Derivatization of carbonyl compounds with 2,4-dinitrophenylhydrazine and their subsequent determination by high-performance liquid chromatography

2-Nitro-4-Carboxyphenylhydrazine and 2,4-Dicarboxylphenylhydrazine as a Pair of Novel Reactive MALDI Matrices for Rapid and Accurate Profiling of N-Glycome in Dual Ion Modes

N-glycosylation is closely linked to a wide range of biological functions in organisms. Owing to the constriction of awful crystals formed by conventional MALDI matrices and the extremely inferior ionization efficiency of N-glycans, the traditional direct detection of N-glycans by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been gradually replaced by postderivatization detection using reactive matrices. Nevertheless, the laborious identification of complex spectral peaks remains the major difficulty in N-glycan profiling. Hence, we logically designed and synthesized two novel reactive matrices, 2-nitro-4-carboxylphenylhydrazine (NCPH) and 2,4-dicarboxylphenylhydrazine (DCPH), and separately combined them with the acidic matrix 2,5-dihydroxybenzoic acid (DHB) to constitute two composite matrices with high on-target derivatization efficiency and significant promotion of N-glycan ionization for productive MALDI analysis in dual ion modes. Using both composite matrices, we can actualize MALDI-MS and MS2 mass calibration in dual ion modes by postderivatization detection and fragmentation of dextrans and selectively enhance the ionization effect of oligosaccharides in mixed systems. Quite homogeneous cocrystals can ensure N-glycan quantification with decent linearity and reproducibility. A fixed mass difference derived from the identical N-glycan in two ion modes is available for rapid identification in complex biological samples. Ultimately, the developed strategy was triumphantly employed to identify and quantify the relative content and alteration tendency of peach N-glycans, which can be referable to the latent correlation between N-glycan expression and peach ripening.

Analytical methods and experimental quality in studies targeting carbonyls in electronic cigarette aerosols

We provide an extensive review of 14 studies (11 independent and three industry-funded) on emissions generated by Electronic Cigarettes (ECs), specifically focusing on the evaluation of carbonyls present in these emissions and emphasizing a meticulous evaluation of their analytical methods and experimental procedures. Since the presence of carbonyl by-products in EC aerosol is concerning, it is important to evaluate the reliability of emission studies quantifying these compounds by verifying their compliance with the following criteria of experimental quality: authors must 1) supply sufficient information on the devices and experimental procedures to allow for potentially reproducing or replicating the experiments, 2) use of appropriate puffing protocols that approach consumer usage as best as possible, 3) use of appropriate analytical methods and 4) usage of blank samples to avoid false positive detection. Outcomes were classified in terms of the fulfilment of these conditions as reliable in seven studies, partially reliable in five studies, and unreliable in two studies. However, only five studies used blank samples and six studies failed the reproducibility criterion. Carbonyl yields were far below their yields in tobacco smoke in all reproducible studies, even in the partially reliable ones, thus supporting the role of ECs (when properly tested and operated) as harm reduction products. This review highlights the necessity to evaluate the quality of laboratory standards in testing EC emissions to achieve an objective assessment of the risk profile of ECs.

A new derivatizing reagent for the determination of 5-nitro-2-furaldehyde in trout muscle by liquid chromatography-tandem mass spectrometry

The 5-nitro-2-furaldehyde (5-NF) is an aldehyde aromatic organic compound that has been envisaged as an alternative marker for detecting nitrofurazone treatment abuse and to avoid the false positive results induced by the semicarbazide. Analyzing 5-NF presents challenges, and its derivatization reaction with hydrazine reagents is required to enhance the capability of its detection and its identification. This study aims at developping an analytical method for 5-NF determination in trout muscle samples based on chemical derivatization prior to analysis by liquid chromatography-tandem mass spectrometry. Four commercially available hydrazine reagents, namely: N,N-Dimethylhydrazine (DMH), 4-Hydrazinobenzoic acid (HBA), 2,4-Dichlorophenylhydrazine (2,4-DCPH) and 2,6-Dichlorophenylhydrazine (2,6-DCPH) were proposed for the first time as derivatizing reagents in the analysis of 5-NF. The derivatization reaction was simultaneously performed along with the extraction method in acidic condition using ultrasonic assistance and followed by liquid extraction using acetonitrile. The efficiency of the chemical reaction with 5-NF was examined and the reaction conditions including the concentration of hydrochloric acid, pH, temperature, reaction time and the concentration of the derivatizing reagents were optimized. Experiments with fortified samples demonstrated that 2,4-DCPH derivatizing reagent at 20 mM for 20 min of ultrasonic treatment under acidic condition (pH 4) gave an effective sample derivatization method for 5-NF analysis. Under the optimized conditions, the calibration curves were linear from 0.25 to 2 μg kg-1 with coefficient of determination >0.99. The recoveries ranged from 89 % to 116 % and precision was less than 13 %. The limit of detection and quantification were 0.1 and 0.2 μg kg-1, respectively.

Development and evaluation of a liquid chromatography-tandem mass spectrometry method for simultaneous measurement of toxic aldehydes from brain tissue

Reactive aldehydes are a class of electrophilic low molecular weight compounds that play an essential role in physiological function and lipid peroxidation. These molecules are implicated in many diseases, especially cardiovascular and neurodegenerative diseases, and are potential endogenous markers of lipid peroxidation. However, there are limited options to accurately quantify multiple reactive aldehydes in brain tissue. This study developed and validated a 3-nitrophenylhydrazine derivatization-based LC-MS/MS method to quantify four reactive aldehydes: malondialdehyde, acrolein, 4-hydroxy-2-hexenal and 4-hydroxy-2-nonenal. Method development involved comparing the sensitivity of detection between widely used derivatization reagents: 2,4-dinitrophenylhydrazine and 3-nitrophenylhydrazine. Our data showed that 3-nitrophenylhydrazine resulted in greater sensitivity. Additional method development included evaluation of hydrolysis sample pretreatment, selection of protein precipitation reagent, and optimization of derivatization conditions. The optimized conditions included no hydrolysis and use of 20 % trichloroacetic acid as the protein precipitation reagent. The optimized derivatization condition was 25 mM 3-nitrophenylhydrazine reacted at 20 °C for 30 min. The chromatographic conditions were optimized to reduce matrix effects, ion suppression, and efficient analysis time (<7-minute analytical run). The four aldehyde species were accurately quantified in brain tissue using stable-labeled internal standards. Application of this assay to a traumatic brain injury mouse model revealed significant accumulation of acrolein, 4-hydroxy-2-hexenal, and 4-hydroxy-2-nonenal at 28 days post injury. Overall, a validated method was developed to rapidly quantify the most prominent reactive aldehydes associated with lipid peroxidation during injury progression following acute brain trauma.

