Identification of metal species by ESI-MS/MS through release of free metals from the corresponding metal-ligand complexes

Discovery of Modified Metabolites, Secondary Metabolites, and Xenobiotics by Structure-Oriented LC-MS/MS

Exogenous compounds and metabolites derived from therapeutics, microbiota, or environmental exposures directly interact with endogenous metabolic pathways, influencing disease pathogenesis and modulating outcomes of clinical interventions. With few spectral library references, the identification of covalently modified biomolecules, secondary metabolites, and xenobiotics is a challenging task using global metabolomics profiling approaches. Numerous liquid chromatography-coupled mass spectrometry (LC-MS) small molecule analytical workflows have been developed to curate global profiling experiments for specific compound groups of interest. These workflows exploit shared structural moiety, functional groups, or elemental composition to discover novel and undescribed compounds through nontargeted small molecule discovery pipelines. This Review introduces the concept of structure-oriented LC-MS discovery methodology and aims to highlight common approaches employed for the detection and characterization of covalently modified biomolecules, secondary metabolites, and xenobiotics. These approaches represent a combination of instrument-dependent and computational techniques to rapidly curate global profiling experiments to detect putative ions of interest based on fragmentation patterns, predictable phase I or phase II metabolic transformations, or rare elemental composition. Application of these methods is explored for the detection and identification of novel and undescribed biomolecules relevant to the fields of toxicology, pharmacology, and drug discovery. Continued advances in these methods expand the capacity for selective compound discovery and characterization that promise remarkable insights into the molecular interactions of exogenous chemicals with host biochemical pathways.

SERS study of classical and newly β-lactams-metal complexation based on in situ laser-induced coral reefs-like silver photomicroclusters: In vitro study of antibacterial activity

The influence of metal complexation of two polar β-lactam antibiotics was investigated using surface enhanced Raman spectroscopy (SERS) technique. SERS method was applied to track the structural changes and the degradation behaviour of the studied compounds upon Zinc (II) ions-complexation. In situ laser-induced coral reefs-like photomicroclusters have been utilized as a SERS platform. The produced coral reefs-like photomicroclusters were characterized using scanning electron microscopy (SEM) and transmission electron microscope (TEM). The antibacterial efficiency of the antibiotics was investigated and compared before and after metal complexation using two techniques; agar well diffusion and growth curve. To provide a detailed elucidation of the complexation reaction, mass fragmentation of metal- antibiotics complexes was investigated using liquid chromatography/mass spectrometric (LC/MS) technique. It was found that metal complexation of classical β-lactam antibiotic (Ticarcillin) promoted the rate of its degradation, leading to a decrease of the antibacterial efficiency. On the other side, the antibacterial activity of the newly developed β-lactam (Faropenem) has been greatly enhanced via metal-complexation reaction.

A curcumin-nicotinoyl derivative and its transition metal complexes: synthesis, characterization, and in silico and in vitro biological behaviors

Curcumin-nicotinoyl (Cur-Nic) was synthesized by the chemical modification of the curcumin structure, characterized, and used as a ligand for the synthesis of copper(II) and zinc(II) complexes. The biological activities of Cur-Nic and its metal complexes were predicted using the PASS and Swiss Target Prediction online software, respectively, and docking studies with tyrosine-protein kinase SRC were performed using the PyRx software to predict their anticancer activities. The toxicity effects of the complexes on a human breast cancer cell line (MCF-7) compared to a healthy breast cell line (MCF-10A) were investigated by the MTS assay. Although the metal complexes maintained the least toxicity against normal cells, the results indicated that compared to curcumin and Cur-Nic, the cytotoxicity toward cancer cells increased due to the complexation process. Moreover, the antibacterial evaluation of the compounds against a Gram-positive bacterium (MRSA) and a Gram-negative bacterium (E. coli) indicated that the Cu(II) complex and Cur-Nic were the best, respectively. Also, the Zn(II) complex was the most stable compound, and the Cu(II) complex was the best ROS scavenger based on the in vitro evaluation.

