Ionic liquid promoted Diels-Alder Reaction between anthrone and maleimides

Ionic liquids (IL) are gaining importance as green solvents. Imidazolium ionic liquid [bmim]⁺[Cl]⁻, an environmentally benign solvent, was found to promote the Diels-Alder reaction between anthrone and maleimides at room temperature with excellent yields. The ionic liquid played a dual role as solvent and catalyst.      

Kinetic spectrophotometric determination of hydrazine

A kinetic spectrophotometric method for hydrazine determination in the range of 9.36×10⁻⁷ to 4.37×10⁻⁵ mol dm⁻³, based on the inhibitory effect of hydrazine on the oxidation of Victoria Blue 4- R by KBrO₃, was developed and validated. Kinetic parameters are reported for both the indicating and the inhibiting reaction. The detection limit was established as 9.98×10⁻⁸ mol dm⁻³. The selectivity of the proposed method was tested considering the influence of different ions that may be present in real samples. The method was successfully applied for hydrazine determination in various samples (very pure water from the water-steam system of a power plant and Isoniazid tablets, a pharmaceutical product).      

Cloud point extraction-preconcentration and flame atomic absorption spectrometric determination of low levels of zinc in water and blood serum samples

A simple, sensitive and selective flotation method is described for the preconcentration and atomic absorption spectrometric determination of zinc ion in water and blood samples. At a solution pH of 5.2, 4-(2-pyridylazo-resorcinol) and Triton X-114 were used as hydrophobic ligand and non-ionic surfactant, respectively. The chemical variables affecting the preconcentration process were optimized. Under the optimized experimental conditions, the selective preconcentration and determination of as low zinc concentration as 6.5 μg L⁻¹ can be made. The proposed method was successfully applied to the preconcentration and low-level determination of zinc in different water and blood serum samples.      

Density functional theory study of the photosensitization mechanisms of indigo

The triplet excited state properties and photosensitization mechanisms of indigo were investigated based on density functional theory calculations. The solvent effects on the photosensitization mechanisms of indigo have also been considered. The thermodynamic feasibility of the possible ¹O₂ and O₂·⁻-photogeneration pathways by triplet excited state indigo in different solvents was explored, in order to gain some deeper insights into the photosensitization characters of the dye.      

Kinetics of base hydrolysis of α-amino acid esters catalyzed by palladium(II) piperazine complex

The kinetics of base hydrolysis of glycine, histidine, and methionine methyl esters in the presence of [Pd(pip)(H₂O)₂]²⁺ complex, where pip is piperazine, is studied in aqueous solutions, at T = 25°C, and I = 0.1 mol dm⁻³. The rate of ester hydrolysis for glycine methyl ester is studied at different temperature and dioxane/water solutions of different compositions. The kinetic data are fit under the assumption that the hydrolysis proceeds in one step. The activation parameters for the base hydrolysis of the complexes are evaluated      

Meldola’s Blue — doped titania sol-gel sensor for NADH determination

Titania layers obtained by a sol-gel technique doped with redox mediator, Meldola’s Blue, were employed for construction of a new NADH senor. Optimization of preparation process as well as experimental conditions affecting the response of the sensor were examined. Under optimal conditions NADH could be determined in the wide linear range from 90 to 2300 μM with detection limit 12 μM and a high sensitivity 12.5 nA μM⁻¹. The usefulness of developed sensor was preliminarily checked in determination of NADH forming during enzymatic oxidation of ethanol catalyzed by alcohol dehydrogenase (ADH).      

The binary system PbO - BiVO4

Phase equilibria established in the PbO - BiVO₄ system over the whole component concentration range up to 1000°C have been investigated. A phase diagram has been constructed using DTA and XRD.      

Dispersive liquid-liquid microextraction and liquid chromatographic determination of pentachlorophenol in water

A simple and sensitive dispersive liquid-liquid microextraction method for extraction and preconcentration of pentachlorophenol (PCP) in water samples is presented. After adjusting the sample pH to 3, extraction was performed in the presence of 1% W/V sodium chloride by injecting 1 mL acetone as disperser solvent containing 15 μL tetrachloroethylene as extraction solvent. The proposed DLLME method was followed by HPLC-DAD for determination of PCP. It has good linearity (0.994) with wide linear dynamic range (0.1–1000 μg L⁻¹) and low detection limit (0.03 μg L⁻¹), which makes it suitable for determination of PCP in water samples.      

