Electron transfer, from ethylene oxygen

Gollnick, K. and Held, S., Single-electron transfer from l,l-fois(p-dimethylaminophenyl)ethylene to singlet oxygen in a polar aprotic solvent, /. Photochem. Photobiol. A Chem., 59, 55,1991. 

It is clear from the kinetics that both ethylene and oxygen adsorption are important since both compounds appear in the rate equations with non-zero orders. Moreover, it is well known that ethylene is not adsorbed on pure silver, but that it does adsorb on a surface that is partially covered with oxygen. This implies that ethylene is either adsorbed on top of pre-adsorbed oxygen or on silver sites that are activated by the presence of oxygen (i.e. by formation of surface oxides, or another form of electron transfer or polarization). Consequently, two different mechanisms arise for the formation of ethylene oxide. The (direct) combustion of ethylene is another point of discussion. Although many favour the idea that different oxygen species are involved, others assume the same oxygen species, but different forms of ethylene adsorption. 

The reducing side of photosystem I (PS I) reaction center of oxygenic photosynthetic organisms is known to consist of five different acceptors (1,2). The primary electron acceptor, called AO, is assumed to be a monomeric chlorophyll molecule. An electron is passed from AO to a secondary acceptor A1 which is believed to be phylloquinone. The electron transfer involves three different iron-sulfur centers, called FX, FB and FA. PS I high-molecular-mass subunits (about 82 kDa) are known to contain AO, Al, and FX as well as P700 (1,2). FA and FB are believed to be located in a small polypeptide of about 9 kDa (3,4). As we demonstrated elsewhere (5), heat treatment of spinach PS I particles in the presence of ethylene glycol (EG) caused the selective destruction of the iron-sulfur centers and led to the dissociation of polypeptides from the particles. A small subunit of about 5 kDa was closely associated with large subunits under this treatment. In this paper, we present the N-terminal amino acid sequence of the 5 kDa polypeptide. 

Although the majority of polymers degrade thermally or photochemically by a free-radical process, there are a few examples vhere covalent bond scission occurs by electron transfer around a six-membered transition state. Thermal degradation of poly(ethylene terephthalate) [Eq. (20)] and side group cleavage in poly(methyl acrylate) and poly(tert-butyl methacrylate) are some examples vhere j5-scission of the alkyl-oxygen bond takes place from a cyclic transition state vithout free-radical formation [4]. 

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