Electron microscopy characterization of nanostructured carbon obtained from chlorination of metallocenes and metal carbides

In this work we report some new well-defined carbon nanostructures produced by direct chlorination of metallocenes (ferrocene and cobaltocene) and NbC, at temperatures from 100 to 900 degrees C. Thus, amorphous carbon nanotubes with variable dimensions depending on reaction temperature were produced from ferrocene. When cobaltocene is the carbon precursor the main product are solid amorphous nanospheres. The high refractory metal carbide NbC as carbon source favours the growth of nanospherical cabbage-like particles with a higher degree of graphene sheets order. Besides, NbC crystallites encapsulated in an amorphous carbon shell were also found at lower temperatures (T< or =700 degrees C).     

Raman Optical Activity (ROA) as a New Tool to Elucidate the Helical Structure of Poly(phenylacetylene)s

Poly(phenylacetylene)s are a family of helical polymers constituted by conjugated double bonds. Raman spectra of these polymers show a structural fingerprint of the polyene backbone which, in combination with its helical orientation, makes them good candidates to be studied by Raman optical activity (ROA). Four different well‐known poly(phenylacetylene)s adopting different scaffolds and ten different helical senses have been prepared. Raman and ROA spectra were recorded and allowed to establish ROA‐spectrum/helical‐sense relationships: a left/right‐handed orientation of the polyene backbone (M_helix/P_helix) produces a triplet of positive/negative ROA bands. Raman and ROA spectra of each polymer exhibited the same profile, and the sign of the ROA spectrum was opposite to the lowest‐energy electronic circular dichroism (ECD) band, indicating a resonance effect. Resonance ROA appears then as an indicator of the helical sense of poly(phenylacetylene)s, especially for those with an extra Cotton band in the ECD spectrum, where a wrong helical sense is assigned based on ECD, while ROA alerts of this misassignment.     

A multicommuted stop-flow system employing LEDs-based photometer for the sequential determination of anionic and cationic surfactants in water

It has been developed an automatic stop-flow procedure for sequential photometric determination of anionic and cationic surfactants in a same sample of water. The flow system was based on multicommutation process that was designed employing two solenoid micro-pumps and six solenoid pinch valves, which under microcomputer control carry out fluid propelling and reagent solutions handling. A homemade photometer using a photodiode as detector and two light emitting diodes (LEDs) with emission at 470 nm (blue) and 650 nm (red) as radiation sources, which was tailored to allow the determination of anionic and cationic surfactants in waters. The procedure for anionic surfactant determination was based on the substitution reaction of methyl orange (MO) by the anionic surfactant sodium dodecylbenzene sulfonate (DBS) to form an ion-pair with the cetyl pyridine chloride (CPC). Features such as a linear response ranging from 0.35 to 10.5 mg L⁻¹ DBS (R = 0.999), a detection limit of 0.06 mg L⁻¹ DBS and a relative standard deviation of 0.6% (n = 11) were achieved. For cationic surfactant determination, the procedure was based on the ternary complex formation between cationic surfactant, Fe(III) and chromazurol S (CAS) using CPC as reference standard solution. A linear response range between 0.34 and 10.2 mg L⁻¹ CPC (R = 0.999), a detection limit of 0.05 mg L⁻¹ CPC and a relative standard deviation of 0.5% (n = 11) were obtained. In both cases, the sampling throughput was 60 determinations per hour. Reagents consumption of 7.8 μg MO, 8.2 μg CPC, 37.2 μg CAS and 21.6 μg Fe(III) per determination were achieved. Analyzing river water samples and applying t-test between the results found and those obtained using reference procedures for both surfactant types provide no significant differences at 95% confidence level.     

Multicommutation-NIR determination of Hexythiazox in pesticide formulations

A multicommutated flow-system was designed in order to increase analytical throughput and for controlling thermal effects on the NIR spectra for determination of Hexythiazox in pesticide formulations. An on-line standard addition was carried out showing the versatility and repeatability of multicommutation for the on-line mixing and dilution of solutions. Results obtained for commercial samples were statistically comparable with those obtained by an HPLC-reference method. Multicommutation-NIR allows the analysis of 52 samples per hour, in front of the 30 samples per hour analyzed by the NIR-batch procedure and the 7 samples per hour analyzed by HPLC-reference method.     

Research note on evaluation of the plastic deformation of beams under transverse impact

The permanent deformation of a rigid perfectly plastic beam subjected to a time-dependent line load is calculated. The beam has finite length, and the load is applied transversely in the middle of the span. At the initial time, the load is zero. Thereafter, the load has a triangular time dependence. For sufficiently large values of the peak load, static and moving plastic hinges appear, and the beam is subjected to plastic bending. Previous studies of this problem have provided a numerical solution of a system of approximate equations. In this article, a numerical solution of the system of exact equations is provided. The numerical results represent a significant improvement over those that were previously available.     

Core–shell nanogels by RAFT crosslinking polymerization: Synthesis and characterization

A synthetic methodology is described for the preparation of core–shell nanogels by reversible addition‐fragmentation chain transfer. Well‐defined macro chain transfer agents (macro‐CTA's) were prepared in a first step using monomers that yield sensitive polymers. In the second step, a crosslinker alone or with the addition of a functionalized comonomer were used to form a crosslinked core. The ratio of crosslinker to macro‐CTA is crucial to yield nanogels. Furthermore, the polymerization time has an impact in the architecture of the nanomaterial obtained: it evolves from a core‐crosslinked star to a core–shell nanogel. Controlling the molecular weight of the macro‐CTA and the type of comonomer in the core forming step, core–shell nanogels with hydrodynamic diameters from 22 to 168 nm and a core that represents from 35 to 77% of the size, were prepared containing functional groups in the core which could be used as catalytic scaffolds. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

Assessment of enzyme-linked immunosorbent assay for the determination of 2,4,5-TP in water and soil

A highly sensitive and specific indirect enzyme-linked immunosorbent assay is described for Silvex, 2-(2,4,5 trichlorophenoxy)propionic acid, (2,4,5-TP). One specific feature of the immunoassay is the use of simple chemical activation of chlorophenoxy acids to prepare both the immunizing and coating conjugates. The assay is based on the use of polyclonal antibodies raised against 2,4,5-TP, and a peroxidase-labeled secondary antibody for colorimetric detection. The effect of different chemical conditions (pH, and salt and detergent concentration) on immunoassay performance has been studied. Under the best conditions the least detectable dose and the sensitivity (IC(50)) for 2,4,5-TP were 0.05 micro g L(-1) and 0.80 micro g L(-1), respectively. The optimized immunoassay was also highly specific, showing little (6.9% for 2,4,5-T) or no cross-reactivity with other similar herbicides. The assay was used to determine 2,4,5-TP in water and soils. The excellent recoveries obtained (mean values ranging between 89% and 104%) make this immunoassay a suitable screening method for either environmental monitoring or laboratory quantification of 2,4,5-TP.     

Phase-object analysis with a speckle interferometer

We describe the characteristics of a double-exposure specklegram obtained through a double-aperture system, by introduction of a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and visibility of the interferometric fringes in the Fourier plane are analyzed. An alternative interferometric technique for phase-object detection is proposed.