Chiral mass spectrometry: An overview

Online-Monitoring of the Enantiomeric Ratio in Microfluidic Chip Reactors Using Chiral Selector Ion Vibrational Spectroscopy

A novel experimental approach for the rapid online monitoring of the enantiomeric ratio of chiral analytes in solution is presented. The charged analyte is transferred to the gas phase by electrospray. Diastereomeric complexes are formed with a volatile chiral selector in a buffer-gas-filled ion guide held at room temperature, mass-selected, and subsequently spectrally differentiated by cryogenic ion trap vibrational spectroscopy. Based on the spectra of the pure complexes in a small diastereomer-specific spectral range, the composition of diastereomeric mixtures is characterized using the cosine similarity score, from which the enantiomeric ratio in the solution is determined. The method is demonstrated for acidified alanine solutions and using three different chiral selectors (2-butanol, 1-phenylethanol, 1-amino-2-propanol). Among these, 2-butanol is the best choice as a selector for protonated alanine, also because the formation ratio of the corresponding diastereomeric complexes is found to be independent of the nature of the enantiomer. Subsequently, a microfluidic chip is implemented to mix enantiomerically pure alanine solutions continuously and determine the enantiomeric ratio online with minimal sample consumption within one minute and with competitive accuracy.

Facile fabrication of Ti4+-immobilized magnetic nanoparticles by phase-transitioned lysozyme nanofilms for enrichment of phosphopeptides

In this study, titanium (IV)-immobilized magnetic nanoparticles (Ti4+-PTL-MNPs) were firstly synthesized via a one-step aqueous self-assembly of lysozyme nanofilms for efficient phosphopeptide enrichment. Under physiological conditions, lysozymes readily self-organized into phase-transitioned lysozyme (PTL) nanofilms on Fe3O4@SiO2 and Fe3O4@C MNP surfaces with abundant functional groups, including -NH2, -COOH, -OH, and -SH, which can be used as multiple linkers to efficiently chelate Ti4+. The obtained Ti4+-PTL-MNPs possessed high sensitivity of 0.01 fmol μL-1 and remarkable selectivity even at a mass ratio of β-casein to BSA as low as 1:400 for phosphopeptide enrichment. Furthermore, the synthesized Ti4+-PTL-MNPs can also selectively identify low-abundance phosphopeptides from extremely complicated human serum samples and their rapid separation, good reproducibility, and excellent recovery were also proven. This one-step self-assembly of PTL nanofilms facilitated the facile and efficient surface functionalization of various nanoparticles for proteomes/peptidomes.

Comprehensive workflow encompassing discovery, verification, and quantification of indicator peptide in snail mucin using LC-quadrupole Orbitrap high-resolution tandem mass spectrometry

Peptidomics analysis was conducted using high-resolution tandem mass spectrometry (MS2) to determine the peptide profile of snail-derived mucin extract (SM). The study was also aimed to identify an indicator peptide and validate a quantification method for this peptide. The peptide profiling and identification were conducted using discovery-based peptidomics analysis employing data-dependent acquisition, whereas the selected peptides were verified and quantified using parallel reaction monitoring acquisition. Among the 16 identified peptides, the selected octapeptide (TEAPLNPK) was quantified via precursor ion ionization (m/z 435.2400), followed by quantification of the corresponding quantifier ion fragment (m/z 639.3824) using MS2. The quantification method was optimized and validated in terms of specificity, linearity, accuracy, precision, and limit of detection/quantification. The validated method accurately quantified the TEAPLNPK content in the SM as 7.5 ± 0.2 μg/g. Our study not only identifies an indicator peptide from SM but also introduces a novel validation method, involving precursor ion ionization and quantification of specific fragments. Our findings may serve as a comprehensive workflow for the monitoring, selection, and quantification of indicator peptides from diverse food resources.

Differentiating enantiomers by directional rotation of ions in a mass spectrometer

Conventional mass spectrometry does not distinguish between enantiomers, or mirror-image isomers. Here we report a technique to break the chiral symmetry and to differentiate enantiomers by inducing directional rotation of chiral gas-phase ions. Dual alternating current excitations were applied to manipulate the motions of trapped ions, including the rotation around the center of mass and macro movement around the center of the trap. Differences in collision cross section were induced, which could be measured by ion cloud profiling at high resolutions above 10,000. High-field ion mobility and tandem mass spectrometry analyses of the enantiomers were combined and implemented by using a miniature ion trap mass spectrometer. The effectiveness of the developed method was demonstrated with a variety of organic compounds including amino acids, sugars, and several drug molecules, as well as a proof-of-principle ligand optimization study for asymmetric hydrogenation.

