Identification of bubble evolution mechanisms during AC electrograining

Bubble evolution during AC-graining is analysed in combination with the variation of the anodic peaks of the potential and the electrode surface morphology. Aluminium samples are grained in hydrochloric acid in an Inverted Rotating Disk Electrode. A roughness tester is used to characterise the electrode surface, while shadow imaging is applied to determine the bubble size distribution. An interpretation of the correlation existing among bubble size, potential peaks evolution, surface properties and smut layer formation is proposed, which provides insights into the mechanisms involved in bubble formation.     

Anion-exchange high performance liquid chromatography hyphenated to inductively coupled plasma-isotope dilution-time-of-flight mass spectrometry for speciation analysis of metal complexes with metallothionein isoforms in gibel carp (Carassius auratus gibelio) exposed to environmental metal pollution

The capability of post-column isotope dilution (ID) combined with anion-exchange HPLC-ICP-time-of-flight (TOF)-MS was for the first time investigated for environmental quality assessment through metal speciation analysis of metallothionein (MT) isoforms in cytosols of gibel carp (Carassius auratus gibelio), used as biomarkers for environmental metal exposure. A full spectral scanning of the biological sample (with 50 microl injection volume) using ICP-TOF-MS in transient mode allowed fast multi-isotope screening of cytosolic metal-containing fractions and to investigate the presence of matrix-induced interferences. The MT cytosolic fraction of liver and kidney of the carp, sampled at three different sampling sites in Belgium, was partially purified using size-exclusion (SE) HPLC. Quantification of the elements Cd (toxic) and Zn and Cu (essential) associated with MT isoforms in this fraction was addressed using an hybrid approach based on post-column addition of the enriched isotopes 65Cu, 67Zn, 106Cd and monitoring on-line the isotope ratios 63Cu/65Cu, 64Zn/67Zn and 114Cd/106Cd by ICP-MS with a time of flight instrument, which was coupled to anion-exchange HPLC. With this separation method, baseline separation of up to five MT isoforms, which is required for quantitative metal speciation by HPLC-ICP-IDMS, was achieved within a run of 15 min. The MT fraction of the cytosols was also analysed for the total metal content using IDMS with size-exclusion HPLC-ICP-MS and species-unspecific calibration. Results showed significant differences between speciation results and total MT concentrations of control fish and fish from the most contaminated sampling sites, revealing the potential of gibel carp MT for sequestering excess intracellular free-ions (essential and toxic elements) and for its protection against metal toxicity. Preferences for metal sequestration of metal complexes with MT isoforms were also found to be tissue-specific: excess of Cd was found preferably bound to a major MT isoform (tR = 8.0 min) in kidney, whereas excess intracellular Zn appeared to be mostly sequestered by four MT isoforms (tR=7.3, 8.0, 12.2 and 14.4 min) in liver, the MT form with tR = 8.0 min being the main Zn scavenger form. Such kind of quantitative speciation information on the preferences of MT isoforms in different fish organs for sequestering heavy metals, reported here for the first time, is important to elucidate the role of isoform-specific induction of vertebrate fish MT in metal detoxification and the use of MT as biomarker.     

Synthesis and optical and electrochemical properties of core-fluorinated perylene bisimides

[reaction: see text] A series of bay position difluoro- or tetrafluoro-substituted perylene bisimides have been synthesized by nucleophilic halogen exchange reaction of the corresponding dibromo- and tetrachloro-substituted perylene bisimides, respectively, with potassium fluoride. Compared to the parent unsubstituted perylene bisimides, these compounds display hypsochromically shifted absorption and fluorescence spectra with fluorescence quantum yields up to unity enabling bright yellow emission. Their electrochemical properties and crystal structures of two perylene bisimides are also reported.     

Rapid determination and confirmation of biogenic amines in tuna loin by gas chromatography/mass spectrometry using ethylchloroformate derivative

A gas chromatography-mass spectrometry (GC/MS) method is described for the easy rapid determination and simultaneous confirmation of the biogenic amines putrescine (PUT), cadaverine (CAD), histamine (HTA), and spermidine (SPD) in fresh frozen tuna loin. The method can also be used to monitor tyramine (TYR). The method involves homogenization of fish tissue, extraction of biogenic amines into trichloroacetic acid solution, centrifugation, alkalization, and derivatization of supernatant with ethylchloroformate. All seafood species were fortified to contain 2.5, 5.0, 10.0, 12.5, and 25.0 microg/g (ppm) PUT, CAD, and SPD; and 10.0, 20.0, 40.0, 50.0, and 100.0 microg/g (ppm) HTA. Determination was based on standard curves for each analyte using peak areas with matrix standards equivalent to a concentration range bracketing the spike level. A set of 5 matrix controls (unfortified tuna tissue) was also analyzed; only endogenous SPD was found in all samples. The interassay average recoveries ranged from 57 to 79% across analytes and spike levels.     

