PAN Complexes Research Articles

Assembling the Proto-Yangtze Block in the late Paleoproterozoic: Constraints from a refined Magmatic-Metamorphic framework of the Cuoke Complex, SW China

The Archean-Paleoproterozoic records of the southwestern and northern Yangtze are key components in establishing the early history of the Yangtze Block as a whole. To date, knowledge of the late Paleoproterozoic evolutionary history of the Yangtze Block has been largely derived from its northern margin. This study documents the presence of ca. 1.93 Ga metamorphic zircons and 1.89–1.86 Ga metamorphic-hydrothermal reset zircons from igneous rocks in the Cuoke Complex of southwestern Yangtze, as well as ca. 1.93 Ga and 1.86 Ga xenotime growths in a meta-volcaniclastic rock (tuff). In addition, the origin of 2.0–1.85 Ga zircons from magmatic rocks in both the Cuoke and Phan Si Pan complexes of the southwestern Yangtze Block are reassessed. Based on new and published CL images, U contents and REE patterns, we argue that the 2.0–1.85 Ga ages are reset from primary 2.3 Ga magmatic zircons during a widespread metamorphic-hydrothermal overprinting event. Integrated U-Pb data reveal two metamorphic peaks at 2.0–1.95 Ga and ca. 1.85 Ga in both northern and southwestern Yangtze, indicating the two domains came together at 2.0–1.95 Ga to form the proto-Yangtze Block. The geological records of northern and southwestern Yangtze match well with those of northern Laurentia and Siberia, respectively, suggesting an internal location for the proto-Yangtze Block within Nuna. This contrasts with its inferred external location within the Rodinia supercontinent, suggesting the transition between the two Proterozoic supercontinents involved significant reconfiguration of at least some of the constituent core continental blocks.

Speciation of inorganic vanadium by direct immersion dual-drop microextraction coupled with graphite furnace atomic absorption spectrometry detection

In this work, a new method based on direct immersion dual-drop microextraction (DIDDME) was proposed for simultaneous speciation and enrichment of V(IV) and V(V) by graphite furnace atomic absorption spectrometry. This strategy was initiated with the chelation of V(IV) and V(V) in sample solutions with 1-(2-Pyridylazo)-2-naphthol (PAN). In the following step, two organic solvent drops hold on needle tips of microsyringes were concurrently immersed in the stirred sample solution to selectively and simultaneously separate V(IV)-PAN and V(V)-PAN complexes under the same pH value. This procedure avoided the tedious and complicated pre-oxidation/pre-reduction and centrifugation/filtration operations, which may cause the risk of sample contamination and analysis errors. Main parameters affecting the separation, preconcentration of the target species were investigated. Under the optimized conditions, the detection limits of this method were 2.4 ng/L and 1.5 ng/L for V(IV) and V(V) with relative standard deviations of 6.1 and 5.3 %, respectively. An enrichment factor of 300-fold was achieved for V(IV) and V(V). This method was applied successfully for the determination of V(IV) and V(V) in water samples. In order to validate the proposed procedure, a certified reference material of water sample was analyzed, and the determined value was in good agreement with the certified value.

Landsat identifies aeolian dust emission dynamics at the landform scale

The modelling of windblown mineral dust emissions remains a challenge. This is in part due to the coarse spatial and temporal resolution of the data on which these models are based, but also because the processes and mechanisms of aeolian dust emission are not well understood. Satellite imagery has been used extensively in the study of dust from the late 1990s with important contributions being made in terms of sources, transport pathways and deposition areas. Using MODIS imagery, the Namib Desert has been identified as one of the largest sources of dust in southern Africa. The opening of the Landsat archive presents the opportunity to investigate these events at a higher spatial resolution (up to 15×15m) than previously possible. Despite the low temporal resolution, we used Landsat imagery to identify 40 major dust episodes over the last 25years that originated primarily from the ephemeral river valleys and pan complexes, providing new insight into the spatial and temporal evolution of the dust sources from dryland surfaces. Examination of the imagery enabled the identification of local-scale landform source points to direct ground based testing of the surfaces responsible for dust emission. Emissivity tests were undertaken using a PI-SWERL portable wind tunnel in three of the major dust producing river systems along the Namib coast, namely the Kuiseb, Omaruru and Huab Rivers. Preliminary observations suggest that human impact on the hydrological systems in two of the river basins, to cater for the increasing demand of water, have dramatically altered the emission patterns of dust. The source areas of greatest dust emission are found to be located on recently deposited fluvial surfaces which are not active in the contemporary environment.

