New pyrolytic and spectroscopic data on Orgueil and Murchison insoluble organic matter: A different origin than soluble?

Pyrolysis with and without tetramethylammonium hydroxide (TMAH), vacuum pyrolysis, and solid state ¹⁵N nuclear magnetic resonance (NMR) were used to examine the macromolecular insoluble organic matter (IOM) from the Orgueil and Murchison meteorites. Conventional pyrolysis reveals a set of poorly functionalized aromatic compounds, ranging from one to four rings and with random methyl substitutions. These compounds are in agreement with spectroscopic and pyrolytic results previously reported. For the first time, TMAH thermochemolysis was used to study extraterrestrial material. The detection of aromatics bearing methyl esters and methoxy groups reveals the occurrence of ester and ether bridges between aromatic units in the macromolecular network.No nitrogen-containing compounds were detected with TMAH thermochemolysis, although they are a common feature in terrestrial samples. Along with vacuum pyrolysis results, thermochemolysis shows that nitrogen is probably sequestered in condensed structures like heterocyclic aromatic rings, unlike oxygen, which is mainly located within linkages between aromatic units. This is confirmed by solid state ¹⁵N NMR performed on IOM from Orgueil, showing that nitrogen is present in pyrrole, indole, and carbazole moieties.These data show that amino acids are neither derived from the hydrolysis of IOM nor from a common precursor. In order to reconcile the literature isotopic data and the present molecular results, it is proposed that aldehydes and ketones (1) originated during irradiation of ice in space and (2) were then mobilized during the planetesimal hydrothermalism, yielding the formation of amino acids. If correct, prebiotic molecules are the products of the subsurface chemistry of planetesimals and are thus undetectable through astronomical probes.     

Amino acid abundances and stereochemistry in hydrothermally altered sediments from the Juan de Fuca Ridge, northeastern Pacific Ocean.

The Juan de Fuca Ridge is a hydrothermally active, sediment covered, spreading ridge situated a few hundred kilometres off the west coast of North America in the northeastern Pacific Ocean. Sediments from seven sites drilled during the Ocean Drilling Program (ODP) Legs 139 and 168 were analyzed for total hydrolyzable amino acids (THAA), individual amino acid distributions, total organic C (TOC) and total N (TN) contents. The aim was to evaluate the effects of hydrothermal stress on the decomposition and transformation of sedimentary amino acids. Hydrolyzable amino acids account for up to 3.3% of the total organic C content and up to 12% of the total N content of the upper sediments. The total amounts of amino acids decrease significantly with depth in all drilled holes. This trend is particularly pronounced in holes with a thermal gradient of around 0.6 degrees C/m or higher. The most abundant amino acids in shallow sediments are glycine, alanine, lysine, glutamic acid, valine and histidine. The changes in amino acid distributions in low temperature holes are characterized by increased relative abundances of non-protein beta-alanine and gamma-aminobutyric acid. In high temperature holes the amino acid compositions are characterized by high abundances of glycine, alanine, serine, ornithine and histidine at depth. D/L ratios of samples with amino acid distributions similar to those found in acid hydrolysates of kerogen, indicate that racemization rates of amino acids bound by condensation reactions may be diminished.     

银在含氨基酸热液中的物理化学行为

考虑到银主要富集在中低温热液阶段，同时考虑到成矿溶液中氨基酸的存在及其不同类型，对含银矿物样品在中性、碱性和酸性氨基酸热液中的物理化学行为分别进行了实验研究。结果表明，含有酸性氨基酸（谷氨酸）的热水溶液，比仅含ＮａＣｌ的热卤水、含碱性氨基酸（赖氨酸）和中性氨基酸（氨基乙酸和氨基丙酸）的热水溶液，更有利于银的活化和迁移。实验同时表明，银与各氨基酸形成的易溶配位化合物的稳定性受到温度的强烈影响。在２５℃左右，是银－氨基酸配位化合物稳定存在的最适宜温度条件；在１００℃以上，随温度的逐渐升高，银在含氨基酸热液中的溶出量明显减少。表明银－氨基酸的配位化合物强烈地分解，而使银得以更多地沉积。银在含氨基酸热液中的这种物理化学行为，和铅在含有酸性氨基酸（谷氨酸）、铜在含有碱性氨基酸（赖氨酸）热液中的活化、迁移与沉积作用不无相似之处     

Summary and implications of reported amino acid concentrations in the Murchison meteorite

