A vectorial algorithm with finite element method for prediction of powder segregation in metal injection molding

The design of the mold and the choice of the injection parameters for metal injection molding (MIM) is required to maintain homogeneity of the filled mixture. However, powder segregation is unavoidable in MIM because of the significant difference in densities of the metallic powder and the polymer binder. To achieve an effective prediction of segregation effect, a biphasic model based on mixture theory is employed. The viscous behaviors of each phase and the interaction coefficient between the flows of the two phases should be determined. The solution of two coupled Navier–Stokes equations results in a tremendous computation effort. The previous development of an explicit algorithm makes the biphasic simulation much faster than that of the classic methods. However, it is strongly desired to reduce or even eliminate the numerous global solutions for pressure fields at each time step. Hence, a new vectorial algorithm is proposed and developed to perform the simulation only by vectorial operations. It provides the anticipated efficiency in the simulation of biphasic modeling, and the advantage to use the classic elements of equal‐order interpolations. Some results produced by the two algorithms are compared with the experimental values to validate the new vectorial algorithm. Copyright © 2012 John Wiley & Sons, Ltd.     

A Convenient Access to Chiral Sulfonic Acids

Neomenthyl and trans myrtanyl sulfonic acids are obtained, free from inorganic salts, starting from the corresponding chiral alcohols.     

Quaterthiophene-based dimers containing an ethylene bridge: molecular design,synthesis, and optoelectronic properties

Two quaterthiophene-based dimers including an ethylene bridge have been designed and efficiently prepared; experimental and computational studies show a promising potential as semiconducting material with a charge transport of higher dimensionality compared to quaterthiophene.     

Mechanism of the Radical Copolymerization of Methyl Methacrylate and Maleic Anhydride

The kinetics of the copolymerization of methyl methacrylate and maleic anhydride was investigated in benzenic solutions at 60 and 70° C and in bulk at 60°C. The microstructure of the copolymers was determined by ¹H-NMR and IR spectrophotometry. In benzene solutions the mechanism of copolymerization involves the participation of an associative species between both comonomers. In bulk a terminal model is sufficient to explain all the results.     

Structure‐oriented UHPLC‐LTQ Orbitrap‐based approach as a dereplication strategy for the identification of isoflavonoids from Amphimas pterocarpoides crude extract

Hyphenated techniques and especially ultra‐high performance liquid chromatography‐mass spectrometry (UHPLC‐MS) are nowadays widely employed in natural products research. However, the complex nature of plant extracts complicates considerably the analysis and the identification of their constituents. Nevertheless, new MS analyzers with increased resolving power and accuracy such as the orbital trap (Orbitrap) could facilitate drastically this process. The objective of this study is the development of a new structure‐oriented approach based on fast UHPLC‐high‐resolution (HR)MS and HRMS/MS methodologies for the identification of isoflavonoids in crude extracts. In addition, aims to assist dereplication procedures, to decrease the laborious isolation steps and orient the focused isolation of compounds of interest. As a proof of concept, the methanol extract of the stem bark of Amphimas pterocarpoides (Leguminosae) was selected. Based on chromatographic (retention time, polarity) and spectrometric features (ultraviolet spectra, accurate m/z, proposed elemental composition, ring double bond equivalent, and relative isotopic abundance) as well as HRMS/MS spectra, several isoflavonoids were identified. In order to verify the proposed structures, 11 isoflavonoids were selectively isolated and unambiguously identified using 1&2D nuclear magnetic resonance techniques. Moreover, the isolated isoflavonoids were studied in HRMS/MS level, employing electrospray ionization and atmospheric pressure chemical ionization sources, in both modes. Useful information regarding their fragmentation patterns was obtained, and characteristic diagnostic ions were defined for the identification of methoxylated isoflavones, dihydroisoflavones and 5‐hydroxylated isoflavonoids. Based on the current results, the proposed dereplication strategy was verified and could comprise a novel approach for the analysis of crude extracts in the future not only for isoflavonoids but also for other chemical classes of natural products. Copyright © 2013 John Wiley & Sons, Ltd.     

Collision cell pressure effect on CID spectra pattern using triple quadrupole instruments: a RRKM modeling

Control of the ion internal energy in mass spectrometry is needed to establish a workable mass spectral library. The purpose of this study is to understand and to compare the pressure effects on the collision‐induced dissociation (CID) spectrum pattern recorded using triple quadrupole instruments. The monoprotonated Leucine enkephalin [YGGFL, H⁺] was used as a thermometer molecule to calibrate the electrospray ionization (ESI) and the CID internal energies deposited on the molecular species and the time scale of ion decompositions. The survival yield and the ratio of a₄/b₄ fragment ions were mainly monitored. The energy uptake for the ESI source geometry used in our study has no impact on the CID spectrum fingerprint. The collision cell pressure for the [YGGFL, H⁺] has a major influence on the SY curves slope and on the experimental time scale. To demonstrate the pressure effect on internal energy distribution, three models (threshold, thermal and collisional) based on RRKM theory were built using the Masskinetics software. As a result, the limit of each model is discussed, and the investigation demonstrates that the thermal model, using truncated Maxwell‐Boltzmann internal energy distribution, is well‐suited for simulating the experimental data at high pressure widely used in the analytical conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Site-specific C content by quantitative isotopic C Nuclear Magnetic Resonance spectrometry: A pilot inter-laboratory study

Isotopic ¹³C NMR spectrometry, which is able to measure intra-molecular ¹³C composition, is of emerging demand because of the new information provided by the ¹³C site-specific content of a given molecule. A systematic evaluation of instrumental behaviour is of importance to envisage isotopic ¹³C NMR as a routine tool. This paper describes the first collaborative study of intra-molecular ¹³C composition by NMR. The main goals of the ring test were to establish intra- and inter-variability of the spectrometer response. Eight instruments with different configuration were retained for the exercise on the basis of a qualification test. Reproducibility at the natural abundance of isotopic ¹³C NMR was then assessed on vanillin from three different origins associated with specific δ¹³C_i profiles. The standard deviation was, on average, between 0.9 and 1.2‰ for intra-variability. The highest standard deviation for inter-variability was 2.1‰. This is significantly higher than the internal precision but could be considered good in respect of a first ring test on a new analytical method. The standard deviation of δ¹³C_i in vanillin was not homogeneous over the eight carbons, with no trend either for the carbon position or for the configuration of the spectrometer. However, since the repeatability for each instrument was satisfactory, correction factors for each carbon in vanillin could be calculated to harmonize the results.     

Amorphous carbon nitride as an alternative electrode material in electroanalysis: Simultaneous determination of dopamine and ascorbic acid

Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CN_x) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CN_x electrode. Thus, an a-CN_x film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L⁻¹ KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CN_x electrode were 0.0656 μmol L⁻¹ for DA and 1.05 μmol L⁻¹ for AA, whereas with the BDD electrode these values were 0.283 μmol L⁻¹ and 0.968 μmol L⁻¹, respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CN_x electrode in electroanalysis.