Paola Calza

Photocatalytic transformation of organic compounds in the presence of inorganic ions

The influence of halide ions on the photocatalytic process on titanium dioxide has been investigated carefully. Chloride and bromide ions, acting as hole scavengers, generate active radical species (e.g., ·Cl and ·Br) that participate in reactions with the organic compounds and the transient intermediates. Chloride and bromide ions have shown to deeply inhibit the degradation rate of chloroform and tetrachloromethane and to modify both the qualitative and quantitative distribution of their intermediates formed during the degradation process. In the presence of bromide, CBrCl3 is detected as intermediate during CCl4 degradation, while in the presence of chloride, formation of CCl4 is observed in the CHCl3 degradation. Fluoride ions, differently from the other halides, cannot be oxidized by the valence hole and may be used as a diagnostic tool in mechanistic studies. The influence of fluoride on phenol has been investigated, and, by choosing appropriate experimental conditions, it was possible to evaluate the role of the different active species in the photocatalytic process.

Characterization of intermediate compounds formed upon photoinduced degradation of quinolones by high-performance liquid chromatography/high-resolution multiple-stage mass spectrometry.

The paper deals with the photocatalytic transformation of two antibacterial agents, ofloxacin and ciprofloxacin, under simulated solar irradiation using titanium dioxide as photocatalyst. The investigation involved monitoring decomposition of the drugs, identifying intermediate compounds, assessing mineralization, and evaluating the toxicity of drug derivatives. High-resolution mass spectrometry was employed to assess evolution of the photocatalyzed process over time. Respectively 15 and 8 main species were identified after transformation of ofloxacin and ciprofloxacin. Through the full analysis of MS and MSn spectra and a comparison with parent drug fragmentation pathways, the different isomers were characterized. In the ofloxacin molecule, the initial transformation attacks are confined to the piperazine moiety and to the methyl groups, while the fluoroquinolone core is unmodified. Conversely, ciprofloxacin degradation involves two parts of the molecule: the piperazinic moiety and the quinolone moiety. All these intermediates are easily degraded and by 4 h mineralization is complete. Toxicity assays using Vibrio fischeri prove that neither ciprofloxacin nor its intermediates exhibit acute toxicity. In ofloxacin the secondary degradation products exhibit toxicity; a correlation exists between the evolution of the intermediate compounds and the toxicity connected to them.

Light-assisted 1,4-dioxane degradation

Abstract The oxidative degradation induced by light of 1,4dioxane been investigated in homogeneous solution in the presence of inorganic peroxides (either hydrogen peroxide or peroxydisulfate) and under heterogeneous photocatalytic conditions in the presence of titanium dioxide. The effect of photon energy spectral distribution, pH, O2 and scavengers has been examined. The degradation mechanism involves common intermediates. Ethylene glycol diformate was observed as the main intermediate. In the presence of UV light peroxydisulfate showed high degradation efficiency. A tentative chain radical oxidation mechanism is postulated. The distinctive features of heterogeneous photocatalytic treatment were the good efficiency under simulated solar spectrum and the absence of inhibition of the degradation rate by HCO3−. The presence of peroxydisulfate enhances the TiO2 photocatalytic degradation rate.

Photocatalytic transformations of chlorinated methanes in the presence of electron and hole scavengers

