Trace amounts of the widely used β-lactam antibiotics (Atbs) in waste water may cause adverse effects on the ecosystems and contribute to the proliferation of antibiotic-resistant bacteria. On these grounds, kinetic and mechanistic aspects of photosensitized degradation of Ceftriaxone (Cft) and Cefotaxime (Ctx), have been studied in pure water by stationary and time-resolved techniques. Additionally, possible implications of these photoprocesses on the antimicrobial activity of the Atbs have also been investigated. Photoirradiation of aqueous solutions of Cft and Ctx produces the degradation of both Atbs in the presence of Riboflavin (vitamin B2), a well known pigment dissolved in natural aquatic systems. The process occurs through Type I and Type II mechanisms, with effective prevalence of the former. The participation of O2(-), OH and O2((1)Δg) is supported by experiments of oxygen consumption carried out in the presence of specific scavengers for such reactive oxygen species. Microbiological assays exhibit a parallelism between the rate of Cft and Ctx photodegradation and the loss of their bactericidal capacity on Staphylococcus aureus strains. Results contribute to both understanding kinetic and mechanism aspects of the degradation and predicting on natural decay of Atbs waste water-contaminants.

The use of biologically active substances with anti-inflammatory properties such as corticosteroids has increased considerably in the last few decades. Particularly, the compound we are interested in, prednisolone (Predn), is a glucocorticoid with high biological activity. This compound absorbs UV radiation and may participate in photochemical processes, which can result in its own decomposition. These processes could result in the formation of free radicals or reactive oxygen species (ROS). On these grounds, the kinetic and mechanistic aspects of the direct photodegradation of Predn have been studied in aqueous medium under different atmospheric conditions by stationary and time-resolved techniques. The mechanism involved in the photodegradation has been elucidated. Predn is capable of generating the excited triplet state ³Predn* as a result of UVB light absorption. In the presence of oxygen, ³Predn* allows the formation of ROS, of which O₂(¹Δ_g) (Φ_Δ = 0.014), H₂O₂ and the radical OH˙ stand out. The latter is generated from the spontaneous dismutation of O₂˙⁻ and subsequent homolytic cleavage, photochemically promoted, of H₂O₂. Predn undergoes unimolecular photodegradation reactions under an inert argon atmosphere. In this study we found that in the presence of oxygen, the Predn photo-consumption is improved. This implies that the attack by ROS involves a very important additional contribution to the photodegradation of Predn under aerobic conditions.

In order to investigate the effect of solar UV light on pharmacological compounds considered as emerging environmental pollutants, we studied the kinetic, mechanistic and toxicological aspects of the direct photolysis of two highly used anti-inflammatory corticosteroids: dexamethasone and prednisone. The photochemical experiments were done in aqueous media under different atmospheric conditions, with the purpose of discerning the participation of oxygen in the photodegradative processes. Moreover, the influence of direct micelles of different surfactants on the behavior of the corticosteroids under UV light was evaluated, and the cytotoxicity of the photoproducts toward the Vero cell line was tested as well. Through static and dynamic spectroscopic techniques, it was possible to detect a dependence between the rate of the photodegradation and the availability of oxygen, since both corticosteroids are capable of photosensitizing the generation of reactive oxygen species, mainly singlet oxygen and the hydroxyl radical, by generating their respective triplet excited state (characterized for the first time in this work). Dexamethasone and prednisone are inert to the action of singlet oxygen but sensitive to the effect of the hydroxyl radical. Also, unimolecular photochemical reactions, namely Norrish type I and II photo-rearrangements, occur due to the presence of carbonyl functional groups in the molecular structures. In the presence of direct micelles of anionic, cationic and non-ionic surfactants, a photoprotective effect was observed for all the studied corticosteroids. The protection phenomenon was attributed to the interaction of the molecules with the micellar interfaces and their overall distribution inside the non-polar micellar core. This behavior seems to be in a close relationship with the dipolar moment of each molecule. On the other hand, the in vitro cytotoxicity bioassays, MTT metabolism and neutral red uptake, reveal that the corticosteroids and their photoproducts obtained under different atmospheric conditions induce cell metabolic alterations at the mitochondrial level, and this effect could be more significant than lysosomal damage. In most cases, photoproducts are found to have greater toxicity than the original drugs. Studies on micellar influence and cytotoxicity also included the corticosteroid prednisolone, whose photodegradation has been previously studied in homogeneous medium.

The 3,3′, 4′,7 tetrahydroxiflavone (fisetin) is a natural therapeutically active and fluorescent polyhydroxyflavone, with important spectroscopic and biological behavior. Fisetin shows dual emission, with a normal band (N) from the S₁→S₀ transition and the one generated in the excited state (phototautomer; PT) from the intramolecular proton transfer (ESIPT) process. The influence of different interfaces on the ESIPT process of fisetin was investigated in reverse micelles media (RMs) made of the anionic sodium 1,4‐bis (2‐ethylhexyl) sulfosuccinate (AOT) and cationic benzyl n‐hexadecyl dimethylammonium chloride (BHDC) surfactants, in benzene. The studies were carried out by absorption, emission spectroscopy, steady‐state anisotropy and time‐resolved fluorescence measurements. Fisetin behavior was also investigated in homogeneous media with special emphasis in water and benzene, which are the polar core and the organic pseudofase in the RMs, respectively. In addition, the effect of concentration in benzene and the variation of the pH in water were studied. Fluorescence lifetime measurements show that in water the ESIPT process is independent on the concentration, while in benzene it was possible to detect fluorescent aggregate species (Nas) formed in the ground state. The effect of the pH in water allowed us to identify the anionic fisetin (A⁻) emission. The studies in RMs show that fisetin interacts specifically with the head of the surfactants, which always results in diminishing the emission of the PT. Also the formation of A⁻ is detected particularly at W₀ > 0. Appreciable high anisotropy values are obtained in RMs, as compared with those in fluid homogeneous media, which are independent of the water content confirming that fisetin molecules are anchored in the anionic as well as in the cationic interfaces.