Versatile Redox Chemistry Complicates Antioxidant Capacity Assessment: Flavonoids as Milieu-Dependent Antiand Pro-Oxidants

Some antioxidants have been shown to possess additional pro-oxidant effects. Diverse methodologies exist for studying redox properties of synthetic and natural chemicals. The latter are substantial components of our diet. Exploration of their contribution to life-extending or -compromising effects is mandatory. Among reactive oxygen species (ROS), hydroxyl radical (^•OH) is the most damaging species. Due to its short half-life, the assay has to contain a specific generation system. Plants synthesize flavonoids, phenolic compounds recognized as counter-agents to coronary heart disease. Their antioxidant activities are affected by their hydroxylation patterns. Moreover, in the plant, they mainly occur as glycosides. We chose three derivatives, quercetin, luteolin, and rutin, in attempts to explore their redox chemistry in contrasting hydrogen peroxide environments. Initial addition of hydrogen peroxide in high concentration or gradual development constituted a main factor affecting their redox chemical properties, especially in case of quercetin. Our study exemplifies that a combination of a chemical assay (deoxyribose degradation) with an electrochemical method (square-wave voltammetry) provides insightful data. The ambiguity of the tested flavonoids to act either as anti- or pro-oxidant may complicate categorization, but probably contributed to their evolution as components of a successful metabolic system that benefits both producer and consumer.     

Temperature and Composition‐Induced Structural Transitions in Bi1−xLa(Pr)xFeO3 Ceramics

Bi_1?xLa_xFeO₃ and Bi_1?xPr_xFeO₃ ceramics of the compositions near the morphotropic phase boundary have been studied by X‐ray and neutron diffraction techniques and differential thermal analysis. The structural phases characterized by the long‐range polar, antipolar, and nonpolar ordering as well as the phase coexistence regions have been identified using the diffraction data depending on the dopant concentration and temperature. As a result of these studies the three phase region has been observed for the Pr‐doped compounds and the phase diagrams have been constructed. The detailed evolution of the structural parameters permitted to itemize the factors affecting the structural phase transitions and clarify the origin of the enhanced electromechanical properties in these materials. The performed structural analysis disclosed different character of the chemical bonds in the La‐ and Pr‐doped BiFeO₃ compounds. Further, the role of the rare‐earth ions in the covalency of the chemical bonds is discussed.     

Performance comparison of modified poly(vinyl alcohol) based membranes in alkaline fuel cells

There are several problems which are holding back the use of fuel cells. The utilization of fuel cells depends on the start-up costs which are very high due to the use of expensive materials for their construction. In that respect, we describe a cost-effective alkaline fuel cell (AFC) that uses solid, polymer based, membrane instead of conventionaly used, highly concentrated, corrosive, liquid alkaline electrolyte. This approach to AFC is potentially the basis of a simple, low-cost system, that can solve one of the problems of the highly-efficient and environment-friendly AFC.The focus of this paper are low cost composite alkaline membranes, based on poly(vinyl alcohol) (PVA). The PVA matrix is made by solution cast method and gamma irradiation crosslinking. Three different types of membranes are obtained in this manner - plain PVA membrane, PVA membrane cross-linked using gamma irradiation (γ-PVA) and composite PVA membrane doped with Mo (PVA-Mo). These membranes are immersed in the alkaline solution and investigated as anion exchange membranes. The performance of the solid alkaline fuel cells (SAFCs) containing these PVA membranes has been studied under hydrogen and oxygen gas flow on the Pt/C catalyst. Both, γ-PVA and PVA-Mo membranes are modified to absorb larger amounts of alkaline solution than the PVA membrane, thus greatly improving the performance of the SAFC, in terms of output power. This is clearly indicated in the polarisation curves. The electrochemical impedance spectroscopy measurements during the SAFC operation were also performed to give better insight in the effect observed. Investigation presented in this paper clearly indicates that solid alkaline PVA membranes can be used for the construction of the SAFCs.     

