Band 69, Heft 7

Due to the importance of B 1 and B 6 vitamins for human health it is useful to develop new cheap and rapid methods for their determination. Voltammetric behavior of these vitamins on a pencil graphite electrode was investigated using cyclic voltammetry in different media. Direct quantitative determination of the two vitamins, one in the presence of the other, was done by differential pulse voltammetry. Vitamin B1 was electroactive only in a NaOH solution generating two irreversible oxidation peaks; the first peak obtained at 250 mV is well-defined and was used in quantitative determinations. In case of vitamin B6, a well-defined oxidation peak was observed in all investigated supporting electrolytes except for HCl. The linear concentration ranges were 10 −5 - 10 −3 M for vitamin B1 in a NaOH solution and 5 × 10 −6 -10 −3 M for vitamin B6 in an acetate buffer solution. The obtained detection limits were 5.34 × 10 −6 M and 2.81 × 10 −6 M for vitamin B1 and vitamin B6, respectively. The developed method is simple and rapid and it was successfully applied in the determination of the two vitamins in pharmaceuticals.

A functional Ag-Fe 3 O 4 -grapheme oxide magnetic nanocomposite was synthesized and used to prepare a nitrite sensor. Morphology and composition of the nanocomposites were characterized by a transmission electron microscope, UV-VIS spectroscopy, X-ray diffraction, and Fourier transform infrared spectra. Electrochemical investigation indicated that the nanocomposites possess excellent electrochemical oxidation ability towards nitrites. The sensor exhibited two linear ranges: one from 0.5 μM to 0.72 mM with a correlation coefficient of 0.996 and sensitivity of 1996 μA mM −1 cm −2 ; the other from 0.72 mM to 8.15 mM with a correlation coefficient of 0.998 and sensitivity of 426 μA mM −1 cm −2 . The limit of detection of this sensing system was 0.17 μM at the signalto- noise ratio of 3. Additionally, the sensor exhibited long-term stability, good reproducibility, and anti-interference.

The inhibitory effect of free ammonia and free nitrous acid on nitrite-oxidising bacteria (NOB) was studied in a laboratory-scale sequencing batch reactor with a suspended microbial culture. The reactor was operated at 15°C, with a dissolved oxygen concentration in excess of 5 mg L −1 and a nitrogen-loading rate of 0.2 kg m −3 d −1 . Diluted reject water with varying total ammonia nitrogen (TAN) concentrations was used as influent. N-NO − 2 represented more than 90 % of all of the oxidised nitrogen, with influent TAN concentrations of 600 mg L −1 , 300 mg L −1 and 150 mg L −1 , respectively. With a TAN concentration of 75 mg L −1 , a gradual increase in N-NO − 3 concentration was detected, indicating the threshold value enabling short-cut nitrification (SN) to be between 150 mg L −1 and 75 mg L −1 under the pertaining conditions. Next, the influent concentration of TAN was gradually increased from 75 mg L −1 to 1000 mg L −1 but the nitrite accumulation was not restored. This indicates that once NOB are established in the suspended microbial culture, even high TAN concentrations are not sufficient for NOB inhibition.

Methylene blue (MB) removal using eco-friendly, cost-effective, and freely available Urtica was investigated. The morphology of the adsorbent surface and the nature of the possible Urtica and MB interactions were examined using SEM analysis and the FTIR technique, respectively. Various factors affecting MB adsorption such as adsorption time, initial MB concentration, temperature, and solution pH were investigated. The adsorption process was analysed using different kinetic models and isotherms. The results showed that the MB adsorption kinetic follows a pseudo-second-order kinetic model and the isotherm data fit the Langmuir isotherm well. Thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were also evaluated, and the results indicated that the adsorption process is endothermic and spontaneous in nature. The MB adsorption capacity of Urtica was found to be as high as 101.01 mg g −1 , higher than those of many other adsorbents studied in the literature. This superior adsorption capacity, along with the ready availability of Urtica, render this adsorbent potentially suitable for practical applications.

