Application of NiTi alloy coated with ZrO2 as a new fiber for solid-phase microextraction for determination of halophenols in water samples

A new fiber for solid-phase microextraction (SPME) employing a metallic support coated with an inorganic material is proposed. A nitinol alloy (NiTi) was used as the support material due to its super elasticity and shape memory properties. Zirconium oxide (ZrO₂) was electrodeposited onto NiTi using chronoamperometry. The surface characteristics and morphology of the coated and uncoated support were evaluated through scanning electronic microscopy and dispersive energy microanalysis. This assembly was applied in the extraction of three halophenols from aqueous samples. A multivariate approach was used for optimization of the variables involved in the system. The Doehlert matrix was used for evaluation of the best derivatization conditions and a Box-Behnken design to obtain the best extraction conditions. In order to investigate the repeatability, one fiber was used for six extraction tests under similar conditions and the relative standard deviations (R.S.D.) were lower than 12.5%. Detection limits were lower than 0.30 ng mL⁻¹. Correlation coefficients were higher than 0.997. Extraction efficiency of the NiTi-ZrO₂ fiber was similar to a PDMS 7 μm commercial fiber, even though it had a lower coating thickness of 1.35 μm. Considering the amount extracted per unit volume, the NiTi-ZrO₂ fiber had a better extraction profile when compared to commercial fibers. The new SPME fiber has a lifetime of over 500 extractions. Thus, it is a promising alternative for low-cost analysis, as the proposed fiber is robust, and easily and inexpensively prepared.     

Accounting for the dependence of P(E',E) on the maximum impact parameter in classical trajectory calculations: application to the H2O-H2O collisional relaxation

In this work we report a novel methodology that is able to predict how energy transfer transition probability density functions [P(E',E)] change with the maximum impact parameter (bmax) used in trajectory calculations (TC's). The method assumes that P(E',E) can be described by a sum of exponential functions and that all the trajectories with an initial impact parameter beyond a certain critical value will contribute only to the elastic peak [P(E',E) for E'=E]. This approach is applied to H2O-H2O collisions at different initial vibrational energies of the excited molecules and temperatures of bath gas. The results show that it is possible to reproduce with high accuracy the whole P(E',E) obtained from a given bmax, using the results of TC's performed at another bmax. The new methodology also leads us to propose a new criterion to choose the value of bmax.     

Dehydrogenation of ethylbenzene to styrene using Pt, Mo, and Pt-Mo catalysts supported on clay nanocomposites

A synthetic clay (TS-1) was modified with a nonionic surfactant (IGEPAL CO-720) and magnesium oxide. The resulting solid was used as a support of Pt, Mo, and Pt-Mo catalysts. The catalysts were prepared by wet impregnation with aqueous solutions of H(2)PtCl(6)6H(2)O and (NH(4))(6)-Mo(7)O(24)4H(2)O. In both monometallic and bimetallic catalysts, the molybdenum content was 3 wt% and the platinum content was 0.5 or 1 wt%. The surface area of the starting material was 454 m(2)/g and after the modification treatment with IGEPAL it increased up to 649 m(2)/g, while platinum and molybdenum catalysts showed surface areas between 495 and 550 m(2)/g. The reduction profiles showed different Pt and Mo species and the existence of metal-support interactions. The reduced catalysts were more active than those in the unreduced form. The most active catalysts for the ethylbenzene dehydrogenation were those of monometallic Pt (0.5 and 1 wt%) with a maximum styrene conversion around 50%. The presence of Mo species masked Pt atoms and reduced the activity.     

Sequential quenching of randomly deposited ellipsoids: anisotropy and spatial patterns

We studied the sequential quenching of prolate ellipsoids on a homogeneous surface by using our proposed pair potential whose repulsive part was that of hard ellipses and attractive part was the r-6 pairwise attraction. Both the strength and range parameters for the attraction were functions of the orientations of the pair of ellipses and related by epsilon proportional, variantsigma-lambda. The parameter lambda determines the relative strength of the side-by-side and end-to-end attractions and thus plays an important role in determining the alignment of the particles. We adopted the value lambda=2.19 by using point-energy additivity to compute the minimum energies for both of these configurations for a pair of ellipsoids of revolution with aspect ratio of 2:1. We investigated the effect of temperature and the parameter lambda on the alignments of ellipses. Both radial distribution function, g(r), and orientational correlation function, G(r), show the expected longer ranges of orientational correlation at lower temperatures and show higher degree of orientational order for lambda=3.5 than lambda=2.19 and 0.10. This can also be seen in the examples of configurations showing that for lambda=3.5, ellipses are more aligned than lambda=2.19 and 0.1.     

