James P. Ferris

HCN and chemical evolution: the possible role of cyano compounds in prebiotic synthesis

Synthese et distribution de HCN. Autocondensation de HCN: obtention de nitriles ou de liants oligomeres. Role possible des composes cyano comme agents de condensation

HCN - A plausible source of purines, pyrimidines and amino acids on the primitive earth

SummaryDilute (0.1M) solutions of HCN condense to oligomers at pH 9.2. Hydrolysis of these oligomers yields 4,5-dihydroxypyrimidine, orotic acid, 5-hydroxyuracil, adenine, 4-aminoimidazole-5-carboxamide and amino acids. These results, together with the earlier data, demonstrate that the three main classes of nitrogen-containing biomolecules, purines, pyrimidines and amino acids may have originated from HCN on the primitive earth. The observation of orotic acid and 4-aminoimidazole-5-carboxamide suggests that the contemporary biosynthetic pathways for nucleotides may have evolved from the compounds released on hydrolysis of HCN oligomers.

Montmorillonite catalysis of 30-50 mer oligonucleotides: laboratory demonstration of potential steps in the origin of the RNA world.

Elongation of the primer 32pdA(pdA)8pA proceeds by thereaction of the 5′-phosphorimidazolides of adenosine and uridine in the presence of montmorillonite clay. Daily addition of the activated nucleotides for up to 14 days results in theformation of 40–50 mers using the 5′-phosphorimidazolide of adenosine (ImpA) and 25–30 mers using the 5′-phosphorimidazolide of uridine (ImpU). The limitation on thelengths of the chains formed is not due to the inhibitors formedsince the same chain lengths were formed using 2–3 times the amount of montmorillonite catalyst. The shorter oligomers formedby the addition of U monomers is not due to its greater rate ofdecomposition since it was found that both the A and the U adducts decompose at about the same rates. Alkaline phosphatase hydrolysis studies revealed that some of the oligomers are cappedat the 5′-end to form, with ImpA,Ap32pdA(pdA)8pA(pA)n. The extent of capping depends on the reaction time and the purine or pyrimidine base inthe activated mononucleotide. Hydrolysis with ribonuclease T2 followed by alkaline phosphatase determined the sites ofthe 3′, 5′- and 2′, 5′-phosphodiester bonding to the primer. The potential significance of the mineral catalyzed formation of 50 mer oligonucleotides to the origin of life basedon RNA (the RNA world scenario) is discussed.

Comet Halley as an aggregate of interstellar dust and further evidence for the photochemical formation of organics in the interstellar medium

Photolysis of mixtures of CO:NH3:H2O at 12 K results in the formation of an organic residue which is not volatile in high vacuum at room temperature. Analysis of this fraction by GC-MS resulted in the detection of C2–C3 hydroxy acids and hydroxy amides, glycerol, urea, glycine, hexamethylene tetramine, formamidine and ethanolamine. Use of isotopically labeled gases made it possible to establish that the observed products were not contaminants. The reaction pathways for the formation of these products were determined from the position of the isotopic labels in the mass spectral fragments. The significance of these findings to the composition of comets and the origins of life is discussed.

Montmorillonite-catalysed formation of RNA oligomers: the possible role of catalysis in the origins of life

Large deposits of montmorillonite are present on the Earth today and it is believed to have been present at the time of the origin of life and has recently been detected on Mars. It is formed by aqueous weathering of volcanic ash. It catalyses the formation of oligomers of RNA that contain monomer units from 2 to 30–50. Oligomers of this length are formed because this catalyst controls the structure of the oligomers formed and does not generate all possible isomers. Evidence of sequence-, regio- and homochiral selectivity in these oligomers has been obtained. Postulates on the role of selective versus specific catalysts on the origins of life are discussed. An introduction to the origin of life is given with an emphasis on reaction conditions based on the recent data obtained from zircons 4.0–4.5 Ga.

Photochemical reactions in interstellar grains photolysis of co, NH3, and H2O

A simulation of the organic layer accreted onto interstellar dust particles was prepared by slow deposition of a CO:NH3:H2O gas mixture on an Al block at 10K, with concomitant irradiation with vacuum UV. The residues were analyzed by GC-MS, HPLC, and near IR; a reaction pathway leading from NH3 to complex alcohol, fatty acid, and amide products in 27 stages is postulated. The astronomical relevance and significance of the observations are discussed.

Synthesis of 35-40 mers of RNA oligomers from unblocked monomers. a simple approach to the RNA world

RNA oligomers greater than 35-40 mers in length form in one day in the montmorillonite clay-catalyzed reaction of unblocked RNA monomers at 25 degrees C in aqueous solution.

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 Cu2+-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 Cu2+-montmorillonite. RNA homopolymers exhibit strong adsorption to Na+- and Cu2+-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.

Mechanism of montmorillonite catalysis in the formation of RNA oligomers.

The montmorillonite clay-catalyzed reactions of nucleotides generate oligomers as long as 50-mers. The extent of catalysis depends on the magnitude of the negative charge on the montmorillonite lattice and the number of cations associated with it. When cations in raw montmorillonites are replaced by sodium ions, the resulting Na(+)-montmorillonite does not catalyze oligomer formation because they saturate the interlayers between the platelets of montmorillonites, which blocks the binding of the activated monomers. Treating the montmorillonite with dilute hydrochloric acid replaces the cations on the raw montmorillonite with protons. The protonated montmorillonite, titrated to pH 6-7, serves as a catalyst for the formation of RNA oligomers. The titration does not add sufficient sodium ions to the interlayers of the montmorillonite platelets to prevent the activated monomer from entering. It was noted that noncatalytic montmorillonites have a higher negative charge on their platelets that is due mainly to the natural substitution of the tetravalent and trivalent elements in the montmorillonite lattice with trivalent and divalent metal ions, respectively. The larger negative charge on these montmorillonites was demonstrated by the almost 2-fold greater amounts of sodium hydroxide needed to titrate noncatalytic montmorillonites as compared to the catalytic montmorillonites. Adsorption isotherms established that the equilibrium binding is strongest for ImpA and weakest for ImpU. Of the 22 montmorillonites investigated, 12 were catalysts. This research provides insight into the mechanism of the catalytic process.

Chemical Markers of Prebiotic Chemistry in Hydrothermal Systems

The goal of this chapter is to suggest some organic compounds which may be indicative of prebiotic processes in hydrothermal systems or laboratory simulations of them. While the exact processes which led to the origins of life are not known, studies of life’s origins of the past forty years have uncovered a plethora of potential precursor molecules. Some of these same molecules were probably present in hydrothermal systems if chemical processes there had a role in the origins of life.