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At least 613 records · Page 34Linked to original sources
PubMed2006

Interstellar chemistry.

In the past half century, radioastronomy has changed our perception and understanding of the universe. In this issue of PNAS, the molecular chemistry directly observed within the galaxy is discussed. For the most part, the description of the molecular transformations requires specific kinetic schemes rather than chemical thermodynamics. Ionization of the very abundant molecular hydrogen and atomic helium followed by their secondary reactions is discussed. The rich variety of organic species observed is a challenge for complete understanding. The role and nature of reactions involving grain surfaces as well as new spectroscopic observations of interstellar and circumstellar regions are topics presented in this special feature.

Astronomy↗
PubMed1993

The wide range of actions of the FMRFamide-related peptides and the biological importance of peptidergic messengers.

The importance of peptides as intercellular messengers is discussed. The view is put forward that peptides evolved early in evolution as chemical messengers and that they have come to exert a wide range of actions. Using as an example the FMRFamide (Phe-Met-Arg-Phe-NH2) related peptide family of molluscs, the wide range of peptide actions on membrane currents is discussed and considered in relation to co-localization of peptides with low molecular weight (or "classical") intercellular messengers.

Amino Acid Sequence↗
PubMed1995

Geochemical constraints on chemolithoautotrophic reactions in hydrothermal systems.

Thermodynamic calculations provide the means to quantify the chemical disequilibrium inherent in the mixing of reduced hydrothermal fluids with seawater. The chemical energy available for metabolic processes in these environments can be evaluated by taking into account the pressure and temperature dependence of the apparent standard Gibbs free energies of reactions in the S-H2-H2O system together with geochemical constraints on pH, activities of aqueous sulfur species and fugacities of H2 and/or O2. Using present-day mixing of hydrothermal fluids and seawater as a starting point, it is shown that each mole of H2S entering seawater from hydrothermal fluids represents about 200,000 calories of chemical energy for metabolic systems able to catalyze H2S oxidation. Extrapolating to the early Earth, which was likely to have had an atmosphere more reduced than at present, shows that this chemical energy may have been a factor of two or so less. Nevertheless, mixing of hydrothermal fluids with seawater would have been an abundant source of chemical energy, and an inevitable consequence of the presence of an ocean on an initially hot Earth. The amount of energy available was more than enough for organic synthesis from CO2 or CO, and/or polymer formation, indicating that the vicinity of hydrothermal systems at the sea floor was an ideal location for the emergence of the first chemolithoautotrophic metabolic systems.

Archaea↗
PubMed2006

Novel drug discovery and molecular biological methods, via DNA, RNA and protein changes using structure-function transitions: Transitional structural chemogenomics, transitional structural chemoproteomics and novel multi-stranded nucleic acid microarray.

Nucleic acids and proteins are dynamic molecules that undergo structural changes which control gene expression. The authors have developed two novel techniques, viz., transitional structural chemogenomics and transitional structural chemoproteomics. Transitional structural chemogenomics is used to regulate gene expression, employing ultrasensitive small-molecule drugs targeted toward nucleic acids. Gene expression can be regulated by using chemicals to target transitional changes in the helical conformations of single-stranded (ss-) and double-stranded (ds-) DNA (e.g., B- to Z-DNA), and RNA (e.g., A- to Z-RNA). This method also targets alternative types of ds- and ss-DNA and RNA (e.g., cruciform DNA), and other multi-stranded nucleic acids (e.g., triplex-DNA). Our second technique, transitional structural chemoproteomics, targets a protein before, during or after post-translational modifications which alters its structure and function. Both a proteins' structured and unstructured regions are targeted. These two novel methods represent the next step in the evolution of chemical genomics and chemical proteomics. They allow for two approaches to regulate gene expression, viz., turning genes "on", "off" or variable control (e.g., dimmer switch). This article also discusses the confusion that exists between the term chemical genomics and other related subdisciplines, such as chemical proteomics. Additionally, we have developed a novel multi-stranded DNA, RNA and plasmid microarray which immobilizes intact nondenatured ds-DNA, alternative, and other multiple-stranded nucleic acids onto a substrate surface. This technique represents the next generation of nucleic acid microarrays, which will enhance the characterization of nucleic acids and the drug discovery process. These three novel techniques allow for a multifaceted approach that will greatly enhance the success of molecular biology, the "omics" and drug discovery. They represent the next era of gene expression tools.

Base Sequence↗
PubMed2001

Simulated cometary matter as a test for enantiomer separating chromatography for use on comet 46P/Wirtanen.

