Ultra high performance liquid chromatography with mass spectrometry method for the simultaneous determination of phenolic constituents in honey from various floral sources using multiwalled carbon nanotubes as extraction sorbents

An ultra high performance liquid chromatography with mass spectrometry method has been developed for the simultaneous separation, identification and determination of 22 phenolic constituents in honey from various floral sources from Yemen. Solid‐phase extraction was used for extraction of the target phenolic constituents from honey samples, while multiwalled carbon nanotubes were used as solid‐phase adsorbent. The chromatographic separation of all phenolic constituents was performed on a BEH C₁₈ column using a linear gradient elution with a binary mobile phase mixture of aqueous 0.1% formic acid and methanol. The quantitation was carried out in selected ion reaction monitoring acquisition mode. The total amount of phenolic acids, flavonoids and other phenols in each analyzed honey was found in the range of 338–3312, 122–5482 and 2.4–1342 μg/100 g of honey, respectively. 4‐Hydroxybenzoic acid was found to be the major phenolic acid. The main detected flavonoid was chrysin, while cinnamic acid was found to be the major other phenol compound. The regeneration of solid phase adsorbent to be reused and recovery results confirm that the proposed method could be potentially used for the routine analysis of phenolic constituents in honey extract.     

Fatigue behaviour and structural health monitoring by acoustic emission of E-glass/epoxy laminates with piezoelectric implant

This paper represents the continuation of our research on built-in piezoelectric sensor for structural health monitoring of composite materials. Experimental research is focused on examining the effects of the embedded sensors on the structural integrity of composite laminates subjected to mechanical tests. A series of composite specimens with and without embedded sensor are tested in fatigue loading while constantly monitoring the response by acoustic emission technique. The acoustic signals are analysed using the classification k-means method in order to identify the different damage mechanisms and to follow the evolution of these mechanisms for both types of composite materials (with and without sensor). The mechanical behaviour of composites with and without embedded sensor shows no difference in the form. The incorporation of piezoelectric sensor causes low degradation of mechanical properties of composites. Comparing embedded sensor to sensor mounted on the surface, the embedded sensor showed a much higher sensitivity. It is thus verified that the embedded acoustic emission sensor had great potential for acoustic emission monitoring in fibre reinforced composite structures.     

Gas‐phase fragmentation study of a novel series of synthetic 2‐oxo‐2H‐benzopyrano[2,3‐d]pyrimidine derivatives using electrospray ionization tandem mass spectroscopy measured with a quadrupole orthogonal time‐of‐flight hybrid instrument

The fragmentation patterns of a series of six novel synthesized benzopyranopyrimidine derivatives 1–6, possessing the same 2‐oxo‐2H‐benzopyrano[2,3‐d]pyrimidine backbone structure, were investigated by electrospray ionization mass spectrometry (ESI‐MS) and tandem mass spectrometry (MS/MS) techniques using a quadrupole orthogonal time‐of‐flight (QqToF)‐hybrid instrument. The series of six pure benzopyranopyrimidine compounds contained three constitutional isobaric isomers (compounds 4–6). A simple methodology, based on the use of ESI (positive ion mode) and increasing the declustering potential in the atmospheric pressure/vacuum interface resulting in collision‐induced dissociation (CID), was used to enhance the formation of the product ions. In general, the novel synthetic benzopyranopyrimidine derivatives 1–6 afforded exact accurate masses for the protonated molecules. This led to the confirmation of both molecular masses and chemical structures of the studied compounds. The breakdown routes of the protonated molecules were rationalized by conducting low‐energy CID‐MS/MS analyses. It was shown that the MS/MS fragmentation routes for the protonated molecules 1 and 2 were similar, and that the MS/MS fragmentations of the constitutional isobaric protonated molecules 5 and 6 were identical. It was also shown that the gas‐phase CID fragmentations of 5 and 6 were different from that of their constitutional isomer 4. Finally, the ESI‐MS and CID‐MS/MS analyses of the protonated molecules that were obtained from the monodeuterated benzopyranopyrimidine derivatives 1–6 confirmed the values obtained for the exact masses, the precise structural assignments of all product ions and all the pathways described in the proposed CID fragmentations. Copyright © 2008 John Wiley & Sons, Ltd.     

Polyvinyl alcohol-acid redox active gel electrolytes for electrical double-layer capacitor devices

Journal of Solid State Electrochemistry - Since the mechanism of charge storage in electrical double-layer capacitors (EDLCs) relies on diffusion of ions into the pores of the electrodes, in...     

The removal of methylene blue as a remedy of dye-based marine pollution: a photocatalytic perspective

Research on Chemical Intermediates - The effluents containing the discarded water from the textile industry are graded as one of the foremost pollutants in all industrial sectors. The wide...     

Theoretical study of the second-order nonlinear optical properties of [N]helicenes and [N]phenylenes

The second-order nonlinear optical properties of helicenes and phenylenes have been theoretically investigated at the time-dependent Hartree-Fock level using the Austin model 1 semiempirical Hamiltonian. Both the antisymmetric isotropic component of the first hyperpolarizability (beta) and its projection on the dipole moment (beta(parallel)) have been determined for increasingly large helical systems as well as for their analogs substituted by donor/acceptor pairs. It is found that (i) in nonsubstituted helicenes and phenylenes, beta increases monotonically with the size of the system and slightly depends on the nature of the helix; (ii) the corresponding beta(parallel) is mostly determined by the radial component of the first hyperpolarizability vector; (iii) in helicenes, beta(parallel) is positive and presents quasiperiodic oscillations with the helix; (iv) in phenylenes, beta(parallel) depends upon the size of the helix and it can be either positive or negative as a result of the differences in evolution with N of the radial components of the dipole moment and first hyperpolarizability. Substituting the helicenes and phenylenes by the prototypical NH2/NO2 donor/acceptor pair provides a diversity of effects on beta and beta(parallel) that encompasses decrease, increase, and change in sign.     

Preparation and structural characterization of tetracoordinated tungsten(II) diazadiene complexes

Reduction in situ of WCl₄(MeCN)₂ with zinc in the presence of diazadiene ligands 1b-f is reported and produces a series of diamagnetic complexes (DAD)WCl₂2b-f. All complexes were characterized by ¹H, ¹³C NMR and IR spectroscopic data. The crystal structures of complexes 2b and 2e were solved by X-ray diffraction methods.     

One-step synthesis of ultra-small amount of Pd-Alloyed Zinc Nanosheets for efficient electrochemical CO2 reduction to CO

The practicality of the electrochemical CO₂ reduction technique depends on the development of cost-effective, robust, and highly selective catalysts. To achieve this goal, we have engineered self-supported 3D electrodes composed of Pd-Zn nanosheets (NSs) for CO₂ electrochemical reduction to CO with minimal Pd content. This innovative electrode with an increased surface area was created using an electrodeposition method employing a dynamic hydrogen bubble template. By precisely adjusting the Pd content, we improved the thickness, porosity, and surface area of the electrodes, resulting in a CO₂-to-CO selectivity reaching as high as 88.5 %, with an average of at least 80 % sustained over 10 hours. This remarkable improved activity can be attributed to the synergistic effects of an appropriate Pd/Zn atomic ratio as well as to the large surface area of nanosheets structures with rich edge active sites. Furthermore, to get around the limitations of CO₂ mass transfer, reactions were done at high pressures conditions ranging from 3 to 9.5 bar; this strategic approach yielded an outstanding partial current density of −304.6 mA cm⁻² for CO. These noteworthy findings establish concepts for constructing effective and earth-abundant CO-producing electrocatalysts.