The role of cometary particle Coalescence in chemical evolution

Important prebiotic organic compounds might have been transported to Earth in dust or produced in vapor clouds resulting from atmospheric explosions or impacts of comets. These compounds coalesced in the upper atmosphere with particles ejected from craters formed by impacts of large objects. Coalescence during exposure to UV radiation concentrated organic monomers and enhanced formation of oligomers. Continuing coalescence added material to the growing particles and shielded prebiotic compounds from prolonged UV radiation. These particles settled into the lower atmosphere where they were scavenged by rain. Aqueous chemistry and evaporation of raindrops containing nomomers in high temperature regions near the Earth's surface also promoted continued formation of oligomers. Finally, these oligomers were deposited in the oceans where continued prebiotic evolution led to the most primitive cell. Results of our studies suggest that prebiotic chemical evolution may be an inevitable consequence of impacting comets during the late accretion of planets anywhere in the universe if oceans remained on those planetary surfaces.     

Laboratory investigations of mars: Chemical and spectroscopic characteristics of a suite of clays as Mars Soil Analogs

Two major questions have been raised by prior explorations of Mars. Has there ever been abundant water on Mars? Why is the iron found in the Martian soil not readily seen in the reflectance spectra of the surface? The work reported here describes a model soil system of Mars Soil Analog Materials, MarSAM, with attributes which could help resolve both of these dilemmas. The first set of MarSAM consisted of a suite of variably iron/calcium-exchanged montmorillonite clays. Several properties, including chemical composition, surface-ion composition, water adsorption isotherms, and reflectance spectra, of these clays have been examined. Also, simulations of the Viking Labeled Release Experiment using the MarSAM were performed. The results of these studies show that surface iron and adsorbed water are important determinants of clay behavior as evidenced by changes in reflectance, water absorption, and clay surface reactions. Thus, these materials provide a model soil system which reasonably satisfies the constraints imposed by the Viking analyses and remote spectral observations of the Martian surface, and which offers a sink for significant amounts of water. Finally, our initial results may provide insights into the mechanisms of reactions that occur on clay surfaces as well as a more specific approach to determining the mineralogy of Martian soils.     

Comparison of the separation of Candida albicans chromosome-sized DNA by pulsed-field gel electrophoresis techniques.

Pulsed-field gel electrophoresis techniques were used to study chromosome-sized DNA molecules of C. albicans. Chromosome-sized DNA of two strains of Candida albicans has been resolved into 8 bands by orthogonal-field-alternation gel electrophoresis (OFAGE). Six bands were observed in chromosomal preparations of C. albicans using field-inversion gel electrophoresis (FIGE). Differences in the electrophoretic mobilities of bands of the strains of C. albicans examined suggests that chromosome-length polymorphisms exist and make it difficult to correlate the banding patterns among strains. These correlations were facilitated, however, by assignment of C. albicans chromosomes by hybridization using a collection of cloned DNA probes specific for each of the 8 observed bands. Southern blotting showed that the 6 FIGE bands consisted of 4 singlets and 2 comigrating doublets, accounting for the 8 bands observed by OFAGE analysis. The agreement between OFAGE and FIGE analysis suggests that the C. albicans haploid genome contains a minimum of 8 chromosomes.     

Synthesis,characterization, and electrocatalytic behaviour of hydrothermally grown nanostructured La2O3 and La2O3/K-complex

Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4-N,N-dimethylaminobenzoate-κO)(μ2–4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La₂O₃ nanomaterials to obtain a nanohybrid La₂O₃/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and ¹H and ¹³C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La₂O₃/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La₂O₃/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour.     

The relation of acyl transfer to the overall reaction of thiolase I from porcine heart

Thiolase I (long chain 3-ketoacyl-CoA-specific) from porcine heart has been characterized kinetically. In the direction of acetoacetyl-CoA cleavage, a variety of thiols including CoASH show the same Vmax at saturating concentrations of acetoacetyl-CoA. At a constant overall velocity of acetoacetyl-CoA disappearance, one of the two acetyl groups from acetoacetyl-CoA will partition between CoASH and 2-mercaptoethanol at increasing 2-mercaptoethanol concentrations. These observations suggest rate-determining formation of an acetyl enzyme intermediate in the direction of acetoacetyl-CoA cleavage. In the direction of acetoacetyl-CoA formation from two molecules of acetyl-CoA, the Vmax of acetoacetyl-CoA formation is identical with the Vmax for an acetyl-CoA in equilibrium CoA isotope exchange reaction and the Vmax for an enzyme-catalyzed acetyl transfer reaction between acetyl-CoA and 2-mercaptoethanol. This suggests that in the direction of acetoacetyl-CoA synthesis, the acetyl transfer half-reaction is rate-limiting. The acetyl intermediate has been isolated and characterized. The equilibrium constant for acetyl enzyme formation from acetyl-CoA and free enzyme is 1 +/- 0.5 X 10(-2). The rate constant for spontaneous hydrolysis of the acetyl enzyme (2.6 X 10(-4) s-1) is a factor of 400 faster than the rate constant for acetyl-CoA hydrolysis under comparable conditions. The acetyl enzyme is thermodynamically and kinetically destabilized compared to acetyl-CoA.     

The search for life on Mars: Viking 1976 gas changes as indicators of biological activity

Gas compositional changes in the headspace of the Viking Biology Gas Exchange Experiment can originate from biological activity as well as redox chamical reactions, sorption and desorption phenomena, acid-base reactions, and trapped gas release. Biological phenomena are differentiated from the nonbiological gas changes by their dynamical qualities, notably by the ability of the M4 medium to sustain biological activity. Medium incompatibilities, with potential microbial types in soils, are demonstrated to be ameliorated by an incubation chamber design that provides thin films of medium around particulate soil masses and salt gradients when the soil is wet from below. Two phenomena in soils, the production and consumption of hydrogen and carbon monoxide, are coupled for a newly isolatedClostridium sp. A decrease in molecular nitrogen production by denitrifying organisms in the second and subsequent incubation cycles results from competitive nitrate utilization by anaerobic organisms. All soils tested from the cold, dry desert regions of Antarctica contain predominantly aerobic organisms while only six of the twelve soils respire using nitrate under anaerobic conditions. Although dry Antarctica soils are not the best simulations of Martian anoxic conditions, their responses show that long incubation times may be needed on Mars to demonstrate biological gas change phenomena.     

Two silicone nontoxic fouling release coatings: Hydrosilation cured PDMS and CaCO3 filled,ethoxysiloxane cured RTV11

Two silicone coatings have been evaluated for barnacle adhesion. One coating is an unfilled hydrosilation cured polydimethylsiloxane (PDMS) network, while the other is a room temperature vulcanized (RTV), filled, ethoxysiloxane cured PDMS elastomer, RTV11^?. The adhesion strength of one species of barnacle, Balanus eburneus, to the hydrosilation coatings is in the range of 0.37–0.60 kg cm^‐2 while the corresponding range for RTV11 is 0.64–0.90 kg cm^‐2. The easier release of B. eburneus from the hydrosilation cured network compared to RTV11 is discussed in relationship to differences in bulk and surface properties. Preliminary results suggest bulk modulus may be the most important parameter in determining barnacle adhesion strength. In light or mechanical property analysis, a re‐evaluation of surface properties and chemical stability is presented.