Free Energy Of Oxidation Research Articles

New molten metal catalysts for CO2 and CH4 conversion to 2 : 1 H2 : CO syngas.

Activity trends for 22 metals and metal alloys are reported for the conversion of CO2 and CH4 to 2 : 1 H2 : CO syngas and carbon. A correlation is observed between CO2 conversion and the free energy of oxidation by CO2 on pure metal catalysts. Indium and indium alloys activate CO2 at the highest rates. We identify a new bifunctional 20 : 80 mol% Sn-In alloy that activates both CO2 and CH4 while catalyzing both reactions.

Influence of thermochemical activation of wood on the physicochemical properties of lignin

The wood matrix is a lignin–carbohydrate nanobiocomposite, thermodynamically quasi-equilibrium heterogeneous system of biopolymers. Changing its thermodynamic equilibrium due to directed chemical and (or) physical impacts opens up new approaches to the study of plant objects. Thermochemical activation, including treatments in sub- (steam explosion) and supercritical conditions (supercritical fluid extraction) having similar mechanisms of action, is one such method. The effect of steam explosion is determined by two components — chemical (the catalytic effect of formed acetic and formic acid) and physical (a sharp adiabatic expansion). The main components of supercritical treatment are increased temperature and pressure in the CO2 medium with cosolvents. The chemical component of this treatment is due to the addition of chemical reagents. Such treatments lead to a change in the thermodynamic state and capillary-porous structure of the lignin–carbohydrate matrix, an increase in its heterogeneity, and the yield of extracted lignin preparations. Lignin is the most reactive component of the wood matrix, and these processes result in changes in its functional nature and reaction properties. Thus, the lignin sample extracted after steam explosion had the greatest increase in the content of phenolic hydroxyl (by 39 rel.%) and carboxyl (by 57 rel.%) groups. Change in the functional composition of lignin leads to a change in its redox state, characterized by the oxidative potential and free energy of oxidation. It was shown that lignin after steam explosion had the highest oxidative potential and the lowest value of the oxidation energy, which indicated the greatest change in its reactivity in redox interactions.

Effects of Annealing on an IGZO-Metal Interface.

The interface reaction between a metal layer and a layer of amorphous indium-gallium-zinc oxide was investigated. Oxygen atoms at the interface bond to the metal atoms and form metal oxide. The reaction depends on the annealing temperature and ambient conditions. The thickness of the metal oxide at the interface increased with the annealing temperatures. The reaction relies on the Gibbs free energy for oxidation. Ta, which has low Gibbs free energy formed a 33 nm layer of tantalum oxide at an annealing temperature of 450 °C. The HR-TEM and EDX observation showed that the metal oxide thicknesses were 5, 10, and 33 nm at annealing temperatures of 350, 400, and 450 °C, respectively. The thicknesses obtained with both Ar and oxygen gas were 4, 8, and 21 nm, respectively. The lower oxide thicknesses were attributed to the lower number of oxygen vacancies in the IGZO deposited using Ar and oxygen, which was identified by XPS analysis.

Selected hydroxycoumarins as antioxidants in cells: physicochemical and reactive oxygen species scavenging studies