A study of literature reports of the concentrations of amino acids in extracts from the Murchison meteorite shows that many of the concentration ratios are constant. There are two possible interpretations of these ratios. One is that they are controlled by the pathways through which the amino acids formed, from which it follows that the amino acids are distributed in the same proportions throughout the meteorite. The other interpretation is that the ratios result from the analytical procedures used to extract the amino acids from the meteorite. These methods rely heavily on high-temperature (100 degrees C) aqueous extraction and subsequent high-temperature acid hydrolysis. A correlation was observed in the present study between the relative concentrations of several amino acids in the meteorite extracts and their relative aqueous solubilities at 100 degrees C (alanine, valine, leucine, isoleucine, norleucine, aspartic acid, glutamic acid and glycine). The extract solutions are dilute, and far from the saturation limits, but these correlations suggest that the sampling procedure affects directly the reported concentrations for these amino acids. Ratios of the concentration of serine to those of glycine are also constant but cannot be accounted for solely by relative solubilities, and, as suggested elsewhere, serine as well as phenylalanine and methionine may be terrestrial contaminants. Data for beta-alanine, alpha-aminobutyric acid, proline, sarcosine, alloisoleucine, beta-aminoisobutyric acid, beta-aminobutyric acid, and threonine also show constant abundances relative to glycine, but lack of solubility data at extraction conditions prohibits evaluating the extent of possible sampling bias for these amino acids. If the extraction process does not bias the results, and all extractable amino acids are removed from meteorite samples, then the properties of amino acids which control both their solubilities and their concentrations in the meteorite need to be established. The possibility of sampling bias needs to be tested experimentally before concluding that extraction is complete, and that the constant relative abundances indicate that the relative concentrations of amino acids are homogeneous in the meteorite.     

Amino acid composition of organic matter associated with carbonate and non-carbonate sediments

Amino acids comprise from 15 to 36% by weight of humic substances from carbonate and non-carbonate sediments. Humic and fulvic acids extracted from carbonate sediments are characterized by an amino acid composition consisting primarily of the acidic amino acids, aspartic and glutamic acid. Humic substances from non-carbonate sediments have a distinctly different amino acid composition consisting primarily of glycine and alanine. Amino acid analyses of various molecular weight fractions of fulvic acids extracted from carbonates show that lower molecular weight fractions have appreciably higher relative abundances of the acidic amino acids compared to higher molecular weight fractions. Based on typical values for carboxyl group content in humic substances, acidic amino acids may be a significant contributor of these functional groups. Carbonate surfaces appear to selectively adsorb aspartic acid-enriched organic matter while non-carbonates do not have this property.     

Influence of Murchison or Allende minerals on hydrogen-deuterium exchange of amino acids

Deuterium-enriched amino acids occur in the Murchison carbonaceous chrondrite. This meteorite underwent a period of aqueous alteration with isotopically light water. With the objective of setting limits on the conditions of aqueous alteration, the exchange of the carbon-bonded hydrogen atoms of amino acids with D2O has been studied from 295 to 380 K as a function of time and meteorite/heavy water ratio. The amount of Murchison or Allende dust present has a significant effect on the rate and amount of hydrogen-deuterium exchange observed. At elevated temperatures, the alpha-hydrogens of all the amino acids studied were found to exchange with deuterium. In glycine and aspartic acid, this process resulted in total exchange of the carbon-bonded hydrogen. A completely deuterated isotopomer of alanine was produced in significant quantities only when the rock/water ratio was greater than 0.5. No exchange of carbon-bonded hydrogens was observed in the case of amino acids which do not possess an alpha-hydrogen atom. The rates of H/D exchange for amino acids observed here did not correspond to deuterium enrichment of the amino acids in the Murchison meteorite. These results suggest that H/D exchange with water had a negligible effect on the observed deuterium enrichment of amino acids found in Murchison and that the temperature at which the amino acids were exposed to liquid water was close to 273 K.     

Modification of amino acids at shock pressures of 3.5 to 32 GPa

Amino acids were subjected to shock impact over a pressure range of 3.5 to 32 GPa both within and without meteoritic mineral matrices. The extent of amino acid destruction, racemization, and conversion to secondary amino acids was examined. Abundances of parent compounds decreased by a factor of 10(3) over this pressure range. Racemization also occurred, but some residual optical activity remained in the amino acids surviving shocks up to 32 GPa. Secondary amino acids formed in the high peak pressure range; those identified were beta-alanine, glycine, alanine, gamma-aminobutyric acid, and beta-aminoisobutyric acid. At 30 GPa, the abundances of these daughter compounds exceeded those of the remaining initial amino acids. As the concomitant effects of high mechanical stress and temperature accompanying shocks cannot be separated in this work, their relative contribution to the observed transformations cannot be estimated. The survival of amino acids in shock experiments suggests that, after formation or emplacement of amino acids in carbonaceous chondrite parent bodies, these objects never experienced impact velocities greater than 5 km/s, which suffices to generate 30 GPa for typical silicate/silicate impacts. These results also provide guidelines for choosing appropriate capture media for interplanetary dust particles on Earth-orbiting platforms.     

