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PubMed1998

Studies on order in prebiological systems at the Laboratory of Chemical Evolution.

The basic tenet of investigations in the Laboratory of Chemical Evolution (LCE) under Cyril Ponnamperuma was that biology is a recapitulation of prebiology, and that protobiology is an outcome of simple molecular interactions, engendered by the physics and chemistry of the molecules themselves. Studies were undertaken to continue research into understanding the determining physical and chemical parameters of molecular interactions leading to increasing complexity in pre- and proto-biological systems. Among other, related work, research was performed on the origin of the genetic code, the origin of order in prebiotic polymers, and related studies on the origins of optical activity in biological macromolecules. Highlights of some these studies are presented here.

Amino Acids↗

PubMed1976

Chemical evolution of photosynthesis.

The principles of biological evolution of photosynthesis are established, but the ways of chemical evolution are unclear yet. The model systems will help to elucidate the problem. Every type of photosynthesis requires photoreceptor absorbing solar radiation. We studied as photoreceptors inorganic components of Earth crust, some coenzymes and porphyrins of abiogenic and biogenic origin. By the aid of inorganic photosensitizers (TiO2, ZnO) the models of photosystems I and II were constructed. Photochemical activation of some coenzymes may serve as an intermediate step from heterotrophic 'dark' to 'light' metabolism. The further evolution led to the separation of catalytic and photosensitizing functions. Porphin, chlorin and bacteriochlorin were formed by abiogenic synthesis. Magnesium complexes of porphyrins are active being excited by light. They are capable to reversible acceptance or donation of an electron to partner molecule. Excited Mg-complexes of porphyrins (P) are capable to transfer an electron from electron-donor (D) to electron-acceptor (A) accompanied by conversion of light quanta energy into potential chemical energy. The primary electron transfer unit (D-P-A) was incorporated into primary membrane. The transition from random to anisotropic arrangement of (D-P-A) in the membrane was plausable as a step of evolution; charge translocation appeared. (D-P-A) units created in the period of chemical evolution were probably used in the course of biological evolution. The (D-P-A) units were coupled with noncyclic and cyclic electron transfer resulting in ATP formation; coupling of two (D-P-A) units led to H2O oxidation and NADP reduction in photosynthetic organisms. The improvement of pigments biosynthesis created the phenomenon of excitation energy migration from the bulk of the pigment to (D-P-A) unit, being reactive center. The models described points the plausible steps of chemical evolution; the real sequence of events will be probably disclosed in the studies of precambrian rocks and space exploration.

Biological Evolution↗

PubMed1983

Chemical evolution and the origin of life.

During the last three decades major advances have been made in our understanding of the formation of carbon compounds in the universe and of the occurence of processes of chemical evolution. 1) Carbon and other biogenic elements (C,H,N,O,S and P) are some of the most abundant in the universe. 2) The interstellar medium has been found to contain a diversity of molecules of these elements. 3) Some of these molecules have also been found in comets which are considered the most primordial bodies of the solar system. 4) The atmospheres of the outer planets and their satellites, for example, Titan, are actively involved in the formation of organic compounds which are the precursors of biochemical molecules. 5) Some of these biochemical molecules, such as amino acids, purines and pyrimidines, have been found in carbonaceous chondrites. 6) Laboratory experiments have shown that most of the monomers and oligomers necessary for life can be synthesized under hypothesized but plausible primitive Earth conditions from compounds found in the above cosmic bodies. 7) It appears that the primitive Earth had the necessary and sufficient conditions to allow the chemical synthesis of biomacromolecules and to permit the processes required for the emergence of life on our planet. 8) It is unlikely that the emergence of life occurred in any other body of the solar system, although the examination of the Jovian satellite Europa may provide important clues about the constraints of this evolutionary process. Some of the fundamental principles of chemical evolution are briefly discussed.

Atmosphere↗

PubMed1983

A laboratory model for interstellar chemical evolution.

The chemistry in a supersonic plasma source flow was studied as a laboratory model for interstellar chemical evolution. It is important to match the similarity parameters for cosmic and laboratory conditions, which connect the temporal and spatial scales of the two cases. The apparatus simulated the conditions in a molecular cloud with respect to molecular-ionic reaction fraction, temperature, and non-equilibrium kinetics. The plasma flow was found to be cold enough, by the radical expansion, to produce polyatomic molecules. From the simple atomic plasma as reactant, cyanopolyyne and unsaturated hydrocarbons were synthesized in the present experiment. These molecules are also inherent in molecular clouds. The reaction mechanism is discussed.

