Publications
283 results found
Perry RS, Sephton MA, 2009, Reply to comments on defining biominerals and organominerals: Direct and indirect indicators of life [Perry et al., Sedimentary Geology, 201, 157-179], SED GEOL, Vol: 213, Pages: 156-156, ISSN: 0037-0738
Martins Z, Sephton MA, 2009, Extraterrestrial amino acids, Origins and Synthesis of Amino Acids., Editors: Hughes, Hughes, Weinheim, Publisher: Wiley-VCH, Pages: 3-42, ISBN: 9789783527324
Court RW, Sephton MA, 2009, Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars, EARTH PLAN SCI LETT, Vol: 288, Pages: 382-385, ISSN: 0012-821X
The presence of methane in the atmosphere of Mars has been suggested as evidence of life, as methane has a short lifetime in the atmosphere of Mars of just a few hundred years, requiring replacement by mechanisms, continuous or episodic, such as biology, volcanism, serpentinization of ultramafic crust or large cometary or asteroidal impacts. The potential of meteoritic infall to deliver significant quantities of methane is restricted by the low abundance of free methane in carbonaceous meteorites. However, the delivery of meteoritic material to the surface of a planet is an energetic process, and the ability of carbonaceous meteorites to generate methane upon ablation during atmospheric entry has not been previously considered. Here, we use analytical pyrolysis to simulate the ablation and pyrolysis of carbonaceous micrometeorites upon atmospheric entry, and Fourier-transform infrared spectroscopy to quantify the subsequent yield of methane. We show that ablation produces a yield of methane that is approximately two orders of magnitude greater than the measured free methane present in the CM2 carbonaceous chondrite, Murchison, but that this previously overlooked source of methane can only account for less than 10 kg of methane annually, a mass far below that required to maintain the abundance of methane observed in the atmosphere of Mars. Our data support attempts to search for life and explore subsurface chemical processes on the Red Planet.
Court RW, Sephton MA, 2009, Quantitative flash pyrolysis Fourier transform infrared spectroscopy of organic materials, Analytica Chimica Acta, Vol: 639, Pages: 62-66, ISSN: 0003-2670
Thermal degradation is a common technique used to investigate the nature of organic materials. However, existing methods for the Fourier transform infrared (FTIR) identification and quantification of volatile products from the thermal degradation of organic materials are limited to the technique of thermogravimetric analysis (TGA)–FTIR, which utilizes relatively low heating rates. However, the thermal degradation products of organic materials are known to vary depending on the rate of heating, with lower heating rates of biomass associated with increased yields of solid char and decreased yields of volatiles, as well as a greater opportunity for secondary reactions between the residue and the pyrolysis products. Hence, it is difficult to relate the products of organic matter thermally degraded at <100 °C min−1 in TGA to the products of flash pyrolysis at up to 20,000 °C s−1. We have developed and applied a novel methodology for quantitative flash pyrolysis–FTIR analysis of the volatile pyrolysis products of organic-rich materials. Calibration curves of water, carbon dioxide and methane have been constructed and used to determine absolute volatile release from wood (ash, Lat. Fraxinus). This technique is quicker and simpler than comparable pyrolysis–gas chromatography–mass spectrometry techniques, and avoids errors associated with the lower rates of temperature increase associated with techniques such as thermogravimetric analysis.
Gomes RL, Meredith W, Snape CE, et al., 2009, Analysis of conjugated steroid androgens: Deconjugation, derivatisation and associated issues, Journal of Pharmaceutical and Biomedical Analysis, Vol: 49, Pages: 1133-1140, ISSN: 0731-7085
Gas chromatography/mass spectrometry (GC/MS) is the preferred technique for the detection of urinary steroid androgens for drug testing in athletics. Excreted in either the glucuronide or sulfated conjugated form, steroids must first undergo deconjugation followed by derivatisation to render them suitable for GC analysis. Discussed herein are the deconjugation and the derivatisation preparative options. The analytical challenges surrounding these preparatory approaches, in particular the inability to cleave the sulfate moiety have led to a focus on testing protocols that reply on glucuronide conjugates. Other approaches which alleviate the need for deconjugation and derivatisation are also highlighted.
