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PubMed2006

195Pt NMR study of the speciation and preferential extraction of Pt(IV)-mixed halide complexes by diethylenetriamine-modified silica-based anion exchangers.

A detailed 195Pt NMR study of the distribution of Pt(IV) complex species resulting from the aquation of H2PtCl6, H2PtBr6, and mixtures of H2PtCl6/H2PtBr6 in water/dilute HClO4 has been carried out to obtain an understanding of the speciation in these solutions as relevant to the recovery of Pt(IV) complexes from process solutions. A species distribution plot of the [PtCl6]2-, [PtCl5(H2O)]-, and [PtCl4(H2O)2] shows that in equilibrated, relatively concentrated H2PtCl6 solutions ([Pt]t > 0.12 M), the [PtCl4(H2O)2] species is below the 195Pt NMR detection limit; for [Pt]t concentrations < 0.1 M, the relative concentrations of the [PtCl5(H2O)]- and [PtCl4(H2O)2] species increase significantly, as a result of relatively rapid aquation of the [PtCl6]2- and [PtCl5(H2O)]- complexes under these conditions. From this (195)Pt NMR data the aquation constants of [PtCl6]2- and [PtBr6]2- of log K6 approximately 1.75 +/- 0.05 and log K6 approximately 2.71 +/- 0.15, respectively, have been determined at 30 degrees C. In mixtures of H2PtCl6/H2PtBr6 in water, a number of previously unidentified aquated complexes of the general formula [PtCl(5-n)Br(n)(H2O)]- (n = 0-5) could be identified, including the possible geometrical isomers of these complexes. These 195Pt NMR assignments were confirmed by remarkably systematic, linear relationships between the 195Pt chemical shift increments induced by substitution of Cl- ions by n Br- ions in [PtCl(6-n)Br(n)]2- and [PtCl(5-n)Br(n)(H2O)]- complexes. Preferential extraction of the [PtX6]2- (X = Cl, Br, or a mixture of the two halides) species over their corresponding aquated [PtX5(H2O)]- counterparts by silica-based diethylenetriamine anion exchangers could be demonstrated by means of 195Pt NMR spectroscopy.

Journal Article↗
PubMed1996

Speciation in Vanadium Bioinorganic Systems. 2. An NMR, ESR, and Potentiometric Study of the Aqueous H(+)-Vanadate-Maltol System.

A systematic study of the physiologically interesting vanadium-maltol (V-MaH) system has been performed in 0.150 M Na(Cl) at 25 degrees C, using NMR, ESR, and potentiometric techniques. Complexation occurs within a wide pH range, from around 1 up to 10.5. However, a pH-, concentration-, and time-dependent spontaneous reduction of vanadium(V) to vanadium(IV) occurs. From ESR spectra the conditions for this reduction are evaluated and discussed. From potentiometric (glass electrode) and quantitative (51)V NMR measurements, the full speciation in the H(+)-H(2)VO(4)(-)-MaH system was determined in the pH range 5-10.5. Data were evaluated with the computer program LAKE, which is able to treat combined emf and NMR data. The pK(a) value for MaH was determined to be 8.437 +/- 0.005. In the ternary system, three complexes are formed: VMa(2)(-), VMa(-), and VMa(2)(-), having log beta(0,1,2) = 7.02 +/- 0.03, log beta(0,1,1) = 2.66 +/- 0.05, and log beta(-)(1,1,1) = -7.37 +/- 0.21. The errors given are 3sigma. The VMa(2)(-) complex appears as the main species in a pH range from 4.5 to 8.5, whereas both mononuclear monoligand species are minor. Equilibrium conditions are illustrated in distribution diagrams, and the structures of the complexes formed are proposed.

Journal Article↗
PubMed2001

Aqueous solution speciation of Fe(III) complexes with dihydroxamate siderophores alcaligin and rhodotorulic acid and synthetic analogues using electrospray ionization mass spectrometry.

Aqueous solutions of Fe3+ complexes of cyclic (alcaligin) and linear (rhodotorulic acid) dihydroxamate siderophores and synthetic linear eight-carbon-chain and two-carbon-chain dihydroxamic acids ([CH3N(OH)C=O)]2(CH2)n; H2Ln; n = 2 and 8) were investigated by electrospray ionization mass spectrometry (ESI-MS). Information was obtained relevant to the structure and the speciation of various Fe(III)-dihydroxamate complexes present in aqueous solution by (1) comparing different ionization techniques (ESI and FAB), (2) altering the experimental parameters (Fe3+/ligand ratio, pH, cone voltage), (3) using high-stability hexacoordinated Fe(III) siderophore complex mixtures (ferrioxamine B/ferrioxamine E) as a calibrant to quantify intrinsically neutral (H+ clustered or protonated) and intrinsically charged complexes, and (4) using mixed-metal complexes containing Fe3+, Ga3+, and Al3+. These results illustrate that for all dihydroxamic acid ligands investigated multiple tris- and bis-chelated mono- and di-Fe(III) species are present in relative concentrations that depend on the pH and Fe/L ratio.