Computer Simulation↗

PubMed1989

The role of cometary particle coalescence in chemical evolution.

Important prebiotic organic compounds might have been transported to Earth in dust or produced in vapor clouds resulting from atmospheric explosions or impacts of comets. These compounds coalesced in the upper atmosphere with particles ejected from craters formed by impacts of large objects. Coalescence during exposure to UV radiation concentrated organic monomers and enhanced formation of oligomers. Continuing coalescence added material to the growing particles and shielded prebiotic compounds from prolonged UV radiation. These particles settled into the lower atmosphere where they were scavenged by rain. Aqueous chemistry and evaporation of raindrops containing nomomers in high temperature regions near the Earth's surface also promoted continued formation of oligomers. Finally, these oligomers were deposited in the oceans where continued prebiotic evolution led to the most primitive cell. Results of our studies suggest that prebiotic chemical evolution may be an inevitable consequence of impacting comets during the late accretion of planets anywhere in the universe if oceans remained on those planetary surfaces.

Amino Acids↗

PubMed2004

Chemical evolution and meteorites: an update.

Carbonaceous chondrites are a primitive group of meteorites, which contain abundant organic material and provide a unique natural record of prebiotic chemical evolution. This material comprises a varied suite of soluble organic compounds that are similar, sometimes identical, to those found in the biosphere, such as amino acids, carboxylic acids, and sugar derivatives. Some amino acids of this suite also show L-enantiomeric excesses, and suggest the possibility they may have contributed to terrestrial homochirality by direct input of meteoritic material to the early Earth. This optical activity appears to be limited to the subgroup of alpha-methyl amino acids which, although not common in the extant biosphere, would have been well suited to provide the early earth with both enantiomeric excesses and means for their amplification by subsequent chemical evolution. We can also envision this exogenous delivery of carbonaceous material by meteorites and comets as having coincided with the endogenous formation of prebiotic precursors and influenced their evolution by complementary reactions or catalysis.

Meteoroids↗

PubMed2002

Behavior of adenine in Na-montmorillonite exposed to gamma radiation: implications to chemical evolution studies.

Adenine is an important compound in biological systems, such as genetic and energy utilization processes. Adenine is readily formed in prebiotic conditions. Its synthesis and stability in environmental conditions are of paramount importance in chemical evolution processes. Clay minerals might have played an important role in the early Earth. Clays are known to have a high affinity for organic compounds, and they may provide protection to adsorbed molecules against high-energy radiation. The purpose of this work is to testthese assumptions. We study the stability of adenine under irradiation, in aqueous solution and also adsorbed in a clay mineral. The recovery of adenine after a gamma irradiation was higher in the system containing clay in relation to a system without clay. Results show that adenine is readily adsorbed in the clay, and that the clay act as surface protector toward the degradation of adenine by the radiation.

Adenine↗

PubMed1994

Did reflexive catalysts drive chemical evolution?

High-energy starting materials and energy sources on the primitive earth would have generated abundant and varied organic molecules of small or medium size. It is questionable, however, whether ordinary chemical evolution could have produced information-carrying polymers. The end point might have been a fixed steady state if some form of autocatalysis had not intervened. Autocatalytic synthesis is possible for small molecules as illustrated by the formose reaction, in which glycolaldehyde condenses with formaldehyde to form sugars, and resulting tetroses may cleave into two molecules of glycolaldehyde. This and other 'reflexive catalysts', some functioning in molecular aggregates, may have energized chemical evolution and carried it to a level at which RNA or an RNA analog could replicate itself.

Adenosine Triphosphate↗

PubMed1989

Chemical evolution of interstellar dust, comets and the origins of life.

It now appears that the chemical evolution of the pre-solar system interstellar dust ensures that a major fraction of comets is in the form of complex organic molecules at least partially of a prebiotic nature and that the submicron interstellar dust preserves its chemical integrity as result of forming a very tenuous low density comet structure whose solid matter occupies approximately 1/5 of the total volume. This low density micro structure further provides a physical basis for comets bringing a significant fraction of the original interstellar organic molecules to the earth unmodified by the impact event. Finally, the evidence for a large number of comet collisions with the early earth ensured that the major organic molecular budget on the earth's surface was "continuously" supplied along with water well before 3.8 billion years ago which is the earliest date for life. The chemistry and morphological structure of a comet nucleus as an aggregate of interstellar dust is used to provide comparisons with a variety of comet Halley results: the density of the nucleus and of the dust; the dust cloud model and its consequences on the production of C+ and CN in the coma by small organic grains; the surface albedo and the low nucleus heat conductivity and high surface temperature; the appearance of 10(-14) g and 10(-17) g dust particles along with higher masses; the mass spectra of dust and infrared spectroscopy as evidence for complex organic grain mantles and of very small (approximately 0.01 micrometer) carbonaceous and silicate grains; the appearance of small grains resulting from breakup of larger grains. The cosmic ray dosage of a comet nucleus during its 4.5 billion years in the Oort cloud appears to be many orders of magnitude less than the dosage of the preaggregated interstellar dust by ultraviolet photons except perhaps in the outer few meters of the nucleus of a new comet. The heat conductivity calculated for aggregated dust is certainly less than 10(-4) that of crystalline ice. This, in combination with the interstellar dust microstructure, provide a basis for showing that solar heating of the interior of a nucleus is lower than previously estimated.

