Recent evidences have suggested that compound-specific stable isotope analysis (CSIA) of amino acids has been employed as a new powerful method with that enables the estimation of trophic level of organisms in not only aquatic but also terrestrial food webs. This CSIA approach is based on contrasting the ¹⁵N-enrichment with each trophic level between two common amino acids: glutamic acid shows significant enrichment of +8.0‰ with each trophic level, whereas phenylalanine shows little enrichment of +0.4‰. These ¹⁵N-enrichments are well consistent in both aquatic and terrestrial organisms. The trophic level of organisms can be estimated within a small error as 1σ=0.12 for aquatic and 0.17 for terrestrial food webs, employing the eq.: [Trophic level]=(δ¹⁵N_{glutamic acid}-δ¹⁵N_{phenylalanine}+β)/7.6+1, where β represents the isotopic difference between these two amino acids in primary producers (-3.4‰ for aquatic cyanobacteria and algae, +8.4‰ for terrestrial C3 higher plants, and -0.4‰ for terrestrial C4 higher plants). Here, we briefly review this new method (i.e. CSIA of amino acids) and its application to natural organisms in terrestrial environments.

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Biomarkers have increasingly become common tools in the reconstruction of past environmental conditions. Molecular analyses of terrestrial biomarker lipids extracted from ocean, lake and bog sediments have been used for reconstructions of paleovegetation and associated paleoclimate histories. Stable carbon and hydrogen isotopic compositions of certain biomarkers provide powerful paleoclimate information. Stable carbon isotopic composition of C_<37> alkenone, which is specific biomarker of certain haptophyte algae, have been used to reconstruct concentration of atmospheric carbon dioxide in a past. Recently developed techniques for measuring compound-specific hydrogen isotope compositions of alkyl lipids has potential as a proxy of temperature, precipitation, relative humidity and hydrological cycles of the past.

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Dietary preferences of archaeological and paleontological animals have been conventionally investigated by stable carbon isotope ratio (δ¹³C) of collagen and tooth enamel in the fossil remains. However, no collagens in bones and teeth are generally preserved in fossil remains deposited older than million-order ages ago. On the other hand, it is known that lipids such as cholesterol and its diagenetic products are usually preserved in ancient fossil material. Therefore, the carbon isotope ratio of cholesterol (including its diagenetic products) in bones has been recently applied as alternative approach for reconstructing palaeodietary of animals. The advantages of this approach are that: (1) the δ¹³C value of cholesterol is correlated with that of bulk diet, (2) cholesterol can be detected from fossil bones older than million-order ages, (3) its diagenetic products such as cholestane do not occur naturally in skin lipids and soils. This paper reviews aspects of the carbon isotope signatures of bone cholesterol as a source of dietary information, and compared those to the conventional palaeodietary approaches by using the isotope analysis of bulk collagen and enamel.

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Substantial amounts of methane with seasonal variation have been discovered from discrete regions of Mars. What is the origin of methane on Mars-abiotic (geochemical) or biotic? Is the methane produced ancient or recently? Compound-specific stable carbon isotope analysis will be a potential tool for addressing this most intriguing question. NASA's Mars Science Laboratory (MSL), which will launch in autumn 2011, loads a Tunable Laser Spectrometer (TLS) into the Sample Analysis at Mars (SAM) instrument to conduct in-situ stable isotope analyses of volatile compounds and organic molecules on Mars with high precision and accuracy. This technique may provide an important, Astrobiological insight for understanding the past and present planetary processes and habitability of our Earth's brother planet.

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Intramolecular carbon isotopic analysis of biosynthetic products has potential to improve our knowledge on organic material cycles in a variety of environments. Glucose is one of the most important starting materials for biosynthetic products and its intramolecular carbon isotope distribution is essential information to understand carbon isotopic composition of biosynthetic products. Characteristics of intramolecular carbon isotope distribution in glucose from plant material and ethanol fermented from glucose are reviewed. At the moment the characteristic of intramolecular carbon isotope distribution in glucose have not been generalized. We need systematic investigation of intramolecular carbon isotope distribution in glucose and its descendents. GC-IRMS and ¹³C-NMR are promising techniques for intramolecular carbon isotopic measurement for biosynthetic products.

