Coupling, isolated electrons

The direct measurement of CH,- radicals, using a matrix isolation electron spin resonance system (MIESR), has previously demonstrated that surface-generated CH,-radicals are produced during the oxidative coupling of CH4 and emanate into the gas phase... 

H+-ATPase in membranes of mitochondria, chloroplasts and bacteria catalyzes ATP synthesis coupled with electron transport.7) The catalytic portion of the enzyme Fi is composed of five different subunits, denoted a through e in order of decreasing molecular weight. The ATPase activity can be reconstituted from isolated a, fi and y subunits, each of which is devoid of catalytic activity in the separated state.7) Interestingly, the y subunit is indispensable for the functional reconstitution, although the catalytic site is suggested to be located on the fi subunit or at the interface of the a and fi subunits.7 ... 

Nitzan [18,34-36], Properties of the surface-modified semiconductor can be derived from an interaction between isolated electronic levels of the surface molecule (especially HOMO and LUMO orbitals) and the electronic continuum of semiconductor under the influence of a radiation held. The total hamiltonian (operator describing components) of the system can be formulated as a sum of hamiltonians for all the components of the system (H) and a coupling operator including all the physical processes of interest (W) (7.21) ... 

In organic conductors composed of isolated dimers, the synchronization of ag vibrations in both moieties of the dimer may result in their symmetrical or antisymmetrical vibrations. It is just the antisymmetrical type of vibrations that is capable of coupling to electron oscillations. As a consequence of this interaction, an abnormal optical absorption of the system can be observed. It is polarized in the direction of the dimer s axis and characterized by a frequency close to that of symmetrically vibrating molecules forming a dimer. 

Commercially available aminophosphine 4 provided even better yields in the coupHng of acycHc secondary amines [42]. The resulting catalyst was found to be so active that the reaction could often be conducted at room temperature. For example, Di- -butylamine was efficiently reacted with 4-bromotoluene in 96% isolated yield at room temperature, Eq. (27). In addition, electron-rich, electronically neutral, and electron-deficient aryl bromides were effectively utihzed with this new system. The 4/Pd-based catalysts also mediate the coupling of J -alkylanihnes that bear electron-donating substituents on the amine partner. A Xantphos/Pd-catalyst is effective in the coupling of electron-poor alkylaryl-amines with electron-poor aryl bromides. 

The use of Xantphos (9), first reported by Van Leeuwen [57], as supporting ligand allows for the efficient coupling of alkylarylamines and aryl bromides [58]. For example, the reaction of 4-bromobenzonitrile and N-ethylaniline proceeds in 85 % isolated yield, Eq. (29). This Hgand is particularly effective in the coupling of electron-deficient alkylarylamines and electron-deficient aryl bromides. 

For a long time stable distortions were thought to be the only evidence for a JT effect. However the papers by Moffitt et al. Longuett-Higgins et al. Bersuker and O Brien showed that, even for weak coupling, the vibronic level scheme was much different from the one obtained in an isolated electronic system. 

As already mentioned, there are two established sites of proton uptake coupled to electron transfer in the thylakoid membrane in the absence of added electron carriers one at the water oxidation reaction and the second at the plastoquinone to iron-sulfur protein reaction. This would predict that the H /e stoichiometry measured during electron transport should be 2. However, designing an unambiguous experiment to determine this exact ratio in isolated thylakoids turned out to be more difficult than it seemed at first. The literature contains, therefore, numerous values for this ratio [12], some of which are indeed close to 2. 

Thallium(III) trifluoroacetate is prepared in >90% yield by heating a suspension of Tl(III) oxide in trifluoroacetic acid. This mixture can be used directly for thallation. Oxidative coupling of electron-rich arenes may be avoided by using 1 1 Tl(III) trifluoroacetate and ether in trifluoroacetic acid . For acid-sensitive substrates, it is preferable first to isolate the solid Tl(III) trifluoroacetate by evaporation of the acid. This can then be used in CHjCN as the thallating agent. ... 

The coupling between electron transport from NADH (or FADH2) to O2 and proton transport across the inner mitochondrial membrane, which generates the proton-motive force, also can be demonstrated experimentally with Isolated mitochondria (Figure 8-14). As soon as O2 is added to a suspension of mitochondria, the medium outside the mitochondria becomes acidic. During electron transport from NADH to O2, protons translocate from the matrix to the Intermembrane space since the outer membrane Is freely permeable to protons, the pH of the outside medium Is lowered briefly. The measured change In pH Indicates that about 10 protons are transported out of the matrix for every electron pair transferred from NADH to O2. 

The monomeric [WOXs] (X = C1, Br) anions have been isolated with a variety of +1 cations. They are easily prepared from WCI5 or K3TW02(C204)2] in concentrated solutions of HCl or HBr in the presence of the desired cation. [WO ] are also known. These are all paramagnetic with magnetic moments close to the in-only value, presumably because tetragonal distortion destroys the spin-orbit coupling. Their electronic spectra have been interpreted. 

Research in the field of intermediates of oxidative phosphorylation has developed in two main directions (1) Some investigators attacked the problem directly and attempted either to reconstruct in vitro the enzyme system responsible for the coupling of electron transport and phosphorylation, or to isolate intermediates (2) others have approached the problem by studying elementary reactions suspected to participate in oxidative phosphorylation. So much data has been gathered on all the aspects of oxidative phosphorylation that it would be unrealistic to attempt to cover the subject comprehensively. We will consider only a few representative experiments in the hope of illustrating the amplitude and complexity of the problem. 

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