Positional Isomers Research Articles

Modulating Electrostatic Properties and Noncovalent Interactions via Structural Isomerism: The Microwave Spectra and Molecular Structures of (E)- and (Z)-1,2,3,3,3-Pentafluoropropene and Their Gas-Phase Heterodimers with the Argon Atom.

Microwave spectra of both the E and Z isomers of 1,2,3,3,3-pentafluoropropene along with all three of the singly substituted 13C isotopologues for each are obtained using broadband chirped-pulse Fourier transform microwave spectroscopy from 2.0-18.1 GHz. Associated quantum chemistry calculations show that the barrier to internal rotation of the CF3 group is significantly higher for the Z isomer, which is stabilized by an intramolecular hydrogen bond, although the barriers in both isomers are sufficiently high to prevent the observation of any effects due to internal rotation. The normal isotopologues of the argon heterodimers for both isomers are also observed in the broadband spectrum and a Balle-Flygare cavity Fourier transform microwave spectrometer is used to obtain the 5.0-20.6 GHz spectra of the corresponding 13C isotopologues. In each case, the argon atom locates so as to maximize its interactions with areas of significant electron density. However, mapped electrostatic potential surfaces indicate that the areas of greatest nucleophilicity are different for the two isomers, suggesting that they may interact differently in forming heterodimers with protic acids.

Versatile photoluminescence behavior of polycyclic hydroxybenzimidazoles driven by intermolecular hydrogen bonding

Herein, the synthesis of polycyclic hydroxybenzimidazole based on 4-hydroxyphthalimide is presented and two isomeric structures are formed. The isomeric structures are capable of forming intermolecular hydrogen-bonded molecular associates. Hydroxybenzimidazole hydrogen-bonded organic frameworks have been shown to be sensitive to different solvent polarity, particularly in proton donor media, resulting in a blue shift in emission. The role of proton donor media has been evaluated using the binary mixture of acetonitrile/water and protonation by trifluoroacetic acid. The results show that by tuning the environment, the aggregation induced emission has appeared in the blue region and larger aggregates are formed compared to the less polar aprotic solvents. Under acidic conditions, the disruption of the hydrogen-bonded dimers was estimated, resulting in deep blue emission. This provides an opportunity to control the molecular associates and tune the optical behavior.

Comprehensive Targeted Profiling of Multiple Steroid Classes in Rodent Plasma Using Liquid Chromatography-Mass Spectrometry

BackgroundReliable quantification of multiple steroid classes in biological fluids within a single method remains an analytical challenge despite many previously published methods. Crosstalk of positional isomers, overlap of stereoisomer fragmentation patterns, differing proton affinities, in-source fragmentation, varying stability of protonated ions in the gas phase across steroid classes, and non-existence of steroid-free matrix are the main challenges limiting the number of simultaneously profiled steroids. ResultsIn this study, we focused on the development of a derivatization-free, achiral, high-throughput, and cost-effective UHPLC-MS/MS approach that allows simultaneous profiling of a spectrum of 38 steroids covering progestogens, androgens, corticosteroids, and estrogens, while properly addressing the hurdles of steroid analysis. Within a 20-minute method, 16 stereoisomers and 15 positional isomers were fully resolved within a single run while separated from 7 additional non-interfering steroids and matrix interferences in rodent plasma. Protein precipitation and supported liquid extraction methods using only 40 μL of sample were developed to achieve the lowest possible limits of quantification. Nevertheless, 5α-dihydroprogesterone and 3α,5α-THDOC could be only qualitatively assessed when using PP. In contrast, DHEA-S could not be quantified or identified when using SLE. A novel surrogate matrix-background subtraction approach, using rat plasma after the animal's adrenalectomy, has been implemented into the optimized PP-UHPLC-MS/MS workflow, successfully validated according to the unified ICH/EMA M10 guidelines, and compared to the traditional quantification strategies. Moreover, the validity of the newly adopted approach has been verified by the targeted profiling of multiple biologically active endogenous steroids in more than 500 samples of mouse plasma in total. SignificanceUnderestimation of hurdles associated with steroid analysis often compromises the accurate steroid quantification. Our comprehensive, fully validated UHPLC-MS/MS method targeting a wide spectrum of endogenous steroids, mitigating steroid crosstalk and using a minimal sample volume together with a novel surrogate matrix-background subtraction approach significantly advances steroid analysis for research and clinical applications covering multiple biological scopes.

