Election transfer

These charge-transfer structures have been studied [4] in terms a very limited number of END trajectories to model vibrational induced electron tiansfer. An electronic 3-21G-1- basis for Li [53] and 3-21G for FI [54] was used. The equilibrium structure has the geometry with a long Li(2)—FI bond (3.45561 a.u.) and a short Li(l)—H bond (3.09017 a.u.). It was first established that only the Li—H bond stietching modes will promote election transfer, and then initial conditions were chosen such that the long bond was stretched and the short bond compressed by the same (%) amount. The small ensemble of six trajectories with 5.6, 10, 13, 15, 18, and 20% initial change in equilibrium bond lengths are sufficient to illustrate the approach. 

Figure 9.29 Photo-induced spin crossover in transition metal ions (a) incident photons can successively promote electrons from the ground t2g state to the high-energy eg state and (b) spin crossover involving election transfer and excitation in KFeCo(CN)6-...

Curves in Figure 4.13a and similar curves corresponding to other values of the two parameters kr°8/DA and kf Sr()/DACA give an idea of the changes to be expected in the current-potential curves as the kinetics of the electrode election transfer starts interfering. One can pass from one curve to the other by adjusting CA, F°, and the rotation rate. The latter two factors will also change the catalysis kinetic parameter, but the former will not. 

Scheme 4 Election-transfer and addition reactions of radicals and radical ions.

The nature of solvent was found to be important for the election transfer behavior. The Fe2S2 complex with two Cys-Gly-Ala-Gly-Ala-Cys ligands shows Ei/2 values of -0.95 V in DMF and -0.76 V in CH3CN. The positive shift of the... 

Figure 17-2 (cr) Schematic energy profile for election transfer from a metal to H30. leading to liberation of H2- (b) Applying a potential to the metal raises the energy of the electron in the metal and decreases the activation energy for electron transfer. 

Photopolymerization of acrylamide by the uranyl ion is said to be induced by electron transfer or energy transfer of the excited uranyl ion with the monomer (37, 38). Uranyl nitrate can photosensitize the polymerization of /S-propiolactone (39) which is polymerized by cationic or anionic mechanism but not by radical. The initiation mechanism is probably electron transfer from /S-propiolactone to the uranyl ion, producing a cation radical which propagates as a cation. Complex formation of uranyl nitrate with the monomer was confirmed by electronic spectroscopy. Polymerization of /J-propiolactone is also photosensitized by sodium chloroaurate (30). Similar to photosensitization by uranyl nitrate, an election transfer process leading to cationic propagation has been suggested. 

The initial election transfer produces a radical-ion (M ) having an extra electron in its lowest anti-bonding 7r-orbital. The relative importance of subsequent steps has been discussed by Szwarc (108). The radical ends disappear rapidly by dimerization in most cases and the... 

In its biochemical functions, ascorbic acid acts as a regulator in tissue respiration and tends to serve as an antioxidant in vitro by reducing oxidizing chemicals. The effectiveness of ascorbic acid as an antioxidant when added to various processed food products, such as meats, is described in entry on Antioxidants. In plant tissues, the related glutathione system of oxidation and reduction is fairly widely distributed and there is evidence that election transfer reactions involving ascorbic acid are characteristic of animal systems. Peroxidase systems also may involve reactions with ascorbic acid In plants, either of two copper-protein enzymes are commonly involved in the oxidation of ascorbic acid. 

Most adsorption processes are exothermic (AH is negative). Adsorption processes involving nonspecific interactions are referred to as physical adsorption, a relatively weak, reversible interaction. Processes with stronger interactions (election transfer) are termed chemisorption. Chemisorption is often irreversible and has higher heat of adsorption than physical adsorption. Most dispersants function by chemisorption, in contrast to surfactants, which lend to physically adsorb. 

Cyclizations of carbonyl-containing a. -unsaturated esters like those illustrated in Scheme 38164>16S are conceptually very similar to ketyl cyclizations, but they may be very different mechanistically. At least for electrochemical cyclizations, Litde has proposed, based on reduction potentials, that the unsaturated ester is reduced first.164 Even though questions remain about the timing of election transfer and proton transfer steps, such cyclizations often provide good yields of products. 

The catalytic effect of acid or metal ions on the thermal or photo-induced election-transfer reactions has been reviewed.60... 

In making rotaxanes usable as parts of molecular devices and with the purpose of studying long range election transfer processes within large molecular systems of well controlled geometries, the introduction of photoactive and electroactive compounds has been a valuable development. Photoinduced electron transfer between porphyrin species has a particular relevance to the primary events occurring in bacterial photosynthetic reaction center complexes, and so is a well studied phenomenon. 

Election transfer remains one of the most important processes explored when using interfacial supramolecular assemblies and given the emerging area of molecular electronics, this trend is set to continue. Therefore, Chapter 2 outlines the fundamental theoretical principles behind the electiochemically and photochemi-cally induced processes that are important for interfacial supramolecular assemblies. In that chapter, homogeneous and heterogeneous electron transfer, photoinduced proton transfer and photoisomerizations are considered. 

Self-assembled and spontaneously adsorbed monolayers offer a facile means of controlling the chemical composition and physical structure of a surface. As discussed later in Chapter 5, applications of these monolayers include modeling election transfer reactions, biomimetic membranes, nano-scale photonic devices, solar energy conversion, catalysis, chemical sensing and nano-scale lithography. 

When such a unimolecular process occurs fastw than back election transfN (ki in equation 6a), electron-transfer oxidation in Scheme 1 proceeds nqiidly despite an unfavorable driving force ( ox + E na s 30 kcal mol ) for election transfer. ... 

A novel procedure for the oxidative removal of benzyl protecting groups by catalytic homogeneous election transfer has been developed by Schmidt and Steckhan (equation 34)." The selectivity of the reaction can be adjusted by altering the substitution on the aromatic rings of the cation radicals (48). Finally, a recent publication describes a photoinduced single electron transfer initiated oxidative cleavage of benzylic ethers. ... 

Redox propcTties of some oxo-bridged di- and tri-nuclear complexes of the second and third transition elements. Re, Ru, Os, and Mo, are discussed with special attention to stability of the mixed-valence states. These complexes display multi-step one-election transfer processes and give fairly stable mixed-valence oxidation state. Stability of the mixed-valence states is discussed in terms of qualitative molecular orbital schemes based on dJt (metal) - prt (bridged oxygen) interactions. 

Fig. 3. Schematic illustration of non-radiative election transfer (horizontal arrows) in the normal (left) and inverted (right) Marcus regions. Associated with each vibronic state is a stack of sublevels representing low-frequency (mainly) solvent modes. In the initial state only one vibrational mode, with j = 0, is mainly occupied, whereas in the final state various vibrational modes, with y = 0,1,2..., may be accessible. Diagonal arrows (in the inverted Marcus region) correspond to radiative electron transfer (charge-transfer fluorescence). Adapted from [55].

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