Simultaneous quantitative chiral analysis of four isomers by ultraviolet photodissociation mass spectrometry and artificial neural network

Although mass spectrometry (MS) has its unique advantages in speed, specificity and sensitivity, its application in quantitative chiral analysis aimed to determine the proportions of multiple chiral isomers is still a challenge. Herein, we present an artificial neural network (ANN) based approach for quantitatively analyzing multiple chiral isomers from their ultraviolet photodissociation mass spectra. Tripeptide of GYG and iodo-L-tyrosine have been applied as chiral references to fulfill the relative quantitative analysis of four chiral isomers of two dipeptides of L/DHisL/DAla and L/DAspL/DPhe, respectively. The results show that the network can be well-trained with limited sets, and have a good performance in testing sets. This study shows the potential of the new method in rapid quantitative chiral analysis aimed at practical applications, with much room for improvement in the near future, including selecting better chiral references and improving machine learning methods.

Drug Adulteration Analysis Based on complexation with CD and Metal Ions Using Ion Mobility Spectrometry

Drug adulteration and contamination are serious threats to human health therefore, their accurate monitoring is very important. Allopurinol (Alp) and theophylline (Thp) are commonly used drugs for the treatment of gout and bronchitis, while their isomers hypoxanthine (Hyt) and theobromine (Thm) have no effect and affect the efficacy of the drug. In this work, the drug isomers of Alp/Hyt and Thp/Thm are simply mixed with α-, β-, γ-cyclodextrin (CD) and metal ions and separated using trapped ion mobility spectrometry-mass spectrometry (TIMS-MS). TIMS-MS results showed that Alp/Hyt and Thp/Thm isomers could interact with CD and metal ions and form corresponding binary or ternary complexes to achieve their TIMS separation. Different metal ions and CDs showed different separation effect for the isomers, among which Alp and Hyt could be successfully distinguished from the complexes of [Alp/Hyt+γ-CD + Cu-H]⁺ with separation resolution (R _P-P) of 1.51; whereas Thp and Thm could be baseline separated by [Thp/Thm+γ-CD + Ca-H]⁺ with R _P-P of 1.96. Besides, chemical calculations revealed that the complexes were in the inclusion forms, and microscopic interactions were somewhat different, making their mobility separation. Moreover, relative and absolute quantification was investigated with an internal standard to determine the precise isomers content, and good linearity (R ² > 0.99) was obtained. Finally, the method was applied for the adulteration detection where different drugs and urine were analyzed. In addition, due to the advantages of fast speed, simple operation, high sensitivity, and no chromatographic separation required, the proposed method provides an effective strategy for the drug adulteration detection of isomers.

Simulation study of inverse diffusion counterbalance method for super-resolution ion mobility spectrometry

Ion mobility spectrometer (IMS) is a powerful chemical composition analysis tool working at atmospheric pressure that can be used to separate complex samples and study molecular structures. Resolution is a key parameter for evaluating the performance of IMS. However, for the pulsed sampling technique used by drift tube IMS, there is an upper limit to the resolution due to the diffusion between ions and the drift gas. In this work, an inverse diffusion counterbalance method is proposed to break the resolution limit. The method is inspired by the stimulated emission depletion (STED). In optical microscopy systems, STED is used to break the optical diffraction limit by a ring of depleted light to counteract diffraction effects of the excited light. We modified this strategy and applied it to an IMS system for counteracting the diffusion effect of the pulsed ion packet. The method can increase the resolution up to 1.55 times through theoretical analysis, and the improvement is verified by simulations. The simulation results find that the initial width of the ion packet has an influence on the effectiveness of the method, and the narrower the initial width, the better the effect. The proposed inverse counterbalance strategy may also be applied to other spectral analysis instruments to break the resolution limit.

Science Autonomy for Ocean Worlds Astrobiology: A Perspective

Astrobiology missions to ocean worlds in our solar system must overcome both scientific and technological challenges due to extreme temperature and radiation conditions, long communication times, and limited bandwidth. While such tools could not replace ground-based analysis by science and engineering teams, machine learning algorithms could enhance the science return of these missions through development of autonomous science capabilities. Examples of science autonomy include onboard data analysis and subsequent instrument optimization, data prioritization (for transmission), and real-time decision-making based on data analysis. Similar advances could be made to develop streamlined data processing software for rapid ground-based analyses. Here we discuss several ways machine learning and autonomy could be used for astrobiology missions, including landing site selection, prioritization and targeting of samples, classification of "features" (e.g., proposed biosignatures) and novelties (uncharacterized, "new" features, which may be of most interest to agnostic astrobiological investigations), and data transmission.