Herbidomicins, two pairs of polyketide tautomers produced by an actinomycete of the genus Herbidospora.

Herbidospora is one of the underexplored actinomycete genera from which only a limited number of secondary metabolites are reported. In our continuing investigation on less explored actinomycetes, a liquid culture of Herbidospora sp. RD 11066 was found to contain unknown metabolites that had no match in our in-house UV database. Chromatographic separation and following structural analysis using NMR and MS identified these metabolites to be chromanone and chromene derivatives, which were respectively composed of an inseparable mixture of two isomeric forms. The former polyketides, designated to be herbidomicins A1 (1) and A2 (2), are positional isomers in terms of a methyl substituent on an aromatic ring that mutually interconvert by acetal exchange by two phenolic hydroxy groups. The latter pair, herbidomicins B1 (3) and B2 (4), is Z/E-isomers regarding an enol ether double bond. Herbidomicins 1-4 were weakly antifungal against a dermatophytic fungus Trichophyton rubrum and were moderately cytotoxic against murine leukemia P388 cells.

Rigidity‐Driven Structural Isomers in the NaCl–Ga2S3 System: Implications for Energy Storage

Alternative energy sources require the search for innovative materials with promising functionalities. Systems with unusual chemical properties represent an insufficiently explored domain, concealing unexpected features. Using diffraction and Raman spectroscopy over a wide temperature range, supported by first‐principles simulations, a rare phenomenon is unveiled: phase‐dependent chemical interactions between binary components in the NaCl–Ga2S3 system. In this unique occurrence, previously intact binary crystalline species transform upon melting into mixed liquid structural isomers, forming bonds with new partners. The chemical combinatorics appears to be fully reversible for stable crystals and liquids. Despite this, rapidly frozen glasses out of thermodynamic equilibrium remain in a metastable isomeric state, offering remarkable properties, particularly a high room‐temperature Na+ conductivity, comparable to the best sodium halide superionic conductors and therefore encouraging for sodium solid‐state batteries and energy applications. A rigidity paradigm is responsible for the observed phenomenon, as the extremely constrained Ga2S3 crystal lattice does not survive viscous flow, breaking up at a short‐range level. The removal of rigidity constraints and dense packing leads to a significant increase in empty space, which is the origin of high sodium diffusivity. Broadly, the rigidity‐driven structural isomerism opens up an inspiring path to the discovery of atypical materials.

Development of LC-FAIMS-MS and its application to lipidomics study of Acinetobacter baumannii infection

The recent advances in mass spectrometry (MS) technologies have enabled comprehensive lipid profiling in biological samples. However, the robustness and efficiency of MS-based lipidomics is compromised by the complexity of biological samples. High-field asymmetric waveform ion mobility spectrometry (FAIMS) is a technology that can continuously transmit one type of ion, independent of the mass-to-charge ratio. Here we present the development and application of LC-FAIMS-MS/MS-based platform for untargeted lipidomics. We used 3 optimally balanced compensation voltages, i.e., 29 V, 34 V and 39 V, to analyze all subclasses of glycerophospholipids. The reproducibility of the method was evaluated using reference standards. The reproducibility of retention times ranged from 0.9% to 1.5% RSD; whereas RSD values of 5%–10% were observed for peak areas. More importantly, the coupling of a FAIMS device can significantly improve the robustness and efficiency. We exploited this NPLC-FAIMS-HRMS to analyze the serum lipid profiles in mice infected intranasally with Acinetobacter baumannii. The temporal profiles of serum lipids after A. baumannii inoculation were obtained for 4 h, 8 h, and 24 h. We found that nearly all ether PC and ether PE lipids were significantly decreased 8 h after inoculation. The resultant volcano plot illustrated the distribution of 28 increased and 28 decreased lipid species in mouse sera 24 h after inoculation. We also found that a single ether PE composition can comprise multiple isomeric structures, and the relative abundance of each isomer could be quantified using the newly developed NPLC-FAIMS-PRM method.