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Prokaryotic activities contribute to geochemical cycles on an Earth environment. To investigate roles of the prokaryotes in the environments, carbon and hydrogen isotopic compositions of lipid biomarkers can be a useful tool. This review describes carbon and hydrogen isotope fractionation associated with variety of metabolic and lipid synthetic pathways, factors controlling the isotope fractionation, and their applications into natural environments. Isotopic compositions of prokaryotic biomarkers potentially provide much information such as source organisms and environmental factors when they were biosynthesized.

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Several recent studies have suggested an innovative method for estimating the food sources, feeding habits, and trophic position of consumers in food webs, based on the compound-specific stable isotope analysis (CSIA) of amino acids. In this study, we used CSIA to study terrestrial mammals in a controlled feeding experiment with captive Asiatic black bears (Ursus thibetanus). The trophic position is estimated to be 1.7-1.9 for the bears, which is consistent with their actual trophic position (approximately 2). We also investigated the feeding habits of six wild Asiatic black bears (the same species as the captive bears; three were test animals suspected of feeding on trout and the others were controls) in the area around a rainbow trout farm. The flux of trout-derived proteins in the bear diet was calculated from the observed isotopic composition of amino acids. The results show that of the three test animals, two clearly fed on rainbow trout from the farm but other did not. Although this study is the first simple and systematic investigation of the ecological application of CSIA of amino acids to modern terrestrial mammals, we conclude that this technique is potentially useful in estimating the trophic position, food sources, and feeding habits of wildlife in ecological and biological studies.

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Molecular compositions of n-alkanes and their stable hydrogen isotope ratios (δD) were studied in atmospheric aerosols collected from Cape Hedo, Okinawa, Japan, to better understand the long-range atmospheric transport of organic aerosols from the Asian continent. The δD values of the C₂₂-C₃₃ n-alkanes range from -201 to -115‰, being similar to those of typical fossil fuels and contemporary higher plant leaf waxes in Far East Asia. A correlation between the δD values and the carbon preference index (CPI) suggests that these n-alkanes originated from fossil fuel combustion residues and/or terrestrial higher plant waxes. The concentrations of fossil fuel-derived n-alkanes increased from mid-November 2009 to February 2010, which is consistent with the enhanced emission of coal-burning aerosols during the winter in China. δD values of the fossil fuel-derived n-alkanes (-174±7‰) in the atmospheric aerosols from Okinawa are much lower (by up to 95‰) than those from Tokyo and Sapporo, Japan, suggesting that they are derived from multiple sources in East Asia and are delivered by complex transport processes.

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We evaluated methyl (MCF) and ethyl chloroformate (ECF) derivatizations as rapid and simple esterification techniques for the compound-specific stable isotope analysis (CSIA) of fatty acids. Although the fatty acids were esterified very rapidly (within 5min) at room temperature in both derivatizations, the yield of derivatives depended strongly on the chemical constituent and pH of the derivative reagent and the carbon-chain length of fatty acids. In this study, quantitative esterification was observed during ethyl esterification with ECF:ethanol:pyridine (2:60:5, v:v). In this esterification process, the accuracy of the carbon isotope (δ¹³C) measurements was always better than 0.3‰.

