Self-Assembled Binuclear Cu(II)–Histidine Complex for Absolute Configuration and Enantiomeric Excess Determination of Naproxen by Tandem Mass Spectrometry

Distinguishing α/β-linkages and linkage positions of disaccharides in galactooligosaccharides through mass fragmentation and liquid retention behaviour

Galactooligosaccharides (GOS) are important prebiotics with function closely related to their structure. However, a comprehensive overview of the structure-function relationship is still limited due to the challenge in characterizing multiple isomers in GOS. This study presents a strategy of combining both hydrophilic interaction liquid chromatography (HILIC) retention time and tandem mass spectrometry (MS/MS) fragmentation pattern to distinguish α/β-linkages and linkage positions of disaccharide isomers in GOS through HILIC-MS/MS analysis. The results indicated that the ratio of m/z 203.0524 to m/z 365.1054 could distinguish α/β-linkages, while the ratios of m/z 347.0947 to m/z 365.1054, m/z 245.0642 to m/z 365.1054 and HILIC retention time could distinguish (1 → 2), (1 → 3), (1 → 4) and (1 → 6) linkages. The above rules enabled effective characterization of disaccharides in GOS-containing food samples, including milk powder, rice flour, drink, yogurt. This method can be used in the quality control of GOS and future research on the structure-specific health effects of GOS.

Exploration of chiral drugs as references for chiral discrimination of valsartan and voriconazole by tandem mass spectrometry

The use of mass spectrometry for chiral recognition and quantification has attracted great interest owing to its speed, sensitivity, specificity, and tolerance. However, searching for chiral selectors in chiral analyses using mass spectrometry is still problematic. In this study, chiral drugs could be applied as references for the chiral recognition and enantiomeric quantification of valsartan and voriconazole. Two novel pairs of metal-bound diastereomeric complex ions were detected by mass spectrometry, namely, nickel (II)-bound dimeric ions [NiII (2R,5S-emtricitabine) (S-valsartan)-H]+ and [NiII (2R,5S-emtricitabine) (R-valsartan)-H]+ and copper (II)-bound dimeric ions [CuII (S,S,S-enalaprilat) (2S,3R-voriconazole)-H]+ and [CuII (S,S,S-enalaprilat) (2R,3S-voriconazole)-H]+ . The resulting diastereomers were successfully identified based on the relative intensities of their characteristic fragments using tandem mass spectrometry. The logarithm of the characteristic fragment ion abundance ratio exhibited a good linear relationship with the enantiomeric excess. Density functional theory calculations were also performed to elucidate the mechanism of the structural differences observed in the MS results. This established approach proves that chiral drugs can serve as ligands for the rapid recognition and quantitative analysis of other chiral drugs without a chiral chromatographic column or complex sample pretreatment.

Exploring a new family of designer copper(II) complexes of anthracene-appended polyfunctional organic assembly displaying potential anticancer activity via cytochrome c mediated mitochondrial apoptotic pathway

The present article describes the systematic study on design and synthesis, physicochemical properties and spectroscopic features, and potential anticancer activities of a family of novel copper(II)-based designer metal complexes [Cu₂(acdp)(μ-Cl)(H₂O)₂] (1), [Cu₂(acdp)(μ-NO₃)(H₂O)₂] (2) and [Cu₂(acdp)(μ-O₂CCF₃)(H₂O)₂] (3) of anthracene-appended polyfunctional organic assembly, H₃acdp (H₃acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol). Synthesis of 1-3 was accomplished under facile experimental conditions, preserving their overall integrity in solution. The incorporation of polycyclic anthracene skeleton within the backbone of organic assembly increases lipophilicity of resulting complexes, thereby dictating the degree of cellular uptake with improved biological activity. Complexes 1-3 were characterized by elemental analysis, molar conductance, FTIR, UV-Vis absorption/fluorescence emission titration spectroscopy, PXRD and TGA/DTA studies, including DFT calculations. The cellular cytotoxicity of 1-3 when studied in HepG2 cancer cell line showed substantial cytotoxic effects, whereas no such cytotoxicity was observed when exposed to normal L6 skeletal muscle cell line. Thereafter, the signaling factors involved in the process of cytotoxicity in HepG2 cancer cells were investigated. Alteration of cytochrome c and Bcl-2 protein expression levels along with modulation of mitochondrial membrane potential (MMP) in the presence of 1-3, strongly suggested the possibility of activating mitochondria-mediated apoptotic pathway involved in halting the cancer cell propagation. However, when a comparative assessment on their bio-efficacies was made, 1 showed higher cytotoxicity, nuclear condensation, DNA binding and damage, ROS generation and lower rate of cell proliferation compared to 2 and 3 in HepG2 cell line, indicating that the anticancer activity of 1 is significantly higher than that of 2 and 3.

