Origins of Life and Evolution of Biospheres最新文献

Background: Coronary ¹⁸F-fluoride positron emission tomography identifies ruptured and high-risk atherosclerotic plaque. The optimal method to identify, to quantify, and to categorize increased coronary ¹⁸F-fluoride uptake and determine its reproducibility has yet to be established. This study aimed to optimize the identification, quantification, categorization, and scan-rescan reproducibility of increased ¹⁸F-fluoride activity in coronary atherosclerotic plaque.

Methods: In a prospective observational study, patients with multi-vessel coronary artery disease underwent serial ¹⁸F-fluoride positron emission tomography. Coronary ¹⁸F-fluoride activity was visually assessed, quantified, and categorized with reference to maximal tissue to background ratios. Levels of agreement for both visual and quantitative methods were determined between scans and observers.

Results: Thirty patients (90% male, 20 patients with stable coronary artery disease, and 10 with recent type 1 myocardial infarction) underwent paired serial positron emission tomography-coronary computed tomography angiography imaging within an interval of 12±5 days. A mean of 3.7±1.8 ¹⁸F-fluoride positive plaques per patient was identified after recent acute coronary syndrome, compared with 2.4±2.3 positive plaques per patient in stable coronary artery disease. The bias in agreement in maximum tissue to background ratio measurements in visually positive plaques was low between observers (mean difference, -0.01; 95% limits of agreement, -0.32 to 0.30) or between scans (mean difference, 0.06; 95% limits of agreement, -0.49 to 0.61). Good agreement in the categorization of focal ¹⁸F-fluoride uptake was achieved using visual assessment alone (κ=0.66) and further improved at higher maximum tissue to background ratio values.

Conclusions: Coronary ¹⁸F-fluoride activity is a precise and reproducible metric in the coronary vasculature. The analytical performance of ¹⁸F-fluoride is sufficient to assess the prognostic utility of this radiotracer as a noninvasive imaging biomarker of plaque vulnerability.

Clinical trial registration: URL: http://www.clinicaltrials.gov. Unique identifiers: NCT02110303 and NCT02278211.

The Structure of carbodiimide has been studied by using quantum chemical methods. Carbodiimide (HNCNH) has been detected towards Sagittarius B2 (N) in interstellar medium (ISM). Two reaction mechanisms have been proposed to study the formation of interstellar Carbodiimide. The first reaction mechanism is based on molecule-radical and the second one is a radical-radical mechanism, through previously detected interstellar molecules or radicals. Quantum chemical calculations have been performed by using density functional theory (DFT) and Moller-Plesset second order perturbation (MP2) theory, in gas phase as well as in polarizable continuum model (PCM). The proposed reaction paths are exothermic and barrierless which indicates the possibility of carbodiimide formation in ISM. Several basis sets have been used to verify the validity and accuracy of the results. The isotropic and anisotropic polarizabilities of carbodiimide have been calculated from relevant tensor components for both reaction mechanisms with the help of data obtained by DFT/B3LYP and MP2 methods using aug-cc-pVTZ basis sets in gaseous phase as well as in PCM.

A new definition of life is proposed and discussed in the present article. It is formulated by modifying and extending NASA's working definition of life, which postulates that life is a "self-sustaining chemical system capable of Darwinian evolution". The new definition includes a thermodynamical aspect of life as a far from equilibrium system and considers the flow of information from the environment to the living system. In our derivation of the definition of life we have assumed the hypothesis, that during the emergence of life evolution had to first involve autocatalytic systems that only subsequently acquired the capacity of genetic heredity. The new proposed definition of life is independent of the mode of evolution, regardless of whether Lamarckian or Darwinian evolution operated at the origins of life and throughout evolutionary history. The new definition of life presented herein is formulated in a minimal manner and it is general enough that it does not distinguish between individual (metabolic) network and the collective (ecological) one. The newly proposed definition of life may be of interest for astrobiology, research into the origins of life or for efforts to produce synthetic or artificial life, and it furthermore may also have implications in the cognitive and computer sciences.

