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Thallium (Tl) is a rare and extremely toxic metal whose toxicity is significantly higher than cadmium (Cd), lead (Pb) and antimony (Sb). The extensive utilization of Tl-bearing minerals, such as mining activities, has led to severe Tl pollution in a variety of natural settings, while little is known to date about its effect on the microbial diversity in paddy soils. Also, the geochemical behavior of Tl in the periodical alterations between dry and wet conditions of paddy soils remains largely unknown. Herein, the sequential extraction method and 16S rRNA gene sequence analysis were adopted to analyze Tl's migration and transformation behavior and the microbial diversity in the paddy soils with different pollution levels. The results indicated that Tl was mainly concentrated in reducible fraction, which is different from other types of soils, and may be closely attributed to the abundance of Fe-Mn (hydr)oxides in the paddy rhizospheric soils. Further analysis revealed that pH, total S, Pb, Sb, Tl and Cd were the dominant environmental factors, and the enrichment level of these potentially toxic metal(loid)s (PTMs) exerted obvious impacts on the diversity and abundance of microorganism in the rhizospheric soils, and regulating microbial community. The geochemical fractionation of Tl was closely correlated to soil microorganisms such as Fe reducing bacteria (Geothrix) and sulfate reducing bacteria (Anaerolinea), playing a critical role in Tl geochemical cycle through redox reaction. Hence, further study on microorganisms of paddy rhizospheric soils is of great significance to the countermeasures for remediating Tl-polluted paddy fields and protect the health of residents., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Among transition and non-transition metals, thallium is a unique case of an element which, despite its known toxicity, provides interesting challenges through its biology and chemistry linked to diagnosis of human pathophysiologies. Poised to investigate in-depth the structural and electronic aspects of thallium involvement in physiological processes, the synthetic exploration of aqueous binary systems of Tl(I) with physiological binders from the family of hydroxycarboxylic acids (glycolic, lactic, mandelic and citric acid) was pursued in a pH-specific fashion. The isolated crystalline coordination polymers, emerging from that effort, were physicochemically characterized through elemental analysis, FT-IR, ESI-MS, 1 H-/ 13 C-NMR, and X-ray crystallography. The coordination environment of thallium in each molecular Tl(I) assembly, along with lattice dimensionality (2D3D), reflects the contributions of the ligands, collectively exemplifying interactions probed into though BVS and Hirshfeld surface analysis. The results portray a well-defined solid-state and solution profile for all species investigated, thereby providing the basis for their subsequent selection into in vitro biological studies involving the (patho)physiological cell lines 3T3-L1, Saos-2, C2C12, and MCF-7. Biotoxicity profiles, encompassing cell viability, morphology, and cell growth support clearly a concentration-, time-, and cell tissue-specific behavior for the chosen Tl(I) compounds in a structure-specific fashion. Collectively, the chemical experimental data support the biological results in formulating a structure-specific behavior for Tl(I)-hydroxycarboxylato species with respect to biotoxicity mechanisms in a (patho)physiological environment. The accrued knowledge stands as the foreground for further investigation into the relevant biological chemistry of Tl(I) and molecular technologies targeting its sequestration and removal from cellular media., (Copyright © 2021 Elsevier Inc. All rights reserved.)

The development of efficient and regenerable adsorbent coupled with advanced oxidation for enhanced thallium (Tl) removal has been a recent focus on wastewater treatment. In this study, a magnetite-based biochar derived from watermelon rinds was synthesized and used as a sustainable adsorbent and catalyst for hypochlorite oxidation and removal of Tl(I) from wastewater. The addition of hypochlorite substantially enhanced the Tl(I) removal under normal pH range (6-9). Maximum Tl adsorption capacity of 1123 mg/g was achieved, which is 12.3% higher than the highest value previously reported. The magnetic biochar can be regenerated using 0.1 mol/L HNO 3 solution for elution in only 5 min, with a Tl desorption efficiency of 78.9%. The Tl removal efficiency was constantly higher than 98.5% during five consecutive recycle tests, indicating the effective reuse performance of the adsorbent. Oxidation, surface precipitation, pore retention and surface complexation were the main mechanisms for Tl(I) removal. The re-dissolution of Tl compounds and ion exchange of Tl cations with proton were the main mechanisms for adsorbent regeneration. Given the fast oxidation rate, high adsorption capacity, steady reusability and facile separability, this magnetic biochar-hypochlorite technique is a promising means for Tl(I) removal from wastewater. The catalytic hypochlorite oxidation induced by the magnetic biochar has also great potential to the effective removal of other pollutants., (Copyright © 2019 Elsevier B.V. All rights reserved.)