Sephton MA, Visscher H, Looy CV, et al., 2009, Chemical constitution of a Permian-Triassic disaster species, GEOLOGY, Vol: 37, Pages: 875-878, ISSN: 0091-7613
One of the most controversial biological proxies of environmental crisis at the close of the Permian is the organic microfossil Reduviasporonites. The proliferation of this disaster species coincides with the mass extinction and numerous geochemical disturbances. Originally Reduviasporonites was assigned to fungi, opportunistically exploiting dying end-Permian forests, but subsequentgeochemical data have been used to suggest an algal origin. We have used high-sensitivity equipment, partly designed to detect interstellar grains in meteorites, to reexamine the geochemical signature of Reduviasporonites. Organic chemistry, carbon and nitrogen isotopes, and carbon/nitrogen ratios are consistent with a fungal origin. The use of this microfossil as a marker of terrestrial ecosystem collapse should not be merely discounted. Unequivocally diagnostic data, however, may have been precluded by post-burial replacement of its organic constituents.
Gomes RL, Meredith W, Snape CE, et al., 2009, Conjugated steroids: analytical approaches and applications, ANAL BIOANAL CHEM, Vol: 393, Pages: 453-458, ISSN: 1618-2642
An introduction to conjugated steroids and the justification for their analysis is provided covering both environmental and biological samples. Determining conjugated steroids or indeed any organic chemical which is conjugated upon excretion from the body has relevance in diagnostic monitoring, forensic screening and environmental analysis (from the endocrine disrupter perspective). The various analytical approaches and the accompanying issues are application-dependent. There are numerous options at each stage of analysis, from extraction, hydrolysis, derivatisation, and detection, and advances can be confined to the specific application for which it was developed. Emphasis is placed on the choice of separation and how gas or liquid chromatography necessitates different preparative stages to enable conjugated steroid determination. Possible future directions and research for conjugated steroid analysis are discussed.
Court RW, Sephton MA, 2009, Meteorite ablation products and their contribution to the atmospheres of terrestrial planets: An experimental study using pyrolysis-FTIR, GEOCHIM COSMOCHIM AC, Vol: 73, Pages: 3512-3521, ISSN: 0016-7037
Martins Z, Alexander CMO, Orzechowska GE, et al., 2008, Amino acid composition of primitive CR2 chondrites, Workshop on Antarctic Meteorites - Search, Recovery, and Classification, Publisher: METEORITICAL SOC, Pages: A90-A90, ISSN: 1086-9379
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- Citations: 5
Needham AW, Smith CL, Sephton MA, et al., 2008, Gamma irradiation effects on martian analogues, Workshop on Antarctic Meteorites - Search, Recovery, and Classification, Publisher: METEORITICAL SOC, Pages: A114-A114, ISSN: 1086-9379
Marlow JJ, Martins Z, Sephton MA, 2008, Mars on Earth: soil analogues for future Mars missions, Astronomy & Geophysics, Vol: 49, Pages: 2.2-2.5
Marlow JJ, Martins Z, Sephton MA, 2008, Mars on Earth: soil analogues for future Mars missions, ASTRON GEOPHYS, Vol: 49, Pages: 20-23, ISSN: 1366-8781
Preparations for missions to Mars are a major concern for scientists. Predicting how equipment and experiments will perform on the planet is difficult because tests are restricted to Earth. Mars soil analogues are being used to solve this problem. These terrestrial materials are chemically and physically similar to martian soils and, because they contain unusual minerals and trace amounts of organic matter, are scientifically interesting in their own right. However,no current analogue is appropriate for all necessary tests. Here we describe Mars soil analogues, identify limitations and suggest the need for new Mars simulants.
Lomax BH, Fraser WT, Sephton MA, et al., 2008, Plant spore walls as a record of long-term changes in ultraviolet-B radiation, Nature Geoscience, Vol: 1, Pages: 592-596, ISSN: 1752-0894
Stratospheric ozone screens the Earth's surface from harmful ultraviolet-B radiation. Concentrations of stratospheric ozone are governed by a variety of natural and anthropogenic factors, including solar cycles1, volcanic aerosols2, ozone-depleting substances3 and climate change4. However, assessing this variability before instrumental records has proved difficult owing to the lack of a well-constrained proxy5. Here, we use microspectroscopy to analyse the chemical composition of herbarium samples of clubmoss (Lycophyta) spores originating from high- and low-latitude localities, where they were exposed to different ultraviolet-B histories. We show that the concentration of two ultraviolet-B-absorbing compounds in the walls of high-northern- and southern-latitude spores is strongly regulated by historical variations in ultraviolet-B radiation. Conversely, we find little change in the concentration of these compounds in spores originating from tropical Ecuador, where ultraviolet levels have remained relatively stable. Using spores from Greenland, we reconstruct past (1907–1993) changes in ozone concentration and ultraviolet-B flux; we reveal strong similarities between spore-wall reconstructions, and independent instrumental records6 and model results7. Our findings suggest that ultraviolet-B-absorbing compounds in plant spore walls have the potential to act as a proxy for past changes in terrestrial ultraviolet-B radiation and stratospheric ozone. The chemical signature of plant spore walls in herbaria, and possibly also in sedimentary and ice-core archives, may therefore prove valuable for reconstructing past variations in stratospheric ozone and their connections with changes in solar radiation and climate.