Time dependence of aldehyde and ketone oxocarboxylic acid photoproduct generation from crude oil-seawater systems under solar irradiation

Aldehyde and ketone oxocarboxylic acid photoproducts were semi-quantitated in the aqueous phase after subjecting Macondo (MC252) crude oil-seawater systems to simulated solar irradiation. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was applied after derivatizing the samples with 2,4-dinitrophenylhydrazine (DNPH). Oil-seawater was irradiated at 27.0 °C using a solar simulator for 1 to 18 h. Following irradiation, the aqueous phase was treated with DNPH to generate aldehyde-DNPH and ketone-DNPH derivatives. Solid-phase extraction enriched the samples before analyzing them using (-) ESI-MS/MS. Precursor and product ion spectra were used to select carboxylic acid-containing aldehydes and ketones and provide semi-quantitation using surrogate standards and an internal standard. Loss of m/z 44 (CO2) in the product ion spectra further confirmed the carboxylic acid character. Near-linear increases in photoproduct concentration in the aqueous phase were observed over the 18 h irradiation period. Among the aldehyde and ketone oxocarboxylic acid photoproducts studied, photoproduction rates ranged from 0.6 - 69 µmol/h·m2 of oil surface. Despite some fluctuations, a general trend of lower production rate with higher molecular weight was observed. These results demonstrate the near-linear dependence of photoproduction on irradiance and provide ranges of rates that can be applied to modeling aldehyde and ketone oxocarboxylic acid photoproduction in ocean spills. STATEMENT OF ENVIRONMENTAL IMPACT: Crude oil on seawater degrades when exposed to sunlight. Oxygenated molecules are produced, including carboxylic acid-containing aldehydes and ketones. The formation of these photoproducts from oil films behaves linearly with solar exposure time. These photoproducts are more soluble than the original oil molecules, allowing them to have increased bioavailability and potentially increased toxicity. The rate of formation of these species when oil is exposed to sunlight determines their environmental impact.

Darobactin Substrate Engineering and Computation Show Radical Stability Governs Ether versus C-C Bond Formation

The Gram-negative selective antibiotic darobactin A has attracted interest owing to its intriguing fused bicyclic structure and unique targeting of the outer membrane protein BamA. Darobactin, a ribosomally synthesized and post-translationally modified peptide (RiPP), is produced by a radical S-adenosyl methionine (rSAM)-dependent enzyme (DarE) and contains one ether and one C-C cross-link. Herein, we analyze the substrate tolerance of DarE and describe an underlying catalytic principle of the enzyme. These efforts produced 51 enzymatically modified darobactin variants, revealing that DarE can install the ether and C-C cross-links independently and in different locations on the substrate. Notable variants with fused bicyclic structures were characterized, including darobactin W3Y, with a non-Trp residue at the twice-modified central position, and darobactin K5F, which displays a fused diether ring pattern. While lacking antibiotic activity, quantum mechanical modeling of darobactins W3Y and K5F aided in the elucidation of the requisite features for high-affinity BamA engagement. We also provide experimental evidence for β-oxo modification, which adds support for a proposed DarE mechanism. Based on these results, ether and C-C cross-link formation was investigated computationally, and it was determined that more stable and longer-lived aromatic Cβ radicals correlated with ether formation. Further, molecular docking and transition state structures based on high-level quantum mechanical calculations support the different indole connectivity observed for ether (Trp-C7) and C-C (Trp-C6) cross-links. Finally, mutational analysis and protein structural predictions identified substrate residues that govern engagement to DarE. Our work informs on darobactin scaffold engineering and further unveils the underlying principles of rSAM catalysis.

Preparation, assay, and application of 4-fluorothreonine transaldolase from Streptomyces sp. MA37 for β-hydroxyl amino acid derivatives

β-Hydroxy-α-amino acids (βHAAs) are an essential class of building blocks of therapeutically important compounds and complex natural products. They contain two chiral centers at Cα and Cβ positions, resulting in four possible diastereoisomers. Many innovative asymmetric syntheses have been developed to access structurally diverse βHAAs. The main challenge, however, is the control of the relative and absolute stereochemistry of the asymmetric carbons in a sustainable way. In this respect, there has been considerable attention focused on the chemoenzymatic synthesis of βHAAs via a one-step process. Nature has evolved different enzymatic routes to produce these valuable βHAAs. Among these naturally occurring transformations, L-threonine transaldolases present potential biocatalysts to generate βHAAs in situ. 4-Fluorothreonine transaldolase from Streptomyces sp. MA37 (FTaseMA) catalyzes the cross-over transaldolation reaction between L-Thr and fluoroacetaldehyde to give 4-fluorothreonine and acetaldehyde (Ad). It has been demonstrated that FTaseMA displays considerable substrate plasticity toward structurally diverse aldehyde acceptors, leading to the production of various βHAAs. In this chapter, we describe methods for the preparation of FTaseMA, and the chemoenzymatic synthesis of βHAAs from various aldehydes and L-Thr using FTaseMA.

Near UV Photodegradation Mechanisms of Amino Acid Excipients: Formation of the Carbon Dioxide Radical Anion from Aspartate and Fe(III)

Carbon dioxide radical anion (•CO2-) is a powerful reducing agent that can reduce protein disulfide bonds and convert molecular oxygen to superoxide. Therefore, the generation of •CO2- can be detrimental to pharmaceutical formulations. Iron is among the most prevalent impurities in formulations, where Fe(III) chelates of histidine (His) can produce •CO2- upon exposure to near-UV light (Zhang and Schöneich, Eur. J. Pharm. Biopharm. 2023, 190, 231-241). Here, we monitor by spin-trapping in combination with electron paramagnetic resonance spectroscopy and/or high-performance liquid chromatography-mass spectrometry analysis the photochemical formation of •CO2- for a series of common amino acid excipients, including arginine (Arg), methionine (Met), proline (Pro), glutamic acid (Glu), glycine (Gly), aspartic acid (Asp), and lysine (Lys). Our results indicate that in the presence of Fe(III), Asp, and Glu produce significant yields of •CO2- under photoirradiation with near-UV light. Notably, Asp demonstrates the highest efficiency of •CO2- generation compared with that of the other amino acid excipients. Stable isotope labeling indicates that •CO2- exclusively originates from the α-carboxyl group of Asp. Mechanistic studies reveal two possible pathways for •CO2- formation, which involve either a β-carboxyl radical or an amino radical cation intermediate.

Benzylic Radical Stabilization Permits Ether Formation During Darobactin Biosynthesis

The Gram-negative selective antibiotic darobactin A has attracted interest owing to its intriguing fused bicyclic structure and unique mode of action. Biosynthetic studies have revealed that darobactin is a ribosomally synthesized and post-translationally modified peptide (RiPP). During maturation, the darobactin precursor peptide (DarA) is modified by a radical S-adenosyl methionine (rSAM)-dependent enzyme (DarE) to contain ether and C-C crosslinks. In this work, we describe the enzymatic tolerance of DarE using a panel of DarA variants, revealing that DarE can install the ether and C-C crosslinks independently and in different locations on DarA. These efforts produced 57 darobactin variants, 50 of which were enzymatically modified. Several new variants with fused bicyclic structures were characterized, including darobactin W3Y, which replaces tryptophan with tyrosine at the twice-modified central position, and darobactin K5F, which displays a fused diether ring pattern. Three additional darobactin variants contained fused diether macrocycles, leading us to investigate the origin of ether versus C-C crosslink formation. Computational analyses found that more stable and long-lived Cβ radicals found on aromatic amino acids correlated with ether formation. Further, molecular docking and calculated transition state structures provide support for the different indole connectivity observed for ether (Trp-C7) and C-C (Trp-C6) crosslink formation. We also provide experimental evidence for a β-oxotryptophan modification, a proposed intermediate during ether crosslink formation. Finally, mutational analysis of the DarA leader region and protein structural predictions identified which residues were dispensable for processing and others that govern substrate engagement by DarE. Our work informs on darobactin scaffold engineering and sheds additional light on the underlying principles of rSAM catalysis.

Aerosol Emissions from Heated Tobacco Products: A Review Focusing on Carbonyls, Analytical Methods, and Experimental Quality

We provide an extensive review of 17 independent and industry-funded studies targeting carbonyls in aerosol emissions of Heated Tobacco Products (HTPs), focusing on quality criteria based on the reproducibility of experiments, appropriate analytic methods, and puffing regimes. Most revised studies complied with these requirements, but some were unreproducible, while others failed to consider analytical variables that may have affected the results and/or produced unrealistic comparisons. We also provide a review of the literature on the physicochemical properties of heated tobacco and HTP aerosols, as well as the evaluation of HTPs by regulatory agencies, addressing various critiques of their relative safety profile. The outcomes from the revised studies and regulatory evaluations tend to agree with and converge to a general consensus that HTP aerosols expose users to significantly lower levels of toxicity than tobacco smoke.