TREK2 (KCNK10, K 2P 10.1) is a two-pore domain potassium (K2P) channel and a potential target for the treatment of pain. Like the majority of the K2P superfamily, there is currently a lack of useful pharmacological tools to study TREK2. Here we present a strategy for identifying novel TREK2 activators. A cell-based thallium flux assay was developed and used to screen a library of drug-like molecules, from which we identified the CysLT1 antagonist Pranlukast as a novel activator of TREK2. This compound was selective for TREK2 versus TREK1 and showed no activity at TRAAK. Pranlukast was also screened against other members of the K2P superfamily. Several close analogues of Pranlukast and other CysLT1 antagonists were also tested for their ability to activate K2P channels. Consistent with previous work, structure activity relationships showed that subtle structural changes to these analogues completely attenuated the activation of TREK2, whereas for TREK1, analogues moved from activators to inhibitors. Pranlukast's activity was also confirmed using whole-cell patch clamp electrophysiology. Studies using mutant forms of TREK2 suggest Pranlukast does not bind in the K2P modulator pocket or the BL-1249 binding site. Pranlukast therefore represents a novel tool by which to study the mechanism of TREK2 activation., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

We studied thallium (Tl) isotope fractionation in white mustard grown hydroponically at different Tl doses. Thallium isotope signatures in plants indicated preferential incorporation of the light 203 Tl isotope during Tl uptake from the nutrient solution. Negative isotope fractionation was even more pronounced in dependence on how much the available Tl pool decreased. This finding corresponds to the concept of isotope overprinting related to a high contamination level in the growing media (solution or soil). Regarding Tl translocation in plants, we observed a large Tl isotope shift with an enrichment in the heavy 205 Tl isotope in the shoots relative to the roots in treatments with low/moderate solution Tl concentrations (0.01/0.05 mg Tl/L), with the corresponding α 205/203 Tl fractionation factors of ˜1.007 and 1.003, respectively. This finding is probably a consequence of specific (plant) reactions of Tl replacing K in its cycle. The formation of the S-coordinated Tl(I) complexes, potentially affecting both Tl accumulation and Tl isotope fractionation in plants, however, was not proven in our plants, since we did not have indication for that on the basis of X-ray absorption spectroscopy, suggesting that Tl was mainly present as free/hydrated Tl + ion or chemically bound to O-containing functional groups., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The channel-forming activity of the lipodepsipeptide syringopeptin 25A (SP25A) was investigated at a tethered bilayer lipid membrane (tBLM) with a dioleoylphosphatidylcholine distal leaflet, anchored to a mercury electrode through a hydrophilic tetraethyleneoxy spacer. SP25A was incorporated in the tBLM from different aqueous solutions by recording a series of impedance spectra over a potential range encompassing non-physiological transmembrane potential (Δϕ) values. Once incorporated, SP25A forms stable ion channels over the narrower range of physiological Δϕ values. Ion flow into and out of the spacer, through the lipid bilayer moiety of the tBLM, was monitored by potential step chronocoulometry and cyclic voltammetry at pH3, 5.4 and 6.8. Potassium ion flow into the hydrophilic spacer along the SP25A channels, during the negative potential scan, proceeds in two stages, except at the higher pH and lower SP25A concentration adopted, where it proceeds in a single stage. In light of the behavior of SP25A single channel currents reported in the literature, the first stage is ascribed to large channels resulting from the aggregation of small ones, while the second more negative stage is associated with the small channels resulting from the disaggregation of the large ones., (Copyright © 2015. Published by Elsevier B.V.)

