Synthesis of silicon (IV)-based Phthalocyanine N3-nucleoside conjugates with absorption, aggregation, solvent effects, and in vitro anticancer activity.

Silicon (IV)-based phthalocyanines (Si(IV)-Pcs) are attractive scaffolds for photodynamic therapy due to their strong absorption in the therapeutic window and tunable photophysical properties. In this work, a novel N3-thymidine-silicon(IV) phthalocyanine conjugate was prepared via axial substitution using a propyl spacer and fully characterized by spectroscopic techniques and high-resolution mass spectrometry. UV-Vis studies revealed pronounced solvent-dependent behavior, with concentration-dependent measurements in DMSO demonstrating strict adherence to the Beer-Lambert law (ε = 2.17 × 105 L·mol-1·cm-1 at 674 nm), indicating that predominantly monomeric species were present under these conditions. The behavior of aggregation induced by solvents was observed in mixtures with a high methanol content. Molecular docking studies suggested an enhanced binding affinity of the conjugate toward selected cancer-relevant protein targets compared to the Si(IV)-Pcs. In vitro biological evaluation showed that the conjugate exhibited improved cytotoxic and anti-migratory activity against breast cancer cell lines relative to the Si(IV)-Pcs. Molecular docking further indicated that both the Si(IV)-Pc dichloride and nucleoside-conjugated silicon phthalocyanine engage key residues implicated in apoptosis regulation and migration, supporting their relevance to the targeted cancer pathways. The conjugates, however, appear to expand the interaction surface at the protein binding sites, increasing the number of contacts and overall binding energy. These findings highlight the potential of nucleoside-conjugated silicon phthalocyanines as scaffolds for controlling aggregation, paving the way for further development in photodynamic and anticancer applications.