Synthesis and structural characterization of pyrroloquinoline quinone grafted carboxymethyl chitosan copolymer with neuroprotective potential

Pyrroloquinoline quinone (PQQ) is a redox cofactor that has been shown to have strong antioxidant capacity and neuroprotective effects and has been extensively studied in recent years. However, PQQ small molecule compounds have poorly stability and low bioavailability in vivo, making it difficult to exert drug activity for long periods of time. In this study, we employed the EDC/NHS method to graft PQQ onto carboxymethyl chitosan (CMCS) to improve the utilization of PQQ. The obtained PQQ-g-CMCS product was a water-soluble copolymer, and the grafting rate could be controlled by adjusting the pH and the raw material feeding ratio. The PQQ-g-CMCS samples were characterized using FT-IR, UR-Vis, NMR, and XRD spectroscopy, suggesting a conjugation reaction between the amino groups of CMCS and the carboxyl groups of PQQ. Specifically, the in vitro antioxidant experiments showed that the Fe2+ chelating activity of the grafted copolymer was significantly enhanced. In addition, the PQQ-g-CMCS copolymer also exhibited good biocompatibility and significant protective effect against H2O2-induced oxidative damage in SH-SY5Y cells. These results preliminarily indicate that PQQ-g-CMCS may be a promising antioxidant material for applications such as drug release and tissue engineering.