In the present manuscript, an electrochemical sensor for the sensitive detection of Tl(+), Pb(2+) and Hg(2+) is described. A new composite electrode has been fabricated using graphene, 1-n-octylpyridinum hexafluorophosphate (OPFP), and [2,4-Cl2C6H3C(O)CHPPh3] (L), as a new synthetic phosphorus ylide. The physicochemical and electrochemical characterizations of fabricated sensor were investigated in details. The advantages of the proposed composite electrode are its ability in simultaneous electrochemical detection of Tl(+), Pb(2+) and Hg(2+) with good selectivity, stability and no need for separating of the three species from complex mixtures prior to electrochemical measurements. The analytical performance of the proposed electrode was examined using square wave voltammetry. Tl(+), Pb(2+) and Hg(2+) can be determined in linear ranges from 1.25×10(-9) to 2.00×10(-7) mol L(-1). Low detection limits of 3.57×10(-10) mol L(-1) for Tl(+), 4.50×10(-10) mol L(-1) for Pb(2+) and 3.86×10(-10) mol L(-1) for Hg(2+) were achieved. Finally, the proposed electrochemical sensor was applied to detect trace analyte ions in various water and soil samples with satisfactory results., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The environmental stability of Tl-rich sphalerite in two contrasting soils was studied. Rhizospheric conditions were simulated to assess the risk associated with sulfide microparticles entering agricultural (top)soils. The data presented here clearly demonstrate a significant effect of 500 μM citric acid, a model rhizospheric solution, on ZnS alteration followed by enhanced Tl and Zn release. The relative ZnS mass loss after 28 days of citrate incubation reached 0.05 and 0.03 wt.% in Cambisol and Leptosol samples respectively, and was up to 4 times higher, compared to H2O treatments. Incongruent (i.e., substantially increased) mobilization of Tl from ZnS was observed during the incubation time. Generally higher (long-term) stability of ZnS with lower Tl release is predicted for soils enriched in carbonates. Furthermore, the important role of silicates (mainly illite) in the stabilization of mobilized Tl, linked with structural (inter)layer Tl-K exchange, is suggested. Thallium was highly bioavailable, as indicated by its uptake by white mustard; maximum Tl amounts were detected in biomass grown on the acidic Cambisol. Despite the fact that sulfides are thought as relatively stable phases in soil environments, enhanced sulfide dissolution and Tl/trace element release (and bioaccumulation) can be assumed in rhizosphere systems., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Three new calixarene Tl(+) ionophores have been utilized in Tl(+) ion-selective electrodes (ISEs) yielding Nernstian response in the concentration range of 10(-2)-10(-6)M TlNO3 with a non-optimized filling solution in a conventional liquid contact ISE configuration. The complex formation constants (logβIL) for two of the calixarene derivatives with thallium(I) (i.e. 6.44 and 5.85) were measured using the sandwich membrane technique, with the other ionophore immeasurable due to eventual precipitation of the ionophore during these long-term experiments. Furthermore, the unbiased selectivity coefficients for these ionophores displayed excellent selectivity against Zn(2+), Ca(2+), Ba(2+), Cu(2+), Cd(2+) and Al(3+) with moderate selectivity against Pb(2+), Li(+), Na(+), H(+), K(+), NH4(+) and Cs(+), noting that silver was the only significant interferent with these calixarene-based ionophores. When optimizing the filling solution in a liquid contact ISE, it was possible to achieve a lower limit of detection of approximately 8nM according to the IUPAC definition. Last, the new ionophores were also evaluated in four solid-contact (SC) designs leading to Nernstian response, with the best response noted with a SC electrode utilizing a gold substrate, a poly(3-octylthiophene) (POT) ion-to-electron transducer and a poly(methyl methacrylate)-poly(decyl methacrylate) (PMMA-PDMA) co-polymer membrane. This electrode exhibited a slope of 58.4mVdecade(-1) and a lower detection limit of 30.2nM. Due to the presence of an undesirable water layer and/or leaching of redox mediator from the graphite redox buffered SC, a coated wire electrode on gold and graphite redox buffered SC yielded grossly inferior detection limits against the polypyrrole/PVC SC and POT/PMMA-PDMA SC ISEs that did not display signs of a water layer or leaching of SC ingredients into the membrane., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Objective: Early statin therapy after acute coronary syndrome reduces atherothrombotic vascular events. This study aimed to compare the effects of hydrophilic and hydrophobic statins on myocardial salvage and left ventricular (LV) function in patients with ST-elevated myocardial infarction (STEMI)., Methods: Seventy-five STEMI patients who had received emergency reperfusion therapy were enrolled and randomized into the hydrophilic statin group (rosuvastatin; 5 mg/day, n = 38) and hydrophobic statin group (atorvastatin; 10 mg/day, n = 37) for 6 months. LV ejection fraction (LVEF), and B-type natriuretic peptide (BNP) and co-enzyme Q10 (CoQ10) levels were measured at baseline and the end of treatment. The myocardial salvage index was assessed by single photon emission computed tomography with (123-)I-β-methyl-iodophenylpentadecanoic acid (ischemic area-at-risk at onset of STEMI: AAR) and (201-)thallium scintigraphy (area-at-infarction at 6 months: AAI) [myocardial salvage index = (AAR-AAI) × 100/AAR (%)]., Results: Onset-to-balloon time and maximum creatine phosphokinase levels were comparable between the groups. After 6 months, rosuvastatin (-37.6% ± 17.2%) and atorvastatin (-32.4% ± 22.4%) equally reduced low-density lipoprotein-cholesterol (LDL-C) levels (p = 0.28). However, rosuvastatin (+3.1% ± 5.9%, p < 0.05), but not atorvastatin (+1.6% ± 5.7%, p = 0.15), improved LVEF. Rosuvastatin reduced BNP levels compared with atorvastatin (-53.3% ± 48.8% versus -13.8% ± 82.9%, p < 0.05). The myocardial salvage index was significantly higher in the rosuvastatin group than the atorvastatin group (78.6% ± 29.1% versus 52.5% ± 38.0%, p < 0.05). CoQ10/LDL-C levels at 6 months were increased in the rosuvastatin group (+23.5%, p < 0.01) and percent changes in CoQ10/LDL-C were correlated with the myocardial salvage index (r = 0.56, p < 0.01)., Conclusion: Rosuvastatin shows better beneficial effects on myocardial salvage than atorvastatin in STEMI patients, including long-term cardiac function, associated with increasing CoQ10/LDL-C., Clinical Trial Registration: URL http://www.umin.ac.jp/ctr/index.htm Unique Identifier: UMIN000003893., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

