Arsenic fate following mining of sulfide ore at mine sites and significance of the reduced state

Arsenic fate at mine sites is influenced by the reduced state of the ore. Comparison of arsenic speciation using XANES spectra with known arsenic compounds of ore from various lead and copper sulfidic mines with tailings from their processing shows that there is a significant difference when comparing near surface or shallow ore with deep mined ore. Subsequent comparison with tailings from different mined sulfidic ores, using XANES scan fitting is useful for understanding the chemical form of As in such samples

Bromide ion binding by a dinuclear gold(I) N-heterocyclic carbene complex : a spectrofluorescence and X-ray absorption spectroscopic study

Fluorescence and X-ray absorption spectroscopy were used to investigate the anion binding properties of a luminescent, dinuclear Au(I) N-heterocyclic carbene (NHC) complex ([1]²⁺) with a short Au(I)···Au(I) contact. The addition of Br(-) ions to a DMSO solution of [1](PF₆)₂ caused a red-shift in the fluorescence emission band from 396 nm to 496 nm. Similarly, the addition of Br(-) ions to [1](PF₆)₂ caused a decrease in the energy of the Au L₃-edge in the X-ray absorption spectrum, consistent with the formation of an association complex between the cation [1]²⁺ and Br(-) ions. Solution-based structural studies of the association complex were carried out using extended X-ray absorption fine structure (EXAFS) modelling of the Au(I)···Au(I) core of the cation. These studies indicate that the association complex results from Au(I)···Br(-) interactions, with the Br(-) ions occupying two partially occupied sites at ~2.9 and 3.9 Å from the Au(I) atoms.8 page(s

Relationship of arsenic speciation and bioavailability in mine wastes for human health risk assessment

Environmental context X-ray absorption near-edge spectroscopy (XANES) was applied to give arsenic chemical forms directly in the solid phase of mine wastes from two mine sites, including fluvial dispersion. The arsenic speciation data explained the variation of in vitro bioaccessibility and in vivo bioavailability (rat uptake) data of the mine wastes. The As speciation from XANES fitting supported the hypothesis that when soil intake is adjusted for bioaccessibility, the potential health risk estimate to local residents is significantly lower. Abstract X-ray absorption near-edge spectroscopy (XANES) was used for arsenic speciation in mine processing and waste samples from two mines in northern Australia. XANES fitting of model compound spectra to samples was used, in combination with in vitro bioaccessibility data for the pure compounds, to predict bioaccessibility of each mine waste sample (Pearson's correlation R2≤0.756, n≤51). The XANES fitting data for a smaller set of the samples (n≤12) were compared with in vivo bioavailability and in vitro bioaccessibility data. The bioavailability of arsenic (As) in the mine wastes, which is dependent, at least in part, on its oxidation state, was found to b

The Fe-heme structure of met-indoleamine 2,3-dioxygenase-2 determined by X-ray absorption fine structure

Multiple-scattering (MS) analysis of EXAFS data on met-indoleamine 2,3-dioxygenase-2 (IDO2) and analysis of XANES have provided the first direct structural information about the axial donor ligands of the iron center for this recently discovered protein. At 10 K, it exists in a low-spin bis(His) form with Fe–Np(av) = 1.97 Å, the Fe–NIm bond lengths of 2.11 Å and 2.05 Å, which is in equilibrium with a high-spin form at room temperature. The bond distances in the low-spin form are consistent with other low-spin hemeproteins, as is the XANES spectrum, which is closer to that of the low-spin met-Lb than that of the high-spin met-Mb. The potential physiological role of this spin equilibrium is discussed

Methylselenocysteine Treatment Leads to Diselenide Formation in Human Cancer Cells: Evidence from X-ray Absorption Spectroscopy Studies

