Accumulation of paralytic shellfish poison (PSP) and biotransformation of its components in oysters, Crassostrea gigas, fed with the toxic dinoflagellate Alexandrium tamarense

As a part of our studies on the mechanism of uptake of paralytic shellfish poison (PSP) and the kinetics of its accumulation in bivalves, oysters Crassostrea gigas were experimentally contaminated with PSP by being fed with the toxic dinoflagellate Alexandrium tamarense for 2, 4, 6, 8 and 10 days. Temporal variations in the PSP contents and their profiles in oysters during the feeding experiment were monitored by high-performance liquid chromatography (HPLC) and the toxin profile of the oysters was compared with that of A. tamarense. Toxins excreted from the infested oysters into the seawater for 2 and 10 days were recovered and analyzed by HPLC. PSP toxicity rapidly appeared in the tissues of oysters and their toxicity levels reached 0.6 (0.3), 2.2 (1.1), 1.0 (0.5), 3.4 (1.6) and 1.1 (0.5) MU/g (nmol/g) shucked meat at 2, 4, 6, 8 and 10 days, respectively. The accumulation rates of toxin, calculated from the total amount (nmol) of toxins expressed by the total cell number fed during the exposure period and the toxicity of the oysters, were 14.1, 18.7, 5.1, 14.9 and 3.2% for 2, 4, 6, 8 and 10 days. During feeding experiments, the toxin profile of oysters changed substantially, showing marked differences from the proportions found in the toxigenic dinoflagellate used as food. The toxin components in this strain existed almost exclusively as beta-epimers, which accounted for 66.3 mol% of the total. This contrasts with the case of the oysters, where the beta-epimers represented 24.8, 29.8, 25.1, 27.3 and 25.2 mol% of the total at 2, 4, 6, 8 and 10 days, respectively. The amount of gonyautoxin-1 (GTX1) accumulated in oysters increased linearly and slowly for 8 days and the maximum content of GTX1 reached 51.3 mol%. The composition of GTX group compounds recovered from the seawater in which the oysters had been reared was a little different from that within the oyster tissues.     

Development of an energy-binned photon-counting detector for X-ray and gamma-ray imaging

The aim of this study is to develop an energy-binned photon-counting (EBPC) detector that enables us to provide energy information of x-rays with a reasonable count statistics. We used Al-pixel/CdTe/Pt semiconductor detectors, which had an active area of 8 mm×144 mm and consisted of 18 modules aligned linearly. The size of a CdTe detector module was 8 mm×8 mm and the thickness of the CdTe crystal was 1 mm. Each module consisted of 40×40 pixels and the pixel size was 200 μm×200 μm. We applied the bias voltage of −500 V to the Pt common electrode. The detector counted the number of x-ray photons with four different energy windows, and output four energy-binned images with pixel depths of 12, 12, 11 and 10 bits at a frame rate of 1200 Hz (300 Hz×4 energy bins). The basic performance of the detector was evaluated in several experiments. The results showed that the detector realized the photon counting rate of 0.4×10⁶ counts/sec/pixel (10⁷ counts/sec/mm²), energy resolution 4.4% FWHM at 122 keV. The integral uniformity of the detector was about 1% and the differential uniformity was about 1%. In addition, the image quality was examined with a resolution chart and step-wedge phantoms made of aluminum and polymethyl methacrylate. And we compared the quality of an acquired image with that acquired with an energy integration detector. The results of these experiments showed that the developed detector had desirable intrinsic characteristics for x-ray photon counting imaging.     

Processing of Al/SiC composites in continuous solid–liquid co-existent state by SPS and their thermal properties

Silicon carbide (SiC)-particle-dispersed-aluminum (Al) matrix composites were fabricated in a unique fabrication method, where the powder mixture of SiC, pure Al and Al–5mass% Si alloy was uniquely designed to form continuous solid–liquid co-existent state during spark plasma sintering (SPS) process. Composites fabricated in such a way can be well consolidated by heating during SPS processing in a temperature range between 798 K and 876 K for a heating duration of 1.56 ks. Microstructures of the composites thus fabricated were examined by scanning electron microscopy and no reaction was detected at the interface between the SiC particle and the Al matrix. The relative packing density of the Al–matrix composite containing SiC was higher than 99% in a volume fraction range of SiC between 40% and 55%. Thermal conductivity of the composite increased with increasing the SiC content in the composite at a SiC fraction range between 40 vol.% and 50 vol.%. The highest thermal conductivity was obtained for Al–50 vol.% SiC composite and reached 252 W/mK. The coefficient of thermal expansion of the composites falls in the upper line of Kerner’s model, indicating strong bonding between the SiC particle and the Al matrix in the composite.     

