Applications of coordination chemistry in the assembly of porphyrin-based supramolecular structures

The use of transition metal coordination chemistry has been explored as a means of bringing together various porphyrin sub-units into multi-chromophore assemblies. A novel porphyrin compound with the capacity for exocyclic metal ion coordination has been synthesized and fully characterized. Exocyclic metal-ion coordination is achieved through a phenanthrolinic moiety fused to the beta-pyrrole positions of the porphyrin with a phenazine linker. Such a structural motif affords a planar highly conjugated molecule. Emission and UV-visible spectroscopy show that the porphyrin pi-system is effectively delocalized into the phenanthrohnic moiety. This molecule allows for a modular approach to the design and construction of complex molecular architectures.;Free-base and zinc porphyrin complexes of CuI, Zn II, and RuII were studied with steady-state spectroscopic techniques to interrogate the effect of different metal ions at the exocychc binding site versus the effect of the porphyrin metallation state on the observed photophysics. Collaborative studies utilizing time-resolved laser spectroscopic methods further elucidated the interactions between the porphyrin and the RuII-phenanthroline chromophores.;It has been shown that the overall photophysical properties of these supramolecular systems can be tuned by either changing the metallation state of the porphyrin core (i.e. free-base, CuII, or ZnII ) or by exocyclic coordination of metal ions that produce energetically accessible metal-to-phenanthrohne or RuII).;The coordination chemistry of copper(II) with iminodiacetic acid (IDA) and histidine (His) has also been investigated for its applicability in the assembly of porphyrin-peptide super molecules. These studies were effectuated using a 5,15-(benzyl-IDA) porphyrin and an alanine rich alpha-helical synthetic peptide containing metal binding His-X3-His sequences. The porphyrin molecule and the peptide self-assembled as a 1:1 porphyrin to peptide complex in aqueous buffered solutions upon addition of two equivalents of CuII ions. Spectopolarametric analysis showed that the rigid porphyrin molecule induces a high degree of alpha-helicity in the peptide at room temperature and that the peptide-strap crosses over the face of the porphyrin molecule.