Rational design and structure-controlled tuning of antioxidant activity in substituted nanocellulose schiff base...

Fine-tuning antioxidant performance of sustainable biomaterials remains a challenge for several researchers, mainly because of limited reported investigations of the impact of structural (substitution and/or conjugation extension) on polysaccharide-based frameworks. In this contribution, we describe the first systematic conceptualization and structure-activity study of a series of tetra-aza-substituted nanocellulose Schiff base derivatives (A-F), where we concomitantly control π-conjugation length and/or substituent effects with precisely moderated characteristics. X-ray characterization shows crystallinity indices spanning from 3.09% in pristine dialdehyde-nanocellulose to 62.67% for naphthol-substituted Schiff base derivatives, showing that hydroxyl donor substitution fused with naphthalene ring favor structural organization. The optical study elucidates advanced red-shifts ranging from 265 nm to 368 nm (nitro derivative), proving controllable photophysical properties. In addition, antioxidant activity assessment through DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)), and FRAP (Ferric Reducing Antioxidant Power) tests reveals an excellent performance: the hydroxyl-naphthalene derivative (D) exhibits the best antioxidant activity; 75% DPPH inhibition (IC₅₀ = 52 μg/mL), 86% ABTS scavenging (IC₅₀ = 57 μg/mL), and 265 μM TE reducing strength. Conversely, the electron-acceptor nitro derivative (E) decreases scavenging activity (29% DPPH inhibition). The gathered structure-activity relationship shows that OH-donor group coupled with extended conjugation outranks halogen and withdrawing substitution, di-imine/amine as well as solo conjugation extension, providing a rational conceptualization platform for antioxidant nano-cellulosic agents. Based on the observed structure-activity relationship, the hydroxyl-naphthalene Schiff base derivative shows particular promise for sustainable antioxidant applications in active food packaging, wound healing hydrogels, and ROS-scavenging biomedical materials.