Speciation analysis of mercury contaminants in water samples by RP-HPLC after solid phase extraction on modified C18 extraction disks with 1,3-bis(2-cyanobenzene)triazene

A highly sensitive and accurate method for preconcentration and determination of ultra trace amounts of inorganic mercury and organomercury compounds in different water samples is proposed. The preconcentration is achieved using octadecyl silica (C₁₈) extraction disks modified with 1,3-bis(2-cyanobenzene)triazene (CBT). The retained analytes as their triazenide complexes on the solid phase was eluted with 10 ml acetonitrile and measured by reversed-phase high-performance liquid chromatography (RP-HPLC). Type and amount of eluent, pH, amount of CBT, flow rates of sample solution and eluent have been optimized in order to obtain quantitative recovery of the analytes. The effect of interfering ions, such as Cu²⁺, Mn²⁺, Fe²⁺, Al³⁺, Zn²⁺, Cd²⁺, Ca²⁺, Mg²⁺, Ba²⁺, Pb²⁺, K⁺ and Na⁺ usually present in water samples on the recovery of the analytes has also been investigated. The enrichment factor of 100 was obtained for all mercury species and the analytical detection limits of phenylmercury, methylmercury and Hg²⁺ were found as 0.8, 1.0 and 1.3 ng l^− 1, respectively. Stability of mercury species after extraction on the modified disks was studied and the results showed that complexes collected on the disks were stable for at least 5 days. The proposed method has been applied to the quantitative determination of mercury species in natural and synthetic water samples with recoveries more than 90%.     

Magnetically separable and recyclable g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanocomposite catalyzed one-pot synthesis of substituted imidazoles

A green, reliable synthetic method and highly efficient one-pot three-component synthesis of 2,4,5-trisubstituted imidazoles from 1,2-diketones, aldehydes and ammonium acetate in the presence of recyclable magnetic graphitic carbon nitride nanocomposite (Fe₃O₄@g-C₃N₄) has been developed. Various imidazole derivatives were obtained in moderate to excellent yields and high purity after recrystallization from ethanol. Interestingly, the low-cost Fe₃O₄@g-C₃N₄ a nontoxic and inexpensive catalyst showed excellent recyclability using an external magnet without loss of parent catalytic activity even after ten cycles and its provides new opportunities for the truly environmental friendliness methodology.     

Magnetic g-C3N4 nanocomposite-catalyzed environmentally benign aminolysis of epoxide

Research on Chemical Intermediates - A magnetic graphitic carbon nitride (g-C3N4) nanocomposite was prepared and used as a novel magnetically retrievable nanocatalyst for efficient ring opening of...     

Selecting the best periodic inventory control and demand forecasting methods for low demand items

The (s,S) form of the periodic review inventory control system has been claimed theoretically to be the best for the management of items of low and intermittent demand. Various heuristic procedures have been put forward, usually justified on the basis of generated data with known properties. Some stock controllers also have other simple rules which they employ and which are rarely seen in the literature. Determining how to forecast future demands is also a major problem in the area. The research described in this paper compares various periodic inventory policies as well as some forecasting methods and attempts to determine which are best for low and intermittent demand items. It evaluates the alternative methods on some long series of daily demands for low demand items for a typical spare parts depot.     

Generalized second derivative linear multistep methods for ordinary differential equations

Numerical Algorithms - This paper is devoted to investigate the modified extended second derivative backward differentiation formulae from second derivative general linear methods point of view....     

Nuclephilic ring opening of epoxides promoted by multi-site phase-transfer catalyst:An efficient and eco-friendly route to synthesis of b-hydroxy-thiocyanate

A highly effective and mild protocol for ring opening of epoxides with NH ₄ SCN in the presence of catalytic amount of a multisite phase-transfer catalyst, α,α',α" -N-hexakis(triethylammoniummethylene chloride)-melamine, is developed. A variety of b-hydroxy thiocyanates as important intermediates in agricultural and pharmaceutical chemistry were obtained in high yields with excellent regioselectivity and in short reaction times.     

Numerical simulation of biological base pairs considering geometric and energetic criteria

The aim of this work is the numerical simulation of the formation of hydrogen-bonded base pairs between adenine, thymine, guanine and cytosine. We use a Monte Carlo diffusion simulation with geometric (molecular distances and orientation) and energetic (acceptance proportional to the Boltzmann factor) criteria. Our results show that the occurrence of the different types of base pairs is strongly influenced by base geometry. Such results can help to understand some mechanisms, which occur at processes related to mutation.     

Synthesis,structural characterization and antibacterial activity of diorganotin(Ⅳ) complexes with ONO tridentate Schiff bases containing pyridine ring

Five organotin（IV） complexes,were obtained by reaction of SnR₂Cl₂（R = Ph,Me,Bu） with ONO donor Schiff bases.The synthesized complexes have been investigated by elemental analysis and IR,¹H NMR,and ¹¹⁹Sn NMR spectroscopy.These data show that the Schiff base acts as a tridentate dianionic ligand and coordinates via the imine nitrogen and two oxygen atoms.The Xray crystallography of complex 4 shows a dimeric structure for this molecule.The in vitro antibacterial activities of the Schiff bases and their complexes have been evaluated against Gram-positive（Bacillus subtilis and Staphylococcus aureus） and Gram-negative （Escherichia coli and Pseudomonas aeruginosa） bacteria and compared with the standard antibacterial drugs.     

Methyl jasmonate influence on silymarin production and plant stress responses in Silybum marianum hairy root cultures in a bioreactor

In this article our aim was to evaluate mass cultivation of S. marianum hairy roots in a bioreactor to produce silymarin. The effects of methyl jasmonate (MJ) elicitation on the accumulation of silymarin and the extent of the MJ-induced oxidative damage were investigated in bioreactor hairy root cultures of S. marianum. The growth rate of the bioreactor hairy root cultures was higher than that of those in a shake flask after 3 weeks. Silymarin accumulation was increased from 0.13?mg?g?1 DW in non-treated hairy roots to 0.22?mg?g?1 DW in hairy roots 72?h after 100?μM?MJ treatment. Guaiacol peroxidase and ascorbate peroxidase were activated by MJ?72?h after treatment, being 3.2- and 1.3-fold higher, respectively, than that of the control. An increase in enzymatic activity suggests increased scavenging of reactive oxygen species, indicating the tolerance to MJ stress. These results suggest that MJ elicitation is beneficial for silymarin production using bioreactor hairy root cultures.