Electron transport across glycerol monooleate bilayer lipid membranes facilitated by magnesium etiochlorin

Abstract

The transport of electrons across biological membranes is believed to play an important role in many biophenomena. Although there have been many examples of systems which may be transporting electrons across Mueller-Rudin bilayer lipid membranes (blm), none has been well characterized. The system we describe here comprises a glycerol monooleate blm containing a magnesium etiochlorin (Mg-C) separating two aqueous phases each containing ferricyanide, ferrocyanide, KCl, and a platinum electrode. The E0s for the Mg-C+/Mg-C and ferri-/ferrocyanide couples are 0.22 and 0.24 V vs. SCE. Thus the MG-C+/Mb-C system is easily poised by the ferri-/ferrocyanide system. When the potentials of the ferri-/ferrocyanide couples are different on each side of the blm we show that the open-circuit membrane potential nearly equals the difference between the redox potentials. This is unequivocal evidence that electrons are being transferred across the blm from one aqueous phase to the other. On the basis of these experiments we deduce that electron transport is the major charge transport mechanism. When redox potentials are the same on each side of the blm, the conductance of the membrane can be greater than 10(-3) S/cm2. The conductance is proportional to the second power of the concentration of Mg-C in the membrane-forming mixture. A number of additional experiments are described which attempt to elucidate the mechanism of electron transfer. We believe that our data are consistent with the idea of an electron-hopping mechanism in which the transmembrane electron transport occurs by a series of second-order electron transfers between membrane-bound electron donors (Mg-C) and acceptors (Mg-C+). Alternative explanations are presented.

Electrochemical Detection of Single Phospholipid Vesicle Collisions at a Pt Ultramicroelectrode

“…According to the VB method applied to redox DMPC vesicles (Figure S4), we can affirm that vesicles irreversibly adsorb onto the Pt UME, but the VR technique presented in Figure 3 clearly demonstrated that electron transfer does not occur through the BLM because electron tunneling and ion transfer is not facile through such a thick barrier. 19,20,31 Thus, in agreement with previous studies about the vesicle adsorption on various substrates, 12,13 DMPC vesicles seem to remain intact during their collision on the Pt UME hydrophilic surface.…”

Photoinduced electron transfer across membranes

“…The same reaction is also suggested by Tien and Joshi [225] for PET across ZnTPP-containing planar BLM. Feldberg et al [226] also came to the conclusion about the existence of the transmembrane electron transfer via exchange reactions of the type of (8), when they found a square dependence of the membrane electrical conductivity on the concentration of the membrane-bound porphyrin (ethiochlorin of Mg(II)).…”

Fast and Efficient Charge Transport across a Lipid Bilayer Is Electronically Mediated by C70 Fullerene Aggregates

“…Electron transport across lipid membranes is a fundamental property of living systems and is exemplified in photosynthesis. The designs of molecular systems for solar energy conversion are mimics of this vectorial photoinduced charge transportation. , However, relatively few synthetic molecules have been shown to transport charge across a lipid bilayer efficiently. − With the recent success in producing macroscopic quantities of C 60 and C 70 fullerene molecules, many properties of these supermolecules have been determined. Since the photophysics of fullerene molecules resembles that of porphyrins and the fullerenes have low reduction potentials, , they are expected to have interesting charge-transfer chemistry in both the ground state and the excited states.…”