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Sulfonamides are one of the oldest groups of veterinary chemotherapeutic agents. Physico-chemical properties, the concentration and the nature of the environment are the factors responsible for the distribution of sulfonamides in the living organism. Although these drug compounds have been in use for more than half a century, knowledge about their behavior is still limited. Physiological activity is currently attributed to the sulfanyl radical. Our study is devoted to the spectral properties of aqueous solutions of sulfaguanidine, in which the formation of complexes with an H-bond and a protonated form takes place. The nature of the fluorescent state of sulfaguanidine was interpreted using computational chemistry, the electronic absorption method and the luminescence method. The structure of sulfaguanidine includes several active fragments: aniline, sulfonic and guanidine. To reveal the role of fragments in the physiological activity of the studied antibiotic, we calculated and compared the effective charges of the fragments of aniline and sulfaguanidine molecules. Chromophore groups were identified in molecules, which determine the intermolecular interaction between a molecule and a proton-donor solvent. The study also revealed the impact of sulfone and guanidine groups, as well as complexation, on the effective charge of the antibiotic fragment responsible for physiological activity and luminescent ability.

The absorption spectra of chloramphenicol aqueous solution were obtained experimentally. The absorption spectra of chloramphenicol isomers and the effect on the spectra of the formation of H-bonded complexes were calculated and interpreted using quantum chemistry methods. Calculation results showed that the absorption spectrum of chloramphenicol by position of bands and their nature is largely determined by the nitrobenzene fragment with little participation of propanol and dichloroacetamide fragments of chloramphenicol. The proton acceptor properties of individual chloramphenicol fragments and the effect of the formation of H-bonded complexes on them have been analyzed. Keywords: chloramphenicol, enantiomers, electronic absorption spectrum.

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