Kinetic and mechanistic investigations of the oxidation of tramadol by ferrate and ozone.

The kinetics and oxidation products (OPs) of tramadol (TRA), an opioid, were investigated for its oxidation with ferrate (Fe(VI)) and ozone (O(3)). The kinetics could be explained by the speciation of the tertiary amine moiety of TRA, with apparent second-order rate constants of 7.4 (±0.4) M(-1) s(-1) (Fe(VI)) and 4.2 (±0.3) × 10(4) M(-1) s(-1) (O(3)) at pH 8.0, respectively. In total, six OPs of TRA were identified for both oxidants using Qq-LIT-MS, LTQ-FT-MS, GC-MS, and moiety-specific chemical reactions. In excess of oxidants, these OPs can be further transformed to unidentified OPs. Kinetics and OP identification confirmed that the lone electron pair of the amine-N is the predominant site of oxidant attack. An oxygen transfer mechanism can explain the formation of N-oxide-TRA, while a one-electron transfer may result in the formation of N-centered radical cation intermediates, which could lead to the observed N-dealkylation, and to the identified formamide and aldehyde derivatives via several intermediate steps. The proposed radical intermediate mechanism is favored for Fe(VI) leading predominantly to N-desmethyl-TRA (ca. 40%), whereas the proposed oxygen transfer prevails for O(3) attack resulting in N-oxide-TRA as the main OP (ca. 90%).

Clinically Approved Drugs Inhibit the Staphylococcus aureus Multidrug NorA Efflux Pump and Reduce Biofilm Formation.

Staphylococcus aureus has acquired resistance to antibiotics since their first use. The S. aureus protein NorA, an efflux pump belonging to the major facilitator superfamily (MFS), contributes to resistance to fluoroquinolones (e.g., ciprofloxacin), biocides, dyes, quaternary ammonium compounds, and antiseptics. Different compounds have been identified as potential efflux pump inhibitors (EPIs) of NorA that result in increased intracellular concentration of antibiotics, restoring their antibacterial activity and cell susceptibility. However, none of the currently known EPIs have been approved for clinical use, probably due to their toxicity profiles. In the present study, we screened approved drugs for possible efflux pump inhibition. By screening a compound library of approximately 1200 different drugs, we identified nilotinib, a tyrosine kinase inhibitor, as showing the best efflux pump inhibitory activity, with a fractional inhibitory concentration index of 0.1875, indicating synergism with ciprofloxacin, and a minimum effective concentration as low as 0.195 µM. Moreover, at 0.39 µM, nilotinib, in combination with 8 µg/mL of ciprofloxacin, led to a significant reduction in biofilm formation and preformed mature biofilms. This is the first description of an approved drug that can be used as an efflux pump inhibitor and to reduce biofilms formation at clinically achievable concentrations.

Optimized efflux assay for the NorA multidrug efflux pump in Staphylococcus aureus.

Real-time fluorescent efflux assays are commonly used for measuring the efflux of bacterial pumps. Here we describe an optimized protocol for the NorA efflux pump in S. aureus using DiOC3 instead of ethidium bromide. Glucose and sodium formate were tested as energy carriers. This novel method is fast and reproducible.

Kinetic assessment and modeling of an ozonation step for full-scale municipal wastewater treatment: micropollutant oxidation, by-product formation and disinfection.

The kinetics of oxidation and disinfection processes during ozonation in a full-scale reactor treating secondary wastewater effluent were investigated for seven ozone doses ranging from 0.21 to 1.24 g O(3) g(-1) dissolved organic carbon (DOC). Substances reacting fast with ozone, such as diclofenac or carbamazepine (k(P, O3) > 10(4) M(-1) s(-1)), were eliminated within the gas bubble column, except for the lowest ozone dose of 0.21 g O(3) g(-1) DOC. For this low dose, this could be attributed to short-circuiting within the reactor. Substances with lower ozone reactivity (k(P, O3) < 10(4) M(-1) s(-1)) were only fully eliminated for higher ozone doses. The predictions of micropollutant oxidation based on coupling reactor hydraulics with ozone chemistry and reaction kinetics were up to a factor of 2.5 higher than full-scale measurements. Monte Carlo simulations showed that the observed differences were higher than model uncertainties. The overestimation of micropollutant oxidation was attributed to a protection of micropollutants from ozone attack by the interaction with aquatic colloids. Laboratory-scale batch experiments using wastewater from the same full-scale treatment plant could predict the oxidation of slowly-reacting micropollutants on the full-scale level within a factor of 1.5. The Rct value, the experimentally determined ratio of the concentrations of hydroxyl radicals and ozone, was identified as a major contribution to this difference. An increase in the formation of bromate, a potential human carcinogen, was observed with increasing ozone doses. The final concentration for the highest ozone dose of 1.24 g O(3) g(-1) DOC was 7.5 µg L(-1), which is below the drinking water standard of 10 µg L(-1). N-Nitrosodimethylamine (NDMA) formation of up to 15 ng L(-1) was observed in the first compartment of the reactor, followed by a slight elimination during sand filtration. Assimilable organic carbon (AOC) increased up to 740 µg AOC L(-1), with no clear trend when correlated to the ozone dose, and decreased by up to 50% during post-sand filtration. The disinfection capacity of the ozone reactor was assessed to be 1-4.5 log units in terms of total cell counts (TCC) and 0.5 to 2.5 log units for Escherichia coli (E. coli). Regrowth of up to 2.5 log units during sand filtration was observed for TCC while no regrowth occurred for E. coli. E. coli inactivation could not be accurately predicted by the model approach, most likely due to shielding of E. coli by flocs.

