Thyroid-gonadal hormonal interplay in zebrafish exposed to sodium perchlorate: Implications for reproductive health.

Perchlorate, a widespread environmental contaminant originating from various industrial applications, agricultural practices, and natural sources, poses potential risks to ecosystems and human health. While previous studies have highlighted its influence on the thyroid endocrine system and its impact on gonadal maturation, reproduction, and sex hormone synthesis, the specific interplay between thyroid and steroid hormones, in this context, remains largely unexplored. Therefore, this study was undertaken to investigate the adverse effects and underlying mechanisms triggered by exposure to sodium perchlorate (SP) on reproductive endocrine activity in zebrafish. For 21 d, the fish were exposed to test SP concentrations (0, 3, 30, 300 mg/L), which were determined based on the exposure concentrations that induced various toxic effects in the fish, considering naturally occurring concentrations. Exposure to SP, except at 3 mg/L in males, significantly decreased the production of thyroid hormone (TH) in both female and male zebrafish. Moreover, gonadal steroid levels were markedly reduced in both sexes. The expression of hepatic vitellogenin (VTG) mRNA in female zebrafish was significantly decreased, whereas aromatase activity in male zebrafish was significantly elevated in the SP exposure groups. The reduced levels of THs and gonadal steroid hormones were strongly correlated. Abnormal responses to SP exposure led to reduced reproductive success in the 300 mg/L SP exposure group. These findings indicate that prolonged and continuous exposure to a specific concentration of SP may lead to long-term reproductive problems in zebrafish, primarily through hormonal imbalances and suppression of hepatic VTG mRNA expression.

Genipin and pyrogallol: Two natural small molecules targeting the modulation of disordered proteins in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by the aggregation of disordered proteins, such as amyloid beta (Aß) and tau, leading to neurotoxicity and disease progression. Despite numerous efforts, effective inhibitors of Aß and tau aggregates have not been developed. Thus, we aimed to screen natural small molecules from crude extracts that target various pathologies and are prescribed for patients with neurological diseases. In this study, we screened 162 natural small molecules prescribed for neurological diseases and identified genipin and pyrogallol as hit compounds capable of simultaneously regulating the aggregation of Aß and tau K18. Moreover, we confirmed the dual modulatory effects of these compounds on the reduction of amyloid-mediated neurotoxicity in vitro and the disassembly of preformed Aß42 and tau K18 fibrils. Furthermore, we observed the alleviatory effects of genipin and pyrogallol against AD-related pathologies in triple transgenic AD mice. Molecular dynamics and docking simulations revealed the molecular interaction dynamics of genipin and pyrogallol with Aß42 and tau K18, providing insights into their suppression of aggregation. Our findings suggest the therapeutic potential of genipin and pyrogallol as dual modulators for the treatment of AD by inhibiting aggregation or promoting dissociation of Aß and tau.

Self-Aggregating Tau Fragments Recapitulate Pathologic Phenotypes and Neurotoxicity of Alzheimer's Disease in Mice.

In tauopathy conditions, such as Alzheimer's disease (AD), highly soluble and natively unfolded tau polymerizes into an insoluble filament; however, the mechanistic details of this process remain unclear. In the brains of AD patients, only a minor segment of tau forms ß-helix-stacked protofilaments, while its flanking regions form disordered fuzzy coats. Here, it is demonstrated that the tau AD nucleation core (tau-AC) sufficiently induced self-aggregation and recruited full-length tau to filaments. Unexpectedly, phospho-mimetic forms of tau-AC (at Ser324 or Ser356) show markedly reduced oligomerization and seeding propensities. Biophysical analysis reveal that the N-terminus of tau-AC facilitates the fibrillization kinetics as a nucleation motif, which becomes sterically shielded through phosphorylation-induced conformational changes in tau-AC. Tau-AC oligomers are efficiently internalized into cells via endocytosis and induced endogenous tau aggregation. In primary hippocampal neurons, tau-AC impaired axon initial segment plasticity upon chronic depolarization and is mislocalized to the somatodendritic compartments. Furthermore, it is observed significantly impaired memory retrieval in mice intrahippocampally injected with tau-AC fibrils, which corresponds to the neuropathological staining and neuronal loss in the brain. These findings identify tau-AC species as a key neuropathological driver in AD, suggesting novel strategies for therapeutic intervention.