Continuous flow catalysis with CuBTC improves reaction time for synthesis of xanthene derivatives

The copper-based metal-organic framework (MOF) CuBTC (where H3BTC = benzene-1,3,5-tricarboxylate) has been shown to be an efficient heterogeneous catalyst for the generation of 1,8-dioxo-octa-hydro xanthene derivatives, which are valuable synthetic targets for the pharmaceutical industry. We have applied this catalytic capability of CuBTC to a continuous flow system to produce the open chain form of 3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione, a xanthene derivative from benzaldehyde and dimedone. An acid work-up after producing the open chain form of the xanthene derivative was used to achieve ring closure and form the final xanthene product. The CuBTC used to catalyze the reaction under continuous flow was confirmed to be stable throughout this process via analysis by SEM, pXRD, and FT-IR spectroscopy, elemental analysis, and XPS. The reaction to produce the open-chain form of the xanthene derivative produced an average yield of 33% ± 14% under the continuous flow (compared to 33% ± 0.12% of performing it under batch conditions). Based on the data obtained from this work, the continuous flow system required 22.5x less time to produce the desired xanthene derivative at comparable yields to batch reaction conditions. These results would allow for the xanthene derivative to be produced much faster, at a lower cost, and require less personal time while also removing the need to perform catalyst remove post reaction.

Ambient temperature CO2 fixation to pyruvate and subsequently to citramalate over iron and nickel nanoparticles

The chemical reactions that formed the building blocks of life at origins required catalysts, whereby the nature of those catalysts influenced the type of products that accumulated. Recent investigations have shown that at 100 °C awaruite, a Ni₃Fe alloy that naturally occurs in serpentinizing systems, is an efficient catalyst for CO₂ conversion to formate, acetate, and pyruvate. These products are identical with the intermediates and products of the acetyl-CoA pathway, the most ancient CO₂ fixation pathway and the backbone of carbon metabolism in H₂-dependent autotrophic microbes. Here, we show that Ni₃Fe nanoparticles prepared via the hard-templating method catalyze the conversion of H₂ and CO₂ to formate, acetate and pyruvate at 25 °C under 25 bar. Furthermore, the ¹³C-labeled pyruvate can be further converted to acetate, parapyruvate, and citramalate over Ni, Fe, and Ni₃Fe nanoparticles at room temperature within one hour. These findings strongly suggest that awaruite can catalyze both the formation of citramalate, the C5 product of pyruvate condensation with acetyl-CoA in microbial carbon metabolism, from pyruvate and the formation of pyruvate from CO₂ at very moderate reaction conditions without organic catalysts. These results align well with theories for an autotrophic origin of microbial metabolism under hydrothermal vent conditions.

Nontarget Approach to Identify Complexing Agents in Atmospheric Aerosol and Rainwater Samples

Atmospheric particles and droplets contain numerous organic substances, some of which form complexes with metal ions, significantly affecting bulk physicochemical properties and chemical reactivity. However, the detection and identification of complexing agents and their corresponding metal complexes remains an analytical challenge. In this study, we developed an LC/HRMS nontarget screening (NTS) approach which allows the selective detection of complexing agents in aerosol particle extracts and rainwater. To achieve this, a T-junction is installed between the LC outlet and the ion source, and a FeCl₃ solution is added for postcolumn complexation. The resulting mass spectra are screened for the three characteristic iron(III)-complexes [M - H + FeCl₃]^-, [M - 2H + FeCl₂]^-, and [M - 3H + FeCl]^- with mass differences (Δm/z) between the complexing agent and the iron complex of 160.8416, 124.8648, and 89.8959, respectively. Up to 29 di- or tricarboxylic acids were identified as complexing agents in aerosol particle samples from two different sites (Melpitz, Germany, and Wangdu, China) at concentrations as low as 50 nM. Thirteen complexing agents were detected even in measurements without postcolumn iron addition from complexation with background Fe³⁺ traces from the analytical system. At least for the highest concentrated complexing agents, the proposed screening approach can thus be exploited in a NTS approach without any device modification. Besides carboxylic acids, 4-nitrophenol and 4-nitrocatechol were identified as further complexing agents, demonstrating the applicability of the approach to other matrices and to a range of different complexing agents.

