PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Evolution, Chemical”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1983

Chemical evolution and the origin of life: bibliography supplement 1981.

This bibliography is the twelfth annual supplement to the comprehensive bibliography on the same subject which was published in Space Life Sci. 2 (1970), 225-295; 3 (1972), 293-304; 4 (1973), 309-329 and in Origins of Life 5 (1974), 505-527; 6 (1975), 285-300; 7 (1976), 75-85; 8 (1977), 59-66; 9 (1978), 67-74; 10 (1980), 69-87; 10 (1980), 379-404; 11 (1981), 273-288; 12 (1982), 93-118.

Amino Acids↗
PubMed1980

Chemical evolution and the origin of life: bibliography supplement 1977.

This bibliography is the eighth annual supplement to the comprehensive bibliography on the same subject which was published in Space Life Sci. 2 (1970), 225-295; 3 (1972), 293-304; 4 (1973), 309-329 and in Origins of Life 5 (1974), 505-527; 6 (1975), 285-300; 7 (1976), 75-85; 8 (1977), 59-66; 9 (1978), 67-74.

Amino Acids↗
PubMed1981

Chemical evolution and the origin of life: bibliography supplement 1979.

This bibliography is the tenth annual supplement to the comprehensive bibliography on the same subject which was published in Space Life Sci. 2 (1970), 225-295; 3 (1972), 293-304; 4 (1973), 309-329 and in Origins of Life 5 (1974), 505-527; 6 (1975), 285-300; 7 (1976), 75-85; 8 (1977), 59-66; 9 (1978), 67-74; 10 (1980), 69-87; 10 (1980), 379-404.

Amino Acids↗
PubMed1984

Chemical evolution and the origin of life: bibliography supplement 1982.

The bibliography is the thirteenth annual supplement to the comprehensive bibliography on the same subject which was published in Space Life Sci. 2(1970), 225-295; 3(1972), 293-304; 4(1973), 309-329 and in Origins of Life 5(1974), 505-527; 6(1975), 285-300; 7(1976); 75-85; 8(1977), 59-66; 9(1978), 67-74; 10(1980), 69-87; 10(1980), 379-404; 11(1981), 273-288; 12(1982), 93-118; 13(1983), 61-80.

Earth, Planet↗
PubMed1985

Trace elements in chemical evolution, I.

Research on trace elements in chemical evolution is reviewed from three points of view. They are: the origin of the essentiality of trace elements in present biological systems; the possible roles of trace elements in chemical evolution; and the origin of enzymatic activity with metal ions, i.e., the origin of metalloenzymes.

Amino Acids↗
PubMed1997

Primary sources of phosphorus and phosphates in chemical evolution.

In this work we consider the role of phosphorus in chemical evolution from an interdisciplinary approach. First we briefly review the presence of this element in different cosmic sites, such as massive stellar cores, circumstellar and interstellar clouds, meteorites, lunar and Martian samples, interplanetary dust particles, cometary dust and planetary atmospheres. Thus we illustrate the fact that phosphorus seems to be, at the same time, scarce and ubiquitous in the solar system. Afterwards, by comparing the phosphorus content of our planet's main reservoirs with the amount of cometary and meteoritic matter captured by the primitive Earth, we conclude that comets may have provided a primary source for phosphorus compounds of prebiotic interest. Finally, we make a number of proposals aimed to gain observational supporting evidence to the above conclusion and other suggestions made in the article.

Cosmic Dust↗
PubMed1990

Impact constraints on the environment for chemical evolution and the continuity of life.

The Moon and the Earth were bombarded heavily by planetesimals and asteroids that were capable of interfering with chemical evolution and the origin of life. In this paper, we explore the frequency of giant terrestrial impacts able to stop prebiotic chemistry in the probable regions of chemical evolution. The limited time available between impacts disruptive to prebiotic chemistry at the time of the oldest evidence of life suggests the need for a rapid process for chemical evolution of life. The classical hypothesis for the origin of life through the slow accumulation of prebiotic reactants in the primordial soup in the entire ocean may not be consistent with constraints imposed by the impact history of Earth. On the other hand, rapid chemical evolution in cloud systems and lakes or other shallow evaporating water bodies would have been possible because reactants could have been concentrated and polymerized rapidly in this environment. Thus, life probably could have originated near the surface between frequent surface sterilizing impacts. There may not have been continuity of life depending on sunlight because there is evidence that life, existing as early as 3.8 Gyr ago, may have been destroyed by giant impacts. The first such organisms on Earth were probably not the ancestors of present life.

Earth, Planet↗
PubMed1987

Selection by differential molecular survival: a possible mechanism of early chemical evolution.

A model is proposed to account for selective chemical evolution, progressing from a relatively simple initial set of abiotic synthetic phenomena up to the elaborately sophisticated processes that are almost certainly required to produce the complex molecules, such as replicatable RNA-like oligonucleotides, needed for a Darwinian form of selection to start operating. The model makes the following assumptions: (i) that a small number of micromolecular substances were present at high concentration; (ii) that a random assembly mechanism combined these molecules into a variety of multimeric compounds comprising a wide repertoire of rudimentary catalytic activities; and (iii) that a lytic system capable of breaking down the assembled products existed. The model assumes further that catalysts supplied with substrates were significantly protected against breakdown. It is shown that, by granting these assumptions, an increasingly complex network of metabolic pathways would progressively be established. At the same time, the catalysts concerned would accumulate selectively to become choice substrates for elongation and other modifications that could enhance their efficiency, as well as their survival. Chemical evolution would thus proceed by a dual process of metabolic extension and catalytic innovation. Such a process should be largely deterministic and predictable from initial conditions.

