Photoactive Hemeprotein Hybrids
The use of photo-active Ru(diimine) complexes to initiate
and measure the rates of electron transfers in metalloprotein has become
an important tool in bioinorganic chemistry. Such use is based on the redox
activity of a long-lived (ca. 700 ns) triplet excited state formed by photo-excitation
into a metal-to-ligand charge transfer band. The triplet state
can act as both a reductant (E = -.77 V) or an oxidant (E = +.86 V); flash/quench
techniques alow the more powerful redox species Ru3+ (E = +1.26
V) or Ru1+ (E = -1.35 V) to be generated.
We want to use these methods to initiate and follow redox-induced transformations important to heme-based catalysis. Our approach is to hardwire the Ru complex directly to the heme active site -- as in the single heme protein myoglobin shown below.
We do this by making a pendant-arm heme cofactor that can be reconstituted with apomyoglobin, reforming the native myoglobin structure but with a photoactive Ru complex covalently linked -- hardwired-- to the heme active site.
Reaction scheme for making photoactive heme cofactors
adapted from Hamachi, Tanaka, Shinkai Chem Letts. 1993
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