Kensei Kobayashi

Effect of nitrogen content on magnetic properties of Sm/sub 2/Fe/sub 17/N/sub x/ (0<x<6)

Effects of nitrogen content on crystal structure and magnetic properties have been investigated in Sm/sub 2/Fe/sub 17/N/sub x/. Sm/sub 2/Fe/sub 17/N/sub x/ specimens with 0 >

Prebiotic synthesis from CO atmospheres: Implications for the origins of life

Most models of the primitive atmosphere around the time life originated suggest that the atmosphere was dominated by carbon dioxide, largely based on the notion that the atmosphere was derived via volcanic outgassing, and that those gases were similar to those found in modern volcanic effluent. These models tend to downplay the possibility of a strongly reducing atmosphere, which had been thought to be important for prebiotic synthesis and thus the origin of life. However, there is no definitive geologic evidence for the oxidation state of the early atmosphere and bioorganic compounds are not efficiently synthesized from CO2 atmospheres. In the present study, it was shown that a CO-CO2-N2-H2O atmosphere can give a variety of bioorganic compounds with yields comparable to those obtained from a strongly reducing atmosphere. Atmospheres containing carbon monoxide might therefore have been conducive to prebiotic synthesis and perhaps the origin of life. CO-dominant atmospheres could have existed if the production rate of CO from impacts of extraterrestrial materials were high or if the upper mantle had been more reduced than today.

AMINO ACID FORMATION IN GAS MIXTURES BY HIGH ENERGY PARTICLE IRRADIATION

Amino acids were formed from carbon monoxide, nitrogen and water, which are possible constituents of the primitive earths atmosphere, by irradiation with high energy particles (components of cosmic rays). Glycine yield was proportional to the total energy deposited to the gas mixture, and its G-value was as high as 0.02 when the carbon monoxide/nitrogen ratio was 1. Based on an estimate of the effective energies of various types of energy sources available in the primitive earths atmosphere for amino acid synthesis, it is suggested that cosmic rays were one of the most important energy sources for the synthesis of amino acids on the primitive earth.

Biogeography and biodiversity in sulfide structures of active and inactive vents at deep-sea hydrothermal fields of the Southern Mariana Trough.

ABSTRACT The abundance, diversity, activity, and composition of microbial communities in sulfide structures both of active and inactive vents were investigated by culture-independent methods. These sulfide structures were collected at four hydrothermal fields, both on- and off-axis of the back-arc spreading center of the Southern Mariana Trough. The microbial abundance and activity in the samples were determined by analyzing total organic content, enzymatic activity, and copy number of the 16S rRNA gene. To assess the diversity and composition of the microbial communities, 16S rRNA gene clone libraries including bacterial and archaeal phylotypes were constructed from the sulfide structures. Despite the differences in the geological settings among the sampling points, phylotypes related to the Epsilonproteobacteria and cultured hyperthermophilic archaea were abundant in the libraries from the samples of active vents. In contrast, the relative abundance of these phylotypes was extremely low in the libraries from the samples of inactive vents. These results suggest that the composition of microbial communities within sulfide structures dramatically changes depending on the degree of hydrothermal activity, which was supported by statistical analyses. Comparative analyses suggest that the abundance, activity and diversity of microbial communities within sulfide structures of inactive vents are likely to be comparable to or higher than those in active vent structures, even though the microbial community composition is different between these two types of vents. The microbial community compositions in the sulfide structures of inactive vents were similar to those in seafloor basaltic rocks rather than those in marine sediments or the sulfide structures of active vents, suggesting that the microbial community compositions on the seafloor may be constrained by the available energy sources. Our findings provide helpful information for understanding the biogeography, biodiversity and microbial ecosystems in marine environments.

Abundance of Zetaproteobacteria within crustal fluids in back-arc hydrothermal fields of the Southern Mariana Trough

To extend knowledge of subseafloor microbial communities within the oceanic crust, the abundance, diversity and composition of microbial communities in crustal fluids at back-arc hydrothermal fields of the Southern Mariana Trough (SMT) were investigated using culture-independent molecular techniques based on 16S rRNA gene sequences. Seafloor drilling was carried out at two hydrothermal fields, on- and off-ridge of the back-arc spreading centre of the SMT. 16S rRNA gene clone libraries for bacterial and archaeal communities were constructed from the fluid samples collected from the boreholes. Phylotypes related to Thiomicrospira in the Gammaproteobacteria (putative sulfide-oxidizers) and Mariprofundus in the Zetaproteobacteria (putative iron-oxidizers) were recovered from the fluid samples. A number of unique archaeal phylotypes were also recovered. Fluorescence in situ hybridization (FISH) analysis indicated the presence of active bacterial and archaeal populations in the fluids. The Zetaproteobacteria accounted for up to 32% of the total prokaryotic cell number as shown by FISH analysis using a specific probe designed in this study. Our results lead to the hypothesis that the Zetaproteobacteria play a role in iron oxidation within the oceanic crust.

