Boronate affinity Metal–Organic frameworks for highly efficient cis-diol molecules in-situ enrichment and surface-assisted laser desorption/ionization mass spectrometric detection

Structure-Assisted Boronic Acid Implanted Mesoporous Metal-Organic Frameworks for Specific Extraction of cis-Diol Molecules

cis-Diol-containing molecules, an essential type of compounds in living organisms, have attracted intensive research interest from various fields. The analysis of cis-diol-containing molecules is still suffering from some drawbacks, including low abundance and abundant interference. Metal-organic frameworks (MOFs) have proven to be an ideal sorbent for sample preparation. However, most of the reported MOFs are mainly restricted to a microporous regime (pore size <2 nm), which greatly limits the application. Herein, a facile strategy is established to construction of boronate affinity MOFs via the postsynthetic ligand-exchange process. Owing to the fact that the ligand-exchange process was assisted by the structural integrity of the primitive metal-organic framework and the great compatibility of click chemistry, the obtained EPBA-PCN-333(Fe) is able to realize the maximum maintaining the porosity and crystallinity of the parent material. Several intriguing features of EPBA-PCN-333(Fe) (e.g., excellent selectivity, efficient diffusion, good accessibility, and size exclusion effect) are experimentally demonstrated via a series of cis-diol-containing molecules with different molecular sizes (small molecules, glycopeptides, and glycoproteins). The binding performance of EPBA-PCN-333(Fe) is evaluated by employing catechol as the test molecule (binding capacity: 0.25 mmol/g, LOD: 200 ng/mL). Finally, the real-world applications of EPBA-PCN-333(Fe) were demonstrated by the detection of nucleosides of human urine samples.

Novel Ag-modified vanadate nanosheets for determination of small organic molecules with laser desorption ionization mass spectrometry

Laser desorption ionization mass spectrometry (LDI-MS) aroused intensive concerns for the merits of label-free and high-throughput analysis. Here, we designed a silver nanoparticles (AgNP)-modified indium vanadate nanosheets with doping samarium (AgNP@InVO4:Sm) nanosheets. The developed AgNP@InVO4:Sm nanosheets (AIVON) were synthesized based on the microemulsion-mediated solvothermal method and ultraviolet-assisted in situ formation of AgNP, then for the first time applied as a matrix in LDI-MS analysis. With the advantages including enhanced MS signal, little matrix-related background, high reproducibility, and good salt tolerance, AIVON exhibited much better prospect than non-modified indium vanadate nanosheets with doping samarium (IVON) and traditional organic matrix, thus allowing sensitive MS detection for a wide range of low-molecular-weight (LMW) molecules. Moreover, by coupling with headspace sampling thin-film microextraction (TFME), a kind of representative pollutant chlorophenols were identified and quantified via AIVON-assisted LDI-MS in environmental and biological samples. Volatile LMW pollutants could be preconcentrated after TFME, hence a sensitive and rapid assay with negligible sample matrix effect was realized by using AIVON-assisted LDI-MS. It is anticipated that this novel nano-matrix AIVON and the proposed TFME coupling detection strategy were of competitive merits for LDI-MS analysis in the fields of environment, biomedicine, and agriculture.

Temporally and spatially resolved molecular profiling in fingerprint analysis using indium vanadate nanosheets-assisted laser desorption ionization mass spectrometry

This study presents the first-ever synthesis of samarium-doped indium vanadate nanosheets (IVONSs:Sm) via microemulsion-mediated solvothermal method. The nanosheets were subsequently utilized as a nano-matrix in laser desorption/ionization mass spectrometry (LDI-MS). It was discovered that the as-synthesized IVONSs:Sm possessed the following advantages: improved mass spectrometry signal, minimal matrix-related background, and exceptional stability in negative-ion mode. These qualities overcame the limitations of conventional matrices and enabled the sensitive detection of small biomolecules such as fatty acids. The negative-ion LDI mechanism of IVONSs:Sm was examined through the implementation of density functional theory simulation. Using IVONSs:Sm-assisted LDI-MS, fingerprint recognitions based on morphology and chemical profiles of endogenous/exogenous compounds were also achieved. Notably, crucial characteristics such as the age of an individual's fingerprints and their physical state could be assessed through the longitudinal monitoring of particular biomolecules (e.g., ascorbic acid, fatty acid) or the specific biomarker bilirubin glucuronide. Critical information pertinent to the identification of an individual would thus be facilitated by the analysis of the compounds underlying the fingerprint patterns.