The present work describes the trace analysis of Tl(I) in acidic medium (0.05 mol L(-1) nitric acid) by square wave anodic stripping voltammetry (SWASV) at a tin film sensor with novel configuration. This "green" electroanalytical device features on-chip metal film electrodes (a Sn-film working electrode, a Ag-film reference electrode and a Pt-film counter electrode), fabricated by sputtering the respective metals on a silicon chip. The effect of preconcentration time, preconcentration potential and SW stripping parameters on the Tl(I) detection was studied in detail. The limit of detection for Tl(I) was 1.1 μg L(-1), while the % relative standard deviation at the same sensor was 5.2% at the 10 μg L(-1) level. Finally, the sensors were successfully applied to the direct determination of Tl(I) in an acidified certified lake water sample., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The study deals with the environmental stability of Tl-modified phases (ferrihydrite, goethite, birnessite, calcite and illite) and phytoavailability of Tl in synthetically prepared soils used in a model vegetation experiment. The data presented here clearly demonstrate a strong relationship between the mineralogical position of Tl in the model soil and its uptake by the plant (Sinapis alba L.). The maximum rate of Tl uptake was observed for plants grown on soil containing Tl-modified illite. In contrast, soil enriched in Ksat-birnessite had the lowest potential for Tl release and phytoaccumulation. Root-induced dissolution of synthetic calcite and ferrihydrite in the rhizosphere followed by Tl mobilization was detected. Highly crystalline goethite was more stable in the rhizosphere, compared to ferrihydrite, leading to reduced biological uptake of Tl. Based on the results obtained, the mineralogical aspect must be taken into account prior to general environmental recommendations in areas affected by Tl., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The interactions of Tl(I), a well known toxic species, with selected oligonucleotides were examined. The oligonucleotide sequences selected for the investigation were taken from gene hOGG1 responsible for repairing of DNA damage. Cyclic voltammetry was particularly useful, since nitrogen N-7 in guanine can be electrooxidized while its binding with Tl(I) leads to the loss of electroactivity. So, this selected interaction could be quantitatively used in drawing Scatchard's plot and calculating the binding constants and the number of active sites in guanine molecules occupied by one metal ion. Further, we have shown that the presence of Tl(I) leads to a decrease in activity of doxorubicin (DOX), a popular anticancer drug, vs. DNA. The obtained circular dichroism (CD) spectra and the measurements with an electrochemical quartz crystal microbalance (EQCM) led to a conclusion that in the presence of monovalent thallium cations the DNA double helix was neither damaged/oxidized nor its conformation changed substantially., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A simple cloud point extraction method is described for the separation and pre-concentration of thallium from the microwave assisted aqua regia extracts of sediment and coal fly ash samples. The method is based on the formation of extractable species of thallium and its interaction with hydrophobic solubilizing sites of Triton X-114 micelles in the presence of aqua regia and electrolyte NaCl. These interactions of micelles are used for extraction of thallium from a bulk aqueous phase into a small micelles-rich phase. The potential chloride interferences are eliminated effectively, which enabled interference free determination of thallium from aqua regia extracts using continuum source ETAAS. The parameters affecting the extraction process are optimized. Under the optimized conditions, pre-concentration factor and limit of detection are 40 and 0.2 ng g(-1), respectively. The recoveries are in the range of 95-102%. A characteristic mass, 13 pg was obtained. The accuracy of the method is verified by analyzing certified reference materials such as NIST 1633b coal fly ash, NIST 1944 marine sediment and GBW 07312 stream sediments. The results obtained are in good agreement with the certified values and method is also applied to real samples., (Copyright © 2012 Elsevier B.V. All rights reserved.)

In the present work, a new, simple and efficient method for simultaneous preconcentration of ultra-trace amounts of gold and thallium is developed using an ion pair based-ultrasound assisted emulsification-solidified floating organic drop microextraction procedure before graphite furnace atomic absorption spectrometry determination. This methodology was used to preconcentrate the ion pairs formed between AuCl(4)(-) and TlCl(4)(-) and [C(23)H(42)]N(+) in a microliter-range volume of 1-undecanol. Several factors affecting the microextraction efficiency, such as HCl volume, type and volume of extraction solvent, sonication time, sample volume, temperature, ionic strength and [C(23)H(42)]NCl volume were investigated and optimized. Under the optimized conditions, the enrichment factor of 441 and 443 and calibration graphs of 2.2-89 and 22.2-667 ng L(-1) for gold and thallium were obtained, respectively. The intra- and inter-day precision of ± 4.4 and ± 4.9% for Au and ± 4.8 and ± 5.4% for Tl were obtained. The detection limit was 0.66 ng L(-1) for Au and 4.67 ng L(-1) for Tl. The results show that the liquid-liquid pretreatment using ion pair forming, is sensitive, rapid, simple and safe method for the simultaneous preconcentration of gold and thallium. The method was successfully applied for determination of gold and thallium in natural water and hair samples., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Besides the dominant species in plants-Tl(I), noticeable amounts of Tl(III) (about 10% of total Tl content) were found in extracts of plants cultivated in the presence of tailing sediments, which are the main source of anthropogenic thallium already present in the environment. It is an important step of gaining knowledge about the detoxification mechanisms developed by Sinapis alba. This plant species is highly tolerant to Tl and it is able to cumulate high amounts of Tl and transport it into the above-ground organs. For more adequate estimation of accumulating abilities of S. alba, the elements' bioavailability was taken into consideration. The obtained bioconcentration factors of Cd (AF=0.6) and Zn (AF=1-2) were significantly lower than of Tl (AF=100-200). The biomass production was similar to the biomass of control cultivation. The results were based on ICP MS measurements of total elements' content and HPLC ICP MS for speciation analysis. The quality of obtained results was evaluated based on the intermethod comparison with voltammetry as a reference method. Comparison of data obtained using ICP MS and electrochemical methods (after a proper chemical treatment) was also used for indication of Tl(III) presence and for proving that Tl(I) was not transferred into Tl(III) during analytical procedures., (Copyright © 2012 Elsevier B.V. All rights reserved.)

