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Is There a Common Chemical Model for Life in the Universe
Abstract
A review of organic chemistry suggests that life, a chemical system capable of Darwinian evolution, may exist in a wide range of environments. These include non-aqueous solvent systems at low temperatures, or even supercritical dihydrogen-helium mixtures. The only absolute requirements may be a thermodynamic disequilibrium and temperatures consistent with chemical bonding. A solvent system, availability of elements such as carbon, hydrogen, oxygen and nitrogen, certain thermodynamic features of metabolic pathways, and the opportunity for isolation, may also define habitable environments. If we constrain life to water, more specific criteria can be proposed, including soluble metabolites, genetic materials with repeating charges, and a well defined temperature range.
... To achieve these characteristics, a living system requires the rapid and efficient chemistry of complex molecules, including polymers, and sufficient chemical diversity in those molecules to allow specificity of chemical interaction. Rapid chemistry between complex molecules, including polymers or macromolecules, requires a dense fluid in which to take place (e.g., Benner et al., 2004;Hoehler et al., 2020). The medium has to be fluid to allow molecules to react, and it has to be dense so that macromolecules do not aggregate or physically fall out of "solution" (Bains, 2004). ...
... We exclude consideration of OOL because there is no consensus on many fundamental aspects of the OOL even on Earth, including no consensus on the environment in which it started (Bains, 2020). This extends to disagreement on such basic aspects as the solvent in which life's chemistry originated (Schoffstall and Laing, 1985;Benner et al., 2004;Sydow et al., 2017;Ziegler et al, 2018;Gull et al., 2023;Sydow et al., 2023). Exploration of origin scenarios for the solvents discussed here remains work for the future. ...
... Compounds that would be extremely unstable at terrestrial temperatures, such as diazomethane and azidomethane, are potentially stable at the temperature of liquid ammonia (or ammonia/water mixtures) (Raulin et al., 1995). Nitrogen-containing analogs of phosphates and carbonyl groups are known and likely to be favored over their oxygen equivalents in liquid ammonia (Aspinall et al., 2002;Bains, 2004;Benner et al., 2004). Ammonia analogs of peptides and sugars are known or have been plausibly modeled (Firsoff, 1963;Raulin et al., 1995;Oliveira et al., 2014), and nucleic acids with one or more oxygen replaced by an NH group are well known from terrestrial biology and pharmacology (Oliveira et al., 2014). ...
... It is a 'universal' need for any form of life, a necessary condition to develop a biosphere on a planet. Other planets could harbour forms of life unknown to us that could 'live' under physicochemical conditions very different from Earth (Benner et al., 2004 ). Several speculations have been made on forms of life based on a different chemistry and solvent and there will be al w ays uncertainties about which physicalchemical conditions are indispensable for life (Benner et al. 2004 ;Schulze-Makuch et al. 2015 ). ...
... Other planets could harbour forms of life unknown to us that could 'live' under physicochemical conditions very different from Earth (Benner et al., 2004 ). Several speculations have been made on forms of life based on a different chemistry and solvent and there will be al w ays uncertainties about which physicalchemical conditions are indispensable for life (Benner et al. 2004 ;Schulze-Makuch et al. 2015 ). One thing is certain: the second law of thermodynamics is universal and unquestionable and must be fulfilled by any forms of life. ...
Any biosphere emerges, lives, and grows producing entropy. Entropy production is a thermodynamic function crucial in the framework of non-equilibrium thermodynamics as it is directly related to the dynamical behavior of far-from equilibrium systems. The extent of entropy production is proportional to the ability of such systems to dissipate free energy and thus to ‘live’, to evolve, to grow in complexity. Generally, a certain threshold of entropy production must be exceeded for the emergence of complex self-organizing structures. Thus, the entropy production can be considered as the thermodynamic thrust that drives life emergence and evolution. In this perspective, we propose that the value of the planetary entropy production (PEP) can provide a first order estimate of the thermodynamic potential of planetary environment to sustain a complex biosphere. Here we use a simplified approach to evaluate the upper limit to the PEP and to the corresponding free energy as function of stellar temperature and orbital parameters of the planet. We found that only Earth-like planets in the circumstellar habitable zone (CHZ) of G and F stars can have a PEP value higher than the Earth value. Further significant thermodynamic differences exist between the inner and outer edge of the CHZ, with the inner edge being thermodynamically more advantageous for the development of complex biospheres. Interestingly, among the recently proposed habitable exoplanets, the ones belonging to the Hycean planets appear the thermodynamically best candidates.
... The debate around the possible parallel evolutionary history of the origin and further evolution from organisms other than the Last Universal Common Ancestor (LUCA) has been alive since the last two decades (Benner et al., 2004;Cleland and Copley, 2006). The existence of such organisms is, however, conjectural until now, as there is no ascertainable evidence for them. ...
... Regarding the hypothetical microbial descendants of an alternative origin of life constituting the "shadow biosphere" (Cleland and Copley, 2006;Cleland, 2007), there cannot exist anything but speculations. Spatially constrained, sulphur-deprived and/or extreme fluctuating thermal settings (between hot and cold) could be potential environments for searching for such kinds of organisms (Benner et al., 2004). However, Cleland (2007) stated that modern technologies could not detect such (microbes) "if they existed". ...
In this paper, the scientific and philosophical implications of the theory that suggests the existence of an intelligent civilisation on Earth prior to mankind is discussed. All available scientific evidence which would constrain such theory is brought into discussion. Therefore, we first review the Drake Equation regarding this hypothesis. We summarily appraise the Shadow Biosphere within the scope of the theory. Subsequently, we thoroughly analyse important geochemical and sedimentological constraints of the proposal, mainly in the context of some Fossillagerstätten. This leads us to discuss the philosophical implications this theory may have for the fields of Astrobiology and Palaeontology, analysing them under empiricist, rationalist, and positivist approaches. We contextually examine the concepts of technological species, intelligence, and industrialisation, taking into account the scope of the theory. Furthermore, we debate on the validity of this hypothesis, considering all constraints it presents regarding the analysed concepts. Finally, we propose to appraise the hypothesis under an epistemological/positivist point of view.
... We begin by outlining the centrality of temperature in regulating a diverse array of ecological and evolutionary parameters and processes [9,21,35,44,46,92] by adopting the general premise that biochemical reactions analogous to metabolism are universal on lifebearing exoplanets [13,16,122]. Subsequently, we construct a global likelihood function for these processes that depends on the planetary temperature. ...