Speciomics as a concept involving chemical speciation and omics

The study of chemical speciation and the refinement and expansion of omics-based methods are both consolidated and highly active research fields. Although well established, such fields are extremely dynamic and are driven by the emergence of new strategies and improvements in instrumentation. In the case of omics-based studies, subareas including lipidomics, proteomics, metallomics, metabolomics and foodomics have emerged. Here, speciomics is being proposed as an "umbrella" term, that incorporates all of these subareas, to capture studies where the evaluation of chemical species is carried out using omics approaches. This paper contextualizes both speciomics and the speciome, and reviews omics applications used for species identification through examination of proteins, metalloproteins, metabolites, and nucleic acids. In addition, some implications from such studies and a perspective for future development of this area are provided. SIGNIFICANCE: The synergic effect between chemical speciation and omics is highlighted in this work, demonstrating an emerging area of research with a multitude of possibilities in terms of applications and further developments. This work not only defines and contextualizes speciomics and individual speciomes, but also demonstrates with some examples the great potential of this new interdisciplinary area of research.

Multi-year field evaluation of nicotianamine biofortified bread wheat

Conventional breeding efforts for iron (Fe) and zinc (Zn) biofortification of bread wheat (Triticum aestivum L.) have been hindered by a lack of genetic variation for these traits and a negative correlation between grain Fe and Zn concentrations and yield. We have employed genetic engineering to constitutively express (CE) the rice (Oryza sativa) nicotianamine synthase 2 (OsNAS2) gene and upregulate biosynthesis of two metal chelators - nicotianamine (NA) and 2'-deoxymugineic acid (DMA) - in bread wheat, resulting in increased Fe and Zn concentrations in wholemeal and white flour. Here we describe multi-location confined field trial (CFT) evaluation of a low-copy transgenic CE-OsNAS2 wheat event (CE-1) over 3 years and demonstrate higher concentrations of NA, DMA, Fe, and Zn in CE-1 wholemeal flour, white flour, and white bread and higher Fe bioavailability in CE-1 white flour relative to a null segregant (NS) control. Multi-environment models of agronomic and grain nutrition traits revealed a negative correlation between grain yield and grain Fe, Zn, and total protein concentrations, yet no correlation between grain yield and grain NA and DMA concentrations. White flour Fe bioavailability was positively correlated with white flour NA concentration, suggesting that NA-chelated Fe should be targeted in wheat Fe biofortification efforts.

Speciation of metals in indigenous plants growing in post-mining areas: Dihydroxynicotianamine identified as the most abundant Cu and Zn ligand in Hypericum laricifolium

Ag, As, Cu, Pb and Zn were found to be the principal metallic contaminants of a post-mining area of Peru (Hualgayoc, Cajamarca). Study of metal distribution amongst roots, stems, and leaves of four indigenous hypertolerant plant species, Arenaria digyna, Puya sp., Hypericum laricifolium, Nicotiana thyrsiflora indicated significant translocation of Zn (0.6 < TF ≤ 10.0) and Cu (0.4 < TF ≤ 6.5) into aerial plant organs and substantial water-extractable fraction (20-60%) of these metals, except for A. digyna (root and stems). A study of the metal speciation by ultrahigh-performance size-exclusion (fast-SEC) and hydrophilic ion interaction (HILIC) liquid chromatography with dual ICP (inductively coupled plasma) and electrospray (ESI) Orbitrap MS detection revealed the presence of nicotianamine and deoxymugineic acid copper and zinc complexes in roots, stem and leaves of N. thyrsiflora and Puya sp., and nicotianamine alone in A. digyna. A previously unreported compound, dihydroxy-nicotianamine was identified as the most abundant Cu and Zn ligand in H. laricifolium. The presence of arsenobetaine and an arsenosugar was confirmed by ESI MS. Ag and Pb were hardly translocated to leaves and were found as high molecular species; one of the Pb-containing species co-eluted in fast-SEC-ICP MS with rhamnogalacturonan-II-Pb complex commonly found in in the walls of plants.

