Development of a size exclusion chromatography-electrochemical detection method for the analysis of total organic and inorganic chloramines

A size exclusion chromatography (SEC) followed by post-column reaction with iodide and electrochemical detection method is developed for analysis of total organic and inorganic chloramines. Ammonium chloride and a group of test compounds (Glycine, Tyrosine, DL-Alanyl-DL-Alanine, Arg-Gly-Asp-Ser, Bradykinin, Aprotinin, and alpha-Lactalbumin) are selected and chlorinated to represent inorganic chloramines and different sizes of organic N-chloramines. An analytical SEC column with pore size of 60A is used and chromatographic conditions including the working electrode potential and flow rate are optimized to gain optimum resolution and sensitivity. The detection limits are estimated to be 0.12 mg/L and 0.05 mg/L, respectively, for tested inorganic and organic chloramines.     

Determination of zearalenone with a glassy carbon electrode modified with nanocomposite consisting of palladium nanoparticles and a conductive polymeric ionic liquid

A glassy carbon electrode (GCE) modified with polymeric nanocomposite consisting of palladium nanoparticles and a conductive polymeric ionic liquid was prepared. The modified GCE was applied to sensitive and fairly selective electrochemical determination of the mycotoxin zearalenone. Electrocatalytic oxidation is performed in a solution containing 20 % (V/V) acetonitrile and 80 % (V/V) of 1 M perchloric acid. Cyclic voltammetry and square wave voltammetry revealed a well-defined electrocatalytic peak current at overpotential of +0.69 V versus Ag/AgCl. Under optimized experimental conditions, there is a linear relationship between anodic peak current and zearalenone concentration in the range from 0.03 to 35 ng?mL￣¹, and the detection limit is 0.01 ng?mL￣¹. The method was successfully applied to the analysis of zearalenone in spiked food samples and gave recoveries between 95.6 and 104.0 %.

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Graphical abstract The nanocomposite (PdVC-PIL) was prepared by polymerization of ionic liquid monomer (PIL) in presence of Pd nanoparticles on Vulcan XC-72R carbon (PdVC). The solution containing nanocomposite was placed on the glassy carbon electrode (GCE). The voltammetry activity of modified electrode (PdVC-PIL/GCE) was compared to a bare GCE for zearalenone determination.

     

Amorphous Silicon: New Insights into an Old Material

Amorphous silicon is synthesized by treating the tetrahalosilanes SiX₄ (X=Cl, F) with molten sodium in high boiling polar and non‐polar solvents such as diglyme or nonane to give a brown or a black solid showing different reactivities towards suitable reagents. With regards to their technical relevance, their stability towards oxygen, air, moisture, chlorine‐containing reaction partners RCl (R=H, Cl, Me) and alcohols is investigated. In particular, reactions with methanol are a versatile tool to deliver important products. Besides tetramethoxysilane formation, methanolysis of silicon releases hydrogen gas under ambient conditions and is thus suitable for a decentralized hydrogen production; competitive insertion into the MeO?H versus the Me?OH bond either yields H‐ and/or methyl‐substituted methoxy functional silanes. Moreover, compounds, such as Me_nSi(OMe)_4?n (n=0–3) are simply accessible in more than 75 % yield from thermolysis of, for example, tetramethoxysilane over molten sodium. Based on our systematic investigations we identified reaction conditions to produce the methoxysilanes Me_nSi(OMe)_4?n in excellent (n=0:100 %) to acceptable yields (n=1:51 %; n=2:27 %); the yield of HSi(OMe)₃ is about 85 %. Thus, the methoxysilanes formed might possibly open the door for future routes to silicon‐based products.     

A mechanistic insight into caspase-7 inhibition by BIR1-2 domains of XIAP and cIAP1

Previous studies failed to demonstrate any role for the BIR1 domain of the inhibitor of apoptosis proteins (IAPs) in inhibition of executioner caspases. In this study, XIAP-BIR1-2 and c-IAP1-BIR1-2 domains have been used to investigate the role of BIR1 in the inhibition of caspase-7. Kinetic analysis confirmed that caspase-7 was inhibited in an uncompetitive manner at lower concentrations of XIAP-BIR1-2, whereas the inhibition was switched to the mixed type mode at higher concentrations of the inhibitor. In contrast, cIAP1-BIR1-2 inhibited caspase-7 in a mixed type mode at all examined concentrations. These data suggest that the presence of BIR1 is essential for inhibition of caspase-7 by cIAP1. Far-UV CD and fluorescence spectroscopy experiments showed that despite similar secondary structures, XIAP-BIR1-2 and cIAP1-BIR1-2 have different biophysical properties. BIR1-2 domain of XIAP was found to be more flexible than cIAP1, which may be the reason behind differences in their kinetic properties.     

