Systematic identification of trimethoprim metabolites in lettuce.

Antibiotics are some of the most widely used drugs. Their release in the environment is of great concern since their consumption is a major factor for antibiotic resistance, one of the most important threats to human health. Their occurrence and fate in agricultural systems have been extensively investigated in recent years. Yet whilst their biotic and abiotic degradation pathways have been thoroughly researched, their biotransformation pathways in plants are less understood, such as in case of trimethoprim. Although trimethoprim has been reported in the environment, its fate in higher plants still remains unknown. A bench-scale experiment was performed and 30 trimethoprim metabolites were identified in lettuce (Lactuca sativa L.), of which 5 belong to phase I and 25 to phase II. Data mining yielded a list of 1018 ions as possible metabolite candidates, which was filtered to a final list of 87 candidates. Molecular structures were assigned for 19 compounds, including 14 TMP metabolites reported for the first time. Alongside well-known biotransformation pathways in plants, additional novel pathways were suggested, namely, conjugation with sesquiterpene lactones, and abscisic acid as a part of phase II of plant metabolism. The results obtained offer insight into the variety of phase II conjugates and may serve as a guideline for studying the metabolization of other chemicals that share a similar molecular structure or functional groups with trimethoprim. Finally, the toxicity and potential contribution of the identified metabolites to the selective pressure on antibiotic resistance genes and bacterial communities via residual antimicrobial activity were evaluated.

Elucidating biotransformation pathways of ofloxacin in lettuce (Lactuca sativa L).

Antibiotics can be uptaken by plants from soil desorption or directly from irrigation water, but their metabolization pathways in plants are largely unknown. In this paper, an analytical workflow based on high-resolution mass spectrometry was applied for the systematic identification of biotransformation products of ofloxacin in lettuce. The targeted metabolites were selected by comparing the mass chromatograms of exposed with control samples using an advanced spectra-processing method (Fragment Ion Search). The innovative methodology presented allowed us to identify a total of 11 metabolites, including 5 ofloxacin metabolites that are being reported for the first time in plants. Accordingly, major transformation pathways were proposed revealing insight into how ofloxacin and related chemicals are metabolized in lettuce. Furthermore, the influence of biotransformation on potential residual antimicrobial activity of identified compounds was discussed. Human exposure to antibiotics at doses below the minimum inhibitory concentrations is crucial in human risk assessment, including food ingestion; however, in the case of ofloxacin presented results reveal that plant metabolites should also be considered so as not to underestimate their risk.

Selector screening for enantioseparation of DL-α-methyl phenylglycine amide by liquid-liquid extraction.

Enantioseparation through liquid extraction technology is an emerging field, e.g., enantioseparations of amino acids (and derivatives thereof), amino alcohols, amines, and carboxylic acids have been reported. Often, when a new selector is developed, the versatility of substrate scope is investigated. From an industrial point of view, the problem is typically approached the other way around, and for a target racemate, a selector needs to be found in order to accomplish the desired enantioseparation. This study presents such a screening approach for the separation of the enantiomers of DL-α-methyl phenylglycine amide (DL-α-MPGA), a model amide racemate with high industrial relevance. Chiral selectors that were reported for other classes of racemates were investigated, i.e., several macrocyclic selectors and Pd-BINAP complexes. It appeared very challenging to obtain both high extraction yields and good enantioselectivity for most selectors, but Pd-BINAP-based selectors performed well, with enantioselectivities up to 7.4 with an extraction yield of the desired enantiomer of 95.8%. These high enantioselectivities were obtained using dichloromethane as solvent. Using less volatile chlorobenzene or 1-chloropentane, reasonable selectivities of up to 1.7 were measured, making these the best alternative solvents for dichloromethane.

Influence of ligand density on antibody binding capacity of cation-exchange adsorbents.

Adsorption properties of a set of polymethacrylate-based cation exchangers designed for purification of monoclonal antibodies were investigated. The materials differed significantly in the density of sulphoisobutyl ligand groups. The ligand density had a pronounced effect on the static adsorption capacity of a polyclonal human immunoglobulin G. An optimal ligand density was observed at any pH and NaCl concentration tested when sharp optima were observed at low pH and ionic strength values. This was caused by effective clogging of pore mouth at high ligand densities. An anomalous effect of ionic strength was observed for the adsorbents with the high ligand density when the adsorption capacity increased with the addition of NaCl at low pH.

Characterization of pore structure of chromatographic adsorbents employed in separation of monoclonal antibodies using size-exclusion techniques.

Structural properties of commercial chromatographic adsorbents designated for separation of monoclonal antibodies were investigated using size-exclusion techniques. A batch technique provided the specific pore volumes distributed among small, medium and large pores. Inverse size-exclusion chromatography yielded the partition coefficients of dextran solute probes in medium pores. These data were fitted with one- and two-parametric models corresponding to different pore-size distribution functions and the suitability of the individual models for the characterization of the examined materials was then assessed. The reliability of estimation of the parameters of log-normal distribution of cylindrical pores was investigated. Large uncertainties and a strong correlation of the mean pore diameter and width of distribution function were observed.