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The distribution and carbon isotope composition of 17β(H), 21β(H)-bishomohopanoic acid (ββC₃₂-HA) were investigated in Miocene to recent marine sediments from Site 1178 of ODP Leg 190, Nankai Trough, offshore Shikoku, Japan. The concentration of ββC₃₂-HA tends to be higher in accreted sediments, which are characterized by a large contribution of terrestrial organic matter. The δ¹³C values of ββC₃₂-HA are lighter in accreted sediments than in slope sediments, indicating different sources to some degree. The constant δ¹³C values within the slope sediments and within the accreted sediments indicate that the sources of ββC₃₂-HA were unchanged during the deposition of each unit. In accreted sediments, the δ¹³C value of ββC₃₂-HA is similar to that in soil components, suggesting that the hopanoic acids in accreted sediments may be mainly terrestrial organic compounds derived from the oxidation products of bacteriohopanepolyols on land.

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A complex mixture of organic compounds, such as amino acids, polycyclic aromatic hydrocarbons, and insoluble organic matter, has been found in carbonaceous chondrites. Extensive studies have revealed that these organic compounds are typically enriched in D, ¹³C, ¹⁵N, and ¹⁸O compared to terrestrial counterparts. These isotopic characteristics are generally regarded as the evidence for their interstellar origin where organic compounds are extremely enriched in heavy isotopes, especially in D. However, because the degree of the D-enrichment significantly differs between interstellar and meteoritic organic compounds, if the latter do have an interstellar origin, some physical/chemical processes which they have experienced after their formation should lower the original enrichments in heavy isotopes for organic compounds. Several laboratory studies have been performed to investigate isotopic fractionations brought by various processes which meteoritic organic compounds may have experienced in space, such as interstellar environments and meteorite parent body. In this paper, I will review the previous laboratory experiments as to isotope fractionation of organic compounds in extraterrestrial environments such as molecular clouds and meteorite parent bodies.

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Short sediment cores were taken from four lakes in Nagano Prefecture, Japan. They are Nishina Three Lakes (Aoki, Nakatsuna and Kizaki) situated at the east foot of the Japan Northern Alps, and Nojiri located to the northeast, about 20km apart from Nagano City. Sediments were analyzed for anthropogenic polynuclear aromatic hydrocarbons (PAHs). Vertical distribution and their accumulations in individual lake sediments were determined since their concentration apparently increased. Despite scarce population and absence of considerable emission sources around the Nishina Three Lakes, PAHs in the sediment cores show significantly high concentration, maximizing in the mid-depth of the cores, which are in the order Kizaki>Nakatsuna>Aoki and evidently higher than that of Nojiri. Particularly high concentration was observed in Kizaki, where it amounted to 3.5μg/g dry sediment. Accumulation of PAHs in the Nishina Three Lake sediments was in the range of 4-8μg/cm², whereas it remained around 1.5μg/cm² in the Nojiri sediments. The Nishina Three Lakes are surrounded by mountains as high as 1,300-1,600m, from which surface water may flow down into the lakes. On the contrary, the catchments of Nojiri are narrow compared with the surface area of the lake basin. Thus an explanation may be possible that PAHs once deposited on the catchments may contribute much to those in the lake sediments.

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Typical geoporphyrins with a skeleton of 32 carbons are accounted for by a mechanism involving decarboxylation of chlorophylls, but the presence has been shown of geoporphyrins with carbon number greater than 32. It was proposed that these high carbon number porphyrins were derived from chlorophylls with extended alkyl substituents, e.g. bacteriochlorophylls, or from a random process such as transalkylation. In this study, to investigate the formation process of these high carbon number geoporphyrins, heating experiments of four vinylporphyrins, which possess 1 to 4 3-methyl-4-vinylpyrrole units, were performed. Chromic acid oxidation of the heating products of vinylporphyrins afforded a characteristic profile of C₈ maleimide formation by one-carbon extension at a side chain of model substrates. We provided the first evidence that a 3-methyl-4-vinylpyrrole unit afforded 2-methyl-3-n-propylmaleimide as the predominant product among the side-chain extension products formed. On the other hand, a 3-ethyl-4-methylpyrrole unit afforded 2,3-diethylmaleimide as the major extension product.

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