Systematic identification of genes involved in metabolic acid stress resistance in yeast and their potential as cancer targets.

ABSTRACTA hallmark of all primary and metastatic tumours is their high rate of glucose uptake and glycolysis. A consequence of the glycolytic phenotype is the accumulation of metabolic acid; hence, tumour cells experience considerable intracellular acid stress. To compensate, tumour cells upregulate acid pumps, which expel the metabolic acid into the surrounding tumour environment, resulting in alkalization of intracellular pH and acidification of the tumour microenvironment. Nevertheless, we have only a limited understanding of the consequences of altered intracellular pH on cell physiology, or of the genes and pathways that respond to metabolic acid stress. We have used yeast as a genetic model for metabolic acid stress with the rationale that the metabolic changes that occur in cancer that lead to intracellular acid stress are likely fundamental. Using a quantitative systems biology approach we identified 129 genes required for optimal growth under conditions of metabolic acid stress. We identified six highly conserved protein complexes with functions related to oxidative phosphorylation (mitochondrial respiratory chain complex III and IV), mitochondrial tRNA biosynthesis [glutamyl-tRNA(Gln) amidotransferase complex], histone methylation (Set1C–COMPASS), lysosome biogenesis (AP-3 adapter complex), and mRNA processing and P-body formation (PAN complex). We tested roles for two of these, AP-3 adapter complex and PAN deadenylase complex, in resistance to acid stress using a myeloid leukaemia-derived human cell line that we determined to be acid stress resistant. Loss of either complex inhibited growth of Hap1 cells at neutral pH and caused sensitivity to acid stress, indicating that AP-3 and PAN complexes are promising new targets in the treatment of cancer. Additionally, our data suggests that tumours may be genetically sensitized to acid stress and hence susceptible to acid stress-directed therapies, as many tumours accumulate mutations in mitochondrial respiratory chain complexes required for their proliferation.

A feedback mechanism between PLD and deadenylase PARN for the shortening of eukaryotic poly(A) mRNA tails that is deregulated in cancer cells.

ABSTRACTThe removal of mRNA transcript poly(A) tails by 3′→5′ exonucleases is the rate-limiting step in mRNA decay in eukaryotes. Known cellular deadenylases are the CCR4-NOT and PAN complexes, and poly(A)-specific ribonuclease (PARN). The physiological roles and regulation for PARN is beginning to be elucidated. Since phospholipase D (PLD2 isoform) gene expression is upregulated in breast cancer cells and PARN is downregulated, we examined whether a signaling connection existed between these two enzymes. Silencing PARN with siRNA led to an increase in PLD2 protein, whereas overexpression of PARN had the opposite effect. Overexpression of PLD2, however, led to an increase in PARN expression. Thus, PARN downregulates PLD2 whereas PLD2 upregulates PARN. Co-expression of both PARN and PLD2 mimicked this pattern in non-cancerous cells (COS-7 fibroblasts) but, surprisingly, not in breast cancer MCF-7 cells, where PARN switches from inhibition to activation of PLD2 gene and protein expression. Between 30 and 300 nM phosphatidic acid (PA), the product of PLD enzymatic reaction, added exogenously to culture cells had a stabilizing role of both PARN and PLD2 mRNA decay. Lastly, by immunofluorescence microscopy, we observed an intracellular co-localization of PA-loaded vesicles (0.1-1 nm) and PARN. In summary, we report for the first time the involvement of a phospholipase (PLD2) and PA in mediating PARN-induced eukaryotic mRNA decay and the crosstalk between the two enzymes that is deregulated in breast cancer cells.

