Biomedical subjects

James E Amonette

Publications and source records attributed to James E Amonette.

9 recordsLinked to original sources

PubMed2006

Metal-based nanoparticle synthesis from the rapid expansion of carbon dioxide solutions.

Synthesis of 10 to 500 nm diameter Fe-based nanoparticles is described. Nanometer-sized droplets of iron carbonyl are generated by the rapid expansion of CO2-based supercritical fluid solutions and are photolyzed in-flight using a UV lamp to remove the carbonyl groups. Solid metal particles are collected electrostatically as coatings or loose particle aggregates on solid surfaces. Upon air oxidation, the iron particles react rapidly to produce an iron oxide phase. Mo-based nanoparticles were similarly produced using a Mo(Co)6 precursor. FTIR analysis of collected nanoparticles suggests that carbonyl groups are more readily photolyzed from the Fe precursor than from the Mo analog.

Carbon Dioxide↗

PubMed2006

Quantification of volatile organics in soil aging experiments using fourier transform infrared spectroscopy.

On-line Fourier transform infrared (FT-IR) spectroscopy was applied to monitor the concentration of halogenated volatile organic compounds in a sample-preparation process that simulates long-term, slow accumulation of contaminants in soils (i.e., aging). Artificial aging is conducted by circulating a supercritical fluid solution containing the contaminant(s) of interest through a packed soil column. Mid-infrared spectra of several volatile halocarbons were measured in supercritical Xe and CO(2) to evaluate possible interferences from the strong absorption of CO(2). Although some of the C-X bands were partially masked in supercritical CO(2), all of the compounds studied had distinct spectral features in the region 1400-700 cm(-1) and could be monitored in either solvent. Quantitative measurements of halogenated volatile organics in supercritical CO(2) were demonstrated with CCl(4). Excellent results were obtained over the range 7-280 mM. Representative artificial aging experiments were conducted on two test soils using CCl(4) as the contaminant. On-line (FT-IR) estimates of the aged soil concentrations were 1.3-4.4 times higher than off-line concentrations obtained by gas chromatography/mass spectrometry. The discrepancies were primarily ascribed to post-aging losses that occurred during depressurization and subsequent sample handling. FT-IR spectroscopy is shown to be a powerful tool for monitoring soil loading behavior and for developing artificial aging protocols.

Carbon↗

PubMed2005

Reoxidation of reduced uranium with iron(III) (hydr)oxides under sulfate-reducing conditions.

In cultures of Desulfovibrio desulfuricans 620 the effects of iron(III) (hydr)oxides (hematite, goethite, and ferrihydrite) on microbial reduction and reoxidation of uranium (U) were evaluated under lactate-limited sulfate-reducing conditions. With lactate present, G20 reduced U(VI) in both 1,4-piperazinediethanesulfonate (PIPES) and bicarbonate buffer. Once lactate was depleted, however, microbially reduced U served as an electron donor to reduce Fe(III) present in iron(III) (hydr)oxides. With the same initial amount of Fe(III) (10 mmol/L) for each iron(III) (hydr)oxide, reoxidation of U(IV) was greater with hematite than with goethite orferrihydrite. As the initial mass loading of hematite increased from 0 to 20 mmol of Fe(III)/L, the rate and extent of U(IV) reoxidation increased. Subsequent addition of hematite [15 mmol of Fe(III)/L] to stationary-phase cultures containing microbially reduced U(IV) also resulted in rapid reoxidation to U(VI). Analysis by U L3-edge X-ray absorption near-edge spectroscopy (XANES) of microbially reduced U particles yielded spectra similar to that of natural uraninite. Observations by high-resolution transmission electron microscopy, selected area electron diffraction, and energy-dispersive X-ray spectroscopic analysis confirmed that precipitated U associated with cells was uraninite with particle diameters of 3-5 nm. By the same techniques, iron sulfide precipitates were found to have a variable Fe and S stoichiometry and were not associated with cells.

Alkanesulfonic Acids↗

PubMed2005

Characterization and properties of metallic iron nanoparticles: spectroscopy, electrochemistry, and kinetics.