Late Precambrian and Early Cambrian in the East European platform

Carbon suboxide polymers reacted with hydroxylamine and ammonia under UV irradiation in aqueous medium to form amino acids such as glycine, alanine, serine, threonine, aspartic acid and glutamic acid. This finding suggests that carbon suboxide is a new candidate as starting material for the synthesis of biomolecules on the primitive earth.     

我国“北京人”、“兰田人”和“元谋人”产地骨化石中氨基酸的地球化学

氨基酸是生命物质中普遍存在的一类重要的有机化合物,它是构成蛋白质的“砖块”。一个最简单的氨基酸分子至少必须含有一个羧基和一个氨基的官能团。在生物的蛋白质中通常只包括有二十种氨基酸,叫做蛋白氨基酸。但是自然界还存在其它种类的氨基酸,因为它们一般不存在于蛋白质中,所以叫做非蛋白氨基酸。除了最简单的甘氨酸外,所有的氨基酸都含有一个以上的不对称的碳原子。含有一个不对称碳原子的氨基酸可以存在L和D型两种结构的对映体。所有的蛋白质氨基酸都属L构型。     

Dissolved free amino acids in interstitial waters of Georgia salt marsh soils

The patterns of concentration of dissolved free amino acids (DFAA) are different and more variable in pore water of soils from a Georgia salt marsh than in most surface waters. Elevated concentrations of DFAA (up to 8850 nmoles liter^?1) and high relative levels of alanine and glutamic acid suggest that bacteria may produce these amino acids. In addition to the common protein amino acids, an unidentified compound was present and was the dominant free amino acid in some sections. This compound appeared to be specific to pore waters as it was not observed in surface waters or in hydrolysates of sediments, bacteria or plants from the marsk.     

Nitrogen-containing compounds in two CR2 meteorites: N composition, molecular distribution and precursor molecules

Amino acids, amines and aldehydes were obtained from the water extracts of two CR2 carbonaceous chondrites from Antarctica and analyzed for their molecular and ¹⁵N isotopic content. These compounds were found to differ significantly from those of CM chondrites in both overall abundances and molecular distribution. The amino acids suites comprise a preponderant abundance of linear, 2-H amino acids, show rapid non-linear decrease with the compounds’ increasing chain length and include protein amino acids never identified in meteorites before, such as threonine, tyrosine and phenylalanine. The presence of tertiary amines as well as a diverse, large abundance of aldehydes and ketones also distinguishes both CR2 organic suites. The δ¹⁵N values determined for CR2 amino acids have a distribution between molecular subgroups that is opposite to the one of their δD values, with 2-H amino acids having higher δ¹⁵N and lower δD values than 2-methyl amino acids, while the opposite is true for 2-methyl amino acids. Based on theoretical data, these isotopic findings would place the formation of the two amino acid groups or their direct precursors at different ISM stages of star formation.     

Characterization of melanoidins by IR spectroscopy—I. Galactose-glycine melanoidins

A comparative IR spectral study was conducted with synthetic melanoidins which were prepared from various ratios of sugars and amino acids and a pseudomelanoidin which was prepared from sugar only. A significant resemblance was observed between the pseudomelanoidin and the melanoidin prepared from a high (9:1) sugar ratio (type 1). Another series of melanoidins (type 2) consists of those prepared from an “excess” of amino acid (9:1 and 1:1).Type 1 showed the presence of carbonyl and hydroxyl groups as well as aromatic vibrations. The same groups were detected in the spectrum of the pseudomelanoidin. These features were observed in a very low concentration in the type 2 melanoidins.Carboxylic groups are present in pseudomelanoidin and in both types of the melanoidins. However, the acid strength of this group is high in melanoidin of type 2, but low in type 1 and in the pseudomelanoidin.The nitrogen atom which is involved in the melanoidin structure is present as a tertiary amine.Heat treatment of KBr discs containing glycine, galactose and a mixture thereof revealed that galactose was converted into pseudomelanoidin; a mixture of galactose-glycine yielded the corresponding melanoidin of type 2; no reaction was observed with glycine.     