Inhibition of Peroxidation Potential and Protein Oxidative Damage by Metal Mangiferin Complexes

Background: Metal coordination complexes of polyphenolic compounds have been claimed to have better antioxidant and protection against protein oxidative damage effects than the isolated ligands. Whereas flavonoids have been extensively studied, xanthones such as mangiferin are lacking extensive research. Methods: Cu (II), Zn (II), and Se (IV) mangiferin complexes were synthesized with different stoichiometric ratios. Products were isolated by preparative chromatography and subjected to spectral analysis by FT-IR, HPLC-DAD, and HPLC-ESI-MS. The inhibition effects on peroxidation potential and protein oxidative damage were determined for all the metal–MF complexes. Results: Eight metal–MF complexes were isolated. Cu (II)–MF complexes did not improve MF antioxidant/protective effects; Zn (II) complexes (stoichiometric ratio 1:2) antioxidant/protective effects had no significant differences to MF; Zn (II)– and Se (IV)–MF complexes (stoichiometric ratio 1:3) showed the best inhibition effects on peroxidation potential (49.06% and 32.08%, respectively), and on the protection against protein oxidative damage (14.49% and 20.81%, respectively). Conclusions: The antioxidant/protective effects of Se (IV)– and Zn (II)–MF coordination complexes were significantly improved as compared to isolated MF, when the reaction between the metal salt and MF was performed with a stoichiometric ratio 1:3.

Synthesis and characterization of zinc derivatized 3, 5-dihydroxy 4', 7-dimethoxyflavone and its anti leishmaniasis activity against Leishmania donovani

This study reports the synthesis and characterization of zinc derivatized 3,5-dihydroxy 4', 7- dimethoxyflavone (DHDM-Zn) compound for the development of new antileishmanial agents. The interaction studies of DHDM with zinc were carried out by UV spectra and fluorescence spectra analysis. Characterization of the complex was further accomplished by multi-spectroscopic techniques such as FTIR, Raman, HRMS, NMR, FESEM-EDX. The morphological and topographical studies of synthesized DHDM-Zn were carried out using FESEM with EDX. Further, it was demonstrated that DHDM-Zn exhibited an excellent in vitro antagonistic effect against the promastigote form of L. donovani. In addition, the possible mechanisms of promastigote L. donovani cell death, by involvement of derivatized compound in arrest of the cell cycle in the G1 phase and residual cell count reduction were investigated. Promastigote growth kinetics performed in the presence of the derivatized compound revealed a slow growth rate. The combination of growth kinetics and cell cycle analysis, made it possible to interpret and classify the cause of leishmanial cell death accurately. These results support that zinc derivatized complex (DHDM-Zn) might work as a lead compound for designing and developing a new antileishmanial drug.

Zinc toxicity in plants: a review

This review highlights the most recent updated information available about Zn phytotoxicity at physiological, biochemical and molecular levels, uptake mechanisms as well as excess Zn homeostasis in plants. Zinc (Zn) is a natural component of soil in terrestrial environments and is a vital element for plant growth, as it performs imperative functions in numerous metabolic pathways. However, potentially noxious levels of Zn in soils can result in various alterations in plants like reduced growth, photosynthetic and respiratory rate, imbalanced mineral nutrition and enhanced generation of reactive oxygen species. Zn enters into soils through various sources, such as weathering of rocks, forest fires, volcanoes, mining and smelting activities, manure, sewage sludge and phosphatic fertilizers. The rising alarm in environmental facet, as well as, the narrow gap between Zn essentiality and toxicity in plants has drawn the attention of the scientific community to its effects on plants and crucial role in agricultural sustainability. Hence, this review focuses on the most recent updates about various physiological and biochemical functions perturbed by high levels of Zn, its mechanisms of uptake and transport as well as molecular aspects of surplus Zn homeostasis in plants. Moreover, this review attempts to understand the mechanisms of Zn toxicity in plants and to present novel perspectives intended to drive future investigations on the topic. The findings will further throw light on various mechanisms adopted by plants to cope with Zn stress which will be of great significance to breeders for enhancing tolerance to Zn contamination.

Recent Approaches for Chemical Speciation and Analysis by Electrospray Ionization (ESI) Mass Spectrometry

In recent years, the chemical speciation of several species has been increasingly monitored and investigated, employing electrospray ionization mass spectrometry (ESI-MS). This soft ionization technique gently desolvates weak metal–ligand complexes, taking them in the high vacuum sectors of mass spectrometric instrumentation. It is, thus, possible to collect information on their structure, energetics, and fragmentation pathways. For this reason, this technique is frequently chosen in a synergistic approach to investigate competitive ligand exchange-adsorption otherwise analyzed by cathodic stripping voltammetry (CLE-ACSV). ESI-MS analyses require a careful experimental design as measurement may face instrumental artifacts such as ESI adduct formation, fragmentation, and sometimes reduction reactions. Furthermore, ESI source differences of ionization efficiencies among the detected species can be misleading. In this mini-review are collected and critically reported the most recent approaches adopted to mitigate or eliminate these limitations and to show the potential of this analytical technique.

