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This review covers the main aspects concerning the chemistry, the biological activity and the analytical determination of oxazolidinones, the only new class of synthetic antibiotics advanced in clinical use over the past 50 years. They are characterized by a chemical structure including the oxazolidone ring with the S configuration of substituent at C5, the acylaminomethyl group linked to C5 and the N-aryl substituent. The synthesis of oxazolidinones has gained increasing interest due to their unique mechanism of action that assures high antibiotic efficiency and low susceptibility to resistance mechanisms. Here, the main features of oxazolidinone antibiotics licensed or under development, such as Linezolid, Sutezolid, Eperezolid, Radezolid, Contezolid, Posizolid, Tedizolid, Delpazolid and TBI-223, are discussed. As they are protein synthesis inhibitors active against a wide spectrum of multidrug-resistant Gram-positive bacteria, their biological activity is carefully analyzed, together with the drug delivery systems recently developed to overcome the poor oxazolidinone water solubility. Finally, the most employed analytical techniques for oxazolidinone determination in different matrices, such as biological fluids, tissues, drugs and natural waters, are reviewed. Most are based on HPLC (High Performance Liquid Chromatography) coupled with UV-Vis or mass spectrometer detectors, but, to a lesser extent are also based on spectrofluorimetry or voltammetry.

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The protonation constants of several N-alkyl-substituted and unsubstituted polyamines (eight diamines, eight triamines, and four tetraamines) were determined at different ionic strengths in NaCl aqueous solutions and at 25°C by potentiometric measurements. For the dependence on ionic strength of protonation constants two approaches were used: a Debye-Hü ckel type equation and Pitzer equations. The empirical parameters calculated for the two models are very similar for the same class of amines, that is, N-alkyl-substituted, partially substituted, and unsubstituted. Therefore, some general parameters and relationships that have quite good predictive value were obtained. A number of literature protonation constants were also examined in NaClO 4 at different ionic strengths using the same procedure and gave results similar to those obtained in this work. The general tertiary > secondary > primary amino group trend was observed for the dependence on ionic strength of protonation constants. The formation of polyammonium cation-Cl -ion pairs was considered in the range 0 < I/mol L -1 e 1, and the relative formation constants are reported.

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