Decoding the Roles of Amyloid-ß (1-42)'s Key Oligomerization Domains toward Designing Epitope-Specific Aggregation Inhibitors.

Fibrillar amyloid aggregates are the pathological hallmarks of multiple neurodegenerative diseases. The amyloid-ß (1-42) protein, in particular, is a major component of senile plaques in the brains of patients with Alzheimer's disease and a primary target for disease treatment. Determining the essential domains of amyloid-ß (1-42) that facilitate its oligomerization is critical for the development of aggregation inhibitors as potential therapeutic agents. In this study, we identified three key hydrophobic sites (17LVF19, 32IGL34, and 41IA42) on amyloid-ß (1-42) and investigated their involvement in the self-assembly process of the protein. Based on these findings, we designed candidate inhibitor peptides of amyloid-ß (1-42) aggregation. Using the designed peptides, we characterized the roles of the three hydrophobic regions during amyloid-ß (1-42) fibrillar aggregation and monitored the consequent effects on its aggregation property and structural conversion. Furthermore, we used an amyloid-ß (1-42) double point mutant (I41N/A42N) to examine the interactions between the two C-terminal end residues with the two hydrophobic regions and their roles in amyloid self-assembly. Our results indicate that interchain interactions in the central hydrophobic region (17LVF19) of amyloid-ß (1-42) are important for fibrillar aggregation, and its interaction with other domains is associated with the accessibility of the central hydrophobic region for initiating the oligomerization process. Our study provides mechanistic insights into the self-assembly of amyloid-ß (1-42) and highlights key structural domains that facilitate this process. Our results can be further applied toward improving the rational design of candidate amyloid-ß (1-42) aggregation inhibitors.

Direct observation of protein structural transitions through entire amyloid aggregation processes in water using 2D-IR spectroscopy.

Amyloid proteins that undergo self-assembly to form insoluble fibrillar aggregates have attracted much attention due to their role in biological and pathological significance in amyloidosis. This study aims to understand the amyloid aggregation dynamics of insulin (INS) in H2O using two-dimensional infrared (2D-IR) spectroscopy. Conventional IR studies have been performed in D2O to avoid spectral congestion despite distinct H-D isotope effects. We observed a slowdown of the INS fibrillation process in D2O compared to that in H2O. The 2D-IR results reveal that different quaternary structures of INS at the onset of the nucleation phase caused the distinct fibrillation pathways of INS in H2O and D2O. A few different biophysical analysis, including solution-phase small-angle X-ray scattering combined with molecular dynamics simulations and other spectroscopic techniques, support our 2D-IR investigation results, providing insight into mechanistic details of distinct structural transition dynamics of INS in water. We found the delayed structural transition in D2O is due to the kinetic isotope effect at an early stage of fibrillation of INS in D2O, i.e., enhanced dimer formation of INS in D2O. Our 2D-IR and biophysical analysis provide insight into mechanistic details of structural transition dynamics of INS in water. This study demonstrates an innovative 2D-IR approach for studying protein dynamics in H2O, which will open the way for observing protein dynamics under biological conditions without IR spectroscopic interference by water vibrations.

Midwavelength Infrared Colloidal Nanowire Laser.

