Solving matrix effect,spectral overlapping and nonlinearity by generalized standard addition method coupled with radial basis functions–partial least squares: simultaneous determination of atorvastatin and amlodipine in urine

For simultaneous determination in conditions with spectral overlap and variation of matrix effects, coupling of the generalized standard addition method (GSAM) with the multivariate nonlinear method of radial basis function–partial least squares (RBF–PLS) was proposed. The nonlinearity caused by the GSAM used to correct matrix effects was studied, and principal component analysis was proposed for identifying it. In the method introduced, the whole sensor range can be used without the collinearity problem encountered in the application of GSAM with classical least squares (CLS), and calibration can be made for each analyte, separately. The introduced method was applied to determine amlodipine and atorvastatin in urine samples. The mean of the percent recoveries was between 95 and 101.12. The percent relative standard deviation values of the method were in most cases below 5%. The results of GSAM–RBF–PLS were compared with those obtained by GSAM–CLS and GSAM–PLS. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of New Stable Phosphorus Ylides and 1,4‐Diionic Organophosphorus Compound from a Reaction between Hexamethyl Phosphorous Triamide and Dimethyl Acetylenedicarboxylate in the Presence of CH‐Acids

A simple and efficient one‐pot three‐component reaction between hexamethyl phosphorous triamide and dimethyl acetylenedicarboxylate (DMAD) in the presence of CH‐acids, such as acetylacetone, 1,3‐indandione, dibenzoylmethane, anthrone, and N,N‐dimethylbarbituric acid, has been studied. In all cases, new and stable phosphorus ylides are obtained in excellent yields. These stable ylides exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon–carbon partial double bond, resulting from conjugation of the ylide moiety with the adjacent carbonyl group. From the reaction of N,N‐dimethylbarbituric acid with DMAD in the presence of hexamethyl phosphorous triamide, a 1,4‐diionic organophosphorus compound is obtained. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 24:84–89, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21067     

Preconcentration and separation of ultra-trace palladium ion using pyridine-functionalized magnetic nanoparticles

We present a study on the application of magnetic nanoparticles (MNPs) prepared from Fe₃O₄ and functionalized with pyridine as an adsorbent for the solid-phase extraction of trace quantities of Pd(II) ion. The pyridine group was immobilized on the surface of the MNPs by covalent bonding of isonicotinamide. The modified MNPs can be readily separated from an aqueous solution by applying an external magnetic field. Effects of pH, the amount of functionalized MNPs, extraction time, type and quantity of eluent, desorption time, break-through volume and interfering ions on the extraction efficiency were optimized. The amount of Pd(II) was then determined using FAAS. Under the optimized conditions, the detection limit and preconcentration factor are 0.15?μg?L^-1 and 196, respectively, and the relative standard deviation (at 20?μgL^?1; for n?=?10) is 3.7?%. The method had a linear analytical range from 1 to 80?μg?L^-1 and was applied to determine Pd(II) in spiked tape water and soil.

Ecofriendly and efficient procedure for hetero-Michael addition reactions with an acidic ionic liquid as catalyst and reaction medium

Abstract  

1-Methylimidazolium trifluoroacetate ([Hmim]TFA) is reported as a cost-effective catalyst for a simple and environmentally benign hetero-Michael reaction. [Hmim]TFA works both as reaction medium and catalyst. The reaction is applicable to various aromatic sulfur and nitrogen nucleophiles. This method has advantages such as high yields, short reaction time, and simple workup. The catalyst could be recycled several times without any loss of activity.     

Steady hydromagnetic flow of a non-Newtonian power law fluid due to a rotating porous disk with heat transfer

The steady magnetohydrodynamic (MHD) flow of an incompressible viscous non-Newtonian power law fluid above an infinite rotating porous disk with heat transfer is studied. A uniform magnetic field is applied perpendicularly to the plane of the disk and a uniform injection or suction is applied through the surface of the disk. Numerical solutions of the nonlinear differential equations which govern the hydromagnetic and heat transfer are obtained. The effects of characteristics of the non-Newtonian fluid, the magnetic field parameter and the suction or injection velocity on the velocity and temperature distributions are considered.     

