Thermosetting polymers from epoxy resin and a Nickel catalyst of diethylenetriamine

The kinetics and mechanism of cure reaction of DGEBA using a chelate of Ni(II) with diethylenetriamine (dien), Ni(dien)₂I_2, as a curing agent was studied by DSC. TG curve of the complex curing agent showed mass loss in two region of temperature: 200–320 and 450–550 °C. Dynamic DSC measurements showed only one exothermic peak with a maximum about 250 °C depending on the heating rate. According to the methods of KAS and Ozawa–Flynn–Wall the values of E _a were 92.5 and 96.2 kJ/mol, respectively. The isoconversional kinetic analysis in whole range of conversion, α = 0.02–0.95, showed small changes in the E _a values in the region of α = 0.04–0.6 and most likely represent some average values (E _a = 110 kJ/mol) between the values of E _a of non-autocatalyzed and autocatalyzed reactions. Using the sole dependence of E _a on α, the time required to reach fully cured materials under isothermal conditions were also predicted and compared with the experimental results.     

The α,5-dicarboxy-2-nitrobenzyl caging group, a tool for biophysical applications with improved hydrophilicity: synthesis, photochemical properties and biological characterization

Earlier we reported on the synthesis of α,4-dicarboxy-2-nitrobenyzl caged compounds (Schaper, K. et al. [2002] Eur. J. Org. Chem., 1037–1046). These compounds have the advantage of an increased hydrophilicity compared with the well-established α-carboxy-2-nitrobenzyl caged compounds; however, the release of the active compound becomes slower due to the introduction of the additional carboxy group. Based upon theoretical calculations we predicted that the release would become faster when the additional carboxy group is moved to the 5-position. Here we describe the synthesis and the photochemical and biological characterization of an α,5-dicarboxy-2-nitrobenyzl caged compound. The high hydrophilicity of the new caging group is maintained due to the fact that the additional carboxy moiety is preserved, while the release of the active species from the new derivative is even faster than for the reference, an α-CNB caged compound.     

Cobalt oxide nanostructure-modified glassy carbon electrode as a highly sensitive flow injection amperometric sensor for the picomolar detection of insulin

Glassy carbon electrode modified with electrodeposited cobalt oxide nanostructure shows an excellent electrocatalytic activity toward insulin oxidation at a wide pH range. Cyclic voltammetry, hydrodynamic amperometry, and flow injection analysis (FIA) were used for insulin determination at a picomolar and higher-concentration range. Amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear range, 100 pM–15 nM; sensitivity of 83.9 nA nM⁻¹ and detection limit 10 pM. FIA yielded the calibration curve with sensitivity and detection limit of 2.0 nA nM⁻¹ and 25 pM, respectively. Furthermore, the RSD of repetitive FIA for 200 pM insulin (n = 13) is 2%. In addition, the interference effect of electroactive existing species (lactic acid, cholesterol, ascorbic acid, uric acid, and glucose) was eliminated by covering the surface of the modified electrode with nafion film. Fast response time, signal stability, high sensitivity, low cost, and ease of preparation are the advantages of the proposed insulin sensor.     

Charge-transfer triiodide ion-selective electrode based on 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane.

A new PVC membrane electrode for the triiodide ion based on a charge-transfer complex of iodine with 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane as a membrane carrier was prepared. The electrode exhibits a Nernstian response for triiodide ions over a wide concentration range (1.0 x 10(-1)-1.0 x 10(-5) M) with a slope of 59.3 +/- 0.9 mV decade(-1) and a detection limit of 6.3 x 10(-6) M. It has a response time of 30 s and can be used for at least 3 months without any divergence in the potential. The potentiometric response is independent of the pH, in the pH range 1.6 - 10.0. The proposed electrode has shown very high selectivity for the triiodide ion over a wide variety of other anions. This electrode was successfully applied as an indicator electrode in the potentiometric titration of ascorbic acid and hydroquinone from pharmaceutical preparations as well as ascorbic acid in orange juice and dissolved O2 in tap water.     

