The thermal conductivities enhancement of mono ethylene glycol and paraffin fluids by adding β-SiC nanoparticles

Changes in the thermal conductivities of paraffin and mono ethylene glycol (MEG) as a function of β-SiC nanoparticle concentration and size was studied. An enhancement in the effective thermal conductivity was found for both fluids (i.e., both paraffin and MEG) upon the addition of nanoparticles. Although an enhancement in thermal conductivity was found, the degree of enhancement depended on the nanoparticle concentration in a complex way. An increase in particle-to-particle interactions is thought to be the cause of the enhancement. However, the enhancement became muted at higher particle concentrations compared to lower ones. This phenomenon can be related to nanoparticles interactions. An improvement in the thermal conductivities for both fluids was also found as the nanoparticle size shrank. It is believed that the larger Brownian motion for smaller particles causes more particle-to-particle interactions, which, in turn, improves the thermal conductivity. The role that the base-fluid plays in the enhancement is complex. Lower fluid viscosities are believed to contribute to greater enhancement, but a second effect, the interaction of the fluid with the nanoparticle surface, can be even more important. Nanoparticle-liquid suspensions generate a shell of organized liquid molecules on the particle surface. These organized molecules more efficiently transmit energy, via phonons, to the bulk of the fluid. The efficient energy transmission results in enhanced thermal conductivity. The experimentally measured thermal conductivities of the suspensions were compared to a variety of models. None of the models proved to adequately predict the thermal conductivities of the nanoparticle suspensions.     

Electrocatalytic oxidation of nitrite at a terpyridine manganese(II) complex modified carbon past electrode

A carbon past electrode modified with [Mn(H₂O)(N₃)(NO₃)(pyterpy)], ( \textpyterpy = 4￠- ( 4 - \textpyridyl ) - 2,2￠:\text6￠,\text2￠￠- \textterpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and nitrite can be determined in the ranges of 5.00 × 10⁻⁶ to 1.55 × 10⁻² mol L⁻¹, with a detection limit of 8 × 10⁻⁷ mol L⁻¹. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10⁻², 0.56× 10⁻⁶, and 7.99 × 10⁻⁶ cm² s⁻¹, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed. This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior, anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical purposes.     

Voltammetric measurement of trace amount of glutathione using multiwall carbon nanotubes as a sensor and chlorpromazine as a mediator

In this work, we propose chlorpromazine as a new mediator for the rapid, sensitive, and highly selective voltammetric determination of glutathione (GSH) using multiwall carbon nanotubes paste electrode (MWCNTPE). The experimental results showed that the carbon nanotubes paste electrode has a highly electrocatalytic activity for the oxidation of GSH in the presence of chlorpromazine as a mediator. Cyclic voltammetry, double potential step chronoamperometry, and differential pulse voltammetry (DPV) are used to investigate the suitability of chlorpromazine at the surface of MWCNTPE as a mediator for the electrocatalytic oxidation of GSH in aqueous solutions. It is shown that chlorpromazine can catalyze the oxidation of GSH in an aqueous buffer solution to produce a sharp oxidation peak current at about +0.70 versus Ag/AgCl as a reference electrode. Kinetic parameters such as electron transfer coefficient and catalytic reaction rate constant, k/h, are also determined. Using DPV and under the optimum conditions at pH 4.0, the electrocatalytic oxidation peak current of GSH shows a linear dependence on GSH concentration in the GSH concentration range of 0.3 to 18.3 µM. The detection limit (3σ) is determined to be 0.16 µM. The relative standard deviation for 1.5 and 5.0 µM GSH are found to be 3.7% and 2.5%, respectively. The proposed method may, thus, also be used as a novel, selective, simple, and precise method for the voltammetric determination of GSH in such real samples as hemolyzed erythrocyte.     

A study of the electrochemical behavior of an oxadiazole derivative electrodeposited on multi-wall carbon nanotube-modified electrode and its application as a hydrazine sensor

In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT−GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k _s, and the charge transfer coefficient, α, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4 ± 0.5 s⁻¹ and 0.51, respectively at pH = 7.0. The obtained results indicate that hydrazine peak potential at OMWCNT−GCE shifted for 14, 109, and 136 mV to negative values as compared with oxadiazole-modified GCE, MWCNT−GCE, and activated GCE surface, respectively. The electron transfer coefficient, α, and the heterogeneous rate constant, k′, for the oxidation of hydrazine at OMWCNT−GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0 μM and 10.0 to 400.0 μM and detection limit of 0.17 μM for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT−GCE was shown to be successfully applied to determine hydrazine in various water samples.

     

Separation and identification of a new saponin from the flowers of Guaiacum officinale L

A triterpenoid saponin, guaianin O (1), oleanolic acid 3-O-{α-L-rhamnopyranosyl-(1 → 2)-[β-D-glucopyranosyl-(1 → 3)]-α-L-arabinopyranoside}-28- O-[β-D-glucopyranosyl]-ester, was isolated from the n-butanol extract of flowers of Guaiacum officinale L. The structural elucidation of 1 was accomplished by extensive studies of both one and two dimensional 1H, 13C-NMR spectra, the FAB mass spectrum, and alkaline and acid hydrolyses.     