Positional Isomerism of Aromatic Heterocyclic Spacer Cations in Two-Dimensional Dion-Jacobson Hybrid Perovskites.

Ligand engineering of aromatic heterocyclic cations in two-dimensional (2D) Dion-Jacobson (DJ) perovskites has been widely explored in recent years. In this study, how the positional isomers of aromatic heterocyclic cations tune the lattice of 2D perovskites, thereby influencing the transport and recombination dynamics of charge carriers, has been investigated through nonadiabatic molecular dynamics simulations. We demonstrate that the meta-substituted 3-(aminomethyl)pyridinium (3AMPY) cations greatly reduce the strength of electron-vibration coupling since the strong hydrogen-bonding network introduced by the changes in the arrangement of spacer cations significantly suppresses the structural thermal fluctuations. Compared to the para-substituted 4-(aminomethyl)pyridinium (4AMPY) cation, using the asymmetric 3AMPY as a spacer cation can achieve improved in-plane transport performance, enhanced thermal stability, and suppressed charge carrier recombination through weakening electron-vibration interactions. Our results explain the observed lifetime difference between the two types of DJ-phase perovskites in experiments and provide new guidance for optimizing the performance of perovskite devices.

Facilitating Charge Separation of Donor–Acceptor Conjugated Microporous Polymers via Position Isomerism Strategy for Efficient CO2 Photoconversion

Photoreduction of CO2 into the chemical feedstocks of fuels provides a green way to help solve both the energy crisis and carbon emission issues. Nevertheless, undesirable charge separation and migration, as well as rapid reverse charge recombination results in the unsatisfactory photocatalytic activity of most conjugated microporous polymers (CMPs). Herein, a pair of donor–acceptor (D-A) CMPs for CO2 photoconversion was developed through position isomerism by altering linkage sites. The results show that Py-D27F with 2,7-site linkage exhibits a completely conjugated structure and a large molecular dipole moment, thus significantly accelerating charge separation and transfer. As a result, Py-D27F achieves a higher yield of 320.9 μmol g−1 h−1 for CO2-to-CO photoreduction (without the addition of any photosensitizers and precious metals), which is about three-fold greater than that of Py-D36F (3,6-site linkage). This study provides a valuable idea for exploring outstanding CMP photocatalysts for the efficient processing of photocatalysis.

Cuneanes as Potential Benzene Bioisosteres Having Chirality

AbstractCuneane, a structural isomer of cubane, possesses C 2v symmetry, unlike the Oh symmetry of cubane. It can exhibit chirality with only a single substituent, differentiating it from cubane. Consequently, cuneane is being explored as a potential benzene bioisostere in pharmaceutical molecules, adding complexity such as chirality through isomerization of the cubane skeleton. Although there has been limited research on the synthesis of cuneane, recent years have seen increased attention devoted to this cage hydrocarbon. In this short review, we will discuss recent advances in the synthesis, utilization, and transformations of the cuneane framework into other cage hydrocarbons.1 Introduction: Absolute Configuration Notation2 Preparation of 1,3- and 2,6-Disubstituted Cuneanes by Constitutional Isomerization of 1,4-Disubstituted Cubanes3 Preparation of 1,2-Disubstituted Cuneanes from 1-Cuneanecarboxamide via Directed ortho-Metalation4 Investigation of the Potential as a Benzene Bioisostere5 Asymmetric Synthesis of Cuneanes6 Cuneane Scaffold Editing7 Conclusion

The Chemistry and Biological Effects of Fused 1,2,4-triazolo[4,3-c]pyrimidines and their Isomeric 1,2,4-triazolo[1,5-c]pyrimidines