Calibration↗
PubMed2004

Impact of molecular speciation on crystal nucleation in polymorphic systems: the conundrum of gamma glycine and molecular 'self poisoning'.

The polymorphism of the simple amino acid glycine has been known for almost a century. It is also known that in aqueous solutions, at the isoelectric point (pI 5.9), the metastable alpha polymorph crystallizes, while the stable gamma form of glycine only nucleates at high and low pH. Despite the importance of understanding the process by which crystals nucleate, the solution and solid-state chemistry underlying this simple observation have never been explored. In this contribution, we have combined solution chemistry, crystallization, and crystallographic data to investigate the mechanisms by which this effect occurs. It is concluded that solution speciation and the consequent interactions between charged species and developing crystal nuclei determine the structural outcome of the crystallization process.

Crystallization↗
PubMed2000

Chemical speciation influences comparative activity of selenium-enriched garlic and yeast in mammary cancer prevention.

A recent human intervention trial showed that daily supplementation with selenized yeast (Se-yeast) led to a decrease in the overall cancer morbidity and mortality by nearly 50%; past research has also demonstrated that selenized garlic (Se-garlic) is very effective in mammary cancer chemoprevention in the rat model. The goal of this study was to compare certain biological activities of Se-garlic and Se-yeast and to elucidate the differences based on the chemical forms of selenium found in these two natural products. Characterization of organic selenium compounds in yeast (1922 microg/g Se) and garlic (296 microg/g Se) was carried out by high-performance liquid chromatography with inductively coupled plasma mass spectrometry or with electrospray mass spectrometry. Analytical speciation studies showed that the bulk of the selenium in Se-garlic and Se-yeast is in the form of gamma-glutamyl-Se-methylselenocysteine (73%) and selenomethionine (85%), respectively. The above methodology has the sensitivity and capability to account for >90% of total selenium. In the rat feeding studies, supplementation of Se-garlic in the diet at different levels consistently caused a lower total tissue selenium accumulation when compared to Se-yeast. On the other hand, Se-garlic was significantly more effective in suppressing the development of premalignant lesions and the formation of adenocarcinomas in the mammary gland of carcinogen-treated rats. Given the present finding on the identity of selenomethionine and gamma-glutamyl-Se-methylselenocysteine as the major form of selenium in Se-yeast and Se-garlic, respectively, the metabolism of these two compounds is discussed in an attempt to elucidate how their disposition in tissues might account for the differences in cancer chemopreventive activity.

Adenocarcinoma↗
PubMed2002

Speciation of thermotolerant Campylobacter isolates involved in foodborne disease by means of DNA restriction analysis and molecular probes.

The molecular identification of several strains of Campylobacter jejuni and Campylobacter coli involved in foodborne disease was carried out by investigating the restriction profiles of their chromosomal DNA and by DNA/DNA hybridization. Cleavage with EcoRV allowed the visualization of a 3 kb DNA fragment characteristic of C. jejuni, whereas restriction with ClaI allowed the identification of a 9.3 kb DNA fragment, also characteristic of C. jejuni, and a DNA duplet of 9.5-10 kb, specific to C. coli. Restriction analysis with enzyme BglII allowed the visualization of DNA fragments of 3.5, 4, and 6.7 kb, characteristic of C. jejuni. C. jejuni subsp. doylei strains investigated shared a higher genetic homology among themselves-as determined by DNA/DNA hybridization-than with C. jejuni subsp. jejuni. A DNA probe, initially designed by Korolik et al. (Korolik, V.; Coloe, P. J.; Krishnapillai, V. J. Gen. Microbiol. 1988, 134, 521-529), including a DNA fragment encoding an antigenic membrane protein of 31.5 kDa in C. jejuni, when used as probe, allowed the specific identification of all strains of C. jejuni through the detection of strong hybridization signals in two BglII DNA fragments of 2.3 and 2.5 kb, which were not observed in C. coli. Cleavage of chromosomal DNA with BglII-either alone or coupled with probing assays with specific probes-proved to be a valuable tool for the speciation of Campylobacter isolates involved in foodborne disease.