Modeling the modulation characteristics of the Bradbury-Nielsen gate in ion mobility spectrometers

The Bradbury-Nelson gate (BNG) is a common device used for ion control in time-of-flight mass spectrometry and ion mobility spectrometry (IMS). A dual-location control model was employed in order to better understand the behavior of ions around a modulated BNG. This model illustrated that the ions are released from the starting location and truncated at the cutoff location. The shapes of the starting and cutoff locations are both curved with similar curvature, and the cutoff location is situated further back. Therefore, the distance between the two locations is a key parameter leading to the ion loss during modulation and is influenced by the gating voltage difference. Through simulations and experiments, the ion loss is verified to increase with the increase in the gating voltage difference. Taking a Fourier transform IMS as an example, by reducing the gating voltage difference from 150 to 50 V, the signal-to-noise ratio of the time domain result was improved from 91.7 to 386.5 and the resolving power was improved from 40.9 to 63.6. In addition, the superposition effect of multicycle modulation is shown and explained by the model. When the modulated frequency is too rapid and the closing time is insufficient for all the ions to be consumed, some ions continue to exist between the two locations, and the residual ions then enter the drift region during the next few cycles. This phenomenon needs to be avoided because the total number of ions entering the drift region will then increase uncontrollably.

Walnut ethylene response factor JrERF2-2 interact with JrWRKY7 to regulate the GSTs in plant drought tolerance

Juglans regia is a world-famous woody oil plant, whose yield and quality are affected by drought stress. Ethylene-responsive factors (ERFs) play vital role in plant stress response. In current study, to comprehend the walnut molecular mechanism of drought stress response, an ERF transcription factor was clarified from J. regia (JrERF2-2) and its potential function mechanism to drought was clarified. The results showed that JrERF2-2 could be induced significantly by drought. The transgenic Arabidopsis over-expression of JrERF2-2 displayed enhanced growth, antioxidant enzyme vitalities, reactive oxygen species scavenging and proline produce under drought stress. Especial the glutathione-S-transferase (GST) activity and most GST genes' transcription were elevated obviously. Yeast one-hybrid (Y1H) and co-transient expression (CTE) methods revealed that JrERF2-2 could recognize JrGST4, JrGST6, JrGST7, JrGST8, and JrGSTF8 by binding to GCC-box, and recognize JrGST11, JrGST12, and JrGSTN2 by binding to DRE motif. Meanwhile, the binding activity was strengthened by drought stress. Moreover, JrERF2-2 could interact with JrWRKY7 to promote plant drought tolerance; JrWRKY7 could also distinguish JrGST4, JrGST7, JrGST8, JrGST11, JrGST12, and JrGSTF8 via binding to W-Box motif. These results suggested that JrERF2-2 could effectively improve plant drought tolerance through interacting with JrWRKY7 to control the expression of GSTs. JrERF2-2 is a useful plant representative gene for drought response in molecular breeding.

Distinguishment of Glycan Isomers by Trapped Ion Mobility Spectrometry

The in-depth study of glycan has drawn large research interests since it is one of the main biopolymers on the earth with a variety of biological functions. However, the distinguishment of glycans is still difficult due to the similarity of the monosaccharide building block, the anomer, and the linkage of glycosidic bonds. In this study, four novel and representative copper-bound diastereoisomeric complex ions were simultaneously detected in a single measurement by trapped ion mobility mass spectrometry, including mononuclear copper-bound dimeric ions [(Cu²⁺)(A)(l-Ser)-H]⁺ and [(Cu²⁺)(A)(l-His)-H]⁺, the mononuclear copper-bound trimeric ion [(Cu²⁺)(A)(l-Ser)(l-His)-H]⁺, and the binuclear copper-bound tetrameric ion [(Cu²⁺)₂(A)(l-Ser)₂(l-His)-3H]⁺ (where A denotes an oligosaccharide, and l-Ser and l-His denote l-serine and l-histidine, respectively). By combining the collision cross sections of complex ions, 23 oligosaccharide isomers were successfully distinguished including two pairs of sialylated glycan linkage isomers. In addition, due to the unique dissociation pathways of the trimeric ion, both the relative and absolute quantification of the individual isomer in the mixture could be determined using a mass spectrometry-based kinetic method. Finally, the method established above was successfully applied to the identification and quantification of glycan isomers in dairy beverages and juice. The method in the present study was sensitive to the fine difference of glycan isomers and might have wide applicability in glycoscience.

