Electrochemical behavior and analytical detection of Imidacloprid insecticide on a BDD electrode using square-wave voltammetric method

A sensitive square-wave voltammetric method for the determination of Imidacloprid(IMD) was developed using electrochemically pretreated boron-doped diamond(BDD) electrode. Aqueous solutions were prepared with Confidor 200 SL as the commercial formulation of IMD. Sodium sulfate(Na_2SO_4) was used as supporting electrolyte. The influence of operating parameters, such as the p H of the medium, frequency, pulse amplitude, scan increment and the concentration of IMD was investigated. An irreversible cathodic peak, corresponding to the reduction of IMD is observed at 1.21 V(vs. SCE) and the electrode reaction was controlled by adsorption. Under optimized conditions, the square-wave reduction peak current was linear over the concentration range of(30–200 μmol L~(-1)) with a detection and quantification limits of 8.60 μmol L~(-1))and 28.67 μmol L~(-1)), respectively. The results were compared with spectrophotometry and HPLC methods under some conditions and found to be in good agreement.To investigate applicability to real samples, the proposed method was applied to the determination of IMD in plum juice.     

On Nash and Carlson’s Inequalities for Symmetric <Emphasis Type="Italic">q</Emphasis>-Integral Transforms

The aim of this paper is to prove an \(\mathcal {L}_q^1 \cap \mathcal {L}_q^2\) versions of Nash and Carlson’s inequalities for a class of q-integral operator \(\mathcal {T}_q\) with a bounded kernel. As applications, we give q-analogues of Nash and Carlson’s inequalities for the q-Fourier-cosine, q-Fourier-sine, q-Dunkl and q-Bessel Fourier transforms.     

More user-friendly phosphines? Molecular structure of methylphosphine and its adduct with borane, studied by gas-phase electron diffraction and quantum chemical calculations

The molecular structures of methylphosphine (CH(3)PH(2)) and methylphosphine-borane (CH(3)PH(2).BH(3)) have been determined from gas-phase electron diffraction data and rotational constants, employing the SARACEN method. The experimental geometric parameters generally showed a good agreement with those obtained using ab initio calculations and previous microwave spectroscopy studies. In order to assess the accuracy of the calculated structures a range of ab initio methods were used, including the CCSD(T) method, with correlation-consistent basis sets. The structural environment around the phosphorus atom was found to change significantly upon complexation with borane, with the P-C bond length shortening and the bond angles widening.     

Stepwise noncovalent synthesis leading to dendrimer-based assemblies in water

We provide detailed insight into complex supramolecular assembly processes by fully characterizing a multicomponent model system using dynamic light scattering, cryogenic transmission electron microscopy, atomic force microscopy, and various NMR techniques. First, a preassembly of a host molecule (the fifth-generation urea-adamantyl poly(propylene imine) dendrimer) and 32 guest molecules (a water- and chloroform-soluble ureidoacetic acid guest) was made in chloroform. The association constant in chloroform is concealed by guest self-association and is therefore higher than 10(3) M(-1). Via the neat state the single-host complex was transferred to water, where larger dendrimer-based assemblies were formed. The core of these assemblies, consisting of multiple host molecules (on average three), is kinetically trapped upon dissolution in water, and its size is constant irrespective of the concentration. The guest molecules forming the corona of the assemblies, however, stay dynamic since they are still in rapid exchange on the NMR time scale, as they were in chloroform. A stepwise noncovalent synthesis provides a means to obtain metastable dynamic supramolecular assemblies in water, structures that cannot be formed in one step.     

Preparation and chromatographic properties of a multimodal chiral stationary phase based on phenyl-carbamate-propyl-beta-CD for HPLC

A phenylcarbamate derivative of 2-hydroxypropyl-beta-CD bonded stationary phase was prepared by a previously described method. Its enantiomeric recognition abilities were evaluated as chiral stationary phase (CSP) in normal, polar organic and RP conditions by HPLC. The relevant structural features of the prepared stationary phase which make it an effective chiral selector are discussed. This material seems to have an excellent enantioselectivity for a variety of racemic analytes in the three modes. Hence it can be considered a highly effective multimodal column. Retention factor (k), selectivity (alpha) and resolution (R(s)) were the chosen parameters to describe the column performance. Optimization of these separations was discussed in terms of mobile phase composition, flow rate and structural patterns of the injected analytes.     