A New and Rapid HPLC Method to Determine the Degree of Deacetylation of Glutaraldehyde-Cross-Linked Chitosan

Chitosan is a linear biopolymer composed of D-glucosamine and N-acetylglucosamine units. The percentage of D-glucosamine in the polymeric chain can vary from one sample to another and is expressed as the degree of deacetylation (DDA). Since this parameter has an impact on many properties, its determination is often critical, and potentiometric titration is a common analytical technique to measure the DDA. Cross-linking with glutaraldehyde is one of the most explored modifications of chitosan; however, the determination of the DDA for the resulting reticulated chitosan resins can be challenging. In this paper, we report a new, rapid, and efficient method to determine the DDA of glutaraldehyde-cross-linked chitosan resins via HPLC. This method relies on the use of 2,4-dinitrophenylhydrazine (DNPH) as a derivatizing agent to measure the level of reticulation of the polymer (LR) after the reticulation step. In this study, we prepare three calibration curves (with an R2 value over 0.92) for three series of reticulated polymers covering a large range of reticulation levels to demonstrate that a correlation can be established between the LR established via HPLC and the DDA obtained via titration. The polymers are derived from three different chitosan starting materials. These standard calibration curves are now used on a routine basis in our lab, and the HPLC method has allowed us to change our DDA analysis time from 20 h to 5 min.

Development of an enhanced method for atmospheric carbonyls and characterizing their roles in photochemistry in subtropical Hong Kong

Carbonyl compounds are ubiquitous and play vital roles in tropospheric photochemistry and oxidation capacity, particularly affecting radical cycling and ozone formation. An enhanced method based on ultra-high-performance liquid chromatography and electrospray ionization tandem mass spectrometry was developed to simultaneously quantify 47 carbonyl compounds with carbon (C) numbers from 1 to 13. Applying this new method to samples collected at ground and ship-borne field campaigns, we investigated the abundance, characteristic distribution, and photochemical activity of carbonyl species in the coastal atmosphere of Hong Kong. The total concentration of detected carbonyls ranged from 9.1 to 32.7 ppbv and exhibited distinct spatial variability. In addition to the usual abundant carbonyl species (formaldehyde, acetaldehyde, and acetone), aliphatic saturated aldehydes with C ≥ 5 (particularly hexaldehyde and nonanaldehyde), and di‑carbonyls, exhibit significant abundance and photochemical reactivity in the coastal site and on the sea. The measured carbonyls could contribute to an estimated peroxyl radical formation rate of 1.88-8.43 ppb/h via OH oxidation and photolysis, greatly enhancing oxidation capacity and radical cycling. The ozone formation potential (OFP) estimated from the maximum incremental reactivity (MIR) was dominated (69 %-82 %) by formaldehyde and acetaldehyde, with significant contribution (4 %-13 %) from di‑carbonyls. Furthermore, another dozens of long-chain carbonyls without MIR values, which were typically below detection or not included in the conventional analytical method, would increase the ozone formation rate by an additional 2 %-33 %. Additionally, the glyoxal, methylglyoxal, benzaldehyde and other α, β-unsaturated aldehydes also exhibited considerable contribution to secondary organic aerosol (SOA) formation potential. This study highlights the importance of various reactive carbonyls in the atmospheric chemistry of urban and coastal regions. The newly developed method can effectively characterize more carbonyl compounds and advance our understanding of their roles in photochemical air pollution.

Simple and fast microderivatization method for determining formaldehyde using narrow-bore liquid chromatography with UV detection

Formaldehyde is a harmful substance that can cause sick building syndrome and other diseases, such as contact allergy, asthma, leukemia, cancer, and brain/neuron disorders. Formaldehyde is a ubiquitous chemical owing to its use in many common products, including as a preservative in household and personal care products. To prevent overexposure to formaldehyde, a simple method for determining and controlling the formaldehyde content in commercial products is required. In this study, 3-aminoquinoline (3-AQ) was used to derivatize formaldehyde under mild conditions (2 min at 30 °C) without the use of catalysts or activators. The derivatized sample solutions were separated using narrow-bore liquid chromatography with an ultraviolet (UV) detector in a run time of only 5 min. All sample extraction and derivatization protocols were performed on the microliter scale to reduce the use of organic solvents. The linear range for the determination was 5-1000 μg mL-1, with a detection limit of approximately 1 μg mL-1 (2 ng per 2 μL injection). The proposed microscale method was successfully applied to the analysis of formaldehyde in commercial household products.

Synthesis of 3-Alkyl Oxazolidines, Derived from 2-Hydroxymethyl Piperidine, as Analytical Standards for the Analysis of Volatile Aldehydes in the Workplace

Hexahydro-3-alkyl-3H-oxazolo[3,4-a]pyridines 4-15 for the quantitative analysis of various aldehydes were obtained in good yield via the condensation reaction of 2-hydroxymethylpiperidine (2-HMP) with aldehydes under mild conditions. When acrolein was used, the bicyclic 17 was obtained. This novel compound has suitable physical characteristics for an analytical standard. The hexahydro-3-vinyl-3H-oxazolo[3,4-a]pyridine 16 can be obtained at higher temperatures using an excess of acrolein (3 equiv). Following the same procedure as for 16, but with an excess of 2-HMP (2 equiv), a diastereomeric mixture of 18/19, which are both bisadducts of 2-HMP with acrolein, was obtained. The latter mixture can be easily converted into pure 18. Mechanistically, a thorough 1H-NMR study did not show any evidence that the condensation reaction proceeded via an enamine. The reaction probably proceeded through an elusive hemiaminal and fleeting iminium ion, which underwent subsequent cyclization to give hexahydro-3-alkyl-3H-oxazolo[3,4-a]pyridines 4-16. The reaction pathways for the preparation of 4-18 are described.

In-pipette-tip kapok fiber-supported liquid extraction/in-situ derivatization coupled with high-performance liquid chromatography for conveniently determining three furfurals

This study presents an in-pipette-tip kapok fiber-supported liquid extraction/in-situ derivatization (in-pipette-tip KF-SLE-ISD) method for simultaneous enrichment and derivatization of furfurals. Briefly, 3 mg of natural kapok fiber, which was loaded in an assembled pipette-tip, was used to support 12.5 μL of extractant (ethyl acetate/toluene, 75:25, v/v) containing 10 mM 2,4-dinitrophenylhydrazine. The in-pipette-tip KF-SLE-ISD procedure was conveniently conducted by aspirating/releasing 1 mL of sample solution 10 cycles, allowing simultaneous extraction and derivatization of furfurals. Then, 100 μL of acetonitrile was aspirated/released 5 cycles for elution, 10 μL of which was directly analyzed by high-performance liquid chromatography. The limits of quantitation were in ranges of 0.10-0.45 μg/mL. The method showed satisfied linearity (R² > 0.99), precision (RSD < 8.53%) and relative recovery (90.34-114.71%), which was successfully applied to determine furfurals in various samples (e.g., honeys, juices and glucose injections). The proposed method has the merits of effectiveness, simplicity, low cost, wide availability and ease of automation.

