Peptide-sandwiched protoporphyrin compounds mimicking hemoprotein structures in solution

Area of Science:

• Supramolecular Chemistry
• Photophysics
• Biophysical Chemistry

Background:

• Peptide-protoporphyrin conjugates are of interest for their potential applications in photodynamic therapy and molecular sensing.
• Understanding the structural and photophysical properties of these molecules is key to designing functional systems.

Purpose of the Study:

• To synthesize and characterize novel peptide-protoporphyrin-naphthalene compounds.
• To investigate their structural features and photophysical behavior in solution.
• To elucidate the mechanism of energy transfer between naphthalene and protoporphyrin.

Main Methods:

• Synthesis of peptide-protoporphyrin-naphthalene compounds with varying peptide lengths.
• Spectroscopic analysis including infrared (IR) and circular dichroism (CD) spectroscopy.
• Steady-state and time-resolved fluorescence experiments.
• Molecular mechanics calculations.

Main Results:

• Synthesized compounds exhibit intramolecularly H-bonded conformations and alpha-helix structures in solution.
• Electronic energy transfer from excited naphthalene to protoporphyrin was observed.
• Molecular mechanics and fluorescence decay data suggest two major conformers with globular, protein-like structures.
• Experimental and theoretical photophysical parameters align when chromophore orientation is considered, indicating slow conformational interconversion.

Conclusions:

• The synthesized peptide-protoporphyrin-naphthalene compounds adopt stable, protein-like structures in solution.
• The photophysical properties are governed by Förster resonance energy transfer, influenced by the specific steric arrangement of naphthalene groups.
• The findings provide insights into the structure-property relationships of complex molecular assemblies for potential applications.