Electrical impedance spectroscopy (EIS) is a non-destructive, rapid and real-time measurement method which does not require special high-tech measurement devices and can be applied to food quality assessment. This method is rapid, effective and affords low-cost investigation of the product. The conventional EIS method requires a set of metal electrodes in direct contact with the medium to be measured. The complicated electrochemical processes on the electrodes-electrolyte interface could substantially affect the value of the impedance measured. The present study sought to explore the possibilities of using the impedance method for quality control in orange juices, to introduce the electrodeless method of electrolyte impedance measurement and to compare this with the conventional impedance methods. The electrical properties of the orange juices were described with the help of an equivalent circuit. An equivalent circuit was designed with constant phase element approximation. The values of the equivalent circuit components were fitted using a non-standard algorithm inspired by the behaviour of actual ant colonies. Implementing the electrodeless method obviated the electrodes phenomena effects and the behaviour of the electrolyte is similar to inductance. The proposed electrodeless method is generally applicable to measuring the electrochemical properties of electrolytes.

Vegetable oils are important constituents of a healthy diet. Still, unsaturated fatty acids present in vegetable oils are susceptible to oxidation, which leads to undesirable changes in sensory, chemical and nutritional properties of oils. To prevent this problem, antioxidants are applied with herbs and spices being one of the most important sources of natural antioxidants. Electron paramagnetic resonance spectroscopy (EPR) can be used to detect free radicals, which are the short-lived intermediates of lipid oxidation, and to monitor changes in oxidation susceptibility. In this study, the ESR spin trapping technique was used as a potential method for the evaluation of the resistance to free radical formation in rapeseed and sunflower oils enriched with herb extracts. The antioxidant effect of herb extracts on vegetable oils was also investigated by measuring their ability to scavenge DPPH free radical using EPR spectroscopy. The herb extracts generally improved the radical scavenging properties of sunflower and rapeseed oils but their influence on the onset of rapid lipid oxidation as measured by spin-trapping EPR depended on the type of oil and on the extract concentration.

Poly(p-phenylene/pyrrole) (PPP-PPY) films were electrochemically synthesised on transparent indium-tin-oxide-covered glass (ITO) electrodes. The presence of two monomers, p-phenylene and pyrrole, in the polymerisation medium facilitated the synthesis process, yielding electroactive, uniform and stable films. In order to obtain materials with improved quality, PPP, PPY and PPP-PPY films were prepared in a mild, dry atmosphere. The morphological, electrochemical and optical properties were compared for different films obtained by varying the number of cycles with and without controlling humidity.

Novel copolymers of poly(aniline-co-m-chloroaniline)-doped dodecylbenzenesulphonic acid (DBSA) with embedded silver nanoparticles were synthesised using the in situ chemical oxidative method. The structural properties of the copolymers were characterised using the UV-VIS and FTIR spectroscopic methods. The crystalline nature of the copolymer was demonstrated by way of the X-ray diffraction (XRD) pattern. Scanning electron microscopy (SEM) revealed the presence of particle agglomerates measuring 50 nm to 100 nm on the surface of the nanocomposites. The electrical conductivity of the copolymer was dependent on the monomer composition and was found to be in the range of 10 −2 S cm −1 to 10 −6 S cm −1 with an increasing chloroaniline content and exhibiting improved solubility.

A facile and rapid procedure for the synthesis of dimethyl-2-[3-amino-5-(2-methoxy-2-oxoethylidene)- 4-oxothiazolidin-2-ylidenehydrazono]succinate, dimethyl {[2-alkylidenehydrazono)-5-(2-methoxy- 2-oxoethylidene)-4-oxothiazolidin-3-yl)amino]succinate and methyl (4-amino-5-oxo-3- thioxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-yl)acetate affording yields of 61-54 %, 22-18 % and 14- 11 %, respectively, via a condensation reaction of dimethyl acetylenedicarboxylate (DMAD) with (substituted ylidene)thiocarbonohydrazides. One of the products was conclusively confirmed by single-crystal X-ray analysis. A mechanism for the formation of the products is presented.

