Synthesis of a Chlorophyllin–Chitosan Conjugate with Potential Application as a Photosensitizer

Chlorophyllin (Chl) is a chlorophyll derivative with a high capacity to absorb radiation in the visible region of the electromagnetic spectrum. This property, together with its ability to generate reactive oxygen species, enables it to act as an efficient photosensitizer. Although it is a natural and biocompatible compound, its solubility is limited, particularly in polar or aqueous media. On the other hand, chitosan (CS) is a biopolymer characterized by its biodegradability, biocompatibility, non-toxicity, and high density of amino and hydroxyl groups, which facilitate its chemical modification and the covalent attachment of various functional molecules. Considering these properties, the covalent conjugation of Chl to CS enables the development of a hybrid material that combines the photosensitizing properties of Chl with the structural and functional advantages of CS.

In this work, a Chl-CS conjugate was synthesized from Chl (40 mg) and CS (200 mg) using 1,3-dicyclohexylcarbodiimide, 1-hydroxybenzotriazole, and 4-(dimethylamino) pyridine as coupling agents. The reaction was carried out in a mixture of N,N-dimethylformamide (DMF) and triethylamine, under stirring for 72 h at room temperature under an argon atmosphere. After completion of the reaction, the solid product was purified by washing with cyclohexane, petroleum ether, and dichloromethane. Finally, Chl-CS was vacuum-dried to afford the pure product in high yield. Furthermore, the absorption and fluorescence spectra of the conjugate in DMF and water demonstrated that Chl retained its spectroscopic properties in both solvents. Therefore, the conjugate Chl-CS represents a promising alternative to be investigated as a new natural photoactive material.