Hostile Chemical Environments Research Articles

Quartz arenites as signatures of cratonisation: examples from the Archaean Stratigraphic Record, southern Africa

Abstract Holocene quartz-rich sands such as in the Orinoco River of Venezuela and Columbia, develop under a unique set of conditions including tectonic stability, intense weathering and long-term storage of sediment prior to burial. This review paper proposes that a similar set of conditions existed on the Mesoarchaean Earth by 3.0 Ga. Compositionally and texturally mature quartz arenites are present in the Mesoarchaean Hospital Hill Subgroup and correlative lower Mozaan Group, in the cover rocks of the Beitbridge Complex in the Limpopo Belt and at Buhwa in southern Zimbabwe as well as the Neoarchaean Manjeri Formation of Zimbabwe. These quartz arenites are interpreted as first-cycle and developed following the formation of stable cratons under conditions of slow subsidence (<10 cm/1 000 years), intense weathering in a hostile chemical environment related to the ambient carbon dioxide-rich atmosphere, long-distance intrabasinal transport by tides and/or waves and microbial processes that influenced the local chemical environment. Similar examples of Mesoarchaean quartz arenites are documented from the Yilgarn Block in Western Australia, the Slave and Superior provinces in Canada and the Dharwar and Singhbhum cratons in India. On a global scale, cratonisation was diachronous with the Kaapvaal Craton stabilised on a regional scale by 3.0 Ga whereas microcontinents existed over the remainder of Earth.

Inhibition of AcrAB-TolC enhances antimicrobial activity of phytochemicals in Pectobacterium brasiliense.

The eons-long co-evolvement of plants and bacteria led to a plethora of interactions between the two kingdoms, in which bacterial pathogenicity is counteracted by plant-derived antimicrobial defense molecules. In return, efflux pumps (EP) form part of the resistance mechanism employed by bacteria to permit their survival in this hostile chemical environment. In this work we study the effect of combinations of efflux pump inhibitors (EPIs) and plant-derived phytochemicals on bacterial activity using Pectobacteriun brasiliense 1692 (Pb1692) as a model system. We measured the minimal inhibitory concentration (MIC) of two phytochemicals, phloretin (Pht) and naringenin (Nar), and of one common antibiotic ciprofloxacin (Cip), either alone or in combinations with two known inhibitors of the AcrB EP of Escherichia coli, a close homolog of the AcrAB-TolC EP of Pb1692. In addition, we also measured the expression of genes encoding for the EP, under similar conditions. Using the FICI equation, we observed synergism between the EPIs and the phytochemicals, but not between the EPIs and the antibiotic, suggesting that EP inhibition potentiated the antimicrobial activity of the plant derived compounds, but not of Cip. Docking simulations were successfully used to rationalize these experimental results. Our findings suggest that AcrAB-TolC plays an important role in survival and fitness of Pb1692 in the plant environment and that its inhibition is a viable strategy for controlling bacterial pathogenicity.

"Smart Decomposition" of Cyclic Alanine-Alanine Dipeptide by VUV Radiation: A Seed for the Synthesis of Biologically Relevant Species.

A combined experimental and theoretical study shows how the interaction of VUV radiation with cyclo-(alanine-alanine), one of the 2,5-diketopiperazines (DKPs), produces reactive oxazolidinone intermediates. The theoretical simulations reveal that the interaction of these intermediates with other neutral and charged fragments, released in the molecular decomposition, leads either to the reconstruction of the cyclic dipeptide or to the formation of longer linear peptide chains. These results may explain how DKPs could have, on one hand, survived hostile chemical environments and, on the other, provided the seed for amino acid polymerization. Shedding light on the mechanisms of production of such prebiotic building blocks is of paramount importance to understanding the abiotic synthesis of relevant biologically active compounds.

