Convergence of the fixed pivot technique for continuous Smoluchowski coagulation equation

In this work, the fixed pivot technique (FPT) [2] is analyzed for nonlinear continuous Smoluchowski coagulation equation on four different types of grids. More importantly, the FPT gives the accuracy of second order for uniform and geometric grids while it reduces the order of accuracy by one on a locally uniform grid. At the end, the scheme is unfortunately zero order accurate on random grids. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Glyphosate and glufosinate detection at electrogenerated NiAl-LDH thin films

An amperometric sensor based on Ni_1−xAl_x(OH)₂NO_3x·nH₂O layered double hydroxide (LDH) has been developed for the electrochemical analysis in one step of two herbicides: glyphosate (N-(phosphonomethyl)glycine, Glyp) and glufosinate ((DL-homoalanine-4-yl)-methylphosphinic acid, Gluf). NiAl-LDH was prepared by coprecipitation or by electrodeposition at the Pt electrode surface. Inorganic films were fully characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Adsorption isotherms of Glyp onto this inorganic lamellar material have been established. Electrocatalytic oxidation of Glyp and Gluf is possible at the Ni³⁺ centres of the structure. The electrochemical responses of the NiAl-LDH modified electrode were obtained by cyclic voltammetry and chronoamperometry at 0.49 V/SCE as a function of herbicide concentration in 0.1 M NaOH solution. The electrocatalytic response showed a linear dependence on the Glyp concentration ranging between 0.01 and 0.9 mM with a detection limit of 1 μM and sensitivity 287 mA/M cm². The sensitivity found for Gluf was lower (178 mA/M cm²).     

Theoretical study of electronic properties of organic photovoltaic materials

It has been proved that fullerene derivatives, in which an oligophenylenevinylene (OPV) group is attached to C(60), present an interesting photophysical phenomenon and can be incorporated into photovoltaic cells. In these systems, the OPV acts as electron donor upon excitation, and then fullerene absorbs photoexcited electrons. These new organic semiconductor materials offer the prospect of lower manufacturing costs and they present several advantages: easy fabrication, large area, flexible and light weight devices when compared with inorganic counter parts. In the present theoretical study, oligomeric chains of p-phenylenevinylene (n-PPV, n = 3-8 units) and C(60)-OPV hybrids have been studied by density functional theory (DFT). Electronic properties such as electronic absorption and emission spectra were calculated in order to determinate how the increment of spectroscopic units affects their electronic behavior. These properties were carried out with time dependent-density functional theory (TD-DFT) and ZINDO semiempirical method. The theoretical calculations of the structural properties of n-PPV and fullerene-OPV hybrids were obtained using PBE1PBE/6-31G and ONIOM two-layered version, respectively. All calculations were done with Gaussian 03W program package.     

Application of external micro-spectrophotometric detection to improve sensitivity on microchips

The goal of this work was to increase the sensitivity of a UV–Vis spectrophotometer by decreasing the background noise and lengthening the optical path. A microphotometer has been modified to precisely select very small parts of a microfluidic channel pattern of a chip and to measure light absorbance on a magnified area of the selected part of the channel. The viability of combining a projection microscope and a spectrophotometer for external absorbance measurements on disposable PDMS chips was studied. Besides the external direct detection above a microfluidic channel, the optical pathlength was lengthened by detecting in the region of the perpendicular exit port. Increasing the cross-sectional area of the zone of irradiation improved the signal-to-noise ratio and the limits of detection (LOD).     

Microwave‐assisted phospha‐michael addition of dialkyl phosphites,a phenyl‐H‐phosphinate,and diphenylphosphine oxide to maleic derivatives

A series of new >P(O)‐substituted succinic derivatives was synthesized by the microwave‐assisted phospha‐Michael addition of dialkyl phosphites, ethyl phenyl‐H‐phosphinate, and diphenylphosphine oxide to N‐phenyl and N‐methyl maleimide, as well as to maleic acid anhydride. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:235–240, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21007     

Controlled cell proliferation on an electrochemically engineered collagen scaffold

Therapies for corneal disease and injury often rely on artificial implants, but integrating cells into synthetic corneal materials remains a significant challenge. The electrochemically formed collagen-based matrix presented here is non-toxic to cells and controls the proliferation in the corneal fibroblasts seeded onto it. Histology and biomolecular studies show a behavior similar to corneal stromal cells in a native corneal environment. Not only is this result an important first step toward developing a more realistic, multi-component artificial cornea, but it also opens possibilities for using this matrix to control and contain the growth of cells in engineered tissues.     