The Cometary Sampling and Composition Experiment on board of European Space Agency's cornerstone mission ROSETTA is designed to identify organic molecules in cometary matter in situ by a combined pyrolysis gas chromatographic and mass spectrometric technique. Its capillary columns coated with chiral stationary phases received considerable attention, because they are designed for separations of non-complex enantiomers to allow the determination of enantiomeric ratios of cometary chiral organic compounds and consequently to provide information about the origin of molecular parity violation in biomolecules. To get gas chromatographic access to organic compounds on the comet, where macromolecules and complex organic polymers of low volatility are expected to make up the main organic ingredients, the combination of two injection techniques will be applied. The pyrolysis technique performed by heating cometary samples stepwise to defined temperatures in specific ovens resulting in thermochemolysis reactions of polymers and a chemical derivatization technique, in which the reagent dimethylformamide dimethylacetal assists pyrolysis derivatization reactions in producing methyl esters of polar monomers. The combination of the reagent assisted pyrolysis gas chromatographic technique with enantiomer separating chromatography was tested with laboratory-produced simulated cometary matter.

Ammonia↗
PubMed2000

Chemistry of the organic-rich hot core G327.3-0.6.

We present gas-phase abundances of species found in the organic-rich hot core G327.3-0.6. The data were taken with the Swedish-ESO Submillimetre Telescope (SEST). The 1-3 mm spectrum of this source is dominated by emission features of nitrile species and saturated organics, with abundances greater than those found in many other hot cores, including Sgr B2 and OMC-1. Population diagram analysis indicates that many species (CH3CN, C2H3CN, C2H5CN, CH3OH, etc.) have hot components that originate in a compact (~2") region. Gas-phase chemical models cannot reproduce the high abundances of these molecules found in hot cores, and we suggest that they originate from processing and evaporation of icy grain mantle material. In addition, we report the first detection of vibrationally excited ethyl cyanide and the first detection of methyl mercaptan (CH3SH) outside the Galactic center.

Astronomical Phenomena↗
PubMed1995

Chemical studies on the possible existence of life on Mars.

Although there is no direct evidence yet for the existence of life on Mars, it is reasonable to conclude that the emergence of life on Earth, which appears to have been controlled by universal laws of physics and chemistry, may have been repeated elsewhere in the universe. The dual approach of synthesis and analysis in our experimental studies has provided ample evidence in support of this hypothesis.

Aluminum Silicates↗
PubMed2001

Life as a set of matter transformation cycles: ecological attributes of life.

An approach to searching for extraterrestrial life on the base of "autotroph" concept of the origin of life is presented in the paper. According to this concept the origin of life took place in three stages. The first stage was developed inside the global geochemical cycle in which the turnover of different chemical transformations was implemented by solar radiation and/or heat energy of bowels of the Earth. At the second stage, after the autocatalytic systems have emerged these systems evolved as a result of "natural selection" by autocatalysis parameters up to emergence of special inheritance systems that drastically improved the autocatalysis parameters. The best in terms of autocatalysis parameters were the autocatalysis systems based on phase-separated particles where complex structures can form not only on the basis of covalent interactions. Such autocatalysis systems can emerge only in liquid in a certain range of temperatures and pressures. At this stage the geochemical cycle complicated involving new substances. At the third stage the evolution involved improvement of inheritance systems resulting in formation of the modern type of genetic apparatus. This concept formed the basis to consider approaches to experimental modeling of major aspects of the origin of life and to outlining some general features of life that can extend the sensitive horizon of searching for extraterrestrial life.

Biological Evolution↗
PubMed2000

Enantioselective magnetochiral photochemistry

Many chemical and physical systems can occur in two forms distinguished solely by being mirror images of each other. This phenomenon, known as chirality, is important in biochemistry, where reactions involving chiral molecules often require the participation of one specific enantiomer (mirror image) of the two possible ones. In fact, terrestrial life utilizes only the L enantiomers of amino acids, a pattern that is known as the 'homochirality of life' and which has stimulated long-standing efforts to understand its origin. Reactions can proceed enantioselectively if chiral reactants or catalysts are involved, or if some external chiral influence is present. But because chiral reactants and catalysts themselves require an enantioselective production process, efforts to understand the homochirality of life have focused on external chiral influences. One such external influence is circularly polarized light, which can influence the chirality of photochemical reaction products. Because natural optical activity, which occurs exclusively in media lacking mirror symmetry, and magnetic optical activity, which can occur in all media and is induced by longitudinal magnetic fields, both cause polarization rotation of light, the potential for magnetically induced enantioselectivity in chemical reactions has been investigated, but no convincing demonstrations of such an effect have been found. Here we show experimentally that magnetochiral anisotropy--an effect linking chirality and magnetism--can give rise to an enantiomeric excess in a photochemical reaction driven by unpolarized light in a parallel magnetic field, which suggests that this effect may have played a role in the origin of the homochirality of life.

Anisotropy↗
PubMed1989

Experimental studies in the origin of life.