Ferrate (Fe(VI)) application for Municipal wastewater treatment: a novel process for simultaneous micropollutant oxidation and phosphate removal.

A novel technology for enhanced municipal wasterwater treatment was assessed based on the dual functions of Fe(VI) to oxidize micropollutants and remove phosphate by formation of ferric phosphates. Second-order rate constants (k) for the reactions of selected pharmaceuticals, endocrine disruptors, and organic model compounds with Fe(VI) were in the range of 1 (trimethylamine) to 9000 M(-1) s(-1) (aniline) in the pH-range 7-8. The selected compounds contained electron-rich moieties (ERM) such as phenols, anilines, amines, and olefins. Oxidation experiments in wastewater spiked with micropollutants at concentrations in the low microM range at pH 7 and 8 showed that Fe(VI) doses higher than 5 mg Fe L(-1) are capable of eliminating various ERM-containing micropollutants by more than 85%. In comparison to ozone, Fe(VI) was as effective or slightly less effective in terms of micropollutants oxidation, with Fe(VI) having the benefit of phosphate removal. To lower phosphate from 3.5 to 0.8 mg PO4-P L(-1) (regulatory limit for wastewater discharge in Switzerland), a Fe(VI) dose of 7.5 mg Fe L(-1) was needed. Overall, this study demonstrates Fe(VI) as a promising tool for an enhanced wastewater treatment to remove micropollutants as well as to control phosphate in a single treatment step.

Elimination of organic micropollutants in a municipal wastewater treatment plant upgraded with a full-scale post-ozonation followed by sand filtration.

The removal efficiency for 220 micropollutants was studied at the scale of a municipal wastewater treatment plant (WWTP) upgraded with post-ozonation followed by sand filtration. During post-ozonation, compounds with activated aromatic moieties, amine functions, or double bonds such as sulfamethoxazole, diclofenac, or carbamazepine with second-order rate constants for the reaction with ozone >10(4) M(-1) s(-1) at pH 7 (fast-reacting) were eliminated to concentrations below the detection limit for an ozone dose of 0.47 g O3 g(-1) dissolved organic carbon (DOC). Compounds more resistant to oxidation by ozone such as atenolol and benzotriazole were increasingly eliminated with increasing ozone doses, resulting in >85% removal for a medium ozone dose (approximately 0.6 g O3 g(-1) DOC). Only a few micropollutants such as some X-ray contrast media and triazine herbicides with second-order rate constants <10(2) M(-1) s(-1) (slowly reacting) persisted to a large extent. With a medium ozone dose, only 11 micropollutants of 55 detected in the secondary effluent were found at >100 ng L(-1). The combination of reaction kinetics and reactor hydraulics, based on laboratory-and full-scale data, enabled a quantification of the results by model calculations. This conceptual approach allows a direct upscaling from laboratory- to full-scale systems and can be applied to other similar systems. The carcinogenic by-products N-nitrosodimethylamine (NDMA) (< or =14 ng L(-1)) and bromate (<10 microg L(-1)) were produced during ozonation, however their concentrations were below or in the range of the drinking water standards. Furthermore, it could be demonstrated that biological sand filtration is an efficient additional barrier for the elimination of biodegradable compounds formed during ozonation such as NDMA. The energy requirement for the additional post-ozonation step is about 0.035 kWh m(-3), which corresponds to 12% of a typical medium-sized nutrient removal plant (5 g DOC m(-3)).