Thermal stability, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of PrNi0.4Fe0.6O3−δ, a potential cathode material for IT-SOFCs

The potential use of a double B mixed-perovskite as a promising cathode material in intermediate temperature solid oxide fuel cells (IT-SOFCs) has been anticipated as a result of this work. A thorough investigation of some important parameters like thermal stability, thermal expansion, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of the PrNi_0.6Fe_0.4O_3−δ ceramic sample have been investigated as functions of temperature (20-1000 °C) and oxygen partial pressure (0.6-21,000 Pa). According to the measurements, the composition was phase stable at pO₂ > 1 Pa up to 1000 °C and shows p-type semiconductivity with a low conductivity versus pO₂ dependence.The perovskite has been found to have comparable thermal expansion coefficients with those of commonly used solid electrolytes like CeO₂ and ZrO₂ based oxides. In case of the chemical diffusion experiments higher oxygen diffusion mobility observed during reduction processes in comparison with those during oxidation have been explained by the already known formation of neutral defect clusters.     

Noncovalent interactions of amino acids with fullerene C60: A dispersion-corrected DFT study

By using the general gradient approximation functional PBE with Grimme's empirical dispersion correction in conjunction with the double numerical basis set DNP, we studied the noncovalent interaction of twenty proteinogenic l-amino acids (AAs) with fullerene C₆₀. The calculations were performed both under vacuum conditions and in aqueous medium. We analyzed the calculated geometries and binding energies for AA+C₆₀ complexes, the shape of HOMO and LUMO orbitals and the corresponding gap energies. Generally, we found a poor correlation between binding energies calculated for AA+C₆₀ complexes in aqueous medium and hydrophobicity scales proposed by other other authors. Despite of C₆₀ cage can be envisioned as a typical hydrophobic surface, the AA adsorption apparently takes place according to a mechanism different from classical hydrophobic interactions, or due to a combination of several types of interactions with a limited contribution of hydrophobic mechanism.     

Recent Theoretical Results for Nonequilibrium Deposition of Submicron Particles

Selected theoretical developments in modeling of deposition of sub-micrometer size (submicron) particles on solid surfaces, with and without surface diffusion, of interest in colloid, polymer, and certain biological systems, are surveyed. We review deposition processes involving extended objects, with jamming and its interplay with in-surface diffusion yielding interesting dynamics of approach to the large-time state. Mean-field and low-density approximation schemes can be used in many instances for short and intermediate times, in large enough dimensions, and for particle sizes larger than few lattice units. Random sequential adsorption models are appropriate for higher particle densities (larger times). Added diffusion allows formation of denser deposits and leads to power-law large-time behavior which, in one dimension (linear substrate, such as DNA), was related to diffusion-limited reactions, while in two dimensions (planar substrate), was associated with evolution of the domain-wall and defect network, reminiscent of equilibrium ordering processes.     

Mutating aspartate in the calcium-binding site of {alpha}-lactalbumin: effects on the protein stability and cation binding

The residue Asp87, which is in the calcium-binding loop of bovine     

X-ray photoelectron spectroscopy study of the initial growth of transition metal nanoscale films on (100) Si substrates

The initial growth stages of materials non-active to a substrate has been extensively studied for decades, whereas there had been fewer studies on the initial growth of active metals on silicon substrate, despite its technological importance. In this paper the very early growth stages of transition metal (Ti, V and Nb) films deposited by rf sputtering on unheated (100) Si substrate were studied by in situ X-ray photoelectron spectroscopy. The following sequence of the phase composition and the growth mechanism changes during deposition process was revealed. Initially in a submonolayer regime, small 3D TiO₂ islands are formed via reduction of a native silicon oxide layer on a substrate followed by formation of a TiO phase between TiO₂ islands and on their top. After deposition of ca. 2 monolayers a metallic Ti phase appears and later only the metal Ti film grows. The same growth behavior takes place at Nb and V deposition with a difference that in the case of Nb the above changes occur at earlier stages what can be explained by the highest niobium activity to the reduction of silicon oxide in the row V, Nb, Ti.