One of the most fundamental questions in exoplanetology is to determine whether a given planet is habitable. We estimate the relative likelihood of a planet's propensity towards habitability by considering key physical characteristics such as the role of temperature on ecological and evolutionary processes, and atmospheric losses via hydrodynamic escape and stellar wind erosion. From our analysis, we demonstrate that Earth-sized exoplanets in the habitable zone around M-dwarfs seemingly display much lower prospects of being habitable relative to Earth, owing to the higher incident ultraviolet fluxes and closer distances to the host star. We illustrate our results by specifically computing the likelihood (of supporting life) for the recently discovered exoplanets, Proxima b and TRAPPIST-1e, which we find to be several orders of magnitude smaller than that of Earth.
... [1][2][3][4] In this regard, understanding the spontaneous formation of the macromolecules that underpin life's crucial biochemical processes, will inform the better design of bio-inspired materials [5][6][7] as well as aid in the search for habitable exoplanets. 8,9 To fold into thermodynamically stable structures and thus to possess well-defined biochemical properties, peptides should be at least 40 amino-acids long. 10 The Miller-Urey experiments showed that only monomeric amino acids form when models of early Earth atmospheres (H 2 O, CH 4 , NH 3 , and H 2 ) are heated and exposed to an electric discharge. ...
We investigate the hypothesis that mineral/water interfaces played a crucial catalytic role in peptide formation by promoting the self-assembly of amino acids. Using force-field-based molecular dynamics simulations, we demonstrate that the -alumina (0001) surface exhibits an affinity of 4 kBT for individual glycine or GG dipeptide molecules, due to hydrogen bonds formed at both the C- and N-termini. In simulations with multiple glycine molecules, surface-bound glycine enhances further adsorption, leading to the formation of long chains connected by hydrogen bonds between the carboxyl and amine groups of glycine molecules. The probability of forming long amino acid chains is examined using metadynamics enhanced sampling and a modified Flory theory. We find that the likelihood of observing chains longer than 10 glycine units increases by at least 5 orders of magnitude at the surface compared to the bulk. This surface-driven assembly is primarily due to local high density and alignment with the alumina surface pattern, resulting in a competition between enthalpy and entropy effects on adsorption. The formation of these chains necessitates the removal of coordinated water molecules. Importantly, our findings reveal that when dipeptides are present, only the N-terminus forms hydrogen bonds with the surface, suggesting that the surface may disfavor the backward hydrolysis of newly formed peptides. Together, these results propose a model for how mineral surfaces can induce configuration-specific assembly of amino acids, thereby promoting condensation reactions.
... The pursuit of the essence of life has compelled a large and multi-disciplinary community of researchers. They have been trying to create life de novo (Ashkenasy et al. 2017;Merindol and Walther 2017), to address its biological origin (Preiner et al. 2020), to understand its metabolic composition (Westheimer 1987;Smith and Morowitz 2004;Koonin and Novozhilov 2017), to develop undisputed biosignatures (Benner et al. 2004;Schwieterman et al. 2018) or to define it (Luisi 1998;Cleland and Chyba 2002;Weber 2010;Benner 2010). In the latter case, researchers have created operational definitions of life by stating the properties we would expect from a living system based on what is known from biology (Cleland and Chyba 2002;Benner 2010). ...
The definition, origin and recreation of life remain elusive. As others have suggested, only once we put life into reductionist physical terms will we be able to solve those questions. To that end, this work proposes the phenomenon of life to be the product of two dissipative mechanisms. From them, one characterises extant biological life and deduces a testable scenario for its origin. The proposed theory of life allows its replication, reinterprets ecological evolution and creates new constraints on the search for life.
... The first category is water and other solvents for which the dynamic transition temperature has been characterized. The second category is hydrocarbons, which have been linked to alternative biochemistries (37,38). The third category is low molecular weight (up to approximately 100 Da) substances made out of elements abundant in the universe such as H, C, N, O, and S (39), which may potentially partake in alternative biochemistries. ...
We propose that spontaneous folding and molecular evolution of biopolymers are two universal aspects that must concur for life to happen. These aspects are fundamentally related to the chemical composition of biopolymers and crucially depend on the solvent in which they are embedded. We show that molecular information theory and energy landscape theory allow us to explore the limits that solvents impose on biopolymer existence. We consider 54 solvents, including water, alcohols, hydrocarbons, halogenated solvents, aromatic solvents, and low molecular weight substances made up of elements abundant in the universe, which may potentially take part in alternative biochemistries. We find that along with water, there are many solvents for which the liquid regime is compatible with biopolymer folding and evolution. We present a ranking of the solvents in terms of biopolymer compatibility. Many of these solvents have been found in molecular clouds or may be expected to occur in extrasolar planets.
... However first, we outline a route that could have generated TCA intermediates on an early Earth based on alkaline thermal vents. This is only one of several possibilities (some others being panspermia [5], Urey/Millertype environments [6][7][8][9], and various subaerial environments such as Darwin's classic "warm little pond", as well as other thermal vents such as the more familiar black smokers) but serves to introduce some important concepts and to bring us to a suitable starting point. ...
Darwin’s theory of evolution by natural selection was revolutionary because it provided a mechanism by which variation could be selected. This mechanism can only operate on living systems and thus cannot be applied to the origin of life. Here, we propose a viable alternative mechanism for prebiotic systems: autocatalytic selection, in which molecules catalyze reactions and processes that lead to increases in their concentration. Crucially, this provides a driver for increases in concentrations of molecules to a level that permits prebiotic metabolism. We show how this can produce high levels of amino acids, sugar phosphates, nucleotides and lipids and then lead on to polymers. Our outline is supported by a set of guidelines to support the identification of the most likely prebiotic routes. Most of the steps in this pathway are already supported by experimental results. These proposals generate a coherent and viable set of pathways that run from established Hadean geochemistry to the beginning of life.
... Silicon can also form polymers, but they can be unstable over a wide temperature range. Organosilicates are a known component of living systems [54,64,65]. Detecting organic compounds, such as organosilicates or silicon polymers, is a positive indicator of the existence of biomolecules. ...
... But not so in a world with silicon-based life: water would lead to the destruction of complex silicon-based structures. Precisely for this reason, we have to consider other universally available solvents (Benner et al., 2004), which do not cause the blocking of silicon chemical bonds, as indicated above. We will return to this topic later. ...
The search for extraterrestrial intelligences has been active for just over 60 years. In all these decades hundreds of scientific papers have been published on the subject. Some have focused on the possibility of extraterrestrial civilisations with a different origin in their biological basis than we can experience on Earth. But there are some premises for life and for intelligence that bring us closer to a couple of necessary, but not sufficient, guidelines: the possibility of the existence of long chemical chains that allow the creation of complex structures (proteins, genetic information), something that is especially characteristic of two atoms: carbon and silicon. We ourselves are the example of how complex structures based on carbon have been able to achieve self-awareness and civilisation. What can we expect from the other atom that we know can build complex structures, silicon? This article aims to launch some hypotheses in this regard. Silicon allows complex chemical structures such as those necessary for life, but it has other characteristics of its own that condition the existence of life, and intelligence, based on silicon.
