Energy donor/acceptor

If therefore the transfer process is diffusion-limited (kt kd), as found for a number of (energy) donor-acceptor systems by Dubois and coworkers,59 it must be concluded that kQC (kMC + 2i kf) with kCM kd. This is in contrast to the findings for triplet energy transfer where the measured rate constant 3kt falls below the diffusion-limited value (Eq. 7) as the energy separation 3A MQ of donor (3M ) and acceptor (3Q ) triplet states is reduced.60 With 3kQC k° + GT = 1/tp the appropriate form of Eq. (37)... 

Campagna and coworkers recently reviewed energy donor/acceptor systems, including Ru complex donor/Os complex acceptor chromophores. The review provides an overview of a number of light harvesting systems [55]. 

Over the past several years, energy donor/acceptor systems have been prepared in which the electronic coupling of the bridging ligand is increased... 

Figure 6. Representation of the spectral overlap relationships between the enzyme tryptophan and substrate dansyl groups, which constitute the energy donor-acceptor pair critical to observation of the ES complex (57)...

Otsuki et al. [27] have demonstrated that amidinium-carboxylate salt bridges, which have been used earlier to construct electron donor-acceptor dyads or a donor-spacer-acceptor triad, can also be used to assemble energy donor-acceptor dyad 13 and pentad 14. The salt bridge consists of complementary double hyi-ogen bonds and electrostatic interactions and, therefore, offers... 

A salient feature of natural surfaces is tliat tliey are overwhelmingly electron donors [133]. This is tlie basis for tlie ubiquitous hydrophilic repulsion which ensures tliat a cell can function, since massive protein-protein aggregation and protein-membrane adsorjition is tliereby prevented. In fact, for biomolecule interactions under typical physiological conditions, i.e. aqueous solutions of moderately high ionic strengtli, tlie donor-acceptor energy dominates. 

Much of chemistry occurs in the condensed phase solution phase ET reactions have been a major focus for theory and experiment for the last 50 years. Experiments, and quantitative theories, have probed how reaction-free energy, solvent polarity, donor-acceptor distance, bridging stmctures, solvent relaxation, and vibronic coupling influence ET kinetics. Important connections have also been drawn between optical charge transfer transitions and thennal ET. 

AG and AH can be expressed as a multiplicative function of hydrogen bonding in different polar and nonpolar solvents by means of enthalpy acceptor factors E - enthalpy donor factors free energy acceptor factors Q, and free energy donor factors Q (Eqs. (32) and (33), where kj, 2- 3 [kcal/mol] are regression coefficients). 

The contribution of this polar structure to the bonding lowers the energy of the transition state. This may be viewed as a lower activation energy for the addition step and thus a factor which promotes this particular reaction. The effect is clearly larger the greater the difference in the donor-acceptor properties of X and Y. The transition state for the successive addition of the same monomer (whether X or Y substituted) is structure [V] ... 

Fig. 2. Representation of the band edges in a semiconductor p—n junction where shallow donor, acceptor energies, and the Fermi level are labeled Ejy E, and E respectively, (a) Without external bias is the built-in potential of the p—n junction (b) under an appHed forward voltage F. ...

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