have been fulfilled. If successful, such an experiment would be the first laboratory demonstration of the spontaneous emergence by natural selection of a genetic, self-replicating, and evolving molecular system, and might represent the first step in the prebiotic environment of true Darwinian evolution toward a living cell.

Base Sequence↗

PubMed1976

Structural characterization of thermal prebiotic polypeptides.

Thermal polycondensation of amino-acids as a possible prebiotic path of chemical evolution of life has been critically examined. The polymeric materials studied by nmr methods have scarce resemblance to natural peptidic material because beta, gamma and eplision peptide bonds largely predominate over a-peptide bonds.

Aspartic Acid↗

PubMed1980

Nucleotide-amino acid interactions and their relation to the genetic code.

The apparent dissociation constants of the complexes of AMP with the methyl esters of amino acids in aqueous solution exhibit good correlations with features of the genetic code and with the frequencies of occurrence of amino acid residues in proteins. Thus it is likely that chemically selective nucleotide-amino acid interactions were involved in the processes of chemical evolution that have led to the emergence of the genetic code. Based on these correlations a storage device for the information regarding nucleotide-amino acid interactions is proposed. It involves processes of simultaneous polymerization to polynucleotides and polypeptides.

Adenosine Monophosphate↗

PubMed1982

Interaction between ATP, metal ions, glycine, and several minerals.

The adsorption of ATP and ADP on montmorillonite, kaolinite, and A1(OH)3 was studied as a function of pH and, for montmorillonite and kaolinite, as a function of the ionic composition of the system. The three minerals exhibit different adsorption characteristics. Mg2+- and Zn2+-montmorillonite adsorb ATP and ADP more than Na+-montmorillonite, presumably because of complex formation. In kaolinite, the effect of these divalent cations is small. Pure ATP decomposes upon heating, and the rate of the decomposition is accelerated by the presence of glycine. Drying and heating glycine to 70 degrees C under vacuum in the presence of ATP results in abiotic peptide formation with yields up to 0.25%. This peptide formation also occurs when kaolinite or montmorillonite is added to the system. The presence of kaolinite, Mg2+- or Zn2+-kaolinite, or Mg2+-montmorillonite results in a reduction in the rate of the ATP decomposition in the abiotic peptide synthesizing system. These results suggest that one role for clays and metal ions in chemical evolution may have been the stabilization of nucleotides during prebiotic peptide synthesis.

Adenosine Diphosphate↗

PubMed1978

Bioorganic chemistry and the origin of life.

A challenging theme in bioorganic chemistry is the unification of established theories of biochemistry and organic chemistry to provide new patterns for interpretation and experimentation. Especially relevant examples of such interactions can be drawn from the field of enzyme catalysis and, in particular, the role of cofactors therein. Knowledge of the chemical mechanisms by which some of the cofactors function has progressed rapidly with the aid of studies of the cofactors themselves (or compounds of related structure, "models") stripped of the accompanying apoenzyme. The striking successes in this field likely arise from a fundamental resemblance between bioorganic chemistry (especially coenzyme models) and chemical evolution before the appearance of coded polypeptide enzymes.

Biochemistry↗

PubMed1981

Reasons for the occurrence of the twenty coded protein amino acids.

Factors involved in the selection of the 20 protein L-alpha-amino acids during chemical evolution and the early stages of Darwinian evolution are discussed. The selection is considered on the basis of the availability in the primitive ocean, function in proteins, the stability of the amino acid and its peptides, stability to racemization, and stability on the transfer RNA. We conclude that aspartic acid, glutamic acid, arginine, lysine, serine and possibly threonine are the best choices for acidic, basic and hydroxy amino acids. The hydrophobic amino acids are reasonable choices, except for the puzzling absences of alpha-amino-n-butyric acid, norvaline and norleucine. The choices of the sulfur and aromatic amino acids seem reasonable, but are not compelling. Asparagine and glutamine are apparently not primitive. If life were to arise on another planet, we would expect that the catalysts would be poly-alpha-amino acids and that about 75% of the amino acids would be the same as on the earth.

Amino Acids↗

PubMed1988

Construction of protocellular structures under simulated primitive earth conditions.