Discrimination of Aminobiphenyl Isomers in the Gas Phase and Investigation of Their Complex Conformations

The analysis of positional isomers is of great significance because their different chemical properties but similar structures make separation difficult. In this work, a simple method for simultaneously discriminating three positional isomers of 2-aminobiphenyl (2-ABP), 3-ABP, and 4-ABP was studied by ion mobility spectrometry (IMS) and quantum mechanical calculations at the molecular level. In the experiments, three ABP isomers were mixed with α-, β-, and γ-cyclodextrins (CD), and the IMS results show that the three ABP isomers were clearly recognized by the formed complex of [α-CD + ABP + H]⁺ via measuring their IMS, in which the different ion mobilities of 1.515, 1.544, 1.585 V·s·com^-2 with the collision cross sections (CCS) of 307.3, 312.5, 320.8 Ų were obtained for [α-CD + 2-ABP + H]⁺, [α-CD + 3-ABP + H]⁺, and [α-CD + 4-ABP + H]⁺, respectively. Collision induced dissociation analysis of the three [α-CD + ABP + H]⁺ isomer complexes were further studied, indicating that the same fragmentation process required different collisional energies, and the greater the CCS for the [α-CD + ABP + H]⁺ with looser structure and the smaller energy required. Besides, the favorable conformation and the CCS value of the different [CD + ABP + H]⁺ isomer complexes were measured via quantum mechanical calculations to detail their intermolecular interactions. It revealed that the intermolecular binding between 2-ABP and α-CD is different from that of 3- and 4-ABP, resulting in different molecular conformations and CCS, and the interaction modes of ABP with β-CD are similar to that with γ-CD, which are very consistent with the experimental observations. Finally, relative quantification of the method was performed, and satisfactory linearity with correlation coefficients (R²) greater than 0.99 was obtained. This method for isomer discrimination and conformation analysis possesses the advantages of simplicity, sensitivity, cost-effectiveness, and as such it may be widely applied in chemistry and pharmaceutical sciences.

Effective Chiral Discrimination of Amino Acids through Oligosaccharide Incorporation by Trapped Ion Mobility Spectrometry

Chiral analysis is critical to many research fields due to different biological functions of enantiomers in living systems. Although the use of ion mobility spectrometry (IMS) has become an alternative technology in the area of chiral measurements, there is still a lack of a general chiral selector for IMS-based chiral recognition, especially for small chiral molecules. Here, a new method using oligosaccharides as the chiral selector has been developed to discriminate chiral amino acids (AAs) by trapped ion mobility spectrometry-mass spectrometry (TIMS-MS). We analyzed 21 chiral amino acids, including small molecules (e.g., alanine and cysteine). Our data showed that the use of nonreducing tetrasaccharides was effective for the separation of chiral AAs, which differentiated 21 chiral AAs without using metal ions. By further incorporating a copper ion, the separation resolution could be improved to 1.64 on average, which accounts for an additional 52% improvement on top of the already achieved separation in metal-free analysis. These results indicate that the use of tetrasaccharides is an effective strategy for the separation of AA enantiomers by TIMS. The method developed in this study may open up a new strategy for effective IMS-based chiral analysis.

Application of Infrared Multiple Photon Dissociation (IRMPD) Spectroscopy in Chiral Analysis

In recent years, methods based on photodissociation in the gas phase have become powerful means in the field of chiral analysis. Among them, infrared multiple photon dissociation (IRMPD) spectroscopy is a very attractive one, since it can provide valuable spectral and structural information of chiral complexes in addition to chiral discrimination. Experimentally, the method can be fulfilled by the isolation of target diastereomeric ions in an ion trap followed by the irradiation of a tunable IR laser. Chiral analysis is performed by comparing the difference existing in the spectra of enantiomers. Combined with theoretical calculations, their structures can be further understood on the molecular scale. By now, lots of chiral molecules, including amino acids and peptides, have been studied with the method combined with theoretical calculations. This review summarizes the relative experimental results obtained, and discusses the limitation and prospects of the method.

Chiral differentiation of l- and d-penicillamine by β-cyclodextrin: Investigated by IRMPD spectroscopy and theoretical simulations

The chirality of penicillamine (Peni) results in different clinic applications. Host-guest complex based drug delivery system that differentiates the two enantiomers and provides delayed release is of significance in medication. We hereby used β-CD to encapsulate d- and l-Peni. IRMPD spectra show different characteristic vibrations to distinguish the two enantiomers. Besides common peaks found at 3000-3100 cm^-1 and 3520 cm^-1, featured peaks are found around 2900 cm^-1 and 3400 cm^-1. It is found that the featured vibrations of [β-CD + l-Peni + H]⁺ are more red-shifted than those of [β-CD + d-Peni + H]⁺. Through DFT calculations on the complex configurations sampled from molecular dynamics simulations, d-Peni is found embedded inside β-CD with a lower free energy of 11.5 kJ mol^-1 in the lowest configuration than that of the lowest [β-CD + l-Peni + H]⁺ configuration, in which l-Peni is found lying upon the β-CD. The featured vibrational peaks are attributed to the specific NH⋯O, OH⋯O intermolecular hydrogen bonds. The red-shifted characteristic peaks of [β-CD + l-Peni + H]⁺ in IRMPD spectra owe to the stronger NH⋯O hydrogen bonds.

Microbial lipases and their industrial applications: a comprehensive review

Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.