The photophysical and photochemical properties of antipyretic drug – paracetamol (PAR) and its two analogs with different substituents (acetanilide (ACT) and N-ethylaniline (NEA)) in 14 solvents of different polarity were investigated by the use of steady–state spectroscopic technique and quantum–chemical calculations. As expected, the results show that the spectroscopic behavior of PAR, ACT, and NEA is highly dependent on the nature of the solute–solvent interactions (non-specific (dipole-dipole) and specific (hydrogen bonding)). To characterize these interactions, the multiparameter regression analysis proposed by Catalán was used. In order to obtain a deeper insight into the electronic and optical properties of the studied molecules, the difference of the dipole moments of a molecule in the ground and excited state were determined using the theory proposed by Lippert, Mataga, McRae, Bakhshiev, Bilot, and Kawski. Additionally, the influence of the solute polarizability on the determined dipole moments was discussed. The results of the solvatochromic studies were related to the observations of the release kinetics of PAR, ACT, and NEA from polyurethane hydrogels. The release kinetics was analyzed using the Korsmayer-Peppas and Hopfenberg models. Finally, the influence of the functional groups of the investigated compounds on the release time from the hydrogel matrix was analyzed.

Polyurethane hydrogels are potentially attractive materials for biomedical applications. They are able to absorb large amount of water, biological fluids or active substances, and thus, they have potential to be used as absorbents or wound-healing dressings. They are also used for the controlled release of therapeutics because of their capacity to embed biologically active agents in their water-swollen network. The presence of organofillized montmorillonite (Cloisite® 30B) in polyurethane nanocomposite hydrogels remarkably improves the swelling capability, but on the other hand slows down the release process of an active substance from the matrix. The swelling of paracetamol solution by the nanocomposite matrix and the release process of this active substance from the hydrogel were investigated using gravimetric analysis and spectroscopic method. The kinetics of both these processes were accurately analyzed by the use of Korsmeyer–Peppas and modified Hopfenberg and Weibull models. In the present paper, three different nanocomposite systems with various amounts of Cloisite® 30B were studied. The results of these studies confirm beneficial impact of the nanosize effect on the drug diffusion processes in polyurethane nanocomposite hydrogels.