Alginate gels have been explored in relevant domains for daily life such as pharmaceutics and environmental. The structural features of alginate allow functionalization which, in extension, can modify the gel...

Host–guest interactions in functionalised alginate gels are evidenced by EPR and fluorescence spectra.

In this work, we explored by means of electron paramagnetic resonance (EPR) spectroscopy the accessibility of a series of spin probes, covering a scale of molecular weights in the range of 200–60,000 Da, in a variety of hydrogels: covalent network, ionotropic, interpenetrating polymer network (IPN) and semi-IPN. The covalent gel network consists of polyethylene or polypropylene chains linked via isocyanate groups with cyclodextrin, and the ionotropic gel is generated by alginate in the presence of Ca2+ ions, whereas semi-IPN and IPN gel networks are generated in a solution of alginate and chitosan by adding crosslinking agents, Ca2+ for alginate and glutaraldehyde for chitosan. It was observed that the size of the diffusing species determines the ability of the gel to uptake them. Low molecular weight compounds can diffuse into the gel, but when the size of the probes increases, the gel cannot uptake them. Spin-labelled Pluronic F127 cannot be encapsulated by any covalent gel, whereas spin-labelled albumin can diffuse in alginate gels and in most of the IPN networks. The EPR spectra also evidenced the specific interactions of spin probes inside hydrogels. The results suggest that EPR spectroscopy can be an alternate method to evaluate the mesh size of gel systems and to provide information on local interactions inside gels.

Gold (Au0) nanoparticles (AuNPs) have been investigated for decades as selective catalysts for a series of reactions including alcohol oxidation, alkene hydrogenation and nucleophilic addition to C-C multiple bonds. In this study, the reduction/oxidation processes mediated by AuNPs embedded within a polymeric hydrogel have been tested. In particular, we monitored two processes: i) the reduction of 4-nitrophenol and ii) the reduction of a TEMPO moiety covalently linked to a fluorescent moiety, in the presence of AuNPs/hydrogel. The hybrid AuNPs/hydrogel material was obtained by reduction of a gold salt within the cross-linked poly(ethylene glycol)/β-cyclodextrin gel following a procedure previously reported. We found that this material is suitable for cyclic reduction of 4-nitrophenol as the material is not structurally modified after the reduction process. The electron paramagnetic resonance (EPR) signal of the TEMPO moiety decreases in the first instance, due to reduction by AuNPs, and slightly increases in time, proving the oxidizing property of AuNPs embedded in hydrogel.