Preparative three-dimensional GC and nuclear magnetic resonance for the isolation and identification of two sesquiterpene ethers from Dictyota Dichotoma

Separation science plays a crucial role in the isolation of novel compounds contained in complex matrices. Yet their rationale employment needs preliminary structure elucidation, which usually requires sufficient aliquots of grade substances to characterize the molecule by nuclear magnetic resonance experiments. In this study, two peculiar oxa-tricycloundecane ethers were isolated by means of preparative multidimensional gas chromatography from the brown alga species Dictyota dichotoma (Huds.) Lam., aiming to assign their 3D structures. Density functional theory simulations were carried out to select the correct configurational species matching the experimental NMR data (in terms of enantiomeric couples). In this case, the theoretical approach was crucial as the protonic signal overlap and spectral overcrowding were preventing any other unambiguous structural information. Just after the identification through the density functional theory data matching of the correct relative configuration it was possible to verify an enhanced self-consistency with the experimental data, confirming the stereochemistry. The results obtained further pave the way toward structure elucidation of highly asymmetric molecules, whose configuration cannot be inferred by other means or strategies.     

Testing the applicability of artificial intelligence techniques to the subject of erythemal ultraviolet solar radiation. Part two: an intelligent system based on multi-classifier technique

The problem we address here describes the on-going research effort that takes place to shed light on the applicability of using artificial intelligence techniques to predict the local noon erythemal UV irradiance in the plain areas of Egypt. In light of this fact, we use the bootstrap aggregating (bagging) algorithm to improve the prediction accuracy reported by a multi-layer perceptron (MLP) network. The results showed that, the overall prediction accuracy for the MLP network was only 80.9%. When bagging algorithm is used, the accuracy reached 94.8%; an improvement of about 13.9% was achieved. These improvements demonstrate the efficiency of the bagging procedure, and may be used as a promising tool at least for the plain areas of Egypt.     

Chemical composition and anticandidal properties of the essential oil isolated from aerial parts of Cotula cinerea: a rare and threatened medicinal plant in Morocco

The chemical composition and anticandidal properties of the essential oil of Moroccan Cotula cinerea aerial parts have been examined. GC-MS data were used to identify 24 constituents. Oxygenated monoterpenes constituted the main fraction with trans-thujone (41.4%), cis-verbenyl acetate (24.7%), 1,8-cineole (8.2%) and camphor (5.5%) as the major components. The anticandidal activity of the essential oil was evaluated using a panel of human pathogenic fungi (Candida albicans CCMM L4 and CCMM L5, C. krusei CCMM L10, C. glabrata CCMM L7 and C. parapsilosis CCMM L18). The oil showed high anticandidal activity against all investigated strains with minimal inhibitory concentrations of 3.2 to 4.7 mg/mL depending on the tested yeast and 5.9 mg/mL as a minimal candidicidal concentration value. These findings add significant information to the pharmacological activity of Cotula cinerea essential oil, which may present a good alternative to antibiotics for the treatment of resistant strains of Candida.     

Antimalarial activity of sesquiterpene lactones from Vernonia cinerea

Two new sesquiterpene lactones, vernolides C and D as well as six known ones were isolated from the dichloromethane fraction of an aqueous extract from Vernonia cinerea. Their structures were elucidated by spectroscopic methods. Among the known sesquiterpene lactones, three of them were described in this plant for the first time. In vitro antiplasmodial evaluation showed that the three major compounds 1, 7 and 8 were active against chloroquine resistant Plasmodium falciparum strain (W2) with IC(50) 3.9, 3.7 and 3.5 microM, respectively.     