Concerning polycyclic heterocyclic compounds, fused triazolopyrimidines and their substituted analogs have been studied recently from a chemical and biological point of view. Triazolopyrimidines have eight different positional isomers based on their structural arrangement and nitrogen atom positions. The present review concerns synthesizing 1,2,4- triazolo[4,3-c]pyrimidines and 1,2,4-triazolo[1,5-c]pyrimidines fused with a fivemembered ring containing one heteroatom. The 1,2,4-triazolo[4,3-c]pyrimidines can be prepared by closing the triazole ring on the 4-hydrazinopyrimidine ring, and the 1,2,4- triazolo[1,5-c]pyrimidines can be prepared by closing the triazole ring on the 4- iminopyrimidine-3-amine ring. The transformation of 1,2,4-triazolo[4,3-c]pyrimidine to the more thermodynamically stable isomer triazolo[1,5-c]pyrimidine derivatives via Dimroth rearrangement under different reaction conditions is also discussed. Moreover, the biological activity of both series is presented.

Schleyer hyperconjugative aromaticity in indene scaffolds

In the present research, the Schleyer hyperconjugative aromaticity was used to enhance the aromaticity of indene scaffolds. The first section of the research focused on examining the thermodynamic stability and electronic characteristics of the four structural isomers of indene. Results indicate that 1H-indene scaffolds are the most stable thermodynamic isomers of indene derivatives exceeding 100 kJ/mol. The hierarchy of stability is as follows: 1H-indenes > 2H-indenes > 5H-indenes > 4H-indenes. The aromaticity of 5- and 6-membered rings in the isomeric structures was investigated using the B3LYP/6–311 + G(d,p) method in the second section of the study. The hyperconjugative aromaticity of 5MR and 6MR was assessed using the harmonic oscillator model of aromaticity index, Bird index, Shannon index, aromatic fluctuation index, and the nucleus independent chemical shift. The results reveal that introducing electron-donating groups on 6MR enhances the aromaticity of 5MR. Moreover, adding two fluorine atoms on the Csp3 site negatively affects the aromaticity and induces antiaromaticity in the indene scaffold. Based on aromaticity data, the order of increasing aromaticity in the presence of different groups is F < CH3 < H < SiH3 < GeH3 < Si(CH3)3 < Ge(CH3)3. The extent of the Schleyer hyperconjugation interaction was also quantified using the E(2) parameter obtained from the NBO calculations.

Structural Isomerism in Bimetallic Ag20Cu12 Nanoclusters.

Structural isomers of atomically precise metal nanoclusters are highly sought after for investigating structure-property relationships in nanostructured materials. However, they are extremely rare, particularly those of alloys, primarily due to the challenges in their synthesis and structural characterization. Herein, for the first time, a pair of bimetallic isomeric AgCu nanoclusters has been controllably synthesized and structurally characterized. These two isomers share an identical molecular formula, Ag20Cu12(C≡CR)24 (denoted as Ag20Cu12-1 and Ag20Cu12-2; HC≡CR is 3,5-bis(trifluoromethyl)phenylacetylene). Single-crystal X-ray diffraction data analysis revealed that Ag20Cu12-1 possesses an Ag17Cu4 core composed of two interpenetrating hollow Ag11Cu2 structures. This core is stabilized by four different types of surface motifs: eight -C≡CR, one Cu(C≡CR)2, one Ag3Cu3(C≡CR)6, and two Cu2(C≡CR)4 units. Ag20Cu12-2 features a bitetrahedron Ag14 core, which is stabilized by three Ag2Cu4(C≡CR)8 units. Interestingly, Ag20Cu12-2 undergoes spontaneous transformation to Ag20Cu12-1 in the solution-state. Density functional theory calculations explain the electronic and optical properties and confirm the higher relative stability of Ag20Cu12-1 compared to Ag20Cu12-2. The controlled synthesis and structural isomerism of alloy nanoclusters presented in this work will stimulate and broaden research on nanoscale isomerism.

Preparation of alkyl microporous organic network-based capillary column for an efficient gas chromatographic separation of position isomers.

