Synthesis and Physical Characterization of Novel Heme-Based Model Systems for Photoinitiated Electron Transfer. 2. Direct Ruthenation of Microperoxidase-11†

This paper describes the design, synthesis, and initial characterization of a second type of model electron transfer system based upon microperoxidase-11 (MP-11) that differs significantly from those described in the preceding article. In this system, a photoactive ruthenium tris(bipyridyl) donor is covalently attached directly to MP-11. Peptide digestion followed by chromatographic analysis was used to establish that the ruthenium moiety bonds to the lysine residue of the MP-11 peptide. This arrangement eliminates complications arising from the equilibrium complexation of ruthenium donor and heme acceptor required for the model systems described in the previous article and leaves an axial position in the octahedral geometry of the heme iron open for ligation. Various optical spectroscopies and molecular modeling calculations were employed to characterize the equilibrium properties and interchromophore interactions of RuMP-11. Preliminary luminescence-quenching, transient absorption, and transient resonan...