... We now seek to bridge this framework to the specific case of looking for alien life. For the moment, we endeavor to maintain a broad scope here, with experiments spanning everything from looking for life in the shadow biosphere (e.g., Benner et al. 2004) to alien radio transmissions (e.g., Cocconi & Morrison 1959), from exoplanet biosignatures (e.g., Seager et al. 2005) to seeking alien artefacts within the Solar System (e.g., Bracewell 1960). ...
The search for extraterrestrial (alien) life is one of the greatest scientific quests, yet it raises fundamental questions about just what we should be looking for and how. We approach alien hunting from the perspective of an experimenter engaging in binary classification with some true- and confounding-positive probabilities (TPP and CPP). We derive the Bayes factor in such a framework between two competing hypotheses, which we use to classify experiments as either impotent, imperfect, or ideal. Similarly, the experimenter can be classified as dogmatic, biased, or agnostic. We show how the unbounded explanatory and evasion capability of aliens poses fundamental problems to experiments directly seeking aliens. Instead, we advocate framing the experiments as looking for that outside of known processes, which means the hypotheses we test do not directly concern aliens per se. To connect back to aliens requires a second level of model selection, for which we derive the final odds ratio in a Bayesian framework. This reveals that it is fundamentally impossible to ever establish alien life at some threshold odds ratio, crit , unless we deem the prior probability that some as-yet-undiscovered natural process could explain the event is less than ( 1 + crit ) − 1 . This elucidates how alien hunters need to carefully consider the challenging problem of how probable unknown unknowns are, such as new physics or chemistry, and how it is arguably most fruitful to focus on experiments for which our domain knowledge is thought to be asymptotically complete.
... In contrast, by simple tautology, OBHs are sans land environments. By the same token, habitats that lie at the interface of 3 Alternative biochemistries may be viable (Firsoff 1963;Bains 2004;Benner et al. 2004;Schulze-Makuch & Irwin 2018), but remain empirically unsubstantiated to this date. Hence, we err on the side of caution and restrict ourselves to lifeforms predicated on the biochemistry of Earth (viz., carbon and water). ...
Current research indicates that (sub)surface ocean worlds essentially devoid of subaerial landmasses (e.g., continents) are common in the Milky Way, and that these worlds could host habitable conditions, thence raising the possibility that life and technological intelligence (TI) may arise in such aquatic settings. It is known, however, that TI on Earth (i.e., humans) arose on land. Motivated by these considerations, we present a Bayesian framework to assess the prospects for the emergence of TIs in land- and ocean-based habitats (LBHs and OBHs). If all factors are equally conducive for TIs to arise in LBHs and OBHs, we demonstrate that the evolution of TIs in LBHs (which includes humans) might have very low odds of roughly 1-in- to 1-in-, thus outwardly contradicting the Copernican Principle. Hence, we elucidate three avenues whereby the Copernican Principle can be preserved: (i) the emergence rate of TIs is much lower in OBHs, (ii) the habitability interval for TIs is much shorter in OBHs, and (iii) only a small fraction of worlds with OBHs comprise appropriate conditions for effectuating TIs. We also briefly discuss methods for empirically falsifying our predictions, and comment on the feasibility of supporting TIs in aerial environments.
... The oceans can either occur on the surface or underneath an icy crust or ice-rock mixture (Vazan et al. 2022); the second case of this 6 In a similar vein, other seemingly unusual circumstances linked to humans include the presence of a large moon (Ward & Brownlee 2000;Benn 2001); the location of Jupiter in the solar system (Ward & Brownlee 2000;Horner & Jones 2008); orbit around a G-type star (Haqq-Misra et al. 2018;Kipping 2021); and existence in the current cosmic epoch (Loeb et al. 2016;Kipping 2021). 7 Alternative biochemistries may be viable (Firsoff 1963;Bains 2004;Benner et al. 2004; Schulze-Makuch & Irwin 2018) but remain empirically unsubstantiated to this date. Hence, we err on the side of caution and restrict ourselves to life forms predicated on the biochemistry of Earth (viz., carbon and water). ...
Current research indicates that (sub)surface ocean worlds essentially devoid of subaerial landmasses (e.g., continents) are common in the Milky Way and that these worlds could host habitable conditions, thence raising the possibility that life and technological intelligence (TI) may arise in such aquatic settings. It is known, however, that TI on Earth (i.e., humans) arose on land. Motivated by these considerations, we present a Bayesian framework to assess the prospects for the emergence of TIs in land- and ocean-based habitats (LBHs and OBHs). If all factors are equally conducive for TIs to arise in LBHs and OBHs, we demonstrate that the evolution of TIs in LBHs (which includes humans) might have very low odds of roughly 1 in 10 ³ to 1 in 10 ⁴ , thus outwardly contradicting the Copernican principle. Hence, we elucidate three avenues whereby the Copernican principle can be preserved: (i) the emergence rate of TIs is much lower in OBHs, (ii) the habitability interval for TIs is much shorter in OBHs, and (iii) only a small fraction of worlds with OBHs comprise appropriate conditions for effectuating TIs. We also briefly discuss methods for empirically falsifying our predictions and comment on the feasibility of supporting TIs in aerial environments.
... Among SCFs, other than N 2 , supercritical carbon dioxide (scCO 2 ) is a promising chemical because of its relatively low critical temperature and pressure (Table 1), nontoxicity, and environmentally friendliness [20]. Within the processes utilizing scCO 2 , the combination of gas and liquid behaviour can be fine-tuned to engineer the density of the SCF with adjustments to the pressure and/or temperature of the process [21,22]. ...
Polymeric foams have characteristics that make them attractive for different applications. However, some foaming methods rely on chemicals that are not environmentally friendly. One of the possibilities to tackle the environmental issue is to utilize supercritical carbon dioxide ScCO2 since it is a “green” solvent, thus facilitating a sustainable method of producing foams. ScCO2 is nontoxic, chemically inert, and soluble in molten plastic. It can act as a plasticizer, decreasing the viscosity of polymers according to temperature and pressure. Most foam processes can benefit from ScCO2 since the methods rely on nucleation, growth, and expansion mechanisms. Process considerations such as pretreatment, temperature, pressure, pressure drop, and diffusion time are relevant parameters for foaming. Other variables such as additives, fillers, and chain extenders also play a role in the foaming process. This review highlights the morphology, performance, and features of the foam produced with ScCO2, considering relevant aspects of replacing or introducing a novel foam. Recent findings related to foaming assisted by ScCO2 and how processing parameters influence the foam product are addressed. In addition, we discuss possible applications where foams have significant benefits. This review shows the recent progress and possibilities of ScCO2 in processing polymer foams.
