1983; de Groot et al. 1985). For the ET from QA to QB a spin-catalytic Gefitinib in vitro role of the non-heme iron to facilitate spin-selective ET has been proposed

(Ivanov et al. 1999). In this concept ISC accelerated by the spin-catalytic active non-heme iron promotes the indirect ET from the triplet radical pair 3[QA −QB −] and therefore the product formation to 1[QAQB 2−]. One may assume that the phenomenon of the solid-state photo-CIDNP effect could be rationalized in terms of nuclear observer spins, on the one hand obtaining nuclear polarization, on the other hand providing a spin-catalyst for ET. Under natural conditions, however, the primary radical pair lives 200 ps, by far too short to allow for hf interaction. Hence, the effect cannot be the cause of the efficiency, but the assumed correlation between the parallel occurrence of effect and high efficiency may be based on common principles. There may be some until now unknown fundamental principles of photosynthetic charge separation and stabilization that leading to both phenomena. In that case, photo-CIDNP MAS NMR would be useful for studies Selleck LY2157299 in artificial photosynthesis for three reasons: (i) as an analytical tool, (ii) as heuristic guide based on the strength of the effect, and (iii) by the possibility for exploration of the fundamental principles.

These fundamental principles may be related to highly optimized constraints in geometry and ET kinetics as chosen

and conserved by nature. It has been pointed out cAMP that both the solid-state photo-CIDNP effect and the efficient light-induced ET require optimized overlap of the wavefunctions (Jeschke and Matysik 2003) corresponding to moderate electron–electron coupling parameters. A clear picture of the required architecture of orbitals, however, is still missing. Such concept of overlapping static orbitals of the cofactors would be sufficient for the microscopic description of both the ET and the coherent origin of the solid-state photo-CIDNP effect. On the other hand, understanding of both processes on the protein level would allow for including the dynamic role of energy dissipation and entropy production in the transfer of electrons and polarization. It is possible that both ET and the solid-state photo-CIDNP effect require optimized dissipation channels. The relevance of protein relaxation for photosynthetic ET has been stressed (Cherepanov et al. 2001). Under conditions of irreversible thermodynamics, self-organized ET, in which improved entropy management allows for active coupling of the ET to a matrix with non-linear response, may lead to negative friction and gating (Tributsch and Pohlmann 1998; Tributsch 2006). Hence, experiments mapping light-induced changes at the atomic resolution may provide the empirical basis for the determination of the origin of the parallel transfer of electrons and of electron polarization to nuclei.