The selenoamino acids methylselenocysteine (MeSeCys) and selenomethionine (SeMet) have disparate efficacies as anticancer agents. Herein, we use X-ray absorption spectroscopy to determine the chemical form of selenium in human neuroblastoma cells. Cells treated with MeSeCys contain a significant diselenide component, which is absent from SeMet-treated cells and suggests that metabolites of MeSeCys are capable of altering the redox status of the cells. The differences in the speciation of Se in the selenoamino acid-treated cells may provide insight into the differing anticancer activities of MeSeCys and SeMet

Synthesis and biological evaluation of a class of mitochondrially-targeted gadolinium(III) agents

A structure–activity relationship study of a library of novel bifunctional GdIII complexes covalently linked to arylphosphonium cations is reported. Such complexes have been designed for potential application in binary cancer therapies such as neutron capture therapy and photon activation therapy. A positive correlation was found between lipophilicity and cytotoxicity of the complexes. Mitochondria uptake was determined by means of inductively coupled plasma mass spectrometry (ICP‐MS), and Gd uptake was determined by means of quantification using synchrotron X‐ray fluorescence (XRF) imaging. A negative correlation between lipophilicity and tumour selectivity of the GdIII complexes was demonstrated. This study highlights the delicate balance required to minimise in vitro cytotoxicity and optimise in vitro tumour selectivity and mitochondrial localisation for this new class of mitochondrially‐targeted binary therapy agents. We also report the highest in vitro tumour selectivity for any Gd agent reported to date, with a T/N (tumour/normal cell) ratio of up to 23.5±6.6.Australian Research Council (ARC

Solid-State Structural Studies of Chromium(III) Nicotinato Nutritional Supplements

While Cr­(III) dietary supplements are widely consumed, some commercial supplements have yet to be structurally characterized. X-ray absorption spectroscopy and other spectroscopic methods were used to characterize Cr­(III) nicotinato nutritional supplements that have long been used in complementary medicine. Different ratios of nicotinic acid and CrCl₃·6H₂O (<i>trans</i>-[CrCl₂(OH₂)₄]­Cl·2H₂O) at different pH values gave a range of products. The local structures of Cr­(III) nicotinato complexes obtained at pH 7 and of the patented complex were characterized by performing multiple-scattering analysis of their EXAFS spectra as well as EPR, UV–vis, and IR spectroscopies. For the first time, these complexes have been definitively characterized as nicotinato-bridged polymers of dihydroxido-bridged dinuclear Cr­(III) cores. In the patented complex used in commercial preparations, each Cr is octahedral with an additional terminal O-bound nicotinato ligand, two bridging nicotinato (one O and one N bound), and an aqua ligand. The other species also have two or three bridging nicotinato ligands and an aqua and, in some cases, a terminal hydroxido ligand, which is dependent upon the stoichiometry of the reactants and the pH value of the solution in which they are prepared

Influence of Equatorial and Axial Carboxylato Ligands on the Kinetic Inertness of Platinum(IV) Complexes in the Presence of Ascorbate and Cysteine and within DLD‑1 Cancer Cells

The rapid and premature reduction of platinum­(IV) complexes in vivo is a significant impediment to these complexes being successfully employed as anticancer prodrugs. This study investigates the influence of the platinum­(IV) coordination sphere on the ease of reduction of the platinum center in various biological contexts. In the presence of the biological reductants, ascorbate and cysteine, platinum­(IV) complexes with dicarboxylato equatorial ligands were observed to exhibit lower reduction potentials and slower reduction rates than analogous platinum­(IV) complexes with dichlorido equatorial ligands. Diaminetetracarboxylatoplatinum­(IV) complexes exhibited unusually long half-lives in the presence of excess reductants; however, the complexes exhibited moderate potency in vitro, indicative of rapid reduction within the intracellular environment. By use of XANES spectroscopy, <i>trans</i>-[Pt­(OAc)₂(ox)­(en)] and <i>trans</i>-[PtCl₂­(OAc)₂(en)] were observed to be reduced at a similar rate within DLD-1 cancer cells. This large variability in kinetic inertness of diamine­tetracarboxylato­platinum­(IV) complexes in different biological contexts has significant implications for the design of platinum­(IV) prodrugs