Biochemical Phenomena↗
PubMed1985

A possible energetic role of mineral surfaces in chemical evolution.

The postulated roles of clays and other minerals in chemical evolution and the origin of life are reconsidered in terms of the interaction of these minerals with penetrating sources of energy such as ionizing radiation and mechanical stress. This interaction, including such facets as excitation, degradation, storage, and transfer, is considered here with regard to its profound potential for altering the capabilities of minerals to serve both as substrates for prebiological chemistry and as inorganic prototypic life forms. The interaction of minerals and energy in relationship to surface chemistry is discussed in terms of the spectroscopic properties of minerals, the interaction of energy with condensed phases, some commonly accepted concepts of heterogeneous catalysis in the absence of electronic energy inputs, and some commonly accepted and novel means by which surface activity might be enhanced in the presence of energy inputs. An estimation is made of the potential contribution of two poorly characterized prebiotic energy sources, natural radioactive decay and triboelectric energy. These estimates place a conservative lower limit on their prebiotic abundance. Also some special properties of these energy sources, relative to solar energy, are pointed out which might give them particular suitability for driving reactions occurring under geological conditions. Skeletal support for this broadly defined framework of demonstrated and potential relationships between minerals, electronic excitation, and surface reactivity, as applied to chemical evolution, is provided from the results of our studies on 1/1 clays. We have discovered and partially characterized a number of novel luminescent properties of these clays, that indicate energy storage and transfer processes in clays. These luminescent properties are interpreted in relationship to the electron spin resonance phenomena, to provide a basis for estimating the potential significance of energy storage and transduction in monitoring or driving clay surface chemistry. Consideration of the electronic structure of abundant minerals in terms of band theory and localized defect centers provides a predictive theoretical framework from which to rationalize the capacity of these materials to store and transduce energy. The bulk crystal is seen as a collecting antenna for electronic energy, with the defect centers serving as storage sites. The clay properties produced by isomorphic substitution appear to be intimately associated with all of the life-mimetic chemical processes that have been attributed to clays.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemical Phenomena↗
PubMed1983

Chemical evolution in space--a source of prebiotic molecules.

In Laboratory Astrophysics at Leiden University a laboratory analog for following the chemical evolution of interstellar dust in space shows that the dust contains the bulk of organic material in the universe. We follow the photoprocessing of low temperature (10 K) mixtures of ices subjected to vacuum ultraviolet radiation in simulation of interstellar conditions. The most important, but necessary, difference is in the time scales for photo-processing. One hour in the laboratory is equivalent to one thousand years in low density regions of space and as much as, or greater than, ten thousand to one million years in the depths of dense molecular clouds. The ultimate product of photoprocessing of grain material in the laboratory is a complex nonvolatile residue which is yellow in color and soluble in water and methanol. The molecular weight is greater than the mid-hundreds. The infrared absorption spectra indicate the presence of carboxylic acid and amino groups resembling those of other molecules of presumably prebiological significance produced by more classical methods. One of our residues, when subjected to high resolution mass spectroscopy gave a mass of 82 corresponding to C4H6H2 after release of CO2 and trace ammounts of urea suggesting amino pyroline rings. The deposit of prebiotic dust molecules occurred as many as 5 times in the first 500-700 million years on a primitive Earth by accretion during the passage of the solar system through a dense interstellar cloud. The deposition rate during each passage is estimated to be between 10(9) and 10(10) g per year during the million or so years of each passage; i.e., a total deposition of 1O(9)-10(10) metric tons of complex organic material per passage.

Cosmic Dust↗
PubMed1986

Chemical evolution of iron containing enzymes: mixed ligand complexes of iron as intermediary steps.

Activities of the iron complexes of evolutionary importance like K4[Fe(CN)6], K4[Fe(CN)5(gly)], and K4[Fe(CN)5(trigly)] have been tested towards some redox reactions of biological significance, namely, decomposition of hydrogen peroxide, dehydrogenation of NADH and ascorbic acid both coupled with reduction of methylene blue. It has been observed that the catalytic activities of iron (II) complexes towards the redox reactions studied at pH 9.18 followed the order, K4[Fe(CN)6] less than K4[Fe(CN)5(gly)] less than K4[Fe(CN)5(trigly)]. Decomposition of H2O2 catalysed by cyanocomplexes of iron (II) has been discussed through the formation of an innersphere complex in which loosly bound ligands like, glycine and triglycine are replaced by hydroperoxide ion. A tentative mechanism for the catalysed decomposition of H2O2 has been discussed. Based upon the experimental observations a hypothesis on the evolution of iron containing enzymes has been envisaged as: iron(II) ion----iron(II) cyanide complexes----mixed ligand iron(II) cyanide and amino acid complexes----iron(II) complexes of macromolecules----pŕoenzyme or early enzyme containing iron(II).

Biological Evolution↗