Electrospray Ionization Mass Spectrometric Analysis Research Articles

The effects of modifiers on electrospray ionization for small-to-medium-sized molecules in comparison with solution-phase ionization.

Modifiers are essential additives in electrospray ionization (ESI) mass spectrometric analysis to enhance the production of ionic species in the gas phase for the detection of small-to-medium-sized molecules in biological and aqueous samples. Therefore, an appropriate modifier, in conjunction with the right ionization polarity, is crucial for sensitive ESI mass spectrometric analysis. However, the charge carried by basic and acidic functional groups in solution is neither quantitatively nor qualitatively reflected in the MS spectrum. For example, adding an acidic modifier will cause sufficient protonation of a basic functional group in solution; however, this may result in inferior positive ESI compared to using a basic modifier. Another example is when the MS spectrum does not reflect the charge distribution of multiply charged molecules in solution. Therefore, this review will summarize and discuss the proposed mechanisms by which modifiers induce and influence ESI. It will also cover molecular characteristics that affect ESI, such as charge state and polarity, which result in a difference between solution-phase ionization and ESI.

Brown Carbon from Photo-Oxidation of Glyoxal and SO2 in Aqueous Aerosol.

Aqueous-phase dark reactions during the co-oxidation of glyoxal and S(IV) were recently identified as a potential source of brown carbon (BrC). Here, we explore the effects of sunlight and oxidants on aqueous solutions of glyoxal and S(IV), and on aqueous aerosol exposed to glyoxal and SO2. We find that BrC is able to form in sunlit, bulk-phase, sulfite-containing solutions, albeit more slowly than in the dark. In more atmospherically relevant chamber experiments where suspended aqueous aerosol particles are exposed to gas-phase glyoxal and SO2, the formation of detectable amounts of BrC requires an OH radical source and occurs most rapidly after a cloud event. From these observations we infer that this photobrowning is caused by radical-initiated reactions as evaporation concentrates aqueous-phase reactants and aerosol viscosity increases. Positive-mode electrospray ionization mass spectrometric analysis of aerosol-phase products reveals a large number of CxHyOz oligomers that are reduced rather than oxidized (relative to glyoxal), with the degree of reduction increasing in the presence of OH radicals. This again suggests a radical-initiated redox mechanism where photolytically produced aqueous radical species trigger S(IV)-O2 auto-oxidation chain reactions, and glyoxal-S(IV) redox reactions especially if aerosol-phase O2 is depleted. This process may contribute to daytime BrC production and aqueous-phase sulfur oxidation in the atmosphere. The BrC produced, however, is about an order of magnitude less light-absorbing than wood smoke BrC at 365 nm.

63Cu(I) binding to human kidney 68Zn7-βα MT1A: determination of Cu(I)-thiolate cluster domain specificity from ESI-MS and room temperature phosphorescence spectroscopy.

Mammalian metallothioneins (MTs) are important proteins in Zn(II) and Cu(I) homeostasis with the Zn(II) and Cu(I) binding to the 20 cysteines in metal-thiolate clusters. Previous electrospray ionization (ESI) mass spectrometric (MS) analyses of Cu(I) binding to Zn7-MT were complicated by significant overlap of the natural abundance isotopic patterns for Zn(II) and Cu(I) leading to impossibly ambiguous stoichiometries. In this paper, isotopically pure 63Cu(I) and 68Zn(II) allowed determination of the specific stoichiometries in the 68Zn,63Cu-βα MT1A species formed following the stepwise addition of 63Cu(I) to 68Zn7-βα MT1A. These species were characterized by ESI-MS and room temperature emission spectroscopy. The key species that form and their emission band centres are Zn5Cu5-βα MT1A (λ = 684nm), Zn4Cu6-βα MT1A (λ = 750nm), Zn3Cu9-βα MT1A (λ = 750nm), Zn2Cu10-βα MT1A (λ = 750nm), and Zn1Cu14-βα MT1A (λ = 634nm). The specific domain stoichiometry of each species was determined by assessing the species forming following 63Cu(I) addition to the 68Zn3-β MT1A and 68Zn4-α MT1A domain fragments. The domain fragment emission suggests that Zn5Cu5-βα MT1A contains a Zn1Cu5-β cluster and the Zn4Cu6-βα MT1A, Zn3Cu9-βα MT1A, and Zn2Cu10-βα MT1A each contain a Cu6-β cluster. The species forming with >10mol. eq. of 63Cu(I) in βα-MT1A exhibit emission from the Cu6-β cluster and an α domain cluster. This high emission intensity is seen at the end of the titrations of 68Zn7-βα MT1A and the 68Zn4-α MT1A domain fragment suggesting that the initial presence of the Zn(II) results in clustered Cu(I) binding in the α domain.