Martins Z, Botta O, Fogel ML, et al., 2008, Extraterrestrial nucleobases in the Murchison meteorite, EARTH PLAN SCI LETT, Vol: 270, Pages: 130-136, ISSN: 0012-821X
Carbon-rich meteorites, carbonaceous chondrites, contain many biologically relevant organic molecules and delivered prebiotic material to the young Earth. We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ13C=+44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These new results demonstrate that organic compounds, which are components of the genetic code in modern biochemistry, were already present in the early solar system and may have played a key role in life's origin.
Sephton MA, Botta O, 2008, Extraterrestrial organic matter and the detection of Life, SPACE SCI REV, Vol: 135, Pages: 25-35, ISSN: 1572-9672
A fundamental goal of a number of forthcoming space missions is the detection and characterization of organic matter on planetary surfaces. Successful interpretation of data generated by in situ experiments will require discrimination between abiogenic and biogenic organic compounds. Carbon-rich meteorites provide scientists with examples of authentic extraterrestrial organic matter generated in the absence of life. Outcomes of meteorite studies include clues to protocols that will enable the unequivocal identification of organic matter derived from life. In this chapter we summarize the diagnostic abiogenic features of key compound classes involved in life detection and discuss their implications for analytical instruments destined to fly on future spacecraft missions.
Bada JL, Ehrenfreund P, Grunthaner F, et al., 2008, Urey: Mars organic and oxidant detector, SPACE SCI REV, Vol: 135, Pages: 269-279, ISSN: 1572-9672
One of the fundamental challenges facing the scientific community as we enter this new century of Mars research is to understand, in a rigorous manner, the biotic potential both past and present of this outermost terrestrial-like planet in our solar system. Urey: Mars Organic and Oxidant Detector has been selected for the Pasteur payload of the European Space Agency’s (ESA’s) ExoMars rover mission and is considered a fundamental instrument to achieve the mission’s scientific objectives. The instrument is named Urey in recognition of Harold Clayton Urey’s seminal contributions to cosmochemistry, geochemistry, and the study of the origin of life. The overall goal of Urey is to search for organic compounds directly in the regolith of Mars and to assess their origin. Urey will perform a groundbreaking investigation of the Martian environment that will involve searching for organic compounds indicative of life and prebiotic chemistry at a sensitivity many orders of magnitude greater than Viking or other in situ organic detection systems. Urey will perform the first in situ search for key classes of organic molecules using state-of-the-art analytical methods that provide part-per-trillion sensitivity. It will ascertain whether any of these molecules are abiotic or biotic in origin and will evaluate the survival potential of organic compounds in the environment using state-of-the-art chemoresistor oxidant sensors.
Gounell M, Morbidelli A, Bland PA, et al., 2008, Meteorites from the Outer Solar System?, The Solar System Beyond Neptune, Editors: Baruchi MA, Boenhardt H, Cruikshank DP, Morbidelli A, Barucci MA, Boehnhardt H, Cruikshank DP, Morbidelli A, Tucson, Arizona, Publisher: The University of Arizona Press, Pages: 525-541, ISBN: 978-0-8165-2755-7
Sephton MA, Carvell RP, Sims MR, et al., 2008, The UK’s search for life on Mars, ASTRON GEOPHYS, Vol: 49, Pages: 33-36, ISSN: 1366-8781
Perry RS, Sephton MA, 2008, Solving the mystery of desert varnish with microscopy, In Focus, Vol: 11, Pages: 62-76, ISSN: 1750-4740
In areas such as Death Valley California whole mountains shimmer as light is reflected from widespread coatings of black opalescent desert varnish (Figure 1). Similar desert varnishes have been found on all continents, in locations such as the Gobi (Figure 2), Sonoran, Mojave, Namibian (Figure 3), Victorian and Atacama Deserts. These dark, lustrous coatings have attracted the interest of scientists for centuries. In 1852, the German naturalist and explorer Alexander Humboldt observed desert varnish on a transatlantic expedition and questioned how this enigmatic feature may have formed. His contemporary, Charles Darwin also engaged in the search for explanations for this unusual rock coating and, in 1871, attempted to satisfy his interest by performing chemical analyses. To date many other noteworthy scientists have examined desert varnish and have commented on its bulk chemistry, the arid conditions in which it forms in and the concentration of manganese that makes it opaque and causes it to be black.