A dinuclear europium(III) complex with thenoyltrifluoroacetonato and 1-(2-pyridylzao)-2-naphtholato ligands and its optical properties

Dinuclear lanthanide complexes of the general for Ln 2(TTA) 4(PAN) 2 (Ln = Eu, Gd, Tb, Yb; TTA and monodeprotonated thenoyltrifluoroacetone and PAN 1-(2-pyridylazo)-2-naphthol, respectively) were prepared and structurally characterized. These novel complexes, representing the first examples of crystallographically characterized lanthanide–PAN complexes, each feature a dinuclear core with the metal atoms bridged by the phenolato O atoms of the chelating-bridging PAN ligands. Electronic spectroscopic and photoluminescence studies were carried out for the Eu(III) complex, and the results are consistent with ligand-mediated energy transfer and ligand-sensitized luminescence characteristic of Eu(III). The Eu(III) complex doped into a polymeric film was shown to effectively limit a nanosecond 523-nm laser pulse, and the limiting effect is rationalized in terms of reverse saturable absorption due to the strong absorption of the metal’s excited triplet states that are populated by intersystem crossing.

Zero-crossing second derivative spectrophotometry for simultaneous determination of palladium and nickel using 1-(2-pyridylazo)-2-naphthol in mixed micellar solutions.

1-(2-Pyridylazo)-2-naphthol (PAN) has been used for the simultaneous determination of nickel and palladium at trace levels. PAN complexes of nickel and palladium in the pH 1.98 form red and green colored complexes, respectively, which are soluble in aqueous 4:1 Triton X-100 to sodium dodecylsulfate (SDS) micellar media with total detergent concentration of 3.2%. Under optimum conditions, calibration graphs for the simultaneous determination by second derivative spectrophotometry were obtained. Zero crossing second derivative spectrophotometry at 668 and 572 nm, respectively for palladium and nickel was used for the simultaneous determination. The method is able to determine palladium to nickel ratio 70:1 to 1:6 (Wt/Wt), accurately. Accuracy and reproducibility of the determination method on the known various amounts of palladium and nickel in their binary mixtures were tested. Effects of diverse ions on the determination of palladium and nickel to investigate selectivity of the method also were studied.

XAD‐4/PAN Solid Phase Extraction System for Atomic Absorption Spectrometric Determinations of Some Trace Metals in Environmental Samples

A simple, fast, and sensitive column solid phase extraction study has been proposed for flame atomic absorption spectrometric determination of lead, cadmium, chromium, nickel, copper, and manganese ions on XAD‐4 as 1‐(2‐pyridylazo)2‐naphthol (PAN) complexes. The analytes were sorbed as PAN complexes on Amberlite XAD‐4 column at the pH range of 8.5–10, and then eluted with 1 M HNO3 in acetone. The effect of pH, reagent amount, sample volume, and matrix of the sample on the sorption of metal ions has also been investigated. The concentration of analytes after separation and preconcentration was in agreement with the added amount of ions. The present method was found to be applicable to the preconcentration of analyte ions in river water from Yesilirmak, lake water from Lake Van, bottled mineral waters, tap water, stream sediment, mushroom, tobacco, and black tea samples with good results (recoveries greater than 95%, relative standard deviations lower than 10%).

Second and first-derivative spectrophotometry for efficient simultaneous and individual determination of palladium and cobalt using 1-(2-pyridylazo)-2-naphthol in sodium dodecylsulfate micellar media.

1-(2-Pyridylazo)-2-naphthol (PAN) has been used for the simultaneous and individual determination of palladium and cobalt at trace levels. PAN complexes of palladium and cobalt at neutral pH form green-color neutral complexes, which are soluble in aqueous SDS micellar media. Under optimum conditions, calibration graphs for individual determinations by zero and first-derivative spectrophotometry, and also for simultaneous determinations by second-derivative spectrophotometry were obtained. A zero-crossing method using second-derivative spectrophotometry at 628 or 578 and 614 nm, respectively, for cobalt and palladium was used for simultaneous determinations. The method is able to determine the cobalt-to-palladium ratio, 5:1 to 1:10 (Wt/Wt), accurately. The accuracy and reproducibility of the determination method for various known amounts of cobalt and palladium in their binary mixtures were tested. The effects of diverse ions on the determination of cobalt and palladium to investigate the selectivity of the method were also studied. The recommended procedures were applied to a synthetic binary alloy, cobalt in vitamin B12 and B-complex ampoules, a Co2O3-Co3O4 laboratorial chemical mixture, some synthetic cobalt-alloy samples, a Pd-charcoal catalyst, and some synthetic palladium alloys.