A green multicomponent synthesis of bioactive pyrimido[4, 5-b]quinoline derivatives as antibacterial agents in water catalyzed by RuCl3·xH2O

An efficient, convenient and environmentally benign one-pot multicomponent reaction for the preparation of pyrimido[4,5-b]quinoline derivatives as biologically, pharmacologically and antibacte- rially active products has been developed using RuC13.xH20 as a reusable homogenous catalyst. Use of water as a green solvent, purification of products by non-chromatographic methods, reusability of transition metal homogenous catalyst, saving energy by employing multicomponent reactions, short reaction times and high yields, are some of the advantages of this process.     

Tantalum Electrodes Modified With Well-Aligned Carbon Nanotube–Au Nanoparticles: Application to the Highly Sensitive Electrochemical Determination of Cefazolin

Carbon nanotube/nanoparticle hybrid materials have been proven to exhibit high electrocatalytic activity suggesting broad potential applications in the field of electroanalysis. For the first time, modification of Ta electrode with aligned multi-walled carbon nanotubes/Au nanoparticles introduced for the sensitive determination of the antibiotic drug, cefazolin (CFZ). The electrochemical response characteristics of the modified electrode toward CFZ were investigated by means of cyclic and linear sweep voltammetry. The modified electrode showed an efficient catalytic activity for the reduction of CFZ, leading to a remarkable decrease in reduction overpotential and a significant increase of peak current. Under optimum conditions, the highly sensitive modified electrode showed a wide linear range from 50 pM to 50 μM with a sufficiently low detection limit of 1?±?0.01 pM (S/N?=?3). The results indicated that the prepared electrode presents suitable characteristics in terms of sensitivity (458.2?±?2.6 μAcm^?2/μM), accuracy, repeatability (RSD of 1.8 %), reproducibility (RSD of 2.9 %), stability (14 days), and good catalytic activity in physiological conditions. The method was successfully applied for accurate determination of trace amounts of CFZ in pharmaceutical and clinical preparations without the necessity for samples pretreatment or any time-consuming extraction or evaporation steps prior to the analysis.     

Electrooxidation of hydrazine in alkaline medium at carbon paste electrode decorated with poly(<Emphasis Type="Italic">P</Emphasis>-phenylendiamine/ZnO) nanocomposite

In this study, poly(P-phenylenediamine/ZnO) (PpPD/ZnO) nanocomposite (NC) under ultrasonic conditions was synthesized and characterized. The presence of zinc oxide nanoparticles changed the morphology of PpPD considerably as confirmed by SEM observations. Hydrazine electrooxidation at novel modified carbon paste electrodes (CPE) with supported NC was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) techniques. Obtained results showed that the NC increases the surface catalytic activity of CPE toward hydrazine electrooxidation. The electrocatalytic current density increased linearly with hydrazine concentration, and the detection limit and sensitivity are determined to be 24 μM and 0.172 mA cm^?2 mM^?1, respectively. As revealed by the EIS measurements, the increased conductivity and decreased R _ct are owing to the presence of ZnO NPs in the PpPD matrix. The CA results indicated that hydrazine electrooxidation results in higher steady-state current density on CPE/PpDP/ZnO electrode system compared to the CPE/PpDP and CPE electrodes.     

Direct Constructions for General Families of Cyclic Mutually Nearly Orthogonal Latin Squares

Two Latin squares and , of even order n with entries , are said to be nearly orthogonal if the superimposition of L on M yields an array in which each ordered pair , and , occurs at least once and the ordered pair occurs exactly twice. In this paper, we present direct constructions for the existence of general families of three cyclic mutually orthogonal Latin squares of orders , , and . The techniques employed are based on the principle of Methods of Differences and so we also establish infinite classes of “quasi‐difference” sets for these orders.