Realizing bright colloidal infrared emitters in the midwavelength infrared (or mid-IR), which can be used for low-power IR light-emitting diodes (LEDs), sensors, and deep-tissue imaging, has been a challenge for the last few decades. Here, we present colloidal tellurium nanowires with strong emission intensity at room temperature and even lasing at 3.6 µm (ω) under cryotemperature. Furthermore, the second-harmonic field at 1.8 µm (2ω) and the third-harmonic field at 1.2 µm (3ω) are successfully generated thanks to the intrinsic property of the tellurium nanowire. These unique optical features have never been reported for colloidal tellurium nanocrystals. With the colloidal midwavelength infrared (MWIR) Te nanowire laser, we demonstrate its potential in biomedical applications. MWIR lasing has been clearly observed from nanowires embedded in a human neuroblastoma cell, which could further realize deep-tissue imaging and thermotherapy in the near future.

Maternal Signatures of Cortisol in First Trimester Small-for-Gestational Age.

The objective of this study was to identify predictable maternal serum signatures of cortisol metabolism during the first trimester of women who are expected to deliver small-for-gestational-age (SGA) neonates. This prospective cohort study included 112 pregnant women (with and without SGA, n = 56 each). Maternal serum samples were collected at 10-14 gestational weeks to quantify the levels of cortisol and its precursors and metabolites by liquid chromatography-mass spectrometry. Increased maternal serum levels of tetrahydrocortisol (11.82 ± 8.16 ng/mL vs. 7.51 ± 2.90 ng/mL, P < 0.005) and decreased 21-deoxycortisol (2.98 ± 1.36 ng/mL vs. 4.33 ± 2.06 ng/mL, P < 0.0001) were observed in pregnant women carrying SGA fetus. In conjunction with individual steroid levels, metabolic ratios corresponding to the activity of related enzymes were calculated. In addition to increased tetrahydrocortisol/cortisol ratio (P < 0.006), the SGA group showed a significant increase in the two metabolic ratios including cortisol/11-deoxycortisol (P < 0.03) and cortisol/21-deoxycortisol (P < 0.0003). The receiver operating characteristic (ROC) curve generated in combination with three variables of 21-deoxycortisol concentration and two metabolic ratios of cortisol/21-deoxycortisol and tetrahydrocortisol/cortisol resulted in an area under the ROC curve = 0.824 (95% confidence interval, 0.713-0.918). A significant decrease in maternal serum levels of 21-deoxycortisol and an increase in two metabolic ratios of cortisol/21-deoxycortisol and tetrahydrocortisol/cortisol, indicating cortisol biosynthetic rate, represent potential biomarkers for the prediction of SGA in the first trimester.

TEMPO-Assisted Free-Radical-Initiated Peptide Sequencing Mass Spectrometry for Ubiquitin Ions: An Insight on the Gas-Phase Conformations.

TEMPO ((2,2,6,6-tetramethylpiperidine-1-yl)oxyl)-assisted free-radical-initiated peptide sequencing mass spectrometry (FRIPS MS) is applied to the top-down tandem mass spectrometry of guanidinated ubiquitin (UB(Gu)) ions, i.e., p-TEMPO-Bn-Sc-guanidinated ubiquitin (UBT(Gu)), to shed a light on gas-phase ubiquitin conformations. Thermal activation of UBT(Gu) ions produced protein backbone fragments of radical character, i.e., a-/x- and c-/z-type fragments. It is in contrast to the collision-induced dissociation (CID) results for UB(Gu), which dominantly showed the specific charge-remote CID fragments of b-/y-type at the C-terminal side of glutamic acid (E) and aspartic acid (D). The transfer of a radical "through space" was mainly observed for the +5 and +6 UBT(Gu) ions. This provides the information about folding/unfolding and structural proximity between the positions of the incipient benzyl radical site and fragmented sites. The analysis of FRIPS MS results for the +5 charge state ubiquitin ions shows that the +5 charge state ubiquitin ions bear a conformational resemblance to the native ubiquitin (X-ray crystallography structure), particularly in the central sequence region, whereas some deviations were observed in the unstable second structure region (ß2) close to the N-terminus. The ion mobility spectrometry results also corroborate the FRIPS MS results in terms of their conformations (or structures). The experimental results obtained in this study clearly demonstrate a potential of the TEMPO-assisted FRIPS MS as one of the methods for the elucidation of the overall gas-phase protein structures.