Campylobacter Infections↗
PubMed2003

Theoretical speciation of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) in agronomic conditions.

The presence of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) as the second largest component in commercial EDDHA iron chelates has recently been demonstrated. Here is reported the speciation of o,p-EDDHA by the application of a novel methodology through the determination of the complexing capacity, protonation, and Ca(2+), Mg(2+), Cu(2+), and Fe(3+) stability constants. The pM values and species distribution in solution, hydroponic, and soil conditions were obtained. Due to the para position of one phenol group in o,p-EDDHA, the protonation constants and Ca and Mg stability constants have different values from those of o,o-EDDHA and p,p-EDDHA regioisomers. o,p-EDDHA/Fe(3+) stability constants are higher than those of EDTA/Fe(3+) but lower than those of o,o-EDDHA/Fe(3+). The sequence obtained for pFe is o,o-EDDHA/Fe(3+) >/= o,p-EDDHA/Fe(3+) > EDTA/Fe(3+). o,p-EDDHA/Fe(3+) can be used as an iron chelate in hydroponic conditions. Also, it can be used in soils with limited Cu availability.

Agriculture↗
PubMed2004

Speciation of aluminum in drink samples by 8-hydroxyquinoline loaded silylanization silica gel microcolumn separation with off-line ICP-MS detection.

A technique using a flow injection microcolumn separation coupled with ICP-MS detection has been developed for the speciation of Al in drink samples. The retention behaviors of different Al species were studied with 8-hydroxyquinoline (8-HQ) loaded silylanization silica gel as the packing material and inorganic acid (HNO3) as the elution. The results indicated that in a pH range of 5.0 to 8.0, all labile monomeric Al species were retained on the microcolumn while nonlabile monomeric Al species were directly passed through the column. Various Al species after separation were detected by ICP-MS. The detection limit of 0.2 ng mL(-1) and a relative standard deviation (RSD) of 4.2% at 10 ng mL(-1) (n = 11) were achieved, and the recoveries for the spiked samples were 95-108%. The proposed method has been applied to the analysis of Al species in tea infusions, coffee, and tap waters with satisfactory results. The results obtained by this method were compared with that obtained by the cation exchange microcolumn separation and ICP-MS detection system, and some valuable conclusions were drawn.

Aluminum↗
PubMed1999

Arsenic toxicity and accumulation in turnip as affected by arsenic chemical speciation.

Arsenic (As) uptake by turnip, growing under soilless culture conditions, was studied. A 4 x 3 factorial experiment was conducted with four As species [arsenite, arsenate, methylarsonic acid (MMAA), dimethylarsinic acid (DMAA)] and three As concentrations (1.0, 2.0, and 5.0 mg L(-)(1)). Arsenic phytoavailability and phytotoxicity were primarily determined by As speciation. Organic arsenicals, especially MMAA, were clearly phytotoxic to this turnip cultivar. Plant As concentrations significantly increased with increasing As application rates. Both organic arsenicals showed a higher upward translocation than their inorganic counterparts, contributing to the greater phytotoxicity and lower dry matter productions of these organic treatments. Both inner root and outer root skin As concentrations were above the maximum limit set for As content in food crops (1.0 mg kg(-)(1)). If turnip plants are exposed to a large pulse of As, as growth on contaminated nutrient solutions, they will accumulate residues at levels that are unacceptable for animal and human consumption.

Animals↗
PubMed2000

Pb and Cu speciation and bioavailability in port wine.

Information about the speciation of Pb and Cu in different types of Port wines (white, single-year and blended aged red, and young red wines) was gathered to estimate their respective bioavailabilities to man. For this purpose, wines were subjected to in vitro simulated gastrointestinal digestion, and the following properties were studied in the wines and its gastric and intestinal digests: (1) average conditional stability constant (K(av)) of the Cu complexes (by potentiometry), of the strongest Pb complexes (those inert to cathodic voltammetry, K'(av)), and of the respective ligand concentrations (CC or CC(inert)); (2) the distribution of the metal among the different groups of compounds of different molecular weights and/or polarities in the different bands separated by reverse phase high-performance liquid chromatography; (3) the total metal concentration present in the wines and the respective fractions present in the soluble and in the dialyzable fractions of the digest (an estimation of the assimilable fraction). The study showed that the complexing affinity for Pb (expressed by either CC(inert) or K'(av)) of white and very aged red Port wines was lower than for the remainder of the wines. For Cu, the strength of the ligands in the white wines was lower (<log K(av) values) than in the other wines, but their concentrations (CC) were higher. For Pb, CC(inert) was much higher after the digestion than for the untreated wines, whereas the log K'(av) values were approximately 1 order of magnitude lower. These parameters could not be determined for Cu in the gastrointestinal digests. For all of the studied wines the dialyzable fraction of Pb during the intestinal digestion was low (10-22% of the total Pb) and the dialyzable fractions of Cu were close to 50% of the total Cu.

