Amperometric determination of sulfide ion by glassy carbon electrode modified with multiwall carbon nanotubes and copper (II) phenanthroline complex

Electrocatalytic oxidation of sulfide ion on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNTs) and a copper (II) complex was investigated. The Cu(II) complex was used due to the reversibility of the Cu(II)/Cu(III) redox couple. The MWCNTs are evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on Cu(II) complex adsorbed on MWCNTs immobilized on the surface of GCE. The modified GCE was applied to the selective amperometric detection of sulfide at a potential of 0.47 V (vs. Ag/AgCl) at pH 8.0. The calibration graph was linear in the concentration range of 5 µM–400 µM; while the limit of detection was 1.2 µM, the sensitivity was 34 nA µM^?1. The interference effects of SO₃ ^2?, SO₄ ^2?, S₂O₃ ^2?, S₄O₆ ^2?, Cysteine, and Cystein were negligible at the concentration ratios more than 40 times. The modified electrode is more stable with time and more easily restorable than unmodified electrode surface. Also, modified electrode permits detection of sulfide ion by its oxidation at lower anodic potentials.      

Isolation and Identification of the Major Chemical Components Found in the Upper Parts of Teucrium Pofium Plants Grown in Khuzestan Province of Iran

Teucrium polium is a dwarf sub-shrub usually 30-60 cm high with many branches, which is fairly distributed throughout Iran, with its flowering being season mainly from April to July. The plant was collected during its flowering season in Baghmalek region in the North-East of Khuzestan province, Iran. After the identification of the genus, species and variety of the plant, the dried whole plant （flowers, fruits and the leaves） was steam distilled with different methods. The isolated essential oil was dried over anhydrous sodium sulphate and stored at 4-6 ℃. Analysis of the essential oil was carried out by GC-MS technique. At least 10 major components were identified （3-carene/α-pinene, β-phellandrene, limonene, germacrene, β-bourbonene, β-caryophylene, γ-muurolene, γ-elemene, spathulenol, β-eudesmol） （totally 97.02%）. Also, successive TLC and column chromatography of the essential oil resulted in the separation of four fractions. Based upon 1^H NMR, IR and mass spectra, the fractions with Rf=0.12 and 0.93 were determined as gualol and a mixture of α-pinene, β-phellandrene and limonene, respectively.     

Trace analysis of some organophosphorus pesticides in rice samples using ultrasound‐assisted dispersive liquid–liquid microextraction and high‐performance liquid chromatography

An ultrasound‐assisted dispersive liquid–liquid microextraction based on solidification of a floating organic drop method followed by high‐performance liquid chromatography was developed for the extraction, preconcentration, and determination of trace amounts of organophosphorus pesticides in rice samples. Variables affecting the performance of both steps were thoroughly investigated. Some effective parameters on extraction were studied and optimized. Under the optimum conditions, recoveries for rice sample are in the range of 58.0–66.0%. The calibration graphs are linear in the range of 4–800 μg/kg and, limits of detection and limits of quantification are in the range of 1.5–3 and 4.2–8.5 μg/kg, respectively. The relative standard deviation for 50.0 μg/kg of organophosphorus pesticides in rice sample are in the range of 4.4–5.1% (n = 5). The obtained results show that proposed method is a fast and simple method for the determination of pesticides in cereals.     

Human serum albumin binding studies of a new platinum(IV) complex containing the drug pregabalin: experimental and computational methods

A new platinum(IV) complex, [Pt(en)(Cl)₂(Pregabalin)₂], containing the drug pregabalin was synthesized and characterized by elemental analysis, FT-IR, ¹H NMR, mass spectrum, thermogravimetric analysis (TGA), molecular docking and RHF/PM6 method. Also, the interaction of Pt(IV) complex with human serum albumin (HSA) was studied by using UV–vis, fluorometric, circular dichroism (CD) spectroscopies and molecular docking techniques. The results demonstrated that the binding of the complex to HSA caused strong fluorescence quenching of HSA through static quenching mechanism. Hydrogen bonds and van der Waals contacts are the major forces in the stability of protein-Pt(IV) complex and the process of the binding of complex with HSA was enthalpy driven (ΔH = –105.8?kJ·mol^?1). The results of CD and UV–vis spectroscopy indicated that the binding of the complex to HSA caused conformational changes in HSA. In addition, the study of molecular docking and RHF/PM6 method confirm the experimental results with respect to the mechanism of binding.     

Direct introduction of amine groups into cellulosic paper for covalent immobilization of tyrosinase: support characterization and enzyme properties

Tyrosinase is used to eliminate phenolic compounds from wastewater. Therefore, its immobilization is important to enhance catalytic efficiency. Papery materials are of particular interest for use as support for enzyme immobilization since the porous microstructure of fiber networks in papers can provide a suitable reaction environment, especially in flow-type catalytic reactions. However, immobilization of protein onto papery structure needs chemical modifications in severe conditions. To overcome this challenge, a cellulosic paper was directly amine-functionalized in moderate conditions and used for tyrosinase immobilization. The support was pretreated with HCl (0.5 N) solution and then sequentially immersed in ethylenediamine (EDA), glutaraldehyde solution (2% v/v) and the crude enzyme. In comparison with the untreated one, the immobilized enzyme on the EDA-treated support offered a 3.7-fold increase in activity. The FTIR spectra as well as EDX analysis proved the presence of amine groups in the cellulosic paper and also covalent immobilization of tyrosinase on the modified support. When considering the effect of pH on the activity at 25 °C, a maximum relative activity of 134% at pH 6 was revealed. Similarly, evaluating the effect of temperature on the activity at pH 7 displayed a maximum relative activity of 152% at 35 °C. The immobilized enzyme was suitable for use for more than four cycles to degrade a phenolic compound at severe pH and temperature conditions. Additionally, the immobilized enzyme was active after treatment of the surface at different pHs and temperatures for 105 min. The chemically modified cellulosic paper can be used as a support for enzyme immobilization.