Multidimensional identification of disaccharide isomers based on non-covalent complexes and tandem mass spectrometry

Glycans are the most abundant organic polymers in nature. They are essential to living organisms and regulate a wide range of biological functions. However, mass spectrometry-based identification of glycan isomers remains challenging due to the complexity of their structures including their complex compositions, linkages, and anomeric configurations. In this study, two novel complex ions, the mononuclear copper-bound dimeric ions [(Cu²⁺)(A)(L-His)-H]⁺ and the mononuclear copper-bound quaternary ions [(Cu²⁺)(A)(L-Ser)₃-H]⁺ (where A denotes a disaccharide, and L-Ser/His denotes l-serine/histidine), were designed for the collision-induced dissociation-based identification and relative quantification of 14 disaccharide isomers. When the unique fragmentation patterns of the above two types of complex ions were mapped into a three-dimensional vector, all the isomers were completely distinguished. Of note, the established method is able to identify mixtures of linkage isomers only using tandem mass spectrometry based on linkage-specific fragment ions of histidine-based complex ions. Finally, the method was successfully applied to the identification and relative quantification of two disaccharide isomers (lactose and sucrose) in dairy beverages. In conclusion, the established method is sensitive to subtle structural differences in disaccharide isomers and has the potential to be used for the differentiation of various glycans.

Selected Ion Monitoring Using Low-Cost Mass Spectrum Detectors Provides a Rapid, General, and Accurate Method for Enantiomeric Excess Determination in High-Throughput Experimentation

High-Throughput Experimentation (HTE) workflows are efficient means of surveying a broad array of chiral catalysts in the development of catalytic asymmetric reactions. However, use of traditional HPLC-UV/vis methodology to determine enantiomeric excess (ee) from the resulting reactions is often hampered by co-elution of other reaction components, resulting in erroneous ee determination when crude samples are used, and ultimately requiring product isolation prior to ee analysis. In this study, using four published reactions selected as model systems, we demonstrate that the use of LC-MS, SFC-MS, and selected ion monitoring (SIM) mass chromatography provides a highly accurate means to determine ee of products in crude reaction samples using commonplace, low-cost MS detectors. By using ion selection, co-eluting signals can be deconvoluted to provide accurate integrations of the target analytes. We also show that this method is effective for samples lacking UV/vis chromophores, making it ideal for HTE workflows in asymmetric catalysis.

The chirality determination of amino acids by forming complexes with cyclodextrins and metal ions using ion mobility spectrometry, and a DFT calculation

Chiral recognition is of highly interest in the areas of chemistry, pharmaceuticals, and bioscience. An effective strategy of enantiomeric determination of amino acids (AAs) was developed in this work. All 19 natural AAs enantiomers can be easily distinguished by ion mobility-mass spectrometry of the non-covalent complexes of AAs with cyclodextrins (α-CD, β-CD and γ-CD) and Mg²⁺ without any chemical derivatization. Differences of the mobilities between the enantiomers' complexes is from 0.006 to 0.058 V s/cm². In addition, the complex of [β-CD + Phe + Mg]²⁺ was selected as an example to study the relative quantification by measuring L/D-Phe at different molar ratio of 10:1 to 1:10 in the μM range, resulting in a good linearity (R² > 0.99) and high sensitivity at 2 μM. A DFT calculation was also performed to illustrate the detailed molecular structure of the complexes of CDs, Mg²⁺ and D- or L-Phe. Both experiment and theoretical calculation showed that Mg²⁺ plays an important role in host/guest interactions, which changed the molecular conformations by non-covalent interaction between Mg²⁺ and CDs, and resulted in the different collision cross-sections of the complex ions of CDs, Mg²⁺ and D- or L-AAs in the gas phase. This effective and convenient strategy could potentially be utilized in scientific research and industry for routine enantiomeric determination of natural AAs, peptides and some other small chiral biomolecules such as non-natural AAs and carboxylic acid-containing drugs.

Molecularly imprinted polymers in toxicology: a literature survey for the last 5 years

The science of toxicology dates back almost to the beginning of human history. Toxic chemicals, which are encountered in different forms, are always among the chemicals that should be investigated in criminal field, environmental application, pharmaceutic, and even industry, where many researches have been carried out studies for years. Almost all of not only drugs but also industrial dyes have toxic side and direct effects. Environmental micropollutants accumulate in the tissues of all living things, especially plants, and show short- or long-term toxic symptoms. Chemicals in forensic science can be known by detecting the effect they cause to the body with the similar mechanism. It is clear that the best tracking tool among analysis methods is molecularly printed polymer-based analytical setups. Different polymeric combinations of molecularly imprinted polymers allow further study on detection or extraction using chromatographic and spectroscopic instruments. In particular, methods used in forensic medicine can detect trace amounts of poison or biological residues on the scene. Molecularly imprinted polymers are still in their infancy and have many variables that need to be developed. In this review, we summarized how molecular imprinted polymers and toxicology intersect and what has been done about molecular imprinted polymers in toxicology by looking at the studies conducted in the last 5 years.