Structural elucidation of 3-nitrophenylhydrazine derivatives of tricarboxylic acid cycle acids and optimization of their fragmentation to boost sensitivity in liquid chromatography-mass spectrometry

Carboxylic acids participate in many metabolic pathways including tricarboxylic acid (TCA) cycle. Therefore, there have been ongoing attempts to develop sensitive liquid chromatography-mass spectrometry methods over the last decades. Derivatization of the carboxylic acids with 3-nitrophenylhydrazine presents a well-established methodology, and yet the derivatized species of polycarboxylic acids and their fragmentation in collision-induced dissociation have not been fully studied before. In our study, we elucidated how annotation of most abundant 3-nitrophenylhydrazine derivatives and optimization of their fragmentation in multiple reaction monitoring can boost the sensitivity, especially for polycarboxylic acids. Finally, the optimized liquid chromatography-tandem mass spectrometry method allowed for low detection limits ranging from 10 pM for 2-oxoglutaric acid to 800 pM for pyruvic acid. All TCA carboxylates were quantified in 20 µL of human plasma and the targeted method was validated in the same matrix. The same methodology with a modified gradient elution was also applied to untargeted screening of fatty acids by using high-resolution mass spectrometry enabling identification of 29 medium- to long-chain fatty acids in human plasma. The TCA carboxylates were also quantified in 10⁵ of C2C12 mouse myuotube cells grown under different treatments to proof applicability of the methodology to biological studies in a wider sense. However, unfortunately all the TCA carboxylates were also found in the derivatized blanks in substantial amounts, which prevents from using the methodology for quantification of the carboxylates in less than 10⁵ cells.

Analytical Toolbox to Unlock the Diversity of Oxidized Lipids

ConspectusLipids are diverse class of small biomolecules represented by a large variety of chemical structures. In addition to the classical biosynthetic routes, lipids can undergo numerous modifications via introduction of small chemical moieties forming hydroxyl, phospho, and nitro derivatives, among others. Such modifications change the physicochemical properties of a parent lipid and usually result in new functionalities either by mediating signaling events or by changing the biophysical properties of lipid membranes. Over the last decades, a large body of evidence indicated the involvement of lipid modifications in a variety of physiological and pathological events. For instance, lipid (per)oxidation for a long time was considered as a hallmark of oxidative stress and related proinflammatory signaling. Recently, however, with the burst in the development of the redox biology field, oxidative modifications of lipids are also recognized as a part of regulatory and adaptive events that are highly specific for particular cell types, tissues, and conditions.The initial diversity of lipid species and the variety of possible lipid modifications result in an extremely large chemical space of the epilipidome, the subset of the natural lipidome formed by enzymatic and non-enzymatic lipid modifications occurring in biological systems. Together with their low natural abundance, structural annotation of modified lipids represents a major analytical challenge limiting the discovery of their natural variety and functions. Furthermore, the number of available chemically characterized standards representing various modified lipid species remains limited, making analytical and functional studies very challenging. Over the past decade we have developed and implemented numerous analytical methods to study lipid modifications and applied them in the context of different biological conditions. In this Account, we outline the development and evolution of modern mass-spectrometry-based techniques for the structural elucidation of modified/oxidized lipids and corresponding applications. Research of our group is mostly focused on redox biology, and thus, our primary interest was always the analysis of lipid modifications introduced by redox disbalance, including lipid peroxidation (LPO), oxygenation, nitration, and glycation. To this end, we developed an array of analytical solutions to measure carbonyls derived from LPO, oxidized and nitrated fatty acid derivatives, and oxidized and glycated complex lipids. We will briefly describe the main analytical challenges along with corresponding solutions developed by our group toward deciphering the complexity of natural epilipdomes, starting from in vitro-oxidized lipid mixtures, artificial membranes, and lipid droplets, to illustrate the diversity of lipid modifications in the context of metabolic diseases and ferroptotic cell death.

Selective determination of formaldehyde by high-performance liquid chromatography with porous graphitic carbon column using N,N'-bis(9-anthrylmethyl)propane-1,3-diamine as derivatizing reagent

Aromatic compounds containing two secondary amino groups were designed and prepared as new derivatizing reagents for aldehydes. One of them, N,N'-bis(9-anthrylmethyl)propane-1,3-diamine (APD), could achieve selective determination of formaldehyde (FA) on a porous graphitic carbon (PGC) column using xylenes, chlorobenzene, and 1-chloronaphthalene as mobile phases by high-performance liquid chromatography (HPLC). The APD-FA derivative was eluted from the PGC column, while the other APD-aldehyde derivatives remained on the column during the HPLC measurements. This specific elution was not observed using mobile phases such as acetonitrile, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, chloroform, benzene, toluene, benzyl alcohol, 2-ethyl-1-hexanol, and pyridine. The APD-FA derivative had a six-membered ring of two tertiary amines identified using ¹H NMR spectroscopy. When the π-π interaction of the solvent molecule of the mobile phase with PGC overcame that between the APD-FA derivative and PGC, the APD-FA derivative could be eluted from the column. The best resolution between the peak of the APD-FA derivative and that of free APD was observed when using o-xylene. The optimum derivatization and the HPLC conditions for selective HPLC determination of FA were to conduct the derivatization of FA by heating in an aqueous phase with APD in o-xylene at 100 °C. In this method, FA could be derivatized with APD at a mildly neutral pH of 6.7, unlike the low pH required for the derivatization of aldehydes with 2,4-dinitrophenylhydrazine (DNPH), which is commonly used for the derivatization of aldehydes. The detection and quantification limits of FA were 0.8 and 3.5 ng mL^-1 in this HPLC method with fluorescent detection, respectively. This selective HPLC method could be applied to the determination of FA in various water samples. It was found that only APD among the derivatizing reagents containing two secondary diamines was useful for the selective determination of FA.

Flaxseed Cyclic Peptide [1-9-NαC]-Linusorb B3 (CLA) Improves Oxidative Stability of Flaxseed Oil by Chelating Metal Ions and Intermediate Oxidative Products

Oxidative rancidity is a major issue limiting the utilization of flaxseed oil (FSO). Peptides possess an antioxidant effect; however, the flax cyclic peptide, a unique ingredient in FSO, has an obscure influence on the oxidation of FSO. Therefore, this study is aimed to investigate the effects of [1-9-NαC]-linusorb B3 (CLA) on the accelerated oxidation of FSO and the underlying mechanism. We found that CLA increased the antioxidant stability of refined flaxseed oil (RFO), indicated by the improved parameters involved in the oxidation after the addition of CLA. After accelerated oxidation, the acid value (AV) of the RFO was increased by 24.14 times, whereas that of the RFO with CLA (CLA-RFO) increased only by 7.21 times. Similarly, the peroxide value (POV) and P-anisidine value (P-AV) of CLA-RFO were significantly decreased. Besides, CLA influenced metal ions-induced oxidation. In the Cu2+ group, the addition of CLA reduced the AV by 18% and the POV by 20%. The results of the molecular docking analysis and fluorescence quenching showed that the metal ions and propionaldehyde interacted with the cavity of CLA, and propionaldehyde had the most stable binding configuration with CLA, indicating that CLA may slow down the oxidation of FSO by chelating the metal ions and the intermediate oxidative products.

Next Challenges for the Comprehensive Molecular Characterization of Complex Organic Mixtures in the Field of Sustainable Energy

The conversion of lignocellulosic biomass by pyrolysis or hydrothermal liquefaction gives access to a wide variety of molecules that can be used as fuel or as building blocks in the chemical industry. For such purposes, it is necessary to obtain their detailed chemical composition to adapt the conversion process, including the upgrading steps. Petroleomics has emerged as an integral approach to cover a missing link in the investigation bio-oils and linked products. It relies on ultra-high-resolution mass spectrometry to attempt to unravel the contribution of many compounds in complex samples by a non-targeted approach. The most recent developments in petroleomics partially alter the discriminating nature of the non-targeted analyses. However, a peak referring to one chemical formula possibly hides a forest of isomeric compounds, which may present a large chemical diversity concerning the nature of the chemical functions. This identification of chemical functions is essential in the context of the upgrading of bio-oils. The latest developments dedicated to this analytical challenge will be reviewed and discussed, particularly by integrating ion source features and incorporating new steps in the analytical workflow. The representativeness of the data obtained by the petroleomic approach is still an important issue.

