Charge-density-dependent selective radical suppression in carboxymethyl cellulose.

Area of Science:

• Biochemistry and Materials Science
• Focus on polysaccharide chemistry and antioxidant mechanisms

Background:

• Carboxymethyl cellulose (CMC) is a biocompatible polysaccharide with known antioxidant properties.
• The precise mechanism behind CMC's radical scavenging activity has remained unclear.
• Understanding CMC's antioxidant function is crucial for its application in various fields.

Purpose of the Study:

• To elucidate the radical scavenging mechanism of CMC.
• To quantify the influence of the degree of substitution (DS) on CMC's antioxidant activity.
• To explore the potential for engineering polysaccharide-based antioxidants.

Main Methods:

• Utilized electron spin resonance (ESR) spin trapping to quantify radical scavenging.
• Investigated three distinct radical-generating systems: H₂O₂ photolysis (•OH), AAPH photolysis (•OOR/•OR/•OH), and K₂S₂O₈ thermolysis (SO₄•⁻).
• Assessed the impact of varying DS on CMC's scavenging efficacy.

Main Results:

• •OH scavenging was independent of DS, suggesting diffusion-controlled reactivity.
• Scavenging of AAPH-derived radicals increased with DS, indicated by lower IC₅₀ and higher k_app values.
• • SO₄•⁻ scavenging was weak and decreased at higher DS due to electrostatic exclusion.

Conclusions:

• CMC functions as a DS-dependent reaction field, not a nonspecific scavenger.
• Chain-averaged charge density, not backbone structure or length, dictates radical suppression.
• Charge density engineering offers a generalizable strategy for tuning polysaccharide antioxidant selectivity.