CHEMICALLY MODIFIED CARRAGEENANS FOR MODULATING BIOLOGICAL RESPONSES: IMPACT OF CARBOXYMETHYLATION AND AMINATION ON ANTIOXIDANT, ANTIBACTERIAL, AND DEGRADATION PROPERTIES.

Abstract

Carrageenans are sulfated polysaccharides derived from red seaweeds that have attracted significant attention for biomedical applications due to their biocompatibility, hydrophilicity, and structural tunability. Therefore, by chemically modifying their native forms we have more libraries of carrageenan derivatives with potential bioactivities in biomedical applications. This study focused on the chemical modification, characterization, and functional evaluation of three commercial types of carrageenan, kappa, iota, and lambda, to possibly alter their antioxidant, antibacterial, and degradation behavior, and to explore their application in layer-by-layer (LbL) polyelectrolyte multilayer (PEM) coatings.Chemical modification was carried out through carboxymethylation and amination using several reaction routes, including Williamson ether synthesis, epichlorohydrin-based ring opening, and EDC/NHS and DMTMM coupling reactions. The structural modifications were confirmed by ¹H and ¹³C NMR and FTIR spectroscopy, which revealed characteristic peaks corresponding to new carboxymethyl (–CH₂COOH) and amine (–NH₂) functional groups. The antioxidant activities of the native and modified carrageenans were assessed using DPPH, ABTS, and FRAP assays. Results indicated a change in radical scavenging capacity for the modified samples. Antibacterial assays were performed against both Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria using the broth microdilution method. The modified carrageenans showed concentration and time dependent inhibition effects. All carrageenan and derivatives exhibited no notable inhibition against P. aeruginosa. These findings suggest that the chemical modification changes bacterial membrane interaction and surface binding through charge-based mechanisms. To evaluate enzymatic degradation, both solution and surface studies were conducted using lysozyme as the enzyme at 0.01 mg/ml 0.25 mg/ml respectively. In solution, the reducing sugar generated was quantified using the p-hydroxybenzoic acid hydrazide (pHBH) assay, which confirmed changes over 10 days. Surface degradation of PEM coatings incubated in lysozyme for up to 21 days was characterized using atomic force microscopy (AFM) revealing changes of surface roughness over time. Polyelectrolyte multilayers were formed using chitosan (CS) as the polycation and modified carrageenans as polyanions through the layer-by-layer (LbL) deposition method. A total of 16 alternating layers were deposited, terminating with the carrageenan derivative as the outermost layer. AFM revealed morphological differences between modified carrageenan PEMs and degraded PEMs. Overall, this work demonstrates that chemical modification influences the functional versatility of carrageenans. Furthermore, their successful incorporation into PEM coatings shows strong potential for applications in biomedical surface engineering, such as antimicrobial coatings, wound dressings, and enzyme-responsive thin films.