Photolysis by UVA-Visible Light of TNT in Ethanolic, Aqueous-Ethanolic, and Aqueous Solutions According to Electrospray and Aerodynamic Thermal Breakup Droplet Ionization Mass Spectrometry.

The mechanism of photolytic degradation of 2-4-6-trinitrotoluene (TNT) by UVA-visible light (>320 nm) in ethanolic, aqueous-ethanolic, and aqueous solutions was investigated by electrospray and aerodynamic thermal breakup droplet ionization mass-spectrometric analyses. For the photolysis, a DRK-120 mercury-quartz lamp was used. Products of the photolysis reaction were compared with known products of TNT transformation in the environment. Because the photochemistry of some compounds in alcohols (in contrast to aqueous solutions) features a transfer of electrons from the solvent to the light-excited compound, we believe that the efficiency of photolysis (polymerization) of TNT in ethanol and aqueous-ethanolic solutions is based on this mechanism.

Kinetics, Products, and Brown Carbon Formation by Aqueous-Phase Reactions of Glycolaldehyde with Atmospheric Amines and Ammonium Sulfate.

Glycolaldehyde (GAld) is a C2 water-soluble aldehyde produced during the atmospheric oxidation of isoprene and many other species and is commonly found in cloudwater. Previous work has established that glycolaldehyde evaporates more readily from drying aerosol droplets containing ammonium sulfate (AS) than does glyoxal, methylglyoxal, or hydroxyacetone, which implies that it does not oligomerize as quickly as these other species. Here, we report NMR measurements of glycolaldehyde’s aqueous-phase reactions with AS, methylamine, and glycine. Reaction rate constants are smaller than those of respective glyoxal and methylglyoxal reactions in the pH range of 3–6. In follow-up cloud chamber experiments, deliquesced glycine and AS seed particles were found to take up glycolaldehyde and methylamine and form brown carbon. At very high relative humidity, these changes were more than 2 orders of magnitude faster than predicted by our bulk liquid NMR kinetics measurements, suggesting that reactions involving surface-active species at crowded air–water interfaces may play an important role. The high-resolution liquid chromatography–electrospray ionization–mass spectrometric analysis of filter extracts of unprocessed AS + GAld seed particles identified sugar-like C6 and C12 GAld oligomers, including proposed product 3-deoxyglucosone, with and without modification by reactions with ammonia to diimine and imidazole forms. Chamber exposure to methylamine gas, cloud processing, and simulated sunlight increased the incorporation of both ammonia and methylamine into oligomers. Many C4–C16 imidazole derivatives were detected in an extract of chamber-exposed aerosol along with a predominance of N-derivatized C6 and C12 glycolaldehyde oligomers, suggesting that GAld is capable of forming brown carbon SOA.

Retro Diels-Alder Fragmentation of Fulvene-Maleimide Bioconjugates for Mass Spectrometric Detection of Biomolecules.

Diels-Alder chemistry is a well-explored avenue for the synthesis of bioactive materials; however, its potential applications have recently expanded following the development of reactions that can be performed in buffered aqueous environments at low temperatures, including fulvene-maleimide [4 + 2] cycloadditions. In this study, we synthesized two novel amine-reactive fulvene linkers to demonstrate the application of this chemistry for generating mass spectrometry-cleavable labels ("mass tags"), which can be used for the labeling and detection of proteins. Successful conjugation of these linkers to maleimide-labeled peptides was observed at low temperatures in phosphate-buffered saline, allowing the non-destructive modification of proteins with such mass tags. The labile nature of fulvene-maleimide adducts in the gas phase also makes them suitable for both matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometric analysis. Unlike previous examples of MALDI mass tags, we show that fulvene-maleimide cycloaddition adducts fragment predictably upon gas-phase activation without the need for bulky photocleavable groups. Further exploration of this chemistry could therefore lead to new approaches for mass spectrometry-based bioassays.

