Aggregation-induced stabilization of pheophorbide, a water-soluble chlorophyll derivative.

BACKGROUND

Chlorophyll (Chl) is a valuable natural pigment, but its application is limited by poor water solubility and photoinstability. This study focuses on the preparation of pheophorbide (Phide), a water-soluble chlorophyll derivative, and investigates the possible role of molecular aggregation in enhancing its photostability.

METHODS

Phide was synthesized from Spirulina-derived chlorophyll through saponification. Structural characteristics were analyzed using Fourier Transform Infrared (FTIR) and UV-Vis spectroscopy. A concentration determination method was established by combining High-Performance Liquid Chromatography (HPLC) with UV-Vis spectroscopy. Photostability was evaluated through a 6-day light exposure experiment. In addition, Independent Gradient Model (IGM), Electrostatic Potential (ESP), and hole-electron analyses were performed on a parallel-stacked dimer model to explore the intermolecular interactions and electronic characteristics of the aggregated state.

RESULTS

Phide exhibited good water solubility and concentration-dependent aggregation behavior in aqueous solution. After 6 days of light exposure, the retention rate of high-concentration Phide reached 63.30%, which was significantly higher than that of the low-concentration system. Spectroscopic characterization and theoretical calculations suggested that Phide molecules tend to adopt a parallel stacking arrangement during aggregation. Van der Waals and electrostatic interactions were identified as major driving forces for aggregate formation. Hole-electron analysis further indicated the presence of charge-transfer characteristics and enhanced electronic delocalization within the aggregated structure.

CONCLUSION

The experimental and theoretical results consistently suggest that molecular aggregation is associated with improved photostability of Phide in aqueous systems. This work provides insight into the aggregation behavior and photostability of dephytylated chlorophyll derivatives and offers a possible explanation for aggregation-associated stability at the electronic level. The findings may provide a useful basis for developing more stable water-soluble chlorophyll-derived colorant systems.