Astronomers point their instruments at distant galaxies in the hope of detecting signs of life somewhere in the universe. So far, they have found many stars that are accompanied by planets, but no signs of life. However, it is plausible that billions of planets with suitable chemical conditions exist at a distance from a star that is favourable for life. Until there is evidence of life on a distant planet, life on Earth will remain a unique phenomenon.
Living things exactly makes life such a unique phenomenon? Biologists and philosophers have been trying to answer this question since time immemorial. What they are looking for is some feature or combination of features that is common to ‘living things’.
An enduring question in astrobiology is how we assess extraterrestrial environments as being suitable for life. We suggest that the most reliable assessments of the habitability of extraterrestrial environments are made with respect to the empirically determined limits to known life. We discuss qualitatively distinct categories of habitability: empirical habitability that is constrained by the observed limits to biological activity; habitability sensu stricto, which is defined with reference to the known or unknown limits to the activity of all known organisms; and habitability sensu lato (habitability in the broadest sense), which is circumscribed by the limit of all possible life in the universe, which is the most difficult (and perhaps impossible) to determine. We use the cloud deck of Venus, which is temperate but incompatible with known life, as an example to elaborate and hypothesize on these limits.
While Earth contains the only known example of life in the universe, it is possible that life elsewhere is fundamentally different from what we are familiar with. There is an increased recognition in the astrobiology community that the search for life should steer away from terran-specific biosignatures to those that are more inclusive to all life-forms. To start exploring the space of possibilities that life could occupy, we can try to dissociate life from the chemistry that composes it on Earth by envisioning how different life elsewhere could be in composition, lifestyle, medium, and form, and by exploring how the general principles that govern living systems on Earth might be found in different forms and environments across the Solar System. Exotic life-forms could exist on Mars or Venus, or icy moons like Europa and Enceladus, or even as a shadow biosphere on Earth. New perspectives on agnostic biosignature detection have also begun to emerge, allowing for a broader and more inclusive approach to seeking exotic life with unknown chemistry that is distinct from life as we know it on Earth.
It is undoubtedly a sad fact that the beginning of space travel, the starting signal for the human ‘reach for the stars’, is located in the context of armed conflicts.
We live in the world, which is teeming with microorganisms. Our bodies are full of microbes and they are crucial for our survival. Origin of life as we know it is tightly connected with microorganisms. First life on Earth was microbial. Without them, there wouldn’t be us. Remnants of bacteria reside in our cells and generate energy for important biological processes. Although microbes are small and relatively simple, they are a very diverse group of organisms. Microorganisms can be found in all three domains of life: Bacteria, Archaea, and Eukarya. Other microscopic entities, which do not belong to any of the three domains of life, but are nevertheless fascinating are viruses, viroids, and prions.
Life emerged when parts of chemical automata self‐assembled to generate automata capable of self‐reproduction and also of evolving. Sometimes, a minor error in the building generated more efficient automata, which became the dominant entities. To behave like an automaton, a chemical system must primarily be autocatalytic. However, autocatalysis is not sufficient because an automaton must also be autonomous, being able to adapt and evolve according to the environment. It has to select the appropriate chemical parts among a very large number of molecules, some of them being potentially deleterious. An automaton must, therefore, possess opportunistic functions capable of categorizing a great number of molecules in a coherent way, i.e., active discriminating capabilities. To determine what an autocatalytic reaction network requires to become an autonomous, self‐producing system has been extensively explored in the past both theoretically (chemoton, autopoiesis, quasi‐species, and hypercycles, computer models) and experimentally. When comparing life and mechanical robots, both need to be autonomous. An impressive number of mechanical robots have been successfully built, whereas the synthesis of living automata is still eagerly awaited. The capability of evolution, not required for robots but mandatory for life, probably explains why chemists have not yet been successful.
Le profilage d’impuretés d’actifs pharmaceutiques (identification et quantification de toutes les impuretés) est une nécessité à tous les stades de développement du
médicament. Pour ce faire, les méthodes chromatographiques, en phase liquide (LC) ou supercritique (SFC), sont largement employées. Une autre méthode en récent essor, nommée chromatographie unifiée (UC), permet l’analyse de familles moléculaires s’étalant sur une large gamme de polarités. En effet, une telle analyse UC débute avec une majorité de CO2 pressurisé (mode SFC) puis se termine avec une majorité de phase liquide, voire 100% de phase liquide (mode LC).
Dans le cadre de cette thèse en lien avec l’Institut de Recherches Servier (IdRS), nous souhaitions explorer l’utilisation de l’UC pour l’analyse des biomolécules l’intérêt pharmaceutique, produites chimiquement ou par des organismes biologiques. En particulier les molécules cibles étaient les flavonoïdes et les peptides de petite taille
(inférieure à 5000 Da).
Pour les flavonoïdes, une méthode générique a d’abord été développée à l’aide de standards pour permettre ensuite l’investigation d’échantillons commerciaux d’intérêt cosmétique et pharmaceutique. Dans le cas des peptides, nous nous sommes appuyés sur une diversité de composés issus de l’IdRS afin d’adapter nos méthodes aux molécules propres à l’entreprise. Dans un premier temps, une méthode UC applicable aux peptides linéaires et cycliques de taille inférieure à 1000 Da a été développée et comparée à la méthode LC établie depuis quelques années. Dans un second temps, les peptides de taille supérieure à 1000 Da, posant d’autres défis, ont nécessité un second développement analytique en chromatographie liquide à fluidité améliorée (EFLC). Enfin, la possibilité de prédire le comportement chromatographique des actifs pharmaceutiques chimiques ou biologiques a également été abordée.
Several permanently cold solar system bodies are being investigated with regard to their potential habitability, including Mars and icy moons. In such locations, microbial life would have to cope with low temperatures and both high and low pressures, ranging from ∼102 to 103 Pa on the surface of Mars to upward of ∼108-109 Pa in the subsurface oceans of icy moons. The bacterial genus Carnobacterium consists of species that were previously shown to be capable of growth in the absence of oxygen at low temperatures and at either low pressure or high pressure, but to date the entire pressure range of the genus has not been explored. In the present study, we subjected 14 Carnobacterium strains representing 11 species to cultivation in a complex liquid medium under anaerobic conditions at 2°C and at a range of pressures spanning 5 orders of magnitude, from 103 to 107 Pa. Eleven of the 14 strains showed measurable growth rates at all pressures tested, representing the first demonstration of terrestrial life forms capable of growth under such a wide range of pressures. These findings expand the physical boundaries of the capabilities of life to occur in extreme extraterrestrial environments.