The large surface area, excellent thermal stability and easy modification make microporous organic networks (MONs) good candidates in the field of gas chromatography (GC). Due to the limited species and highly conjugated networks of MONs, their applications are still in infancy and restricted. To accelerate their developments and to enrich their types in GC, here we report the first example of synthesizing alkyl MON and its capillary column for GC separation of position isomers. Linear 1,8-dibromooctane is used as the alkyl monomer instead of traditional aromatic ones to construct novel alkyl MON to decrease the inherent conjugated characteristic of MONs. The alkyl MON exhibits good thermal stability (up to 350°C), large surface area (1173m2g-1), and non-polar character, allowing good resolution for alkanes, alkyl benzenes, alcohols, ketones, and diverse position isomers, including dichlorobenzene, trichlorobenzene, bromotoluene, nitrotoluene, methylbenzaldehyde, and ionone with the limits of detection (0.003mgmL-1) and limits of quantitation of (0.10mgmL-1). The in situ growth-prepared alkyl MON column demonstrates remarkable duration time and precisions for the retention relative standard deviations, (RSDs%, intra-day, n=7), 0.06%-0.53% (intra-day, n=7), and 2.87%-10.59% (column-to-column, n=3). In addition, the fabricated alkyl MON-coated capillary column offers better resolution than three commercial GC columns for the resolution of methylbenzaldehyde, bromotoluene, and chlorotoluene isomers. This work reveals the practicability for synthesizing alkyl MONs and demonstrates their prospects for position isomers separation.

Identification of bile acids in snake bile by hydrogen/deuterium exchange mass spectrometry and quantitative structure-retention relationship analysis

Natural bile acids, a class of steroids with a valeric acid side chain at the C-17 position, present significant challenges in separation and analysis due to structural similarities, isomerism, and large polarity differences. Therefore, advanced analytical methods are essential for the accurate identification and quantification of bile acids. This study conducted a comprehensive qualitative analysis of bile acids by integrating liquid chromatography-tandem mass spectrometry (LC-MS/MS), hydrogen-deuterium exchange tandem mass spectrometry (HDX-MS/MS), and quantitative structure-retention relationship (QSRR) methods. Firstly, LC-MS/MS conditions were optimized to enhance chromatographic separation and improve the reliability of characteristic fragment ions. MS/MS fragmentation rules for bile acids were derived from the mass spectral data of bile acid standards and validated through HDX-MS/MS experiments. Secondly, potential bile acids in snake bile were identified based on these validated fragmentation rules, and a QSRR model was established to predict the retention times of the proposed structures. Thirdly, HDX-MS/MS was applied to assist in identifying bile acid isomers. Finally, a total of 150 bile acids, including 11 free bile acids (free BA), 5 glyco-bile acids (GBA) and 134 tauro-bile acids (TBA), were detected in snake bile. Thirteen bile acids were accurately characterized by comparing their retention time and MS/MS spectra with standards. Forty-nine bile acids were reasonably annotated using the QSRR model and HDX-MS/MS. This study is notable for being the first to utilize the QSRR and HDX-MS/MS techniques for the annotation of bile acids in snake bile, providing a robust framework for the structural elucidation of these compounds.

Anti-inflammation Mechanisms of Flavones Are Highly Sensitive to the Position Isomers of Flavonoids: Acacetin vs Biochanin A.

Acacetin (ACA) and biochanin A (BCA) are isomeric monomethoxyflavones with different structural positions of the 4'-methoxy-phenyl group. Both of them are present in many commonly consumed foods, such as citrus fruits and vegetables, and have been discovered with anti-inflammatory activities, but their mechanisms of action are not clearly elucidated at the molecular level. Herein, we reported the structure-activity relationship of ACA and BCA regarding their potency in inhibiting nitric oxide (NO) production, proinflammatory enzyme expression, and mRNA expression of proinflammatory cytokines in the lipopolysaccharide (LPS)-induced RAW 264.7 cells. Furthermore, transcriptome analysis was conducted to map out the overall pathways impacted by these two isomers. Our results showed that ACA possessed higher suppressive activity in nitric oxide (NO) production (IC50 = 23.93 ± 1.74 μM for ACA and IC50 = 71.41 ± 8.07 μM for BCA), inducible nitric oxide synthase (iNOS) expression, and proinflammatory interleukin (IL)-1β mRNA expression, but lower inhibitory activity in IL-6 mRNA expression as compared with BCA. Although two compounds were revealed to bind to c-Src protein according to drug affinity responsive target stability (DARTS) and western blotting results, molecular docking and molecular dynamics (MD) simulation showed that they had different binding sites, which subsequently resulted in different signaling transduction. ACA primarily exerted anti-inflammatory activity through the mitogen-activated protein kinase (MAPK) signaling pathway, the tumor necrosis factor (TNF) signaling pathway, and the hypoxia-inducible factor (HIF)-1 signaling pathway, while BCA was particularly involved in the Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway, the nuclear factor kappa B (NF-κB) signaling pathway, the TNF signaling pathway, and the toll-like receptor (TLR) signaling pathway. Moreover, two isomers remained stable in the cell culture medium and did not encounter the biotransformation process in RAW 264.7 cells. However, BCA exhibited insufficient cellular uptake ability and transport efficiency in macrophages compared to ACA. Taken together, ACA is more promising for controlling inflammation and worthy of further study for human use.