A series of indolizine derivatives have been synthesized and subjected to antibacterial screening studies. Antibacterial activity of 21 derivatives was investigated against Staphylococcus aureus, Mycobacterium smegmatis, Salmonella typhimurium and Escherichia coli; also, the sensitivity of model yeast Candida parapsilosis and some model filamentous fungi Aspergillus fumigatus, Alternaria alternata, Botrytis cinerea and Microsporum gypseum was tested. Newly synthesized indolizine derivatives have shown selective toxicity to Gram-positive bacteria S. aureus and were also considered to be able to inhibit the acidoresistant rod M. smegmatis. Derivative XXI has shown the highest inhibition effect with the bacteriostatic effect on the cells at the concentration of 25 μg mL −1 . The best antifungal activity has been detected in the presence of derivative XIII. Derivative XIII did also affect the morphology of hyphal tips of B. cinerea, which led to enhanced ramification of hyphae. Finally, the antimutagenic activity of derivatives was investigated. Significant antimutagenic activity was registered in case of derivative VIII. The number of induced revertants by mutagen [2-(5-nitrofuryl)acrylic acid] was decreased almost to the level of spontaneous revertants in the lowest applied concentration (50 μg per plate).

A series of anthranilic diamides with a hydrazone substructure was synthesised and characterised using 1 H NMR, 13 C NMR, IR and elemental analyses. The in vitro insecticidal activity of all the compounds was tested against Plutella xylostella. The results showed the synthesised compounds to possess good insecticidal activity. The LC50 values of compounds VIIg, VIIl, VIIm, VIIn exhibited excellent insecticidal activities, with the LC 50 affording 7.92 mg L −1 , 12.01 mg L −1 , 0.62 mg L −1 and 10.71 mg L −1 , respectively. These may prove to be useful as potential insecticidal agents.

An oil-soluble antioxidant, alkylated diphenylamine (ADPA), was prepared by alkylation of diphenylamine. The influence of ADPA on the thermal-oxidative stability of poly-α-olefin (PAO8) was evaluated by thermogravimetry (TG). For comparison, the thermal-oxidative stability of PAO8 with zinc dialkyl dithiophosphate (ZDDP) was also investigated. Activation energy (E a ) of the corresponding thermal-oxidative degradation process was evaluated by the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. To demonstrate the reliability of the kinetic study, the antioxidant performance of ADPA and ZDDP in PAO8 was also studied by the pressure drop (PDT) and accelerated oxidation (AOT) tests. The results indicate that ADPA has better antioxidant ability than ZDDP in increasing the E a value and enhancing the oxidative stability of PAO8. Good correlation between the applied test methods was established.

Maleic anhydride undergoes C-phosphorylation under the action of tris(diethylamino)phosphine to afford 3-dihydrofuranylidene-4-phosphorylidene-oxolane-2,5,5′-trione whereas 2,3-diphenylmaleic anhydride under the same conditions turns into N,N,N′,N′-tetraethyl-2,3-diphenylbut-2-enediamide. The latter reaction can serve as a novel approach for the synthesis of dicarboxylic acids diamides from corresponding cyclic anhydrides. Their structures were established by NMR and X-ray diffraction.

A facile and efficient one-pot synthesis of polysubstituted benzenes was achieved via the Michael addition of malononitrile with α,β-unsaturated imines and a sequential tandem reaction. This reaction generates polysubstituted 2,6-dicyanoanilines in high yields (15 examples, isolated yields of 57-91 %), and proceeds under mild reaction conditions (60°C, 10 min). In addition, a possible mechanism accounting for the reaction is proposed.