Numerical investigation of thermosolutal natural convection in a rectangular enclosure of an aspect ratio four with heat and solute sources

A numerical study of double-diffusive natural convection in an enclosure with a partial vertical heat and mass sources for an aspect ratio Ar = 4 has been carried out. The influence of various dimensionless parameters (Rayleigh number, buoyancy ratio, source location, Lewis number, and source length) on the flow behavior are investigated. Correlations of average Nusselt and Sherwood numbers are obtained as function of two parameters (Ra, d) and (Le, d), respectively.     

An existence result for a coupled system modeling a fully equivalent global pressure formulation for immiscible compressible two-phase flow in porous media

A new model describing immiscible, compressible two-phase flow, such as water-gas, through heterogeneous porous media is considered. The main feature of this model is the introduction of a new global pressure and the full equivalence to the original equations. The resulting equations are written in a fractional flow formulation and lead to a coupled system which consists of a nonlinear parabolic equation (the global pressure equation) and a nonlinear diffusion-convection one (the saturation equation). Under some realistic assumptions on the data, we show an existence result with the help of appropriate regularizations and a time discretization. We use suitable test functions to get a priori estimates. In order to pass to the limit in nonlinear terms, we also obtain compactness results which are nontrivial due to the degeneracy of the system.     

Synthesis and characterization of high-dimensional structure based on paradodecatungstate clusters and sodium–aminoacetic acid complex subunits

An organic–inorganic hybrid material based on paradodecatungstate building blocks and sodium–aminoacetic acid complex subunits,{Na₁₀(H₃N–CH₂–COO)₂[H₂W₁₂O₄₂]}·28H₂O (1), have been synthesized under mildly acidic conditions. This compound was characterized by single-crystal X-ray diffraction, elemental analysis, IR and UV–visible spectroscopies, and cyclic voltammetry. The compound crystallizes in the triclinic space group P-1 with a = 11.879(2) Å, b = 12.706(2) Å, c = 13.067(2) Å, α = 74.11(3)°, β = 79.71(3)°, γ = 65.95(3)°, V = 1727.2(5) Å³, and Z = 1. The crystal structure consists of infinite 2D layers constructed from [H₂W₁₂O₄₂]^10? clusters and sodium–aminoacetic acid complexes; adjacent layers are further joined by the complex units and sodium cations to yield a three-dimensional network.     

Theoretical study of hydrogen and deuterium bond in glutaric acid crystal dimer

In the spirit of the work of Blaise et al. [J Chem Phys, 2005, 122, 64306], we have extended their quantum theoretical approach by accounting for the intrinsic anharmonicity of the slow frequency mode, which is described by a Morse potential to reproduce the polarized infrared line shapes of glutaric acid dimer and its deuterium derivative at different temperatures. In this approach, the adiabatic approximation is performed for each separate H‐bond bridge of the dimer, and a strong nonadiabatic correction is introduced into the model via the resonant exchange between the fast mode excited states of the two moieties. Working within the strong anharmonic coupling theory, according to which the high‐frequency mode is anharmonically coupled to the H‐bond bridge, this approach incorporated the Davydov coupling between the excited states of the two moieties, the quantum direct and indirect dampings and the intrinsic anharmonicity of the H‐bond bridge. The spectral density was obtained within the linear response theory by Fourier transform of the damped autocorrelation functions. The numerical results show that the theoretical line shapes of the glutaric acid dimer are in fairly good agreement with the experimental ones. Using a minimum number of independent parameters, this theoretical approach fits correctly the experimental line shapes of the glutaric acid dimer. The effects of deuteration and temperature have been successfully reproduced by our calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Microstructural analysis of atomistic models of Si-rich amorphous silicon-germanium alloys

A detailed microstructural analysis of amorphous silicon-germanium alloys with Ge fraction ranging from 0.1 to 0.5 is performed by means of a numerical modeling technique. By substituting Ge atoms for Si atoms in the nanoporous paracrystalline network of amorphous silicon, several amorphous silicon-germanium structures have been generated. Our main aim in the present work is to study the effect of compositional heterogeneities on the structural properties of amorphous silicon-germanium alloys in comparison with the standard case, that of a homogeneous random distribution of the atoms. We have limited ourselves here to the borderline case, that of segregation of Ge atoms at the nanoscale. The microstructure of our structural models is analyzed by examining the macroscopic mass density, the intensity of X-ray diffraction, the pair distribution functions, the bond lengths and the coordination numbers within the first coordination shell of Si and Ge atoms. Our structural models account for the experimentally derived mass densities regardless of the Ge distribution pattern. They also account for the intense small-angle X-ray scattering observed for some amorphous silicon-germanium samples. The short-range compositional disorder, reflected in the bond lengths and the coordination numbers within the first coordination shell of Ge atoms, is found to be very sensitive to how these atoms are arranged in the alloys.