Reducing Antioxidant Capacity Evaluated by Means of Controlled Potential Electrolysis

An analytical method suitable for an antioxidant sensor is presented following the response of these substances to an extensive oxidation imposed by electrochemical means. The electrochemical assay simulates the action of a reactive oxygen species (ROS) by means of electrolyses carried out at a potential which is settled at the formal potential of the ROS. The antioxidant activities of trolox and ascorbic, gallic and caffeic acids and of mixtures of these antioxidants were estimated from the charge required for the complete oxidation of the antioxidants from assays where the oxidative attack by O₂ and by O₂^.? were simulated.     

Heterogeneous ceramics formed by grain boundary engineering

Two examples were selected to emphasize the potential of grain boundary engineering in the performance design of heterogeneous ceramics. Gadolinium-doped ceria-based powders were co-fired with additions of silica, and silica and lanthanum oxide, to test the silica scavenging role of lanthanum. The formation of one ionic conducting secondary phase, instead of an insulating phase, was attempted. The structural, microstructural, and electrical characterization of these samples confirmed the formation of one apatite-type lanthanum silicate-based phase and a significant enhancement of the grain boundary conductivity of these materials. One second approach addressed the formation of one mixed conductor, with electronically conductive grain boundaries, surrounding the grains of one lanthanum gallate-based electrolyte (core-shell type microstructure). Fe-doped grain boundaries were formed by selective Fe-diffusion (thermally assisted) from lanthanum ferrite screen printed layers. Combined microstructural and electrical characterization showed that the adopted solution was also effective.     

On the defect pattern evolution in sapphire irradiated by swift ions in a broad fluence range

Sapphire samples, irradiated with swift Kr (245 MeV) ions at room temperature in a broad fluence range, were investigated using a continuous and a pulsed positron beam to study the defect structure created by the passage of the ions in depths of a few micrometers. At small doses, monovacancies were identified as dominant defects and positron trapping centres. These monovacancies are assumed to be highly concentrated inside a cylindrical volume around the ion path with an estimated radius of ∼1.5 nm. For higher doses a second type of trapping centre emerges. This second class of structural imperfection was associated with the overlap of the individual ion tracks leading to the formation of larger vacancy clusters or voids.     

Room temperature photoluminescence of BCT prepared by Complex Polymerization Method

It was used the Complex Polymerization Method to synthesize barium calcium titanate powders (BCT). Crystalline Ba_0.8Ca_0.2TiO₃ perovskite-type phase could be identified by X-ray diffraction and confirmed by Raman spectroscopy in the powders heat treated at 600 °C. Inherent defects, linked to structural disorder, facilitate the photoluminescence emission. The photoluminescent emission peak maximum was around of 533 nm (2.33 eV) for the Ba_0.8Ca_0.2TiO₃. The photoluminescence process and the band emission energy photon showed dependence of both the structural order–disorder and the thermal treatment history. The results revealed that Ba_0.8Ca_0.2TiO₃ (BCT20) is a highly promising candidate material for optical applications.     

C–H···π and C=O···π Intermolecular Interactions in Dibenzyl-3,6-dimethylpyrazine-2,5-dicarboxylate

Abstract A new pyrazine compound, has been synthesised and characterised by single-crystal X-ray diffraction: monoclinic, P2₁/c with a = 11.0707(3) ?, b = 5.23700(10) ?, c = 16.6997(5) ?, β = 103.5385(16)°, Mr = 376.40, V = 941.30(4) ?³, Z = 2. Each molecule possesses C _i symmetry with the two halves of the molecule related by an inversion centre. C–H···π and C=O···π interactions held the molecules together. Index Abstract C–H···π and C=O···π intermolecular interactions in dibenzyl-3,6-dimethylpyrazine-2,5-dicarboxylate Joana A. Silva, Ana C. Santos, Ana T. Marques, Manuela Ramos Silva, Ana Matos Beja, Abílio J. F. N. Sobrala In dibenzyl-3,6-dimethylpyrazine-2,5-dicarboxylate, each molecule possesses C _i symmetry. The molecules are assembled in chains via carbonyl···π interactions. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

The Pnictogen Bond: The Covalently Bound Arsenic Atom in Molecular Entities in Crystals as a Pnictogen Bond Donor

In chemical systems, the arsenic-centered pnictogen bond, or simply the arsenic bond, occurs when there is evidence of a net attractive interaction between the electrophilic region associated with a covalently or coordinately bound arsenic atom in a molecular entity and a nucleophile in another or the same molecular entity. It is the third member of the family of pnictogen bonds formed by the third atom of the pnictogen family, Group 15 of the periodic table, and is an inter- or intramolecular noncovalent interaction. In this overview, we present several illustrative crystal structures deposited into the Cambridge Structure Database (CSD) and the Inorganic Chemistry Structural Database (ICSD) during the last and current centuries to demonstrate that the arsenic atom in molecular entities has a significant ability to act as an electrophilic agent to make an attractive engagement with nucleophiles when in close vicinity, thereby forming σ-hole or π-hole interactions, and hence driving (in part, at least) the overall stability of the system’s crystalline phase. This overview does not include results from theoretical simulations reported by others as none of them address the signatory details of As-centered pnictogen bonds. Rather, we aimed at highlighting the interaction modes of arsenic-centered σ- and π-holes in the rationale design of crystal lattices to demonstrate that such interactions are abundant in crystalline materials, but care has to be taken to identify them as is usually done with the much more widely known noncovalent interactions in chemical systems, halogen bonding and hydrogen bonding. We also demonstrate that As-centered pnictogen bonds are usually accompanied by other primary and secondary interactions, which reinforce their occurrence and strength in most of the crystal structures illustrated. A statistical analysis of structures deposited into the CSD was performed for each interaction type As···D (D = N, O, S, Se, Te, F, Cl, Br, I, arene’s π system), thus providing insight into the typical nature of As···D interaction distances and ∠R–As···D bond angles of these interactions in crystals, where R is the remainder of the molecular entity.     

ChemInform Abstract: Identification of Novel Cu,Ag, and Au Ternary Oxides from Global Structural Prediction.

Ab initio global structural prediction and specifically, the minima hopping method combined with high‐throughput calculations are used to explore the periodic table in search of novel oxide phases.     

Critical exponent of Fujita type for semilinear wave equations in Friedmann–Lemaître–Robertson–Walker spacetime

We consider the nonlinear massless wave equation belonging to some family of the Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime. We prove the global in time small data solutions for supercritical powers in the case of decelerating expansion universe.