The photocatalytic degradation in the aqueous phase of CCl4, CHCl3 and CH2Cl2 over irradiated TiO2 has been investigated in the presence of electron and hole scavengers, including atmospheric oxygen. Chloromethanes degrade through combined reductive and oxidative processes, the importance of which varies on going from CCl4, to CHCl3 and CH2Cl2.Under aerated conditions at pH 5, almost complete conversion into CO2 and HCl has been observed. Although chloride ions were evolved stoichiometrically, at pH 11 persistent formation of formaldehyde and formic acid was observed. Stable intermediates, either chlorinated or dechlorinated (formic acid, formaldehyde and methanol) have been quantified. An initial reductive dominance was observed for CCl4 even in the presence of oxygen. CH2Cl2 degradation was largely oxidative, even from the early stages of degradation, whereas the roles of the oxidative and reductive pathways were comparable for CHCl3.The effect of hole and electron scavengers highlights the importance of reductive and oxidative pathways. Reductants suchas alcohols (methanol, propan-2-ol, tert-butanol) enhance CCl4 degradation remarkably, have a limited effect on CHCl3 andstrongly decrease the degradation rate of CH2Cl2. Electron scavengers like periodate and peroxydisulfate decrease the degradation rate of CCl4 and have limited effects on CHCl3. Halides (chloride and bromide) show a peculiar behaviour. Acting as hole scavengers, they produce active species (ClNsbd and BrNsbd) that participate in reactions with transient intermediates. During degradation of CHCl3 in the presence of chloride, formation of CCl4 was reported. Interestingly, for CCl4 the degradation rate decreases and in the presence of bromide CBrCl3 is detected at trace level.

Fate of antibacterial spiramycin in river waters

Spiramycin, a widely used veterinary macrolide antibiotic, was found at traceable levels (nanograms per litre range) in Po River water (N-Italy). The aqueous environmental fate of this antibiotic compound was studied through drug decomposition, the identification of the main and secondary transformation products (TPs), assessment of mineralisation and the investigation of drug TPs toxicity. Initially, laboratory experiments were performed, with the aim of stimulating the antibacterial transformation processes followed in aquatic systems. The TPs were identified through the employment of the liquid chromatography (LC)-mass spectrometry technique. Under illumination, spiramycin degraded rapidly and transformed into numerous organic (intermediate) compounds, of which 11 could be identified, formed through five initial transformation routes. These laboratory simulation experiments were verified in situ to check the mechanism previously supposed. Po River water was sampled and analysed (by LC-high-resolution mass spectrometry) at eight sampling points. Among the previously identified TPs, five of them were also found in the river water. Three of them seem to be formed through a direct photolysis process, while the other two are formed through indirect photolysis processes mediated by natural photo sensitisers. The transformation occurring in the aquatic system involved hydroxylation, demethylation and the detachment of forosamine or mycarose sugars. Toxicity assays using Vibrio fischeri proved that even if spiramycin did not exhibit toxicity, its transformation proceeded through the formation of toxic products.

Characterization of atenolol transformation products on light‐activated TiO2 surface by high‐performance liquid chromatography/high‐resolution mass spectrometry

We have studied the photocatalytic transformation of atenolol, 4-[2-hydroxy-3-[(1-methyl)amino]propoxyl]benzeneacetamide, a cardioselective beta-blocking agent used to treat cardiac arrhythmias and hypertension, under simulated solar irradiation using titanium dioxide as photocatalyst. The investigation involved monitoring drug decomposition, identifying intermediate compounds, assessing mineralization, and evaluating toxicity. High-performance liquid chromatography (HPLC) coupled to high-resolution mass spectrometry (HRMS) via an electrospray ionization (ESI) interface was a powerful tool for the identification and measurement of the degradation products; 23 main species were identified. Intermediates were characterized through their chromatographic behavior and evolution kinetics, coupled with accurate mass information. Through the full analysis of MS and MS(n) spectra and a comparison with parent drug fragmentation pathways, the diverse isomers were characterized. Neither atenolol nor the intermediates formed exhibit acute toxicity. All intermediates are easily degraded and no compound identified could withstand 2 h irradiation. Photomineralization of the substrate in terms of carbon mineralization and nitrogen release was rapid and, within 4 h of irradiation, organic nitrogen and carbon were completely mineralized.