Kinetic Modulation of Amyloid-ß (1-42) Aggregation and Toxicity by Structure-Based Rational Design.

Several point mutations can modulate protein structure and dynamics, leading to different natures. Especially in the case of amyloidogenic proteins closely related to neurodegenerative diseases, structural changes originating from point mutations can affect fibrillation kinetics. Herein, we rationally designed mutant candidates to inhibit the fibrillation process of amyloid-ß with its point mutants through multistep in silico analyses. Our results showed that the designed mutants induced kinetic self-assembly suppression and reduced the toxicity of the aggregate. A multidisciplinary biophysical approach with small-angle X-ray scattering, ion mobility-mass spectrometry, mass spectrometry, and additional in silico experiments was performed to reveal the structural basis associated with the inhibition of fibril formation. The structure-based design of the mutants with suppressed self-assembly performed in this study could provide a different perspective for modulating amyloid aggregation based on the structural understanding of the intrinsically disordered proteins.

Cisplatin fastens chromatin irreversibly even at a high chloride concentration.

Cisplatin is one of the most potent anti-cancer drugs developed so far. Recent studies highlighted several intriguing roles of histones in cisplatin's anti-cancer effect. Thus, the effect of nucleosome formation should be considered to give a better account of the anti-cancer effect of cisplatin. Here we investigated this important issue via single-molecule measurements. Surprisingly, the reduced activity of cisplatin under [NaCl] = 180 mM, corresponding to the total concentration of cellular ionic species, is still sufficient to impair the integrity of a nucleosome by retaining its condensed structure firmly, even against severe mechanical and chemical disturbances. Our finding suggests that such cisplatin-induced fastening of chromatin can inhibit nucleosome remodelling required for normal biological functions. The in vitro chromatin transcription assay indeed revealed that the transcription activity was effectively suppressed in the presence of cisplatin. Our direct physical measurements on cisplatin-nucleosome adducts suggest that the formation of such adducts be the key to the anti-cancer effect by cisplatin.

Ion Mobility Mass Spectrometry Analysis of Oxygen Affinity-Associated Structural Changes in Hemoglobin.

Hemoglobin (Hb) is a major oxygen-transporting protein with allosteric properties reflected in the structural changes that accompany binding of O2. Glycated hemoglobin (GHb), which is a minor component of human red cell hemolysate, is generated by a nonenzymatic reaction between glucose and hemoglobin. Due to the long lifetime of human erythrocytes (∼120 days), GHb is widely used as a reliable biomarker for monitoring long-term glucose control in diabetic patients. Although the structure of GHb differs from that of Hb, structural changes relating to the oxygen affinity of these proteins remain incompletely understood. In this study, the oxygen-binding kinetics of Hb and GHb are evaluated, and their structural dynamics are investigated using solution small-angle X-ray scattering (SAXS), electrospray ionization mass spectrometry equipped with ion mobility spectrometry (ESI-IM-MS), and molecular dynamic (MD) simulations to understand the impact of structural alteration on their oxygen-binding properties. Our results show that the oxygen-binding kinetics of GHb are diminished relative to those of Hb. ESI-IM-MS reveals structural differences between Hb and GHb, which indicate the preference of GHb for a more compact structure in the gas phase relative to Hb. MD simulations also reveal an enhancement of intramolecular interactions upon glycation of Hb. Therefore, the more rigid structure of GHb makes the conformational changes that facilitate oxygen capture more difficult creating a delay in the oxygen-binding process. Our multiple biophysical approaches provide a better understanding of the allosteric properties of hemoglobin that are reflected in the structural alterations accompanying oxygen binding.

DNA repair and cholesterol-mediated drug efflux induce dose-dependent chemoresistance in nutrient-deprived neuroblastoma cells.

