Evidences of the evolution from solid solution to surface segregation in Ni‐doped SnO2 nanoparticles using Raman spectroscopy

Ni‐doped SnO₂ nanoparticles, promising for gas‐sensing applications, have been synthesized by a polymer precursor method. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) data analyses indicate the exclusive formation of nanosized particles with rutile‐type phase (tetragonal SnO₂) for Ni contents below 10 mol%. The mean crystallite size shows a progressive reduction with the Ni content. Room‐temperature Raman spectra of Ni‐doped SnO₂ nanoparticles show the presence of Raman active modes and modes activated by size effects. From the evolution of the A_1g mode with the Ni content, a solubility limit at ∼2 mol% was estimated. Below that content, Raman results are consistent with the occurrence of solid solution (ss) and surface segregation (seg.) of Ni ions. Above ∼2 mol% Ni, the redshift of A_1g mode suggests that the surface segregation of Ni ions takes place. Disorder‐activated bands were determined and their integrated intensity evolution with the Ni content suggest that the solid‐solution regime favors the increase of disorder; meanwhile, that disorder becomes weaker as the Ni content is increased. Copyright © 2010 John Wiley & Sons, Ltd.     

Gold nanoparticles on a thiol-functionalized silica network for ascorbic acid electrochemical detection in presence of dopamine and uric acid

A simple preparation methodology able to stabilize gold nanoparticles and to obtain an electrode which detects ascorbic acid, uric acid, and dopamine by different techniques is presented. A 3-mercaptopropyl-functionalized silica network was synthesized using the sol–gel method. Gold nanoparticles (nAu) were immobilized on the material at synthesis by adding a sol of these previously prepared particles to the reaction mixture. The electrochemical behavior of the SiO₂/MPTS/Au carbon paste electrode was studied using cyclic voltammetry in the presence of a hexacyanoferrate probe molecule. The presence of nAu in the functionalized silica network changes the electrochemical characteristics of the material, favoring the electron transfer process of this complex ion. The SiO₂/MPTS/Au electrode was proven to be an efficient tool in the simultaneous determination of ascorbic acid (H₂AA), dopamine (DA), and uric acid (UA) using square wave voltammetry techniques. With the nAu on the electrode, an increase in the peak current related to the redox process of the H₂AA, DA, and UA was observed. The separations of the anodic peak potentials between DA/H₂AA and UA/H₂AA were 310 and 442?mV, respectively. The results obtained show that the SiO₂/MPTS/Au electrode can be used in the simultaneous determination of H₂AA, DA, and UA.     

The Development of Boronic Acids as Sensors and Separation Tools

Synthetic receptors for diols that incorporate boronic acid motifs have been developed as new sensors and separation tools. Utilizing the reversible interactions of diols with boronic acids to form boronic esters under new binding regimes has provided new hydrogel constructs that have found use as dye‐displacement sensors and electrophoretic separation tools; similarly, molecular boronic‐acid‐containing chemosensors were constructed that offer applications in the sensing of diols. This review provides a somewhat‐personal perspective of developments in boronic‐acid‐mediated sensing and separation, placed in the context of the seminal works of others in the area, as well as offering a concise summary of the contributions of the co‐authors in the area. DOI 10.1002/tcr.201200006     

Lightly doped La2-xSrxCuO4 as a Lifshitz helimagnet

We study the static magnetic correlations in lightly doped La2-xSrxCuO4 within the framework of a dipolar frustration model for a canted antiferromagnet. We show that the stability of the canted Néel state for x < 2% is due to the Dzyaloshinskii-Moriya and XY anisotropies. For higher doping, the ground state is unstable towards a helicoidal magnetic phase, where the transverse components of the staggered magnetization rotate in a plane perpendicular to the orthorhombic b axis. Our theory reconciles, for the first time, the incommensurate peaks observed in elastic neutron scattering with Raman and magnetic susceptibility experiments in La2-xSrxCuO4 .     