Fabrication of a new multi-walled carbon nanotube paste electrode for stripping voltammetric determination of Ag(I)

A new modified carbon paste electrode based on multi-walled carbon nanotubes and a synthesized Schiff base of N,N'-bis(2-hydroxybenzylidene)-2,2'(aminophenylthio) ethane, acting as a chelating agent for Ag(I) ions, is described. The electroanalytical procedure for the determination of Ag(I) was comprised of two steps: the chemical accumulation of the analyte under open-circuit conditions followed by replacing the medium with a 0.1 M HCl solution where the accumulated Ag(I) was reduced for 20 s in -0.7 V. The potential was then scanned from -0.2 to +0.2 V to obtain the voltammetric peak. The effective parameters in the sensor response were examined. Under optimized operational conditions, a linear response range from 0.5-200 ng mL(-1) was obtained. The detection limit for silver determination was 0.092 ng mL(-1). For 7 successive determinations of 15.0 and 60.0 ng mL(-1) of Ag(I), relative standard deviations of 2.2% and 1.2% were obtained, respectively. The procedure was applied in determining Ag(I) in X-ray photographic films and water samples.     

Semi-exact solution for thermo-mechanical analysis of functionally graded elastic-strain hardening rotating disks

In this paper, distributions of stress and strain components of rotating disks with non-uniform thickness and material properties subjected to thermo-elasto-plastic loading are obtained by semi-exact method of Liao’s homotopy analysis method (HAM) and finite element method (FEM). The materials are assumed to be elastic-linear strain hardening and isotropic. The analysis of rotating disk is based on Von Mises’ yield criterion. A two dimensional plane stress analysis is used. The distribution of temperature is assumed to have power forms with the hotter point located at the outer surface of the disk. A mathematical technique of transformation has been proposed to solve the homotopy equations which are originally hard to be handled. The domain of the solution has been substituted by a new domain through which the unknown variable has been taken out from the argument of the function. This makes the solution much easier. A numerical solution of the governing differential equations is also presented based on the Runge–Kutta’s method. The results of three methods are presented and compared which shows good agreements. This verifies the implementation of the HAM and demonstrates its applicability to provide accurate solution for a very complicated case of strongly high nonlinear differential equations with no exact solution. It is important to notice that compared with other methods, HAM needs significant more computation time and computer hardware requirements which limit its application for those problems that other methods can easily handle them.     

Shape-selective production of zinc phosphate in aqueous and nonaqueous media using (2-hydroxyethyl) trimethylammonium hydroxide-assisted sonochemical route

Zinc phosphate molecular sieves were synthesized using zinc chloride, phosphoric acid and (2-hydroxyethyl) trimethylammonium hydroxide as template, respectively. Synthesized samples were characterized by XRD, SEM and FT-IR techniques. The morphology and crystal size of the samples were investigated using ultrasonic during aging process. Large particle size (7.2?×?20.4???m) was obtained by ultrasonication. Imperfect orthorhombic particles were obtained when the sample was mixed with magnetic stirrer; meanwhile, some rod-like particles were obtained when the mixture was stirred with ultrasonic. In addition, the rod-like ??-Zn₃(PO₄)₂·4H₂O phase was prepared using ethylene glycol as co-solvent.     

Wideband omnidirectional infrared absorber with a patchwork of plasmonic nanoantennas

In this Letter, we demonstrate experimentally that a patchwork of four metal-insulator-metal patches leads to an unpolarized wideband omnidirectional infrared absorption. Our structure absorbs 70% of the incident light on a 2.5 μm bandwidth at 8.5 μm. It paves the way to the design of wideband efficient plasmonic absorbers in the infrared spectrum.     

Investigation on the mechanical properties of sintered porous copper compacts

In line with recent attention on porous metals having low and medium porosities in the range of 20-50%, this paper studies the effect of porosity on the mechanical properties of sintered copper compacts. Experiments were designed to investigate the effect of porosity, applied stress and sliding velocity on the wear rate of copper compacts, leading to the finding that the effects of both porosity and applied stress of the wear test on the wear rate are approximately similar and higher than that of sliding velocity. The investigation concerning the effect of porosity on compressive strength indicated that the stress-strain curve of high-porosity compact exhibited identifiable ultimate strength points, though low-porosity compact showed distinct stages of elastic plastic behavior.