Neuroblastoma is a solid, heterogeneous pediatric tumor. Chemotherapy is widely used to treat neuroblastoma. However, dose-dependent responses and chemoresistance mechanisms of neuroblastoma cells to anticancer drugs remain challenging. Here, we investigated the dose-dependent effects of topotecan on human neuroblastoma cells (SK-N-SH, SH-SY5Y, and SK-N-BE) under various nutrient supply conditions. Serum-starved human neuroblastoma cells showed reduced toxicity. Their survival rate increased upon treatment with a high concentration (1 µM) of topotecan. Quantitative profiling of global and phosphoproteome identified 12,959 proteins and 48,812 phosphosites, respectively, from SK-N-SH cells. Network analysis revealed that topotecan upregulated DNA repair and cholesterol-mediated topotecan efflux, resulting in topotecan resistance. Results of DNA damage assay, cell cycle, and quantitative analyses of membrane cholesterol supported the validity of these resistance factors and their applicability to all neuroblastoma cells. Our results provide a model for high dose-dependent chemoresistance in neuroblastoma cells that could enable a patient-dependent chemotherapy screening strategy.

Effect of packing density of lipid vesicles on the Aß42 fibril polymorphism.

The aggregation of amyloid-ß 1-42 (Aß42) on lipid membranes is closely related to the pathology of Alzheimer's disease (AD). Herein, we demonstrated the effect of the packing density of lipid vesicles on the Aß42 fibrillation kinetics and fibril morphology. We used three distinct phosphatidylcholine (PC) lipids, containing different numbers of cis-double bonds in acyl chains, and therefore, a different packing density in the lipid vesicles. Our results showed that the fibrillation of Aß42 was greatly enhanced and the formed fibrils became shorter as the number of double bonds in lipids increased. Due to the low-density characteristics of dioleoyl phosphatidylcholine (DOPC), Aß42 monomers were able to interact with the hydrophobic acyl chain of lipids exposed to the aqueous phase, thereby inducing rapid fibrillation and short fibril morphologies. Furthermore, the effects of the anionic lipids dioleoyl phosphatidylserine (DOPS) and dioleoyl phosphatidylglycerol (DOPG), and mixed vesicles of DOPC/DOPS and DOPC/DOPG on Aß42 fibrillations were investigated. The tight binding of Aß42 to the lipid head groups via electrostatic interactions was able to suppress the modulation of Aß42 fibrillations compared to accelerated fibrillations on loosely packed membranes. Our proposed mechanism regarding the influence of lipid packing density on Aß42 fibrillations provides an advanced understanding of lipid-associated amyloid fibrillations.

Probing drug delivery and mechanisms of action in 3D spheroid cells by quantitative analysis.

Human tumor cells in a 3-dimensional (3D) spheroid can reflect the characteristics of solid tumors by forming cell-cell interactions and microenvironments. This makes 3D cell culture useful for preclinical stability and drug efficacy tests. In this study, the drug delivery and action mechanisms in SK-N-SH neuroblastoma cells cultured in 3D spheroids were quantitatively compared to those cultured in 2D monolayers using confocal microscopy imaging and inductively coupled plasma-mass spectrometry. In the 3D spheroids, cisplatin only accessed the surface, accumulating in the cells on the spheroid exterior. As a result, an increased cellular amount of cisplatin was required to obtain similar cytotoxicity in the 3D spheroid cells to that in 2D monolayers. The mechanisms of reduction of drug efficacy by dimethyl sulfoxide (DMSO) in the 3D spheroid cells compared to those in the 2D monolayer cells were further investigated. DMSO reduced the drug cytotoxicity by forming stable DMSO-substituted compounds that inhibited the cellular uptake of cisplatin and DNA-Pt adduct formation. The quantitative analysis used in this study is promising for understanding drug delivery and drug action mechanisms in cells in various microenvironments.

