Rationalising the retro-Diels-Alder fragmentation pattern of viscutins using electrospray interface-tandem mass spectrometry coupled to theoretical modelling.

RATIONALE: Although mass spectrometry (MS) is a powerful tool in structural elucidation of unknown flavonoids based on their unique fragmentation patterns, proposing the correct fragmentation mechanism is still a challenge from tandem mass spectrometry data only. In recent years, computational tools such as molecular networking and MS2LDA have played a major role in the identification of structurally related compounds through an in-depth survey of their fragmentation patterns. METHODS: Therefore, in this study, three viscutin molecules in Viscum combreticola Engl. crude extracts were characterised using ultra-high-performance liquid chromatography-quadrupole-time-of-flight tandem mass spectrometry and MS2LDA, a computational tool. Ion-trap mass spectrometry and density functional theoretical modelling were used as confirmatory tools to rationalise the unique fragmentation patterns observed for these molecules. RESULTS: Here, MS2LDA revealed the presence of a unique Mass2Motif in all the three viscutin molecules at m/z 137, which was confirmed to be a 1,3 A- RDA (retro-Diels-Alder) fragmentation product using liquid chromatography-ion-trap mass spectrometry and density functional theoretical modelling. Moreover, MS2LDA proved to be useful in differentiating this spectral feature that was specific to viscutin molecules in the presence of other isobaric ions at m/z 137 occurring in compounds in other molecular families. CONCLUSION: Therefore, the results of the current study showed that computational tools such as MS2LDA are essential in uncovering some gas-phase fragmentation reactions of molecules in MS and that theoretical modelling is a powerful tool in rationalising these reactions in metabolite identification.

Diverse chemical modifications of the chlorogenic acid composition of Viscum combreticola Engl.: A premise for the state of readiness against excessive sunlight exposure.

Mistletoe plants that are positioned on the canopy of their hosts are more susceptible to UV radiation exposure. These aerial plants are resistant to damage by UV radiation due the presence of epidermal constituents such as the cuticle, cork layer, trichomes and antioxidant secondary metabolites. In response to the photo-oxidative stress associated with UV exposure, plants generally deploy photo-protective responsive mechanisms that involve the biosynthesis of UV absorbing phenolic compounds such as chlorogenic acids (CGAs). The hydroxycinnamic acid moieties of these CGAs are predominantly in the trans configuration, naturally. However, excessive sunlight exposure of plants containing these compounds can result in geometrical isomerisation, characterized by the formation of cis isomers. Therefore, in this study, the effect of UV light radiation on the CGA composition of Viscum combreticola Engl. (Santalacaeae) plants using an in vitro model was unravelled through UHPLC-q-TOF-MS-based metabolic profiling. Interestingly, the findings of this study revealed that this plant has a diverse chemical composition of CGAs that is characterized by epimerization, monoacylation, homodiacylation and heterodiacylation of the quinic acid (QA), thereby, contributing to the state of readiness in these plants against sunlight or UV exposure. In addition to the commonly reported cinnamoyl containing heterodiacylated CGAs, hydroxybenzoyl containing heterodiacylated CGAs were also reported in this study. Moreover, cis isomers (24 in total) of some CGAs were identified in the non-irradiated samples and the formation of these compounds has been reported to help plants in the mitigation of photo-oxidative stress. An additional 28 cis isomers of CGAs and HCA derivatives were observed in the UV-irradiated samples, hence, further increasing the complexity of the metabolome of this plant, with a total of 108 compounds identified in this study. The presence of epimers, positional and geometrical isomers of these compounds could be a biochemical strategy to maximize the chemical arsenal of this plant to withstand the photo-oxidative stress posed by UV radiation from the sunlight. Due to purported pharmacological properties associated with the identified compounds these parasitic plants can be a rich source of prospective therapeutic compounds that can be employed as drug discovery leads. Moreover, UV radiation might be essential in future to produce potent drugs since plants naturally produce these compounds in low quantities.

Enrichment of tetracycline residues from honey samples using carrier-mediated hollow fibre liquid-phase micro-extraction and quantification by LC-Q-TOF/MS.

BACKGROUND: In this study, development and validation of a simple, miniaturized and, environmentally friendly carrier-mediated three-phase hollow-fibre liquid-phase micro-extraction (HFLPME) technique was investigated for the enrichment of tetracycline residues in honey samples. The extracts were analysed using UV-visible spectrophotometry and liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS). Parameters affecting the extraction efficiency of HFLPME such as pH of the donor and acceptor solutions, salt addition, agitation speed and extraction time were optimized. RESULTS: The calibration curves showed good linearity, in the range of 1-100 µg kg-1 with correlation coefficients ranging between 0.9943 and 0.9992, under the optimized conditions. Recoveries of blank honey samples at three spiking levels (1, 10 and 20 µg kg-1 ) ranged from 81.2% to 107.5%. Relative standard deviations for the precision of the method were less than 15.0%. Limits of detection and limits of quantification were in the range of 0.0861-0.2628 µg kg-1 and 0.2610-0.7964 µg kg-1 , respectively. Finally, the proposed method was successfully applied in the extraction of five tetracyclines from honey samples. Doxycycline residue detected in one of the commercial honey samples was below the limit of quantification. CONCLUSION: Because of the advantages offered by HFLPME, this method can be employed as an alternative to conventional extraction techniques for the clean-up and pre-concentration of antibiotics in complex matrices, including food samples. © 2021 Society of Chemical Industry.

Critical review of solid phase extraction for multiresidue clean-up and pre-concentration of antibiotics from livestock and poultry manure.

The release of antibiotics into the environment from agricultural industries has received tremendous attention in recent years. Nonpoint source contamination of the terrestrial environment by these compounds can result from fertilisation of agricultural soils with manure. The presence of antibiotics and their metabolites in manure may pose a threat to agro-ecosystems. This may result in the emergence of antibiotic resistance bacteria in humans through the food chain and this is a major concern globally at the moment. Therefore, monitoring of manure for antibiotic residues is of vital importance in order to assess the risks of environmental pollution to human health by these drugs. Several sample pre-treatment techniques have been developed for the extraction of antibiotic residues from complex matrices including manure over the years. Despite new developments in recent years in separation science where the common trend is miniaturisation and green approaches, solid-phase extraction is still the most widely used technique in the extraction of antibiotics from agricultural wastes such as manure. In view of this, the aim of this review was to give a critical overview of studies that have been conducted in the past 6 years on the extraction of antibiotic residues from manure employing solid-phase extraction based on Oasis HLB and Strata-X. Adsorption mechanisms of these sorbents were also briefly discussed.

Application of sorptive micro-extraction techniques for the pre-concentration of antibiotic drug residues from food samples - a review.

Antibiotic residues have become a major concern worldwide as food contaminants due to the risk that they may pose to human health. The presence of these residues in food is due to improper veterinary practices. Consequently, rapid and cost-effective clean-up methods prior to analysis for these residues in food matrices are increasingly becoming necessary in order to ensure food safety. Miniaturised extraction and pre-concentration techniques have been developed as alternatives to conventional extraction procedures in recent years. Furthermore, the current trends in analytical sample preparation favour extraction techniques that comply with the principles of green analytical chemistry. Solid phase micro-extraction, stir bar sorptive extraction, stir cake sorptive extraction and fabric phase sorptive extraction methods are very promising sorbent-based sorptive micro-extraction techniques, and they are compliant to the principles of green chemistry. This review critically discusses the application of these techniques in the extraction and pre-concentration of antibiotic residues from food samples in the years 2015 to 2020.