Scanning Electron Microscopy and Transmission Electron Microscopy Aspects of Synergistic Antitumor Activity of Vitamin C - Vitamin K3 Combinations Against Human Prostatic Carcinoma Cells

A MTT/formazan assay was used to evaluate the antitumor activity of vitamin C (Vit C), vitamin K3 (Vit K3), or vitamin C:vitamin K3 combinations against a human prostatic carcinoma cell line (DU145). Both Vit C and Vit K3 alone exhibited antitumor activity, but only at elevated doses. When Vit C and Vit K3 were combined at a C:K3 ratio of 100:1 and administered to the carcinoma cells, the 50% cytotoxic concentrations (CD50) of the vitamins decreased 10-to 60-fold. Subsequently, the DU145 cells were examined with transmission and scanning electron microscopy (TEM and SEM) following a 1 hour treatment with Vit C, Vit K3, or Vit C/K3 combined at their 50% cytotoxic dose. Our morphological data suggest that vitamin treatment with individual vitamins affects the cytoskeleton, the mitochondria, and other membranous components of the cell. Treatment with the vitamin combination appears to potentiate the effects of the individual vitamin treatment. Specifically, there are abundant necrotic cells. The surviving cells display morphological defects characteristic of cell injury

Speciation-dependent kinetics of uranium(VI) bioreduction

The kinetics of uranium(VI) reduction by Shewanella oneidensis strain MR-1 was studied for varied pH and concentrations of dissolved inorganic carbon (DIC) and calcium. These are key variables affecting U(VI) speciation in aqueous systems. For all conditions studied, a nearly log-linear decrease of [U(VI)] suggested pseudo-first-order kinetics with respect to U(VI). The reduction rate constants (k) decreased with increasing DIC and calcium concentration, and were sensitive to pH. A positive correlation was found between k and the logarithm of the total concentration of U(VI)-hydroxyl and U(VI)-organic complexes. Linear correlations of the rate constant with the redox potential (E-H) of U(VI) reduction and the associated Gibbs free energy of reaction (Delta G(r)) were found for both Ca-free and Ca-containing systems. Both E-H and Delta G(r) are strong functions of aqueous U(VI) speciation. Because the range in Delta G(r) among the experimental conditions was small, the differences in k are more likely to be due to differences in EH or to differences in individual rate constants of U(VI) species. Calculation of conditional reduction rate constants for the major groups of U(VI) complexes revealed highest constants for the combined groups of U(VI)-hydroxyl and U(VI)-organic species, lower rate constants for the U(VI)-carbonate group, and much lower constants for the Ca-U(VI)-carbonate group. Mechanistic explanations for these findings are discussed

An experimental study of the carbonation of serpentinite and partially serpentinised peridotites

In situ sequestration of CO2 in mantle peridotites has been proposed as a method to alleviate the amount of anthropogenic CO2 in the atmosphere. This study presents the results of 8-month long laboratory fluid-rock experiments on representative mantle rocks from the Oman-United Arab Emirates ophiolite to investigate this process. Small core samples (3 cm long) were reacted in wet supercritical CO2 and CO2-saturated brine at 100 bar and 70◦C. The extent of carbonate formation, and hence the degree of carbon sequestration, varied greatly depending on rock type, with serpentinite (lizardite-dominated) exhibiting the highest capacity, manifested by the precipitation of magnesite MgCO3 and ferroan magnesite (Mg,Fe)CO3. The carbonate precipitation occurred predominantly on the surface of the core and subordinately within cross-cutting fractures. The extent of the CO2 reactions appeared to be principally controlled by the chemical and mineralogical composition of the rock, as well as the rock texture, with all these factors influencing the extent and rate of mineral dissolution and release of Mg and Fe for subsequent reaction with the CO2. It was calculated that ≈0.7 g of CO2 was captured by reacting ≈23 g of serpentinite, determined by the mass of magnesite formed. This equates to ≈30 kg CO2 per ton of host rock, equivalent to ≈3% carbonation in half a year. However, recycling of carbonate present in veins within the original rock sample could mean that the overall amount is around 2%. The increased reactivity of serpentinite was associated with preferential dissolution of more reactive types of serpentine minerals and brucite that were mainly present in the cross-cutting veins. The bulk of the serpentinite rock was little affected. This study, using relatively short term experiments, suggests that serpentinite might be a good host rock for CO2 sequestration, although long term experiments might prove that dunite and harzburgite could be as effective in an engineered system of CCSM. Wet scCO2 proved to be chemically more aggressive than CO2-saturated brine and its ingress along fractures and grain boundaries resulted in greater host rock dissolution and subsequent carbonate precipitation

Relative Reactivity of Biogenic and Chemogenic Uraninite and Biogenic Non-Crystalline U(IV)