We have developed experimental approaches for the construction of protocellular structures under simulated primitive earth conditions and studied their formation and characteristics. Three types of envelopes; protein envelopes, lipid envelopes, and lipid-protein envelopes are considered as candidates for protocellular structures. Simple protein envelopes and lipid envelopes are presumed to have originated at an early stage of chemical evolution, interaction mutually and then evolved into more complex envelopes composed of both lipids and proteins. Three kinds of protein envelopes were constructed in situ from amino acids under simulated primitive earth conditions such as a fresh water tide pool, a warm sea, and a submarine hydrothermal vent. One protein envelope was formed from a mixture of amino acid amides at 80 degrees C using multiple hydration-dehydration cycles. Marigranules, protein envelope structures, were produced from mixtures of glycine and acidic, basic and aromatic amino acids at 105 degrees C in a modified sea medium enriched with essential transition elements. Thermostable microspheres were also formed from a mixture of glycine, alanine, valine, and aspartic acid at 250 degrees C and above. The microspheres did not form at lower temperatures and consist of silicates and peptide-like polymers containing imide bonds and amino acid residues enriched in valine. Amphiphilic proteins with molecular weights of 2000 were necessary for the formation of the protein envelopes. Stable lipid envelopes were formed from different dialkyl phospholipids and fatty acids. Large, stable, lipid-protein envelopes were formed from egg lecithin and the solubilized marigranules. Polycations such as polylysine and polyhistidine, or basic proteins such as lysozyme and cytochrome c also stabilized lipid-protein envelopes.

Amino Acids↗

PubMed1988

Genetic information could be integrated extrinsically for simplest life forms.

Polynucleotides and proteins coupled in mutual synthesis are widely believed to have been needed for the origin of life, but this theory encounters grave problems. Simple catalysts reproducing by positive feedback, sometimes advocated as an alternative, lack a built-in mechanism for generating and accumulating genetic information. Modern organisms, however, integrate genetic information by extrinsic in addition to intrinsic mechanisms, and extrinsic mechanisms were available even at the beginning of chemical evolution for any self-reproducing entities that might have appeared. Novel molecules were generated by reactions among prevailing molecules, and a catalyst multiplying by positive feedback would have transmitted structural information not only to progeny molecules of its kind, but to derivatives and by-products. New molecules derived immediately or remotely from successfully reproducing catalysts would be favored to have catalytic properties. New catalysts with effective positive feedback would increase autocatalytically and be integrated with others into a metabolizing system by natural selection.

Biological Evolution↗

PubMed1990

Diketopiperazine-mediated peptide formation in aqueous solution.

Though diketopiperazines (DKP) are formed in most experiments concerning the prebiotic peptide formation, the molecules have not been paid attention in the studies of chemical evolution. We have found that triglycine, tetraglycine or pentaglycine are formed in aqueous solution of glycine anhydride (DKP) and glycine, diglycine or triglycine, respectively. A reaction of alanine with DKP resulted in the formation of glycylglycylalanine under the same conditions. These results indicate that the formation of the peptide bonds proceeds through the nucleophilic attack of an amino group of the amino acids or the oligoglycines on the DKP accompanied by the ring-opening. The formation of glycine anhydride, di-, tri- and tetraglycine was also observed in a mixed aqueous solution of urea and glycine in an open system to allow the evaporation of ammonia. A probable pathway is proposed for prebiotic peptide formation through diketopiperazine on the primitive Earth.

Amino Acid Sequence↗

PubMed1989

The adsorption of nucleotides and polynucleotides on montmorillonite clay.

The binding of adenine derivatives to Na(+)-montmorillonite increases in the order 5'AMP, 3'-AMP, 5'ADP < adenosine < purine, adenine. With the exception of cytosine, cytosine derivatives bind less strongly than the corresponding adenine derivatives in the order 5'-CMP < cytidine < cytosine. There is little difference in the binding of uracil derivatives and these compounds bind less strongly than the corresponding adenine analogs. It is concluded that the adenine ring in adenine derivatives is protonated by the acidic montmorillonite surface and binding is a consequence of the electrostatic interaction between the protonated base and the negative charges on the surface of the montmorillonite. Different binding trends were observed with Cu(2+)-montmorillonite with AMP binding more strongly than adenosine and UMP binding more strongly than uridine. It is concluded that ligation to the Cu2+ is a major force in the binding of nucleotides to Cu(2+)-montmorillonite and are not readily washed from the clay. Factors contributing to the binding are discussed. Watson-Crick hydrogen bonding of 5'-AMP to poly(U) and 5'GMP to poly(C) was observed when the homopolymers are bound to the surface of the clay. No association of 5'-UMP to poly(U) bound to clay was detected. The possible role of montmorillonite clays in the prebiotic formation of RNA is discussed.

Adenine↗

PubMed1985

Life as a planetary phenomenon.

The success of recent spacecraft from the U.S.A. and the U.S.S.R. has given us a wealth of new data about the planets in our solar system. We can now develop a much better rationale for the reasons that abundant life is only found on our planet. Mars, smaller and more distant from the Sun, may nevertheless hold clues to the early development of Earth's atmosphere. The origin of life on Mars early in that planet's history cannot be ruled out. Titan offers a contemporary example of extremely primitive conditions, where chemical reactions resembling those that preceded the development of life on Earth may be occurring today. Venus and Jupiter illustrate the need for a planet to be the right size and the right distance from the sun if chemical evolution leading to the origin of life is to occur.

Atmosphere↗