ATP Kinetically Modulates Pathogenic Tau Fibrillations.

Advanced understanding of Alzheimer's disease (AD) and several tauopathies over the past decades indicates the pathological importance of tau aggregation in these diseases. Herein, we demonstrated that adenosine triphosphate (ATP), a highly charged anionic molecule found abundantly in the cytosol of cells, catalyzes fibrillation of tau as well as human islet amyloid polypeptide, a representative of basic intrinsically disordered proteins. Our results showed that ATP attracts multiple lysine residues of the four-repeat domain of tau (K18) via supramolecular complexation, thereby forming dimers that are converted to nuclei and accelerate fibril elongation. However, ATP was not directly incorporated into the K18 fibrils, suggesting that ATP plays the role of a catalyst, rather than a reactant, during K18 fibrillation. We also characterized the correlation between ATP dyshomeostasis and tau aggregation in the cellular environment. Our multiple biophysical approaches, including native mass spectrometry (MS), small-angle X-ray scattering (SAXS), and molecular dynamics (MD) simulation, provided insights into the molecular-level influence of ATP on the structural changes and fibrillation of tau.

Selective LC-MRM/SIM-MS based profiling of adrenal steroids reveals metabolic signatures of 17α-hydroxylase deficiency.

Adrenal steroids are generated in the adrenal cortex and metabolized by various enzymes such as hydroxylases, dehydrogenases, and reductases. Determining the comprehensive metabolic signatures of adrenal steroids can provide insight into their metabolic functions and roles in the pathophysiology of adrenal diseases, including Cushing's syndrome (CS) and congenital adrenal hyperplasia (CAH). To this end, we developed an advanced quantitative profiling method of serum adrenal steroids with liquid chromatography-mass spectrometry (LC-MS) under molecular-specific scan modes. Twenty-seven steroids were separated on a 1.9-µm particle C18 column (50 × 2.1 mm) at a flow rate of 250 µL/min and quantified via triple-quadrupole MS with electrospray ionization. During validation, linearities ( r2) were higher than 0.940 with a limit of quantification of 0.1-5.0 ng/mL, and precision (coefficient of variation) and accuracy (%bias) of 3.7-14.3 % and 96.3-113.1 %, respectively. In contrast with the significantly increased serum levels of mineralocorticoids (P <  0.001), the present LC-MS assay revealed remarkably decreased levels of all glucocorticoids and androgens in a patient diagnosed with 17α-hydroxylase deficiency CAH (P <  0.001) compared to those of age- and sex-matched healthy and CS subjects. In the CAH patient, the metabolic ratios for 17α-hydroxylase were significantly decreased, whereas there was no reduction in the metabolic ratio of 17-hydroxyprogesterone to androstenedione, indicating 17,20-lyase activity. In particular, both pregnenolone and dehydroepiandrosterone sulfates, and their metabolic ratio, were identified as potential biomarkers for 17α-hydroxylase deficiency (all P <  0.001), which were also distinct from those of CS patients. The devised LC-MS assay clearly revealed the metabolic signatures of 17α-hydroxylase deficiency, as a rare phenotype of CAH, compared to both healthy and CS subjects, indicating its utility for screening adrenal diseases.

Highly active ruthenium metathesis catalysts enabling ring-opening metathesis polymerization of cyclopentadiene at low temperatures.

Development of versatile ruthenium olefin-metathesis catalysts with high activity, stability, and selectivity is a continuous challenge. Here we report highly controllable ruthenium catalysts using readily accessible and versatile N-vinylsulfonamides as carbene precursors. Catalyst initiation rates were controlled in a straightforward manner, from latent to fast initiating, through the facile modulation of the N-vinylsulfonamide ligands. Trifluoromethanesulfonamide-based catalysts initiated ultrarapidly even at temperatures as low as -60 °C and continuously propagated rapidly, enabling the enthalpically and entropically less-favored ring-opening metathesis polymerizations of low-strained functionalized cyclopentene derivatives, some of which are not accessible with previous olefin-metathesis catalysts. To our surprise, the developed catalysts facilitated the polymerization of cyclopentadiene (CPD), a feedstock that is easily and commonly obtainable through the steam cracking of naphtha, which has, to the best of our knowledge, not been previously achieved due to its low ring strain and facile dimerization even at low temperatures (below 0 °C).