Determination of methanol-derivatives in drying oils after metal oxide-based dispersive solid phase extraction/QuEChERS clean-up

The determination of secondary volatile degradation products in drying oil extracts is substantial to prevent formation of undesirable metal formates in paintings and/or other artefacts. This study develops a simple, cost-effective, and reliable, high-performance liquid chromatography with diode array detector (HPLC-DAD) method to determine three secondary volatile degradation products (methanol, formaldehyde, and formic acid) in drying oils, including linseed, poppy-seed, and walnut oil. Extraction of analytes was performed using QuEChERS-based procedure followed by metal oxide-based dispersive solid-phase extraction (d-SPE) clean-up and presented a good performance for all of the volatile analytes of interest with recoveries in the range of 90-120% after application of the nanostructured cerium oxide-based (CeO₂) and zirconia-based (ZrO₂) sorbents prepared by favorable and ecological-friendly methods. With a new clean-up solution for samples with high-fat content, it was possible to achieve higher recoveries than with commercial Z-Sep/C18 sorbent. In all cases, relative standard deviations (RSD) of less than 10% were achieved. No significant matrix interference was observed due to the application of effective sorbents in nanostructured form. The developed method was applied to samples of drying oils, and it was found that after storage for three months, all methanol was most likely oxidized to formaldehyde and formic acid. The concentrations of formaldehyde were in the range of 260 - 304 μg∙g^-1, while formic acid concentrations ranged between 72 - 386 μg∙g^-1. The highest concentration of formaldehyde (304 μg∙g^-1) and formic acid (386 μg∙g^-1) was found in linseed oil.

Absolute Configuration and Biological Evaluation of Novel Triterpenes as Possible Anti-Inflammatory or Anti-Tumor Agents

Two new compounds, ardisiapunine B (1) and ardisiapunine C (2), were isolated from Ardisia lindleyana D. Dietr. Their structures were examined using HR-ESI-MS, IR, (1D, 2D) NMR spectroscopic analyses, single-crystal X-ray diffraction, and ECD calculation. It was found that the two new compounds belong to unusual oleanane-type triterpenes, with compound 1 bearing an acetal unit and a C-13-C-18 double bond, and compound 2 bearing a C-28 aldehyde group and a C-18-C-19 double bond. The anti-inflammatory properties of compounds 1 and 2 were tested on NO production and cellular morphology using RAW264.7 cells, and their anti-tumor properties were tested on cytotoxic activities, cellular morphology, cell apoptosis, and cell cycle. The results showed that compound 1 exhibited a potent cytotoxicity against HepG2 cell lines with an IC₅₀ of 12.40 μM. Furthermore, it is possible that compound 1 inhibits cell proliferation by blocking the cell G2/M phase and promoting cell apoptosis. Compound 2 exhibited a potential anti-inflammatory activity by decreasing the production of NO in LPS-stimulated RAW264.7 cells. Comparative analysis of the structures of compounds 1 and 2 revealed that the acetal structure and double bond positions were the main differences between them, and these are presumed to be the main reasons for the extreme differences in their cytotoxicity and anti-inflammatory activities. From these new findings, two promising lead compounds were identified for the future development of potential anti-inflammatory or anti-tumor agents.

Chemical characterisation of the vapour emitted by an e-cigarette using a ceramic wick-based technology

Fourth-generation 'pod' e-cigarette devices have been driven by technological advances in electronic atomization of the e-liquid. Use of microporous ceramic as a wicking material improves heating efficiency, but how it affects the chemical emissions of these devices is unclear. We assessed the emissions of a pod e-cigarette with innovative ceramic wick-based technology and two flavoured e-liquids containing nicotine lactate and nicotine benzoate (57 and 18 mg mL-1 nicotine, respectively). Among the studied harmful and potentially harmful constituents (HPHCs) listed by the US FDA and/or WHO TobReg, only 5 (acetone, acetaldehyde, formaldehyde, naphthalene and nornicotine) were quantified at levels of 0.14 to 100 ng puff-1. In the combustible cigarette (Kentucky reference 1R6F), levels were from 0.131 to 168 µg puff-1. Nicotine levels ranged 0.10-0.32 mg puff-1 across the 3 study products. From the 19 proposed HPHCs specifically of concern in e-cigarettes, only 3 (glycerol, isoamyl acetate and propylene glycol) were quantified. The low/undetectable levels of HPHCs reflect not only the optimal operating conditions of the e-cigarette, including an efficient supply of e-liquid by the ceramic wick without overheating, but also the potential of the e-cigarettes to be used as an alternative to combustible cigarettes.

Novel Method of Analysis for the Determination of Residual Formaldehyde by High-Performance Liquid Chromatography

Formaldehyde is commonly used as an alkylating agent in the pharmaceutical industry. Consequently, its residual level in drug substances and/or their intermediates needs to be accurately quantified. Formaldehyde is a small, volatile molecule with a weak chromophore (the carbonyl group), and its direct analysis by GC-FID and HPLC-UV is difficult. For these reasons, the majority of papers found in the literature are based upon a derivatisation process (most commonly using the desensitised explosive 2,4-dinitrophenylhydrazine) prior to the analysis of formaldehyde. A novel high-performance liquid chromatography (HPLC) method with UV detection for its quantification in a pharmaceutical is described in this paper. The method proposed herein is based upon a derivatisation reaction between formaldehyde and 4-methylbenzenesulfonohydrazide (MBSH) before analysis by HPLC-UV. Selectivity, linearity, limit of quantification, accuracy, repeatability, intermediate precision, and solution stability were successfully assessed as per ICH guideline Q2(R1), and the method has also been validated in a good manufacturing practice (GMP) laboratory in the UK.

Spatial localization of β-unsaturated aldehyde markers in murine diabetic kidney tissue by mass spectrometry imaging

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Limitations in current diagnosis and screening methods have sparked a search for more specific and conclusive biomarkers. Hyperglycemic conditions generate a plethora of harmful molecules in circulation and within tissues. Oxidative stress generates reactive α-dicarbonyls and β-unsaturated hydroxyhexenals, which react with proteins to form advanced glycation end products. Mass spectrometry imaging (MSI) enables the detection and spatial localization of molecules in biological tissue sections. Here, for the first time, the localization and semiquantitative analysis of “reactive aldehydes” (RAs) 4-hydroxyhexenal (4-HHE), 4-hydroxynonenal (4-HNE), and 4-oxo-2-nonenal (4-ONE) in the kidney tissues of a diabetic mouse model is presented. Ionization efficiency was enhanced through on-tissue chemical derivatization (OTCD) using Girard’s reagent T (GT), forming positively charged hydrazone derivatives. MSI analysis was performed using matrix-assisted laser desorption ionization (MALDI) coupled with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR). RA levels were elevated in diabetic kidney tissues compared to lean controls and localized throughout the kidney sections at a spatial resolution of 100 µm. This was confirmed by liquid extraction surface analysis–MSI (LESA-MSI) and liquid chromatography–mass spectrometry (LC–MS). This method identified β-unsaturated aldehydes as “potential” biomarkers of DN and demonstrated the capability of OTCD-MSI for detection and localization of poorly ionizable molecules by adapting existing chemical derivatization methods. Untargeted exploratory distribution analysis of some precursor lipids was also assessed using MALDI-FT-ICR-MSI.

