Studying of antifungal activity of functionalized multiwalled carbon nanotubes by microwave‐assisted technique

In this paper, we reinforced the antifungal activity of multi‐walled carbon nanotubes (MWCNTs) using an effective technique. Covalent functionalization of MWCNTs was performed by lysine and arginine under microwave radiation. To prove functionalization phenomenon, the grafted chemical groups on the surfaces of MWCNTs were analyzed by Fourier transform infrared and Raman spectroscopy. Antifungal activities of functionalized MWCNTs as well as pristine MWCNTs were tested against different fungal species based on minimal inhibitory concentration (MIC) and radial diffusion assay. MIC results showed that the antifungal activity of MWCNTs‐lysine, in comparison to pristine MWCNTs against fungi, including Aspergillus niger, Aspergillus fumigatus, Candidate albicans, Penicillium chrysogenum, Saccharomyces cerevisiae, Fusarium culmorum, Microsporum canis, Trichophyton mentagrophytes, Trichophyton rubrum and Penicillium lilacinum were increased 1.92, 2.36, 2.35, 1.3, 1.5, 1.1, 2.54, 1.23, 1.42 and 2.1 times, respectively. Similarly, the antifungal activity of MWCNTs‐arginine was increased 1.98, 2.40, 2.55, 1.8, 1.9, 1.7, 2.64, 1.36, 2.1 and 2.55 times, respectively. On the basis of the results of this study, it is clearly indicated that covalent groups of lysine and arginine could improve the antifungal activity of MWCNTs. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of 3-nitroaniline in water samples by directly suspended droplet three-phase liquid-phase microextraction using 18-crown-6 ether and high-performance liquid chromatography

Liquid–liquid–liquid microextraction (LLLME) with directly suspended droplet in high-performance liquid chromatography (HPLC) has been applied as a new, rapid and easy method for the determination of 3-nitroaniline in environmental water samples. The target compound was extracted from the aqueous sample solution (donor phase, pH 13) into an organic phase and then was back-extracted into a directly suspended droplet of an acidic aqueous solution (acceptor phase, pH 0.3). In this method, without using a microsyringe as supporting device, an aqueous large droplet is freely suspended at the top-center position of an immiscible organic solvent, which is laid over the aqueous sample solution while being agitated. Then, the droplet was withdrawn into the microsyringe and directly was injected into the HPLC system with UV detection at 227 nm. Up to 148-fold enrichment of the analyte could be obtained under the optimal conditions [i.e. donor phase: 0.1 M sodium hydroxide solution (4.5 mL); organic phase: o-xylene/1-octanol (90:10, v/v; 250 μL); acceptor phase: 0.5 M hydrochloric acid and 500 mM 18-crown-6 ether (6 μL); extraction time: 60 s; back-extraction time: 6 min and stirring rate: 600 rpm]. The limit of detection was 1 μg/L (n = 7) and the relative standard deviation (RSD, n = 5) was 4.9 at S/N = 3. The calibration graph was linear in the range of 5–1500 μg/L with r = 0.9983. All experiments were carried out at room temperature (22 ± 0.5 °C).     

Magnetotransport and magnetoelastic effects in Co-doped La0.7Sr0.3MnO3 nanocrystalline perovskites

La_0.7Sr_0.3Mn_1−xCo_xO₃ (x=0, 0.05, 0.1) nanoparticles, prepared by sol-gel method, were studied by means of X-ray diffraction, transmission electron microscopy, resistivity, magnetoresistance, thermal expansion and magnetostriction measurements. Results show that partial substitution of Mn by Co leads to a reduction in lattice parameters, enhancement of resistivity and room temperature magnetoresistance MR, decrease of metal-insulator transition temperature T_MI and T_C, an increase in thermal expansion coefficient, volume magnetostriction and anisotropic magnetostriction. The latter increases about one order of magnitude with 10% Co substitution. In comparison with Mn ions, the Co ions possess higher anisotropy energy, larger magnetostriction effect, smaller ionic size and spin state transitions with increase in temperature and magnetic field; this suggests that Co substitution leads to double-exchange interaction weakening, resulting in suppression of ferromagnetic long-range order and metallic state and increase of magnetic anisotropy. Furthermore, our samples have a relatively lower T_MI and T_C, higher resistivity and MR, compared with the reported values for similar compounds with larger particle sizes. This is attributed to the nanometric grain size and spin-polarized tunneling between neighboring grains.     