Modern astronomy suggests that planets are plentiful in the Universe and that the conditions suitable for life are commonplace. Advances in biochemistry have pointed out the unity of the biosphere and lead to the belief that all life had a common chemical origin. Laboratory experiments indicate that almost all the building blocks of life can be synthesized under simulated primitive Earth conditions. The analysis of meteorites and the study of the interstellar medium indicate that molecules of biological interest are commonplace in the Universe, thus leading to the conclusion that the evolutionary process which has taken place on Earth may have also occurred elsewhere in the cosmos leading to extraterrestrial civilisations.

Astronomical Phenomena↗
PubMed1997

A study of the physics and chemistry of TMC-1.

We present a comprehensive study of the physical and chemical conditions along the TMC-1 ridge. Temperatures were estimated from observations of CH3CCH, NH3, and CO. Densities were obtained from a multitransition study of HC3N. The values of the density and temperature allow column densities for 13 molecular species to be estimated from statistical equilibrium calculations, using observations of rarer isotopomers where possible, to minimize opacity effects. The most striking abundance variations relative to HCO+ along the ridge were seen for HC3N, CH3CCH, and SO, while smaller variations were seen in CS, C2H, and HCN. On the other hand, the NH3, HNC, and N2H+ abundances relative to HCO+ were determined to be constant, indicating that the so-called NH3 peak in TMC-1 is probably a peak in the ammonia column density rather than a relative abundance peak. In contrast, the well-studied cyanopolyyne peak is most likely due to an enhancement in the abundance of long-chain carbon species. Comparisons of the derived abundances to the results of time-dependent chemical models show good overall agreement for chemical timescales around 10(5) yr. We find that the observed abundance gradients can be explained either by a small variation in the chemical timescale from 1.2 x 10(5) to 1.8 x 10(5) yr or by a factor of 2 change in the density along the ridge. Alternatively, a variation in the C/O ratio from 0.4 to 0.5 along the ridge produces an abundance gradient similar to that observed.

Alkynes↗
PubMed1980

Interstellar molecules.

The study of interstellar molecules broadly includes two areas of interest. One area uses the unique ability of molecules to act as probes of the physical conditions in the cold, dense, visually opaque component of the interstellar medium. The physical properties of this and other components of the interstellar medium are summarized. The other area deals with the chemistry of interstellar molecules, recent aspects of which are emphasized in this review. Gas-phase chemistry, shock chemistry, and grain surface chemistry are discussed in the context of recent observations. No present observations suggest that surface reactions are relevant, but neither can they be ruled out. Ion-molecule reactions are clearly operative, at least for the simpler species. Chemical isotope fractionation is reviewed, and it is concluded that the complexities of the chemistry allow no cosmological conclusions to be drawn from observations of deuterium in interstellar molecules, while the presence of 13C in interstellar molecules permits an estimate of the 12C/13C ratio which is consistent with the current concepts of the nucleosynthesis history of the Galaxy. Possible connections between interstellar molecules and the early molecular history of the solar system are discussed.

Biological Evolution↗
PubMed1997

On the crucial stages in the origin of animate matter.

Theories of the origin of life have proposed hypotheses to link inanimate to animate matter. The theory proposed here derived the crucial stages in the origin of animate matter directly from the basic properties of inanimate matter. It asked what were the general characteristics of the link, rather than what might have been its chemical details. Life and its origin are shown to be one continuous physicochemical process of replication, random variation, and natural selection. Since life exists here and now, animate properties must have been initiated in the past somewhere. According to the theory, life originated from an as yet unknown elementary autocatalyst which occurred spontaneously, then replicated autocatalytically. As it multiplied to macroscopic abundance, its replicas gradually exhausted their reactants. Random chemical drift initiated diversity among autocatalysts. Diversity led to competition. Competition and depletion of reactants slowed down the rates of net replication of the autocatalysts. Some reached negative rates and became extinct, while those which stayed positive "survived." Thus chemical natural selection appeared, the first step in the transition from inanimate to animate matter. It initiated the first animate property, fitness, i.e., the capacity to adapt to the environment and to survive. As the environment was depleted of reactants, it was enriched with sequels-namely, with decomposition products and all other products which accompany autocatalysis. The changing environment exerted a selective pressure on autocatalysts to replace dwindling reactants by accumulating sequels. Sequels that were incorporated into the autocatalytic process became internal components of complex autocatalytic systems. Primitive forms of metabolism and organization were thus initiated. They evolved further by the same mechanism to ever higher levels of complexity, such as homochirality (handedness) and membranal enclosure. Subsequent evolution by the same mechanism generated cellular metabolism, cell division, information carriers, and a genetic code. Theories of self-organization without natural selection are refuted.

