Hydrogels Based on a L-Cysteine–Silver Nitrate Aqueous Solution with Sodium Alginate

Hydrogels based on a supramolecular low-concentrated gel-precursor―a cysteine–silver solution (CSS)―and the polysaccharide sodium alginate (SA), which is a polyanion, were obtained in this work. Gelation initiated in the cysteine–silver solution by the polysaccharide or by the MgSO4 electrolyte anion was studied in various systems (CSS–SA, CSS–SA–MgSO4, CSS–MgSO4) using vibroviscometry, UV spectroscopy, dynamic and electrophoretic light scattering, and scanning electron microscopy. It was found that the introduction of SA into the cysteine–silver solution at concentrations ranging from 0.01 to 0.05 mg/mL does not lead to hydrogel formation; gels are formed only in the presence of a sulfate-containing electrolyte at a concentration of 0.3 to 0.6 mM, but they are not strong and are easily disrupted by mechanical action. UV spectroscopy showed that in the gel-precursor spectrum, under the influence of SA macromolecules, the intensity of the absorption bands at ~312 and ~390 nm decreases due to a change in the geometry of the cluster chains of silver mercaptide ---Ag–S(R)—Ag–S(R)---ₙ. According to dynamic and electrophoretic light scattering data, positively charged aggregates are formed in the CSS–SA system due to electrostatic interactions between the chain structures of CSS and SA molecules.