Electrochemical oxidation of κ-carrageenan with hydrogen peroxide and a copper electrode for green synthesis of functional polysaccharides

Oxidation of carbohydrates and polysaccharides is crucial in the chemical industry, producing biocompatible dialdehyde crosslinkers for various applications. Conventional oxidation methods, including sodium periodate, sodium hypochlorite, TEMPO, and hydrogen peroxide, face limitations such as sensitivity to oxidant concentration, temperature, light, reaction time, pH, potential side reactions, environmental impact, and cost. To overcome these challenges, a green, safe, and simple electrochemical oxidation process for polysaccharides is reported for the first time. In this study, the oxidation process was performed by dispersing polysaccharides in heated ethanol containing hydrogen peroxide, followed by the application of an optimized voltage of 2 V in short, controlled durations using a simple two-electrode system. After completion, the reaction mixture was filtered and dried in an oven at 70 °C for 3 h. This method was specifically applied to kappa-carrageenan (k-Car). Characterization by FTIR, ¹H NMR, ¹³C NMR, TGA, and SEM confirmed the introduction of aldehyde groups and structural modifications that result in a successful oxidation process. The antibacterial activity of the oxidized k-Car (Ok-Car) was evaluated against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) using the dilution method. The reactive aldehyde groups in Ok-Car contribute to its antimicrobial properties, with inhibition zone diameters averaging 12 mm for E. coli and 11 mm for S. aureus. This fact demonstrates significant antibacterial efficacy against both gram-negative and gram-positive bacteria. The method was also applied to several other polysaccharides to assess the generalizability of the approach. Their FTIR and ¹H NMR data, provided as Supporting Information, showed similar spectral patterns to Ok-Car, further validating the effectiveness of the method. This environmentally friendly, facile oxidation strategy offers a promising alternative for polysaccharide functionalization in biomedical and industrial fields.