SpheriCal® -ESI: A dendrimer-based nine-point calibration solution ranging from m/z 273 to 1716 for electrospray ionization mass spectrometry peptide analysis.

RationaleA calibration solution for mass spectrometry needs to cover the range of interest with intense and sufficiently narrowly spaced peaks. Limited options fulfilling this may lead to compromises between performance and ease of use. SpheriCal®‐ESI was designed to combine high calibration performance for electrospray ionization (ESI) mass spectrometric analysis of peptides in positive mode with quick and easy use.MethodsThe developed calibration solution was tested using three mass spectrometers: two ion traps and one tandem quadrupole. The m/z errors of SpheriCal®‐ESI itself and of a tryptic digest of cytochrome C were measured after calibration. The results were compared with those achieved with ESI Tuning Mix. The memory effects of the dendrimers, and contamination from Na+ in the calibration solution, were evaluated.ResultsSpheriCal®‐ESI showed good shelf life as powder and was quickly reconstituted for use. Achieving intense and stable signals was straightforward. The accuracies and precisions were as expected for the instruments. SpheriCal®‐ESI was more precise and at least as accurate as ESI Tuning Mix. The memory effects and Na+ contamination were found to be negligible in typical peptide solvents. In addition, the dendrimers showed predictable dissociations with product ions common to collision‐induced dissociation in both ion trap and tandem quadrupole mass spectrometers.ConclusionsSpheriCal®‐ESI provided easily accessible calibration by showing intense signals at low infusion rates and at source settings equal or similar to those used in peptide analysis. Nine calibration points in the range of interest gave precise and accurate results. Memory effects and contamination were negligible even without rinsing.

Overcharging Effect in Electrospray Ionization Mass Spectra of Daunomycin-Tuftsin Bioconjugates.

Peptide-based small molecule drug conjugates for targeted tumor therapy are currently in the focus of intensive research. Anthracyclines, like daunomycin, are commonly used anticancer drug molecules and are also often applied in peptide-drug conjugates. However, lability of the O-glycosidic bond during electrospray ionization mass spectrometric analysis hinders the analytical characterization of the constructs. “Overprotonation” can occur if daunomycin is linked to positively charged peptide carriers, like tuftsin derivatives. In these molecules, the high number of positive charges enhances the in-source fragmentation significantly, leading to complex mass spectra composed of mainly fragment ions. Therefore, we investigated different novel tuftsin-daunomycin conjugates to find an appropriate condition for mass spectrometric detection. Our results showed that shifting the charge states to lower charges helped to keep ions intact. In this way, a clear spectrum could be obtained containing intact protonated molecules only. Shifting of the protonation states to lower charges could be achieved with the use of appropriate neutral volatile buffers and with tuning the ion source parameters.

Sensitive analysis of trace macrolide antibiotics in complex food samples by ambient mass spectrometry with molecularly imprinted polymer-coated wooden tips

In this article, an ambient mass spectrometric method with molecularly imprinted polymer (MIP)-coated wooden tips was developed for sensitive analysis of trace macrolide antibiotics in complex food samples. A novel solid-phase microextraction (SPME) probe was prepared, via the modification of a layer MIP coating (with roxithromycin as template molecule) on the surface of wooden tips. The obtained MIP-coated wooden-tip SPME probe can be applied directly to enrich trace macrolide antibiotics from complex food samples, with enrichment factors of 244–1604, 72–370, and 12–82 folds for analysis of five investigated macrolide antibiotics in drinking water, honey, and milk samples, respectively. After extraction, a high voltage and some spray solvent were applied on the loaded SPME probe to desorb and ionize analytes enriched on the probe surface for electrospray ionization mass spectrometric (ESI-MS) analysis under ambient and open-air conditions. The method showed good linearity, with correlation coefficient values (r2) no less than 0.9904, and the calibration function was verified via Mandel's fitting test (p > 0.063). The limits of detection were in the range of 0.003–0.05, 1.1–5.1, and 1.9–15.8 ng/g for analysis of drinking water, honey, and milk samples, respectively. Recoveries of the five targeted macrolide antibiotics in honey and milk samples ranged from 73.4% to 98.1%, with the standard deviations no higher than 8.6%. As a result, MIP-coated wooden-tip ESI-MS method could be feasibly used as a sensitive method for determination of trace macrolide antibiotics in complex food samples.

