Photosensitized electron transfer bilayer membranes

Since these interfaces are usually constructed of charged detergents a diffuse electrical double layer is produced and the interfacial boundary can be characterized by a surface potential. Consequently, electrostatic as well as hydrophilic and hydrophobic interactions of the interfacial system can be designed. In this report we will review our achievements in organizing photosensitized electron transfer reactions in different microenvironments such as bilayer membranes and water-in-oil microemulsions.In addition, a novel solid-liquid interface, provided by colloidal Si02 particles in an aqueous medium will be discussed as a means of controlling photosensitized electron transfer reactions. 

Experimentally, electron transfer across vesicle membranes with an asymmetrically embedded photosensitizers was first observed in System 17 of Table 1. Katagi et al. [64, 65] succeeded in embedding a photosensitizer (ZnC18TMPyP3+) into the bilayer membrane both uniformly and selectively in its outer monolayer, i.e. asymmetrically. In the latter case no electron transfer across the membrane took place until the other photosensitizer (ZnTPP) was introduced into the membrane uniformly. The proposed mechanism of electron transfer involved two photochemical steps ... 

In Systems 29 and 30 suggested by Sudo and Toda [82-84] no intermediate acceptor At was added. Instead of A1 the photosensitizer itself which is able to penetrate through a lipid bilayer both in oxidized and reduced states, performs electron transfer across the membrane. System 30 allows one to accumulate and store the products of electron transfer from the reversible donor, Fe2+, to the reversible acceptor, Fe(CN)g Note that in homogeneous solution it is impossible to accumulate and store the products of this reaction. It is well known that back recombination of the products formed upon PET from Fe2+ to thiazine dyes... 

Two celebrated early investigations of transmembrane oxidation-reduction were interpreted in terms of direct electron exchange between redox partners bound at the opposite vesicle interfaces. One involved apparent reduction of diheptylviologen [( 7)2 V +] in the inner aqueous phase of phosphatidylcholine liposomes by EDTA in the bulk phase that was mediated by membrane-bound amphiphilic Ru(bpy)3 + analogs the ruthenium complexes acted as photosensitizers and were presumed to function as electron relays by undergoing Ru(II)-Ru(III) electron exchange across the bilayer [105]. The other apparently involved direct electron transfer between photoexcited Ru(bpy)3 + and bound at the opposite interfaces of asym-... 

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