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PubMed1976

Melanoidin and aldocyanoin microspheres: implications for chemical evolution and early precambrian micropaleontology.

Two new classes of organic microspheres are described. One of them (melanoidin) is synthesized from amino acids and sugars in heated aqueous solutions. The other (aldocyanoin) is formed in aqueous solutions of ammonium cyanide and formaldehyde at room temperature. The general properties of these microspheres, including conditions of synthesis, size and shape, mechanical and pH stability, and solubility, are compared with corresponding properties of other "protocell" model systems. It is concluded that melanoidin and aldocyanoin microsphreres are plausible candidates for precellular units in the primitive hydrosphere. Since the bulk of the organic carbon in early Precambrian sediments is insoluble kerogen-melanoidin, it is suggested that some Precambrian "microfossils" may be abiotic melanoidin microspheres of the type described herein.

Aldehydes↗
PubMed1982

Comets: chemistry and chemical evolution.

Lasting commitment to cosmic chemistry and an awareness of the fascinating role of comets in that study was a consequence of an association with Harold Urey early in my astronomical career. Urey's influence on cometary research spread as colleagues with whom I was associated, in turn, developed their own programs in cometary chemistry. One phase of the Chicago research shows that Whipple's icy nucleus would be below about 250 K. This property, combined with their small internal pressure, means cometary interiors remain essentially unchanged during their lifetime. Observations of cometary spectra indicate that they are rich in simple organic species. Experiments on comet-like ice mixture suggests that the extensive array of interstellar molecules also may be found in comets. The capture of cometary debris by the earth or the impact of comets would have been an early source of biochemically significant molecules. Recent hypotheses on radiogenic heating and melting of water ice in the central zone of nuclei do not seem consistent with recent observations or ideas of structure. Thus comets are not a likely place for life to develop.

Astronomical Phenomena↗
PubMed1988

Chemical evolution of peroxidase--amino acid pentacyanoferrate (II) complexes as model.

Complexes of the type [Fe(II)(CN)5(L)]n- (where n = 3, or 4; L = glycine, histidine, imidazole, and triglycine) are proposed as evolutionary model of peroxidases. Detailed kinetic investigation for disproportionation of hydrogen peroxide catalysed by [Fe(II)(CN)5(L)]n- complexes at 40 degrees C and pH 9.18 are discussed. Decomposition of hydrogen peroxide catalysed by above complexes conforms to Michaelis-Menten type kinetics.

Amino Acids↗
PubMed1987

Soluble minerals in chemical evolution. II. Characterization of the adsorption of 5'-AMP and 5'-CMP on a variety of soluble mineral salts.

The adsorption of 5'-AMP and 5'-CMP was studied in saturated solutions of several soluble mineral salts (NaCl, Na2SO4, MgCl2 X 6H2O, MgSO4 X 7H2O, CaCl2 X 2H2O, CaSO4 X 2H2O, SrCl2 X 6H2O, SrSO4, and ZnSO4 X 7H2O) as a function of pH, ionic strength, and surface area of the solid salt. The adsorption shows a pH dependence; this can be correlated with the charge on the nucleotide molecule which is determined by the state of protonation of the N-1 nitrogen of 5'-AMP or N-3 nitrogen of 5'-CMP and the phosphate oxygens. The adsorption which results from the binding between the nucleotide molecule and the salt surface is proposed as being due to electrostatic forces. It was concluded that the adsorption was reversible in nature. The adsorption shows a strong dependence upon ionic strength and decreases with increasing ionic strength. Surface area is shown to be an important factor in evaluating and comparing the magnitude of adsorption of nucleotides onto various mineral salts. The implications of the results of the study are discussed in terms of the importance of soluble mineral salts as adsorption sites in the characterization of the adsorption reactions of an adsorbed template in biogeochemical cycles.

Adenosine Monophosphate↗
PubMedDate not supplied

Chemical evolution of the citric acid cycle: sunlight photolysis of the amino acids glutamate and aspartate.

Sunlight photolysis of the amino acids glutamate and aspartate were carried out on 0.1 M aqueous solutions at pH = 7.0. The non-volatile products were identified by GC-MS analysis of derived methyl esters. The major product from glutamic acid was succinic acid, and, analogously, aspartic acid photolyzed to malonic acid. The photochemical oxidative decarboxylation of glutamate parallels its metabolism in modern cells and may provide an evolutionary link between simple amino acids and reactions of the citric acid cycle.