There are reports that nano-sized zero-valent iron (Fe0) exhibits greater reactivity than micro-sized particles of Fe0, and it has been suggested that the higher reactivity of nano-Fe0 may impart advantages for groundwater remediation or other environmental applications. However, most of these reports are preliminary in that they leave a hostof potentiallysignificant(and often challenging) material or process variables either uncontrolled or unresolved. In an effort to better understand the reactivity of nano-Fe0, we have used a variety of complementary techniques to characterize two widely studied nano-Fe0 preparations: one synthesized by reduction of goethite with heat and H2 (Fe(H2)) and the other by reductive precipitation with borohydride (Fe(BH)). Fe(H2) is a two-phase material consisting of 40 nm alpha-Fe0 (made up of crystals approximately the size of the particles) and Fe3O4 particles of similar size or larger containing reduced sulfur; whereas Fe(BH) is mostly 20-80 nm metallic Fe particles (aggregates of <1.5 nm grains) with an oxide shell/coating that is high in oxidized boron. The FeBH particles further aggregate into chains. Both materials exhibit corrosion potentials that are more negative than nano-sized Fe2O3, Fe3O4, micro-sized Fe0, or a solid Fe0 disk, which is consistent with their rapid reduction of oxygen, benzoquinone, and carbon tetrachloride. Benzoquinone-which presumably probes inner-sphere surface reactions-reacts more rapidly with FeBH than Fe(H2), whereas carbon tetrachloride reacts at similar rates with FeBH and Fe(H2), presumably by outer-sphere electron transfer. Both types of nano-Fe0 react more rapidlythan micro-sized Fe0 based on mass-normalized rate constants, but surface area-normalized rate constants do not show a significant nano-size effect. The distribution of products from reduction of carbon tetrachloride is more favorable with Fe(H2), which produces less chloroform than reaction with Fe(BH).

Chemical Precipitation↗

PubMed2004

Synthesis of colloidal Mn2+:ZnO quantum dots and high-TC ferromagnetic nanocrystalline thin films.

We report the synthesis of colloidal Mn(2+)-doped ZnO (Mn(2+):ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn(2+):ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)(2) was found to strongly inhibit oxidation of Mn(2+) by O(2), allowing the synthesis of Mn(2+):ZnO to be performed aerobically. Mn(2+) ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn(2+):ZnO colloids of nearly spherical shape and uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn(2+) with very homogeneous speciation, differing from bulk Mn(2+):ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin-coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 micro(B)/Mn(2+) and T(C) > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn(2+):ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.

Colloids↗

PubMed2004

Uranium complexes formed at hematite surfaces colonized by sulfate-reducing bacteria.

Modeling uranium (U) transport in subsurface environments requires a thorough knowledge of mechanisms likely to restrict its mobility, such as surface complexation, precipitation, and colloid formation. In closed systems, sulfate-reducing bacteria (SRB) such as Desulfovibrio spp. demonstrably affect U immobilization by enzymatic reduction of U(VI) species (primarily the uranyl ion, UO2(2+), and its complexes) to U(IV). However, our understanding of such interactions under chronic U(VI) exposure in dynamic systems is limited. As a first step to understanding such interactions, we performed bioreactor experiments under continuous flow to study the effect of a biofilm of the sulfate-reducing bacterium Desulfovibrio desulfuricans attached to specular hematite (alpha-Fe2O3) surfaces on surface-associated U(VI) complexation, transformation, and mobility. Employing real-time microscopic observation and X-ray photoelectron spectroscopy (XPS), we show that the characteristics of the U(VI) complex(es) formed at the hematite surface are influenced by the composition of the bulk aqueous phase flowing across the surface and bythe presence of surface-associated SRB. The XPS data further suggest higher levels of U associated with hematite surfaces colonized by SRB than with bacteria-free surfaces. Microscopic observations indicate that at least a portion of the U(VI) that accumulates in the presence of the SRB is exterior to the cells, possibly associated with the extracellular biofilm matrix. The U4f7/2 core-region spectrum and U5f2 valence-band spectrum provide preliminary evidence that the SRB-colonized hematite surface accumulates both U(VI) and U(IV) phases, whereas only the U(VI) phase(s) accumulates on uncolonized hematite surfaces. The results suggest that mineral surfaces exposed to a continuously replenished supply of U(VI)-containing aqueous phase will accumulate U phases that may be more representative of those that exist in U-contaminated aquifers than those which accumulate in closed experimental systems. These phases should be considered in models attempting to predict U transport through subsurface environments.