我国东部几个中新生代盆地泥质岩中的氨基酸

从现代沉积物到前寒武纪的沉积岩中都发现有氨基酸的存在。关于它们的组成、含量及其地质意义在许多文献中都曾涉及到,特别是对近代各种环境沉积中的氨基酸及其在成岩作用过程中的变化,已经积累了相当多的分析资料。本文对以渤海第三纪沉积盆地为主的我国东部地区中新生代泥质岩样品进行了氨基酸的分析,并初步讨论了这些分析结果与沉积环境的关系。     

Resolving the bulk δN values of ancient human and animal bone collagen via compound-specific nitrogen isotope analysis of constituent amino acids

Stable nitrogen isotope analysis is a fundamental tool in assessing dietary preferences and trophic positions within contemporary and ancient ecosystems. In order to assess more fully the dietary contributions to human tissue isotope values, a greater understanding of the complex biochemical and physiological factors which underpin bulk collagen δ¹⁵N values is necessary. Determinations of δ¹⁵N values of the individual amino acids which constitute bone collagen are necessary to unravel these relationships, since different amino acids display different δ¹⁵N values according to their biosynthetic origins. A range of collagen isolates from archaeological faunal and human bone (n = 12 and 11, respectively), representing a spectrum of terrestrial and marine protein origins and diets, were selected from coastal and near-coastal sites at the south-western tip of Africa. The collagens were hydrolysed and δ¹⁵N values of their constituent amino acids determined as N-acetylmethyl esters (NACME) via gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The analytical approach employed accounts for 56% of bone collagen nitrogen. Reconstruction of bulk bone collagen δ¹⁵N values reveals a 2‰ offset from bulk collagen δ¹⁵N values which is attributable to the δ¹⁵N value of the amino acids which cannot currently be determined by GC-C-IRMS, notably arginine which comprises 53% of the nitrogen unaccounted for (23% of the total nitrogen). The δ¹⁵N values of individual amino acids provide insights into both the contributions of various amino acids to the bulk δ¹⁵N value of collagen and the factors influencing trophic position and the nitrogen source at the base of the food web. The similarity in the δ¹⁵N values of alanine, glutamate, proline and hydroxyproline reflects the common origin of their amino groups from glutamate. The depletion in the δ¹⁵N value of threonine with increasing trophic level indicates a fundamental difference between the biosynthetic pathway of threonine and the other amino acids. The δ¹⁵N value of phenylalanine does not change significantly with trophic level, reflecting its conservative nature as an essential amino acid, and thus represents the isotopic composition of the nitrogen at the base of the food web. Δ¹⁵N_Glu-Phe values in particular are shown to reflect trophic level nitrogen sources within a food web. In relation to the reconstruction of ancient human diet the contribution of marine and terrestrial protein are strongly reflected in Δ¹⁵N_Glu-Phe values. Differences in nitrogen metabolism are also shown to have an influence upon individual amino acid δ¹⁵N values with Δ¹⁵N_Glu-Phe values emphasising differences between the different physiological adaptations. The latter is demonstrated in tortoises, which can excrete nitrogen in the form of uric acid and urea and display negative Δ¹⁵N_Glu-Phe values whereas those for marine and terrestrial mammals are positive. The findings amplify the potential advantages of compound-specific nitrogen isotope analysis in the study of nitrogen flow within food webs and in the reconstruction of past human diets.     

无机盐类对天然矿物低温催化混合酯生烃反应的影响

脂肪酸酯是一类重要的生烃母质。选择了十四烷酸甲酯、十六烷酸甲酯和十八烷酸甲酯的混合酯为模型反应物,以方解石、白云石、伊利石、钙蒙脱石和黄铁矿为催化剂,分别考察了氯化钾、氯化镁、氯化钠、硫酸钠以及混合盐对天然矿物低温催化混合酯生烃反应的影响。结果表明,无机盐类对矿物催化下混合酯的生烃反应均有不同程度的影响,硫酸钠具有反催化作用,其它盐类具有正催化作用。且在各无机盐存在下,不同的矿物表现出不同的催化活性。     

A reexamination of amino acids in lunar soils: implications for the survival of exogenous organic material during impact delivery

Using a sensitive high performance liquid chromatography technique, we have analyzed both the hot water extract and the acid hydrolyzed hot water extract of lunar soil collected during the Apollo 17 mission. Both free amino acids and those derived from acid labile precursors are present at a level of roughly 15 ppb. Based on the D/L amino acid ratios, the free alanine and aspartic acid observed in the hot water extract can be entirely attributed to terrestrial biogenic contamination. However, in the acid labile fraction, precursors which yield amino acids are apparently present in the lunar soil. The amino acid distribution suggests that the precursor is probably solar wind implanted HCN. We have evaluated our results with regard to the meteoritic input of intact organic compounds to the moon based on an upper limit of < or = 0.3 ppb for alpha-aminoisobutyric acid, a non-protein amino acid which does not generally occur in terrestrial organisms and which is not a major amino acid produced from HCN, but which is a predominant amino acid in many carbonaceous chondrites. We find that the survival of exogenous organic compounds during lunar impact is < or = 0.8%. This result represents an example of minimum organic impact survivability. This is an important first step toward a better understanding of similar processes on Earth and on Mars, and their possible contribution to the budget of prebiotic organic compounds on the primitive Earth.     

