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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.