Type C Non-Specific 3-Point PCET

In this PCET configuration, a donor (De/Dp) transfers an electron to an acceptor (Ae) and loses a proton to the bulk (Eq. (C) in Fig. 17.3). Though there is no specific proton acceptor, the PCET event may be tightly coordinated and correlated to bulk properties of the medium, particularly the pH. 

Hammarstrbm and coworkers have conducted a thorough investigation of dissociative PCET from tyrosine (Y) using ruthenium-tyrosine model complexes. The work is motivated by the crucial role that tyrosine residues, play in charge-separation reactions in biology, particularly in Photosystem II (PS II). The model systems do not contain a specific PT coordinate as in PSII [148-156], yet the simplicity of the system permits the balance of stepwise versus concerted PCET to be studied in a controlled fashion. 

where the previous model is modified to include a repulsive surface for proton motion in the final state [21]. The PCET rates are found to be rather sensitive to the nature of the repulsive surface - which is coupled to the solvent. 

Thorp and coworkers examined the oxidation of G in duplex DNA using a series of metal-polypyridyl oxidants of varying driving force [78]. A Marcus plot yields a slope of—0.8. As discussed in Section 17.3.1, a stepwise mechanism with a ratedetermining ET step produces a slope of -0.5 whereas a rate-determining PT step produces a slope of-1.0. The observations of an intermediate slope and attendant KIE of 2.1 signify that a PCET mechanism is operable. It is noted that in other 

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