Syntheses under shock in nitrogen bubbled samples of the water - formamide - bicarbonate - sodium hydroxide system at pH 8.63, 9.46 and 10.44 were performed in the stainless steel preservation capsules. The maximum temperature and pressure in the capsules reached 545 K and 12.5 GPa respectively. Using the LC-MS-MS analysis, the 21 synthesis products have been identified, including amines and polyamines, carboxamide, acetamide and urea derivatives, compounds containing aniline, pyrrolidine, pyrrole, imidazole, as well as alcohol groups. It was found that the Fischer-Tropsch-type syntheses with catalysis on the surface of the stainless steel of the conservation capsule associated with the adsorbed hydrogen cyanide reactions and transamidation processes play the main role in the shock syntheses. Formation reactions of all the above-mentioned compounds have been suggested. It was proposed that hydrogen cyanide, ammonia, isocyanic acid, aminonitrile, aminoacetonitrile, as well as adsorbed species H_(a), CH_(a), CH_2(a), CHOH_(a), NH_2(a) and H₂CNH_(a) are especially important for the formation of the products. A reduction reaction of adsorbed bicarbonate with hydrogen to formaldehyde has been first postulated. In the studied system also classical reactions take place - Wöhler's synthesis of urea and Butlerov's synthesis of methenamine. It was suggest that material of meteorites may be an effective catalyst in the Fischer-Tropsch-type syntheses at falling of the iron-nickel meteorites in the water - formamide regions on the early Earth. It was concluded that life could have originated due to the impact of meteorites on alkaline water-formamide lakes located near volcanoes on the early Earth.

The riddle of the origin of life is unsolved as yet. One of the best ways to solve the riddle would be to find a vestige of the first life from databases of DNA and/or protein of modern organisms. It would be, especially, important to know the origin of tRNA, because it mediates between genetic information and the amino acid sequence of a protein. Here I attempt to find a vestige of the origin and evolution of tRNA from base sequences of Pseudomonas aeruginosa tRNA gene. It was first perceived that 5' anticodon (AntiC) stem sequences of P. aeruginosa tRNA for translation of G-start codon (GNN) are intimately and mutually related. Then, mutual relations among all of the forty-two 5' AntiC stem sequences of P. aeruginosa tRNA were examined. These relationships imply that P. aeruginosa tRNA originated from four anticodon stem-loops (AntiC-SL) translating GNC codons to the corresponding four amino acids, Gly, Ala, Asp and Val (where N is G, C, A, or T). In contrast to the case of AntiC-stem sequence, a mutual relation map could not be drawn with D-, T- and acceptor-stem sequences of P. aeruginosa tRNA. Thus I conclude that the four AntiC-SLs were the first primeval tRNAs.

The primordial RNA world is a hypothetical era prior to the appearance of protein and DNA, when RNA molecules were the sole building blocks for early forms of life on Earth. A critical concern with the RNA-world hypothesis is the instability of the cytosine nucleobase compared to the other three bases (adenine, guanine, and uracil). The author proposes that cytosine residues could have stably existed in the primordial world in the RNA i-motif, a four-stranded quadruplex structure formed by base-pairing of protonated and unprotonated cytosine residues under acidic conditions. The i-motif structure not only increases the lifetime of cytosine residues by slowing their deamination rate, but could also allow RNA polymers to bind to certain ligands (e.g., anions) to perform critical functions. Future studies focused on determining the rate of cytosine deamination in RNA i-motifs over a range of pH, temperature, and pressure conditions, and on interrogating the interactions between ligands and RNA i-motifs, could uncover new evidence of the origin of life on Earth.

