Screening of tetrodotoxin in puffers using gas chromatography-mass spectrometry

Tetrodotoxin (TTX), a toxic compound found in some puffers can cause death to humans through consumption. We have developed a simplified method for the screening of TTX in puffers using GC-MS. A puffer tissue of 0.5g was treated with 5mL of 0.1% acetic acid, followed by alkaline hydrolysis, LLE or liquid-liquid extraction and N-methyl-N-TMS-trifluoroacetamide derivatization. The developed method used only a small sample and solvent, simplified LLE and derivatization procedures and short chromatographic analysis (8.2min). All of these contribute to cost-saving, enhanced sample throughput and high sensitivity of the screening assay. The developed method was validated and proved to be within the acceptable range.     

Efficient singlet oxygen generation by luminescent 2-(2′-thienyl)pyridyl cyclometalated platinum(II) complexes and their calixarene derivatives

Luminescent cyclometalated platinum(II) complexes, namely [Pt(Thpy)(PPh₃)X]ⁿ⁺ (HThpy = 2-(2′-thienyl)pyridine; X = Cl⁻ ( 1 ), n = 0; X = CH₃CN ( 2 ), pyridine ( 3 ), n = 1) and [Pt(Thpy)(HThpy)Y] ^{n +} (Y = Cl⁻ ( 4 ), n = 0; Y = pyridine ( 5 ), n = 1), exhibit structured emission with peak maximum at ∼556 and 598 nm in degassed acetonitrile and with emission quantum yield and lifetime of up to 0.38 and 26 μs, respectively. These complexes are efficient photosensitizers of singlet oxygen with yields up to >90%. Complex 5 exhibited photocytotoxicity towards cancer cells and fluorescence microscopic images of cells incubated with 5 reveal substantial uptake at the nucleus and mitochondria.     

Anthraquinones with antiplasmodial activity from the roots of Rennellia elliptica Korth. (Rubiaceae)

Dichloromethane root extract of Rennellia elliptica Korth. showed strong inhibition of Plasmodium falciparum growth in vitro with an IC?? value of 4.04 μg/mL. A phytochemical study of the dichloromethane root extract has led to the isolation and characterization of a new anthraquinone, 1,2-dimethoxy-6-methyl-9,10-anthraquinone (1), and ten known anthraquinones: 1-hydroxy-2-methoxy-6-methyl-9,10-anthraquinone (2), nordamnacanthal (3), 2-formyl-3-hydroxy-9,10-anthraquinone (4), damnacanthal (5), lucidin-ω-methyl ether (6), 3-hydroxy-2-methyl-9,10-anthraquinone (7), rubiadin (8), 3-hydroxy-2-methoxy-6-methyl-9,10-anthraquinone (9), rubiadin-1-methyl ether (10) and 3-hydroxy-2-hydroxymethyl-9,10-anthraquinone (11). Structural elucidation of all compounds was accomplished by modern spectroscopic methods, notably 1D and 2D NMR, IR, UV and HREIMS. The new anthraquinone 1, 2-formyl-3-hydroxy-9,10-anthraquinone (4) and 3-hydroxy-2-methyl-9,10-anthraquinone (7) possess strong antiplasmodial activity, with IC?? values of 1.10, 0.63 and 0.34 μM, respectively.     

A characteristics-mixed covolume method for a convection-dominated transport problem

In this paper, we propose a characteristics-mixed covolume method for approximating the solution to a convection dominated transport problem. The method is a combination of characteristic approximation to handle the convection term in time and mixed covolume method spatial approximation to deal with the diffusion term. The velocity and press are approximated by the lowest order Raviart-Thomas mixed finite element space on rectangles. The projection of a mixed covolume element is introduced. We prove its first order optimal rate of convergence for the approximate velocities in the L² norm as well as for the approximate pressures in the L² norm.     

Multi-degree cyclic scheduling of a no-wait robotic cell with multiple robots

This paper addresses cyclic scheduling of a no-wait robotic cell with multiple robots. In contrast to many previous studies, we consider r-degree cyclic (r > 1) schedules, in which r identical parts with constant processing times enter and leave the cell in each cycle. We propose an algorithm to find the minimal number of robots for all feasible r-degree cycle times for a given r (r > 1). Consequently, the optimal r-degree cycle time for any given number of robots for this given r can be obtained with the algorithm. To develop the algorithm, we first show that if the entering times of r parts, relative to the start of a cycle, and the cycle time are fixed, minimizing the number of robots for the corresponding r-degree schedule can be transformed into an assignment problem. We then demonstrate that the cost matrix for the assignment problem changes only at some special values of the cycle time and the part entering times, and identify all special values for them. We solve our problem by enumerating all possible cost matrices for the assignment problem, which is subsequently accomplished by enumerating intervals for the cycle time and linear functions of the part entering times due to the identification of the special values. The algorithm developed is shown to be polynomial in the number of machines for a fixed r, but exponential if r is arbitrary.     