Novel rhodamine probe for colorimetric and fluorescent detection of Fe3+ ions in aqueous media with cellular imaging

A novel rhodamine-pyridine conjugated spectroscopic probe RhP was synthesized and its X-ray single crystalline properties were revealed with tabulation. The RhP displayed a distinct pale-pink colorimetric and "turn-on" fluorescent response to Fe³⁺ in aqueous media [H₂O:DMSO (95:5, v/v)] than that of other interfering ions. During the Fe³⁺ recognition, the absorption (UV-Vis) and photoluminescence (PL) spectral studies revealed new peaks at 561 and 592 nm, respectively. The 1:1 stoichiometry and binding sites were verified by Job's plot, ESI-mass, and ¹H NMR titrations. Subsequently, LOD and binding constant for RhP + Fe³⁺ complex were estimated as 102.3 nM and 6.265 × 10⁴ M^-1 from linear fitting and Benesi-Hildebrand plots, correspondingly. Sensor reversibility of RhP + Fe³⁺ by EDTA was demonstrated by UV/PL and TRPL investigations. Moreover, the photoinduced energy transfer mechanism and band gap changes were established from the DFT interrogations. Lastly, cellular imaging studies were carried out to authenticate the real applicability of RhP in Fe³⁺ detection.

Opportunities for plant-derived enhancers for iron, zinc, and calcium bioavailability: A review

Understanding of the mechanism of interactions between dietary elements, their salts, and complexing/binding ligands is vital to manage both deficiency and toxicity associated with essential element bioavailability. Numerous mineral ligands are found in both animal and plant foods and are known to exert bioactivity via element chelation resulting in modulation of antioxidant capacity or micobiome metabolism among other physiological outcomes. However, little is explored in the context of dietary mineral ligands and element bioavailability enhancement, particularly with respect to ligands from plant-derived food sources. This review highlights a novel perspective to consider various plant macro/micronutrients as prospective bioavailability enhancing ligands of three essential elements (Fe, Zn, and Ca). We also delineate the molecular mechanisms of the ligand-binding interactions underlying mineral bioaccessibility at the luminal level. We conclude that despite current understandings of some of the structure-activity relationships associated with strong mineral-ligand binding, the physiological links between ligands as element carriers and uptake at targeted sites throughout the gastrointestinal (GI) tract still require more research. The binding behavior of potential ligands in the human diet should be further elucidated and validated using pharmacokinetic approaches and GI models.

Rapid quantification of ruthenium(ii) polypyridyl anti-cancer drugs using a selective ligand dissociation LC-MS/MS method

Research on Ru anti-cancer drugs is on the rise with many complexes in clinical trials. Inductively coupled plasma-mass spectrometry (ICP-MS) has been the standard technique for bioanalytical studies on Ru and Pt complexes in biological media. Tedious ICP-MS methods rely on detecting and quantifying the element while lacking important structural information of the original complexes. Despite being equally sensitive, more accessible, and highly selective to the target species, liquid chromatography-tandem mass spectrometry (LC-MS/MS) has not been validated for the analysis of Ru drugs. Using USFDA guidelines, we report here the optimization and validation of a facile LC-MS/MS method for the detection and quantification of three Ru(ii) polypyridyl complexes in cells, plasma, and urine matrices. Importantly, a fast (10 min), single-step procedure was efficient for both extraction and sample purification, and analytes were rapidly eluted over a 3 min simple isocratic run. Specific parent ions were differentially fragmented by tandem MS, thus forming a unique and rational ligand dissociation chemistry that exhibits high selectivity to the target species with no measurable interferences or matrix effects. The developed LC-MS/MS method was advantageous vis-à-vis the prototypical ICP-MS based techniques both in vitro and in vivo, paving the way for its utilization in elaborate cellular uptake, pharmacokinetics, and pharmacodynamics studies.