Status, conservation and ecology of the exceptionally rare metallophyte Cornish Path-moss (Ditrichum cornubicum Paton)

Cornish Path-moss is one of the world’s rarest bryophytes, presently known from just three sites, former copper mines in the UK and Ireland. Covering the two UK sites, for the first time this study provides a set of location coordinates (x-, y- and z-axis) that is comprehensive, accurate and precise, in addition to investigating aspects of its ecology and assessing the success of trial habitat management plots. The species is shown to be rare, with a total population occupying 490 Ordnance Survey (OS) 10 cm grid cells, 77% at Phoenix United Mine and the remainder at South Caradon Mine, confined to bare patches of metalliferous soil that are especially high in the phytotoxins arsenic, cobalt and copper. Whilst the hostile chemical environment limits competition, various tolerant and larger bryophytes, lichens and vascular plants are shown to occupy the same niche, so that competitive exclusion is a constant threat. Turf-stripping of trial habitat management plots using a mechanical excavator at Phoenix United Mine, re-exposing bare metalliferous ground, is shown to be remarkably successful, providing a 20-fold increase in the population, presently making it the most important site for the plant in the world. Priorities for future survey and research are considered.

The radiation response of mesoporous nanocrystalline zirconia thin films

The next generation of nuclear systems will require materials capable of withstanding hostile chemical, physical and radiation environments over long time-frames. Aside from its chemical and physical stability, crystalline zirconia is one of the most radiation tolerant materials known. Here we report the first ever study of the radiation response of nanocrystalline and mesoporous zirconia and Ce3+-stabilized nanocrystalline zirconia (Ce0.1Zr0.9O2) thin films supported on silicon wafers. Zirconia films prepared using the block copolymer Brij-58 as the template had a thickness of around 60–80 nm. In the absence of a stabilizing trivalent cation they consisted of monoclinic and tetragonal zirconia nanocrystals with diameters in the range 8–10 nm. Films stabilized with Ce3+ contained only the tetragonal phase. The thin films were irradiated with iodine ions of energies of 70 MeV and 132 keV at low fluences (1013 - 1014 cm−2) corresponding to doses of 0.002 and 1.73 dpa respectively, and at 180 keV and high fluences (2 × 1016 cm−2) corresponding to 82.4 dpa. The influence of heavy ion irradiation on the nanocrystalline structure was monitored through Rietveld analysis of grazing incidence X-ray diffraction (GIXRD) patterns recorded at angles close to the critical angle to ensure minimum contribution to the diffraction pattern from the substrate. Irradiation of the mesoporous nanocrystalline zirconia thin films with 70 MeV iodine ions, for which electronic energy loss is dominant, resulted in slight changes in phase composition and virtually no change in crystallographic parameters as determined by Rietveld analysis. Iodine ion bombardment in the nuclear energy loss regime (132–180 keV) at low fluences did not provoke significant changes in phase composition or crystallographic parameters. However, at 180 keV and high fluences the monoclinic phase was totally eliminated from the GIXRD pattern of films prepared at both 350 and 500 °C implying either a monoclinic-to-tetragonal or a monoclinic-to-amorphous transition. This irradiation at very high doses resulted in film shrinkage and a loss of mesopore ordering but little or no degradation of the crystallinity of the tetragonal phase. A small increase in the crystalline domain size of the tZrO2 phase was noted in these films. In contrast, single-phase Ce3+-stabilized tetragonal nanocrystalline zirconia mesoporous films prepared at 350 °C suffered considerable loss of crystalline order when irradiated at 82 dpa. This loss of crystallinity was less pronounced in films heated to 500 °C. The loss of crystallinity of the tetragonal phase in the Ce-stabilized tetragonal zirconia thin films w.r.t. the tetragonal phase in the unstabilized films was attributed to the oxygen vacancies introduced in the latter due to the need for charge compensation.

Effect of Process Conditions on the Microstructure of Particle-Stabilized Al2O3Foam

foam is an important engineering material because of its exceptional high-temperature stability, low thermal conductivity, good wear resistance, and stability in hostile chemical environment. In this work, foams were designed to control the microstructure, porosity, and cell size by varying different parameters such as the amount of amphiphile, solid loading, and stirring speed. Particle stabilized direct foaming technique was used and the particles were partially hydrophobized upon the adsorption of valeric acid on particles surface. The foam stability was drastically improved when these particles were irreversibly adsorbed at the air/water interface. However, there is still considerable ambiguity with regard to the effect of process parameters on the microstructure of particle-stabilized foam. In this study, the foam with open and closed-cell structure, cell size ranging from to having single strut wall and porosity from 75% to 93% were successfully fabricated by sintering at for 2 h in air.