Catalysis↗
PubMedDate not supplied

Terraforming: making an Earth of Mars.

As we understand more about life on Earth and about the chemical and biological potential of other planets and objects in our solar system, it's not too much of a leap to consider creating a habitable environment on another planet. Scientists have begun to ponder the possibility of transforming Mars, the most Earthlike of the nearby planets. Various scenarios have been proposed, and in many ways these scenarios duplicate the processes that transformed the early Earth. Here we look at some of the possibilities.

Atmosphere↗
PubMed2006

Interferometric observations of large biologically interesting interstellar and cometary molecules.

Interferometric observations of high-mass regions in interstellar molecular clouds have revealed hot molecular cores that have substantial column densities of large, partly hydrogen-saturated molecules. Many of these molecules are of interest to biology and thus are labeled "biomolecules." Because the clouds containing these molecules provide the material for star formation, they may provide insight into presolar nebular chemistry, and the biomolecules may provide information about the potential of the associated interstellar chemistry for seeding newly formed planets with prebiotic organic chemistry. In this overview, events are outlined that led to the current interferometric array observations. Clues that connect this interstellar hot core chemistry to the solar system can be found in the cometary detection of methyl formate and the interferometric maps of cometary methanol. Major obstacles to understanding hot core chemistry remain because chemical models are not well developed and interferometric observations have not been very sensitive. Differentiation in the molecular isomers glycolaldehdye, methyl formate, and acetic acid has been observed, but not explained. The extended source structure for certain sugars, aldehydes, and alcohols may require nonthermal formation mechanisms such as shock heating of grains. Major advances in understanding the formation chemistry of hot core species can come from observations with the next generation of sensitive, high-resolution arrays.

Astronomy↗
PubMedDate not supplied

Soil and water and its relationship to the origin of life.

Soils of the terrestrial planets form at the boundaries between lithosphere, atmosphere and hydrosphere. Biogenesis occurred in these zones; thus, it is axiomatic that some, perhaps many, stages of biogensis occurred in intimate association with the mineral constituents of soils. Because of a high surface to mass ration and, consequently, a high surface reactivity, the layer lattice clay minerals are the most important of these. According to the geological record, clay minerals appeared very early on the primordial Earth. Recent investigations have confirmed their presence in carbonaceous meteorites and have indicated their occurrence on Mars. In this paper we collect pertinent physico-chemical data and summarize the organic reactions and interactions that are induced or catalyzed by clays. Many clay-organic reactions that do not occur readily at high water contents proceed rapidly at adsorbed water contents corresponding to surface coverages of one or two molecular layers. One or two monolayers of adsorbed water correspond to extremely dry or cold planetary environments. Some consequences of these facts vis á vis biogenesis on Mars are considered.

Adsorption↗
PubMed2006

Hydrothermal reactions of pyruvic acid: synthesis, selection, and self-assembly of amphiphilic molecules.

Selection and self-assembly of organic compounds in aqueous phases must have been a primary process leading to emergent molecular complexity and ultimately to the origin of life. Facile reactions of pyruvic acid under hydrothermal conditions produce a complex mixture of larger organic molecules, some of which are amphiphiles that readily self-assemble into cell-sized vesicular structures. Chemical characterization of major components of this mixture reveals similarities to the suite of organic compounds present in the Murchison carbonaceous chondrite, some of whose molecules also self-assemble into membranous vesicles. Physical properties of the products are thus relevant to understanding the prebiotic emergence of molecular complexity. These results suggest that a robust family of prebiotic reaction pathways produces similar products over a range of geochemical and astrochemical environments.

Catalysis↗
PubMed2002

Fast proton spectroscopic imaging with high signal-to-noise ratio: spectroscopic RARE.

A new fast spectroscopic imaging (SI) method is presented which is based on spatial localization by the fast MRI method of rapid acquisition with relaxation enhancement (RARE) and encoding of the chemical shift information by shifting the position of a refocusing 180 pulse in a series of measurements. This method is termed spectroscopic RARE. In contrast to spectroscopic ultrafast low-angle RARE (U-FLARE), the formation of two echo families (odd and even) is suppressed by using a train of 180 RF pulses with an internal four-step phase cycle. By this means a high signal-to-noise ratio (SNR) per unit measurement time is obtained, because the separation of odd and even echoes, as well as dummy echoes to stabilize the echo amplitudes, is not needed anymore. The method is of particular interest for detecting signals of coupled spins, as effective homonuclear decoupling can be achieved by use of constant evolution time chemical shift encoding. The pulse sequence was implemented on a 4.7 T imaging system, tested on phantoms, and applied to the healthy rat brain in vivo. Spectroscopic RARE is particularly useful if T2* double less-than sign T2, which is typically fulfilled for in vivo proton SI measurements at high magnetic field strength.

Animals↗