Characterization of Cytochalasins and Steroids From the Ascomycete Daldinia concentrica and Their Cytotoxicity

One new cytochalasin daldinin (1), 2 known cytochalasins 2 and 3, along with 2 steroids 4 and 5, were characterized from the methanol extracts of the fruiting bodies of Daldinia concentrica. The structure of new compound 1 was elucidated using a combination of 1- and 2-dimensional nuclear magnetic resonance spectroscopic and high-resolution electrospray ionization mass spectrometric analyses. In addition, the isolated compounds were examined for their cytotoxicity against several tumor cell lines and the tested compounds demonstrated moderate-to-weak cytotoxicity.

Online investigation of reaction acceleration and reaction mechanism by thermospray ionization mass spectrometry

Thermospray ionization (TSI) technique was used for online monitoring of Borsche–Drechsel reaction, Diels-Alder reaction, and Combes reaction. The TSI was able to provide abundant thermal energy for the reactions solution and the droplets of reaction solution formed by thermospray online in very short time, therefore reaction acceleration effects in TSI condition could be observed, especially for the reaction with normally the need of high temperature in bulk-phase condition. Moreover, some short-lived intermediates could be captured by the TSI due to supersonic spray and the informative mass spectra were obtained to elucidate the reaction mechanism. In contrast to TSI, some reaction products were hard to obtain by electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectrometric analysis. Subsequently, the TSI was further improved by the introduction of a corona probe (i.e. corona-assisted TSI) to promote further reaction and enhance ionization efficiency. The TSI and corona-assisted TSI as flexible and versatile techniques may be potentially useful in reaction monitoring especially the reaction of high temperature.

On the [2+2] cycloaddition reaction of configurationally locked polyenes – An experimental and theoretical study

This paper provides experimental and theoretical study of reaction of [2 + 2] cycloaddition of substituted α–unsaturated isophorone dyes, involving high resolution electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) tandem mass spectrometric (MS/MS) analysis in solution and in gas–phase (GP) of substituted 3-[2-(X-substituted-phenyl)-vinyl]-5,5-dimethyl-cyclohex-2-enone and configurationally locked polyenes (CLP). The ab initio and density functional theoretical (DFT) examining provides information about molecular geometry, thermodynamics, kinetics and ionization potentials of sixty six isomers of dimeric dyes, including corresponding cis-anti-cis and cis-syn-cis head-to-tail and head-to-head forms. The comparative collision induced dissociation (CID) or collision activated MS and theoretical analyses carried out bring light into the mechanisms of competitive dimerization within the frame of 3-[2-(X-substituted-phenyl)-vinyl]-5,5-dimethyl-cyclohex-2-enone; molecular and environmental factors governing regioselectivity of reaction. The analyses involve both qualitative and quantitative kinetics and thermodynamics of experimental MS data along with corresponding theoretical examining of CLP dimers. As far as 3-[2-(X-substituted-phenyl)-vinyl]-5,5-dimethyl-cyclohex-2-enone and CLP dyes have already found an industrial scale application as non-linear optical materials (NLO) for THz wave generation and detection as well as pharmaceutics for treatment of and preventing of neurodegenerative diseases, this study has a strong transdisciplinary impact to many research fields as well as to still not well understood, but crucial to fields of organic synthesis and catalysis, molecular level fundamentals of chemical reactivity in gas– and condense phases. Following the latter lines of contributions of the work, we might hopefully expect that the prospective highlighted in this study should inspired further research effort devoted to correlative quantitative thermodynamic and kinetic CID mass spectrometric and quantum chemical analyses, which allow to improve the reaction effectiveness depending on the complexity of the wanted CLP scaffolds.

Electrokinetic Removal of Dodecyl Sulfate Micelles from Digested Protein Samples Prior to Electrospray-Ionization Mass Spectrometry.