A mesoporous graphene @ zirconium-based metal–organic frameworks as a matrix and an adsorbent for steroid detection using surface-assisted laser desorption/ionization time-of-flight mass spectrometry

Endocrine-disrupting chemicals (EDCs) in environmental water samples, a rapid, sensitive, and high-throughput method should be developed. In this study, an in situ-synthesized composite material of three-dimensional mesoporous graphene (3D-MG) and zirconium-based metal-organic frameworks (MOFs), denoted as MG@UiO-66, was used as both the adsorbent and matrix in surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) for steroid detection. Both graphene-based materials and MOFs have proven to be ineffective in detecting steroids as a matrix; however, their composites can detect steroids with higher sensitivity and lower interference. After screening different types of MOFs, a composite of UiO-66 and 3D-MG was selected as the new matrix for steroid detection. The combination of 3D-MG and UiO-66 further enhanced the ability of the material to enrich steroids, and reduced the limit of detection (LOD) of steroids. The method was evaluated for linearity, LODs, limit of quantitation (LOQs), reproducibility, and precision under optimized conditions. The results showed that the linear relationships of three steroids are kept in the range of 0-300 nM/L with a correlation coefficient r ≥ 0.97. The LODs and LOQs of the steroids were in the range of 3-15 and 10-20 nM/L, respectively. Recoveries (n = 5) of 79.3-97.2% were obtained at three spiked levels in the blank water samples. This fast and efficient method of using SALDI-TOF MS can be extended to detect the steroids in EDCs in environmental water samples.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

[Advances in enrichment and separation of cis-diol-containing compounds by porous organic frameworks]

The design and synthesis of boronate affinity materials that show high efficiency, high selectivity, and high enrichment performance have gained significant attention. The principle of boronate affinity relies on the reversible covalent reactions, including the formation of stable five-membered or six-membered cyclic esters with cis-diol-containing compounds in alkaline aqueous media and dissociation of cyclic esters in an acidic surrounding to release cis-diol-containing compounds. Recently, various boronate affinity materials have been synthesized and utilized for selective enrichment of these compounds. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have been widely used in chromatographic separation and sample pretreatment because of their adjustable pore size, high porosity, high specific surface area, tunable skeleton structure, and favorable chemical and thermal stability. To promote the enrichment selectivity of MOFs and COFs for cis-diol-containing compounds, boronic acid-functionalized MOFs and COFs with various structures and categories have been synthesized. This review summarizes more than 80 investigations into the categories, synthetic strategies, and applications of boronic acid-functionalized MOFs and COFs from the Science Citation Index. These synthesis methods include metal ligand-fragment co-assembly, post-synthetic modification, and bottom-up modification of boronic acid-functionalized porous materials. Although two modification strategies (post-synthetic and metal ligand-fragment co-assembly) have been introduced for the preparation of boronic acid-functionalized MOFs, the latter is more commonly adopted as it improves the enrichment selectivity and enrichment efficiency of MOFs. The common limitations of MOFs such as aggregation and aperture issues were also resolved. Boron affinity MOFs possessing favorable properties according to the characteristics of cis-diol-containing compounds, have also been synthesized. Furthermore, to facilitate enrichment and separation, many boronic acid-functionalized magnetic material MOFs have been developed for the enrichment and analysis of cis-diol-containing compounds. Additionally, the luminescent properties of Ln-MOFs have been used in combination with boronic acid affinity for the enrichment, separation, and subsequent detection of cis-diol-containing compounds. Post-synthetic modification and the bottom-up strategy are the primary methods for the preparation of boronic acid-functionalized COFs. Boronic acid-functionalized COFs are less investigated than boronic acid-functionalized MOFs, likely due to the greater complexity of COF synthesis. This work aims to summarize the research advances, synthesis ideas, and synthesis methods related to boric acid-functionalized porous organic frameworks, which will provide theoretical guidance and technical support for its applications while accelerating the commercialization of such organic frameworks.

Optimized Glycopeptide Enrichment Method-It Is All about the Sauce

Protein glycosylation is a family of posttranslational modifications that play a crucial role in many biological pathways and diseases. The enrichment and analysis of such a diverse family of modifications are very challenging because of the number of possible glycan–peptide combinations. Among the methods used for the enrichment of glycopeptides, boronic acid never lived up to its promise. While most studies focused on improving the affinity of the boronic acids to the sugars, we discovered that the buffer choice is just as important for successful enrichment if not more so. We show that an amine-less buffer allows for the best glycoproteomic coverage, in human plasma and brain specimens, improving total quantified glycopeptides by over 10-fold, and reaching 1598 N-linked glycopeptides in the brain and 737 in nondepleted plasma. We speculate that amines compete with the glycans for boronic acid binding, and therefore the elimination of them improved the method significantly.