Gas-phase conformations of intrinsically disordered proteins and their complexes with ligands: Kinetically trapped states during transfer from solution to the gas phase.

Flexible structures of intrinsically disordered proteins (IDPs) are crucial for versatile functions in living organisms, which involve interaction with diverse partners. Electrospray ionization ion mobility mass spectrometry (ESI-IM-MS) has been widely applied for structural characterization of apo-state and ligand-associated IDPs via two-dimensional separation in the gas phase. Gas-phase IDP structures have been regarded as kinetically trapped states originated from conformational features in solution. However, an implication of the states remains elusive in the structural characterization of IDPs, because it is unclear what structural property of IDPs is preserved. Recent studies have indicated that the conformational features of IDPs in solution are not fully reproduced in the gas phase. Nevertheless, the molecular interactions captured in the gas phase amplify the structural differences between IDP conformers. Therefore, an IDP conformational change that is not observed in solution is observable in the gas-phase structures obtained by ESI-IM-MS. Herein, we have presented up-to-date researches on the key implications of kinetically trapped states in the gas phase with a brief summary of the structural dynamics of IDPs in ESI-IM-MS.

Recommendations for reporting ion mobility Mass Spectrometry measurements.

Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporting recommendations should help researchers, authors and reviewers to contribute comprehensive reports, so that the ion mobility data can be reused more confidently. Starting from the concept of the definition of the measurand, we emphasize that (i) mobility values (K0 ) depend intrinsically on ion structure, the nature of the bath gas, temperature, and E/N; (ii) ion mobility does not measure molecular surfaces directly, but collision cross section (CCS) values are derived from mobility values using a physical model; (iii) methods relying on calibration are empirical (and thus may provide method-dependent results) only if the gas nature, temperature or E/N cannot match those of the primary method. Our analysis highlights the urgency of a community effort toward establishing primary standards and reference materials for ion mobility, and provides recommendations to do so. © 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc.

Chiral differentiation of d- and l-isoleucine using permethylated ß-cyclodextrin: infrared multiple photon dissociation spectroscopy, ion-mobility mass spectrometry, and DFT calculations.

Chiral differentiation of protonated isoleucine (Ile) using permethylated ß-cyclodextrin (perCD) in the gas-phase was studied using infrared multiple photon dissociation (IRMPD) spectroscopy, ion-mobility, and density functional theory (DFT) calculations. The gaseous protonated non-covalent complexes of perCD and d-Ile or l-Ile produced by electrospray ionization were interrogated by laser pulses in the wavenumber region of 2650 to 3800 cm-1. The IRMPD spectra showed remarkably different IR spectral features for the d-Ile or l-Ile and perCD non-covalent complexes. However, drift-tube ion-mobility experiments provided only a small difference in their collision cross-sections, and thus a limited separation of the d- and l-Ile complexes. DFT calculations revealed that the chiral distinction of the d- and l-complexes by IRMPD spectroscopy resulted from local interactions of the protonated Ile with perCD. Furthermore, the theoretical results showed that the IR absorption spectra of higher energy conformers (by ∼13.7 kcal mol-1) matched best with the experimentally observed IRMPD spectra. These conformers are speculated to be formed from kinetic-trapping of the solution-phase conformers. This study demonstrated that IRMPD spectroscopy provides an excellent platform for differentiating the subtle chiral difference of a small amino acid in a cyclodextrin-complexation environment; however, drift-tube ion-mobility did not have sufficient resolution to distinguish the chiral difference.