Preston LJ, Benedix GK, Genge MJ, et al., 2008, A multidisciplinary study of silica sinter deposits with applications to silica identification and detection of fossil life on Mars, Icarus, Vol: 198, Pages: 331-350, ISSN: 0019-1035
Surface features observed on Mars and evidence from martian meteorites both suggest that hydrothermal systems have operated in the crust of the planet. Hydrothermal systems are a potential habitat for living organisms and identifying these on Mars is, therefore, important in the search for life beyond the Earth. One of the surface expressions of hydrothermal systems on Earth are silica sinters, deposited during the cooling of hydrothermal solutions. In this paper we present analyses of the mineralogy, textures, chemistry and organic chemistry of silica sinters from two very different geothermal provinces, Waiotapu, New Zealand and Haukadalur, Iceland, in order to determine common features by which silica sinters can be identified. Infrared reflectance spectroscopy was utilised in combination with textural studies to evaluate the mineralogy of sinter deposits in terms of the abundances of different polymorphs of SiO2. Concentrations of organic molecules, principally lipids, within regions of the sinters in which there is textural evidence for micro-organisms were identified in the infrared spectral data and their presence was confirmed using gas chromatography mass spectroscopy. The results of this study indicate that reflectance spectra in the wavelength region from 2.5 to 14 μm, when calibrated against natural terrestrial analogues, can be used to identify silica sinters, as well as the possible presence of recent microbial communities on Mars.
Aubrey AD, Chalmers JH, Bada JL, et al., 2008, The Urey Instrument: An Advanced In Situ Organic and Oxidant Detector for Mars Exploration, Astrobiology, Vol: 8, Pages: 583-595, ISSN: 1531-1074
The Urey organic and oxidant detector consists of a suite of instruments designed to search for several classes of organic molecules in the martian regolith and ascertain whether these compounds were produced by biotic or abiotic processes using chirality measurements. These experiments will also determine the chemical stability of organic molecules within the host regolith based on the presence and chemical reactivity of surface and atmospheric oxidants. Urey has been selected for the Pasteur payload on the European Space Agency's (ESA's) upcoming 2013 ExoMars rover mission. The diverse and effective capabilities of Urey make it an integral part of the payload and will help to achieve a large portion of the mission's primary scientific objective: “to search for signs of past and present life on Mars.” This instrument is named in honor of Harold Urey for his seminal contributions to the fields of cosmochemistry and the origin of life.
Carvell RP, Sims MR, Sephton MA, et al., 2008, The Search for Life on Mars, Science in Parliament, Vol: 65, Pages: 12-13, ISSN: 0263-6271
Jiao D, Perry RS, Engel MH, et al., 2008, Biomarker indicators of bacterial activity and organic fluxes during end Triassic mass extinction event (art. no. 709709), Conference on Instruments, Methods, and Missions for Astrobiology XI, Publisher: The International Society for Optical Engineering, Pages: 1-12
Bada JL, Ehrenfreund P, Grunthaner F, et al., 2008, Urey: Mars Organic and Oxidant Detector, STRATEGIES OF LIFE DETECTION, Editors: Botta, Bada, GomezElvira, Javaux, Selsis, Summons, Publisher: SPRINGER, Pages: 269-279, ISBN: 978-0-387-77515-9
Sephton MA, Botta O, 2008, Extraterrestrial Organic Matter and the Detection of Life, STRATEGIES OF LIFE DETECTION, Editors: Botta, Bada, GomezElvira, Javaux, Selsis, Summons, Publisher: SPRINGER, Pages: 25-35
Sephton MA, Meredith W, Sun C-G, et al., 2007, Biomedical and forensic applications of combined catalytic hydrogenation-stable isotope ratio analysis, Analytical Chemistry Insights, Vol: 2, Pages: 37-42, ISSN: 1177-3901
Studies of biological molecules such as fatty acids and the steroid hormones have the potential to benefit enormously from stable carbon isotope ratio measurements of individual molecules. In their natural form, however, the body’s molecules interact too readily with laboratory equipment designed to separate them for accurate measurements to be made.Some methods overcome this problem by adding carbon to the target molecule, but this can irreversibly overprint the carbon source ‘signal’. Hydropyrolysis is a newly-applied catalytic technique that delicately strips molecules of their functional groups but retains their carbon skeletons and stereochemistries intact, allowing precise determination of the carbon source. By solving analytical problems, the new technique is increasing the ability of scientists to pinpoint molecular indicators of disease, elucidate metabolic pathways and recognise administered substances in forensic investigations.