Hollow fibre liquid phase microextraction of parabens

A hollow fibre liquid phase microextraction for gas chromatographic determination of some p-hydroxybenzoic acid esters has been developed. Chlorobenzene containing tetradecane as internal standard was used for the extraction. Optimized extraction was carried out at room temperature for 40 min in the presence of 0.4 g mL⁻¹ NaCl in the sample solution. Calibration was linear up to 30 mg L⁻¹. Correlation coefficients were 0.996–0.998. Enrichment factors were 21, 95 and 154, and detection limits were 0.20, 0.03 and 0.01 μg mL⁻¹ for methylparaben, ethylparaben and propylparaben, respectively. Reproducibility was acceptable with relative standard deviations up to 11.7%. The technique was tested for water and urine analysis.      

High surface area nano-sized La0.6Ca0.4MnO3 perovskite powder prepared by low temperature pyrolysis of a modified citrate gel

Single phase nanocrystalline La_0.6Ca_0.4MnO₃ powder was synthesized by both the usual and a modified citrate gel precursor method, and the effects on the formation of homogeneous nano-sized powder with a perovskite structure were investigated. In the modified method, single phase La_0.6Ca_0.4MnO₃ powder with an average particle size of 17.2 nm was obtained when the powder was pyrolyzed at 520°C for 2 h. Its specific surface area was 40.7 m² g⁻¹, about 4-fold larger than that of powder made by the usual citrate gel method.      

Influence of EDTA,carboxylic acids,amino- and hydroxocarboxylic acids and monosaccharides on the generation of arsines in hydride generation atomic absorption spectrometry

The influence of EDTA, carboxylic acids, amino-and hydroxocarboxylic acids, monosaccharides and humic substances on the generation of arsines in hydride generation atomic absorption spectrometry (HGAAS) was investigated. EDTA (0.02 mol L⁻¹), ascorbic acid (0.02 mol L⁻¹) and glucose or fructose (0.2 mol L⁻¹) are useful additives for levelling sensitivities for As(III), monomethylarsonate (MMA) and dimethylarsinate (DMA). The presence of glycine, malonic, tartaric acids, BICIN and soil humin extracts leads to differences in analytical signal response between these arsenic species. An analytical application to the determination of the sum of As(III), monomethylarsonate (MMA) and dimethylarsinate (DMA) as well as the sum of toxicologically relevant hydride forming arsenic fraction As(III) + As(V) + MMA + DMA in EDTA soil/sediment extracts using continuous flow HGAAS was demonstrated. The limit of detection was 0.2 mg kg⁻¹ As. Within-day and between-day precision were in the range 3–7% and 4–10%, respectively, for arsenic contents of 0.7–25 mg kg⁻¹, with recoveries 95–103%.      

Mechanistic aspects of oxidation on L-tyrosine by diperiodatocuprate(III) complex in alkali media: a kinetic model

Oxidation of an amino acid, L-tyrosine (L-Tyr) by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of 0.1 mol dm⁻³ was studied spectrophotometrically at different temperatures (288.1–313.1 K). The reaction between DPC and L-Tyr in alkaline medium exhibits 1:4 stoichiometry (L-Tyr:DPC). Intervention of free radicals was observed in the reaction. Based on the observed orders and experimental evidence, a mechanism involving monoperiodatocuprate(III) (MPC) as the reactive oxidant species has been proposed. A suitable mechanism is proposed through the formation of a complex and free radical intermediate. The products were identified by spot test and characterized by spectral studies. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism were computed and are discussed. The thermodynamic quantities were determined for different equilibrium steps. Isokinetic temperature was also calculated and found to be 252.3 K.      

Removal of Pb and Cd from aqueous media and fish liver using novel polyurethane foam functionalized with pyrazolone as a new metal ion collector

In the present paper, an off-line preconcentration procedure for the determination of cadmium and lead by flame atomic absorption spectrometry (FAAS) is proposed. Polyurethane foam (PUF) functionalized with o-aminophenol (o-AP) followed by Pyrazolone (Pyr) packed in a minicolumn was used as a sorbent material. The metals were retained on the modified PUF, from which it could be eluted and effectively preconcentrated. The detection limits were 0.072 and 0.016 μg L⁻¹ for Pb and Cd respectively. Enrichment factors were 250 and 319 for lead and cadmium respectively. The procedure has been applied successfully to metal determination in water samples, fish liver and reference material.      

Solar-driven electrochemically assisted semiconductor-catalyzed iodide ion oxidation. Enhanced efficiency by oxide mixtures

Oxidation of iodide ion from an air-saturated solution under natural sunlight (900±50 W m⁻²) on the surfaces of TiO₂, ZnO, Fe₂O₃, MoO₃ and CeO₂ enhances by 6 to 12-fold on application of a cathodic bias of −0.2 to −0.3 V (vs NHE) to the semiconductors; light, the semiconductor and dissolved oxygen are essential for iodine generation. The semiconductors under an anodic bias of +0.2 to +0.3 V (vs NHE) fail to oxidize iodide ion from air-saturated solution under sunlight. Under cathodic bias, semiconductor mixtures like TiO₂-ZnO, TiO₂-Fe₂O₃ and ZnO-Fe₂O₃ show enhanced photocatalytic activity, indicating improved charge separation in oxide mixtures. The mechanism of photocatalysis under cathodic bias is discussed.      