Taste, Reward, and Physiology

Taste is an intermediary between the traditional externally oriented senses and visceral sensation. It possesses typical features of other senses, such as identification of stimulus quality and intensity through a spatiotemporal code. But taste may be classified as a visceral afferent system according to its embryological, anatomical, and functional characteristics. The sense of taste may be viewed as the beginning of a body-long chemosensory tube with receptors throughout that are sensitive to the molecules being liberated by the digestive process. Chemicals stimulating taste receptors, however, are only candidates for ingestion—the commitment to accept them has not yet been made. Thus, it is the obligation of the taste system to assess the desirability of consuming a prospective food relative to the momentary physiological needs of the animal it serves. Vision and olfaction give evidence, but taste is the final arbiter in determining which subset of the unruly and often hostile chemical environment will be permitted entry into the tightly monitored biochemical world within. Thus, taste may be viewed as a Janus head, placed on an ancient city gate, one face turned outward to assess the goods and perils surrounding its walls, the other facing in to determine what its inhabitants need at the moment. Taste is well suited to its task of matching availability to need through its anatomy and function, which will first be described in chemically oriented rodents, then in visually dominated primates. The two will be treated separately because they use quite different strategies to carry out similar activities. Moreover, nearly all the hindbrain data are from rodents, and most of the forebrain data are from primates.

Wear and oxidation behaviour of shrouded plasma sprayed fly ash coatings

In a wide variety of applications, mechanical components are subjected to severe conditions, such as high load, speed or temperature and hostile chemical environment. Thus, their surface modification is necessary in order to protect them against various types of degradation. Thermal spraying has emerged as an important tool of increasingly sophisticated surface engineering technology. Plasma spraying is a rather simple process from a practical point of view. In the present investigation, the fly ash coating has been obtained by shrouded plasma spray process on carbon steel. The coating was characterized with relative to important behavioural parameters. Wear, oxidation and salt corrosion behaviour have also been evaluated. The coating has found to posses much higher hardness values than base steel and its porosity is slightly higher than the range of porosity for plasma spray coatings. The coating was effective to increase the oxidation and salt corrosion resistance of the given carbon steel. However, the wear resistance of fly ash coated steel was observed to be lesser than the bare steel probably due to coarse grain size.

Liposomes as Protective Capsules for Active Silica Sol−Gel Biocomposite Synthesis

Using liposome to shield an enzyme from hostile chemical environments during the sol-gel formation process has resulted in a novel approach to synthesizing silica sol-gel biocomposite materials. By reporting the encapsulation of horseradish peroxidase and firefly luciferase, we demonstrate that this new protocol can produce silica biocomposites that are more active than trapping the enzymes directly into hydrogels.

Column: News from Canada

Plastics Resins that Sound like Metal was presented by W. E. Sattich, Product Development Specialist from Chevron Phillips Chemical Company. The speaker described the exceptional properties of Poly(phenylene sulphide) (PPS) and its applications. He pointed out the recent developments of blends and alloys of PPS with other polymers, leading to compounds with excellent thermal stability, high modulus, creep resistance, inherent non-flammability, and good dimensional stability at elevated temperatures and in hostile chemical environments. Special Effects in Your Resin was presented by S. D. Swain, Product Manager Color RTP Company. This presentation dealt with the addition of extraordinary colors, fragrances, antimicrobial and microtags.

The effect of carbon encapsulation on the magnetic properties of Ni nanoparticles producedby arc discharge in de-ionized water

Despite intensive research on optimizing the methods for depositing carbon encapsulatedferromagnetic nanoparticles, the effect of the carbon cages remains unclear. Inthe present work, the effect of the graphitic cages on the magnetization of theferromagnetic core has been studied by comparing the magnetic properties of pure andcarbon encapsulated Ni particles of the same size. The carbon encapsulated Niparticles were formed using an electric arc discharge in de-ionized water between asolid graphite cathode and an anode consisting of Ni and C in a mass ratio ofNi:C = 7:3. This method is shown to have potential for low cost production of carbon encapsulated Ninanoparticle samples with narrow particle size distributions. X-ray diffraction(XRD) and high resolution transmission electron microscopy (HRTEM) analysiswere used to study the crystallography, morphology, and size distribution of theencapsulated and pure Ni nanoparticle samples. The availability of encapsulatedparticles with various sizes allowed us to elucidate the role of carbon cages insize-dependent properties. Our data suggest that even though encapsulation isbeneficial for protection against hostile chemical environments and for avoiding lowproximity phenomena, it suppresses the saturation magnetization of the Ni cores.

