MIXED-VALENCE STATE IN IRONPORPHYRIN AGGREGATES

In biological systems, metalloporphyrins play a central role in energy and electron transfer process. Our aim is to understand the influence of ligands and iron coordination of ironporphyrin on the electron transfer. The lyophilized ironporphyrin, enriched in Fe-57 up to 90% has been studied by Mossbauer spectroscopy between 2.8 and 313 K. Above room temperature the bounded diffusion of the ferric iron was observed. Below 293 K a part of iron appears in mixed Fe+3 <-> Fe+2 valence state with 10 meV activation energy for the electron trapping. Below 4 K a part of iron shows magnetic ordering with a broad distribution of the hyperfine field. The results are discussed in terms of metalloporphyrin aggregation process.