Glassy carbon and boron doped glassy carbon electrodes for voltammetric determination of linuron herbicide in the selected samples

In this study the application of home-made unmodified (GC) and bulk modified boron doped glassy carbon (GCB) electrodes for the voltammetric determination of the linuron was investigated. The electrodes were synthesized with a moderate temperature treatment (1000°C). Obtained results were compared with the electrochemical determination of the linuron using a commercial glassy carbon electrode (GC-Metrohm). The peak potential (E _p ) of linuron oxidation in 0.1 mol dm⁻³ H₂SO₄ as electrolyte was similar for all applied electrodes: 1.31, 1.34 and 1.28 V for GCB, GC and GC-Metrohm electrodes, respectively. Potential of linuron oxidation and current density depend on the pH of supporting electrolyte. Applying GCB and GC-Metrohm electrodes the most intensive electrochemical response for linuron was obtained in strongly acidic solution (0.1 mol dm⁻³ H₂SO₄). Applying the boron doped glassy carbon electrode the broadest linear range (0.005–0.1 μmol cm⁻³) for the linuron determination was obtained. The results of voltammetric determination of the linuron in spiked water samples showed good correlation between added and found amounts of linuron and also are in good agreement with the results obtained by HPLC-UV method. This appears to be the first application of a boron doped glassy carbon electrode for voltammetric determination of the environmental important compounds.      

Preparation of SAMS-CMC-CS bipolar membrane and its application in electro-generating FeO 4 2−

The preparation of SAMS-CMC-CS bipolar membrane grafted onto CMC by SAMS was reported. The cross-section view of SAMS-CMC-CS BM were studied by SEM. FT-IR spectrum indicated that SAMS-CMC-CS BM contained-SO ₃ ⁻ ,-COO⁻ and −N=CHR functional groups. Compared with CMC-CS BM, SAMS-CMC-CS BM appears to have better mechanical strength and chemical stability in alkali solution at [OH⁻]≥9.5 mol/L, with a swelling of 55 %. The electrochemical properties of SAMS-CMC-CS BM were also studied. SAMS-CS-CMC BM not only effectively prevented FeO ₄ ²⁻ from diffusing into the cathode chamber, but also played an important role in the supply of OH⁻ consumed during the electro-generated FeO ₄ ²⁻ process.      

ZrOCl<Subscript>2</Subscript> · 8H<Subscript>2</Subscript>O: An efficient catalyst for rapid one-pot synthesis of 3-carboxycoumarins under ultrasound irradiation in water

In this report, a rapid, efficient and environmental friendly synthesis of 3-carboxycoumarins under ultrasound irradiation in water media is described. The Knoevenagel condensation of Meldrum’s acid with substituted benzaldehydes in the presence of zirconium oxide chloride (ZrOCl₂·8H₂O) and ultrasonic irradiation in water gave the corresponding 3-carboxycoumarins in good to excellent yields.      

Comparative studies on conventional and microwave-assisted synthesis of a series of 2,4-di and 2,3,4-trisubstituted benzimidazo[1,2-a] pyrimidines and their antimicrobial activities

Comparative studies were performed on a series of 2,4-di and 2,3,4-trisubstituted benzimidazo[1,2-a]pyrimidines, which were synthesized with conventional and microwave heating methods. In microwave irradiation method, approximately, 95–97.5% of the reaction time was increased and 1–45% yield increase was obtained. All compounds were able to inhibit the growth of the screened microorganisms in vitro with MIC values between 3.9–250 μg mL⁻¹. The highest activity was expressed by compound IIId (2,4-diphenyl-benzo[4,5]imidazo[1,2-a] pyrimidine), which has the MIC value of 3.9 μg mL⁻¹ and 31.2 μg mL^-1 for Penicillium natatum ATCC 24791 and E. faecalis ATCC 29212, respectively.      

Influence of complexation on the composition of equilibrium phases in the system of Ce2(SO4)3-La2(SO4)3

The cocrystallization of Ce₂(SO₄)₃ and La₂(SO₄)₃ is studied in aqueous and H₂SO₄ (150 g/dm³) solutions at 25 °C and 64 °C. The effect of the formation of inner sphere sulfate complexes of the type LnSO ₄ ⁺ in determining the composition of the equilibrium phases is revealed.