Pyridinium salts—versatile reagents for the regioselective synthesis of functionalized thiazocino[2,3-b]indoles by tandem dinucleophilic reactions of thiooxindoles

The reaction of thiooxindoles with various 2- and 3-substituted pyridinium salts afforded a variety of functionalized thiazocinoindoles. The products have been prepared in good to excellent yields by regioselective dinucleophilic C/S-cyclocondensation of thiooxindoles with pyridinium salts.     

Repeat space theory applied to carbon nanotubes and related molecular networks. III

The present article is part III of a series devoted to extending the Repeat Space Theory (RST) to apply to carbon nanotubes and related molecular networks. In this part III, four problems concerning the above-mentioned extension of the RST have been formulated. Affirmative solutions of these problems imply (i) asymptotic analysis of carbon nanotubes (CNTs) via the new techniques of normed repeat space, Banach algebra, and C*-algebra becomes possible; (ii) a new linkage is formed between the investigations of CNTs and those of ‘spectral symmetry’. In the present paper, we give affirmative solutions to all of the four problems, together with (a) estimates of the norms of matrix sequences representing CNTs, (b) Challenging Problem A^#, which complements Problems A, (c) several pictures of ‘CNT Matrix Art’ which has heuristic power to lead one to get the affirmative answers to the problems formulated in an abstract algebraic manner.     

Characterization of RF Discharge in Liquid n-Hexane and its Application to Synthesize Carbon Nano-Particles

The RF plasma discharge in liquid n-hexane is used to synthesize carbon nanoparticles. The results show that amorphous carbon nanoparticles with size of 5?C25?nm are the main product in the plasma in liquid n-hexane. Carbon nano-tubes of average diameter of 19?nm and length of 500?nm are also observed. The energy efficiency for carbon nanoparticles production is 2.9?mg/kJ which is more than 10 times larger than that of typical arc discharge synthesis method. The high speed observation indicates that the RF plasma in liquid has an alternating behaviour and it does not continuously emit light. The OES results show that H and C₂ are the main observed species in the plasma. Based on the OES data, it is shown that plasma temperature is 4,030?K and the electron density is 2.54?×?10²²?m^?3. Our results suggest that this method can be considered as a new route for carbon nanostructures production.     

Identification of volatile organic compounds in flowers of Astragalus lagopoides

Composition of volatile organic compounds (VOCs) in flowers of Astragalus lagopoides was studied using a hydrodistillation extraction procedure coupled with gas chromatography-mass spectrometry. The analyses allowed the identification of a number of 25 compounds, among which the presence of several bioactive aromatic derivatives such as guaiacol, eugenol, linalool, α- and 4-terpineol as well as nerol was attention-grabbing. Moreover, some other compounds like cyclohexane, 2-bromoethyl with repellent function also appeared to be present in the flower. As a result, the floral VOCs profile of A. lagopoides might reflect an adaptation to attract specialised pollinator insects. These findings provide important information for advances in understanding the ecological and evolutionary perspectives of pollination biology of the giant genus Astragalus.     

A critical assessment of the specific role of microwave irradiation in the synthesis of ZnO micro- and nanostructured materials

A rapid, microwave-assisted hydrothermal method has been developed to access ultrafine ZnO hexagonal microrods of about 3-4 μm in length and 200-300 nm in width by using a 1:5 zinc nitrate/urea precursor system. The size and morphology of these ZnO materials can be influenced by subtle changes in precursor concentration, solvent system, and reaction temperature. Optimized conditions involve the use of a 1:3 water/ethylene glycol solvent system and 10 min microwave heating at 150 °C in a dedicated single-mode microwave reactor with internal temperature control. Carefully executed control experiments ensuring identical heating and cooling profiles, stirring rates, and reactor geometries have demonstrated that for these preparations of ZnO microrods no differences between conventional and microwave dielectric heating are observed. The resulting ZnO microrods exhibited the same crystal phase, primary crystallite size, shape, and size distribution regardless of the heating mode. Similar results were obtained for the ultrafast preparation of ZnO nanoparticles with diameters of approximately 20 nm, synthesized by means of a nonaqueous sol-gel process at 200 °C from a Zn(acac)(2) (acac=acetylacetonate) precursor in benzyl alcohol. The specific role of microwave irradiation in enhancing these nanomaterial syntheses can thus be attributed to a purely thermal effect as a result of higher reaction temperatures, more rapid heating, and a better control of process parameters.