Oxide acceptor

Lux (1939) developed an acid-base theory for oxide melts where the oxide ion plays an analogous but opposite role to that of the hydrogen ion in the Bronsted theory. A base is an oxide donor and an acid is an oxide acceptor (Lux, 1939 Flood Forland, 1947a,b Flood, Forland Roald, 1947) ... 

By acting both as a dioxygenase and as a peroxidase, this enzyme [EC 1.14.99.1] catalyzes the reaction of ara-chidonate with reduced acceptor AH2 and two dioxygen molecules to produce prostaglandin H2, oxidized acceptor A, and water. 

CO2 molecule, or Mg + and CO2 play the role of oxide acceptor to form water, carbonate, and MgC03, respectively [38]. The reactions of the iron carboxylate with these Lewis acids are thought to be fast and not rate determining. For the cobalt and nickel macrocyclic catalysts, CO2 is the ultimate oxide acceptor with formation of bicarbonate salts in addition to CO, but it is not clear what the precise pathway is for decomposition of the carboxylate to CO [33]. The influence of alkali metal ions on CO2 binding for these complexes was discussed earlier [15]. It appears the interactions between bound CO2 and these ions are fast and reversible, and one would presume that reactions between protons and bound CO2 are rapid as well. 

Hie base (GaO) is an oxide donor and (be add (SiO,) is an oxide acceptor The usefulness of the Lux-Flood definition is mostly limited lo systems such as molten oxides. 

Consider the transfer of electrons from a reduced molecule, Dred, to an oxidized acceptor, Aox. AG° for the reaction is proportional to the difference between the E° values of the two molecules (AE°). 

Two different metal-C02 complex intermediates have been proposed for the production of CO-metallocarboxylates and metal formates. The difference between the two species is based on the site of protonation, at the carbon atom in metallocarboxylates and at one of the oxygen atoms in metal formates. Carbon-protonation has not been observed experimentally, while oxygen-protonation is well known [9]. Isomerization can occur between metallocarboxylates and metal formates, and loss of a hydroxide group from the metal formate species yields the M-CO complex. Similarly, the direct reaction of metal complexes with free, dissolved C02 has also been described. In this mechanism, the metal complex reacts with an oxide acceptor, such as C02, generating the metal-CO complex and C032- [9],... 

Figure 13.7 Light-induced electron transfer (ET) between CO-bound porphyrin (PFe -CO) in haemoprotein and the oxidized acceptor protein (A). Acceptor protein can be the same protein possessing an additional active site, which can accept electrons or an externally bound protein in an oxidized state [82]...

Researchers working with glasses often think of acid-base reactions in terms of oxide donors and oxide acceptors. The oxide ion is... 

Although, as stated above, olefin epoxidation is commonly referred to as an electrophilic oxidation, recent theoretical calculations suggest that the electronic character of the oxygen transfer step needs to be considered to fully understand the mechanism [451]. The electronic character, that is, whether the oxidant acts as an electrophile or a nucleophile is studied by charge decomposition analysis (CDA) [452,453]. This analysis is a quantitative interpretation of the Dewar-Chatt-Dimcanson model and evaluates the relative importance of the orbital interactions between the olefin (donor) and the oxidant (acceptor) and vice versa [451]. For example, dimethyldioxirane (DMD) is described as a chameleon oxidant because in the oxidations of acrolein and acrylonitrile, it acts as a nucleophile [454]. In most cases though, epoxidation with peroxides occurs predominantly by electron donation from the 7t orbital of the olefin into the a orbital of the 0-0 bond in the transition state [455,456] (Fig. 1.10), so the oxidation is justifiably called an electrophilic process. 

Oxide Acceptor group Acid oxide strength (H ) modified oxide... 

The mechanism depicted in Scheme 1 may be proposed. The first step of the process is assumed to be the formation, by the reaction of Co(l) with CO2, of a cobalt-carboxylate. The presence of an alkali cation such as Li appears to be of fundamental importance for this step. The CO2 complex first reacts with another CO2 molecule and then, after being further reduced, is transformed into a carbonyl complex by an oxide transfer reaction. Here CO2 itself acts as an oxide acceptor and this indeed explains the formation of COa - concomitantly with CO. 

Fig. 12 Energy diagrams indicating recombination events in a DSC of eiectrons in TiC>2 semiconductor nanoparticle by transfer to the oxidized acceptor species of the redox coupie in the electrolyte. is the energy of the conduction band, Epo >s the equilibrium Fermi ievei in the semiconductor, that initially is in equilibrium with the redox level in the electrolyte, and fh >s the Fermi level in the semiconductor when the Xi02 photoelectrode is at the potential Fp. (a) Electron transfer from a surface state at the energy to an oxidized ion in electrolyte with probability (b) Model including the various channels for electron transfer between the surface of Ti02 nanoparticles and the oxidized species in the electrolyte (or hole conductor) in a DSC, namely, the transfer from extended states of the semiconductor conduction band with probability I ei , and the transfer from a distribution of surface states, each with a probability...

Studies of conjugated polymer-porous metal oxide (i.e., TiOa) structures have focused on optimization of the layer structure of the device and choice of polymer materials. By optimization of the device thickness and electrode choice, groups achieved photocurrent external quantum efficiency (EQE) values of 10,23, and 40 % [36-38]. The reduction of the polymer and TiOa layer thicknesses to the region of 50-100 nm is a key step for this optimization. In polymer-porous metal oxide structures, the porous metal oxide acceptor layer is normally deposited on top of a TCO substrate (i.e., ITO), the polymer is then fabricated on the metal oxide, and an evaporated metal is deposited on top of the active layers as a hole collecting contact. This polarity is the opposite of most commonly reported organic solar cell structures, so the hybrid cell is also called inverted organic solar cell. ... 

Solution reactions also show parallel and, in like terms, sensible trends. In particular, the oxygen-bridged anions Cr207, 8207 , and P207 decompose further, and hence function as stronger oxide acceptors, the smaller or more polarizing the cation (Flood and Muan, 1950 Flood and Forland, 1947b Flood and co-workers, 1947). The stability order K+ > Na+ T1+ > Li+ > Ag+ is found for... 

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