Certification of a new selenized yeast reference material (SELM-1) for methionine, selenomethinone and total selenium content and its use in an intercomparison exercise for quantifying these analytes

A new selenized yeast reference material (SELM-1) produced by the Institute for National Measurement Standards, National Research Council of Canada (INMS, NRC) certified for total selenium (2,059±64 mg kg⁻¹), methionine (Met, 5,758±277 mg kg⁻¹) and selenomethionine (SeMet, 3,431±157 mg kg⁻¹) content is described. The ±value represents an expanded uncertainty with a coverage factor of 2. SeMet and Met amount contents were established following a methanesulfonic acid digestion of the yeast using GC-MS and LC-MS quantitation. Isotope dilution (ID) calibration was used for both compounds, using ¹³C-labelled SeMet and Met. Total Se was determined after complete microwave acid digestion based on ID ICP-MS using a ⁸²Se spike or ICP-OES spectrometry using external calibration. An international intercomparison exercise was piloted by NRC to assess the state-of-the-art of measurement of selenomethione in SELM-1. Determination of total Se and methionine was also attempted. Seven laboratories submitted results (2 National Metrology Institutes (NMIs) and 5 university/government laboratories). For SeMet, ten independent mean values were generated. Various acid digestion and enzymatic procedures followed by LC ICP-MS, LC AFS or GC-MS quantitation were used. Four values were based on species-specific ID calibration, one on non-species-specific ID with the remainder using standard addition (SA) or external calibration (EC). For total selenium, laboratories employed various acid digestion procedures followed by ICP-MS, AFS or GC-MS quantitation. Four laboratories employed ID calibration, the remaining used SA or EC. A total of seven independent results were submitted. Results for methionine were reported by only three laboratories, all of which used various acid digestion protocols combined with determination by GC-MS and LC UV. The majority of participants submitted values within the certified range for SeMet and total Se, whereas the intercomparison was judged unsuccessful for Met because only two external laboratories provided values, both of which were outside the certified range.     

Mitochondrial Responses of Normal and Injured Human Skin Fibroblasts Following Low Level Laser Irradiation—An In Vitro Study

Laser irradiation has proved to be very efficient in speeding and improving the quality of healing in pathological conditions of diverse etiologies. However, the mechanisms by which the beneficial effects are attained are not clear. Mitochondria are the primary phototargets during irradiation. The study aimed to establish if laser irradiation had an effect on hypoxic and acidotic cells. The study also aimed to use existing information regarding the possible mechanism of action (established in wounded cells) and apply these principles to acidic and hypoxic irradiated cells to determine whether laser has a stimulatory or inhibitory effect. Cell cultures were modified to simulate conditions of hypoxia (hypoxic gas mixture 95% N₂ and 5% O₂) and acidosis (pH 6.7) whereas the central scratch model was used to simulate a wound. Cells were irradiated with a helium–neon (632.8 nm, 3 mW cm^?2) laser using 5 or 16 J cm^?2 on days 1 and 4. Mitochondrial responses were measured 1 or 24 h after laser irradiation by assessing changes in mitochondrial membrane potential (MMP), cyclic AMP, intracellular Ca²⁺ and adenosine triphosphate (ATP) cell viability. Hypoxia and acidosis significantly reduced MMP when compared with normal nonirradiated control cells. Wounded, hypoxic and acidotic cells irradiated with 5 J cm^?2 showed an increase in mitochondrial responses when compared with nonirradiated cells while 16 J cm^?2 showed a significant decrease. The study confirmed that laser irradiation with 5 J cm^?2 stimulated an increase in intracellular Ca²⁺ which resulted in an increase in MMP, ATP and cAMP, which ultimately results in photobiomodulation to restore homeostasis of injured cells.     

The first total synthesis of heteromine B, and an improved synthesis of heteromine A; natural products with antitumor activities

Efficient total syntheses of heteromines A and B (antitumor compounds previously isolated from the plant Heterostemma brownii Hayata) from commercially available 2-amino-6-chloropurine have been developed. The synthesis of heteromine A is considerably shorter than the previously reported synthesis, only requiring four steps, whereas the iodide salt of heteromine B was prepared in five steps. Heteromines A and B showed no significant antibacterial activity and therefore appear to be selective toward cancer cell lines.     

A new fractal algorithm to model discrete sequences

Employing the properties of the affine mappings, a very novel fractal model scheme based on the iterative function system is proposed. We obtain the vertical scaling factors by a set of the middle points in each affine transform, solving the difficulty in determining the vertical scaling factors, one of the most difficult challenges faced by the fractal interpolation. The proposed method is carried out by interpolating the known attractor and the real discrete sequences from seismic data. The results show that a great accuracy in reconstruction of the known attractor and seismic profile is found, leading to a significant improvement over other fractal interpolation schemes.     

Influence of steric and electronic properties of the defect site, lanthanide ionic radii, and solution conditions on the composition of lanthanide(III) alpha1-P2W17O6110- polyoxometalates

This study identifies the principles that govern the formation and stability of Ln complexes of the (alpha(1)-P(2)W(17)O(61))(10-) isomer. The conditional stability constants for the stepwise formation equilibria, K(1cond) and K(2cond), determined by (31)P NMR spectroscopy, show that the high log K(1cond)/log K(2cond) ratio predicts the stabilization of the 1:1 Ln/ (alpha(1)-P(2)W(17)O(61))(10-) species. The value of log K(1cond) increases as the Ln series is traversed, consistent with the high charge/size requirement of the basic alpha(1) defect site. The conditional stability constants, K(2), are very low and are highly dependent on the countercations in the buffer. The source of the instability is understood from the crystal structures of the early-mid lanthanide analogues, where the close contact of the (alpha(1)-P(2)W(17)O(61))(10-) units result in severe steric encumbrance. The electronic properties of the alpha(1) defect along with the lanthanide ionic radii and countercation composition are important parameters that need to be considered for a rational synthesis of lanthanide polyoxometalates.