Chapter 8 An experimental approach to chemical evolution in submarine hydrothermal systems

The discovery of submarine hydrothermal vents in the late 1970s (Corliss et al., 1979) stimulated geophysical, geochemical, microbiological, ecological and ore deposit research on submarine hydrothermal systems. Since these systems represent reducing, energy-rich, and metal ion-rich conditions in the present terrestrial environment, they are considered to be ideal sites for present-day abiogenic synthesis of organic compounds and have been suggested as a possible environment for chemical evolution toward the origin of life (Corliss et al., 1981; Baross and tIoffman,1985). However, it has also been suggested before the discovery of submarine hydrothermal vents that an important relationship may exist between the evolution of the Earths crust such as a hydrogeothermal zone associated with axes of plate spreading and the process of chemical evolution (Ingmanson and Dowler, 1977; Degens, 1979). From the point of view of chemical evolution, reducing environments are attractive because amino acids can be synthesized abiotically from reduced gas mixtures with spark discharges (Miller, 1953), heat (Harada and Fox, 1964), ultraviolet light (Sagan and Khare, 1971), and shock waves (Bar-Nun et al., 1970). These experiments demonstrate that if the primitive earth atmosphere was reduced, consisting of a mixture of methane, ammonia and water, amino acids and other organic compounds could have been easily obtained with the available energy sources on the early Earth. Recent studies on the formation of planets have suggested, however, that high velocity impacts of small bodies into a growing planet can result in impact-degassing of volatiles and formation of an impact-induced, high temperature atmosphere (Abe, 1986; Holloway, 1988; Kasting, 1990; Matsui and Abe, 1986a,b). According to this hypothesis, such an atmosphere contains carbon monoxide or carbon dioxide as a major carbon source. In addition, results of photochemical studies with an early Earth atmosphere show that the presence of hydroxyl radicals from the photodissociation of H20, together with the greater flux of UV radiation from the young sun, would have limited the half

Abiotic synthesis of amino acids and imidazole by proton irradiation of simulated primitive earth atmospheres

Proton irradiation of simulated primitive earth atmosphere was performed, and amino acids and imidazole were analyzed. A mixture of carbon monoxide and nitrogen over water was irradiated by high energy protons (3 MeV, 0.6 µA) generated by a Van de Graaff accelerator for 2–5 h. Various kinds of proteinous and non-proteinous amino acids were detected in the irradiation products. Imidazole present in the irradiation products was also detected by high-performance liquid chromatography and mass spectrometry. The present results suggest that compounds of biological importance such as amino acids could be synthesized from primitive earth atmosphere by radiation of cosmic rays and/or solar flare particles.

Formation of bioorganic compounds in simulated planetary atmospheres by high energy particles or photons

Various types of organic compounds have been detected in Jupiter, Titan, and cometary coma. It is probable that organic compounds were formed in primitive Earth and Mars atmospheres. Cosmic rays and solar UV are believed to be two major energy sources for organic formation in space. We examined energetics of organic formation in simulated planetary atmospheres. Gas mixtures including a C-source (carbon monoxide or methane) and a N-source (nitrogen or ammonia) was irradiated with the followings: High energy protons or electrons from accelerators, gamma-rays from 60Co, UV light from a deuterium lamp, and soft X-rays or UV light from an electron synchrotron. Amino acids were detected in the products of particles, gamma-rays and soft X-rays irradiation from each gas mixture examined. UV light gave, however, no amino acid precursors in the gas mixture of carbon monoxide, nitrogen and nitrogen. It gave only a trace of them in the gas mixture of carbon monoxide, ammonia and water or that of methane, nitrogen and water. Yield of amino acid precursors by photons greatly depended on their wavelength. These results suggest that nitrogen-containing organic compounds like amino acid precursors were formed chiefly with high energy particles, not UV photons, in Titan or primitive Earth/Mars atmospheres where ammonia is not available as a predominant N-source.

An Experimental Approach to Chemical Evolution in Submarine Hydrothermal Systems

The discovery of submarine hydrothermal vents in the late 1970’s (Corliss et al., 1979) stimulated geophysical, geochemical, microbiological, ecological and ore deposit research on submarine hydrothermal systems. Since these systems represent reducing, energy-rich, and metal ion-rich conditions in the present terrestrial environment, they are considered to be ideal sites for present-day abiogenic synthesis of organic compounds and have been suggested as a possible environment for chemical evolution toward the origin of life (Corliss et al., 1981; Baross and Hoffman, 1985). However, it has also been suggested before the discovery of submarine hydrothermal vents that an important relationship may exist between the evolution of the Earth’s crust such as a hydrogeothermal zone associated with axes of plate spreading and the process of chemical evolution (Ingmanson and Dowler, 1977; Degens, 1979).

Excitation energy transfer and population dynamics in a quantum dot system induced by optical near-field interaction

Energy transfer and exciton population dynamics in a two-quantum dot system coupled with a phonon heat-bath system are examined using the density matrix formalism. In such a system, optical near-field interactions induce energy transfer between quantum dots, and exciton–phonon interactions guarantee the unidirectional excitation energy transfer. Our theoretical investigation shows that the population dynamics change drastically depending on the coupling strengths due to optical near-field interactions and exciton–phonon heat-bath interactions. The temperature effect promotes frequent energy back-transfer from the heat-bath to the quantum dot system. Applying our theoretical formulation, we numerically calculate the time evolution of populations, and estimate energy transfer time or state-filling time for a CuCl quantum dot system. The estimated time is suitable for the elements in our proposed optical nano-switch and nano-photonic devices.