To develop a real-time thallium flux assay for high-throughput screening (HTS) of human KCNQ4 (Kv7.4) potassium channel openers, we used CHO-K1 cells stably expressing human KCNQ4 channel protein and a thallium-sensitive dye based on the permeability of thallium through potassium channels. The electrophysiological and pharmacological properties of the cell line expressing the KCNQ4 protein were found to be in agreement with that reported elsewhere. The EC(50) values of the positive control compound (retigabine) determined by the thallium and (86)rubidium flux assays were comparable to and consistent with those documented in the literature. Signal-to-background (S/B) ratio and Z factor of the thallium influx assay system were assessed to be 8.82 and 0.63, respectively. In a large-scale screening of 98,960 synthetic and natural compounds using the thallium influx assay, 76 compounds displayed consistent KCNQ4 activation, and of these 6 compounds demonstrated EC(50) values of less than 20 μmol/L and 2 demonstrated EC(50) values of less than 1 μmol/L. Taken together, the fluorescence-based thallium flux assay is a highly efficient, automatable, and robust tool to screen potential KCNQ4 openers. This approach may also be expanded to identify and evaluate potential modulators of other potassium channels., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Thallium (III) ion-imprinted polymer (IIP) particles were synthesized by preparing the ternary complex of thallium (III) ions with 5,7-dichloroquinoline-8-ol (DCQ) and 4-vinylpyridine (VP). Thermal copolymerization with methyl methacrylate (functional monomer, MMA) and ethyleneglycoldimethacrylate (cross-linking monomer, EGDMA) was then performed in the presence of acetonitrile (porogen) and 2,2- azobisisobutyronitrile(initiator, AIBN). The imprinted ion was removed from polymer by stirring of the above particles with 5M HNO(3) to obtain the leached IIP particles. Moreover, control polymer (CP) particles were similarly prepared without the thallium (III) ions. The unleached and leached IIP particles were characterized by surface area analysis (BET), X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), thermo gravimetric analysis (TGA) and scanning electron microscopy (SEM). The preconcentration of thallium (III) from aqueous solution was studied during rebinding with the leached IIP particles as a function of pH, the weight of the polymer material, the uptake and desorption times, the aqueous phase and the desorption volumes. Electrothermal atomic absorption spectrometry (ETAAS) was employed for determination of thallium in aqueous solution. The limit of detection for the method was 0.02 ng mL(-1), while the relative standard deviation for five replicates was 2.6%., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The influence of different soil conditions and the presence of LMWOA (Low Molecular Weight Organic Acids) on anthropogenic Tl dynamics were discussed in this study. A shift from the "labile" to the residual fraction during the ageing was identified, indicating Tl incorporation into stable phases (e.g., illite and/or amorphous silicates). The increased water-soluble Tl concentration (1.8-fold, in maximum) after the split application of LMWOA (simulating root exudation) was observed in all soils; partial dissolution of relatively "insoluble" Tl-bearing phases (silicates and eventually oxides) in the presence of LMWOA is suggested. Thermodynamic modeling showed that Tl mobilization in the presence of citric and oxalic acids was indirect and could be attributed to complexation of major elements (Ca, Mg, Al) originating from the dissolution of various soil phases. On the contrary, H(+)-promoted dissolution by acetic acid was assumed as the predominant mechanism of Tl mobilization. Manganese(III,IV) oxides, illite and probably amorphous silicates were evaluated as the dominant phases responsible for Tl retention in the soils. In carbonate-rich soils, Tl coprecipitation with the newly formed carbonates seems to be an important factor influencing Tl release. Therefore, we suggest data on CEC, pH(ZPC) and soil mineralogy to be critical for assessment of Tl behavior in soil systems.

An approach for the separation and determination of inorganic thallium species is described. A new sorbent, L-tyrosine-carbon nanotubes (L-tyr-CNTs), was used and applied to the analysis of tap water samples. At pH 5.0, L-tyr was selective only towards Tl(III), while total thallium was determined directly by stabilized temperature platform furnace-electrothermal atomic absorption spectrometry (STPF-ETAAS). The Tl(III) specie, which was retained by L-tyrosine, was quantitatively eluted from the column with 10% of nitric acid. An on-line breakthrough curve was used to determine the column capacity, which resulted to be 9.00 micromol of Tl(III) g(-1) of L-tyr-CNTs with a molar ratio of 0.14 (moles of Tl bound to moles of L-tyr at pH 5). Transient peak areas revealed that Tl stripping from the column occurred instantaneously. Effects of sample flow rate, concentration and flow rate of the eluent, and interfering ions on the recovery of the analyte were systematically investigated. The detection limit for the determination of total thallium (3sigma) by STPF-ETAAS was 150 ng L(-1). The detection limit (3sigma) for Tl(III) employing the separation system was 3 ng L(-1), with an enrichment factor of 40. The precision of the method expressed as the relative standard deviation (RSD) resulted to be 3.4%. The proposed method was applied to the speciation and determination of inorganic thallium in tap water samples. The found concentrations were in the range of 0.88-0.91 microg L(-1) of Tl(III), and 3.69-3.91 microg L(-1) of total thallium.