Facile isolation of bisimines based on 3,3'-diaminobenzidine: direct access to unsymmetrical bimetallic salphen building blocks

Diimines obtained from 3,3'-diaminobenzidine and tert-butyl-substituted salicylaldehydes in MeOH can be readily isolated in 60-90% yield and were obtained as a mixture of geometrical isomers. Two distinct diimine intermediates (4 and 5) with a higher molecular symmetry as related to the other isomeric diimine products were both isolated by crystallization of which 5 was subsequently used to demonstrate that nonsymmetrical bis-salphen complexes with different functional groups and metal centers can be assembled via a three-component one-pot procedure.     

Glucose oxidation reaction at palladium-carbon nano-onions in alkaline media

Journal of Solid State Electrochemistry - The glucose oxidation reaction, at Pd on unsupported carbon nano-onions (Pd/CNOs), has been studied by using physical and electrochemical characterization...     

New insights about the electrochemical production of ozone

Ozone is a rather attractive oxidant, it is very efficient in the oxidation of pollutants and in the killing of pathogens and does not generate any hazardous waste during its use. Its generation has been constantly sought in an effective way, focusing on obtaining high concentrations of ozone at the lowest possible cost. Recently, electrochemical production of ozone show advantages over conventional corona discharge generation, since this technology do not need very high voltages, feeding oxygen or pure air or dissolving the ozone into wastewater to be treated. However, it is still at early development stage and there is still a long way to reach the high technology readiness levels needed to complete its value chain. Equipment considerations and operation conditions are the key points that need to be understood in order to increase efficiently. Recent novelties in the state of the art of research are summarized in this work.     

Unraveling the Bonding Nature Along the Photochemically Activated Paterno-Büchi Reaction Mechanism

The photochemically activated Paterno-Büchi reaction mechanism following the singlet excited-state reaction path was analyzed based on a bonding evolution framework. The electronic rearrangements, which describe the mechanism of oxetane formation via carbon-oxygen attack (C−O), comprises of the electronic activation of formaldehyde and accumulation of pairing density on the O once the reaction system is approaching the conical intersection point. Our theoretical evidence based on the ELF topology shows that the C−O bond is formed in the ground-state surface (via C−O attack) returning from the S₁ surface accompanied by 1,4-singlet diradical formation. Subsequently, the reaction center is fully activated near the transition state (TS), and the ring-closure (yielding oxetane) involves the C−C bond formation after the TS. For the carbon-carbon attack (C−C), both reactants (formaldehyde and ethylene) are activated, leading to C−C bond formation in the S₁ excited state before reaching the conical intersection region. Finally, the C−O formation occurs in the ground-state surface, resulting from the pair density flowing primarily from the C to O atom.     

A Bibliometric Evaluation of the Top 100 Cited Dimethyl Fumarate Articles

Dimethyl fumarate is a cytoprotective and immunomodulatory drug used in the treatment of multiple sclerosis. We performed a bibliometric study examining the characteristics and trends of the top 100 cited articles that include dimethyl fumarate in the title. On 21 September 2020 we carried out an electronic search in the Web of Science (WOS), seeking articles that include the following terms within the title: dimethyl fumarate, BG-12, or Tecfidera. To focus our investigation on original research, we refined the search to include only articles, early access, others, case report, and clinical trials. We obtained a total of 1115 items, which were cited 7169 times, had a citation density of 6.43 citations/item, and an h-index of 40. Around 2010, there was a jump in the number of published articles per year, rising from 5 articles/year up to 12 articles/year. We sorted all the items by the number of citations and selected the top 100 most cited (T100). The T100 had 4164 citations, with a density of 37 citations/year and contained 16 classic research articles. They were published between 1961 and 2018; the years 2010–2018 amassed nearly 80% of the T100. We noted 17 research areas with articles in the T100. Of these, the number one ranking went to neurosciences/neurology with 39 articles, and chemistry ranked second on the T100 list with 14 items. We noticed that the percentage of articles belonging to different journals changed depending on the time period. Chemistry held the highest number of papers during 1961–2000, while pharmacology andneurosciences/neurology led the 2001–2018 interval. A total of 478 authors from 145 institutions and 25 countries were included in the T100 ranking. The paper by Gold R et al. was the most successful with 14 articles, 1.823 citations and a density of 140.23 citations/year. The biotechnological company Biogen led the T100 list with 20 articles. With 59 published articles, the USA was the leading country in publications. We concluded that this study analyzed the use of and research on dimethyl fumarate from a different perspective, which will allow the readership (expert or not) to understand the relevance of classic and recent literature on this topic.