Biological Availability↗
PubMed2006

Alkaline treatment of iron-containing MFI zeolites. Influence on mesoporosity development and iron speciation.

The effects of alkaline treatment on the mesoporosity development and iron speciation in Fe-MFI zeolites have been investigated. To this end, a variety of samples derived from different synthetic routes and having distinct Si/Al ratios and Fe content were treated in NaOH solutions and characterized by N2 adsorption, SEM, TEM, UV/vis spectroscopy, and EPR. The alkaline treatment induces a significant intracrystalline mesoporosity development by framework silicon extraction and promotes disintegration of oligomeric iron species. Iron in framework positions has shown to provoke mesopore formation, whereas nonframework iron species suppresses silicon leaching and lowers the extent of extra porosity.

Journal Article↗
PubMed2005

Metal speciation dynamics in colloidal ligand dispersions.

In this work we propose a dynamic metal speciation theory for colloidal systems in which the complexing ligands are localized on the surface of the particles; i.e., there is spatial heterogeneity of binding sites within the sample volume. The differences between the complex formation and dissociation rate constants of complexes in colloidal dispersions and those in homogeneous solutions originate from the differences in kinetic and mass transport conditions. In colloidal systems, when the effective rate of dissociation of the surface complexes becomes fully diffusion controlled, its value is defined via the geometrical parameters of the particle. We assess the extent to which the conventional approach of assuming a homogeneously smeared-out ligand distribution overestimates the lability of surface complexes in colloidal ligand dispersions. The validity of the theory is illustrated by application to binding of lead and cadmium by carboxyl modified latex particles: our approach correctly predicts the formation/dissociation rate constants, which differ by several orders of magnitude from their homogeneous solution counterparts.

Journal Article↗
PubMed2006

Citrate does not change uranium chemical speciation in cell culture medium but increases its toxicity and accumulation in NRK-52E cells.

Uranium (U), as a heavy metal, is a strong chemical toxicant, which induces the damage to proximal tubule kidney cells. In order to reproduce U toxicity in vitro and to avoid precipitation, it is necessary to complex it with a strong ligand such as bicarbonate before dilution with cell culture medium. It was recently shown, in vitro on the NRK-52E normal renal tubular epithelial cells, that citrate increased the toxicity of U(VI)-bicarbonate complexes. This property was attributed to a change in U speciation, characterized by the occurrence of U(VI)-citrate complexes, which were supposed to be more toxic than U(VI)-bicarbonate. Here, we present the results of extended X-ray absorption fine structure spectroscopy (EXAFS) analyses of the media that were used to expose cells in vitro. Resulting data show that even when citrate is added to the exposure medium, the predominant species is U(VI)-bicarbonate. Nonetheless, citrate increases U(VI) toxicity and accelerates its intracellular accumulation kinetics, without inducing precipitation. This study emphasizes another parameter that modulates U(VI) toxicity for renal tubule cells and further characterizes the mechanisms of U(VI) toxicity.

Animals↗
PubMed2002

Ancient tetraploidy and slow molecular evolution in Scaphiophryne: ecological correlates of speciation mode in Malagasy relict amphibians.

Karyotypes of three microhylid frog species of the Malagasy relict genus Scaphiophryne were studied: Scaphiophryne gottlebei, S. madagascariensis and S. spinosa. The latter two showed a plesiomorphic ranoid karyotype of 2n = 26. In contrast, tetraploidy was demonstrated in S. gottlebei, which constitutes an exceptional state among Malagasy amphibians. A combination of different banding techniques and of rDNA-FISH provided evidence for allopolyploidy in the species and for a completed subsequent functional and structural diploidization. Phylogenetic analysis of mitochondrial 16S rDNA sequences revealed a significant deceleration of nucleotide substitution rates in Scaphiophryne. The tetraploidy of S. gottlebei probably occurred early in their radiation. Ecological and behavioural patterns of Scaphiophryne probably favoured intraspecific gene flow and hybridization events, thereby leading to slow molecular substitution rates and to allopolyploid chromosome speciation in S. gottlebei.