Bringing together the latest scientific advances and some of the most enduring subtle philosophical puzzles and problems, this book collects original historical and contemporary sources to explore the wide range of issues surrounding the nature of life. Selections ranging from Aristotle and Descartes to Sagan and Dawkins are organised around four broad themes covering classical discussions of life, the origins and extent of natural life, contemporary artificial life creations and the definition and meaning of 'life' in its most general form. Each section is preceded by an extensive introduction connecting the various ideas discussed in individual chapters and providing helpful background material for understanding them. With its interdisciplinary perspective, this fascinating collection is essential reading for scientists and philosophers interested in astrobiology, synthetic biology and the philosophy of life.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
The search for life in the Universe, once the domain of science fiction, is now a robust research program with a well-defined roadmap, from studying the extremes of life on Earth to exploring the possible niches for life in the Solar System and discovering thousands of planets far beyond it. In addition to constituting a major scientific endeavor, astrobiology is one of the most popular topics in astronomy, and is of growing interest to a broad community of thinkers from across the academic spectrum. In this volume, distinguished philosophers, theologians, anthropologists, historians and scientists discuss the big questions about how the discovery of extraterrestrial life, whether intelligent or microbial, would impact society. Their remarkable and often surprising findings challenge our foundational concepts of what the discovery of alien life may hold for humankind. Written in easily accessible language, this thought-provoking collection engages a wide audience of readers from all backgrounds.
A fundamental question in exobiology remains the degree to which
habitats on Venus, past and present, were, or are suitable for life.
This has relevance for assessing the exobiological potential of
extrasolar Venus-like greenhouse planets. In this paper the parameters
of the Venusian surface and atmosphere are considered and the
biochemical adaptations required to survive them are explored in the
light of new information on microbial adaptations to extreme
environments. Neither the pressure (9.5 MPa) nor the high carbon dioxide
concentrations (97%) represent a critical constraint to the evolution of
life on the surface or in the atmosphere. The most significant
constraints to life on the surface are the lack of liquid water and the
temperature (464°C). In the lower and middle cloud layers of Venus,
temperatures drop and water availability increases, generating a more
biologically favorable environment. However, acidity and the problem of
osmoregulation in hygroscopic sulfuric acid clouds become extreme and
probably life-limiting. If it is assumed that these constraints can be
overcome, considerations on the survival of acidophilic sulfate-reducing
chemoautotrophs suspended as aerosols in such an environment show that
Venus does come close to possessing a habitable niche. Conditions on the
surface and in the atmosphere may have been greatly ameliorated on early
Venus and may also be ameliorated on extrasolar planets with early
Venus-like characteristics where temperatures are less extreme and
liquid water is available.
Arctic wintertime sea-ice cores, characterized by a temperature gradient of 2t o20°C, were investigated to better understand constraints on bacterial abundance, activity, and diversity at subzero temperatures. With the fluorescent stains 4,6-diamidino-2-phenylindole 2HCl (DAPI) (for DNA) and 5-cyano-2,3-ditoyl tetrazo- lium chloride (CTC) (for O2-based respiration), the abundances of total, particle-associated (>3-m), free- living, and actively respiring bacteria were determined for ice-core samples melted at their in situ temperatures ( 2t o20°C) and at the corresponding salinities of their brine inclusions (38 to 209 ppt). Fluorescence in situ hybridization was applied to determine the proportions of Bacteria, Cytophaga-Flavobacteria-Bacteroides (CFB), and Archaea. Microtome-prepared ice sections also were examined microscopically under in situ conditions to evaluate bacterial abundance (by DAPI staining) and particle associations within the brine-inclusion network of the ice. For both melted and intact ice sections, more than 50% of cells were found to be associated with particles or surfaces (sediment grains, detritus, and ice-crystal boundaries). CTC-active bacteria (0.5 to 4% of the total) and cells detectable by rRNA probes (18 to 86% of the total) were found in all ice samples, including the coldest (20°C), where virtually all active cells were particle associated. The percentage of active bacteria associated with particles increased with decreasing temperature, as did the percentages of CFB (16 to 82% of Bacteria) and Archaea (0.0 to 3.4% of total cells). These results, combined with correlation analyses between bacterial variables and measures of particulate matter in the ice as well as the increase in CFB at lower temperatures, confirm the importance of particle or surface association to bacterial activity at subzero temperatures. Measuring activity down to 20°C adds to the concept that liquid inclusions in frozen envi- ronments provide an adequate habitat for active microbial populations on Earth and possibly elsewhere.
Interstellar glycolaldehyde (CH2OHCHO) has been detected in emission toward the Galactic center source Sagittarius B2(N) by means of millimeter-wave rotational transitions. Glycolaldehyde is an important biomarker since it is structurally the simplest member of the monosaccharide sugars that heretofore have gone undetected in interstellar clouds. There is no consensus as to how any such large complex molecules are formed in the interstellar clouds. It may be that the typical environment of dense interstellar clouds is favorable to glycolaldehyde synthesis by means of the polymerization of formaldehyde (H2CO) molecules either on grain surfaces or in the gas phase. Alternatively, we speculate that glycolaldehyde and other complex molecules may undergo assembly from functional molecular groups on grain surfaces. Utilizing common chemical precursors, a chance process could account for the high degree of isomerism observed in complex interstellar molecules (e.g., methyl formate, acetic acid, and glycolaldehyde). This work suggests that the phenomenon of isomerism be investigated further as a means of potentially constraining interstellar chemistry routes for those individual sources where the condition of good source-beam coupling can be achieved.
Experiments are described with algae grown in a new environment of pure CO 2 under pressure and in an acidic nutrient medium at elevated temperatures. One species found in hot-springs was observed to grow. If the planet Venus has acidic polar seas as we suggest, they may harbor photosynthetic life.
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Naturally occurring ribozymes catalyze a limited range of trans-esterification and hydrolysis reactions. We and others have addressed the question of whether this is an intrinsic limitation of RNA by using in vitro selection to isolate several new classes of ribozymes from large pools of random or partially random sequence RNAs. A variety of ribonucleases, ligases, kinases, as well as self-alkylating and self-aminoacylating activities have been recovered and are being characterized. It is now clear that ribozymes are not limited phosphate chemistry, but can accelerate reactions at carbon centers as well; since RNAs can bind and precisely position metal ions and other cofactors, it is likely that RNA catalysts for a wide range of reactions will eventually be isolated. It is widely thought that RNA enzymes played an important role in the early evolution of life. For such RNA World models to be plausible, RNA must be able to catalyze its own replication; for the RNA World to evolve into our current protein dominated biology, RNA must be able to catalyze the basic reactions involved in protein synthesis. We have isolated ribozymes that carry out the chemical transformations required for both replication and protein synthesis. These ribozymes will be described. Quantitative analysis of the activity of ribozymes recovered from random sequence pools has led to a correlation between ribozyme abundance and activity. This correlation can be interpreted as specifying the amount of information that must be encoded within a sequence in order to obtain a certain level of catalytic activity.
