Akira Shimoyama

Clay and the origin of life

Research concerning the possible role of clay in chemical evolution is reviewed. The probable importance of clays in the origin of life is assessed.

Possible Surface Reactions on Mars: Implications for Viking Biology Results

The results of two of the three biology experiments carried out on the Viking Mars landers have been simulated. The mixture of organic compounds labeled with carbon-14 used on Mars released carbon dioxide containing carbon-14 when reacted with a simulated martian surface and atmosphere exposed to ultraviolet light (labeled release experiment). Oxygen was released when metal peroxides or superoxides were treated with water (gas exchange experiment). The simulations suggest that the results of these two Viking experiments can be explained on the basis of reactions of the martian surface and atmosphere.

Amino acids in a carbonaceous chondrite from Antarctica

SummaryA carbonaceous chondrite from the Antarctic, referred to as the Allan Hills meteorite 77306, appears to be free from terrestrial organic contamination. The presence of both protein and non-protein amino acids and an equal abundance of D- and L-enantiomers of amino acids, is testimony to the extraterrestrial nature of these compounds.

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

SummaryThe adsorption of protein and non-protein amino acids by Na-mont-morillonite 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,α-alanine andβ-alanine,α-amino-butyric acid and γ-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 adsorp-tion ofβ-and γ-amino acids, respectively, than theirα-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.

Search for amino acids in apollo returned lunar soil

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.

Adsorption of amino acid entantiomers by Na-montmorillonite

In separate experiments, (D,L)~-alanine, (D,L) s-aminobutyric acid, (D,L) valine and (D,L) norvaline were incubated with Na-montmorillonite at three hydrogen ion concentrations. The recovered nonadsorbed and adsorbed fractions were analyzed by ion exchange chromatography for amino acid quantities, and by gas chromatography and liquid chromatography for relative enantiomer abundances. A mass balance was obtained from this data, indicating 100% recovery of the amino acids and also recovery of equal quantities of D and L isomers.

Evidence for amino acids in hydrolysates of compounds formed by ionizing radiations. I. Aqueous solutions of HCN, NH4CN, and NaCN.

Dilute, O2-free aqueous cyanides were exposed to multikilorad doses of a radioactive cobalt source. After the removal of unreacted cyanides and of volatile radiolytic products, the residue was ydrolyzed and the resulting material analyzed for amino acids. The results show the presence of five protein amino acids and five amino acids which do not occur in natural proteins. The amino acids of enantiomeric derivatives separated on an optically active column, appeared to consist of approximately equal amounts of D and L isomers. Radiation-chemical yields of amino acids were determined at various radiation doses. The results obtained support the previous findings that the free-radical initiated process is the source of oligomers which on hydrolysis release the amino acids.

Possible Selective Adsorption of Enantiomers by Na-Montmorrillonite

If clay minerals can preferentially adsorb two enantiomers of an organic molecule, they might provide a mechanism for concentration of homogeneous optical isomers. The conflicting reports concerning the selective adsorption of the L-enantiomer of amino acids by clays prompted us to examine the preferential adsorption of optical isomers of amino acids. Racemic amino acids were incubated with Na-montmorillonite at 100% CEC at three hydrogen ion concentrations. The amino acids used were (D,L) α-alanine, (D,L) α-aminobutyric acid, (D,L) valine, (D,L) norvaline. Quantities of amino acids adsorbed on the clay as well as those non-adsorbed were determined by ion exchange chromatography. Analysis of enantiomers was by gas chromatography. A mass balance was obtained from these experiments, leaving no question that 100% of the amino acids was recovered. Differences in the quantities of D and L enantiomers in any of the fractions were no larger than a few percent. Although a large difference in the adsorption of amino acid enantiomers was not observed, our analysis may indicate a small preferential adsorption by Na-montmorillonite.

Amino acids from the late precambrian thule group greenland

Amino acids were recovered at a concentration level of 10−9 M/g from the interior of chert and dolomite of the Late Precambrian Thule Group. Examination of the stability of amino acids in chert under dry-heating conditions suggests that these amino acids have been preserved with a predominance of L-enantiomers in the Precambrian chert. Enantiomer analysis of amino acids in dolomite showed a thermal effect resulting from a late Precambrian igneous intrusion. This evidence indicates that the amino acids isolated from the Thule samples were chemical fossils and not recent contaminants.

Organic analysis of the Antarctic carbonaceous chondrites

In the search for extraterrestrial evidence of chemical evolution, organic analysis of carbonaceous chondrites has proven to be very fruitful. Recently, the discovery of a large number of meteorites in Antarctica has provided new opportunities to further our knowledge of meteorite composition and, hence, the conditions during the formative stages of the solar system. We have acquired two carbonaceous chondrites for analysis and have identified amino acids of extraterrestrial origin in the Allan Hills (77306) and the Yamato (74662). Chromatographic analysis combined with mass spectrometry indicates the presence of more than 25 different amino acids. More importantly, these Antarctic meteorites appear to be uncontaminated by terrestrial organic matter.