New understanding on iota-carrageenan oxidation by hydrogen peroxide with or without copper sulphate and the properties of oxidized iota-carrageenan.

To explore the oxidation mechanism of iota-carrageenan (IC) and the potential applications of oxidized IC (OIC), a series of OIC samples were firstly synthesized under hydrogen peroxide or hydrogen peroxide/copper sulphate, their purification process, chemical composition, chemical structure, molecular weight, physical property, biosafety and antibacterial activity were systematically evaluated. Our results firstly found that only the combination of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) pre-treatment and dialysis could realize successful purification of OIC due to the strong electrostatic attractions between positive copper ions and negative sulphate ions. The introduction of copper ions could effectively speed up the oxidation of OIC, enhancing the content of aldehyde and carboxyl groups, resulting in the hydrolysis of the ether bonds in IC, inhibiting the detachment of sulphate, decreasing the molecular weight, thermal stability, characteristic temperature (i.e. gelling and melting temperature). It was worth mentioning that K+ and Zn2+ could also inhibit the de-sulfation during the oxidation via the chelating interactions. In addition, purified OIC samples possessed excellent cytocompatibility and blood compatibility, which could also promote the proliferation and migration of fibroblast cells. Meanwhile, all OIC samples possessed antibacterial activity. In summary, our investigations shed new lights on OIC synthesis, purification, properties and potential applications.