Carbon↗

PubMed2003

'Reverse chemical evolution': a new method to search for thermally stable biopolymers.

The primitive sea on Earth may have had high-temperature and high-pressure conditions similar to those in present-day hydrothermal environments. If life originated in the hot sea, thermal stability of the constituent molecules would have been necessary. Thus far, however, it has been reported that biopolymers hydrolyze too rapidly to support life at temperatures of more than 200 degrees C. We herein propose a novel approach, called reverse chemical evolution, to search for biopolymers notably more stable against thermal decomposition than previously reported. The essence of the approach is that hydrolysis of a protein or functional RNA (m-, t-, r-RNA) at high temperature and high pressure simulating the ancient sea environment may yield thermally stable peptides or RNAs at higher concentrations than other peptides or RNAs. An experimental test hydrolyzing bovine ribonuclease A in aqueous solution at 205 degrees C and 25 MPa yielded three prominently stable molecules weighing 859, 1030 and 695 Da. They are thermally some tens or hundreds times more stable than a polyglycine of comparable mass. Sequence analyses of the 859- and 1030-Da molecules revealed that they are a heptapeptide and its homologue, respectively, elongated by two amino acids at the N-terminal region, originally embedded as residues 112-120 in the protein. They consist mainly of hydrophobic amino acids.

Amino Acid Sequence↗

PubMed1995

Role of trace metal ions in chemical evolution. The case of free-radical reactions.

We have studied the effect of iron in the free-radical oligomerization of hydrogen cyanide and acetic acid, and found that iron(II) and iron(III) readily reduces or oxidizes free radicals, respectively. The transient species produced by these reactions do not induce a chain oligomerization process and, therefore, they protect the solute molecules from degradation. Analysis of the available kinetic data for the reactions of a variety of transition metal ions with free radicals indicate that transition metal ions behave similarly to iron. Since Fe, Zn and Mo are essential to all living organisms, and there seems to be no apparent difference in chemical reactivity among transition metal ions towards free radicals, we suggest that these metal ions probably protected the biomolecules from degradation induced by free-radical reactions in the later stages of chemical evolution.

Acetic Acid↗

PubMed2004

Interaction of tryptophan and phenylalanine with metal ferrocyanides and its relevance in chemical evolution.

The interaction of two naturally occurring aromatic alpha-amino acids, namely, tryptophan and phenylalanine, with zinc, nickel, cobalt, and copper ferrocyanides has been studied. Both amino acids showed a high adsorption affinity toward metal ferrocyanides at neutral pH (7.0). Adsorption trends followed the Langmuir adsorption isotherm. Values of the Langmuir constants K(L) and X(m) suggest tryptophan is a better adsorbate than phenylalanine. Zinc ferrocyanide showed the highest adsorption, while the minimum adsorption was found in the case of copper ferrocyanide. Infrared spectral studies of adsorbate, adsorbent, and adsorption adducts indicate that adsorption occurs because of the interaction of adsorbate molecules with outer divalent metal ions present in the lattice of metal ferrocyanides. The present investigation supports the hypothesis that metal ferrocyanides might have concentrated the biomonomers on their surface in primeval seas during the course of chemical evolution.

Adsorption↗

PubMed1980

Adsorption of protein and non-protein amino acids on a clay mineral: a possible role of selection in chemical evolution.

