نشریه شیمی کاربردی روز
پیاپی 25 (زمستان 1391)

The chemiluminescence arising from the reaction of bis (2،4،6-trichlorophenyl) oxalate (TCPO) with hydrogen peroxide in the presence of fluorescent brighteners 4،4’-Bis{[4-anilino-6-bis (2-hydroxyethyl) amino-1،3،5-triazin-2-yl]amino} stilbene-2،2’-disulfonic acid- disodium salts (Triaz I)، 4،4’-Bis {[4-6-anilino -1،3،5-triazin-2-yl] amino} stilbene-2،2’-disulfonic acid- disodium salts (Triaz II) has been studied. The influence of concentration of Triazinyl، TCPO، hydrogen peroxide، catalysts concentration، catalyst type and temperature on the chemiluminescence was investigated. The kinetic parameters for the peroxyoxalate-chemiluminescence of Triazinyl were appraise from computer fitting of the resulting intensity–time plots. The activation parameters such as Ea and G، were evaluated from temperature dependence of the corresponding fall rate constants.

The kinetic and mechanistic aspects of the oxygen reduction reaction as well as the electrocatalytic effect of copper surface in alkaline solution were studied by cyclic voltammetry and rotating disk electrode technique. In the potential range of -0. 4 to -1. 4 V/SCE time dependent cathodic peaks at -0. 9 V/SCE، -1. 2 V/SCE and plateau extending through this domain were observed. Direct reduction of oxygen along with the dominating reduction of copper oxides which formed during time delay at open circuit potential is discussed in the light of electrochemical techniques. The number of electrons transferred per O2 molecule (n) obtained on different copper surface is close to 4 on oxide free surface and gradually decreases to 2 when the oxide layers cover the copper surface. Moreover calculation of rate constant of oxygen reduction on copper surface، demonstrated a faster kinetic of reaction on oxide free surface of copper. Tearing down and building up of the surface causing increased surface area is also observed.

A quantitative spectroscopic method using multivariate data models based upon ultraviolet spectroscopy، is proposed for the simultaneous analysis of binary mixtures of uracil (UR) and 5-fluorouracil (5-FU). By multivariate calibration methods، such as partial least squares (PLS)، it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. In this study، the calibration model is based on absorption spectra in the 220–314 nm range for 25 different mixtures of UR and 5-FU. PLS was used for the construction of the calibration sets containing UR and 5-FU in the concentration range of 1. 12-28. 02 and 1. 30-38. 76 (in μg mL-1)، respectively. Prediction error sum of squares (PRESS) was 0. 5172 and 3. 8191 and the root mean standard error of prediction (RMSEP) was 0. 2936 and 0. 7978 for UR and 5-FU، respectively. This procedure allows the simultaneous determination of UR and 5-FU in synthetic and spiked real samples.

Nanoparticles of Cd1-xZnxS (x = 0-0. 3) were prepared in ethylene glycol using microwave irradiation. Zinc acetate، cadmium acetate and thioacetamide were used as the sources of zinc، cadmium and sulfur respectively. Diffraction peaks in powder X-ray diffraction (XRD) patterns of the nanoparticles showed a gradual shift to higher angles with increase in zinc content. Diffuse reflectance spectroscopy (DRS) of the specimens revealed that the absorption edges for Cd1-xZnxS nanoparticles blue-shifted upon increasing x value. Energy dispersive X-ray analysis (EDX) data proved the ability of microwave in producing a desired compound. FTIR studies of the specimens revealed the presence of Zn in the produced compounds.