The environment controlled effect of thiacalix[4]arene on the transition thermodynamics and kinetics of bovine serum albumin

Complexation ability of water-soluble thiacalix[4]arene-tetrasulfonate towards three aromatic amino acids (Phenylalanine, Tyrosine and Tryptophane) was studied in water–ethanol mixtures by photoluminescence (PL) method as a function of the ethanol content of the bulk solutions. Job’s method followed by the application of the van’t Hoff theory was used to determine the thermodynamic parameters of the molecular association. Results show quite different thermodynamics of formation of calixarene–amino acid complexes at low and higher ethanol content of the solutions. The considerable stability of the individual calixarene–aromatic amino acids complexes supports their existence also in the case when the amino acids are in a protein. To test this idea the conversion rate, enthalpy and entropy change associated to the structural transition of BSA (bovine serum albumin) were investigated by Differential Scanning Calorimetry (DSC) in the absence and in the presence of calixarene. Results show that presence of calixarene changes significantly both the thermodynamics and the kinetics of the transition of BSA and the information collected for the individual calixarene–amino acid complexes gives insights about the possible processes at molecular level.     

On the Irreducible Components of the Form Ring and an Application to Intersection Cycles

Let A be a commutative Noetherian ring and I an ideal in A. We characterize algebraically when all the minimal primes of the associated graded ring G _I A contract to minimal primes of A/I. This, applied to intersection theory, means that there are no embedded distinguished varieties of intersection. The characterization is in terms of the analytic spread of certain localizations of I, the symbolic Rees algebra, and the normalization of the Rees algebra, and extends results of Huneke, Vasconcelos, and Martí-Farré.     

Electrokinetic chromatographic characterization of novel pseudo-phases based on N-alkyl-N-methylpyrrolidinium ionic liquid type surfactants

MEKC and linear solvation free energy relationships (LSFERs) have been used to characterize the solute distribution between water and self-assemblies formed from ionic liquid type mono-chain cationic surfactants containing a cyclic pyrrolidinium head group. Several features of the solvation environment afforded by these micellar solutions were found to be quite different from that of CTAB, a structurally analogous cationic surfactant with a conventional, acyclic quaternary ammonium head group. None of the LSFER coefficients were found to vary in any systematic way with increasing alkyl chain length for these unique surfactants. Overall, however, these surfactants display different behavior than do all known cationic detergents such as CTAB. In chemical terms, pseudo-phases formed by these N-alkyl-N-methylpyrrolidinium bromides interact more strongly with polar compounds and less strongly with compounds having nonbonding or pi-electrons and are more cohesive compared to the well-studied CTAB.     

Determination of chitin and protein contents during the isolation of chitin from shrimp waste

Accurate determination of chitin and protein contents in crustacean biomass and the intermediate products during the industrial isolation of chitin cannot be made directly from the total nitrogen content, unless the appropriate corrections are applied. This method, however, is affected by the presence of other nitrogen-containing chemical species that are formed endogenously or by the action of microorganisms during the handling of the sample. Therefore, an alternative rapid method to estimate the contents of these components can be very useful both in research and in various fields of application. An original method has been developed to address this problem. The method consists of the development of a set of equations based on the stoichiometric contents of nitrogen of chitin and protein whereby the amounts of each component can be estimated from the value of the total nitrogen content, provided the rest of the proximate composition of the sample is accurately known. In order to validate the procedure, a set of model mixtures of pure chitin and protein concentrate in the solid state, both extracted from shrimp head waste, are used. Excellent agreement between the predicted and real values of chitin and protein are obtained (R2=0.98, slope=0.90). When the proposed method is tested in the analysis of real samples obtained from five different processing protocols of pretreatment of raw shrimp head, it is found that in general the values of protein and chitin contents throughout the various stages of the process vary as expected. [GRAPH: SEE TEXT] Variation of the measured total nitrogen versus calculated stoichiometric total nitrogen of the chitin-protein mixtures.