Pyrite and organic matter closely coexist in some hydrothermally-altered gabbroic xenoliths from the Hyblean Plateau, Sicily. The representative sample consists of plagioclase, Fe-oxides, clinopyroxene, pyrite and minor amounts of many other minerals. Plagioclase displays incipient albitization, clinopyroxene is deeply corroded. Pyrite grains are widely replaced by spongy-textured magnetite, which locally hosts Ca-(and Fe-)sulfate micrograins and blebs of condensed organic matter. Whole-rock trace element distribution evidences that incompatible elements, particularly the fluid-mobile Ba, U and Pb, are significantly enriched with respect to N-MORB values. The mineralogical and geochemical characteristics of the sample, and its U-Pb zircon age of 216.9 ± 6.7 MA, conform to the xenolith-based viewpoint that the unexposed Hyblean basement is a relict of the Ionian Tethys lithospheric domain, mostly consisting of abyssal-type serpentinized peridotites with small gabbroic intrusions. Circulating hydrothermal fluids there favored the formation of hydrocarbons trough Fischer-Tropsch-type organic synthesis, giving also rise to sulfidization episodes. Subsequent variations in temperature and redox conditions of the system induced partial de-sulfidization, Fe-oxides precipitation and sulfate-forming reactions, also promoting poly-condensation and aromatization of the already-formed hydrocarbons. Here we show organic matter adhering to a crystal face of a microscopic pyrite grain. Pyrite surfaces, as abiotic analogues of enzymes, can adsorb and concentrate organic molecules, also acting as catalysts for a broad range of proto-biochemical reactions. The present data therefore may support established abiogenesis models suggesting that pyrite surfaces carried out primitive metabolic cycles in suitable environments of the early Earth, such as endolithic recesses in mafic rocks permeated by hydrothermal fluids.

To understand the effects of fluctuations on achieving homochirality, we employ a Monte-Carlo method where autocatalysis and enantiomeric cross-inhibition, as well as racemization and deracemization reactions are included. The results of earlier work either without autocatalysis or without cross-inhibition are reproduced. Bifurcation diagrams and the dependencies of the number of reaction steps on parameters are studied. In systems with 30,000 molecules, for example, up to a billion reaction steps may be needed to achieve homochirality without autocatalysis.

Of the six known autotrophic pathways, the Wood-Ljungdahl pathway (WL) is the only one present in both the acetate producing Bacteria (homoacetogens) and the methane producing Archaea (hydrogenotrophic methanogens), and it has been suggested that WL is one of the oldest metabolic pathways. However, only the so-called carbonyl branch is shared by Archaea and Bacteria, while the methyl branch is different, both in the number of reactions and enzymes, which are not homologous among them. In this work we show that some parts of the methyl branch of archaeal Wood-Ljungdahl pathway (MBWL) are present in bacteria as well as in non-methanogen archaea, although the tangled evolutionary history of MBWL cannot be traced back to the Last Common Ancestor. We have also analyzed the different variants of methanogenesis (hydrogenotrophic, acetoclastic and methylotrophic pathways), and concluded that each of these pathways, and every different enzyme or subunit (in the case of multimeric enzymes), has their own intricate evolutionary history. Our study supports the scenario of hydrogenotrophic methanogenesis being older than the other variants, albeit not old enough to be present in the last archaeal common ancestor.

Chiral recognition between tryptophan (Trp) and carbohydrates such as D-glucose (D-Glc), methyl-α-D-glucoside (D-glucoside), D-maltose, and D-cellobiose in cold gas-phase cluster ions was investigated as a model for chemical evolution in interstellar molecular clouds using a tandem mass spectrometer containing a cold ion trap. The photodissociation mass spectra of cold gas-phase clusters that contained Na⁺, Trp enantiomers, and D-maltose showed that Na⁺(D-Glc) was formed via the glycosidic bond cleavage of D-maltose from photoexcited homochiral Na⁺(D-Trp)(D-maltose), while the dissociation did not occur in heterochiral Na⁺(L-Trp)(D-maltose). The enantiomer-selective dissociation was also observed in the case of D-cellobiose. The enantiomer-selective glycosidic bond cleavage of disaccharides suggested that photoexcited D-Trp could prevent chemical evolution of sugar chains from D-enantiomer of carbohydrates in molecular clouds. The spectra of gas-phase clusters that contained Na⁺, Trp enantiomers, and D-Glc indicated that enantiomer-selective protonation of L-Trp from D-Glc could induce enantiomeric excess via collision-activated dissociation of the protonated L-Trp. In the case of protonated clusters, photoexcited H⁺(L-Trp) dissociated via C_α-C_β bond cleavage in the presence of D-Glc or D-glucoside, where the excited states of H⁺(L-Trp) contributed to the enantiomer-selective reaction in the clusters. These enantiomer selectivities in cold gas-phase clusters indicated that chirality of a molecule induced enantiomeric excess of other molecules via enantiomer-selective reactions in molecular clouds.