Martins Z, Alexander CMO, Orzechowska GE, et al., 2007, Indigenous amino acids present in CR primitive meteorites, 70th Annual Meeting of the Meteoritical-Society, Publisher: METEORITICAL SOC, Pages: A97-A97, ISSN: 1086-9379
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- Citations: 7
Watson JS, Sephton MA, Sephton SV, et al., 2007, Rapid determination of spore chemistry using thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy, PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, Vol: 6, Pages: 689-694, ISSN: 1474-905X
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- Citations: 45
Siegert MJ, Behar A, Bentley M, et al., 2007, Exploration of ellsworth subglacial lake: A concept paper on the development, organisation and execution of an experiment to explore, measure and sample the environment of a West Antarctic subglacial lake, Life in Extreme Environments, Pages: 25-43, ISBN: 9781402062841
Antarctic subglacial lakes have, over the past few years, been hypothesised to house unique forms of life and hold detailed sedimentary records of past climate change. Testing this hypothesis requires in situ examinations. The direct measurement of subglacial lakes has been considered ever since the largest and best-known lake, named Lake Vostok, was identified as having a deep water-column. The Subglacial Antarctic Lake Environments (SALE) programme, set up by the Scientific Committee on Antarctic Research (SCAR) to oversee subglacial lakes research, state that prior exploration of smaller lakes would be a prudent way forward. Over 145 subglacial lakes are known to exist in Antarctica, but one lake in West Antarctica, officially named Ellsworth Subglacial Lake (referred to hereafter as Lake Ellsworth), stands out as a candidate for early exploration. A consortium of over 20 scientists from seven countries and 14 institutions has been assembled to plan the exploration of Lake Ellsworth. An eight-year programme is envisaged: 3 years for a geophysical survey, 2 years for equipment development and testing, 1 year for field planning and operation, and 2 years for sample analysis and data interpretation. The science experiment is simple in concept but complex in execution. Lake Ellsworth will be accessed using hot water drilling. Once lake access is achieved, a probe will be lowered down the borehole and into the lake. The probe will contain a series of instruments to measure biological, chemical and physical characteristics of the lake water and sediments, and will utilise a tether to the ice surface through which power, communication and data will be transmitted. The probe will pass through the water column to the lake floor. The probe will then be pulled up and out of the lake, measuring its environment continually as this is done. Once at the ice surface, any water samples collected will be taken from the probe for laboratory analysis (to take place over subsequent y
Parbhakar A, Cuadros J, Sephton MA, et al., 2007, Adsorption of L-lysine on montmorillonite, COLLOID SURFACE A, Vol: 307, Pages: 142-149, ISSN: 0927-7757
Amino acid adsorption on smectite is relevant to prebiotic processes involving possible catalytic reactions in the early Solar System, as implied by the clay-organic correlation found in meteorites, and the generation and modification of organic components essential for the origin of life. Here we report the results of a study investigating the adsorption of l-lysine (0.025–0.4 M) onto montmorillonite. The reaction products were studied using X-ray diffraction, chemical analysis and infrared spectroscopy.We find that lysine adsorption is first dominated by cation exchange and then by adsorption of electrically neutral lysine (as a zwitterion), as indicated by chemical and FTIR evidence. At the maximum concentration, lysine displaces only ∼1/3 of the original interlayer cations. The d-spacing of the smectite–lysine complex increases from 1.2 to 2.1 nm as more lysine enters the interlayer space, and water is expelled. We propose a structural model of lysine sorption in the interlayer in which lysine is oriented at >45–90◦ to the plane of siloxane O atoms.
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