A simple and rapid dispersive liquid-liquid microextraction method followed by GC-FID for determination of N-methylpyrrolidine in cefepime

A simple, rapid and efficient sample preparation technique, dispersive liquid-liquid microextraction, coupled with gas chromatography-flame ionization detection has been developed to determine N-methylpyrrolidine in cefepime. The effect of various experimental factors on the preparation procedure, such as the nature and volume of extraction and disperser solvents, extraction time, the nature of buffer and its pH, and salt effect, was investigated, optimized and the following results were obtained: extraction solvent, chloroform; dispersive solvent and solvent for dissolving cefepime, a mixture of methanol/water (88:12, v/v); salting out agent, NaCl; and buffer, carbonate/bicarbonate (C=0.5?M, pH=12). The optimized conditions were applied to the real sample (cefepime) for the extraction and determination of N-methylpyrrolidine. The calibration graph is linear from 0.02 to 850?mg/L with the square of correlation coefficient 0.999. LOD and LOQ are 6.4 and 21.2?μg/L in solution, respectively, and 0.2 (2×10(-5) ) and 0.6 (6×10(-5) ) μg/g (%, w/w) in cefepime powder, respectively, using sample size 50?mg. Repeatability of the method is good and RSD% for six repeated experiments (C=170?mg/L) is 6.35%.     

Optimized ultrasound‐assisted extraction procedure for the analysis of opium alkaloids in papaver plants by cyclodextrin‐modified capillary electrophoresis

This study investigated the use of ultrasound‐assisted extraction to improve the extraction efficiency of morphine, codeine and thebaine from the papaver plants. Extraction conditions such as type of solvent, temperature, duration, frequency and power level of ultrasonic were optimized and the influences of different parameters on resolution of alkaloids in CE were studied. The optimized condition for CE separation includes a sodium phosphate buffer (100 mM, pH 3.0) containing 5 mM α‐CD. The optimized extraction conditions for ultrasound‐assisted extraction was an extraction time of 1 h, an ultrasonic frequency of 60 kHz with water–methanol (80:20) at 40°C as the extraction solvent. The LOD for alkaloids was found to be 0.1 μg/mL at a signal‐to‐noise ratio of 3:1. The RSDs for peak areas were in the range of 1.4–4.4%. The amounts of opium alkaloids (mg/100 g dried sample) in four Iranian papaver plants were found to be in the range of 7.8–8.7 (morphine), 5.5–9.5 (codeine) and 1.4–10.4 (thebaine). It should be emphasized that no cleanup of the filtered extract was required; hence, direct determination after extraction drastically simplifies the analytical process.     

Étude structurale de britholite au césium Sr7La2Cs(PO4)5(SiO4)F2

Several studies demonstrated the ability of britholites to retain radionuclides such as the caesium and actinides. Therefore, three compounds with formulas Sr₈LaCs(PO₄)₆F₂, Sr₇La₂Cs(PO₄)₅(SiO₄)F₂ and Sr₂La₇Cs(SiO₄)₆F₂, were prepared by solid state reaction. However, it seems that only the mono-silicated composition was obtained in a pure state. In this present work, the X-ray diffraction and magnetic nuclear resonance have been used to investigate the structure for this composition. The results showed that in fact this phase was not pure, but it was mixed with a secondary phase, SrLaCs(PO₄)₂. The refinement by the Rietveld method allowed also to precise the distribution of La³⁺ and Cs⁺ ions between the two cationic sites of the apatite.     

Quantitative determination of chemical constituents from seeds of Nigella sativa L. using HPLC-UV and identification by LC-ESI-TOF

An HPLC method was developed for the simultaneous determination of nine compounds of Nigella sativa L. The separation was achieved within 23 min by using C18 column material, a water-acetonitrile mobile phase, both containing 0.1% acetic acid gradient system and a temperature of 35 degrees C. The method was validated for linearity, repeatability, LOD, and LOQ. The LOD and LOQ of nine compounds were in the range of 0.09-10 and 0.3-25 microg/mL, respectively. The wavelength used for quantification with the diode array detector was 205 and 260 nm. LC/MS coupled with electrospray ionization interface method is described for the identification of compounds in N. sativa L. samples. This method involved the use of [M+H]+ and [M+Na]+ ions in the positive ion mode with extracted ion chromatogram.     

In vitro antitumor and antibacterial assay of organotin(IV) complexes of 2,3-methylenedioxybenzoic acid; X-ray crystal structure of [(C2H5)2Sn(C8H5O4)2]

New organotin(IV) compounds containing the carboxylate ligand 2,3-methylenedioxybenzoic acid (HL) have been synthesized with the general formula R₂SnL₂ (R = Me, Et, n-Bu, Ph and n-Oct) and R₃SnL (R = n-Bu). All compounds have been studied in the solution state by multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn) by using the non-coordinating solvent and also in solid sate by FTIR, mass spectrometry and X-ray crystallography. Spectroscopic data have shown that methylenedioxy moiety does not coordinate with tin atom and the coordination site is actually -COO group, as is proved by X-ray structure determination. The solid state structure of compound (2) has been determined by X-ray crystallography which shows that the complex (2) has distorted octahedral geometry. These complexes have been evaluated in vitro against crown gall tumor and antibacterial activity. Interesting results were noticed during the bio-activity screenings, which proved their in vitro biological potential and possible use as drugs.