Preliminary assessment of the performance of oyster shells and chitin materials as adsorbents in the removal of saxitoxin in aqueous solutions

ABSTRACT: BACKGROUND: This study evaluated the adsorption capacity of the natural materials chitin and oyster shell powder (OSP) in the removal of saxitoxin (STX) from water. Simplified reactors of adsorption were prepared containing 200 mg of adsorbents and known concentrations of STX in solutions with pH 5.0 or 7.0, and these solutions were incubated at 25 [DEGREE SIGN]C with an orbital shaker at 200 RPM. The adsorption isotherms were evaluated within 48 hours, with the results indicating a decrease in STX concentrations in different solutions (2[EN DASH]16 mug/L). The kinetics of adsorption was evaluated at different contact times (0[EN DASH]4320 min) with a decrease in STX concentrations (initial concentration of 10 mug/L). The sampling fractions were filtered through a membrane (0.20 mum) and analyzed with high performance liquid chromatography to quantify the STX concentration remaining in solution. RESULTS: Chitin and OSP were found to be efficient adsorbents with a high capacity to remove STX from aqueous solutions within the concentration limits evaluated (> 50 % over 18 h). The rate of STX removal for both adsorbents decreased with contact time, which was likely due to the saturation of the adsorbing sites and suggested that the adsorption occurred through ion exchange mechanisms. Our results also indicated that the adsorption equilibrium was influenced by pH and was not favored under acidic conditions. CONCLUSIONS: The results of this study demonstrate the possibility of using these two materials in the treatment of drinking water contaminated with STX. The characteristics of chitin and OSP were consistent with the classical adsorption models of linear and Freundlich isotherms. Kinetic and thermodynamic evaluations revealed that the adsorption process was spontaneous (DeltaGads < 0) and favorable and followed pseudo-second-order kinetics.     

The weakly coordinating perchlorate group in bis(N,N′‐dimethylethylenediamine‐κ2N,N′)bis(perchlorato‐κO)copper(II) studied at 100, 250 and 400 K

The crystal structure of the title compound, [Cu(ClO₄)₂(C₄H₁₂N₂)₂], (I), is reported at 100, 250 and 400 K. The Cu^II cation in this complex is coordinated in a distorted octahedral mode characteristic of Jahn–Teller systems. The coordination of the perchlorate ligands via longer, and presumably weaker, axial Cu—O distances varies significantly as a function of temperature. One of the Cu—O distances increases between 100 and 250 K, and one of the Cu—O—Cl angles expands between 250 and 400 K. At all temperatures, the complex forms a two‐dimensional N—H...O hydrogen‐bond network in the (001) plane.     

Growth mechanisms and defect structures of B12As2 epilayers grown on 4 H-SiC substrates

Epitaxial growth of icosahedral B₁₂As₂ on c-plane 4 H-SiC substrates has been analyzed. On on-axis c-plane 4 H-SiC substrates, Synchrotron white beam x-ray topography (SWBXT) revealed the presence of a homogenous solid solution of twin and matrix B₁₂As₂ epilayer domains. High resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) both revealed the presence of an ～20 nm thick, disordered transition layer at the interface. (0003) twin boundaries are shown to possess fault vectors such as 1/3[1–100]_B12As2, which originate from the mutual shift between the nucleation sites. On the contrary, B₁₂As₂ epilayers grown on c-plane 4 H-SiC substrates intentionally misoriented from (0001) towards [1–100] is shown to be free of rotational twinning. SWBXT, HRTEM and STEM all confirmed the single crystalline nature and much higher quality of the films. In addition, no intermediate layer between the epilayer and the substrate was observed. It is proposed that the vicinal steps formed by hydrogen etching on the off-axis 4 H-SiC substrate surface before deposition cause the film to adopt a single orientation during nucleation process. This work also demonstrates that c-plane 4 H-SiC with offcut toward [1–100] is potentially a good substrate choice for the growth of high-quality, single crystalline B₁₂As₂ epilayers for future device applications.     

The local power of the gradient test

The asymptotic expansion of the distribution of the gradient test statistic is derived for a composite hypothesis under a sequence of Pitman alternative hypotheses converging to the null hypothesis at rate n ^−1/2, n being the sample size. Comparisons of the local powers of the gradient, likelihood ratio, Wald and score tests reveal no uniform superiority property. The power performance of all four criteria in one-parameter exponential family is examined.     

A role for the membrane protein M6 in the Drosophila visual system

Background

Members of the proteolipid protein family, including the four-transmembrane glycoprotein M6a, are involved in neuronal plasticity in mammals. Results from our group previously demonstrated that M6, the only proteolipid protein expressed in Drosophila, localizes to the cell membrane in follicle cells. M6 loss triggers female sterility, which suggests a role for M6 in follicular cell remodeling. These results were the basis of the present study, which focused on the function and requirements of M6 in the fly nervous system.

Results

The present study identified two novel, tissue-regulated M6 isoforms with variable N- and C- termini, and showed that M6 is the functional fly ortholog of Gpm6a. In the adult brain, the protein was localized to several neuropils, such as the optic lobe, the central complex, and the mushroom bodies. Interestingly, although reduced M6 levels triggered a mild rough-eye phenotype, hypomorphic M6 mutants exhibited a defective response to light.

Conclusions

Based on its ability to induce filopodium formation we propose that M6 is key in cell remodeling processes underlying visual system function. These results bring further insight into the role of M6/M6a in biological processes involving neuronal plasticity and behavior in flies and mammals.     