In this study antioxidant properties and total phenolic content of the extracts of Nelumbo nucifera seeds were examined. The extracts were prepared using the solvents water، methanol، water: methanol (1:1)، ethyl acetate، acetone and chloroform. Two experimental methods including DPPH (1،1-Diphenyl-2-picryl-hydrazyl) radical scavenging activity and total antioxidant capacity were used for characterization of antioxidant activity of the extracts. The six extracts showed varying degrees of efficacy in each assay in a dose-dependent manner. The acetone extract with the highest amount of total phenolic content (20. 12 ± 0. 02 g GAE/100 g dried extract)، was the most potent antioxidant in both assays used. The LSA exhibited strong free radical scavenging activity as evidenced by the low EC50 values in DPPH assay (4. 28 μg/ml) and in total antioxidant assay by maximum activity (25% of ascorbic acid). On the basis of the results، the acetone extract of Nelumbo nucifera seeds were found to serve as a potential source of natural antioxidants.

In this study، the essential oil of Ajowan seeds was extracted by subcritical water extraction process (SWE). Thymol as the main component of the extracted essential oils was quantified by GC and GC–mass spectrometry. This extraction has been performed using Taguchi design approach under following conditions: temperature (100، 150 and 175 ◦C)، mean particles size (0. 25، 0. 5 and 1 mm) and water flow rates (1. 0، 2. 0 and 4. 0 mL/min). The optimum conditions as obtained from signal-to-noise ratio analysis in terms of amount Thymol were as follows: 175 ◦C، 0. 25 mm and 2. 0 mL/min. The SWE efficiency at optimized conditions was compared with the other conventional methods such as hydrodistillation and Soxhlet extraction. The SWE results showed a higher amount of Thymol (25. 248 mg/g dried sample) than hydrodistillation (13. 992) and Soxhlet extraction (7. 209).

The Chromazurol s has been electropolymerized on the glassy carbon electrode and the Poly- Chromazurol s modified glassy carbon electrode (PCSMGCE) has shown excellent electrocatalytic activity toward the oxidation of ascorbic acid in phosphate buffer solution (pH=3). It was used for the simultaneous determination of ascorbic acid (AA)، dopamine (DA)، and uric acid (UA). Analytical parameters were optimized and electrochemical behavior of modified electrode was studied. The calibration curves were obtained over the range of 3. 0-2200. 0 µmol L–1 AA، 0. 09-980. 0 µmol L–1 DA، and 0. 05-900. 0 µmol L–1 UA. Detection limits of 1. 7 µmol L–1 AA، 0. 05 µmol L–1 DA، and 0. 03 µmol L–1 UA were obtained at pH 3. 0. Prepared modified electrode had satisfactory results for determination of DA، AA and UA in dopamine injection solution، vitamin C tablets and human urine samples.

In this paper we report synthesis and application of ZnO nanoparticle (ZnO/NPs) and 1، 3-dipropylimidazolium bromide as high sensitive sensors for voltammetric determination of ascorbic acid (AA) using carbon paste electrode. The ZnO/NPs was characterized with different methods such as TEM and XRD. The cyclic voltammogram showed an irreversible oxidation peak at 0. 35 V (vs. Ag/AgClsat)، which corresponded to the oxidation of AA. Compared to common carbon paste electrode، the electrochemical response was greatly improved. The electro-oxidation of AA occurred in a pH-dependent 2e− and 2H+ process، and the electrode reaction followed a diffusion-controlled pathway. Under the optimum conditions، the voltammetric oxidation peak current of AA showed two linear dynamic ranges with a detection limit of 0. 04 μM for AA. The novel sensor has been found selective and successfully implemented for the determination of AA in fresh vegetable juice; fruit juices، tablet and tablet samples without previous preparation and were compared with a published electrochemical method.

In this paper، polysalisylaldehyde (PSA) has been synthesized from the oxidative polycondensation (OP) of 2-[(2،4-dichlorophenylimino) methyl]-phenol (sal-2،4-Clan) with NaOCl in an aqueous alkaline medium between 50 and 90°C and characterized by 1H-NMR، FT-IR، UV-Vis and TGA/DTA techniques. The conversion of PSA was 61. 23% in optimum conditions such as [sal-2،4-Clan] 0 = 0. 02، [KOH] 0= 0. 1 [NaOCl] 0 = 0. 12 mol/L at 90°C for 10 h. Additionally، the crystal structure of sal-2،4-Clan has been determined by single-crystal X-ray crystallography.