Animals↗
PubMed2003

Seasonal variation of total dissolved arsenic and arsenic speciation in a polluted surface waterway.

Seasonal differences in the dissolved arsenic concentration and speciation in a contaminated urban waterway in northwest England have been determined using a coupled ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS) technique. Waters sampled in the vicinity of an industrial works during relatively dry conditions in April 2000 were found to contain total arsenic concentrations (sigma As) of up to 132 micrograms L-1, more than an order magnitude greater than the 4 micrograms L-1 maximum found in December 2000. The difference in sigma As between the April and December sampling periods is speculated to be largely due to the irregular anthropogenic supply of arsenic to the watercourse. For both sampling periods, the dissolved arsenic was exclusively inorganic in nature and had an As(V)/sigma As ratio of between 0.6 and 0.8. Analysis of samples taken downstream of the industrial site, after the confluence with a relatively As-poor stream, revealed that As(III), As(V) and sigma As concentrations were lower than would be expected from conservative mixing. The As(V)/sigma As ratio was also observed to decrease markedly. The loss of arsenic from solution is thought to be due to adsorption on the iron oxyhydroxide-rich sediment observed to coat the riverbed downstream of the confluence. The reduction in the As(V)/sigma As ratio is believed to be due to the more rapid adsorption of As(V) compared to that of As(III). Deviations from conservative behaviour were more marked during the relatively dry April 2000 sampling period and suggest the increased importance of adsorption processes controlling arsenic availability during this time.

Arsenic↗
PubMed2003

Levels and speciation of heavy metals in soils of industrial Southern Nigeria.

A knowledge of the total content of trace metals is not enough to fully assess the environmental impact of polluted soils. For this reason, the determination of metal species in solution is important to evaluate their behaviour in the environment and their mobilization capacity. Sequential extraction procedure was used to speciate five heavy metals (Cd, Pb, Cu, Ni and Zn) from four contaminated soils of Southern Nigeria into six operationally defined geochemical species: water soluble, enchangeable, carbonates, Fe-Mn oxide, organic and residual. Metal recoveries were within +/- 10% of the independently determined total Cd, Pb, Cu, Ni and Zn concentrations. The highest amount of Cd (avg. 30%) in the nonresidual fractions was found in the exchangeable fraction, while Cu and Zn were significantly associated with the organic fraction. The carbonate fraction contained on average 14, 18.6, 12.6, 13 and 11% and the residual fraction contained on average 47, 18, 33, 50 and 25% of Cd, Pb, Cu, Ni and Zn respectively. Assuming that mobility and bioavailability of these metals are related to the solubility of the geochemical form of the metals, and that they decrease in the order of extraction sequence, the apparent mobility and potential bioavailability for these five metals in the soil were: Pb > Zn > Cu > Ni > Cd. The mobility indexes of copper and nickel correlated positively and significantly with the total content of metals, while mobility indexes of cadmium and zinc correlated negatively and significantly with the total content of metals.

Environmental Monitoring↗
PubMed2004

An operationally defined method to determine the speciation of mercury.

This paper presents a modified method of an operationally determined speciation of mercury in soil. The analytical work was mainly concerned to suit properly with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Soil samples analysed in this study were selected from open areas around a crematorium, a waste incinerator, and two power plants. Results show that both topsoil and subsoil samples were dominated by elemental mercury Hg(0) and mercuric sulphide (HgS). The significant correlation between sulphur concentration and HgS was found in topsoil samples.

Geologic Sediments↗
PubMed2002

The speciation of conger eel galectins by rapid adaptive evolution.

Many cases of accelerated evolution driven by positive Darwinian selection are identified in the genes of venomous and reproductive proteins. This evolutional phenomenon might have important consequences in their gene-products' functions, such as multiple specific toxins for quick immobilization of the prey and the establishment of barriers to fertilization that might lead to speciation, and in the molecular evolution of novel genes. Recently, we analyzed the molecular evolution of two galectins isolated from the skin mucus of conger eel (Conger myriaster), named congerins I and II, by cDNA cloning and X-ray structural analysis, and we found that they have evolved in the rapid adaptive manner to emergence of a new structure including strand-swapping and a unique new ligand-binding site. In this review article we summarize and discuss the molecular evolution, especially the rapid adaptive evolution, and the structure-function relationships of conger eel galectins.

Animals↗