The photobehavior of fluoroquinolone antibiotics, one of the most successful classes of drugs in therapeutic applications, has recently been the object of increasing interest due to the finding of their phototoxic and photocarcinogenic properties. The main results obtained for a series of structurally related, representative fluoroquinolone drugs is reviewed. Both activation of oxygen and various degradation pathways have been identified and the effects of medium and structure have been rationalized. The results can help in the understanding of the photochemistry occurring in biological environments and in the assessing of the correlation between structural characteristics and biological photodamage.

In an attempt to improve our understanding of the basic mechanisms of the degradation of aromatic pollutants in water by TiO2 photocatalysis, quinoline (benzo[b]pyridine) was selected as a molecular probe, principally because of the difference in electron density over its two rings. This study was based on the identification and quantification of the primary products or principal secondary products of quinoline degradation either by TiO2 photocatalysis at pH 3 and 6 or by OH• radicals generated via the photo-Fenton reaction (Fe(II/III)−H2O2−UV) at pH 3. In this latter case, the three major products were those expected from the preferential electrophilic attack of OH• radicals on the electron-richer benzene moiety, viz., 5-, and 8-hydroxyquinolines and quinoline-5,8-dione derived from them. TiO2 photocatalysis did not yield this dione, and at the same percentages of degraded quinoline, the amounts of 5-hydroxyquinoline were lower by a factor of ca. 2 at pH 3 and ca. 10 at pH 6 (those of the 8-isomer were also decreased but no accurate measurements were obtained). In addition, at pH 6, we observed marked increases in the amounts of products corresponding to the oxidation of the pyridine moiety, viz., 4-quinolinone and especially 2-aminobenzaldehyde (the major product) and its N-formyl derivative. These results show that oxidative steps in TiO2 photocatalysis do not involve only OH• radicals. It was also observed that, at pH 6, superoxide dismutase (SOD), which catalyzes the elimination of O2 •- species, decreased the TiO2 photocatalytic rate of quinoline disappearance, almost suppressed the formation of 2-aminobenzaldehyde, and lowered the amount of 4-quinolinone. The SOD and pH effects suggest a mechanism involving quinoline activation by hole transfer, followed by superoxide addition to the resulting radical cation. The nucleophilic character of superoxide implies addition to the pyridine moiety, i.e., with a regioselectivity opposite that of the OH• radical pathway.

Where to look for really 'green' synthetic methods, under conditions as mild as those nature uses? A hundred years ago, a great scientist, Giacomo Ciamician, confronted the problem. He had no doubt of the answer: it was solar light. The approach and the discoveries by Ciamician are illustrated in connection with present-day green chemistry.