Nanocomposites of boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymers as a novel desorption/ionization matrix for the capture and direct detection of cis-diol-flavonoid compounds coupled with MALDI-TOF-MS

Novel boronic acid-functionalized magnetic multi-walled carbon nanotubes with flexible branched polymer (Fe₃O₄@MWCNTs@ε-PL@BA) nanocomposites were fabricated and applied as the desorption/ionization matrix for the MALDI-TOF-MS determination of low molecular weight flavonoids. The prepared nanocomposite was systematically characterized by various techniques. Compared to the traditional organic matrix, the proposed Fe₃O₄@MWCNTs@ε-PL@BA matrix has excellent ionization efficiency and low-background noise interference due to the MWCNTs unique electron-phonon interaction and the high introduction density of boronic acid functional groups. Good sensitivity and ultra-high salt tolerance of the Fe₃O₄@MWCNTs@ε-PL@BA-assisted MALDI-TOF-MS were permitted for the determination and quantification of flavonoids in actual samples. Noticeably, the limits of detection (LODs) for the target flavonoids were in the range 17-33 nM. The relative standard deviations (RSDs) of spot-to-spot and sample-to-sample (n = 10) were ≤ 9.8% and ≤ 10.1%, respectively. Furthermore, the wide linear ranges (0.1 - 500 µg/mL) and satisfactory calibration plot coefficients (R² > 0.99) of flavonoids were achieved by MALDI-TOF-MS with the Fe₃O₄@MWCNTs@ε-PL@BA matrix. Good recoveries (92-105.5%) were achieved for the target flavonoids in practical food samples. Hence, the prepared Fe₃O₄@MWCNTs@ε-PL@BA nanocomposites have applications in the selective and efficient capture of target flavonoids active biomolecules coupled with MALDI-TOF-MS determination in actual samples.

A selectivity-enhanced ratiometric fluorescence imprinted sensor based on synergistic effect of covalent and non-covalent recognition units for ultrasensitive detection of ribavirin

Development of methods with high selectivity and sensitivity for detection of trace ribavirin (RBV) is of great importance for environmental protection and food safety. Herein, we proposed a simple yet valid strategy to construct the highly selective ratiometric fluorescence sensing platform (BA-LMOFs@MIP) for analysis of RBV based on boric acid-functionalized lanthanide metal-organic framework (BA-LMOFs) coupled with molecularly imprinted polymer (MIP). In this strategy, BA-LMOFs featured with dual-emission and pH-responsive behavior were first synthesized as supporter. Benefiting from boric acid group of BA-LMOFs, RBV was easily immobilized onto its surface, taking advantage of template immobilization-based surface imprinting means to fabricate BA-LMOFs@MIP with dual recognition sites for the first time. The synergistic effect of covalent boronate affinity-based recognition unit and non-covalent imprinting sites enabled BA-LMOFs@MIP to exhibit superior selectivity and binding efficiency to RBV. BA-LMOFs as signal tag endowed BA-LMOFs@MIP with desirable sensitivity, photostability and hydrophilicity. More importantly, BA-LMOFs@MIP-based sensor displayed a wide linear range for RBV from 25 to 1200 ng mL^-1 with a detection limit down to 7.62 ng mL^-1. The sensor was finally applied to RBV determination in real samples, and the obtained results revealed that BA-LMOFs@MIP would be a promising candidate for monitoring of RBV in complex systems.

Combination of pipette tip solid phase extraction and high performance liquid chromatography for determination of plant growth regulators in food samples based on the electrospun covalent organic framework/polyacrylonitrile nanofiber as highly efficient sorbent

Facile and sensitive determination of plant growth regulators (PGRs) in food samples is important but still remains great challenge. Herein, a pipette tip solid phase extraction (PT-SPE) method was developed for fast and sensitively detecting PGRs. The PT-SPE adsorbent was prepared by integrating a novel covalent organic framework (COF) of schiff base network 3 (SNW-3) and polyacrylonitrile (PAN) through electrospinning. The SNW-3 can easily adsorb PGRs with high special affinity through electrovalent bands between the ammonium ions of SNW-3 and the carboxy groups of PGRs. The polymer of PAN acts as scaffold material for SNW-3, which can lower seepage pressure hence accelerates adsorption/desorption kinetics. By combination with HPLC-DAD, a satisfactory method was successfully developed for simultaneous determination of ten PGRs in watermelon. Good analytical performances were achieved with this proposed method, including good linearity (5-500 ng/mL) with high correlation coefficients (R ≥ 0.9981), low limits of detection (S/N = 3, 0.24-3.19 ng/mL) and limits of quantification (S/N = 10, 1.65-5.72 ng/mL), satisfactory precision (intra-day RSDs ≤ 2.7%, inter-day RSDs ≤ 3.7%), and high accuracy (recovery: 82.8-113.0%). The method developed in this study shows high potential for design of high target-affinity adsorbents for food sample preparing.

