Transfer processes intermolecular, irreversible

Both reactions, namely tte intermolecular process (131) and the intramolecular one (132) can be either reversible or irreversible (termination). In the case of reversible reactions true chain transfer takes place vdien the rate constant of the backward reaction (kj ) becomes comparable with the rate constant of M-opaptun. This applies to the polymerization of cyclic acetals where the product of chain traiKfer is equally active in propaption. 

Natui al photosynthesis undoubtedly represents an exemplary system for supramolecular photochemistry. In a series of irreversible electron transport processes in bacterial photosynthesis, an electron was ejected from bacteriochloro-phyll dimer (specif pair) [43S-438] and transferred to quinone [439-441] via bacteriopheophytin [442-444]. Ferrocytochrome c supplies an electron to the hole of a special pair [445]. The charge separation and each electron transfer have been supposed to proceed at almost 100% efficiency. Those postulates were actually verified in a series of elegant works on structural analyses of reaction center from Rhodopseudomonas (Rps.) viridis and Rb. sphaeroides by Deisen-hofer et al. [428-430]. In 1984 they fotmd that the special pair and bacteriopheophytin were beautifully aligned and oriented with each other in the system [428]. The intermolecular center-to-center distance within the special pair was revealed to be 7.0 A and the distances between the two molecular planes were 3.0 A for Rps. and 3.5 A for Rb., respectively [428-434,446-450] (Fig. 39). 

My background led me to view chemical kinetics as closely related to transport phenomena. While the relationship of these topics is well known, it is often ignored, except for brief discussions of irreversible thermodynamics. In fact, the physics underlying such apparently dissimilar processes as reaction and energy transfer is not so very different. The intermolecular potential is to transport what the potential-energy surface is to reactivity. 

---