Nanosecond and picosecond absorption and emission spectroscopic techniques were applied to the investigation of the reactivity from the lowest excited states of some 6-fluoro-7-piperazino-4-quinolone-3-carboxylic acids (FQs) in aqueous media at neutral pH, in the absence and presence of different sodium salts. Following the detection of various transients, we proposed a mechanism for the cleavage of the carbonÀfluorine bond that proceeded through different reaction pathways, dependent on the molecular structure and the characteristics of the medium. The drug lomefloxacin (LOM), a 6,8-difluoroquinolone derivative, underwent heterolytic cleavage of the C8ÀF bond from the excited singlet state. With the 6-monofluoroquinolone norfloxacin (NOR) and the corresponding 1,8-naphthyridinone enoxacin (ENX), the lowest singlet state was not significantly reactive and an important deactivation channel was intersystem crossing (ISC) to the triplet manifold. The lowest triplet state underwent cleavage of the C6ÀF bond through a solvent mediated process possibly via a cyclohexadienyl anionic adduct. In the presence of sulfite or phosphate buffer a novel defluorination mechanism, induced by electron transfer from the inorganic anions to the FQ triplet state, was observed. The correlation between the transients observed and the final photoproducts in the different media was elucidated.

The photochemistry of some fluorinated 7-amino-4-quinolone-3-carboxylic acids used in therapy as antibacterials and known to be phototoxic has been investigated in water. All of them undergo heterolytic defluorination, and this appears to be a path for the generation of aryl cations in solution. 6-Fluoro derivatives such as norfloxacin (Phi(dec) = 0.06) and enoxacin (Phi(dec) = 0.13) give the corresponding phenols. Insertion of an electron-donating substituent makes defluorination inefficient; thus, ofloxacin, an 8-alkoxy derivative, is found to be rather photostable (Phi(dec) = 0.001) and reacts in part via a process different from defluorination (degradation of the N-alkyl side chain). With a 6,8-difluoro derivative, lomefloxacin, the reaction is more efficient (Phi = 0.55) and selective for position 8. Contrary to the previous cases, the aryl cation undergoes insertion in the neighboring N-ethyl group rather than solvent addition (a carbene-like chemistry). With all of the above fluoroquinolones an intensive triplet-triplet absorption is detected and is quenched by sulfite (k(q) = (1-5) x 10(8) M(-)(1) s(-)(1)). Under this condition, reductive defluorination via the radical anion takes place. The relation of the above chemistry to the phototoxicity of these drugs is commented upon briefly.

Mineral nutrition of plants greatly depends on both environmental conditions, particularly of soils, and the genetic background of the plant itself. Being sessile, plants adopted a range of strategies for sensing and responding to nutrient availability to optimize development and growth, as well as to protect their metabolisms from heavy metal toxicity. Such mechanisms, together with the soil environment, meaning the soil microorganisms and their interaction with plant roots, have been extensively studied with the goal of exploiting them to reclaim polluted lands; this approach, defined phytoremediation, will be the subject of this review. The main aspects and innovations in this field are considered, in particular with respect to the selection of efficient plant genotypes, the application of improved cultural strategies, and the symbiotic interaction with soil microorganisms, to manage heavy metal polluted soils.

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The genetic engineering of plants to facilitate the reclamation of soils and waters contaminated with inorganic pollutants is a relatively new and evolving field, benefiting from the heterologous expression of genes that increase the capacity of plants to mobilize, stabilize and/or accumulate metals. The efficiency of phytoremediation relies on the mechanisms underlying metal accumulation and tolerance, such as metal uptake, translocation and detoxification. The transfer of genes involved in any of these processes into fast-growing, high-biomass crops may improve their reclamation potential. The successful phytoextraction of metals/metalloids and their accumulation in aerial organs have been achieved by expressing metal ligands or transporters, enzymes involved in sulfur metabolism, enzymes that alter the chemical form or redox state of metals/metalloids and even the components of primary metabolism. This review article considers the potential of genetic engineering as a strategy to improve the phytoremediation capacity of plants in the context of heavy metals and metalloids, using recent case studies to demonstrate the practical application of this approach in the field.

The photochemical fate of Marbofloxacin (MAR) and Enrofloxacin (ENR), two Fluoroquinolones (FQs) largely used as veterinary bactericides known to be present in surface waters, was investigated in aqueous solution. The degradation of these pollutants (5-50 microg L(-1) starting concentration) was complete in about 1 h by exposure to solar light (summer) and obeyed a first-order kinetics. The structure of the primary photoproducts was determined. Those from ENR arose through three paths, namely, oxidative degradation of the piperazine side-chain, reductive defluorination, and fluorine solvolysis. More heavily degraded products that had been previously reported were rationalized as secondary photoproducts from the present ones. As for MAR, this underwent homolytic cleavage of the tetrahydrooxadiazine moiety to give two quinolinols. All of the primary products were themselves degraded in about 1 h. The photoreactions rates were scarcely affected by Ca(2+) (200 mg L(-1)), Mg(2+) (30 mg L(-1)), Cl(-) (30 mg L(-1)), and humic acid (1 mg L(-1)), but increased in the presence of phosphate (20 mg L(-1)). The fastest degradation of ENR occurred at pH about 8 where the zwitterionic form was present, while in the case of MAR the cationic form was the most reactive.

The products of irradiation of some 6‐fluoro‐7‐piperazino‐4‐quinolone‐3‐carboxylic acids in phosphate buffer arise from a combination of reductive defluorination of the heteroaryl ring and oxidative fragmentation of the piperazine side chain. This unusual reaction contrasts with the fluorine atom substitution observed in neat water. The results of steady‐state and time‐resolved experiments are consistent with initiation of the process by electron‐transfer quenching of the triplet state of these heterocycles by the phosphate anion. For one of the compounds, a transient band (λmax = 670 nm), previously attributed to the defluorinated cation, must now be reassigned to the radical anion. This intermediate undergoes inefficient reductive defluorination of the ring. In the process, a phosphate radical anion is expected to be formed and to abstract a hydrogen atom from the piperazine group, leading to degradation of the latter.

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