Aqueous chemical extractions and X-ray absorption spectroscopy (XAS) analyses were conducted to investigate the reactivity of chemogenic uraninite, nanoparticulate biogenic uraninite, and biogenic monomeric U(IV) species. The analyses were conducted in systems containing a total U concentration that ranged from 1.48 to 2.10 mM. Less than 0.02% of the total U was released to solution in extractions that targeted water-soluble and ion exchangeable fractions. Less than 5% of the total U was solubilized via complexation with a 0.1 M solution of NaF. Greater than 90% of the total U was extracted from biogenic uraninite and monomeric U(IV) after 6 h of reaction in an oxidizing solution of 50 mM K2S2O8. Additional oxidation experiments with lower concentrations (2 mM and 10 mM) of K2S2O8 and 8.2 L-1 dissolved oxygen suggested that monomeric U(IV) species are more labile than biogenic uraninite; chemogenic uraninite was much less susceptible to oxidation than either form of biogenic U(IV). These results suggest that noncrystalline forms of U(IV) may be more labile than uraninite in subsurface environments. This work helps fill critical gaps in our understanding of the behavior of solid-associated U(IV) species in bioremediated sites and natural uranium ore deposits

Comparative dissolution kinetics of biogenic and chemogenic uraninite under oxidizing conditions in the presence of carbonate

The long-term stability of biogenic uraninite with respect to oxidative dissolution is pivotal to the success of in situ bioreduction strategies for the subsurface remediation of uranium legacies. Batch and flow-through dissolution experiments were conducted along with spectroscopic analyses to compare biogenic uraninite nanoparticles obtained from Shewanella oneidensis MR-1 and chemogenic UO2.00 with respect to their equilibrium solubility, dissolution mechanisms, and dissolution kinetics in water of varied oxygen and carbonate concentrations. Both materials exhibited a similar intrinsic solubility of similar to 10(-8) M under reducing conditions. The two materials had comparable dissolution rates under anoxic as well as oxidizing conditions, consistent with structural bulk homology of biogenic and stoichiometric uraninite. Carbonate reversibly promoted uraninite dissolution under both moderately oxidizing and reducing conditions, and the biogenic material yielded higher surface area-normalized dissolution rates than the chemogenic. This difference is in accordance with the higher proportion of U(V) detected on the biogenic uraninite surface by means of X-ray photoelectron spectroscopy. Reasonable sources of a stable U(V)-bearing intermediate phase are discussed. The observed increase of the dissolution rates can be explained by carbonate complexation of U(V) facilitating the detachment of U(V) from the uraninite surface. The fraction of surface-associated U(VI) increased with dissolved oxygen concentration. Simultaneously, X-ray absorption spectra showed conversion of the bulk from UO2.0 to UO2+x. In equilibrium with air, combined spectroscopic results support the formation of a near-surface layer of approximate composition UO2.25 (U4O9) coated by an outer layer of U(VI). This result is in accordance with flow-through dissolution experiments that indicate control of the dissolution rate of surface-oxidized uraninite by the solubility of metaschoepite under the tested conditions. Although U(V) has been observed in electrochemical studies on the dissolution of spent nuclear fuel, this is the first investigation that demonstrates the formation of a stable U(V) intermediate phase on the surface of submicron-sized uraninite particles suspended in aqueous solutions. (C) 2009 Elsevier Ltd. All rights reserved

Inducing mineral precipitation in groundwater by addition of phosphate

<p>Abstract</p> <p>Background</p> <p>Induced precipitation of phosphate minerals to scavenge trace elements from groundwater is a potential remediation approach for contaminated aquifers. The success of engineered precipitation schemes depends on the particular phases generated, their rates of formation, and their long term stability. The purpose of this study was to examine the precipitation of calcium phosphate minerals under conditions representative of a natural groundwater. Because microorganisms are present in groundwater, and because some proposed schemes for phosphate mineral precipitation rely on stimulation of native microbial populations, we also tested the effect of bacterial cells (initial densities of 10⁵and 10⁷mL^-1) added to the precipitation medium. In addition, we tested the effect of a trace mixture of propionic, isovaleric, formic and butyric acids (total concentration 0.035 mM).</p> <p>Results</p> <p>The general progression of mineral precipitation was similar under all of the study conditions, with initial formation of amorphous calcium phosphate, and transformation to poorly crystalline hydroxylapatite (HAP) within one week. The presence of the bacterial cells appeared to delay precipitation, although by the end of the experiments the overall extent of precipitation was similar for all treatments. The stoichiometry of the final precipitates as well as Rietveld structure refinement using x-ray diffraction data indicated that the presence of organic acids and bacterial cells resulted in an increasing <it>a </it>and decreasing <it>c </it>lattice parameter, with the higher concentration of cells resulting in the greatest distortion. Uptake of Sr into the solids was decreased in the treatments with cells and organic acids, compared to the control.</p> <p>Conclusions</p> <p>Our results suggest that the minerals formed initially during an engineered precipitation application for trace element sequestration may not be the ones that control long-term immobilization of the contaminants. In addition, the presence of bacterial cells appears to be associated with delayed HAP precipitation, changes in the lattice parameters, and reduced incorporation of trace elements as compared to cell-free systems. Schemes to remediate groundwater contaminated with trace metals that are based on enhanced phosphate mineral precipitation may need to account for these phenomena, particularly if the remediation approach relies on enhancement of <it>in situ </it>microbial populations.</p