Unveiling the pH-Dependent Yields of H2O2 and OH by Aqueous-Phase Ozonolysis of m-Cresol in the Atmosphere

Hydrogen peroxide (H₂O₂) and hydroxyl radical (OH) are important oxidants in the atmospheric aqueous phase such as cloud droplets and deliquescent aerosol particles, playing a significant role in the chemical transformation of organic and inorganic pollutants in the atmosphere. Atmospheric aqueous-phase chemistry has been considered to be a source of H₂O₂ and OH. However, our understanding of the mechanisms of their formation in atmospheric waters is still incomplete. Here, we show that the aqueous-phase reaction of dissolved ozone (O₃) with substituted phenols such as m-cresol represents an important source of H₂O₂ and OH exhibiting pH-dependent yields. Intriguingly, the formation of H₂O₂ through the ring-opening mechanism is strongly promoted under lower pH conditions (pH 2.5-3.5), while higher pH favors the ring-retaining pathways yielding OH. The rate constant of the reaction of O₃ with m-cresol increases with increasing pH. The reaction products formed during the ozonolysis of m-cresol are analyzed by an Orbitrap mass spectrometer, and reaction pathways are suggested based on the identified product compounds. This study indicates that aqueous-phase ozonolysis of phenolic compounds might be an alternative source of H₂O₂ and OH in the cloud, rain, and liquid water of aerosol particles; thus, it should be considered in future model studies.

Screening check test to confirm the relative reactivity and applicability of 2,4‐dinitrophenylhydrazine impregnated‐filters for formaldehyde on other compounds

Objectives

Methods

Results

Conclusions

The Simultaneous Formation of Acrylamide, β-carbolines, and Advanced Glycation End Products in a Chemical Model System: Effect of Multiple Precursor Amino Acids

This study investigated the effect of multiple precursor amino acids on the simultaneous formation of acrylamide, β-carbolines (i. e., harmane and norharmane), and advanced glycation end products (AGEs) [i.e., N^ε-(carboxymethyl)lysine and N^ε-(carboxyethyl)lysine] via a chemical model system. This model system was established with single or multiple precursor amino acids, including lysine–glucose (Lys/Glu), asparagine–glucose (Asn/Glu), tryptophan–glucose (Trp/Glu), and a combination of these amino acids (Com/Glu). Kinetic parameters were calculated by multiresponse non-linear regression models. We found that the k values of the AGEs and of acrylamide decreased, while those of harmane increased in the Com/Glu model when heated to 170 and 200°C. Our results indicated that the precursor amino acid of acrylamide and AGEs compete for α-dicarbonyl compounds, leading to a decrease in the formation of AGEs and acrylamide. Moreover, compared with asparagine, the precursor amino acid of β-carbolines was more likely to react with acetaldehyde by Pictet–Spengler condensation, which increased the formation of harmane and decreased the formation of acrylamide via the acrolein pathway.

Assessing Photosensitized Membrane Damage: Available Tools and Comprehensive Mechanisms

Lipids are important targets of the photosensitized oxidation reactions, forming important signaling molecules, disorganizing and permeabilizing membranes, and consequently inducing a variety of biological responses. Although the initial steps of the photosensitized oxidative damage in lipids are known to occur by both Type I and Type II mechanisms, the progression of the peroxidation reaction, which leads to important end-point biological responses, is poorly known. There are many experimental tools used to study the products of lipid oxidation, but neither the methods nor their resulting observations were critically compared. In this article, we will review the tools most frequently used and the key concepts raised by them in order to rationalize a comprehensive model for the initiation and the progression steps of the photoinduced lipid oxidation.

Distribution of aldehydes compared to other oxidation parameters in oil matrices during autoxidation

Distribution of aldehydes between headspace (HS) and inner matrix (IM) of bulk oil or oil-in-water (O/W) emulsion was determined and contents of aldehydes were compared with other oxidation parameters in soybean oil or O/W emulsion during 50 °C autoxidation. Bulk oil matrix had higher portion of IM aldehydes than O/W emulsion. HS aldehydes in O/W emulsion reflected aldehyde content better than in bulk oil. Moisture content in soybean oil increased distinctively before the generation of oxidation products including hydroperoxides and volatiles. HS aldehydes and other oxidation parameters were simultaneously increased in soybean oil. In case of O/W emulsion, HS aldehydes had a sudden increase point while lipid hydroperoxides and conjugated did not show such increase during autoxidation. HS aldehydes reflected oxidation stage better in O/W emulsion than in bulk oil based on partition distribution and linear changes during autoxidation.

A sensitive chemiluminescence detection approach for determination of 2,4-dinitrophenylhydrazine derivatized aldehydes using online UV irradiation - luminol CL reaction. Application to the HPLC analysis of aldehydes in oil samples

Aldehydes are toxic carbonyl compounds that are identified in various matrices surrounding us. For instance, aldehydes could be formed during the cooking and frying of foods which affects the food quality and safety. Derivatization is a must for the determination of aldehydes as they lack intrinsic chromophoric groups. 2,4-Dinitrophenyl hydrazine (DNPH) is the most used derivatizing reagent for aldehydes and the formed hydrazones could be determined by either HPLC-UV or LC-MS. However, UV detection is non-sensitive, and the MS equipment is expensive and not widely available. Thus, herein we report a smart chemiluminescence (CL) detection method for the DNPH aldehydes derivatives. These derivatives are supposed to possess photosensitization ability due to the presence of strong chromophoric structures; nitrobenzene and phenyl hydrazone. Upon their UV irradiation, singlet oxygen is found to be produced which then converts the DNPH-aldehyde derivative into hydroperoxide. Next, the hydroperoxide reacts with luminol in an alkaline medium producing a strong CL. An HPLC system with online UV irradiation and online reaction with luminol followed by CL detection was constructed and used for the determination of aldehydes after their derivatization with DNPH. The developed method showed excellent sensitivity with detection limits down to 1.5-18.5 nM. The achieved sensitivity is superior to that obtained by HPLC-UV and LC-MS detection methods for DNPH-aldehydes derivatives. Additionally, our approach is an chemiluminogenic where the DNPH reagent itself does not produce CL which is an excellent advantage. The method was applied successfully for the determination of aldehydes in canola oil samples using simple liquid-liquid extraction showing good recovery (87.0-106.0%), accuracy (87.2-106.6), and precision (RSD≤10.2%). After analysis of fresh and heated oil samples, it was demonstrated that heating of oil, even for short time, strongly elevated the level of their aldehydes' content. At last, it was found that the results of the analysis of aldehydes in oil samples using the proposed method perfectly matched those obtained by a reference LC-MS method.

Towards Aldehydomics: Untargeted Trapping and Analysis of Reactive Diet-Related Carbonyl Compounds Formed in the Intestinal Lumen

Lipid peroxidation and subsequent formation of toxic aldehydes, such as 4-hydroxynonenal, is known to be involved in numerous pathophysiological processes, possibly including the development of colorectal cancer. This work aimed at the development of an untargeted approach using high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) for tracking aldehydes in both suspect screening and untargeted methods in fecal water, representing the aqueous environment of colon epithelial cells. This original approach is based on the introduction of a characteristic isotopic labeling by selective derivatization of the carbonyl function using a brominated reagent. Following a metabolomics workflow, the developed methodology was applied to the characterization of aldehyde compounds formed by lipid peroxidation in rats fed two different diets differentially prone to lipoperoxidation. Derivatized aldehydes were first selectively detected on the basis of their isotopic pattern, then annotated and finally identified by tandem mass spectrometry. This original approach allowed us to evidence the occurrence of expected aldehydes according to their fatty acid precursors in the diet, and to characterize other aldehydes differentiating the different diets.

