Origins of life

In this paper we propose a logical connection between the physical and biological worlds, one resting on a broader understanding of the stability concept. We propose that stability manifests two facets - time and energy, and that stability’s time facet, expressed as persistence, is more general than its energy facet. That insight leads to the logical formulation of the Persistence Principle, which describes the general direction of material change in the universe, and which can be stated most simply as: nature seeks persistent forms. Significantly, the principle is found to express itself in two mathematically distinct ways: in the replicative world through Malthusian exponential growth, and in the ‘regular’ physical/chemical world through Boltzmann’s probabilistic considerations. By encompassing both ‘regular’ and replicative worlds, the principle appears to be able to help reconcile two of the major scientific theories of the 19th century – the Second Law of Thermodynamics and Darwin’s theory of evolution – within a single conceptual framework.

The lunar samples from Apollo flights 11 through 17 provided the students of chemical evolution with an opportunity of examining extraterrestrial materials for evidence of early prebiological chemistry in the solar system. Our search was directed to water-extractable compounds with emphasis on amino acids. Gas chromatography, ion-exchange chromatography and gas chromatography combined with mass spectrometry were used for the analysis. It is our conclusion that amino acids are not present in the lunar regolith above the background levels of our investigations.

To understand chiral symmetry breaking on the molecular level, we developed a method to efficiently investigate reaction kinetics of single molecules. The model systems include autocatalysis as well as a reaction cascade to gain further insight into the prebiotic origin of homochirality. The simulated reactions start with a substrate and only a single catalyst molecule, and the occurrence of symmetry breaking was examined for its degree of dependence on randomness. The results demonstrate that interlocking processes, which e.g., form catalysts, autocatalytic systems, or reaction cascades that build on each other and lead to a kinetic acceleration, can very well amplify a statistically occurring symmetry breaking. These results suggest a promising direction for the experimental implementation and identification of such processes, which could have led to a shift out of thermodynamic equilibrium in the emergence of life.

In a famous experiment Stanley Miller showed that a large number of organic substances can emerge from sparking a mixture of methane, ammonia and hydrogen in the presence of water (Miller, Science 117:528–529, 1953). Among these substances Miller identified different amino acids, and he concluded that prebiotic events may well have produced many of Life’s molecular building blocks. There have been many variants of the original experiment since, including different gas mixtures (Miller, J Am Chem Soc 77:2351–2361, 1955; Oró Nature 197:862–867, 1963; Schlesinger and Miller, J Mol Evol 19:376–382, 1983; Miyakawa et al., Proc Natl Acad Sci 99:14,628–14,631, 2002). Recently some of Miller’s remaining original samples were analyzed with modern equipment (Johnson et al. Science 322:404–404, 2008; Parker et al. Proc Natl Acad Sci 108:5526–5531, 2011) and a total of 23 racemic amino acids were identified. To give an overview of the chemical variety of a possible prebiotic broth, here we analyze a “Miller type” experiment using state of the art mass spectrometry and NMR spectroscopy. We identify substances of a wide range of saturation, which can be hydrophilic, hydrophobic or amphiphilic in nature. Often the molecules contain heteroatoms, with amines and amides being prominent classes of molecule. In some samples we detect ethylene glycol based polymers. Their formation in water requires the presence of a catalyst. Contrary to expectations, we cannot identify any preferred reaction product. The capacity to spontaneously produce this extremely high degree of molecular variety in a very simple experiment is a remarkable feature of organic chemistry and possibly prerequisite for Life to emerge. It remains a future task to uncover how dedicated, organized chemical reaction pathways may have arisen from this degree of complexity.

We wish to propose a mechanism for reciprocal information transfer in prebiotic molec-ular evolution, based on heterologous pairing complex formation between oligoribonucleotides and oligopeptides. In this proposed pairing complex, the bases of the oligoribonucleotide and the side chains of the oligopeptide may form three types of complementary Watson-Crick-type hydrogen bonds. The structural basis for the pairing is the close correspondence of the distances between the side chains in the two molecules. Both the inter-nucleotide spacing of the RNA and the inter-side-chain spacing of the peptide are approximately 3.4 Å. The proposed pairing mode would allow both specific and nonspecific interactions required for reciprocal information transfer. Thus, it represents a simple and versatile coding system that could have had significant implications in prebiotic molecular selection and evolution. In addition, we propose several testable experimental approaches based on the pairing mode of oligoribonucleotides and oligopeptides to verify our hypothesis.

Catalytic action of rare earth element, Ce(IV) to hydrolyzephosphomonoester bonds was confirmed. This effect wasconsidered to suppress abiotic synthesis ofnucleotides and nucleic acids in the primitive sea,and hence the origin of life. However, we found thatthe presence of proteins, especially albumin, stronglyinhibited the catalytic action of Ce(IV). Thisfinding was supported by preferential binding of rare earthelements (REEs) to proteins which was revealed using the radioisotopes of these REEs. Consequently, if a large amount ofproteins was synthesized in the primitive sea, abioticsynthesis of phosphomonoester compounds, and hencenucleic acids, might have been possible.

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.

The chemistry induced by atmospheric pressure DC discharges above a water surface in CO2/N2/H2O mixtures was investigated. The gaseous mixtures studied represent a model prebiotic atmosphere of the Earth. The most remarkable changes in the chemical composition of the treated gas were the decomposition of CO2 and the production of CO. The concentration of CO increased logarithmically with the increasing input energy density and an increasing initial concentration of CO2 in the gas. The highest achieved concentration of CO was 4.0 ± 0.6 vol. %. The production of CO was crucial for the synthesis of organic species, since reactions of CO with some reactive species generated in the plasma, e. g. H ${\scriptstyle\bullet}$ or N ${\scriptstyle\bullet}$ radicals, were probably the starting point in this synthesis. The presence of organic species (including the tentative identification of some amino acids) was demonstrated by the analysis of solid and liquid samples by high-performance liquid chromatography, infrared absorption spectroscopy and proton-transfer-reaction mass spectrometry. Formation of organic species in a completely inorganic CO2/N2/H2O atmosphere is a significant finding for the theory of the origins of life.