Racemization of amino acids in marine sediments determined by gas chromatography

Ratios of d- to l-amino acids in acid hydrolysates from foraminifera of two deep-sea cores from the Caribbean Sea and Atlantic Ocean increase with depth and consequently with age over a span from 40,000 to 2,000,000 yr. The changing ratios do not seem to follow first-order reversible rate laws. Valine, leucine and glutamic acid apparently racemize (isoleucine epimerizes) at slower rates than do phenylalanine, alanine, aspartic acid and proline. The general relative order for rates of racemization of total (free and bound) amino acids may depend on the electron-withdrawing capacity of the R substituents of the amino acids and on the rates with which the amino acids are naturally hydrolyzed. In contrast to the total amino acids, the free amino acids in these samples are more extensively racemized, probably as a result of various catalytic and hydrolytic reactions.Previous related work based on ion-exchange chromatography has considered only ratios of alloisoleucine to isoleucine. With the gas chromatographic method used here, d/l ratios of all common asymmetric amino acids can be estimated. Measurement of the extent of racemization of amino acids in marine sediments seems to provide the basis for a geochronological tool covering the last few million years.     

Amino acid precursors in lunar fines: limits to the contribution of jet exhaust

A sample of lunar fines collected at a maximum distance, 6.5 km, from the descent engine on Apollo 17 has been analyzed for total amino acids obtainable by hydrolysis of aqueous extracts. The minimum amounts of amino acids, calculated for a disc of 6 km radius are 10⁴–10⁵ times those which could be contributed by the lunar module jet exhaust, on the basis of conservatively limiting assumptions. The amino acids thus obtained are not explainable as due to chemical or biological contamination; their source is accordingly inferred as lunar. Under the conditions of hydrolysis of lunar extracts, cyanide is found to be converted, almost exclusively to glycine, to an extent of 10^?4.     

Non-racemic amino acids in the Murray and Murchison meteorites.

Small (1.0-9.2%) L-enantiomer excesses were found in six alpha-methyl-alpha-amino alkanoic acids from the Murchison (2.8-9.2%) and Murray (1.0-6.0%) carbonaceous chondrites by gas chromatography-mass spectroscopy of their N-trifluoroacetyl or N-pentafluoropropyl isopropyl esters. These amino acids [2-amino-2,3-dimethylpentanoic acid (both diastereomers), isovaline, alpha-methyl norvaline, alpha-methyl valine, and alpha-methyl norleucine] are either unknown or rare in the terrestrial biosphere. Enantiomeric excesses were either not observed in the four alpha-H-alpha-amino alkanoic acids analyzed (alpha-amino-n-butyric acid, norvaline, alanine, and valine) or were attributed to terrestrial contamination. The substantial excess of L-alanine reported by others was not found in the alanine in fractionated extracts of either meteorite. The enantiomeric excesses reported for the alpha-methyl amino acids may be the result of partial photoresolution of racemic mixtures caused by ultraviolet circularly polarized light in the presolar cloud. The alpha-methyl-alpha-amino alkanoic acids could have been significant in the origin of terrestrial homochirality given their resistance to racemization and the possibility for amplification of their enantiomeric excesses suggested by the strong tendency of their polymers to form chiral secondary structure.     

Pyrite surface interaction with selected organic aqueous species under anoxic conditions

The interaction between low-molecular weight organic compounds and pyrite under anoxic conditions has been studied using a combination of electrophoresis and batch sorption experiments. The results suggest that acetate, carbamide, ethylamine, formamide, purine, D-ribose, and adenine, as well as the amino acids alanine, cysteine and glycine, interact within the electrophoretic shearplane of the pyrite surface. The observed surface interaction between the negatively charged surface of pyrite and the organic aqueous species takes place regardless of the formal charge of the aqueous species of interest. This indicates that the interaction of organic molecules with pyrite surfaces under anoxic conditions is dictated by interactions with specific surface sites (thiol or iron surface sites) rather than electrostatic forces. Dissolved metals typically enhance the interaction of the organics species. This enhancement is either due to an alteration in the distribution of thiol and iron groups on the pyrite surface or by the formation of ternary surface complexes.