Development and validation of a novel method for the analysis of chlorinated pesticides in soils using microwave-assisted extraction–headspace solid phase microextraction and gas chromatography–tandem mass spectrometry

A new procedure for determining eleven organochlorine pesticides in soils using microwave-assisted extraction (MAE) and headspace solid phase microextraction (HS-SPME) is described. The studied pesticides consisted of mirex, α- and γ-chlordane, p,p′-DDT, heptachlor, heptachlor epoxide isomer A, γ-hexachlorocyclohexane, dieldrin, endrin, aldrine and hexachlorobenzene. The HS-SPME was optimized for the most important parameters such as extraction time, sample volume and temperature. The present analytical procedure requires a reduced volume of organic solvents and avoids the need for extract clean-up steps. For optimized conditions the limits of detection for the method ranged from 0.02 to 3.6 ng/g, intermediate precision ranged from 14 to 36% (as CV%), and the recovery from 8 up to 51%. The proposed methodology can be used in the rapid screening of soil for the presence of the selected pesticides, and was applied to landfill soil samples.     

DNA microarraying on compact disc surfaces. Application to the analysis of single nucleotide polymorphisms in Plum pox virus

The potential of using compact discs as high throughput screening platforms for DNA microarraying is discussed and applied to discriminate genetic variations of Plum pox virus.     

Screening of Food Grade Lipases to be Used in Esterification and Interesterification Reactions of Industrial Interest

Seven food grade commercially available lipases were immobilized by covalent binding on polysiloxane–polyvinyl alcohol (POS-PVA) hybrid composite and screened to mediate reactions of industrial interest. The synthesis of butyl butyrate and the interesterification of tripalmitin with triolein were chosen as model reactions. The highest esterification activity (240.63 μM/g min) was achieved by Candida rugosa lipase, while the highest interesterification yield (31%, in 72 h) was achieved by lipase from Rhizopus oryzae, with the production of about 15 mM of the triglycerides C₅₀ and C₅₂. This lipase also showed a good performance in butyl butyrate synthesis, with an esterification activity of 171.14 μM/g min. The results demonstrated the feasibility of using lipases from C. rugosa for esterification and R. oryzae lipase for both esterification and interesterification reactions.     

A kinetic study of the thermal decomposition of mesoionic compounds within scope of its application in nonlinear optical devices

The mesoionic compounds are pentagonal heterocyclic betaines with their potential use mainly in the pharmacology field due to the diversity of their biological activities. Their exceptional electric properties lead the compounds to be investigated in the field such as the nonlinear optical devices. In this study, five mesoionic compounds of the 1,3-thiazole-5-thiolate system had been synthesized from amino acids derived from glycine through 1,3-dipolar cycloaddition/cycloreversion reaction. The compounds were characterized by the use of infrared spectrometry, thermogravimetry and differential scanning calorimetry techniques. Thermal stability of each structure was determined and characterized by the kinetic study of the thermal decomposition by non-isothermal thermogravimetry. The DSC curves for MI-1, MI-2, MI-3, MI-4, and MI-5 demonstrated their fusion and subsequent decomposition with the exception of MI-3, which presented only decomposition stages. The kinetic models that better described the thermal decomposition mechanism of the mesoionic compounds achieved by the non-isothermal methods were R1, R2 and R3 (based on the geometric models).     

Thermal characterization of indinavir sulfate using TG,DSC and DSC-photovisual

The object of the present work is to study the thermal characteristics of indinavir sulfate and to evaluate the quality of the raw materials. Indinavir A, B, C and reference samples were obtained from different suppliers and submitted to TG, DSC and DSC-photovisual analyses. TG/DTG curves indicated a desolvation and dehydration processes and were confirmed by DSC. According to the DSC curves the fusion took place at about 141–142°C for indinavir C and Reference sample B and about 146–149°C for the others. DSC-photovisual showed insoluble raw materials for indinavir C at 160°C. Indinavir sulfate is highly hygroscopic drug which requires attention during storage and manufacture by pharmaceutical industry.