Biotransformations of Antidiabetic Vanadium Prodrugs in Mammalian Cells and Cell Culture Media: A XANES Spectroscopic Study

The antidiabetic activities of vanadium­(V) and -(IV) prodrugs are determined by their ability to release active species upon interactions with components of biological media. The first X-ray absorption spectroscopic study of the reactivity of typical vanadium (V) antidiabetics, vanadate ([V^VO₄]^3–, <b>A</b>) and a vanadium­(IV) bis­(maltolato) complex (<b>B</b>), with mammalian cell cultures has been performed using HepG2 (human hepatoma), A549 (human lung carcinoma), and 3T3-L1 (mouse adipocytes and preadipocytes) cell lines, as well as the corresponding cell culture media. X-ray absorption near-edge structure data were analyzed using empirical correlations with a library of model vanadium­(V), -(IV), and -(III) complexes. Both <b>A</b> and <b>B</b> ([V] = 1.0 mM) gradually converged into similar mixtures of predominantly five- and six-coordinate V^V species (∼75% total V) in a cell culture medium within 24 h at 310 K. Speciation of V in intact HepG2 cells also changed with the incubation time (from ∼20% to ∼70% V^IV of total V), but it was largely independent of the prodrug used (<b>A</b> or <b>B</b>) or of the predominant V oxidation state in the medium. Subcellular fractionation of A549 cells suggested that V^V reduction to V^IV occurred predominantly in the cytoplasm, while accumulation of V^V in the nucleus was likely to have been facilitated by noncovalent bonding to histone proteins. The nuclear V^V is likely to modulate the transcription process and to be ultimately related to cell death at high concentrations of V, which may be important in anticancer activities. Mature 3T3-L1 adipocytes (unlike for preadipocytes) showed a higher propensity to form V^IV species, despite the prevalence of V^V in the medium. The distinct V biochemistry in these cells is consistent with their crucial role in insulin-dependent glucose and fat metabolism and may also point to an endogenous role of V in adipocytes

The endothelium-derived hyperpolarizing factor, H2O2, promotes metal-ion efflux in aortic endothelial cells: elemental mapping by a hard x-ray microprobe

Copyright © 2006 American Chemical SocietyHydrogen peroxide (H(2)O(2)) is a physiologic oxidant implicated in vascular cell signaling, although little is known about the biochemical consequences of its reaction with endothelial cells. Submicrometer-resolution hard X-ray elemental mapping of cultured porcine aortic endothelial cells (PAEC) has provided data on the global changes for intracellular elemental density within PAEC and indicates an efflux of metal ions and phosphorus from the cytoplasm after H(2)O(2) treatment. The synchrotron-radiation-induced X-ray emission experiments (SRIXE) show that H(2)O(2)-treated cells are irregularly shaped and exhibit blebbing indicative of increased permeability due to the damaged membrane. The SRIXE results suggest that H(2)O(2)-induced damage is largely restricted to the cell membrane as judged by the changes to membrane and cytoplasmic components rather than the cell nucleus. The SRIXE data also provide a mechanism for cell detoxification as the metal-ion efflux resulting from the initial H(2)O(2)-mediated changes to cell membrane potentially limits intracellular metal-mediated redox processes through Fenton-like chemistry. They may also explain the increased levels of these ions in atherosclerotic plaques, regardless of whether they are involved in plaque formation. Finally, the SRIXE data support the notion that cultured endothelial cells exposed to H(2)O(2) respond with enhanced cellular metal-ion efflux into the extracellular space.Paul K. Witting, Hugh H. Harris, Benjamin S. Rayner, Jade B. Aitken, Carolyn T. Dillon, Roland Stocker, Barry Lai, Zhonghou Cai, and Peter A. La