Evaluation of hydrogen absorption behaviour during acid etching for surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys

The hydrogen absorption behaviour during acid etching for the surface modification of commercial pure Ti, Ti-6Al-4V and Ni-Ti superelastic alloys has been investigated on the basis of the surface morphology, electrochemical behaviour and hydrogen thermal desorption analysis. To simulate the conventional acid etching for the improvement of the biocompatibility of Ti alloys, the specimens are immersed in 1 M HCl, 1 M H₂SO₄ or 0.5 M HCl + 0.5 M H₂SO₄ aqueous solution at 60 °C. Upon immersion, commercial pure Ti absorbs substantial amounts of hydrogen irrespective of the type of solution. In H₂SO₄ or HCl + H₂SO₄ solutions, the hydrogen absorption occurs for a short time (10 min). For Ti-6Al-4V alloy, no hydrogen absorption is observed in HCl solution, whereas hydrogen absorption occurs in other solutions. For Ni-Ti superelastic alloy, the amount of absorbed hydrogen is large, resulting in the pronounced degradation of the mechanical properties of the alloy even for an immersion time of 10 min, irrespective of the type of solution. The hydrogen absorption behaviour is not necessarily consistent with the morphologies of the surface subjected to corrosion and the shift of the corrosion potential. The hydrogen thermal desorption behaviour of commercial pure Ti and Ni-Ti superelastic alloy are sensitively changed by acid etching conditions. The present results suggest that the evaluation of hydrogen absorption is needed for each condition of acid etching, and that the conventional acid etching often leads to hydrogen embrittlement.     

Tiliroside, a glycosidic flavonoid, inhibits carbohydrate digestion and glucose absorption in the gastrointestinal tract

Scope Recent studies have reported that tiliroside, a glycosidic flavonoid, possesses anti‐diabetic activities. In the present study, we investigated the effects of tiliroside on carbohydrate digestion and absorption in the gastrointestinal tract. Methods and results This study showed that tiliroside inhibits pancreatic α‐amylase (IC₅₀ = 0.28 mM) in vitro. Tiliroside was found as a noncompetitive inhibitor of α‐amylase with K_i values of 84.2 μM. In male ICR mice, the increase in postprandial plasma glucose levels was significantly suppressed in the tiliroside‐administered group. Tiliroside treatment also suppressed hyperinsulinemia after starch administration. Tiliroside administration inhibited the increase of plasma glucose levels in an oral glucose tolerance test, but not in an intraperitoneal glucose tolerance test. In human intestinal Caco‐2 cells, the addition of tiliroside caused a significant dose‐dependent inhibition of glucose uptake. The inhibitory effects of both sodium‐dependent glucose transporter 1 (SGLT1) and glucose transporter 2 (GLUT2) inhibitors (phlorizin and phloretin, respectively) on glucose uptake were significantly inhibited in the presence of tiliroside, suggesting that tiliroside inhibited glucose uptake mediated by both SGLT1 and GLUT2. Conclusion These findings indicate that the anti‐diabetic effects of tiliroside are at least partially mediated through inhibitory effects on carbohydrate digestion and glucose uptake in the gastrointestinal tract.     

A bona fide two-dimensional percolation model: an insight into the optimum photoactivator concentration in La2/3-xEuxTa2O7 nanosheets

