Interaction of microcrystalline chitosan with graphene oxide (GO) and magnesium ions in aqueous solution

Thanks to its specific chemical and physical properties, graphene has aroused growing interest in many fields of Science and Technology. The present study focuses on the properties of microcrystalline chitosan (MCCh): a compound known to increase the biocompatibility of various matrices, including those made of graphene layers, enabling the controlled release of molecules of therapeutic compounds. The study exploits the potential of MCCh to complex with metal ions, in this case Mg²⁺, and attempts to describe such interactions when the system is enriched with graphene oxide (GO). These findings would open completely new areas of knowledge about GO as a drug carrier.

Potentiometric analysis found that in the GO-Mg system, complexes of ML' type were formed, where M = Mg²⁺; L' = GO (log β _11'0 = 9.5 (3)) and ML'₂ (log β _12'0 = 13.2 (4)), whereas in the GO-Mg²⁺-MCCh system, a mixed-type complex MLL' was also formed, in which L = MCCh: this complex demonstrated the overall stability constants log β _111' = 11.2 (3) for degree of deacetylation DD 74.4% and log β _111' = 12.4 (4) for DD 97.7%. FT-IR analysis showed interactions in the GO-Mg²⁺-MCCh (DD = 97.7%) system. In addition, the amide II-NH band was displaced from 1623 cm^-1 to two bands at 1633 cm^-1 and 1648 cm^-1, resulting from the interaction of the metal ion, and the absorption band of the corresponding NH in the chitosan acetyl group was shifted from 1304 to 1351 cm^-1. When chitosan with a deacetylation degree lower than 74.4% was applied, the amide bands I and II differed only in their intensity. A greater impact on absorption was observed for the acetyl NH group of chitosan, for which the corresponding band shifted from 1319 to 1361 cm^-1.

The results confirm the ability of GO-Mg²⁺-MCCh to create complex arrangements. It can form a basic complex of one metal ion and one ligand molecule (GO) in the case of ML' (where L' = GO), or two molecules of GO with a metal ion M (Mg²⁺) in the case of ML'₂. A mixed complex of MLL' type is also formed, with two ligands: L = MCCh with deacetylation degrees DD = 74.4% and 97.7% and graphene oxide L' = GO. In the latter case, FT-IR spectroscopy was used to confirm the mode of interaction. The GO-Mg²⁺-MCCh system may be used as carrier in modern magnesium containing medicines or as auxiliary substances in pharmacy.