Subtle influence on alginate gel properties through host–guest interactions between covalently appended cyclodextrin and adamantane units

Alginate gels have been explored in different fields for applications in daily life such as pharmaceuticals and environmental remediation. The structural features of alginate allow its functionalization, which can modify its gel properties to a certain extent. Herein, we explored the properties of ionotropic gels resulting from the complexation of alginate chains functionalized with cyclodextrin (as host) or adamantane (as guest) units by calcium ions. Several commonly used physico-chemical methods together with electron paramagnetic resonance (EPR) spectroscopy were employed as characterisation tools in this study. The SEM images of alginate xerogels revealed morphological changes in gel networks, which were induced by the functionalization of polysaccharide chains and subsequent interactions between the appended host and guest units. The rheological properties of alginate hydrogels were also influenced by derivatization and host-guest interactions. Higher storage and elastic moduli values were recorded for gels obtained from a mixture of adamantane-functionalized and cyclodextrin-functionalized alginates. Furthermore, spin labelling of the alginate chain made it possible to use EPR spectroscopy to characterise these gel systems. The EPR method allowed us to evidence the local host-guest interactions and to correlate the information with data provided by techniques offering comprehensive gel properties. Overall, these investigations demonstrated that although host-guest interactions are not the driving force for the generation of alginate gels, their presence influences and can modulate the properties of gels.