Altered biochemical profile and gene expression in aflatoxin B-1-transformed C3H10T1/2 cells

A transformed cell line 7SA, obtained by transformation of C3H10T1/2 cells with irt vitro activated aflatoxin B-1 (AFB(1)), was used to investigate biochemical and molecular alterations associated with transformation by AFB(1). 7SA cells demonstrate an altered biochemical phenotype characterized by alterations in phase I and phase II enzymes in a manner that would allow these cells to survive in a hostile chemical environment. Investigations of the molecular basis of transformation revealed no mutations in codons 12/13 and 61 of ras genes (Ha-, Ki- and N-ras) and in exons 5, 6, 7 and 8 of p53 tumor suppressor gene. However, subtractive hybridization led to the isolation of seven novel cDNA clones that demonstrated 2 to 10-fold overexpression of the mRNAs corresponding to the five cDNAs (SK1, SK2, SK3, SK4 and SK5) and >400 fold overexpression of the mRNAs corresponding to the other two cDNAs (SK67 and SK153). In addition, part of the sequence of the cDNA clone SK5 demonstrated >88% identity with L1-like mobile genetic element and Southern analysis of the DNA with SK5 cDNA as a probe revealed gene rearrangement in 7SA DNA, compared to DNA from C3H10T1/2 cells.

Computerized in vitro test for chemical toxicity based on Tetrahymena swimming patterns

An apparatus and a method for rapidly determining chemical toxicity have been evaluated as an alternative to the rabbit eye initancy test (Draize). The toxicity monitor includes an automated scoring of how motile biological cells ( Tetrahymena pyriformis) slow down or otherwise change their swimming patterns in a hostile chemical environment. The method, called the Motility Assay (MA), is tested for 30 s to determine the chemical toxicity in 20 aqueous samples containing trace organics and salts. With equal or better detection limits, results compare favorably to in vivo animal tests of eye irritancy.

Reduction of Fused-Silica-Fiber Raman Backgrounds in High-Temperature Fiber-Optic Raman Spectroscopy via the Measurement of Anti-Stokes Raman Spectra

Measurements of laser Raman spectroscopy using optical fibers have recently become an active area of study. The technique requires minimum alignment of samples with respect to an input laser beam or collection optics, and the sample may be located some distance from the spectrometer in a hostile environment. Most fiber-optic probes employed for such spectroscopic measurements have been constructed by sealing the collecting fibers and one input fiber into a metal or glass protective tube with a special kind of epoxy cement. These materials in a probe impose difficulties in the collection of spectra in some hostile chemical environments because of chemical reactions of the epoxy resin with the surrounding environment. Recently we have reported the fabrication of an all-fused-silica fiber-optic probe that is useful for measuring Raman spectra of molten salt systems at high temperature. A drawback of fiber-optic remote Raman spectroscopy is the large background Raman signals generated from the optical fiber itself. Therefore, the major requirement of remote Raman spectroscopy is the reduction of the unwanted background signals to a level below that of the sample Raman signals. Myrick and Angel have reported the use of optical interference filters to filter out the background fiber signals. In that study, a bandpass filter was used at the tip of the excitation optical fiber to reject any fluorescence or unwanted background signals from the excitation fiber, which, at the same time, allows transmission of the large portion of the laser beam. Similar techniques have also been employed by Sharma and his co-workers in their recent remote fiber-optic studies. Usually, these optical filters cannot survive high-temperature conditions. Here we want to report a simple and yet efficient method to minimize the fiber background signals for high-temperature remote Raman spectroscopy. The performance of the method was characterized by the measurement of Raman spectra of magnesium tetrachloride ion in a high-temperature molten salt medium.

