Effect of intermacrocyclic interactions: Modulation of metal spin-state in oxo/hydroxo/fluoro-bridged diiron(III)/dimanganese(III) porphyrin dimers

Abstract

The family of multiheme proteins and enzymes constitutes one of the most fascinating molecular machineries designed by Nature and have emerged as a new and very important research area in the highly interdisciplinary field of science today. The relative arrangement of the heme centers and the intermacrocyclic interactions therein have been proposed to exhibit important roles in the function of such a widely distributed family. The diheme cytochrome c (DHC2) from G. sulfurreducens, the simplest member of such multi-heme family, has two structurally and spectroscopically different heme groups as a result of an efficient interaction between two heme centers. Our broad interest lies in unmasking the roles played by heme–heme interactions in modulating structure-function of the individual heme centers using synthetic dihemes, unencumbered by any biological superstructure, as convenient systems for testing various mechanistic hypotheses and gaining insights regarding the fundamental processes. Such interactions have been found critical in modulating iron spin-states in synthetic dihemes which have been exploited for the unusual stabilization of two different spin states of iron in a single molecular framework. This chapter provides a brief account of our recent efforts to explore these interesting aspects using a series of isoelectronic oxo/hydroxo/fluoro-bridged diiron(III)/dimanganese(III) porphyrin dimers.