The complexation of cefotaxime with an anionic polysaccharide, sodium alginate, in aqueous solutions with different pH values was studied by conductometry and by UV and IR spectroscopy. The compositions and stability constants of the complexes were determined. At pH 2.0, 5.6, and 7.2, the composition of the complex of cefotaxime with alginate corresponds to the [cefotaxime] : [alginate] molar ratio of 4.0 : 1.0, 2.3 : 1.0, and 1.0 : 1.0, respectively. The cefotaxime–alginate complex is most stable in strongly acidic media.

pH-Responsive chitosan-modified calcium alginate microspheres with an average diameter of 2.0 ± 0.05 mm for immobilization of antibiotic cefotaxime are obtained by the ionotropic gelation technique. The efficiency of cefotaxime encapsulation is 95–97%. The formation of polyelectrolyte complex alginate-chitosan in media with different pH values is studied by conductometry and dynamic light scattering. It is shown that the swelling of microspheres and the release of cefotaxime under in vitro conditions in media simulating biological fluids in the human body at peroral delivery are pH-dependent processes. Analysis of the kinetic data on the swelling of microspheres and the release of drug within the framework of the Korsmeyer-Peppas mathematical model demonstrates that the diffusion mechanism deviates from the classical Fick mechanism. This finding can probably be explained by interaction of the drug with the polymer matrix. It is found that presence of the surface chitosan layer on calcium alginate microspheres makes it possible to increase the release time of cefotaxime.

Chitosan-modified calcium alginate microspheres with the mean diameter of 2.0 ± 0.05 mm for immobilizing Cefotaxime antibiotic were prepared by ionotropic gelation. The formation of gel microspheres is influenced by the composition of the starting reactants and by the conditions of particle formation. The Cefotaxime encapsulation efficiency was 93–95%. The formation of the alginate–chitosan polyelectrolyte complex in aqueous solutions was studied by conductometry, dynamic light scattering, and IR spectroscopy. The kinetics of the drug release from calcium alginate microparticles into saline was studied in vitro. The presence of a chitosan surface layer on calcium alginate microspheres allows the Cefotaxime release time to be increased. The kinetic curves of the drug release were analyzed using the Korsmeyer–Peppas mathematical model. The analysis revealed significant deviation of the Cefotaxime diffusion mechanism from the classical mechanism. The probable cause is interaction of Cefotaxime with chitosan.

Multilayer microcapsules with the encapsulated model drug (acetylsalicylic acid) are formed by the layer-by-layer adsorption of natural polysaccharides, chitosan and sodium carboxymethyl cellulose, onto microparticles of calcium carbonate. Three encapsulation methods are considered: physical adsorption of acetylsalicylic acid in the pores of calcium carbonate microparticles, coprecipitation of an acid with an inorganic template material during its preparation, and incorporation of an acid into hollow capsules by varying the permeability of their shells. To vary the shell permeability, it is proposed to change the polarity of the solvent by introducing 50 vol% ethanol into an aqueous solution. The method has the highest efficiency in encapsulation of acetylsalicylic acid and does not allow the release of acid from the capsules in acidic environments.

The complexation of chitosan and anionic surfactant, sodium dodecyl sulfate (DDS), in aqueous-alcohol media with a variable content of an organic cosolvent (methanol, ethanol, and propan-1-ol) was studied. A complicated effect of the composition of mixed solvents on the binding parameters of DDS by chitosan was observed. The introduction of 10–20 vol.% ethanol and propan-1-ol is accompanied by an increase in the degree of cooperative binding of DDS compared to that found in an aqueous solution, which leads to a decrease in the critical concentration of association and an increase in the cooperativity parameters.