Biological Availability↗

PubMed2004

Uranium immobilization by sulfate-reducing biofilms.

Hexavalent uranium [U(VI)] was immobilized using biofilms of the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans G20. The biofilms were grown in flat-plate continuous-flow reactors using lactate as the electron donor and sulfate as the electron acceptor. U(VI)was continuously fed into the reactor for 32 weeks at a concentration of 126 microM. During this time, the soluble U(VI) was removed (between 88 and 96% of feed) from solution and immobilized in the biofilms. The dynamics of U immobilization in the sulfate-reducing biofilms were quantified by estimating: (1) microbial activity in the SRB biofilm, defined as the hydrogen sulfide (H2S) production rate and estimated from the H2S concentration profiles measured using microelectrodes across the biofilms; (2) concentration of dissolved U in the solution; and (3) the mass of U precipitated in the biofilm. Results suggest that U was immobilized in the biofilms as a result of two processes: (1) enzymatically and (2) chemically, by reacting with microbially generated H2S. Visual inspection showed that the dissolved sulfide species reacted with U(VI) to produce a black precipitate. Synchrotron-based U L3-edge X-ray absorption near edge structure (XANES) spectroscopy analysis of U precipitated abiotically by sodium sulfide indicated that U(VI) had been reduced to U(IV). Selected-area electron diffraction pattern and crystallographic analysis of transmission electron microscope lattice-fringe images confirmed the structure of precipitated U as being that of uraninite.

Biofilms↗

PubMed2004

Identification of sporulated and vegetative bacteria using statistical analysis of fourier transform mid-infrared transmission data.

A combined mid-infrared spectroscopic/statistical modeling approach for the discrimination and identification, at the strain level, of both sporulated and vegetative bacterial samples is presented. Transmission mode spectra of bacteria dried on ZnSe windows were collected using a Fourier transform mid-infrared (FT-IR) spectrometer. Five Bacillus bacterial strains (B. atrophaeus 49337, B. globigii Dugway, B. thuringiensis spp. kurstaki 35866, B. subtilis 49760, and B. subtilis 6051) were used to construct a reference spectral library and to parameterize a four-step statistical model for the systematic identification of bacteria. The statistical methods used in this initial feasibility study included principal component analysis (PCA), classification and regression trees (CART), and Mahalanobis distance calculations. Internal cross-validation studies successfully classified 100% of the samples into their correct physiological state (sporulated or vegetative) and identified 67% of the samples correctly as to their bacterial strain. Analysis of thirteen blind samples, which included reference and other bacteria, nonbiological materials, and mixtures of both nonbiological and bacterial samples, yielded comparable accuracy. The primary advantage of this approach is the accurate identification of unknown bacteria, including spores, in a matter of minutes.

Bacillus↗

PubMed2003

Identification of bacterial spores using statistical analysis of Fourier transform infrared photoacoustic spectroscopy data.

Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) has been applied for the first time to the identification and speciation of bacterial spores. A total of forty specimens representing five strains of Bacillus spores (Bacillus subtilis ATCC 49760, Bacillus atrophaeus ATCC 49337, Bacillus subtilis 6051, Bacillus thuringiensis subsp. kurstaki, and Bacillus globigii Dugway) were analyzed. Spores were deposited, with minimal preparation, into the photoacoustic sample cup and their spectra recorded. Principal component analysis (PCA), classification and regression trees (CART), and Mahalanobis distance calculations were used on this spectral library to develop algorithms for step-wise classification at three levels: (1) bacterial/nonbacterial, (2) membership within the spore library, and (3) bacterial strain. Internal cross-validation studies on library spectra yielded classification success rates of 87% or better at each of these three levels. Analysis of fifteen blind samples, which included five samples of spores already in the spectral library, two samples of closely related Bacillus globigii 01 spores not in the library, and eight samples of nonbacterial materials, yielded 100% accuracy in distinguishing among bacterial/nonbacterial samples, membership in the library, and bacterial strains within the library.

Acoustics↗