A technique for the speciation analysis of metal-chelator complexes in aqueous matrices using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry

Chelators, capable of creating soluble complexes with metals, may disrupt the natural speciation of metals in environmental matrices. Detection of environmental speciation of such complexes has remained challenging as obtaining the precise inherent nature of metal-chelator complexes is difficult by using routine techniques. Herein, we report a rapid and sensitive technique for the speciation analysis of complexes of five metal ions (Ni, Pb, Co, Fe and Ca) with two aminopolycarboxylate chelator variants, namely, EDTA (ethylenediaminetetraacetic acid) and EDDS (ethylenediamine-N,N'-disuccinic acid), including the simultaneous quantification of those complexes. EDTA is characterized as environmentally persistent among the chelators used in the current work whereas EDDS is biodegradable. The speciation analysis was performed using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UPLC-Q-TOF-MS). The separation was achieved by using hydrophilic interaction liquid chromatographic column. The effect of various operating parameters on analytes such as mobile-phase composition, buffer concentrations and pH, sample diluents, sample injection volume, and column temperature on the peak shape and sensitivity were systematically optimized. The dilution was the only requirement for preparing the samples for analysis. The average relative uncertainty was 2.4% with the average precision (as RSD, n= 7) of 3.5%. For the metal-EDTA complexes, LOD range was 3 to 76 nmol L-1 with satisfactory recovery from a simulated mix matrix (recovery: 79-97%) and river water by standard addition (recovery: 82-94%). For metal-EDDS complexes, LOD range was 66 to 293 nmol L-1 with recovery from a simulated mix matrix (recovery: 56-97%) and river water by standard addition (recovery: 61-91%). The proposed method will be applicable in speciation analysis and simultaneous detection of metal-chelator complexes from environmental samples.

Binding ability of arsenate towards Cu2+ and Zn2+: thermodynamic behavior and simulation under natural water conditions

A study on the sequestering ability between arsenate, AsO43-, and Cu2+ and Zn2+ in aqueous solution is reported. The results of the elaboration of potentiometric data include only species with 1 : 1 metal to ligand ratio for Cu2+-arsenate system, namely CuLH2, CuLH, CuL, and CuLOH (L = AsO43-). For the Zn2+-arsenate system, a speciation model with only two species with both 1 : 1 and 1 : 2 metal to ligand ratios was obtained, namely ML and ML2. Spectrophotometric titrations were also employed in the study of the Cu2+-AsO43- system, and the results of the analysis of experimental data fully confirmed potentiometric ones. The potentiometric titrations were performed under different conditions of temperature (288.15 ≤ T/K ≤ 310.15, at I = 0.15 mol L-1) and ionic strength (0.15 ≤ I/mol L-1 ≤ 1 in NaCl). The dependence of formation constants of the complex species on ionic strength and temperature was also evaluated, as well as the enthalpy and entropy change values were obtained. Laser desorption mass spectrometry (LD MS) and tandem mass spectrometry (MS/MS) were exploited to confirm Cu2+-AsO43- and Zn2+-AsO43- complex formation and to determine both their composition and structural characteristics. Simulation of speciation profiles under natural water conditions was performed. The sequestering ability of arsenate towards Cu2+ and Zn2+ was quantified under different conditions of pH, temperature and ionic strength, typical of several natural waters. Examples of arsenate distribution under seawater and freshwater conditions were reported.

Elucidation of a Copper Binding Site in Proinsulin C-peptide and Its Implications for Metal-Modulated Activity

The connecting peptide (C-peptide) is a hormone with promising health benefits in ameliorating diabetes-related complications, yet mechanisms remain elusive. Emerging studies point to a possible dependence of peptide activity on bioavailable metals, particularly Cu(II) and Zn(II). However, little is known about the chemical nature of the interactions, hindering advances in its therapeutic applications. This work uncovers the Cu(II)-binding site in C-peptide that may be key to understanding its metal-dependent function. A combination of spectroscopic studies reveal that Cu(II) and Zn(II) bind to C-peptide at specific residues in the N-terminal region of the peptide and that Cu(II) is able to displace Zn(II) for C-peptide binding. The data point to a Cu(II)-binding site consisting of 1N3O square-planar coordination that is entropically driven. Furthermore, the entire random coil peptide sequence is needed for specific metal binding as mutations and truncations reshuffle the coordinating residues. These results expand our understanding of how metals influence hormone activity and facilitate the discovery and validation of both new and established paradigms in peptide biology.