The first naturally occurring thiepinols and thienol from an endolichenic fungus Coniochaeta sp

Coniothiepinols A (1) and B (2) and coniothienol A (3), the first naturally occurring thiepinols (1 and 2) and thienol (3), have been isolated from the crude extract of an endolichenic fungus Coniochaeta sp. 1 possesses a unique 8-oxa-2-thia-bicyclo[3.2.1]octane skeleton, and its structure was assigned by NMR spectroscopy and X-ray crystallography. 1 showed significant activity against the gram-positive bacteria, Enterococcus faecium and Enterococcus faecalis.     

Oxidative Dissolution of Silver Nanoparticles by Biologically Relevant Oxidants: A Kinetic and Mechanistic Study

The oxidative dissolution of silver nanoparticles (AgNPs) plays an important role in the synthesis of well‐defined nanostructured materials, and may be responsible for their activities in biological systems. In this study, we use stopped‐flow spectrophotometry to investigate the kinetics and mechanism of the oxidative dissolution of AgNPs by H₂O₂ in quasi‐physiological conditions. Our results show that the reaction is first order with respect to both [Ag⁰] and [H₂O₂], and parallel pathways that involve the oxidation of H₂O₂ and HO₂^? are proposed. The order of the reaction is independent of the size of the AgNPs (≈5–20 nm). The rate of dissolution increases with increasing pH from 6.0 to 8.5. At 298 K and I=0.1 M , the value of k_b is five orders of magnitude higher than that of k_a (where k_a and k_b are the rate constants for the oxidative dissolution of AgNPs by H₂O₂ and HO₂^?, respectively). In addition, the effects of surface coating and the presence of halide ions on the dissolution rates are investigated. A possible mechanism for the oxidative dissolution of AgNPs by H₂O₂ is proposed. We further demonstrate that the toxicities of AgNPs in both bacteria and mammalian cells are enhanced in the presence of H₂O₂, thereby highlighting the biological relevance of investigating the oxidative dissolution of AgNPs.     

1‐Alkyl‐1H‐imidazole‐Based Dipolar Organic Compounds for Dye‐Sensitized Solar Cells

A series of donor–π–acceptor‐type organic dyes based on 1‐alkyl‐1H‐imidazole spacers 1 , 2 , 3 , 4 , 5 have been developed and characterized. The two electron donors are at positions 4 and 5 of the imidazole, while the electron‐accepting cyanoacrylic acid is incorporated at position 2 by a spacer‐containing heteroaromatic rings, such as thiophene and thiazole. Detailed investigation on the relationship between the structure, spectral and electrochemical properties, and performance of DSSC is described here. Dye‐sensitized solar cells (DSSCs) using dyes as the sensitizers exhibit good efficiencies, ranging from 3.06 to 6.35 %, which reached 42–87 % with respect to that of N719‐based device (7.33 %) fabricated and measured under similar conditions. Time‐dependent density functional theory (TDDFT) calculations have been performed on the dyes, and the results show that both electron donors can contribute to electron injection upon photo‐excitation, either directly or indirectly by internal conversion to the lowest excited state.     

Vertical inventories and fluxes of <Superscript>210</Superscript>Pb, <Superscript>228</Superscript>Ra and <Superscript>226</Superscript>Ra at southern South China Sea and Malacca Straits

Inventories and fluxes of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were determined in sediment cores collected at nine stations covering of the southern South China Sea and Malacca Straits with the thickness of water column between 42 and 83 m depth. The inventories of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were calculated range from 0.15–2.55 Bq cm⁻², 0.05–0.40 Bq cm⁻² and 6.83–83.63 Bq cm⁻², meanwhile the fluxes ranged from 0.005–0.079 Bq cm⁻² yr⁻¹, 0.009–0.048 Bq cm⁻² yr⁻¹ and 0.003–0.037 Bq cm⁻² yr⁻¹, respectively. The results show that the highest inventories and fluxes for ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were found at station WC 01 and EC 05. Because there are additional sources of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra, where water transport will brings more dissolved isotopes, influence of the transportation and deposition of suspended particles, fast rate of regeneration and greater production of those radionuclides and others.