Reduced solvent and reagent amounts: effect on carbonyl dinitrophenylhydrazone measurements at low concentrations

This work aims to advance towards a more affordable laboratory procedure for sample treatment to determine carbonyl compounds by derivatization with 2,4-dinitrophenylhydrazine (DNPH). The proposal is based on reducing the amount of DNPH and solvents. A simple addition of standard carbonyls in a solution containing DNPH to prepare hydrazone standards is described and evaluated. Tedious recrystallization steps are avoided. Formaldehyde, acetaldehyde, acetone, tolualdehyde and hexanal, as carbonyl models, were quantified using a DNPH concentration of 400 μg mL^-1 and 3.8 mM H₂SO₄ and by keeping for 24 hours at room temperature. Analytical coefficients of variation between 10 and 25% were found from the analysis of blanks under intermediate conditions (two different devices, very different concentrations of DNPH and analysis on two days). From these values of relative standard deviations and background levels, quantification limits were estimated between 15 and 40 ng mL^-1. The reduction of reagent amounts allows the operator to better control the background levels in the use of DNPH, as well as making the method more cost-effective and easy to use. In short, it leads to a more sustainable adaptation of the classical method. The versatility in analytical application was tested to estimate the levels of formaldehyde, acetaldehyde and acetone in very different types of environmental samples. In particular, outdoor and indoor samples were collected in filters and impregnated cartridges, respectively. Moreover, tars in 2-propanol and particulate matter from gasification processes were also tested.

A novel pathway for initial biotransformation of dinitroaniline herbicide butralin from a newly isolated bacterium Sphingopyxis sp. strain HMH

Butralin (N-sec- Butyl-4-tert-butyl-2,6-dinitroaniline) is a highly persistent dinitroaniline herbicide frequently detected in the environment. In this study, butralin-degrading soil bacterium, Sphingopyxis sp. strain HMH was isolated from agricultural soil samples. Based on whole genome sequence analysis of the strain HMH, the gene encoding a nitroreductase NfnB was identified and expressed in Escherichia coli (E. coli), and protein was purified to homogeneity. NfnB is a flavin-nitroreductase, found to be a functional tetramer, composed of subunit molecular mass of 25 kDa. The metabolites from butralin degradation by strain HMH and purified NfnB were identified using ultra performance liquid chromatography high resolution mass spectrometry (UPLC-HRMS), and a novel mechanism of butralin degradation was proposed. NfnB selectively nitro-reduced butralin into N- (sec-Butyl)-4-(tert-butyl)-6-nitrobenzene- 1,2-diamine, followed by formation of 5-(tert-Butyl)-3 -nitrobenzene-1,2-diamine and butanone by N- dealkylation through possible hydroxylation reaction onto the carbon linked amine of the N-(sec-Butyl) moiety. In our study, we could not detect the hydroxylated product 2-(2-Amino-4-tert-butyl-6-nitro- phenylamino)-butan-2-ol) (carbinolamine), instead its Schiff base product (E)-2-(Butan-2-yildeneamino)-5- (tert-butyl)-3-nitroaniline was detected. The release of butanone was further confirmed by derivatization with 2,4- dinitrophenylhydrazine (DNPH) followed by MS analysis. In conclusion, this study explores a novel multi-functional flavin- nitroreductase family enzyme NfnB, catalyzing unique and sequential nitroreduction and N-dealkylation through oxidative hydroxylation of dinitroaniline herbicide butralin.

Animal and Plant Protein Oxidation: Chemical and Functional Property Significance

Protein oxidation, a phenomenon that was not well recognized previously but now better understood, is a complex chemical process occurring ubiquitously in food systems and can be induced by processing treatments as well. While early research concentrated on muscle protein oxidation, later investigations included plant, milk, and egg proteins. The process of protein oxidation involves both radicals and nonradicals, and amino acid side chain groups are usually the site of initial oxidant attack which generates protein carbonyls, disulfide, dityrosine, and protein radicals. The ensuing alteration of protein conformational structures and formation of protein polymers and aggregates can result in significant changes in solubility and functionality, such as gelation, emulsification, foaming, and water-holding. Oxidant dose-dependent effects have been widely reported, i.e., mild-to-moderate oxidation may enhance the functionality while strong oxidation leads to insolubilization and functionality losses. Therefore, controlling the extent of protein oxidation in both animal and plant protein foods through oxidative and antioxidative strategies has been of wide interest in model system as well in in situ studies. This review presents a historical perspective of food protein oxidation research and provides an inclusive discussion of the impact of chemical and enzymatic oxidation on functional properties of meat, legume, cereal, dairy, and egg proteins based on the literature reports published in recent decades.

Determination of 2,4-decadienal in edible oils using reversed-phase liquid chromatography and its application as an alternative indicator of lipid oxidation

As a major product of linoleic acid-rich oils, 2,4-decadienal has unique reactivity that may be potentially toxic to human body. In this study, a reliable reversed-phase liquid chromatography method for the determination of carbonyls was developed, and 2,4-decadienal as the target aldehyde was validated. Furthermore, the possibility of 2,4-decadienal as a lipid oxidation marker was evaluated. The optimal sample pretreatment method was extraction by 2 mL of acetonitrile three times, followed by derivatization at 40 °C for 30 min. The method was linear, sensitive, and accurate with detection and quantification limits of 15 and 50 nmol/L, respectively, and had good average recoveries for 2,4-decadienal in oil samples. In tested edible oils, during heating at 180 °C, the level of 2,4-decadienal rose faster than other aldehydes, including one of the characteristic aldehydes, hexanal. Moreover, good linear relationships between the 2,4-decadienal content and other oxidation indices (R² = 0.858 to 0.984 for the anisidine value; R² = 0.876 to 0.986 for the total oxidation value) were observed in sunflower and corn oils under 8 hr heating at three temperatures (120, 150, and 180 °C), indicating that 2,4-decadienal can predict the oxidation of oil. PRACTICAL APPLICATION: 2,4-Decadienal is a toxic aldehyde produced by the oxidation of linoleic acid-rich oils, which is closely related to human health. This work is the first to demonstrate that 2,4-decadienal can be used as an alternative oxidation indicator for linoleic acid-rich oils and is of great significance for the quality control of edible oil in the food industry.

Saliva as a non-invasive tool for monitoring oxidative stress in swimmers athletes performing a VO2max cycle ergometer test

Biomarkers of oxidative stress are generally measured in blood and its derivatives. However, the invasiveness of blood collection makes the monitoring of such chemicals during exercise not feasible. Saliva analysis is an interesting approach in sport medicine because the collection procedure is easy-to-use and does not require specially-trained personnel. These features guarantee the collection of multiple samples from the same subject in a short span of time, thus allowing the monitoring of the subject before, during and after physical tests, training or competitions. The aim of this work was to evaluate the possibility of following the changes in the concentration of some oxidative stress markers in saliva samples taken over time by athletes under exercise. To this purpose, ketones (i.e. acetone, 2-butanone and 2-pentanone), aldehydes (i.e. propanal, butanal, and hexanal), α,β-unsaturated aldehydes (i.e. acrolein and methacrolein) and di-carbonyls (i.e. glyoxal and methylglyoxal) were derivatized with 2,4-dinitrophenylhydrazine, and determined by ultra-high performance liquid chromatography coupled to diode array detector. Prostaglandin E₂, F₂/E₂-isoprostanes, F₂-dihomo-isoprostanes, F₄-neuroprostanes, and F₂-dihomo-isofuranes were also determined by a reliable analytical procedure that combines micro-extraction by packed sorbent and ultra-high performance liquid chromatography-electrospray ionization tandem mass spectrometry. Overall the validation process showed that the methods have limits of detection in the range of units of ppb for carbonyls and tens to hundreds of ppt for isoprostanes and prostanoids, very good quantitative recoveries (90-110%) and intra- and inter-day precision lower than 15%. The proof of applicability of the proposed analytical approach was investigated by monitoring the selected markers of oxidative stress in ten swimmers performing a VO_2max cycle ergo meter test. The results highlighted a clear increase of salivary by-products of oxidative stress during exercise, whereas a sharp decrease, approaching baseline values, of these compounds was observed in the recovery phase. This study opens up a new approach in the evaluation of oxidative stress and its relation to aerobic activity.