Nanostructured Substrates as Matrices for Surface Assisted Laser Desorption/Ionization Mass Spectrometry: A Progress Report from Material Research to Biomedical Applications

Within the past two decades, the escalation of research output in nanotechnology fields has boosted the development of novel nanoparticles and nanostructured substrates for use as matrices in surface assisted laser desorption/ionization mass spectrometry (SALDI-MS). The application of nanomaterials as matrices, rather than organic matrices, offers remarkable characteristics that allow the analysis of small molecules with fewer matrix interfering peaks, and share higher detection sensitivity, specificity, and reproducibility. The technological advancement of SALDI-MS has in turn, propelled the application of the analytical technique in the field of biomedical analysis. In this review, the properties and fabrication methods of nanostructured substrates in SALDI-MS such as metallic-, carbon-, and silicon-based nanostructures, quantum dots, metal-organic frameworks, and covalent-organic frameworks are described. Additionally, the latest progress (most within 5 years) of biomedical applications in small molecule, large biomolecule, and MS imaging analysis including metabolite profiling, drug monitoring, bacteria identification, disease diagnosis, and therapeutic evaluation are demonstrated. Key parameters that govern nanomaterial's SALDI efficiency in biomolecule analysis are also discussed. Finally, perspectives of the future development are given to provide a better advancement and promote practical application in clinical MS.

Sulfonic acid functionalized hierarchical porous covalent organic frameworks as a SALDI-TOF MS matrix for effective extraction and detection of paraquat and diquat

Design and construction of a matrix with specific adsorption on the target compounds can effectively reduce the detection limit of surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) analysis. Sulfonic acid functionalized hierarchical porous covalent organic frameworks (H-COF-SO₃H) was synthesized by defect-structure and post-modification method, and then used as matrix and adsorbent for the determination of quaternary ammonium herbicides paraquat (PQ) and diquat (DQ). N₂ adsorption-desorption experiments confirmed that H-COF-SO₃H possesses hierarchical porosity with pore widths concentrated at 1.3,1.5, and 2.8 nm. The strong UV absorption at 200-450 nm and good thermal stability made H-COF-SO₃H being a promising matrix without background interference. H-COF-SO₃H can efficiently enrich PQ and DQ via electrostatic attraction, and the key role of -SO₃H group on specific adsorption was confirmed by density functional theory (DFT) calculations. The limits of detection (LODs) for PQ and DQ with H-COF-SO₃H enrichment were 0.5 and 0.1 ng·mL^-1, respectively, which were 20 and 60 times higher than those without H-COF-SO₃H enrichment, respectively. The spiked recoveries of PQ and DQ for the three food samples were 92.0-113.2% and 80.1-102.6% with RSDs of 2.2-9.2% and 2.0-8.7%, respectively. This work provides an analyte-oriented approach for fabricating SALDI-TOF MS matrix.

ZIF-based boronic acid functionalized metal-organic frameworks for the enrichment of cis-diol-containing luteolin from food samples prior to HPLC

Zeolite imidazole framework-based boronic acid-functionalized metal-organic frameworks (ZIF-67@PDA@BA-Zr-MOFs) were developed as an adsorbent for solid phase extraction (SPE) of luteolin (LTL) from peanut shell samples. Herein, ZIF-67 as a support matrix, polydopamine (PDA) as a coating to introduce amino and hydroxyl groups on the matrix surface to fix metal-organic frameworks (MOFs), zirconium tetrachloride (ZrCl₄) as a precursor, terephthalic acid (TPA), and 3-carboxyphenylboronic acid (3-CPBA) as the mutual organic building blocks, and 3-CPBA was also a boronate affinity functional monomer. The effects of synthesis conditions, SPE conditions, selectivity, competitivity, reproducibility, and reusability were evaluated in detail. Under the optimal conditions, the maximum adsorption capacity is 71.4 mg g^-1. The utility of ZIF-67@PDA@BA-Zr-MOFs as an adsorbent for SPE of LTL is supported by the presence of the abundant pore structure, as well as the boronate affinity sites facilitated the rapid binding of the adsorbent to the template. The concentration of the extracted LTL was determined by the high-performance liquid chromatography-ultraviolet (HPLC-UV), with calibration plots being linear in the concentration range 0.05-100 mg L^-1 and a limit of detection (LOD) of 0.035 mg L^-1. The method was applied to determine the LTL in peanut shell samples and recovered the target analyte in the range 85.6% to 99.2% (the standard deviations are less than 3.3%, n = 3). In addition, we incorporated boronate affinity and MOFs material into an SPE system to provide a promising strategy to detect other cis-diol-containing analytes in the complex matrix.