The selective determination of norfloxacin in mixtures with other fluorquinolones was achieved by synchronous scanning solid surface room-temperature phosphorimetry (SSRTP) and Th(NO(3))(4) as selective phosphorescence inducer. The method also allowed the determination of levofloxacin in a sequential way. The optimization of experimental conditions was made through an univariate approach, in order to find the best conditions for norfloxacin phosphorescence, followed by a 2(3) factorial design in order to verify interaction among relevant variables, to check robustness for each variable and to perform final adjustment of parameters. Absolute limit of detection (ALOD) for norfloxacin was 12ng with a linear signal response extending up to 400ng. Under the same experimental conditions set for norfloxacin, the ALOD for levofloxacin was 13ng with linear signal response up to 450ng. Accuracy of the method, using Th (IV) as selective phosphorescence inducer, was evaluated through the analysis of commercial and simulated pharmaceutical formulations with recoveries between 94.4 and 101% for norfloxacin and 95.9 and 103.8% for levofloxacin. The use of Cd (II), a traditional phosphorescence inducer for fluorquinolones, did not allow selective determination of norfloxacin. Further studies indicated the potential application of the method in urine samples.

A novel sorbent, nano-Al(2)O(3) was employed for the removal of thallium from aqueous solution in batch equilibrium experiments, in order to investigate its adsorption properties. The removal percentage of thallium by the sorbent increased with increasing pH from 1 to 5. The adsorption capacities and removal percentage of Tl(III) onto nano-Al(2)O(3) were evaluated as a function of the solution concentration and temperature. Results have been analyzed by the Langmuir, Freundlich adsorption isotherms. Adsorption isothermal data could be well interpreted by the Langmuir model. The mean energy of adsorption 9.32 kJ mol(-1) was calculated from the Dubinin-Radushkevich (D-R) adsorption isotherm. The kinetic experimental data properly correlated with the second-order kinetic model. The thermodynamic parameters for the process of adsorption have been estimated. The DeltaH(0) and DeltaG(0) values of thallium(III) adsorption on nano-Al(2)O(3) showed endothermic adsorption.

A simple solvent extraction study for thallium has been conducted based on the extraction of thallium as a chlorocomplex (tetrachlorothallate (III) anion) with tribenzylamine. Radiolabelled Tl (III) was used to study the extraction behavior of thallium. The beta activity of the extracted ion-association complex has been monitored using liquid scintillation counting and Geiger Muller counter. The effect of various diluents such as toluene, chloroform and isobutylmethylketone (MIBK) were studied. The extraction efficiency was 95% when chloroform and MIBK were used as diluents for tribenzylamine at an overall concentration of 0.25 mol dm(-3) NaCl and 0.5 mol dm(-3) H(2)SO(4). The phenomenon of severe chemical quenching was observed with chloroform as the diluent. The recovery of thallium was found to be 95% at varying concentrations ranging from 5 to 20 microg ml(-1) Tl (III) with a relative standard deviation of 2.5%.

Daphnia magna was used to evaluate the aquatic toxicity of Tl(III) compounds including Tl(III) nitrate, Tl(III) chloride, and Tl(III) acetate. The results clearly show that Tl(III) is extremely toxic to daphnids. The 48-h LC50 values for Tl(III) nitrate, Tl(III) chloride, and Tl(III) acetate are 24, 61, and 203 microg/L, respectively. Tl(III) is much more toxic than Tl(I) and many other metals such as Cd(II), Cu(II), and Ni(II); it is similar to the toxicity that of Hg(II). The formation of Tl(III)-complexes would significantly reduce Tl(III) toxicity.

The total concentrations combined with the chemical speciation of thallium (Tl) were examined in order to track the distribution of natural and anthropogenic Tl in the soils in an industrial pyrite slag disposing area. Their geochemical behaviors in the soils were further discussed. Soil samples were collected from three soil profiles adjacent to a large open-disposed pile of industrial Tl-rich pyrite slag, and from one soil profile in the background area. The results show that the soil contamination with Tl derived from slag (slag-Tl) is generally limited; slag-Tl was mainly accumulated in the upper part (< 16.5 cm) of the vicinal soils of the slag pile and shows large variation in concentration among different sampling sites. Basically, the soils surrounding the slag pile within 5 m are more Tl-contaminated than those under the slag pile and those far away from the slag pile. In respect of the concentrations of total Tl, the deeper soils of the studied profiles seem to be uncontaminated. However, the percentages of Tl in the easily reducible fraction indicate that these soils have been actually contaminated by slag-Tl. Natural Tl and anthropogenic Tl are distributed differently among the soil components in the studied soils. Natural Tl in the background soils is predominantly hosted in the residual fraction ( approximately 98%), while anthropogenic Tl was significantly incorporated into the more labile fractions of the soil (up to approximately 80%), especially in the acid-extractable fractions and easily reducible fraction (up to approximately 30% and approximately 45%, respectively). Detailed analysis of speciation data of Tl suggests that despite being predominantly controlled by the degree of Tl pollution, the distribution of slag-Tl in the soils can be further affected by the general differences in soil properties. In this study, the order for preferential immobilization of anthropogenic Tl among major soil components can be roughly summarized as: Tl(III) carbonates and hydroxides > Mn oxide-hydroxides > Fe oxide-hydroxides > adsorption sites on the surface of soil, while the order can be significantly mediated by the pH conditions in the soils. The correlations between the fractions of Tl in the slag and in the soils indicate that the anthropogenic Tl in the soils in the studied slag disposing area should be mainly derived from the dissolved slag-Tl that was leached by rainwater rather than from the washed-out particles of slag.