La–Eu solid solution nanosheets La_2/3−xEu_xTa₂O₇ have been synthesized, and their photoluminescence properties have been investigated. La_2/3−xEu_xTa₂O₇ nanosheets were prepared from layered perovskite compounds Li₂La_2/3−xEu_xTa₂O₇ as the precursors by soft chemical exfoliation reactions. Both the precursors and the exfoliated nanosheets exhibit a decrease in intralayer lattice parameters as the Eu contents increase. However, there is a discontinuity in this trend between the nominal Eu content ranges x≤ 0.3 and x ≥ 0.4. This discontinuity is attributed to the difference in degree of TaO₆ octahedra tilting for the La- and Eu-rich phases. La_2/3−xEu_xTa₂O₇ nanosheets exhibit red emission, characteristic of the f–f transitions in Eu³⁺ photoactivators. The photoluminescence emission can be obtained from both host and direct photoactivator excitation. However, photoluminescence emission through host excitation is much more dominant than that through direct photoactivator excitation, and this behavior is consistent with that of all the other rare-earth photoactivated nanosheets reported previously. The absolute photoluminescence quantum efficiency of the La_2/3−xEu_xTa₂O₇ nanosheets increases as the experimentally determined Eu contents increase up to x=0.45 and decrease above it. This result is in good agreement with the optimum photoactivator concentration expected from the percolation theory. These solid solution La_2/3−xEu_xTa₂O₇ nanosheets are excellent models for validating the theory of optimum photoactivator concentration in the truly two-dimensional photoactivator matrix.     

Detection of tris(2,4-di-tert-butylphenyl)phosphite (Irgafos 168, antioxidant in plastics) and its oxide in commercial frozen vegetables

Two peaks, A and B, detected in chromatograms of commercial frozen vegetable extracts during analysis of organophosphorus pesticide residues by GC-FPD, were identified as tris(2,4-ditert-butylphenyl)phosphite (Irgafos 168) and Irgafos 168 oxide, respectively, from their mass spectra. Irgafos 168 is used as an antioxidant in plastics, and there has been no report of its detection in foods. We analyzed Irgafos 168 and its oxide in 38 samples of commercial frozen vegetables, and they were detected from 4 samples (0.02-0.80 microgram/g as total amount of Irgafos 168 and its oxide).     

Selection of soldering temperature for ultrasonic-assisted soldering of 5056 aluminum alloy using Zn-Al system solders

The conditions for sound butt-joints of 5056 aluminum alloy containing 4.6 mass% Mg using Zn-xAl (x = 5, 13, and 38 mass%) solder at the relevant temperatures were investigated. Each solder foil was inserted between faying surfaces of 5056 aluminum rods. Ultrasonic vibration at a frequency of 19 kHz was applied to the faying surfaces through an aluminum substrate at soldering temperatures for 4 s in air. The strength of obtained solder joints was measured by tensile tests. The microstructure in the solder layer after the soldering process was evaluated with an SEM-EDX. The results of tensile tests revealed that joints soldered under the liquidus temperature of Zn-Al solders showed higher strength than joints soldered over the liquidus temperature. In the joints soldered over the solder liquidus temperature, the joint strength decreased with an increase in soldering temperature. It was caused by the formation of MgZn₂ in the solder layer due to dissolution of 5056-Al into the solder liquid during the soldering process. On the other hand, ultrasonic-assisted soldering under the solder liquidus temperature suppressed dissolution of 5056-Al and improved the joint strength by reducing the formation of MgZn₂.     

NOTE: SOLVENT EXTRACTION OF PLATINUM(IV) BY TRIOCTYLPHOSPHINE OXIDE

The equilibrium distribution of platinum(IV) between hydrochloric acid and trioctylphosphine oxide (T0P0) in toluene at 303 K was examined. From the concentration dependencies of the distribution ratio, it was determined that platinum(IV) is extracted as follows:

The extraction.equilibrium constant was found to be Ke = 3.6×10³.     

SOLVENT EXTRACTION EQUILIBRIA OF GALLIUM (III) WITH ACIDIC ORGANOPHOSPHORUS COMPOUNDS FROM AQUEOUS NITRATE MEDIA

A comparative investigation on the solvent extraction equilibria of gallium(III) from aqueous nitrate media was conducted with three kinds of acidic organophosphorus compounds, di (2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl 2-ethyl-hexylphosphonic acid (EHEHPA) and di (2,4,4'-trimethylpentyl) phosphinic acid (DTMPPA), in toluene at 303 K. It was found that gallium(III) is extracted as 1:4 metal:reagent complexes with D2EHPA and EHEHPA and as a 1:3 complex with DTMPPA in the region of low loading ratio while it is extracted as 1:3 complexes with all reagents at high loading ratio. The extraction equilibrium constants with these extractants were evaluated for the former complexes as follows: K_e = 2.3xl0^-2, 8.5xl0^-3 and 1.3xl0^-4 for D2EHPA, EHEHPA and DTMPPA respectively.