Artificial intramolecular electron transfer

The intramolecular electron transfer kg, subsequent to the rapid reduction, must occur because the Ru(III)-Fe(II) pairing is the stable one. It is easily monitored using absorbance changes which occur with reduction at the Fe(III) heme center. Both laser-produced Ru(bpy)3 and radicals such as CO (from pulse radiolysis (Prob. 15)) are very effective one-electron reductants for this task (Sec. 3.5).In another approach," the Fe in a heme protein is replaced by Zn. The resultant Zn porphyrin (ZnP) can be electronically excited to a triplet state, ZnP which is relatively long-lived (x = 15 ms) and is a good reducing agent E° = —0.62 V). Its decay via the usual pathways (compare (1.32)) is accelerated by electron transfer to another metal (natural or artificial) site in the protein e. g.. 

The field of light-induced electron transfer remains in a state of rapid development in many of the areas on which this brief history has touched and in others that could not be included here. Exciting progress is being made in the delineation of the first picosecond of photosynthesis, in further characterizing photosynthetic reaction centers, in the area of artificial models. The dependence of intramolecular electron transfer upon distance, solvent, orientation is being delineated. Many of these developments are detailed in the following chapters. 

The feasibility of intramolecular electron- and energy-transfer depends on distance and is usually studied in covalently linked systems. However, donor-acceptor dyads can be also arranged by self-assembly what resembles the situation of electron transfer in biological systems. Artificial dyads tethered by a small number of hydrogen bonds immediately dissociate in methanol or water. To improve the binding while keeping the reversibility, a photoinducible electron donor-acceptor dyad linked by a kinetically labile bond was designed. [19]... 

Electronic energy transfer from an excited state donor to a suitable acceptor is a fundamental process in photochemistry and is of prime importance in artificial photosynthesis. A variety of mechanisms exist by which energy migration and transfer can take placeand such processes have been used to create the so-called antenna effect . In particular, much research has concentrated on designing molecular systems in which an organic host is used to bind a lanthanide cation in such a way that photoexcitation of the host results in intramolecular energy transfer to the bound cation. ... 

The validity of this model requires that the intermolecular forces (most often van der Waals) be much weaker than their intramolecular analogs, which are associated with the chemical bonds. To be more precise, provided the exact local field factors are used, the microscopic quantities deduced from or do not correspond to the p (first hyperpolarizability) and y (second hyperpolarizability) values of the gas phase species but rather to those of the molecule dressed by its surroundings. Conversely, using the hyperpolarizabilities of the isolated molecules, Eq. (3) provides the susceptibilities of an artificial crystal because the geometry and/or the electronic properties of the constituent units may not be consistent with the true crystal. Of course, the gap between the model and the true values depends upon how large the van der Waals forces, the intermolecular charge transfer effects, the hydrogen bonds, and so on, are. Its... 

In such manner, fusion enzymes comprised of RhFRed and the monooxygenase domains of either P450cam or CYP177A1 were successfully produced [152]. These artificial P450 systems were shown to be expressed in a soluble form and to be catalytically active. Importantly, electrons from NADPH were shown to be transferred primarily intramolecularly to the P450 heme domain. The robustness and universal apphcability of LICRED was demonstrated by generating a... 

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