We have characterized three porphyrin-peptide systems through optical spectroscopy, using meso-tetra(4-sulfonatophenyl)-porphyrin (TPPS) and three variants of a 22-residue peptide having three, lysine rich, TPPS-binding motifs, each in various pH environments. Absorbance and fluorescence data confirmed the transition of TPPS from the unbound state to the excitonically coupled J-aggregate state when bound to the peptides at low pH (1.8, 3.6) and the existence of a bound, uncoupled state at neutral pH (7.6). The peptides were designed with a fluorophore near one of the binding motifs and revealed a preference in binding sequence within these motifs. Using absorbance to determine the presence of TPPS monomer vs aggregate, we have also confirmed the pH-dependent reversibility of the porphyrin structure when bound to each peptide. Circular dichroism spectra provided information on secondary structure, demonstrating a pH dependent structural transition correlated with J-aggregate formation.

Reversible self-assembly of excitonically coupled peptide-porphyrin complexes

244th National Meeting (2012)

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