The Biosynthesis Mechanism Involving 2,3-Pentanedione and Aminoacetone Describes the Production of 2-Ethyl-3,5-dimethylpyrazine and 2-Ethyl-3,6-dimethylpyrazine by Bacillus subtilis

2-Ethyl-3,5(3,6)-dimethylpyrazines (EDMPs) have a pleasant aroma of roasted cocoa or nuts with an extreme low odor threshold that have potential in industrial applications as food fragrances. The food fermentation process can accumulate EDMPs, and this might be the chance to study the biosynthesis mechanism of EDMPs under mild conditions for "natural" EDMPs' production. In this study, an EDMP-producing strain was isolated from baijiu fermentation. This strain was identified as Bacillus subtilis, a generally regarded as safe organism. After reasonable assumption and substrate addition and isotope-labeled experiments, we found that EDMPs are produced from l-threonine and d-glucose at environmental temperature and pressure. In addition, aminoacetone, the metabolite of l-threonine, and 2,3-pentanedione, the metabolite of l-threonine and d-glucose, are intermediates for the production of EDMPs. This study proposed and confirmed the biosynthesis pathway of EDMPs. It will be helpful for the industrial production of EDMPs and provides reference for the biosynthetic mechanism analysis of other valuable pyrazines.

Translating In Vitro Acrolein-Trapping Capacities of Tea Polyphenol and Soy Genistein to In Vivo Situation is Mediated by the Bioavailability and Biotransformation of Individual Polyphenols

SCOPE

Acrolein (ACR) is a highly toxic unsaturated aldehyde. Humans are both endogenously and exogenously exposed to ACR. Long-term exposure to ACR leads to various chronic diseases. Dietary polyphenols have been reported to be able to attenuate ACR-induced toxicity in vitro via formation of ACR-polyphenol conjugates. However, whether in vitro ACR-trapping abilities of polyphenols can be maintained under in vivo environments is still unknown.

METHODS AND RESULTS

Two most commonly consumed dietary polyphenols, (-)-epigallocatechin-3-gallate (EGCG) from tea and genistein from soy, are evaluated for their anti-Acrolein behaviors both in vitro and in mice. Tea EGCG exerts a much higher capacity to capture ACR than soy genistein in vitro. But translation of in vitro anti-ACR activity into in vivo is mainly mediated by bioavailability and biotransformation of individual polyphenols. It is found that 1) both absorbed EGCG and genistein can trap endogenous ACR by forming mono-ACR adducts and eventually be excreted into mouse urine; 2) both absorbed EGCG and genistein can produce active metabolites, methyl-EGCG (MeEGCG) and orobol, to scavenge endogenous ACR; 3) both MeEGCG and non-absorbed EGCG show ability to trap ACR in the gut; 4) considerable amounts of microbial metabolites of genistein display enhanced anti-ACR capacity both in the body and in the gut, compared to genistein; and 5) biotransformation of genistein is able to boost its in vivo anti-ACR capacity, compared to EGCG.

CONCLUSION

The findings demonstrate that in vivo anti-ACR ability of dietary polyphenols cannot be reflected solely based on their in vitro ability. The bioavailability and biotransformation of individual polyphenols, and especially the gut microbiome, contribute to in vivo anti-ACR ability of dietary polyphenols.

Oxidative stress in microbes after exposure to iron nanoparticles: analysis of aldehydes as oxidative damage products of lipids and proteins

Due to their enhanced reactivity, metal and metal-oxide nanoscale zero-valent iron (nZVI) nanomaterials have been introduced into remediation practice. To ensure that environmental applications of nanomaterials are safe, their possible toxic effects should be described. However, there is still a lack of suitable toxicity tests that address the specific mode of action of nanoparticles, especially for nZVI. This contribution presents a novel approach for monitoring one of the most discussed adverse effects of nanoparticles, i.e., oxidative stress (OS). We optimized and developed an assay based on headspace-SPME-GC-MS analysis that enables the direct determination of volatile oxidative damage products (aldehydes) of lipids and proteins in microbial cultures after exposure to commercial types of nZVI. The method employs PDMS/DVB SPME fibers and pentafluorobenzyl derivatization, and the protocol was successfully tested using representatives of bacteria, fungi, and algae. Six aldehydes, namely, formaldehyde, acrolein, methional, benzaldehyde, glyoxal, and methylglyoxal, were detected in the cultures, and all of them exhibited dose-dependent sigmoidal responses. The presence of methional, which was detected in all cultures except those including an algal strain, documents that nZVI also caused oxidative damage to proteins in addition to lipids. The most sensitive toward nZVI exposure in terms of aldehyde production was the yeast strain Saccharomyces cerevisiae, which had an EC₅₀ value of 0.08 g/L nZVI. To the best of our knowledge, this paper is the first to document the production of aldehydes resulting from lipids and proteins as a result of OS in microorganisms from different kingdoms after exposure to iron nanoparticles.

Analysis of Oxidative Carbonyl Compounds by UPLC-High-Resolution Mass Spectrometry in Milk Powder

Long-chain polyunsaturated fatty acids are highly susceptible to lipid oxidation which causes undesirable odors and flavors in food. We present the development, validation, and application of a semiquantitative screening method to monitor volatile and nonvolatile carbonyl compounds generated from lipids oxidation after 7-(diethylamino)-2-oxochromene-3-carbohydrazide (CHH) derivatization using liquid chromatography high-resolution mass spectrometry. An inclusion list containing eligible compounds was used in full scan mode to identify potential oxidative markers. In an antioxidants study using lecithin and tocopherols, the proposed method was successfully used to monitor the docosahexaenoic acid (DHA)-specific oxidative markers in a model milk powder system enriched with fish oils. The results showed that lecithin inhibits oxidation by reducing the peroxidation rate, while δ-tocopherol delays the oxidation with distinct induction periods. Here, we explore the optimum concentration of soy lecithin and δ-tocopherol needed to limit lipid oxidation in a complex food matrix such as milk powder.

Method for the determination of residual formaldehyde in an inactivated Zika vaccine formulated with aluminum hydroxide gel

A simple method for the determination of low levels of residual formaldehyde in an inactivated Zika vaccine formulated with aluminum hydroxide gel was developed for the assessment of drug product quality. Formaldehyde was reacted with 2,4-dinitrophenylhydrazine (DNPH) and the derivatized product was detected by HPLC with an UV detector at 360 nm. The derivatization reaction could be carried out in a 2-mL HPLC vial and the sample was analyzed directly. The method was fully validated according to the International Conference on Harmonization Q2 guidelines. Aluminum hydroxide gel up to 1.0 mg/mL (aluminum concentration) did not interfere with the determination of formaldehyde in drug product. Formaldehyde concentrations of 0.05 μg/mL (quantitation limit) to 1.00 μg/mL in the Zika vaccine could be precisely determined. Hence, this method proved to be suitable for quality control of the Zika vaccine.