Online monitoring oxidative products and metabolites of nicotine by free radicals generation with Fenton reaction in tandem mass spectrometry

Structural Characterization and Electrochemical Studies of Selected Alkaloid N-Oxides

In this work, we synthesized and confirmed the structure of several alkaloid N-oxides using mass spectrometry and Fourier-transform infrared spectroscopy. We also investigated their reduction mechanisms using voltammetry. For the first time, we obtained alkaloid N-oxides using an oxidation reaction with potassium peroxymonosulfate as an oxidant. The structure was established based on the obtained fragmentation mass spectra recorded by LC-Q-ToF-MS. In the FT-IR spectra of the alkaloid N-oxides, characteristic signals of N-O group vibrations were recorded (bands in the range of 928 cm⁻1 to 971 cm⁻1), confirming the presence of this functional group. Electrochemical reduction studies demonstrated the reduction of alkaloid N-oxides at mercury-based electrodes back to the original form of the alkaloid. For the first time, the products of the electrochemical reduction of alkaloid N-oxides were detected by mass spectrometry. The findings provide insights into the structural characteristics and reduction behaviors of alkaloid N-oxides, offering implications for pharmacological and biochemical applications. This research contributes to a better understanding of alkaloid metabolism and degradation processes, with potential implications for drug development and environmental science.

Oxygen Limitation Accelerates Regeneration of Active Sites on a MnO2 Surface: Promoting Transformation of Organic Matter and Carbon Preservation

Birnessite (δ-MnO₂) is a layered manganese oxide widely present in the environment and actively participates in the transformation of natural organic matter (NOM) in biogeochemical processes. However, the effect of oxygen on the dynamic interface processes of NOM and δ-MnO₂ remains unclear. This study systematically investigated the interactions between δ-MnO₂ and fulvic acid (FA) under both aerobic and anaerobic conditions. FA was transformed by δ-MnO₂ via direct electron transfer and the generated reactive oxygen species (ROS). During the 32-day reaction, 79.8% of total organic carbon (TOC) in solution was removed under anaerobic conditions, unexpectedly higher than that under aerobic conditions (69.8%), suggesting that oxygen limitation was more conducive to the oxidative transformation of FA by δ-MnO₂. The oxygen vacancies (O_V) on the surface of δ-MnO₂ were more exposed under anaerobic conditions, thus promoting the adsorption and transformation of FA as well as regeneration of the active sites. Additionally, the reaction of FA with δ-MnO₂ weakened the strongly bonded lattice oxygen (O_latt), and the released O_latt was an important source of ROS. Interestingly, a part of organic carbon (OC) was preserved by forming MnCO₃, which might be a novel mechanism for carbon preservation. These findings contribute to an improved understanding of the dynamic interface processes between MnO₂ and NOM and provide new insights into the effects of oxygen limitation on the cycling and preservation of OC.

Evaluation of peroxidative stress of cancer cells in vitro by real-time quantification of volatile aldehydes in culture headspace

RATIONALE

Peroxidation of lipids in cellular membranes results in the release of volatile organic compounds (VOCs), including saturated aldehydes. The real-time quantification of trace VOCs produced by cancer cells during peroxidative stress presents a new challenge to non-invasive clinical diagnostics, which as described here, we have met with some success.

METHODS

A combination of selected ion flow tube mass spectrometry (SIFT-MS), a technique that allows rapid, reliable quantification of VOCs in humid air and liquid headspace, and electrochemistry to generate reactive oxygen species (ROS) in vitro has been used. Thus, VOCs present in the headspace of CALU-1 cancer cell line cultures exposed to ROS have been monitored and quantified in real time using SIFT-MS.

RESULTS

The CALU-1 lung cancer cells were cultured in 3D collagen to mimic in vivo tissue. Real-time SIFT-MS analyses focused on the volatile aldehydes: propanal, butanal, pentanal, hexanal, heptanal and malondialdehyde (propanedial), that are expected to be products of cellular membrane peroxidation. All six aldehydes were identified in the culture headspace, each reaching peak concentrations during the time of exposure to ROS and eventually reducing as the reactants were depleted in the culture. Pentanal and hexanal were the most abundant, reaching concentrations of a few hundred parts-per-billion by volume, ppbv, in the culture headspace.

CONCLUSIONS

The results of these experiments demonstrate that peroxidation of cancer cells in vitro can be monitored and evaluated by direct real-time analysis of the volatile aldehydes produced. The combination of adopted methodology potentially has value for the study of other types of VOCs that may be produced by cellular damage.

Comparison of TiO2 photocatalysis, electrochemically assisted Fenton reaction and direct electrochemistry for simulation of phase I metabolism reactions of drugs

The feasibility of titanium dioxide (TiO2) photocatalysis, electrochemically assisted Fenton reaction (EC-Fenton) and direct electrochemical oxidation (EC) for simulation of phase I metabolism of drugs was studied by comparing the reaction products of buspirone, promazine, testosterone and 7-ethoxycoumarin with phase I metabolites of the same compounds produced in vitro by human liver microsomes (HLM). Reaction products were analysed by UHPLC-MS. TiO2 photocatalysis simulated the in vitro phase I metabolism in HLM more comprehensively than did EC-Fenton or EC. Even though TiO2 photocatalysis, EC-Fenton and EC do not allow comprehensive prediction of phase I metabolism, all three methods produce several important metabolites without the need for demanding purification steps to remove the biological matrix. Importantly, TiO2 photocatalysis produces aliphatic and aromatic hydroxylation products where direct EC fails. Furthermore, TiO2 photocatalysis is an extremely rapid, simple and inexpensive way to generate oxidation products in a clean matrix and the reaction can be simply initiated and quenched by switching the UV lamp on/off.

A Derivative Method with Free Radical Oxidation to Predict Resveratrol Metabolites by Tandem Mass Spectrometry

In this study, we demonstrated an oxidative method with free radical to generate 3,5,4′-trihydroxy-trans-stilbene (trans-resveratrol) metabolites and detect sequentially by an autosampler coupling with liquid chromatography electrospray ionization tandem mass spectrometer (LC-ESI–MS/MS). In this oxidative method, the free radical initiator, ammonium persulfate (APS), was placed in a sample bottle containing resveratrol to produce oxidative derivatives, and the reaction progress was tracked by autosampler sequencing. Resveratrol, a natural product with purported cancer preventative qualities, produces metabolites including dihydroresveratrol, 3,4′-dihydroxy-trans-stilbene, lunularin, resveratrol monosulfate, and dihydroresveratrol monosulfate by free radical oxidation. Using APS free radical, the concentrations of resveratrol derivatives differ as a function of time. Besides simple, convenient and time- and labor saving, the advantages of free radical oxidative method of its in situ generation of oxidative derivatives followed by LC-ESI–MS/MS can be utilized to evaluate different metabolites in various conditions.