Rational Molecular Design of Phenanthroimidazole-Based Fluorescent Materials toward High-Efficiency Deep-Blue OLEDs by Molecular Isomer Engineering.

Organic light-emitting diodes (OLEDs) have been extensively investigated in full-color displays and energy-saving lighting owing to their unique advantages. However, deep-blue OLEDs based on nondoped emitting layers with a satisfactory external quantum efficiency (EQE) are still rare for applications. In this work, six hot exciton materials, PPIM-12F, PPIM-22F, PPIM-13F, PPIM-23F, PPIM-1CN, and PPIM-2CN, are designed and synthesized via an isomer engineering design strategy and their photophysical properties and OLED performance are systematically investigated. These emitters all possess wide band gaps (3.53-3.69 eV), hybrid local and charge transfer (HLCT) characteristics, and good thermal stabilities. The C2 series compounds, PPIM-22F, PPIM-23F, and PPIM-2CN, all show redder emission peaks than the N1 series counterparts of PPIM-12F, PPIM-13F, and PPIM-1CN. In addition, the LUMO energy levels decrease consecutively in the sequence of PPIM-22F < PPIM-23F < PPIM-2CN and are all lower than their respective N1 series position isomers of PPIM-12F, PPIM-13F, and PPIM-1CN. The CV measurements indicate that such a design strategy renders the fine-tuning of LUMO energy levels, and the incorporation of electron acceptors at the extended C2 position of the PI unit is a better choice to improve the electron injection ability. Theoretical simulations indicate that they may harvest the triplet exciton through an upper-level reverse intersystem crossing process, which decreases the gathering of triplet excitons and allows the OLEDs to be fabricated by nondoping technology. Among them, PPIM-22F with a difluorobenzene substituent at the C2 position manifests the best performance in OLEDs, which exhibits the maximum EQE of 7.87% and Commission Internationale de ĺEclairage (CIE) coordinates of (0.16, 0.10). This work demonstrates an effective strategy for considerable improvement in device performance by a subtle change in the molecular structure through isomer engineering.

Separation and identification of oligonucleotides impurities and degradation products by reversed phase ultra-high performance liquid chromatography using phenyl-bonded stationary phases without ion pairs - A step towards sustainability

This manuscript discusses the development of a reversed-phase ultra high-performance liquid chromatography (RP UHPLC) method based on phenyl-bonded stationary phases without ion-pairs for the separation and identification of oligonucleotides. The elimination of ion-pair reagents makes the proposed protocol as more compliant to the principles of green chemistry, compared to the traditional ion-pair reversed-phase liquid chromatography methods (IP RP LC). In detail, three phenyl-based stationary phases were tested, namely a C18/AR (a C18 stationary phase with the addition of aromatic groups), a Phenyl-hexyl, and a Diphenyl. Generally, the retention of oligonucleotides increases with the increase of salt concentration and the decrease of the pH, thus confirming the significant impact of van der Waals interactions, salting-out effect, and π-electrons interactions in the retention mechanism. The highest retention and best peak symmetry were observed for the C18/AR stationary phase, while the lowest retention for the Phenyl-hexyl, with retention influenced by the type of salt in the mobile phase. The obtained methods using C18/AR stationary phases allow for the effective separations of positional isomers and for identifying impurities and degradation products using RP UHPLC Q-TOF-MS in a comparatively short time. The application of RP UHPLC Q-TOF-MS provides reasonable selectivity for the resolution of 33 impurities and two degradation products. Both groups of compounds are mainly 3′N and 5′N-shortmers, but in the case of impurities, modifications of cyclic phosphate and phosphate groups were also identified. Nevertheless, Diphenyl and Phenyl-Hexyl may be applied to separate modified oligonucleotides with higher salt concentrations. The proposed separation methods without ion-pair reagents contribute to a more sustainable approach in oligonucleotide analysis.

