Macromol. Chem. Phys. zyxwvu 195, zyxwvu 1031 -1041 (1994) zyxwvu 1031 zy Electron transfer catalyzed by manganese tetratolyl- porphyrinate across poly(y-methyl L-glutamate) membrane Takehisa Dewa, Mitsuru Satoh, Jiro Komiyama zyxw * Department of Polymer Science, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan Mamoru Nango, Kazuichi Tsuda Department of Applied Chemistry, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466, Japan (Received: May 18, 1993; revised manuscript of August 3, 1993) SUMMARY A poly(y-methyl L-glutamate) (PMLC) membrane containing manganese tetratolylporphyri- nate (MnTTP) was prepared in order to examine the transmembrane electron transfer in a redox system constructed as S,O:-/membrane/Fe(CN)i-. Electron transfer was observed in 0,l zy M pH 7,O imidazole (Im) buffer but not in 0,l M pH 7,O phosphate buffer. The apparent transfer rate increased with MnTTP content and also with the Im concentration in the buffer, indicating that electron is transferred by MnTTP, which is coupled with proton transport by Im distributed in the membrane. The transfer catalyzed by MnTTP was more effectively accelerated with Im than with 2-methylimidazole (2-MeIm) but not at all with 1-methylimidazole (1-MeIm). This implies that the 1-N site on the imidazoles as the axial ligand of MnTTP is a crucial position for the mediation of electron transfer between MnTTP’s. In the pH range 6,O-8,5 of Im buffer, the electron transfer rate showed a maximum at pH 7,O. This pH dependence is discussed in terms of the concentration and mobility of proton in the membrane. Introduction Electron transfer across biomembranes has been extensively investigated from the viewpoint of clarification and application of bioenergetical transduction systems The detailed mechanism of electron transfer catalyzed by porphyrin complexes, especially in chlorophyll and cytochromes, however, has not been fully understood, mainly because of the many participating factors, such as orientation, distance, redox potential, axial ligands, the ambient of the porphyrins, and also the coupled flow in the relevant systems 3). For this reason, artificial models constructed with lipid bilayer 2*4), LB 5), liquid4+@ and solid membranes ’) have been expected to provide insight into the effects of these factors. Such studies may be extended in search for applications as electroorganic materials. Until now, however, only a few studies have been reported on transmembrane electron transfer systems composed of a solid membrane substrate for model studies. Furthermore, there have been few studies of ground state electron transfer of porphyrins in protein membranes with attention to the presence of histidine in the electron transfer system. As a model study for such systems, we now present the transmembrane electron transfer catalyzed by MnTTP in PMLG membrane in the presence of various imidazoles. The PMLG can be expected as a good membrane substrate, since the poly- z 0 1994, Hiithig & Wepf Verlag, Basel CCC 1022-1 352/94/$08.00