The synthesis of potentially natural nucleic acid alternatives and comparison of some of their chemical properties with those of RNA and DNA have led to findings that we consider to be relevant in the context of a chemical etiology of nucleic acid structure.
The mechanisms of solid-phase reactions that can be directly related to the formation of organic substances in space and their delivery to the Earth as well as the problems of prebiotic evolution are considered. These mechanisms are molecular tunneling (the hypothesis of the cold prehistory of life), polycondensation of solid monomers in shock waves (the problem of delivery of organic substances to the Earth with meteorites), thermal and thermal-wave explosions and oscillations of the radical concentration and temperature of cold small particles in the irradiation fields, and mechanochemical explosions and autowave propagation of chemical reactions us a result of the positive feedback between destruction of solids and reactions on newly formed surfaces.
TNAs [(l)-α-threofuranosyl oligonucleotides] containing vicinally connected (3′→2′) phosphodiester bridges undergo informational base
pairing in antiparallel strand orientation and are capable of cross-pairing with RNA and DNA. Being derived from a sugar containing
only four carbons, TNA is structurally the simplest of all potentially natural oligonucleotide-type nucleic acid alternatives
studied thus far. This, along with the base-pairing properties of TNA, warrants close scrutiny of the system in the context
of the problem of RNA's origin.
The atmospheres of the giant planets Jupiter, Saturn, Uranus, and Neptune are in many ways fundamentally different from the atmospheres of the terrestrial planets and they provide a variety of problems to test our understanding of how atmospheres work. These atmospheres are very deep and the internal energy for three of them (Uranus is the exception) is greater than the solar energy available to drive weather. Their rotation rates are fast and so the Coriolis force becomes more important, resulting in patterns of strong zonal (east–west) winds. Understanding the dominant physical processes that control the strengths, direction, and widths of the winds is still a very active area of research. This chapter highlights the salient features of the giant planet atmospheres, including their chemistry, clouds and colors, dynamics, and processes in the high atmosphere such as the aurora.
Nonenzymatic rates of hydrolytic deamination of adenosine and cytidine by acids and bases analogous to side chains of naturally occurring amino acids are compared with the rates of uncatalyzed deamination in water and with the rates of the hydroxide- and hydrogen ion-catalyzed reactions. For adenosine, hydroxide ion is an effective catalyst, with a second-order rate constant of 7.5 × 10−6m−1 s−1 at 85°C and an energy of activation of 19.9 kcal/mol. Acid-catalyzed deamination of adenine proceeds with a second-order rate constant of 1.5 × 10−6m−1 s−1 at 85°C. At concentrations of 1 m and at pH values corresponding to their respective pKa values, dimethylamine, acetate, selenide, imidazole, phosphate, and zinc(II) do not enhance the rate of deamination of adenosine beyond that observed in water, and 2-mercaptoethanol produces only a modest rate enhancement. The uncatalyzed rate of adenosine deamination in water is 8.6 × 10−9 s−1 at 85°C: extrapolation to 37°C and comparison with kcat for rat hepatoma adenosine deaminase yield a rate enhancement by the enzyme of approximately 2 × 1012-fold. 1,6-Dimethyladenosine, the conjugate acid of which has a pKa value much higher than that of adenosine, is not readily deaminated, suggesting that the uncatalyzed deamination of adenosine does not proceed by hydroxide ion attack on the rare protonated form of adenosine, but rather by attack on the neutral species. Deamination of cytidine is catalyzed most effectively by hydroxide ion, with a second-order rate constant of 4.5 × 10−4m−1 s−1 at 85°C and an energy of activation of 28.5 kcal/mol. The uncatalyzed rate of deamination of cytidine in water, which also exhibits an energy of activation of 28.5 kcal/mol, is 8.8 × 10−8 s−1 at 85°C. Comparison of the rate extrapolated to 25°C with kcat for bacterial cytidine deaminase gives a rate enhancement for the enzyme of 4 × 1011-fold. The C-5 proton of the pyrimidine ring of cytidine does not exchange with solvent during alkaline hydrolysis, suggesting that deamination under these conditions does not involve prior addition of water across the 5,6 double bond.
The extinction coefficient of the singlet-triplet transition of alpha-chloronaphthalene in ethyl iodide is found to increase almost linearly with the density of the compressed mixture. Study of a 1 : 2 volume ratio of these components over a pressure range from 1 to 3644 atmospheres resulted in about a two fold increase in light absorption, with little other changes in band envelope. No increase in absorption coefficient was obtained for pure liquid alpha-chloronaphthalene subjected to comparable increase in hydrostatic pressure. The increase in extinction coefficient is attributed to the increase in collisional frequency resulting from the increase in concentration of the constituents and the corresponding decrease in the liquid ``cage'' dimensions with increased density.
The lower cloud level of the Venusian atmosphere is an environmental niche that could harbor microbial life. Particularly the mode 3 particles that are enriched in this atmospheric layer are of astrobiological interest. We propose here a sample collection mission to the atmosphere of Venus and evaluate three mission options. The first option is a Stardust-type spacecraft used for sample collection, the second option is a Rotating Probe Tether System, and the third option is a Parachute Drop - Balloon Floatation System. Given the current state of technology, the result of our preliminary analysis is that the Parachute Drop - Balloon Floatation Mission is the most feasible and practical option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Energy, chemistry, solvents, and habitats -- the basic elements of
living systems - define the opportunities and limitations for life on
other worlds. This study examines each of these parameters in crucial
depth and makes the argument that life forms we would recognize may be
more common in our solar system than many assume. It also considers,
however, exotic forms of life that would not have to rely on carbon as
basic chemical element, solar energy as a main energy source, or water
as primary solvent. Finally the question of detecting bio- and
geosignature of such life forms is discussed, ranging from Earth
environments to deep space. While speculative considerations in this
emerging field of science cannot be avoided, the authors have tried to
present their study with the breadth and seriousness that a scientific
approach to this issue requires. They seek an operational definition of
life and investigate the realm of possibilities that nature offers to
realize this very special state of matter and avoid scientific jargon
wherever possible to make this intrinsically interdisciplinary subject
understandable to a broad range of readers.
This book was planned at a Workshop held in Glasgow in the summer of 1983 for participants with research experience in clay mineralogy. The objectives were to critically consider how life could have started, and the extent to which clay minerals might have been suitable as bio-materials to make such things as the genes, catalysts and membranes of the first organisms. 23 individual papers are presented within 9 chapters entitled: 1)Historical background; 2) Introducing clay; 3) Structures and forces; 4) Clay synthesis; 5) Clays on the early Earth; 6) Clays in the solar system; 7) Clays as catalysts; 8) Clays as genes; and 9) Questions and prospects: a conversation between the editors. Each chapter is abstracted separately.-E.Redpath
There are considered mechanisms of solid-phase reactions which were investigated experimentally and theoretically during recent decades and can have direct connections to the formation of organic substances in space and their delivery to the Earth, to the problems of prebiotic evolution. Among such mechanisms are the molecular tunneling (hypothesis of the cold prehistory of life), polycondensation of solid monomers by shock waves (problem of the delivery of organic substances to the Earth by meteorites), thermal and thermal-wave explosions and oscillations of temperature and radical concentrations in small cold particles under the radiation exposure, mechanochemical explosions and autowave propagation of chemical reactions due to the positive feedback between fragile destruction of solids and reactions at freshly formed surfaces.