Nicotianamine-chelated iron positively affects iron status, intestinal morphology and microbial populations in vivo (Gallus gallus)

Wheat flour iron (Fe) fortification is mandatory in 75 countries worldwide yet many Fe fortificants, such as Fe-ethylenediaminetetraacetate (EDTA), result in unwanted sensory properties and/or gastrointestinal dysfunction and dysbiosis. Nicotianamine (NA) is a natural chelator of Fe, zinc (Zn) and other metals in higher plants and NA-chelated Fe is highly bioavailable in vitro. In graminaceous plants NA serves as the biosynthetic precursor to 2' -deoxymugineic acid (DMA), a related Fe chelator and enhancer of Fe bioavailability, and increased NA/DMA biosynthesis has proved an effective Fe biofortification strategy in several cereal crops. Here we utilized the chicken (Gallus gallus) model to investigate impacts of NA-chelated Fe on Fe status and gastrointestinal health when delivered to chickens through intraamniotic administration (short-term exposure) or over a period of six weeks as part of a biofortified wheat diet containing increased NA, Fe, Zn and DMA (long-term exposure). Striking similarities in host Fe status, intestinal functionality and gut microbiome were observed between the short-term and long-term treatments, suggesting that the effects were largely if not entirely due to consumption of NA-chelated Fe. These results provide strong support for wheat with increased NA-chelated Fe as an effective biofortification strategy and uncover novel impacts of NA-chelated Fe on gastrointestinal health and functionality.

Distinct pathways for zinc metabolism in the terrestrial slug Arion vulgaris

In most organisms, the concentration of free Zn2+ is controlled by metallothioneins (MTs). In contrast, no significant proportions of Zn2+ are bound to MTs in the slug, Arion vulgaris. Instead, this species possesses cytoplasmic low-molecular-weight Zn2+ (LMW Zn) binding compound that divert these metal ions into pathways uncoupled from MT metabolism. Zn2+ is accumulated in the midgut gland calcium cells of Arion vulgaris, where they associate with a low-molecular-weight ligand with an apparent molecular mass of ~ 2,000 Da. Mass spectrometry of the semi-purified LMW Zn binding compound combining an electrospray ion source with a differential mobility analyser coupled to a time-of-flight mass spectrometer revealed the presence of four Zn2+-containing ion signals, which arise from disintegration of one higher MW complex resulting in an ion-mobility diameter of 1.62 nm and a molecular mass of 837 Da. We expect that the novel Zn2+ ion storage pathway may be shared by many other gastropods, and particularly species that possess Cd-selective MT isoforms or variants with only very low affinity to Zn2+.

Investigation of Nicotianamine and 2' Deoxymugineic Acid as Enhancers of Iron Bioavailability in Caco-2 Cells

Nicotianamine (NA) is a low-molecular weight metal chelator in plants with high affinity for ferrous iron (Fe2+) and other divalent metal cations. In graminaceous plant species, NA serves as the biosynthetic precursor to 2' deoxymugineic acid (DMA), a root-secreted mugineic acid family phytosiderophore that chelates ferric iron (Fe3+) in the rhizosphere for subsequent uptake by the plant. Previous studies have flagged NA and/or DMA as enhancers of Fe bioavailability in cereal grain although the extent of this promotion has not been quantified. In this study, we utilized the Caco-2 cell system to compare NA and DMA to two known enhancers of Fe bioavailability-epicatechin (Epi) and ascorbic acid (AsA)-and found that both NA and DMA are stronger enhancers of Fe bioavailability than Epi, and NA is a stronger enhancer of Fe bioavailability than AsA. Furthermore, NA reversed Fe uptake inhibition by Myricetin (Myr) more than Epi, highlighting NA as an important target for biofortification strategies aimed at improving Fe bioavailability in staple plant foods.