The formation of polyelectrolyte complexes between natural polysaccharides, chitosan and carboxymethyl cellulose sodium salt, in water–ethanol media was studied. It was found that, with an increase in the content of ethanol in the solvent to 50 vol %, the intensity of the Coulomb interactions between oppositely charged groups of polyelectrolytes gradually weakens and, as a consequence, the complexing ability of polymers decreases. The layer-by-layer adsorption of polyelectrolytes onto calcium carbonate microparticles yielded microcapsules with a different number of layers. An approach is proposed to control the permeability of polyelectrolyte microcapsule walls by changing the solvent polarity upon addition of 50 vol % ethanol to an aqueous solution. Microcapsules with a high efficiency of inclusion of a model drug substance, acetylsalicylic acid, were obtained using this approach.

The formation of polymer-colloid complexes of chitosan and anionic surfactant—sodium dodecyl sulfate—in water–alcohol mixtures is studied by potentiometry using ion-selective electrodes. The influence of the nature and content of organic cosolvent (methanol, ethanol, and 2-propanol) on the parameters of binding of surfactant with chitosan and the stability of complexes is discussed. The obtained data are analyzed in terms of the model of cooperative binding and pseudophase model. It is shown that addition of 10–20 vol % of ethanol and 2-propanol to aqueous solution intensifies cooperative binding of sodium dodecyl sulfate with chitosan, which leads to the decrease in the critical association concentration and increase in the parameters of cooperativity and stability of complexes.

The association of chitosan in aqueous-alcohol solutions is studied via probe fluorescence spectroscopy and dynamic light scattering. It is shown that, if a certain critical concentration is reached, the associates of macromolecules 12–38 nm in size are formed in chitosan solutions. The addition of 5–60 vol % ethanol to the solvent leads to reduction in the critical association concentration. The tendency of chitosan macromolecules toward association is the most pronounced at 34 vol % alcohol.

The effect of additions of sodium tetradecyl sulfate as an anionic surfactant on the association of chitosan macromolecules in aqueous-glycerol solutions was studied by fluorescence probe spectroscopy and dynamic light scattering. Associates of 40–170 nm size are formed on reaching a certain critical concentration of chitosan in solutions. The critical association concentration of chitosan in solutions containing 10–30 vol % glycerol is higher than in aqueous solutions. Formation of chitosan–surfactant complexes enhances the tendency of chitosan macromolecules to association in water–glycerol mixed solvents.

The complexing of protonated chitosan with dodecyl sulfate ions in water solutions is studied using IR spectroscopy data and quantum-chemical calculations. It is established that the electrostatic interaction between the protonated amino groups of chitosan and dodecyl sulfate ions is apparent in the IR spectrum as a band at 833 cm−1. The need to consider the effect the solvent has on the formation of hydrogen-bound ion pairs [CTS+ ⋅ C12H25O 3 - ] is shown via a quantum-chemical simulation of the equilibrium geometry and the energy characteristics of complexing and hydration.

The effects of addition of ethanol and propan-1-ol on sodium tetradecyl sulfate micelle formation in an aqueous solution are studied via microprobe fluorescence microscopy and conductometry. The critical micelle concentration, quantitative characteristics of micelles, and thermodynamic parameters of micelle formation are determined. Addition of 5–15 vol % of ethanol or 5–10 vol % of propan-1-ol is shown to result in a lower critical micelle concentration than in the aqueous solution, and in the formation of mixed spherical micelles whose sizes and aggregation numbers are less than those for the systems without alcohol. The contribution from the enthalpy factor to the free energy of sodium tetradecyl sulfate micelle formation is found to dominate in mixed solvents, in contrast to aqueous solutions.

The influence of the length of the hydrocarbon radical in sodium alkyl sulfates and of the solvent composition on the formation of polymer-colloid complexes with chitosan in aqueous-ethanol solution was studied. The critical association constants, binding cooperativity parameters, and dissociation constants of the complexes were determined. An increase in the length of the alkyl radical leads to enhancement of the association of sodium alkyl sulfates with chitosan at an ethanol concentration in solution of up to 30 vol %. In solutions with higher ethanol concentrations, the solvent composition becomes the decisive factor of the complex formation of chitosan with sodium alkyl sulfate.