Das ′Phthalimidomethylphosphonat (Ia) wird zu (Ib) chloriert bzw. durch Behandeln mit Hydrazin in Äthanol bei Raumtemperatur zu dem Aminomethylphosphonat (II) abgebaut.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Experimental studies on the solid-phase polymerization (SPP) of poly(ethylene terephthalate) (PET) for different particle sizes at temperatures of 190–220°C were carried out at different gas flow velocities. The SPP mechanism of PET changes under different operating conditions. At a given gas flow velocity, the SPP reaction mechanism for a large-sized sample changes from chemical reaction control to interior diffusion control with increasing temperature. At a given reaction temperature, the SPP reaction control mechanism for a small-sized sample changes from surface diffusion control to chemical reaction control with increasing gas flow velocity. At a given reaction temperature and gas flow velocity, the SPP reaction mechanism changes from interior diffusion control to surface diffusion control with decreasing particle size. The SPP reaction rate is not determined by a single control mechanism but by both diffusion and chemical reactions in the temperature range of 200–220°C. The primary control mechanism can be discerned based on the operating parameters.
Sur la base de la decouverte d'activites enzymatiques de certains ARN (chez E. coli au cours de la maturation des ARN+ et chez Tetrahymena avec un exon d'un ARNr a auto-epissage), l'auteur postule un systeme, auto-replicatif a l'origine uniquement compose de molecules d'ARN
The synthesis of 1-(2,4-dideoxy-β-D-erythro-hexopyranosyl)thymine, starting from the well known carbohydrate precursors 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose (12 steps) or from tri-O-acetyl-D-glucal (11 steps) is described.
Critical p(T) curves have been measured for the twelve mixtures: helium+, hydrogen+, nitrogen+, argon+, carbon monoxide+, sulfur hexafluoride+, ethene+, propene+, methylpropene+, benzene+, cyclohexane+, and methanol + ammonia. The six mixtures of (a hydrocarbon + ammonia) and of (methanol + ammonia) exhibit an uninterrupted critical curve; and the other six mixtures, an interrupted critical curve. As is expected (sulfur hexafluoride + ammonia) displays barotropic behaviour of the two liquid phases on the llg curve shortly before the (liquid + liquid) upper critical end point (ll-UCEP) is reached. This is always the case, when the substance with the lower critical temperature in a binary mixture with an interrupted critical curve has a higher density than that with the higher critical temperature. Another barotropic effect occurs for (sulfur hexafluoride + ammonia), and for (argon + ammonia) in the high-temperature and high-pressure range. That can always be expected, when the more volatile substance with the higher liquid density attains liquid-like densities at supercritical temperatures, if the pressure is raised until the vapour-phase density of the mixture becomes greater than the liquid-phase density.
The enhancement of solubility of a solid in a supercritical solvent is interpreted with emphasis placed on binary mixtures of the second class. The selection of supercritical solvent ; the choice of temperature and pressure for supercritical fluid extractions; the characteristics of solubility curves between and in the vicinities of the upper critical and the lower critical end points; the effects of density and density- dependent properties; and the addition of an entrainer and its chemical affinity on the solubility enhancement are discussed. The correlations using a cubic equation of state for solid solubilities in a solvent with or without a cosolvent are presented.
The synthesis of 1-(2,4-dideoxy-beta-D-erythro-hexopyranosyl)thymine, starting from the well known carbohydrate precursors 1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose (12 steps) or from tri-O-acetyl-D-glucal (11 steps) is described
The influence of hydrostatic pressure upon the equilibrium between solid naphthalene and its vapor in various inert gases has been measured over pressure ranges extending from 1 to 1100 atm and temperature ranges of 20° to 75°C, using spectrophotometric techniques.
The variation of naphthalene vapor concentration with the diluent gas density has been used to evaluate second virial coefficients representing diluent—naphthalene interactions for the following diluent gases: He, H2, Ar, N2, CH4, and C2H4. Although the virial coefficients thus obtained vary from large negative values for the systems involving the hydrocarbon gases to small positive values for the helium—naphthalene system, attractive 6–12 intermolecular potentials may be fitted to all the data.
WHILE the surface conditions of Venus make the hypothesis of life there implausible, the clouds of Venus are a different story altogether. As was pointed out some years ago1, water, carbon dioxide and sunlight—the prerequisites for photosynthesis—are plentiful in the vicinity of the clouds. Since then, good additional evidence has been provided that the clouds are composed of ice crystals at their tops2,3, and it seems likely that there are water droplets toward their bottoms4. Independent evidence for water vapour also exists5. The temperature at the cloud tops is about 210° K, and at the cloud bottoms is probably at least 260–280° K (refs. 4 and 6). Atmospheric pressure at this temperature level is about 1 atm.7. The observed planetary albedo falls steeply in the violet and ultra-violet8, which accounts for the pale lemon yellow colour of Venus. The albedo decline would not be expected for pure ice particles, and must therefore be caused by some contaminant. Dust, ozone, C3O2 and other gases may possibly explain these data but, whatever the explanation, the ultra-violet flux below the clouds is likely to be low. If small amounts of minerals are stirred up to the clouds from the surface, it is by no means difficult to imagine an indigenous biology in the clouds of Venus. What follows is one such speculation.
The organic chemistry of silicon is barely a century old but it is now very actively pursued. In particular, there is now great interest in polysilanes bearing functional groups. This article reviews the various synthetic routes that have been developed to achieve particular polymeric configurations and then discusses, in the light of their unique properties, the many potential applications in the electronic field.
