Spectroscopic properties of norfloxacin and sulfadiacine. Molecular interactions in solution

Otro; IV Reunión Internacional de Ciencias Farmacéuticas (RICiFa); 2016

Norfloxacin (NOR) and sulfadiazine (SDZ) are Active Pharmaceutical Ingredients (APIs) with antibacterial properties but low solubility.The study of molecular interaction of APIs in solution allows understanding their solubility, stability and other biopharmaceutical properties in biological environments. In this framework, our objective was to study the interactions solute-solvent of NOR and SDZ in neat and binary mixtures of solvents, and the interactions solute-solute and solute-solvents of an equimolecular mixture of NOR and SDZ in binary mixtures of solvents.Concentrations of the solute were 5.0 x 10-5 M. The binary mixtures of solvents were prepared by mixing buffer pH 7.4 and increasing mole fractions of MeOH, EtOH or acetonitrile (ACN) respectively. The electronic absorption UV spectra were recorded in the wavelength range 200-400 nm. The results were analyzed by the Taft and Kamlet?s linear free energy relationship method. Furthermore, the effect of the temperature (from 25 to 75 °C) on the UV-Vis spectra of aqueous solutions of NOR, SDZ and a their equimolecular mixture were analyzed.NOR and SDZ acted as hydrogen bond donors (α) and acceptors (β) in the solvents assayed. The solvation of NOR was also determined by the solvent dipolar interactions (π). In buffer:MeOH, SDZ showed preferential solvation (PS) by buffer, but in buffer:EtOH, it was done by EtOH in the range of 20-60 % v/v. In the mixture buffer:ACN, SDZ was solvated by ACN. On the other hand, NOR showed PS by MeOH, EtOH and ACN. The equimolecular mixture of NOR+SDZ showed PS in all proportions of EtOH and ACN and by MeOH in the range 60-100% v/v.Thermochromic assays exhibited bathochromic displacements of the UV-Vis absorption in all the samples of studied APIs, evidencing intramolecular equilibrium by transference of H, from a COOH group to a NH.