TXRF heavy metal analysis after immobilization as PAN complexes

Abstract1‐(‐2‐Pyridylazo)‐2‐naphthol (PAN) forms stable complexes with many metals of environmental interest. A few micrograms of PAN were immobilized in a Nafion membrane, the membrane was put on quartz reflectors and the reflectors were immersed in standard aqueous solutions containing nickel, copper, manganese and vanadium salts at very low concentrations (µg l−1 level). The reflectors were left in the solutions for many hours at constant temperature. When the equilibration stage was finished, they were cleaned with ultra‐pure water and left to dry. Analysis of the samples was performed by total reflection x‐ray fluorescence (TXRF) spectrometry. A few µg l−1 of the above metals were determined. The effects of equilibration time and temperature on the measured x‐ray yields were examined. Copyright © 2003 John Wiley & Sons, Ltd.

Adsorptive stripping voltammetric measurements of trace amounts of platinum(II) and ruthenium(III) in the presence of 1-(2-pyridylazo)-2-naphthol

An extremely sensitive stripping voltammetric procedure for low level measurements of platinum (II, IV) or ruthenium (III, IV) is reported. The method is based on the interfacial accumulation of the platinum (II) or ruthenium (III)-1-(2-pyridylazo)-2-naphthol complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The peak potential was found to be −0.8 V vs. Ag/AgCl electrode and the reduction current of the adsorbed complex ions of platinum (II) or ruthenium (III) was measured by differential pulse cathodic stripping voltammetry. The optimum experimental conditions were: 1.5×10−7 mol/l of 1-(2-pyridylazo)-2-naphthol solution of pH 9.3, preconcentration potential of −0.2 V, accumulation time of 3 min and pulse amplitude of 50 mV with 4 mV s−1 scan rate in the presence of ethanol-water (30% v/v) — sodium sulphate (0.5 mol/l). Linear response up to 6.4 × 10−8 and 5.1 × 10−8 mol/l and a relative standard deviation (at 1.2×10−8 mol/l) of 2.4 and 1.6% (n=5) for platinum (II) and ruthenium (III) respectively were obtained. The detection limits of platinum and ruthenium were 3.2×10−10 and 4.1×10−10 mol/l, respectively. The electronic spectra of the Pt(II) — PAN and Ru(III) — PAN complexes were measured at pH 9.3 and the stoichiometric ratios of the complexes formed were obtained by the molar ratio method. The effects of some interfering ions on the proposed procedure were critically investigated. The method was found suitable for the sub-microdetermination of ruthenium (IV) and platinum (IV) after their reduction to ruthenium (III) and platinum (II) with sulphur dioxide in acid media. The applicability of the method for the analysis of binary mixtures of ruthenium (III) and (IV) or platinum (II) and (IV) has also been carried out successfully. The method is simple, rapid, precise, and promising for the determination of the tested metal ions at micro-molar concentration level.

Photoacoustic Determination of Cobalt after Solid-Phase Concentration on an Empore Silica-gel Thin-Layer Plate

A method used to determine trace amounts of samples in aqueous solutions is proposed. Cobalt ion was extracted as a 1-(2-pyridylazo)-2-naphthol (PAN) complex into chloroform. The extract was filtered through an Empore silica-gel TLC plate (2.5cm square) having no backing material. Excessive PAN and other metal-PAN complexes were washed out through the TLC plate by filtering twice 5ml of chloroform. Using these procedures only the cobalt-PAN complex was concentrated on the surface of the TLC plate. The photoacoustic signal of the TLC plate was detected by using a He-Ne laser as a light source. A linear relationship was obtained between the concentration of cobalt and the photoacoustic intensities in the 0.1-20ppb range. A five-hundred-times concentration of Ni, Cu and Fe did not significantly interfere with the photoacoustic signal. The determination limit of cobalt when the sample volume was 100ml was about 0.15ppb.

