Photoinduced electron transfer across membranes

Enhanced Photoinduced Electron Transfer at the Surface of Charged Lipid Bilayers

“…They provide a scaffold on which directional electron transfer can take place, either from the inside of a nanoparticle to its surface or from one side of a lipid membrane to the other. By positioning the donor and acceptor molecules on either side of a lipid bilayer, for example, electron transfer can be achieved, [18,19,[21][22][23][24][25][26][27] although lipid membranes are rather thick and the observed transmembrane redox reactions are sometimes caused by transfer of a reduced electron acceptor across the membrane. [25,[28][29][30][31][32][33] Although these experiments paved the way for biomimetic artificial photosynthesis, evidence that the photogenerated electrons can be transported away from the photo-catalytic center is still lacking, as ultimately these electrons should reach another photocatalytic site at which proton or CO 2 reduction should occur.…”

Electron transfer through vesicle membranes: Mechanistic ambiguities

“…A two-photon ionization of a porphyrin dimer on one side of the membrane has also been proposed as the initial reaction step, explaining the quadratic dependence on the number of photons (Jusupov et al 1985). It seems possible that the relatively hydrophobic porphyrins could be distributed in the membrane in the same way as the chl-a (vide supra) allowing for short-range, multi-step electron transfer, even if some results indicate that most porphyrins are located closer to the interface of the membrane than to the middle (Lymar et al 1991). In the latter case the observed two-photon dependence could be explained by the dimer-process according to Jusupov et al (1985).…”

“…For photoinduced reactions in many systems, it has been observed that the transmembrane electron transfer is a two-photon process. This has sometimes been taken as evidence for a long-range self-exchange reaction between a photo-oxidized porphyrin on one side of the membrane and a photo-excited or photo-reduced porphyrin on the other (Katagi et al 1981(Katagi et al , 1982Lymar et al 1991). However, in other systems there was a carrier for the electron acting as a mediator via diffusion between the porphyrins (Matsuo et al 1980).…”

“…This was explained by transmembrane diffusion of the viologen radical and its subsequent reoxidation 3 by internal Fe(CN)6-. In flash-photolysis, the observed kinetic trace deviated from a single exponential and could be accounted for by a model where the created transmembrane electric potential following tunnelling of one electron slows down the tunnelling of the next (Lymar et al 1991). This model assumed that the rate of the charge-compensating ionic flow was slower than the electron tunnelling.…”

“…However, it is necessary to control and understand the simple vesicular systems better before trying to incorporate more complicated molecules. Despite the great number of articles describing transmembrane electron transfer in vesicles (for recent reviews, see , Robinson and Cole-Hamilton 1991, Lymar et al 1991, the general understanding of these systems is still very limited, especially concerning the mechanism of transmembrane electron transfer.…”