Nanocomposite-Based Matrices in Laser Desorption/Ionization Mass Spectrometry for Small-Molecule Analysis

The efficient detection of small molecules is of significance for environmental monitoring, pharmacology, metabolomics, and lipidomics. The laser desorption/ionization mass spectrometry (LDI MS) platform enables high sensitivity, accuracy, resolution, and throughput in molecular analysis, but its analytical capability with respect to small molecules is limited due to inherent drawbacks arising from conventional organic matrices. The selection of an appropriate matrix is thus a precondition for small molecule detection by LDI MS. To date, various inorganic matrices have been developed, with a growing interest in composite materials displaying synergetic effects. This Minireview highlights the development of nanocomposites as LDI matrices driven by numerous innovations in material science, and their emerging use in small-molecule analysis.

Microwave-prepared mesoporous graphene as adsorbent and matrix of surface-assisted laser desorption/ionization mass spectrometry for the enrichment and rapid detection of polyphenols in biological samples

In this work, a three-dimensional mesoporous graphene (3D-MG) prepared by microwave-assisted method was used as both the adsorbent and the matrix of SALDI-TOF MS for polyphenols analysis in biological samples. The outstanding microstructure of 3D-MG made it sensitive in small molecule analysis with low background interference and able to enrich trace polyphenols from complex samples. 3D-MG performed much better in the detection of small molecules than graphene prepared by ordinary method, and could further improve sensitivity and reduce detection limit by enrichment. Due to its unique hierarchical mesoporous structure, the interference of biological macromolecules in SALDI analysis could be eliminated after treatment by 3D-MG. Finally, 3D-MG was successfully applied to the screening of polyphenols in biological samples with simple process and high throughput. Moreover, this strategy had also promoted the development of new matrix in SALDI-TOF MS analysis, in which the matrix properties, adsorption capabilities and size effects of graphene-based materials were combined for the first time.

Selective adsorption and separation of stevioside and rebaudioside A by a metal-organic framework with boronic acid

The boronic acid functionalization metal-organic frameworks (MOFs), as unique boronate affinity adsorbents, have desired specific molecular affinity for the separation and enrichment of cis-diol-compounds. Herein, the boronic acid functionalized Zn-based MOF adsorbent (MOF-BA) was synthesized through a simple one-step microwave method and used for the recognition and isolation of steviol glycosides (SGs). This MOF-BA exhibits the same spherical structure and isostructure with the parent framework composed only of the primitive ligand as verified by SEM and XRD characterization. It was confirmed that changing the ratio of ligands could achieve the adjustability of the boron content in the framework. At the same time, the MOF-BA-1.0 showed a suitable pore size (4.69 nm), and the presence of boric acid functional groups showed favorable selectivity for stevioside (STV). The static adsorption results showed that adsorption performances of rebaudioside A (RA) and STV from crude sugar solution (5.0 mg mL−1, pH 8) on MOF-BA-1.0 were investigated at 303 K for 15 h. The adsorption capacities for STV and RA were 42.93 mg g−1 and 22.96 mg g−1, respectively, and the adsorption selectivity (αSTV/RA) reached 4.35. The adsorption isotherm and kinetic data of MOF-BA-1.0 for RA and STV obeyed the Langmuir isotherm model and pseudo second order kinetic model, respectively. The study demonstrated that MOF-BA-1.0 adsorbent could be used as a potential adsorbent to purify the active ingredients of stevia and obtain a high concentration of RA products.

Sn(OH)x-assisted synthesis of mesoporous Mn-porphyrinic frameworks and their carbon derivatives for electrocatalysis

5,10,15,20-Tetrakis (4-aminophenyl) Mn-porphyrin and 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde were combined into a new mesoporous organic framework by a Schiff-base-type reaction.

Synthesis, structure, fluorescence and electrochemical properties of a new Zn(ii)–organic framework constructed by a tricarboxylic acid ligand

A new efficient fluorescent sensor [Zn₃(L)(HL)(OH)(H₂O)₃]·H₂O (1) for detecting Cr₂O₇²⁻ anions has been synthesized. Moreover, compound 1 has been calcined to prepare a new electrocatalyst R-C@800 for HER.