Electron acceptor complexes

Fig. 5. Energy scheme for pho-toinduced electron transfer through an activated photosensitizer-electron acceptor complex...

Fig. 6. Sites of inhibitory action of DCMU in photosynthetic electron transport chain. The abbreviations are as follows - Cyt f cytochrome f, Fd ferredoxin, Mn water-splitting complex (manganese-containing), P680 pigment complex of photosystem II, P700 pigment complex of photosystem I, PC plastocyanin, PQ plastquinone, Q quencher, Rd NADP reductase and X direct electron acceptor complex...

Charge transfer complex — A charge transfer complex is an electron-donor-electron-acceptor complex. It is characterized by electronic transition (s) to an... 

Within the Hush formalism of electron transfer [129], the electronic coupling through hydrogen bond interfaces may be deduced from the intensity of a mixed-valence transition between juxtaposed donor-acceptor pairs. We highlight the only such detailed study in this section. Curtis and coworkers have studied a collection of hydrogen-bonded mixed-valence adducts formed between ruthenium(II) electron-donor and ruthenium(III) electron-acceptor complexes in solution [130]. Using acetonitrile or nitromethane as a solvent, hydrogen-bonded assemblies of the type [(tpy)(bpy)Ru (CN)]2, (en)2Ru (bpy) 5+ 45 (bpy = 2,2 -bipyridine, tpy = 2, 6", 2 -terpyridine, en = ethylenediamine) and [(bpy)2Ru (CN)2]2, (en)2Ru (bpy) +... 

Studies of extraction with apolar solvents and reconstitution with pure plastoquinone have offered the final demonstration of the chemical nature of A 2 [89]. Both P-682 photooxidation and the splitting of the ESR signal due to Af 2 were eliminated upon extraction of the membrane with slightly polar solvents (e.g., hexane containing traces of methanol) both phenomena could be reconstituted with pure plastoquinone [89]. As a general conclusion all these studies converge to indicate a very close similarity between PSII-RC and bacterial RC in the nature and organization of the electron acceptor complex. 

Electron Transfer Reactions and Exciolexes - Photoinduced electron transfer is one of the most important areas of research. A review of photoinduced electron transfer and electron acceptor complexes usefully surveys the subject . Details of the mechanisms can be obtained by very short time resolution spectroscopy. Dynamic solvent effects on intramolecular electron-transfer involve solvent fluctuations. Time resolved ps emission spectroscopy has been used to examine the kinetics of intramolecular charge transfer in bis(4-aminophenyl)sulphone in ethanol as a function of temperature in this respect 2. it has... 

FJE van Miegham, W Nitschke, P Mathis and AW Rutherford (1989) The influence of the quinone-iron electron acceptor complex on the reaction centre photochemistry of photosystem II. Biochim Biophys Acta 977 207-214... 

MOW Evans SG Reeves and R Cammack (1974) Determination of the oxidation-reduction potential of the bound iron-sulfur proteins of the primary electron acceptor complex of photosystem I in spinach chloroplasts. FEBS Lett 49 111-114... 

EH Evans, R Cammack and MCW Evans (1976) Properties of the primary electron acceptor complex of photosystem I in the blue green alga Chlorogloea fritschii. Biochem Biophys Res Commun 68 1212-1218... 

R Malkin (1986) On the function of two vitamin moiecuies in the PS-1 electron acceptor complex. FEBS Lett 208 343-346... 

Diner, B. A. Petrouleas, V. Wendoloski, J. J. "The Iron-Quinone Electron-Acceptor Complex of Photosystem n, PhysioL Plant. 1991,81,423-436. 

Artificial electron acceptors have the opposite effect of inhibitors. That is they relieve the build-up of electrons at a specific point arising from an inhibitor. For example, if mitochondria were treated with both antimycin A (an inhibitor) and methylene blue (an artificial electron acceptor). Complex I would be oxidized relative to CoQ, due to release of electrons from complex I to methylene blue. CoQ would remain reduced, however, because it would be blocked from transferring its electrons to the next carrier. Complex III. 

The electron acceptor complex of photosystem 2 from Phormidium laminosum. 

The redox state of components of the photosystem 2 electron acceptor complex can be investigated by measurements of the EPR signals arising from the components (1 ), or by observing the potential dependence of P680 rereduction following flash excitation in samples in which water oxidation is inhibited (2 i. In spinach, both these approaches have indicated the presence of low potential acceptors in addition to tlie two iron quinones and Qt>) and pheophytin (I). 

Redox titrations using EPR and laser flash absorption spectroscopy of the electron acceptor complex in Phormidium laminosum photosystem 2 particles which apparently lack (4) are reported as these preparations offer a model system to determine the identity of the components of the electron acceptor complex. The g=1.6 EPR signal previously described in Synechocystis has also been observed in P. laminosum (5). The redox properties and effect of inhibitors and pH on the g=1.6 signal suggest its appearance reflects the redox behaviour of Qj. ... 

EPR and laser flash kinetic absorption spectroscopy at room temperature were used to investigate the electron acceptor complex in the cyanobacterium P. laminosum. Previous redox titrations of the iron-semiquinone required the use of formate. We have now been able to titrate native samples and have shown the redox potential of is largely unaffected by the presence of formate or DCMU. 

THE INFLUENCE OF THE QUINONE-IRON ELECTRON ACCEPTOR COMPLEX ON THE REACTION CENTRE PHOTOCHEMISTRY OF PHOTOSYSTEM II... 

The Electron Acceptor Complex of Photosystem 2 from Phormidium laminosum 523... 

The Influence of the Quinone-Iron Electron Acceptor Complex on the Reaction Centre... 

The intermolecular transfer of electrons is also made easier by the formation of electron donor-electron acceptor complexes. The complex of poly[(styrene)45%-co-(l-butyl-2-vinyl pyridine)55%] and tetracyano-p-quinodimethane (with 15% tetracyano-p-quinodimethane), for example, possesses a specific conductivity of cr = 1 x 10 mho/cm. Contrary to the cross-linked, semiconducting polymers, these products are also soluble and can be cast into films. 

A second way to use benzyllithium in this one-step process is to form a lithium/electron-acceptor complex in THF before addition of the mixture of reactants. For example, lithium can be dissolved in a naphthalene solution in THF to form a dark green solution of lithium/naphthalene. When the halide-carbonyl mixture was added to an excess of this complex an extremely fast... 

Another equilibrium of interest is the formation of complexes, hi this process, complex compounds are formed by the combination of ligands with a central ion. Characteristic for complexes is the coordinate bond. It forms when an electron donor donates an electron pair to an electron acceptor. Complex formation equihbria can be depicted by the following general scheme, where M stands for a central ion and L for a hgand ... 

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