A set of seven hydroxycoumarin derivatives (1–7) were tested to evaluate their antioxidant properties. These molecules were selected on the basis of the number of hydroxyl groups and the presence of electron‐donating and electron‐withdrawing groups in their scaffolds. Electrochemical studies showed that oxidation process occurs at low potentials, especially with the catechol‐containing coumarins. Electron spin resonance (ESR) experiments corroborated the formation of semiquinone radicals in all compounds. The antioxidant properties against peroxyl and hydroxyl radicals were evaluated using two different assays, namely oxygen radical antioxidant capacity (ORAC) and non‐catalytic Fenton system by ESR measurements. Our results indicated that monohydroxycoumarin derivatives (1 and 2) displayed better ORAC values relative to the standard molecule Trolox. These values are comparable with known flavonoids such as quercetin and catechin. On the other hand, compounds bearing catechol and resorcinol groups, including derivative 4, gave high hydroxyl radical‐scavenging properties. Antioxidant properties were further rationalized using density functional theory calculations. The theoretical results showed good trends among the obtained experimental data, calculated bonding dissociation enthalpy, highest occupied molecular orbital values, free energies of oxidation (ΔGox) and spin density distribution. Finally, in vitro studies revealed low toxicity for most of the coumarins studied. The cytoprotection assays in bovine aortic endothelial cells indicated that compounds 1 and 2 showed better protective properties against peroxynitrite and hydrogen peroxide‐induced cell death than dihydroxycoumarin derivatives. Using confocal microscopy, we have observed intracellular compartmentalization. These results confirm that 1 or 2 would be a good target for future in vivo studies against oxidative stress. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of Cation Substitution on Bipolar Resistance Switching Behavior in Epitaxially Grown NiO Films

Epitaxial NiO films (epi-NiO) were successfully doped with Al by performing sequential deposition of NiO and AlOx by pulsed laser deposition. Surface morphology and crystallinity were confirmed by atomic force microscope images and X-ray diffraction, indicating that the samples were grown epitaxially. Resistance switching (RS) phenomena of Al-doped NiO films were investigated using epitaxial SrRuO3 (SRO) and CaRuO3 (CRO) as the bottom (BE) and top electrode (TE), respectively. When the epi-NiO/SRO interface was modified by inserting either a 1-nm-thick epitaxial AlOx layer or a 5-nm-thick epitaxial 10% Al-doped NiO (Al0.1Ni0.9Ox) layer, the RS of epi-NiO remained unchanged. However, when the CRO/epi-NiO interface was modified by inserting a 1-nm-thick epitaxial AlOx layer or a 5-nm-thick Al0.1Ni0.9Ox layer, switching behavior was significantly changed; in the case of the 1-nm-thick epitaxial AlOx layer, the switching behavior completely disappeared, while in the case of 5-nm-thick Al0.1Ni0.9Ox layer, number of cells which exhibited RS was drastically decreased. The switching phenomena may be suppressed due to the presence of Al cations whose free energy for oxidation is much lower than that of Ni. Our experimental results suggest that oxygen ions migration at the TE/epi-NiO interface may play a critical role in bipolar RS of epi-NiO. The relation between RS and free energy for oxidation is discussed.

Microstructures of Oxidized Primary Carbides on Superalloy Inconel 718

The oxidation behavior of carbides on Inconel 718 surface was investigated. Oxidation tests were performed at the temperature range of 300 to 650°C. Two types of carbide, NbC and TiC were detected, and the amount of NbC was significantly higher than that of TiC. The oxidation of NbC started at the carbide surface and the matrix interface, and propagated into the interior of the carbide and eruption subsequently occurred with increasing oxidation time. In case of TiC, the oxidation occurred at the outer surface of the carbide and the matrix interface, but did not propagated into the interior of the carbide. Oxides formed on the outer surface of the TiC contained a relatively large amount of elemental Nb. The cross-section of oxidized specimen was investigated. NbC was oxidized more easily due to the significantly lower Gibbs free energy of oxidation than that of TiC. Eruption occurred mainly at the NbC because the Pilling-Bedworth ratio of Nb is higher than the critical value of 2.3 where eruption typically occurs.

Novel Methods of Forming Self-Assembled Nanostructured Materials: Ni Nanodots in Al<SUB>2</SUB>O<SUB>3</SUB> and TiN Matrices

We have developed two novel methods of growing self-assembled nanodot arrays of uniform size (diameter 2-50 nm) of a variety of materials in crystalline as well as amorphous matrices. These methods employ a pulsed laser deposition technique and are classified as: (a) sequential growth method; and (b) simultaneous growth method. In the first method, the nanodots and matrix material are formed sequentially, while in the second method, nanodots and matrix materials grow simultaneously. In the sequential growth, self-assembly of nanodots is controlled by the flux of materials, interfacial energy, intervening matrix layer, substrate and laser parameters. For the simultaneous growth method of self-assembly of nanodots, there is additional requirement that the material of the nanodot and the matrix should be such that the Gibb's free energy of oxidation of the constituent of matrix material is much lower than that of the nanodot material.