Wake-boundary layer interaction behind an elliptic cylinder at different Reynolds numbers

In this paper, hot-wire anemometry (HWA) is used to experimentally investigate interactions between a fully developed turbulent boundary layer and wake of an elliptic cylinder where axis ratio (AR) of the cylinder is 2. The elliptic cylinder was located inside and outside a turbulent boundary layer with a thickness (δ) of 0.38B. Furthermore, experiments were conducted at different Reynolds numbers (13,250 and 26,500) based upon the smallest cylinder diameter (B). Mean velocity, turbulence intensity and higher-order central moments of velocity signals (i.e. skewness and flatness) measurements were performed using HWA upon wake-boundary layer interactions on a flat plate. Results showed that profiles of stream-wise mean velocity and turbulence intensity were greatly dependent on gap ratio (G/B) and Reynolds number (Re) in near-wake region. It was also observed that, except for G/B = 0.1, the wake-boundary layer interactions were faster at Reynolds number of 26,500 rather than 13,250. The interactions occurred earlier upon fluctuating the velocity rather than the case where a fixed mean velocity was considered. The results further show that an increase in the gap ratio increases Strouhal number almost independent of δ/B. Behind the cylinder, relatively smaller wake region was obtained at Re = 26,500 rather than Re = 13,250, where the velocity profiles quickly converged to the flat plate boundary layer velocity profiles.     

Biological synthesis of silver nanoparticles in Tribulus terrestris L. extract and evaluation of their photocatalyst,antibacterial, and cytotoxicity effects

In recent years, progress of biological synthesis of nanoparticles is inevitable due to its important applications. In this research, a new and simple method for the synthesis of AgNPs from plant extracts is presented. The extract from shoots of the plant Tribulus terrestris L. was mixed with AgNO₃ with the aim of biologically synthesizing AgNPs. The biomolecules existing in the extract were accountable for the fast reduction of silver ions (Ag⁺) to AgNPs. Characterization of biosynthesized AgNPs was performed by UV–Vis, TEM, DLS, and XRD. The AgNPs exhibit a strong peak at 434 nm, and sphere-shaped AgNPs were found to be ~?25 nm. The biosynthesized silver nanoparticles have demonstrated high antibacterial effect against pathogenic bacteria (i.e., Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa). In addition, the in vitro cytotoxicity effect of biosynthesized silver nanoparticles was also investigated and was detected to be up to 15.62 μg/mL in the treated Neuro2A cells. The plant-mediated biosynthesis of AgNPs has comparatively rapid, eco-friendly, inexpensive and wide-ranging application in modern medicine and the food industry.

     

Magnetic solid‐phase extraction of polycyclic aromatic hydrocarbons in water samples by Fe3O4@polypyrrole/carbon nanotubes

A magnetic solid‐phase extraction method coupled with gas chromatography was proposed for the determination of polycyclic aromatic hydrocarbons in the environmental water samples. The magnetic adsorbent was prepared by incorporating Fe₃O₄ nanoparticles, multi‐walled carbon nanotubes, and polypyrrole. The main factors affecting the extraction efficiency including the amount of the sorbents, desorption conditions, extraction time, salt concentration, and sample solution pH were investigated and optimized. Under the optimum conditions, good linearity was obtained within the range of 0.03?100 ng/mL for all analytes, with correlation coefficients ranging from 0.9942 to 0.9973. The method detection limits (S/N = 3) were in the range of 0.01–0.04 ng/mL and the limits of quantification (S/N = 10) were 0.03–0.1 ng/mL. Repeatability of the method was assessed through five consecutive extractions of independently prepared solutions at concentrations of 0.1, 10, and 100 ng/mL of the compounds. The observed repeatability ranged 3.4–10.9% depending of the compound considered. The proposed method was successfully applied in the analysis of PAHs in environmental samples (tap, well, river, and wastewater). The recoveries of the method ranged between 93.4 and 99.0%. The procedure proved to be efficient and environmentally friendly.     

Algal transformation of hydrocortisone by the cyanobacterium Nostoc ellipsosporum

The potential of Nostoc ellipsosporum for biotransformation of hydrocortisone was studied. The microorganism was isolated during a screening program from soil samples collected from the paddy fields in the north of Iran and had not been previously examined for this purpose. The biotransformation yielded 11β,17α,20β, 21-tetrahydroxypregn-4-en-3-one and 11β-hydroxyandrost-4-ene-3,17-dione. Both of the metabolites were purified chromatographically and characterized using instrumental analyses. Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 572–574, November–December, 2006.     

Determination of Trace of Methyl tert-Butyl Ether in Water Using Liquid Drop Headspace Sampling and GC

The possibility of applying headspace microextraction into a single drop of solvent for the determination of methyl tert -butyl ether in aqueous solutions has been demonstrated. A drop of benzyl alcohol is used for extraction. The analyte is extracted by suspending a 1.8 μL extracting drop directly from the tip of a microsyringe fixed above an extraction vial with a septum such that the needle passes through the septum and the needle tip is positioned above the surface of the solution. After the extraction is finished, the drop is retracted back into the needle and injected directly into a GC column. Optimization of experimental variables (time, temperature, stirring rate and ionic strength of the solution) with respect to the extraction efficiency was investigated. The calibration range for methyl tert-butyl ether was 0.01–10 ppm and the detection limit 7 ppb. The relative standard deviation for 0.1 ppm methyl tert -butyl ether in water was 5.5%.     

Biological synthesis and characterization of gold nanoparticles using Verbascum speciosum Schrad. and cytotoxicity properties toward HepG2 cancer cell line

Research on Chemical Intermediates - Gold nanoparticles (AuNPs) are considered as one of the best modes of drug releasing plans for the treatment of various diseases. AuNPs have different...