The adsorption of protein and non-protein amino acids by Na-montmorillonite was studied at pH 3, 7, and 10, in order to determine whether clays could have played a part in selection of protein over non-protein amino acids in prebiotic times. Five pairs of amino acids, containing two to six carbons, were used at a concentration equal to 100% cation exchange capacity of the clay in adsorption experiments. The following pairs of protein and non-protein amino acids were used: glycine and sarcosine, alpha-alanine and beta-alanine, alpha-aminobutyric acid and gamma-aminobutyric acid, valine and norvaline, L-isoleucine and D-alloisoleucine. No selective adsorption of protein amino acids occurred at varying hydrogen ion concentrations. The one difference observed in the adsorption of amino acids in the mixtures was a three- and four-fold greater adsorption of beta- and gamma-amino acids, respectively, than their alpha-amino acid counterparts under acidic and neutral conditions. Strong and weak adsorption of amino acids on the clay were correlated with mechanisms such as cation exchange and hydrogen bonding. The results of this research are significant to understanding the role of clay in chemical evolution because they do not support the role of preferential adsorption of protein over non-protein amino acids by clays.

Adsorption↗

PubMed2005

Chemical evolution of RNA under hydrothermal conditions and the role of thermal copolymers of amino acids for the prebiotic degradation and formation of RNA.

The roles of thermal copolymers of amino acids (TCAA) were studied for the prebiotic degradation of RNA. A weak catalytic ability of TCAA consisted of Glu, L-Ala, L-Val, L-Glu, L-Asp, and optionally L-His was detected for the cleavage of the ribose phosphodiester bond of a tetranucleotide (5'-dCrCdGdG) in aqueous solution at 80 degees C. The rate constants of the disappearance of 5'-dCrCdGdG were determined in aqueous solutions using different pH buffer and TCAA. The degradation rates were enhanced 1.3-3.0 times in the presence of TCAA at pH 7.5 and 8.0 at 80 degrees C, while the hydrolysis of oligoguanylate (oligo(G)) was accelerated about 1.6 times at pH 8.0. A weak inhibitory activity for the cleavage of oligo(G) was detected in the presence of 0.055 M TCAA-Std. On the other hand, our recent study on the influences of TCAA for the template-directed reaction of oligo(G) on a polycytidylic acid template showed that TCAA has an acceleration activity for the degradation of the activated nucleotide monomer and an acceleration activity for the formation of G5' ppG capped oligo(G). This series of studies suggest that efficient and selective catalytic or inhibitory activities for either the degradation or formation of RNA under hydrothermal conditions could have hardly emerged from the simple thermal condensation products of amino acids. A scenario is going to be deduced on the chemical evolution of enzymatic activities and RNA molecules concerning hydrothermal earth conditions.

Amino Acids↗

PubMed1984

The evolution of prebiological self-organization: probable colloid-chemical evolution of first prokaryotic cells.

This is an attempt to analyse the mechanisms of self-assembly in the course of the origin and early evolution of life on the Earth. A special attention is paid to the investigation of transient stages between the physico-chemical and biological bases of self-assembly, including experimental models and paleontological results. The theory of coacervate-in-coacervate is discussed from the point of view of evolution of first procaryotic cells. Many of the high developed structures of the contemporary cells, such as ribosomes, chromosomes, lipid membranes, some other organelles etc., are claimed to posses a rudimentary polyionic coacervate character.

Biological Evolution↗

PubMed1977

Chemical evolution and the evolution of the earth's crust.

It is hypothesized that there is a close relationship between the geologic evolution of the global plates of the Earth's crust and the chemical evolution of life on the Earth. Characteristics of the axes of plate spreading are discussed in relation to postulated environments conductive to the synthesis of chemical compounds thought to be important biological precursors. Likely locations for in situ measurements to test the hypothesis are identified.

Biological Evolution↗

PubMed1982

Study on the chemical evolution of low molecular weight compounds in a highly oxidized atmosphere using electric discharges.

The molecular basis for the chemical evolution of low molecular compounds was studied using electric discharges on a highly oxidized atmosphere comprised of CO2, N2 and H2O. In the gas phase, O2 and CO were formed by the decomposition of CO2 and their yields were enhanced by the addition of N2 to the gas mixture. It was demonstrated that H2O suppressed the reduction of CO2 while H2O also had a role in producing organic compounds such as formic acid and formaldehyde. Infrared analysis of the water soluble products and the inner surface of the reaction vessel indicated the production of compounds more complex than formic acid and formaldehyde. These compounds contained the chemical bonds which were identified to be OH, CO, CN and/or CC.

Biological Evolution↗

PubMed2002

A new approach for the cooperative chemical evolution of nucleic acids and proteins under the primitive earth environment.

In order to evaluate cooperative chemical evolution of nucleic acids and proteins, we have examined possible activity of thermal copolymers of amino acids (TCAA) for prebiotic formation and degradation of RNA. Several types of TCAA involving aromatic amino acids were prepared and the influence on the template-directed formation of oligoguanylate and prebiotic ribonuclease activity were kinetically studied.

Chromatography, High Pressure Liquid↗