Mass Spectrometry Imaging for the Characterization of C═C Localization in Unsaturated Lipid Isomers at the Single-Cell Level.

Unsaturated lipids with carbon-carbon double bonds (C═C) have been implicated in the pathogenesis of various diseases. While mass spectrometry imaging (MSI) has been employed to map the distribution of lipid isomers in tissue sections, the identification of lipid C═C positional isomers at the single-cell level using MSI poses a significant challenge. In this study, we developed a novel approach utilizing ToF-SIMS in conjunction with the Paternò-Büchi (P-B) photochemical reaction to characterize the C═C localization in unsaturated lipid isomers at the single-cell level. The P-B reaction was employed to produce adduct products, which were subsequently subjected to collision-induced dissociation by the primary ion beam of ToF-SIMS to generate characteristic ion pairs indicative of the presence of C═C bonds. Utilizing this approach, lipid isomers in brain and skeletal tissues from mice, as well as different cell lines, were visualized at single-cell resolution. Furthermore, distinct variations in the composition of FA 18:1 isomers across different microregions and cell types were revealed. Our P-B ToF-SIMS approach enables the accurate identification and characterization of complex lipid structures with remarkable spatial resolution and can be helpful in understanding the physiological role of these C═C positional isomers.

Supercritical fluid chromatography- Nanospray ionization-mass spectrometry (SFC-nSI-MS)

A nanospray emitter coupled to a supercritical fluid chromatograph (SFC-nSI-MS) for mass spectrometric (MS) analysis of fatty acids (FA) positional isomers is introduced. The experimental setup uses conventional bore columns before the SF back-pressure regulator (pre-BPR). The flow is then split and nanosprayed using a short emitter post-BPR. A C18 column was used to resolve positional isomers of unsaturated FA with a 5 min gradient. Chromatographic resolution of the nSFC was compared to a LC-MS system with superior resolving power demonstrated in the nSFC MS system. This system has proven quantitative performance for analyzing pharmaceutical effects on FA composition in a complex biological matrix like E coli lysate.

Development, validation, and clinical assessment of a liquid chromatography-tandem mass spectrometry serum assay for per- and polyfluoroalkyl substances (PFAS) recommended by the National Academies of Science, Engineering, and Medicine (NASEM).

Per- and polyfluoroalkyl substances (PFAS) are widely used in industry, residential, and consumer products. Studies have shown associations between high PFAS exposure and adverse health effects. In 2022, the National Academies of Science, Engineering, and Medicine (NASEM) published Guidance on PFAS Exposure, Testing, and Clinical Follow-up providing laboratory and clinical direction. The Guidance suggests nine PFAS should be measured in serum or plasma specimens and summed to provide a total PFAS concentration using a NASEM-recommended method. Follow-up clinical recommendations are based on the calculated PFAS NASEM summation. We developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in accordance with NASEM recommendations but distinguished by the ability to separate closely related structural isomers. As part of our validation, PFAS prevalence was evaluated in a population survey comprised of clinical donor and remnant specimens (n = 1023 in total). In this study, 82.2% of the specimens had PFAS NASEM summations of 2 to < 20ng/mL and 2.5% had a summation ≥ 20ng/mL. The median PFAS NASEM summation was 4.65ng/mL in this study, lower than the 7.74ng/mL median observed in the 2017-2020 Centers for Disease Control and Prevention, National Health and Nutrition Examination Survey (n = 3072). This lower median PFAS NASEM summation may reflect a decline in PFAS population levels over time or sample population exposure differences.