Identification of the unknown transformation products derived from clarithromycin and carbamazepine using liquid chromatography/high‐resolution mass spectrometry

RATIONALE A comprehensive study of the environmental fate of pollutants is more and more required, above all on new contaminants, i.e. pharmaceuticals. As high-resolution mass spectrometry (HRMS(n)) may be a suitable analytical approach for characterization of unknown compounds, its performance was evaluated in this study. METHODS The analyses were carried out using liquid chromatography (LC) (electrospray ionization (ESI) in positive mode) coupled with a LTQ-Orbitrap analyzer. High-resolution mass spectrometry was employed to assess the evolution of the drug transformation processes over time; accurate masses of protonated molecular ions and sequential product ions were reported with an error below 5 millimass units, which guarantee the correct assignment of their molecular formula in all cases, while their MS(2) and MS(3) spectra showed several structurally diagnostic ions that allowed characterization of the different transformation products (TPs) and to distinguish the isobaric species. RESULTS The simulation of phototransformation occurring in the aquatic environment and identification of biotic and abiotic transformation products of the two pharmaceuticals were carried out in heterogeneous photocatalysis using titanium dioxide, aimed to recreate conditions similar to those found in the environmental samples. Twenty-eight main species were identified after carbamazepine transformation and twenty-nine for clarithromycin. CONCLUSIONS This study demonstrates that HRMS, combined with LC, is a technique able to play a key role in the evaluation of the environmental fate of pollutants and allows elucidation of the transformation pathways followed by the two drugs.

Ion trap tandem mass spectrometry study of dexamethasone transformation products on light activated TiO2 surface

The photocatalytic transformation of dexamethasone and the formation of its intermediate compounds have been studied using titanium dioxide as a photocatalyst. The degradation of dexamethasone occurs easily through the formation of several hydroxy derivatives whose characterization has been made by HPLC/MS/MS. Even if both oxidative and reductive processes can be operating, only oxidative products have been identified in air saturated aqueous suspensions. A pattern of reaction pathways accounting for the observed intermediates is proposed. The obtained experimental evidence may be rationalized postulating the existence of a double initial mechanism. A single oxidation step resulting from the attack by one ·OH radical leading to the formation of five hydroxy-derivatives and a concomitant attack involving two ·OH radicals leading to the hydroxylation of the quinoid moiety of the molecule.

Hernia-repair prosthetic devices functionalised with chitosan and ciprofloxacin coating: Controlled release and antibacterial activity

Polypropylene nets are widely used as hernioplasty prostheses. The reproduction of bacteria within the net fibers intersections can occur after the application of the prosthesis causing infections. For this reason, bacteria have to be removed in the very early stage of surgical implantation. Activation of the prosthesis surface was done by an innovative oxidizing plasma treatment (APP-DBD) working under atmospheric conditions in order to favor the deposition of an antibacterial coating of chitosan (biocompatible carbohydrate) and ciprofloxacin (broad spectrum antibiotic). Two different coating mixtures were realised and the antibacterial properties of such functionalised nets were investigated, together with their effectiveness. Physico-chemical characterisations of meshes were carried out before and after functionalisation by SEM-EDS and infrared spectroscopy. The release of both chitosan and ciprofloxacin, under controlled experimental conditions, was followed respectively by colorimetric determination (using UV-Visible spectroscopy) and chromatographic analysis (using HPLC). In vitro tests allow verifying antimicrobial activity (inoculation of specimens in a Staphylococcus aureus suspension).

Fate of selected pharmaceuticals in river waters

The aqueous environmental fate of two antibiotics, lincomycin and clarithromycin, and an antiepileptic drug, carbamazepine, was investigated by monitoring drugs decomposition and identifying intermediates in Po river water (North Italy). Initially, control experiments in the dark and under illumination were performed on river water spiked with drugs to simulate all possible transformation processes occurring in the aquatic system. Under illumination, these pharmaceuticals were degraded and transformed into numerous organic intermediate compounds. Several species were formed and characterised by analysing MS and MSn spectra and by comparison with parent molecule fragmentation pathways. River water was sampled at three sampling points in an urban area. The selected pharmaceuticals were detected in all samples. Eight transformation products identified in the laboratory simulation were found in natural river water from carbamazepine degradation, three from clarithromycin and two from lincomycin. Their transformation occurring in aquatic system mainly involved mono- and poly-hydroxylation followed by oxidation of the hydroxyl groups.