Electrochemical determination of captopril in the presence of acetaminophen,tryptophan, folic acid,and l-cysteine at the surface of modified carbon nanotube paste electrode

Ionics - A novel carbon paste electrode (CPE) modified with 2,2′-[1,7–heptanediylbis(nitrilomethylidene)]-bis(4-hydroxyphenol) (DHB) and carbon nanotubes (CNTs) was prepared. At first,...     

Opportunities and Challenges in the Use of TiO2 Nanoparticles Modified with Citric Acid to Synthesize Advanced Nanocomposites Based on Poly(amide-imide) Containing N,N′-(Pyromellitoyl)-bis-L-leucine Segments

In this study, the goal was the preparation, characterization, and surface morphology of poly(amide-imide)/TiO₂-citric acid nanocomposites (PAI/TiO₂-CA NCs). Owing to the high surface energy and tendency for agglomeration, the surface of TiO₂ nanoparticles was modified with citric acid. Then poly(amide-imide) was synthesized by direct polycondensation reaction of N,N′-(pyromellitoyl)-bis-L-leucine diacid with 4,4′-diaminodiphenylmethane by triphenyl phosphite and tetra-n-butylammonium bromide as a green medium. The attained polymer and modified TiO₂ nanoparticles were used to prepare PAI/TiO₂-CA NCs through ultrasonic irradiation. The resulting PAI/TiO₂-CA NC was characterized with FT-IR spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis.     

The analysis of structural and electronic properties for assessment of intramolecular hydrogen bond (IMHB) interaction: a comprehensive study into the effect of substitution on intramolecular hydrogen bond of 4-nitropyridine-3-thiol in ground and electronic excited state

The hydrogen bond strength, molecular geometry, π-electron delocalization, and physical properties such as dipole moment, chemical potential, and chemical hardness of 4-nitropyridine-3-thiol and its 29 derivatives have been studied by means of density functional method with 6-311++G** basis set in gas phase and water solution. Also, the excited-state properties of intramolecular hydrogen bonding in these systems have been investigated theoretically using the time-dependent density functional theory method. The HOMA, NICS, PDI, ATI, FLU, and FLU_π indices as well-established aromaticity indicators have been examined. Natural bond orbital analysis is also performed for better understanding the nature of intramolecular interactions. The electron density and Laplacian (?² ρ) properties, estimated by AIM calculations, indicate that H···O bond possesses low ρ and positive ?² ρ values, which are in agreement with electrostatic character of the HBs, whereas S–H bond has covalent character. Numerous correlations between topological, geometrical, and energetic parameters are also found.     

Designing of an Intensification Process for Biosynthesis and Recovery of Menaquinone-7

A nutritional food rich in menaquinone-7 has a potential in preventing osteoporosis and cardiovascular diseases. The static fermentation of Bacillus subtilis natto is widely regarded as an optimum process for menaquinone-7 production. The major issues for the bulk production of menaquinone-7 are the low fermentation yield, biofilm formation and the use of organic solvents for the vitamin extraction. In this study, we demonstrate that the dynamic fermentation involving high stirring and aeration rates enhances the yield of fermentation process significantly compared to static system. The menaquinone-7 concentration of 226 mg/L was produced at 1,000 rpm, 5 vvm, 40 °C after 5 days of fermentation. This concentration is 70-fold higher than commercially available food products such as natto. Additionally, it was found that more than 80 % of menaquinone-7 was recovered in situ in the vegetable oil that was gradually added to the system as an anti-foaming agent. The intensification process developed in this study has a capacity to produce an oil rich in menaquinone-7 in one step and eliminate the use of organic solvents for recovery of this compound. This oil can, therefore, be used for the preparation of broad range of supplementary and dietary food products rich in menaquinone-7 to reduce the risk of osteoporotic fractures and cardiovascular diseases.