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.

Enantio-separation of pregabalin by ternary complexation using trapped ion mobility spectrometry

Rationale The rapid identification of small-molecule chiral drugs is challenging due to subtle structural differences. Different enantiomers of chiral drugs may produce inverse biological effects through their different pharmacokinetics. Therefore, it is highly desirable to distinguish the chirality of drug molecules.

METHODS

The chirality of pregabalin was distinguished by studying the ion mobility spectra of the ternary non-covalent complexes formed with cyclodextrins (CDs), pregabalin, and alkali-earth cations using trapped ion mobility spectrometry (TIMS). The ternary non-covalent complex ions were determined by electrospray ionization of mixed solutions. The analyzed sample was simply mixed, without derivatization or sample pretreatment. The relative contents of pregabalin enantiomers were derived using a calibration curve method.

RESULTS

The ion mobility spectra of several ternary non-covalent complexes formed with α-, β-, and γ-CD, pregabalin, and alkali-earth cations were obtained. We compared their ability to distinguish the chirality of pregabalin. The best peak-to-peak resolution (R_p-p ) was estimated to be 2.20 for [2β-CD + pregabalin + Sr]²⁺ , which can be ascribed as baseline separation. The derived relative contents for S-pregabalin were in agreement with the actual contents.

CONCLUSIONS

A novel and convenient method for discriminating the chirality of the pregabalin molecule by TIMS was developed and optimized. The chirality of pregabalin was recognized by studying the ion mobility spectra of the ternary non-covalent complexes, such as [2β-CD + pregabalin + Sr]²⁺ . This TIMS method could also be used to quantify the relative contents of pregabalin enantiomers.

Chiral molecularly imprinted polymeric stir bar sorptive extraction for naproxen enantiomer detection in PPCPs

Chiral micropollutant analysis in pharmaceuticals and personal care products (PPCPs) is interesting but challenging. We firstly developed a series of chiral molecularly imprinted polymeric (CMIP) stir bar sorptive extraction coatings by combining a chiral template with chiral functional monomers via a click reaction for naproxen enantiomer analysis in PPCPs. Heterochiral selectivity was observed in the molecule recognition of the CMIP coatings, which demonstrated good adsorption capability for the chiral template and its structurally similar chiral compounds. The coatings also exhibited excellent enrichment capability for chiral analytes in an aqueous matrix. The surface morphology and pore structure of the CMIP coatings were characterized. The molecular interactions between the chiral template and chiral functional monomer were investigated through UV-vis spectroscopy and theoretical calculations to prove the effective interactions existing in the heterochiral MIPs. The CMIP coatings were used to enrich naproxen enantiomers in chiral drug and environmental water samples, and satisfactory recoveries (83.98 %-118.88 %) with a relative standard deviation of 3.49 %-13.08 % were achieved. The heterochiral imprinted coating-based method provided a sensitive, selective, and effective enrichment strategy for chiral micropollutant analysis in PPCPs. This technique is critical for chiral molecule recognition and enantiomer analysis in complex samples.

One-pot synthesis of an anionic cyclodextrin-stabilized bifunctional gold nanoparticles for visual chiral sensing and catalytic reduction

A facile one-pot synthetic method for preparing gold nanoparticles by employing sugammadex (SUG), a carboxylic acid functionalized γ-cyclodextrin derivative, as reducing-cum-stabilizing agent herein was reported for the first time. The SUG protected gold nanoparticles (SUG-AuNPs) can work as a colorimetric sensor for visual chiral recognition of α-amino acids enantiomers, especially for lysine (Lys) and asparagine (Asn) enantiomers. The chiral recognition assay was successfully applied to determining the enantiometric excess of L-Lys and L-Asn ranging from -100 % to 100 % respectively. Moreover, the prepared SUG-AuNPs was found to exhibit efficient catalytic activity towards the reduction of toxic 4-nitrophenol by NaBH₄ and the efficiency of the system was further demonstrated through the reduction of other typical nitroaromatics under mild condition. The as-synthesized SUG-AuNPs shows good performance for both chiral sensing and reduction activity and thus may facilitate the practical application in the area of both chiral discrimination and catalysis.