Applicability of the Rayleigh equation for enantioselective metabolism of chiral xenobiotics by microsomes, hepatocytes and in-vivo retention in rabbit tissues

Enantioselective degradation of ofloxacin and levofloxacin by the bacterial strains Labrys portucalensis F11 and Rhodococcus sp. FP1

Fluoroquinolones are a class of antibiotics widely prescribed in both human and veterinary medicine of high environmental concern and characterized as environmental micropollutants due to their ecotoxicity and persistence and antibacterial resistance potential. Ofloxacin and levofloxacin are chiral fluoroquinolones commercialized as racemate and in enantiomerically pure form, respectively. Since the pharmacological properties and toxicity of the enantiomers may be very different, understanding the stereochemistry of these compounds should be a priority in environmental monitoring. This work presents the biodegradation of racemic ofloxacin and its (S)-enantiomer levofloxacin by the bacterial strains Labrys portucalensis F11 and Rhodococcus sp. FP1 at a laboratory-scale microcosm following the removal and the behavior of the enantiomers. Strain F11 could degrade both antibiotics almost completely when acetate was supplied regularly to the cultures. Enrichment of the (R)-enantiomer was observed in FP1 and F11 cultures supplied with ofloxacin. Racemization was observed in the biodegradation of the pure (S)-ofloxacin (levofloxacin) by strain F11, which was confirmed by liquid chromatography - exact mass spectrometry. Biodegradation of ofloxacin at 450 µg L^-1 by both bacterial strains expressed good linear fits (R² > 0.98) according to the Rayleigh equation. The enantiomeric enrichment factors were comprised between - 22.5% to - 9.1%, and - 18.7% to - 9.0% in the biodegradation of ofloxacin by strains F11 and FP1, respectively, with no significant differences for the two bacteria under the same conditions. This is the first time that enantioselective biodegradation of ofloxacin and levofloxacin by single bacteria is reported.

High-performance liquid chromatography quantification of enantiomers of a Dihydroxylated tetrahydrofuran natural product

Both enantiomers of petromyroxol are putative pheromones in sea lamprey (Petromyzon marinus). Here, we describe the separation and quantification of the petromyroxol enantiomers using high-performance liquid chromatography tandem mass spectrometry. The separation was tested on a wide range of chiral columns with normal phases, and effects of the chromatographic parameters such as mobile phase and temperature on the separation were optimized. The AD-H column showed the best separation of enantiomers with n-hexane and ethanol as the mobile phase. The enantiomers were detected by multiple reaction monitoring with a positive atmospheric-pressure chemical ionization on triple quadrupole mass spectrometer. Validation revealed that the method was specific, accurate, and precise. The validated method was applied to measure the amount of petromyroxol enantiomers in water conditioned with sea lamprey larvae, the source of the putative pheromone. This method will be applied in quantifying the natural scalemic petromyroxol mixture, enabling further investigations of a rare non-racemic enantiomeric pheromone mixture in a vertebrate species.

Enantioselective reductive transformation of climbazole: A concept towards quantitative biodegradation assessment in anaerobic biological treatment processes

An efficient chiral method-based using liquid chromatography-high resolution-mass spectrometry analytical method has been validated for the determination of climbazole (CBZ) enantiomers in wastewater and sludge with quantification limits below the 1 ng/L and 2 ng/g range, respectively. On the basis of this newly developed analytical method, the stereochemistry of CBZ was investigated over time in sludge biotic and sterile batch experiments under anoxic dark and light conditions and during wastewater biological treatment by subsurface flow constructed wetlands. CBZ stereoselective degradation was exclusively observed under biotic conditions, confirming the specificity of enantiomeric fraction variations to biodegradation processes. Abiotic CBZ enantiomerization was insignificant at circumneutral pH and CBZ was always biotransformed into CBZ-alcohol due to the specific and enantioselective reduction of the ketone function of CBZ into a secondary alcohol function. This transformation was almost quantitative and biodegradation gave good first order kinetic fit for both enantiomers. The possibility to apply the Rayleigh equation to enantioselective CBZ biodegradation processes was investigated. The results of enantiomeric enrichment allowed for a quantitative assessment of in situ biodegradation processes due to a good fit (R² > 0.96) of the anoxic/anaerobic CBZ biodegradation to the Rayleigh dependency in all the biotic microcosms and was also applied in subsurface flow constructed wetlands. This work extended the concept of applying the Rayleigh equation towards quantitative biodegradation assessment of organic contaminants to enantioselective processes operating under anoxic/anaerobic conditions.

Novel N-Doped Carbon Dots/β-Cyclodextrin Nanocomposites for Enantioselective Recognition of Tryptophan Enantiomers

Based on N-doped carbon dots/β-cyclodextrin nanocomposites modified glassy carbon electrodes (N-CDs/β-CD/GCE), an effective electrochemical sensor for enantioselective recognition of tryptophan (Trp) enantiomers was developed by differential pulse voltammograms (DPVs). Fluorescent N-CDs were synthesized through a hydrothermal method and characterized by spectroscopic approaches. The N-CDs/β-CD nanocomposites were efficiently electrodeposited on the surface of GCE through C-N bond formation between N-CDs and electrode. The obtained N-CDs/β-CD/GCE was characterized by multispectroscopic and electrochemical methods. Such N-CDs/β-CD/GCE generated a significantly lower Ip and more negative Ep in the presence of l-Trp in DPVs, which was used for the enantioselective recognition of Trp enantiomers. The N-CDs/β-CD nanocomposites showed different binding constants for tryptophan enantiomers, and they further selectively bonded with l-Trp to form inclusion complexes. This N-CDs/β-CD/GCE combined advantages of N-CDs with strong C-N binding ability and β-CD with specific recognition of Trp enantiomers to fabricate a novel sensing platform for enantioselective recognition of Trp enantiomers. This strategy provided the possibility of using a nanostructured sensor to discriminate the chiral molecules in bio-electroanalytical applications.