X-ray crystal structure analyses have been performed on the beta-dipeptide (anthranoyl)anthranilic acid [HAnthAnthOH] and its lithium, sodium and thallium salts [HAnthAnthOM] to give a first set of data for this representative model ligand. Crystals of the beta-dipeptide are orthorhombic, space group Pca2(1). The unit cell contains two molecules of (anthranoyl)anthranilic acid which form a dimer via hydrogen bonds. The components of the beta-dipeptide are rotated into the trans-conformation which allows for internal hydrogen bonds. The pKS value of (anthranoyl)anthranilic acid (9.80+/-0.14) shows a slight decrease as compared to anthranilic acid; the metal salts can therefore be prepared by direct neutralization of the beta-dipeptide with metal hydroxides or carbonates. The alkali compounds crystallize as the trihydrates [HAnthAnthOM(H2O)3, M=Li, Na] in the triclinic space group p1. Both metal ions show a clear preference for water molecules over the (anthranoyl)anthranilate anions as ligands in their coordination spheres. As a consequence, the [HAnthAnthO]- anions are only partially involved in metal complexation. The cell plots of both compounds exhibit a stacking with an alternation of oppositely charged layers. The negatively charged layers are composed exclusively of (anthranoyl)anthranilate anions. The thallium compound crystallizes as the hemihydrate [HAnthAnthOTl(H2O)0.5] in the monoclinic space group C2/c. In the dinuclear units, the thallium ions accommodate one nitrogen and four oxygen atoms of the anions in their coordination sphere and in addition entertain weak Tl-arene contacts. In contrast to the alkali compounds, the water molecules are not involved in metal complexation, but contribute to a network of hydrogen bonding.

A number of metal trifluoroacetates were reacted with the olefin 3beta-acetoxyandrost-5-en-17-one (6). Palladium(II) trifluoroacetate afforded bis[micro-trifluoroacetato(alpha-5,7-eta-3beta-acetoxyandrostenyl-17-one)palladium(II)] (20), a new ring B pi-allyl steroid-palladium complex, in quantitative yield. Thallium(III) trifluoroacetate gave 3beta-acetoxy-5alpha-hydroxy-6beta-trifluoroacetoxyandrostan-17-one (16), 3beta-acetoxy-6beta-trifluoroacetoxyandrost-4-en-17-one (9), 3beta-acetoxy-4beta-trifluoroacetoxyandrost-5-en-17-one (10), and 3beta-acetoxy-5alpha,6beta-dihydroxyandrostan-17-one (17). Lead(IV) trifluoroacetate yielded 9, 10 and 16. 3beta-Acetoxy-5alpha,6beta-bis(trifluoroacetoxy)androstan-17-one (15), a new compound, was also formed in this reaction. During the course of the lead(IV) studies the dichlorosteroid 21 and the rearranged allylic oxidation product 24 were formed. Their formation was attributed to the generation of lead(IV) chloride in the reaction. Silver(I) and copper(II) trifluoroacetates proved to be unreactive towards 6.

In spite of the fact that Group 13 metal ions (Al(3+), Ga(3+), In(3+) and Tl(+/3+)) show no main biological role, they are NMR-active nuclides which can be used in magnetic resonance spectroscopy of biologically relevant systems. The fact that these metal ions are quadrupolar (with the exception of thallium) means that they are particularly sensitive to ligand type and coordination geometry. The line width of the NMR signals of their complexes shows a strong dependence on the symmetry of coordination, which constitutes an effective tool in the elucidation of structures. Here we report published NMR studies of this family of elements, applied to systems of biological importance. Special emphasis is given to binding studies of these cations to biological molecules, such as proteins, and to chelating agents of radiopharmaceutical interest. The possibility of in vivo NMR studies is also stressed, with extension to (27)Al-based MRI (magnetic resonance imaging) experiments.

The hypothesis that thallium (Tl) interaction with membrane phospholipids could result in the alteration of membrane physical properties was investigated. Working with liposomes composed of brain phosphatidylcholine and phosphatidylserine, we found that Tl(+), Tl(3+), and Tl(OH)(3) (0.5-25 microM): (a) increased membrane surface potential, (b) decreased the fluidity of the anionic regions of the membrane, in association with an increased fluidity in the cationic regions, and (c) promoted the rearrangement of lipids through lateral phase separation. The magnitude of these effects followed the order Tl(3+), Tl(OH)(3)>Tl(+). In addition, Tl(3+) also decreased the hydration of phospholipid polar headgroups and induced membrane permeabilization. The present results show that Tl interacts with membranes inducing major alterations in the rheology of the bilayer, which could be partially responsible for the neurotoxic effects of this metal.