Effect of catalyst preparation on the yield of carbon nanotube growth

Multi-wall carbon nanotubes (MWCNTs) were synthesized by catalytic chemical vapor deposition (CVD) on catalytic iron nanoparticles dispersed in a silica matrix, prepared by sol gel method. In this contribution, variation of gelation condition on catalyst structure and its influence on the yield of carbon nanotubes growth was studied. The precursor utilized were tetraethyl-orthosilicate and iron nitrate. The sols were dried at two different temperatures in air (25 or 80 °C) and then treated at 450 °C for 10 h. The xerogels were introduced into the chamber and reduced in a hydrogen/nitrogen (10%v/v) atmosphere at 600 °C. MWCNTs were formed by deposition of carbon atoms from decomposition of acetylene at 700 °C. The system gelled at RT shows a yield of 100% respect to initial catalyst mass whereas the yield of that gelled at 80 °C was lower than 10%. Different crystalline phases are observed for both catalysts in each step of the process. Moreover, TPR analysis shows that iron oxide can be efficiently reduced to metallic iron only in the system gelled at room temperature. Carbon nanotubes display a diameter of about 25–40 nm and several micron lengths. The growth mechanism of MWCNTs is base growth mode for both catalysts.     

Dynamical behavior of the phase transition of strained from atomistic simulations

Using an atomistic shell model we study the temperature dependence of the ferroelectric properties of BaTiO₃ under biaxial compressive strain applicable to growth on perovskites substrate. Molecular dynamics simulations show a “r→c→p” sequence of phase transitions when temperature is increased, and the absence of an “ac phase”. The first-order paraelectric-to-ferroelectric phase transition presents in bulk changes to a second-order one as a consequence of the in-plane constraint imposed by the mechanical boundary conditions. From the tetragonal ferroelectric c phase, the transition takes place in a finite range of temperature where the lattice parameter normal to the plane keeps approximately constant until T_c is reached. Analysis of the local polarization behavior reveals an order–disorder dynamics as the dominant mechanism of the transition.     

Thallus structure and isidium development in two Parmeliaceae species (lichenized Ascomycota)

(Thallus structure and isidium development in two Parmeliaceae species (lichenized Ascomycota)). Conventional techniques for structural studies under light microscope and scanning electron microscope were employed to describe and compare the histology of thallus and isidia development in Parmotrema tinctorum and Parmelinopsis minarum. Although presenting layers typical of the heteromerous structure of Parmeliaceae lichens, the studied species have very distinct anatomical details including: the type of upper cortex, medulla thickness, hyphal orientation pattern and distinct strata in this layer, variations of crystal shape, color, location and degree of association with medullary hyphae, rhizines thickness and covering by a cortical layer. Isidium formation starts with cortical cell proliferation, which results in a small protuberance on the thallus surface, followed by the photobiont cell proliferation. Medullary hyphal intrusions occur only after the formation of this protuberance. In this stage medullary hyphae grow, ramifying or not inside the protuberance. In a posterior stage, the isidium base becomes constricted, which facilitates its detachment from the thallus.     

Syntheses of Enantiomerically Pure 2‐Substituted Pyrrolidin‐3‐ones via Lithiated Alkoxyallenes – An Auxiliary‐Based Synthesis of both Enantiomers of the Antibiotic Anisomycin

The hydrochlorides of both enantiomers of the antibiotic anisomycin were prepared starting with the ‘diacetone‐fructose’‐substituted allene 1 and the N‐Boc‐protected imine precursor 2a . Addition of an excess of lithiated 1 to 2a provided a 2 : 1 mixture 3a of diastereoisomers, which were cyclized to 4a under base promotion (Scheme 2). The two diastereoisomers of 4a were separated and converted into enantiomerically pure pyrrolidin‐3‐ones (2R)‐ 5a and (2S)‐ 5a . A similar sequence yielded the N‐Tos‐protected compounds (2R)‐ 5b and (2S)‐ 5b . Compounds 5a were converted into silyl enol ethers 6 and by subsequent regio‐ and stereoselective hydroboration into pyrrolidine derivatives 7 (Scheme 3). Straightforward functional‐group transformations led to the hydrochlorides 9 of anisomycin (Scheme 3). The (2R) series provided the hydrochloride (2R)‐ 9 of the natural occurring enantiomer, whereas the (2S) series furnished the antipode (2S)‐ 9 . The overall sequence to the natural product involved ten steps with eight purified intermediates and afforded an overall yield of 8%. Our stereochemically divergent approach to this type of hydroxylated pyrrolidines is highly flexible and should easily allow preparation of many analogues.     

Xanthone Receptors as Oxyanion‐Hole Mimics in Artificial Enzymes

Different xanthone‐based receptors ( 2 – 10 ) for lactones and lactams have been prepared, and the feasibility of these compounds to mimic the known enzymatic ‘oxyanion‐hole’ structure is discussed. The self‐association of the receptors was found to pose a serious drawback for complex formation. X‐Ray crystal structures of receptor dimers allowed us to understand the reasons for their self‐association and to improve the design of the catalysts. The catalytic activity of the receptors has been tested towards the nucleophilic addition of pyrrolidine to unsaturated lactones. Since the resulting complexes were very weak in organic solvents, new receptors were developed for lactams, which showed better stabilities, and their catalytic activities were studied.