Rapid Spectrophotometric Determination of Scandium(III) with (Pyridylazo)- and (Thiazolylazo)naphthols

Abstract Scandium(III) reacts with 1-(2-pyridylazo)-2-naphthol [PAN] and 1-(2-thiazolylazo)-2-naphthol [TAN] in weakly acidic media to yield red colored 1:1 and 1:2 chelates, respectively. These complexes are sparingly soluble in water but readily soluble in ≥24% (v/v) acetone and ≥32% (v/v) methanol, giving maximum absorbances at 545 and 570 nm for the PAN and TAN complexes, respectively. Beer’s law is obeyed over the concentration ranges of 0.16 to 1.40 μg and 0.08 to 1.40 μg of Sc(III) per ml with PAN and TAN. The scandium(III) complexes formed with PAN and TAN have the molar absorptivities of 1.90×104 and 2.93×104 dm3 mol−1 cm−1 at their absorption maxima, respectively. The effect of diverse ions on the determination of scandium with these reagents is also investigated.

Thorium(IV) and uranium(VI) complexes with some heterocyclic azo dyes in absolute ethanol

Thorium(IV) and uranium(VI) chelate complexes with PAN, PAR, TAN and TAR have been studied in absolute ethanol. The uranyl ion forms complexes with PAN, PAR, TAN and TAR in the metal to ligand molar ratio of 1:1. Thorium(IV) forms complexes with PAR, TAR and TAN in the molar ratio of 1:2. In case of Th(IV)-PAN complexes the molar ratio is 1:2.4. The stability constants for all the above complexes have been worked out using the mole ratio method. The kinetics of aquation of Th(IV)-PAN complexes indicate that PAN acts as a tridentate ligand.

Determination of trace cobalt in high-purity nickel

Cobalt in trace amounts in nickel was determined photometrically. The metals were initially converted to the EDTA complexes. Cobalt was then displaced from its EDTA complex by bismuth and extracted into chloroform as the cobalt(III)-PAN complex. The nickel was masked kinetically as the EDTA complex. In the extract, small amounts of the PAN complexes of nickel and bismuth were destroyed by an acid treatment and cobalt was determined photometrically. The method is highly accurate, reliable, and applicable to parts per million of cobalt in nickel or, with a concentration step included, to parts per 10 million. No interferences were encountered from foreign ions at the levels expected in high-purity nickel. Several characteristics of the analytical system have been exploited to attain the selectivity and sensitivity: the high stability, robust nature, large absorptivity, and the wavelength of the absorbance miximum of the cobalt(III)-PAN complex, and the low reaction rate of the nickel-EDTA complex at room temperature.

Spectrophotometric determination of traces of gallium and indium with 1-(2-pyridylazo)-2-naphthol

1-(2-Pyridylazo)-2-naphthol (PAN) reacts with either gallium or indium at pH 5–6 giving a red complex in an aqueous medium in the presence of N.N-dimethyl-formamide. The maximum absorption of both PAN complexes of gallium and indium in an aqueous solution is at 545 mμ. The gallium-PAN complex shows a characteristic enhancement of color by addition of small amounts of ethers. Based on this selective enhancement reaction, gallium can be determined in the presence of other metals without separation. The results of determining gallium and indium in the presence of each other are reported. Both gallium and indium form M 2(PAN) 3; but in the presence of certain organic solvents, a different gallium complex, Ga(PAN) 5, and the same indium complex, In 2(PAN) 3, are formed. The reaction of PAN with cadmium can be masked by iodide; an example of determining indium in the presence of cadmium is given. The PAN method has a sensitivity of 0.003 μg/cm 2 for gallium and 0.005μg/cm 2 for indium and an absorptivity of 24,900 for the Ga-PAN complex and of 24,500 for the In-PAN complex, respectively. The methods have been successfully applied to the determination of both gallium and indium in germanium thin films.