Photoinduced Electron Transfer between DNA and Water-Soluble Porphyrins

Area of Science:

• Photochemistry
• Biophysical Chemistry
• Spectroscopy

Background:

• Porphyrins are versatile molecules with applications in medicine and materials science.
• Understanding porphyrin-DNA interactions is crucial for developing novel therapeutic and diagnostic agents.
• Previous studies have explored porphyrin binding to DNA, but detailed photophysical investigations are ongoing.

Purpose of the Study:

• To investigate the photophysical properties of five porphyrins complexed with model DNA.
• To elucidate the binding modes and dynamics of porphyrin-DNA interactions.
• To explore the occurrence and kinetics of electron transfer processes.

Main Methods:

• Steady-state absorption spectroscopy
• Circular dichroism (CD) spectroscopy
• Femtosecond transient absorption spectroscopy

Main Results:

• H₂TMPyP and PdTMPyP showed significant hypochromism and red shifts upon DNA complexation, indicating strong interactions.
• Binding modes varied, including partial intercalation (H₂TMPyP-ctDNA), full intercalation (PdTMPyP-ctDNA), and groove binding (ZnTMPyP-ctDNA).
• Fast electron transfer (ET) from guanine to H₂TMPyP and PdTMPyP was observed upon S₂ excitation, with forward rates ≥ 1.0 × 10¹³ s⁻¹.

Conclusions:

• H₂TPPS and ZnTPPS showed minimal interaction with DNA.
• The complexation with DNA can influence the fluorescence lifetime of porphyrins.
• The study highlights the distinct binding and photophysical behaviors of different porphyrin-DNA complexes.