A calix[4]arene derivative containing ethoxycarbonylmethoxy groups in the coordination sphere and an iminopyridinium indicator group was studied by FT-IR spectroscopy in acetonitrile solution. The characteristic changes of v(C=O) stretching vibration offered an opportunity for the improvement on selectivity of the ion recognition process of this ligand. The shift of the carbonyl stretching vibration band depended on complex formation as well as on the equilibrium constants of complex formation. In the case of sodium complex, a well-defined isobestic point was detected in the v(C=O) region while altering the sodium concentration. The affinity of thallium(III) to form complex with calixarene 1 was found comparable with those of lithium, sodium or calcium. The complex was found to be an M2L type supramolecule, whereas one molecule of triethylamine was necessary for the formation of each complex.

A procedure for directly fitting the potential energy curve of a diatomic molecule has been applied to the X1sigma+ ground states of LiCl, TlCl, RbF and CsF. Extensive, high-precision infrared and pure-rotational data sets for all isotopomers of the aforementioned molecules have been employed in direct least-squares fits of a radially dependent Hamiltonian operator. The Born-Oppenheimer potentials are represented by a modified Lennard-Jones function that is shown to be flexible and provide the proper behavior in the long-range region of the potential. While the potential fits of LiCl and TlCl required the inclusion of Born-Oppenheimer breakdown functions, no such functions were necessary for either RbF or CsF.

The various crystalline forms of an original bicyclic compound [ethyl (2-chloromethyl-2,3-dihydro-5H-oxazolo[3, 2-a]pyrimidin-5-one)-6-carboxylate); EOC] have been obtained and characterized by powder and single-crystal X-ray diffraction, differential scanning calorimetry (DSC), and infrared (IR) and Raman spectroscopy. At 4 degrees C in methanol, a monoclinic racemate (form II) crystallized from the racemic mixture, whereas at 20 degrees C, an orthorhombic racemate (form I) was isolated in trichloroethylene. By increasing the temperature, a solid-solid transition from the stable form II to the stable form I was observed with a Guinier-Simon camera. A I --> II transformation was observed at ambient temperature by DSC., (Copyright 2000 Wiley-Liss, Inc.)

The sarcin/ricin domain of 23 S - 28 S ribosomal RNA is essential for protein synthesis because it forms a critical part of the binding site for elongation factors. A crystal structure of an RNA of 27 nucleotides that mimics the domain in Escherichia coli 23 S rRNA was determined at 1.11 A resolution. The domain folds into a hairpin distorted by four non-canonical base-pairs and one base triple. The fold is stabilized by cross-strand and intra-stand stacking; no intramolecular stabilizing metal ions are observed. This is the first structure to reveal in great detail the geometry and the hydration of two common motifs that are conserved in this rRNA domain, a GAGA tetraloop and a G-bulged cross-strand A stack. Differences in the region connecting these motifs to the stem in the E. coli and in the rat sarcin/ricin domains may contribute to the species-specific binding of elongation factors. Correlation of nucleotide protection data with the structure indicates that the domain has two surfaces. One surface is accessible, lies primarily in the major groove, and is likely to bind the elongation factors. The second lies primarily in the minor groove, and is likely to be buried in the ribosome. This minor groove surface includes the Watson-Crick faces of the cytosine bases in the unusual A2654.C2666 and U2653.C2667 water-mediated base-pairs., (Copyright 1999 Academic Press.)

A new homologous series of thallium(I) hydrogen dialkanoates, fatty acid thallium soaps, from the dipropane up to the ditetradecane is reported for the first time. This association with 1:1 stoichiometry is the only one exhibited by the thallium derivatives. They have been prepared by solidification of molten mixtures with equimolar proportions of acid and corresponding neutral salt, through crystallization from an anhydrous ethanolic solution of the mixture has also been successful in getting pure compounds with largest chain lengths. Vibrational spectroscopies clearly characterize these crystalline compounds as very strong hydrogen bonding systems. Assignations of active modes in proton and carbon nuclear magnetic resonance spectrometry (NMR) (in ethanol) and infrared (IR) and Raman spectra (in solid state) are reported. According to X-ray diffraction (XRD) they have monomolecular lamellar structures with the acyl chains arranged up and down to the cation/H-bond network in a methyl-to-methyl fashion, and vertically oriented to the basal plane. The acyl chains present all-trans conformation and alternating configuration (perpendicular orthorhombic subcell), like the beta'-phases of other kinds of lipids. Lamellar thickness is reported for the six room-temperature crystalline members. The molecular compounds present polymorphism, one crystal/crystal transition at temperatures close to the peritectical melting. Phase transition thermodynamics are also given and discussed with respect to their acid and salt parents. Their incongruent melting involves nearly 90% of the total enthalpic increments of both constituents' melting processes, making these compounds potential thermal energy storage materials.