The p(T) projections of (liquid + liquid) (ll), (liquid + gas) (lg), critical curves, and of (liquid + liquid + gas) (llg) three-phase curves for 18 binary mixtures of (an n-alkane + ammonia) with alkane-carbon numbers i = 1 to 12, and i = 14, 16, 18, 19, 20, and 36 were measured. The critical curves for the i = 1 and i > 18 mixtures are interrupted, whereas the values for all mixtures with carbon numbers between i = 2 and i = 18 form an uninterrupted lg-critical curve and an llg three-phase curve that terminates in a (liquid + liquid) upper critical end point (ll-UCEP). The ll-critical curves start from this ll-UCEP and rapidly approach high pressures with increase in temperature. The mixtures with i = 2 to 5 form positive azeotropes up to the critical region. The uninterrupted critical curve for (ethane + ammonia) passes through a temperature minimum and a pressure maximum, whereas those for i = 3 to 5 pass through only a temperature minimum. A temperature minimum, a pressure minimum, and a pressure maximum occur in the three lg-critical curves for i = 6 to 8. The critical curves for i = 9 to 11 pass through a pressure minimum and maximum but not through a temperature minimum. The lg-critical curves for i = 12 to 18 exhibit only a pressure maximum, but a point of inflection still exists between it and the critical point of ammonia. Pseudo-binary mixtures [{xC18H38 + (1 − x)C19H40} + ammonia], where x is 0.50 and 0.75, were taken to demonstrate the continuous transition in phase behaviour from type II through type IV to type III. The classification is that of Scott and van Konynenburg. Types II and IV are separated in the borderline case where an ll-UCEP and an LCEP collapse into a hypercritical point; and type IV and III, in the borderline case where an LCEP and an lg-UCEP collapse into a tricritical point. To demonstrate the similar pattern of phase behaviour for (an n-alkane + a polar compound), the p(T) projections of lg-critical curves have been measured additionally for (hexane or nonane or dodecane or hexatricontane + methanol), all of which exhibit an uninterrupted lg-critical curve.
An account is given on polysilane-based micelles of amphiphilic diblock copolymer. The polymer described is poly(1,1-dimethyl-2,2-dihexyldisilene)-b-poly(2-hydroxyethyl methacrylate) (PMHS-b-PHEMA). These amphiphilic polysilane copolymers are important as materials for further applications as a means of controlling the nanoscale molecular organization.
Polysilanes with carboxylic acids were synthesized by the reaction of phenol-linked polysilanes with carboxylic acid anhydrides. Saturated carboxylic acid and the unconjugated double bond were easy to introduce, but the introduction of allyl and conjugated double bonds was not achieved satisfactorily. The introduction of carboxylic acid drastically increased the solubility of the polysilanes to an aqueous basic solution. The unsaturated double bond in the carboxylic moiety reacted when polysilanes were photodecomposed. In this case, molecular scission surpassed the cross-linking which was brought by the reaction of the unsaturated bond. However, the double bond reacted thermally at 170°C to cause cross-linking. An exothermic reaction occurred drastically at 250°C. The base solubility depended on the content of carboxylic acid moieties and the molecular weight. The base solubility of the polysilanes increased rapidly under Mw = 5 × 10-4. Lines (0.3 μm) and spaces were fabricated.
Two routes are presented for the synthesis of 3',5'-bishomodeoxyribonucleosides, building blocks needed to synthesize oligodeoxynucleotide analogues where the OPO2O groups are replaced by CH2SCH2, CH2SOCH2, and CH2SO2CH2 units. Two of these have been coupled to create an uncharged analogue of a dinucleotide. As isosteric, achiral, and nonionic analogues of natural oligonucleotides stable to both enzymatic and chemical hydrolysis, such molecules have potential application as probes in the laboratory, in studies of the role of individual genes in biological function, and as ''antisense'' oligonucleotide analogues for the treatment of diseases.
The solution structure of a dimethylenesulfone-linked analogue of the RNA dimer UPC was determined using two-dimensional NMR and restrained molecular dynamics. In CDCl3, the RNA analogue forms a parallel duplex with a single U:U base pair and roughly antiparallel orientation of the two ribose rings within each strand. A hydrogen bonding network stabilizing this duplex was indirectly deduced from the NMR data. Besides the two-pronged hydrogen bonding between the uridines, this network includes two hydrogen bonds from the ribose hydroxyls of one strand to O2 of the cytosine bases of the opposite strand, and intrastrand hydrogen bonds from the 2‘ hydroxyls of the 5‘-terminal residues to hydroxyls of the 3‘-terminal residue. The melting point of the duplex determined via NMR chemical shift analysis was found to be 91 °C for a 11 mM solution in 1,1,2,2-tetrachloroethane-d2. Based on van't Hoff analysis of the available UV melting data in 1,2-dichloroethane, duplex formation is associated with a ΔS° of −47 cal K-1 mol-1 and a ΔH° of −22 kcal mol-1. The observation that an RNA analogue rendered nonionic and removed from an aqueous environment forms an exceptionally stable non-Watson−Crick duplex with backbone-to-nucleobase and backbone-to-backbone hydrogen bonds suggests that a charged backbone and the solubility in aqueous medium that it conveys are important for limiting the repertoire of strand−strand interactions of oligoribonucleotides.
Analogs of RNA have been synthesized where each of the phosphodiester linking groups is replaced by dimethylene sulfone units (sulfone-linked nucleic acid analogs of RNA, or “rSNAs”). These are the first fully nonionic analogs of RNA to be prepared as oligomers. Sequences leading to the octamer 5‘-r(ASO2USO2GSO2GSO2USO2CSO2ASO2U)-3‘ have been prepared from 3‘,5‘-bishomo-β-ribonucleoside derivatives as building blocks prepared from diacetone d-glucose, and their chemistry has been explored. Coupling was performed in solution via SN2 reactions between a thiol from one fragment and a bromide from the other, oxidation of the resulting thioether to the sulfone, and deprotection of a terminal primary hydroxyl group and regioselective conversion of itin the presence of secondary hydroxyl groupsto an active group (thiol or bromide) to yield another fragment for coupling. Base-labile protecting groups were used for the nucleobases, and one-step full deprotection was achieved using 1 M NaOH. The target octamer and each isolated intermediate were characterized by NMR, UV spectroscopy, and mass spectrometry. While chemical reactions involving longer rSNAs were in several cases retarded relative to analogous reactions with monomers, some rates were enhanced. In water, the rSNA octamer displayed a thermal transition in the UV spectrum above 65 °C with a large hyperchromicity. The behaviors of rSNAs suggest roles for the polyanionic backbone in DNA and RNA beyond its role in conferring aqueous solubility. The repeating anionic charges in natural oligonucleotides evidently also control the potent molecular recognition properties of these richly functionalized molecules, direct strand−strand interactions to the part of the biopolymer distant from the backbone (the Watson−Crick edge of the nucleobases), cause the polymer to favor an extended conformation, and ensure that the physical properties of the oligonucleotide are largely independent of its sequence. This suggests structural features that must be built into nonionic oligonucleotide analogs generally.
Synthese d'oligonucleosides analogues contenant un ou plusieurs nucleotides ayant un aldilol (glycerol) comme unite osidique. La synthese de phosphate-3d' «O»-[thymidyl-1 methyl]-2 glycerol est realise a partir principalement de benzyloxy-3 propanediol-1,2, de bis-trimethylsilyl thymine et d'O-[cyano-2 ethyl] N,N-diisopropyl-phosphoramidite