Aspartic Acid↗
PubMed1989

Population dynamics in a spin-glass model of chemical evolution.

We introduce a simple model describing the evolution of a population of information-carrying macromolecules. We discuss the asymptotic dependence of the variability of the population on different parameters, representing the severity or the fluctuations of the environment. We show the existence of a transition separating a neutralist evolutionary regime from a trapped one. We investigate the dependence of the evolutionary behavior of the population on the correlation properties of the fitness landscape.

Biological Evolution↗
PubMed1977

beta-structures of alternating polypeptides and their possible role in chemical evolution.

The tendency of copolypeptides with alternating hydrophilic and hydrophobic residues to form water soluble beta-structures in presence of salt, already described for poly(Val-Lys) (Brack and Orgel, 1975), was generalized to optically pure poly(Lys-Leu-Lys-Leu) and poly(Leu-Glu-Leu- G lu). Substitution of about 10% of L-lysyl residues by their enantiomers did not prevent the coli to beta transition but had nervertheless a sensitive effect on the beta-structures. Disruption of the alternation by insertion of extra glycyl or L-prolyl residues as in poly(Gly-Lys-Leu-Lys-Leu) and poly(Pro-Lys-Leu-Lys-Leu) decreased dramatically the tendency to form beta-structures. However, by using strong interaction ions such as perchlorate ions or by lengthening the alternating sequences as in the semi-random copoly(Gly-Lys-Leu-Lys-Leu1, Lys-Leu-Lys-Leu1) and copoly(Pro-Lys-Leu-Lys-Leu1, Lys-Leu-Lys-Leu1) it was possible to obtain soluble beta-structures which showed differences in the CD spectra. The binding properties of the beta-surface are examined.

Circular Dichroism↗
PubMed2006

Structural-chemical evolution within exfoliated clays.

The exfoliated (delaminated) structures of lamellar clays offer potential as precursors for the formation of various nanostructured materials. In this article, Lucentite and Laponite phyllosilicate clays, which both have empirical formulas of Na(0.33)[Mg(2.67)Li(0.33)Si4O10(OH)2] but differ in nanodimensions, have been exfoliated. Experiments were carried out for mixtures containing approximately 1 wt % phyllosilicate in a 5% aqueous solution of poly(acrylic acid) at different temperatures. X-ray diffraction and photoemission spectroscopy measurements for the solid products recovered after stirring the mixtures at 20 degrees C showed that the fully extended chains of poly(acrylic acid) were intercalated within the interlayer spaces between the silicate plates of the clays. At 85 degrees C, however, the clays were exfoliated and/or partially exfoliated. Photoemission spectroscopy also indicated that the exfoliated structures primarily consisted of silica nanoplates. 29Si nuclear magnetic resonance and oxygen K-edge near-edge X-ray absorption fine structure indicated that the surfaces of the plates were terminated by high concentrations of the silanol (-SiOH) groups, which created structural branches during intercalation. A model was developed in which intercalation and the removal of ions from the clays after the poly(acrylic acid) interactions reduced the electrostatic van der Waals forces between the plates. It was also shown that the formation of branches created a steric effect that inhibited the stacking of the plates. Together these resulted in exfoliation.

Journal Article↗
PubMed2002

Possible impact of a primordial oil slick on atmospheric and chemical evolution.

Low molecular weight liquid hydrocarbons from various sources, could have formed an oil layer covering the primeval ocean (present already 4.0-4.4 x 10(9) yr ago), preventing water from evaporating into the atmosphere. Water from other sources, precipitated by cold traps at higher altitude in the atmosphere, becomes trapped in the ocean. In a thereby more dry and presumably reducing atmosphere (before 3.9 x 10(9) yr ago) even more hydrocarbons, as well as reactive molecules will form. An oil layer can possibly act as a dry solvent for reactions, where the reactive molecules can produce monomers and condensing agents. Monomers and eventual polymers formed could become strongly concentrated at the oil-water interface, favouring molecular interactions at high mobility and low dilution, without exposure to the destructive action of UV-light. Increased water leakiness of the oil layer due to accumulation of polar molecules within, would lead to photooxidation of liquid hydrocarbons, and subsequent emulsification at the oil-water interface, forming cellular structures. The atmosphere would then have lost its reducing character.

Atmosphere↗