Interaction between catabolism and anabolism in the oxidative assimilation of dissolved organic carbon

Catabolism is tightly coupled to anabolism in substrate-limited cultures. However, the dissolved organic carbon (DOC) distribution between catabolism and anabolism has been hardly studied. Based on a balanced DOC reaction, the DOC distribution between catabolism and anabolism was defined using a ratio of the DOC channeled into CO2 (\(S_{CO_2 } \)) to that DOC converted to biomass (Sg). A \(S_{CO_2 } \)/Sg-dependent growth yield model was proposed for substrate-limited cultures and was verified using the literature data obtained in the oxidative assimilation processes of different types of organic substrates. The model showed that the growth yield (Ys) was proportional to anabolic activity, but was inversely related to catabolic activity. Results indicated that both Ys and \(S_{CO_2 } \)/Sg varied markedly with the free energy of oxidation of the organic substrate. Further, the observed phenomena were closely associated with maintenance metabolism under substrate-limited conditions.

Electrostatic control of midpoint potentials in the cytochrome subunit of the Rhodopseudomonas viridis reaction center.

The photosynthetic reaction center of Rhodopseudomonas viridis has four hemes in a linear arrangement with alternating high- and low-potential sites. Their midpoints are -60, 20, 310, and 380 mV [Dracheva, S. M., Drachev, L. A., Konstantinov, A. A., Semenov, A. Y., Skulachev, V. P., Arutjunjan, A. M., Shuvalov, V. A. & Zaberezhnaya, S. M. (1988) Eur. J. Biochem. 171, 253-264]. Electrostatic calculations reproduce the 440-mV midpoint spread and assignments of high- and low-potential hemes. When calculations on model compounds to connect the theoretical midpoints to the standard hydrogen electrode are used, the absolute electrochemical midpoints for the reaction center hemes are also in good agreement with experiment. The free energy of oxidation is found to be dependent on pairwise interactions with charged amino acids, heme propionic acids, previously oxidized hemes, and axial ligands and on the reaction field induced by heme oxidation.

Thermodynamic properties of the V2O3−V4O7 system at temperatures from 1400° to 1700°K

Phase equilibria in the V2O3−V4O7 system were studied at 1400°, 1500°, 1600°, and 1700°K by varying the oxygen partial pressure. Besides the three phases of V2O3, V3O5, and V4O7 which were stable in this system, the vanadium sesquioxide has an extensive range of solid solution at the above mentioned temperatures. The standard free energies of oxidation of both V2O3 to V3O5 and V3O5 to V4O7 were precisely determined on the basis of equilibrium oxygen partial pressures at each above temperature. The standard enthalpy and the entropy changes of these reactions were also calculated from the free energy data.

Energy Concepts of Aerobic Microbial Metabolism

Three different energy concepts of cell yield are investigated using synthesis data measured in mixed aerobic cultures for 15 different substrates. These include, the energy-synthesis concepts of McKinney, Servizi and Bogan, and McCarty. Growth, substrate removal, and oxygen uptake measurements at 25○ C. are correlated with various thermodynamic functions including enthalpy and free energy. Efficiency measurements based upon free energy computations agree with McCarty's results. However, the study results conflict with the magnitude of cell yield per unit change of free energy of oxidation as estimated by Servizi and Bogan. Conclusions regarding the validity of McKinney's heat loss-cell yield relationship were not possible although the proportionality between heat of reaction and oxygen utilization was verified. This latter relationship is based upon hypothetical oxidative assimilation equations computed from the experimental data and assumed protoplasm formulations. Substrates used in the study included compounds representing the basis food substances of carbohydrates, fatty and amino acids.