Synthesis of Fluorescent 1,7-Dipyridyl-bis-pyrazolo[3,4-b:4',3'-e]pyridines: Design of Reversible Chemosensors for Nanomolar Detection of Cu2

An efficient access toward novel tridentate ligands based on 1,7-dipyridinyl-substituted bis-pyrazolo[3,4-b:4',3'-e]pyridines (BPs) and their usefulness as fluorescent probes for cation detection is reported. The synthesis proceeds by a three-step sequence starting from 2-chloropyridine (1), all reactions were performed using microwave radiation under solvent-free conditions, and an overall yield of up to 63% was obtained. Photophysical properties of three representative 1,7-dipyridinyl-BPs (PBPs, 6a-6c) substituted at position 4 with different donor (D) or acceptor (A) groups were investigated. Compounds exhibited large Stokes shift in different solvents and strong blue light emission in both solution and solid state, and quantum yields were as high as 88% for some of them; thus, a twisted intramolecular charge transfer (TICT) fluorescence mechanism characteristic of the 1,4,7-triaryl-BPs was confirmed. The 4-phenyl-substituted probe (Ph-PBP, 6b) was used successfully in the detection of some metals (Cu²⁺, Co²⁺, Ni²⁺, and Hg²⁺) by fluorescence quenching phenomena, which could be reversed in the presence of ethylenediamine. This probe showed a greater sensitivity toward Cu²⁺ in concentrations as low as 26 nM, and in the process of "on-off-on" for this fluorescent molecular switch, only 1 equiv of the analyte was used.

Determination of multiple chelator complexes in aqueous matrices using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry

The determination of aminopolycarboxylate chelators in environmental samples has remained an analytical challenge due to the structural similarities of these species and their minute concentrations in such matrices. Herein, we report a fast and sensitive technique for the determination of multiple chelator complexes in an aqueous matrix using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UPLC-Q-TOF-MS). Eight chelators, including non-biodegradable (EDTA, EDTAOH, GEDTA, DPTAOH and DTPA) and biodegradable (EDDS, GLDA, and MGDA) variants were examined after complexation with Cu^II. The detection of these species using reverse-phase chromatography was compared with that achieved with hydrophilic interaction chromatography based on the corresponding peak resolution and retention time. The effect of varying the composition and pH of the mobile phase on the corresponding peak profiles and intensities for the chelator complexes was also evaluated. The Cu^II-derivatives of the chelators were individually detected under the optimized operating conditions. Relative to high-performance liquid chromatography equipped with a photodiode array detector, the developed UPLC-Q-TOF-MS technique provides rapid determination of chelator complexes in aqueous matrices with high sensitivity and superior peak resolution. The limit of detection ranged from 1.7-36 nmol L^-1, and the limit of quantification ranged from 5.7-120 nmol L^-1 for the eight chelator complexes in solution. The coefficients of determination (R²) were 0.962-0.999 for the chelators with an average relative uncertainty of 2.2%. The method was validated using a simulated mixed matrix and river water by standard addition (recovery: 83-100%).

DeltaMS: a tool to track isotopologues in GC- and LC-MS data

INTRODUCTION

Stable isotopic labeling experiments are powerful tools to study metabolic pathways, to follow tracers and fluxes in biotic and abiotic transformations and to elucidate molecules involved in metal complexing.

OBJECTIVE

To introduce a software tool for the identification of isotopologues from mass spectrometry data.

METHODS

DeltaMS relies on XCMS peak detection and X¹³CMS isotopologue grouping and then analyses data for specific isotope ratios and the relative error of these ratios. It provides pipelines for recognition of isotope patterns in three experiment types commonly used in isotopic labeling studies: (1) search for isotope signatures with a specific mass shift and intensity ratio in one sample set, (2) analyze two sample sets for a specific mass shift and, optionally, the isotope ratio, whereby one sample set is isotope-labeled, and one is not, (3) analyze isotope-guided perturbation experiments with a setup described in X¹³CMS.

RESULTS

To illustrate the versatility of DeltaMS, we analyze data sets from case-studies that commonly pose challenges in evaluation of natural isotopes or isotopic signatures in labeling experiment. In these examples, the untargeted detection of sulfur, bromine and artificial metal isotopic patterns is enabled by the automated search for specific isotopes or isotope signatures.

CONCLUSION

DeltaMS provides a platform for the identification of (pre-defined) isotopologues in MS data from single samples or comparative metabolomics data sets.