Study of the fracture toughness and fracture morphology of polybenzimidazole

Polybenzimidazole (PBI) is a relatively new polymeric material exhibiting unusual properties that are attributable to its aromatic-heterocyclic monomer structure. Owing to its high strength, stiffness and excellent stability in hostile chemical and thermal environments, PBI is being used increasingly in critical applications. As a result, understanding the failure mechanisms of the material is vital. This paper presents the results of a study of the fracture toughness and fracture morphology of polybenzimidazole. The standard compact tension specimen was used as the basic experimental specimen in this study. The fracture tests were performed in an Instron tensile testing machine. The effects of varying the loading rate, and the ratio of the initial crack length,a, to the ligament length,W, were investigated. The fracture surface morphology was examined using optical and scanning electron microscopy. The results of this study indicate that the precracking technique significantly affects the measured fracture toughness. Also, an increase in the loading rate causes a significant decrease in fracture toughness. Examination of the fracture morphology reveals that PBI fracture surfaces exhibit many of the characteristics expected of a tough engineering plastic.

Genetic factors in neurotoxicology and neuropharmacology: A critical evaluation of the use of genetics as a research tool

Animals have evolved a detoxication system to enable them to survive in a hostile chemical environment in which foods contain many non-nutrient chemicals. Detoxication depends on enzymes which are often genetically polymorphic. As a result, inter-individual variation is common, and in humans several Mendelian loci have been identified. However, most variation in response is probably due to the action of several genes. Genetic variation in response to the neurotoxin MPTP and to chemically and physically-induced seizures is reviewed. In the former case, differences between pigmented and white mouse strains have been noted which are consistent with the hypothesis that humans are more sensitive than mice or rats because of the presence of melanin in human brains. However, variation in sensitivity probably also depends on other genes. In the case of audiogenic seizures, a single locus has been identified and mapped, but its relationship with seizures induced by other agents is not clear. Genetic variation in response to alcohol is also discussed. The failure of most toxicologists to consider genetic variation as a potentially confounding variable, and as a powerful research tool, is discussed critically in relation to non-repeatability of research on the neurotoxic effects of lead, and in relation to the genetic variation in MPTP, seizures, and alcohol response already noted. It seems clear that genetic methods provide a powerful research tool which is largely being ignored by toxicologists.

Polymer-supported metal complex oxidation catalysts

Abstract

Survivability of thermal barrier coatings

Thermal barrier ceramic oxide coatings are gaining wide acceptance for applications in heat engines. Such ceramic thermal shields are used in conjunction with MCrAlY-type intermediate bond coatings, applied over superalloy substrates. The thermal barrier coatings must endure extreme thermal cycling and hostile chemical environments. A discussion is presented on the various important features which need to be addressed in the design of viable thermal barrier coating systems.

Cockpits for 2010 and Beyond

Truly optimal weapon system performance is highly dependent on the level of man-machine cockpit integration resulting from the intelligent application of crew station technologies. Future cockpits will incorporate a wide range of enhancements. Heavy application of artificial intelligence techniques can be expected to encompass the entire spectrum of crew station technologies; from data fusion, to optimized display resource management, to real-time onboard maintenance and fault reporting, and even to the optimization of pilot physiological needs. Emphasis on exploiting applications of the ultimate human resource, the mind, can be expected through the use of biocybernetics; initially to control previously manual and/or automated cockpit functions, and eventually to allow bidirectional communications. Future enhancements can also be expected to improve aircrew performance by allowing the pilot to take full advantage of aircraft maneuvering capability, and to operate effectively in hostile chemical, biological and radiological environments. New high resolution, full color, three dimensional crew station display devices will complement enlarged sensor suites and enhance aircrew situational awareness. Does the pilot really need to see the outside world to fly and fight effectively? Or, can panoramic display techniques, in an encapsulated environment, coupled with 4π steradian sensor coverage, increase performance? This paper strives to illustrate some ``no holds barred'' approaches to making future fighter cockpits an ``in-tune'' extension of the operator, based on current and projected tactical needs.