In proteomics, dodecyl sulfate (DS-) as sodium salt is commonly used in protein solubilization prior to tryptic digestion, but the presence of the DS- hampers the electrospray ionization mass spectrometric (ESI-MS) analysis. The development of DS- depletion techniques is therefore important especially when dealing with small samples where there could be poor sensitivity due to sample loss or dilution during sample preparation. Here, we present a simple and fast electrokinetic removal method of DS- from small volumes of peptide and digested protein samples prior to ESI-MS. The selective removal was accomplished using an acidic extraction solution (ES) containing acetonitrile (ACN) inside a fused-silica capillary that was dipped into the sample. The use of acidic ES suppressed the electroosmotic flow; allowing the electrokinetic movement of DS- monomers and micelles into the capillary. The high amount of ACN present at the tip of the capillary served to collapse the micelles migrating into the capillary, thereby releasing the peptides that were bound to these micelles, facilitating peptide retention in the sample and efficient DS- removal. Increased % MS signal intensity (SI) restoration of the peptide was observed, while DS- removal was unaffected when the amount of ACN in the ES was increased. This is because of the micelle to solvent stacking mechanism (effective electrophoretic mobility reversal) working at high concentration of ACN for the improved recovery of the peptides. % MS SI restoration for the Z-Gly-Gly-Val and bradykinin peptides were 75-83% while % MS SI reduction of DS- was up to 99% under optimal conditions, that is, 40% ACN in the ES. Higher % peptide recoveries from digested protein samples were obtained using the proposed method compared to the conventional cold acetone precipitation method.

The application of multiple analyte adduct formation in the LC-MS3 analysis of valproic acid in human serum.

LC-MS using electrospray ionisation (negative ion mode) and low-energy collision-induced dissociation tandem mass spectrometric (CID-MS/MS) analysis, together with the multiple analyte adduct formation with the components of the mobile phase, were applied to analyse valproic acid in human serum with LC-MS3. The CID-fragmentation of the precursor analyte adduct [M+2CH3COONa-H]- was applied in the method validation (307.1/225.1/143.0). Chromatographic separation was performed with a Luna 5μm C18 (2) 100A, 150mm×2mm column and the elution with a mobile phase consisting of A (H2O/methanol=95/5, v/v) and B (H2O/methanol=3/97, v/v), both with 10mM ammonium acetate and 0.1% acetic acid. A binary flow pumping mode with a total flow rate of 0.400mL/min was used. The calculated limit of detection/quantification of the method calibrated in the range of 10-200μg/mL was 0.31/1.0μg/mL. The sample preparation based on protein precipitation with 1mL of H2O/methanol solution (3/97, v/v) with 10mM sodium acetate and 100mM acetic acid. On the basis of the experiments performed could be demonstrated, that multiple analyte adduct formation can be applied to generate MS3 quantitation of analytes with problematic fragmentation. The presented new strategy makes the analysis of small drugs, which do not produce any stable product ions at all, on the basis of LC-MS3 possible.

Hyaluronic Acid in Normal and Neoplastic Colorectal Tissue: Electrospray Ionization Mass Spectrometric and Fluor Metric Analysis

Aim: The aim of the study was to analyze the expression of hyaluronic acid (HA) and its type in human colorectal cancer (CRC) and non-neoplastic mucosa tissues. Methods : The study included 64 adult CRC patients, who met all the inclusion and exclusion criteria. Two tissue samples (neoplastic and non-neoplastic mucosa) from each patient's large intestine were collected and were subjected to electrospray ionization mass spectrometry (ESI-MS) and fluorimetric assays. Results: The analysis of colorectal neoplastic tissue and non-neoplastic mucosa by ESI-MS allowed the identification of HA and its oligosaccharide fragments. Low molecular weight (LMW), nonbiotinylated isoform of HA, and its fragments were identified in both neoplastic and non-neoplastic mucosa. The expression of HA was found to be slightly lower in tumor tissue (0.561 mg HA/g tissue) than in colorectal non-neoplastic mucosa (0.579 mg HA/g tissue), although the difference was not statistically significant ( P = 0.87). This result was probably influenced by the nonbiotinylated LMW-HA. For the specific group of patients that did not present lymph node metastasis, the average HA levels were higher in tumor tissue (0.674 mg HA/g tissue) than in non-neoplastic tissue (0.529 mg HA/g tissue), which managed to reach statistical significance ( P = 0.04). For the group of patients with lymph node involvement, no difference between tumor and nontumor tissue was observed. The HA expression among the tumor tissues within the variables of each clinicopathological parameters assessed failed to elicit any significant difference (location, P = 0.62; size, P = 0.13; lymph node invasion, P = 0.57; degree of cellular differentiation, P = 0.46; venous infiltration, P = 0.73; lymphatic infiltration, P = 0.36; neural infiltration, P = 0.28; tumor node metastasis classification, P = 0.15; and presence of synchronous metastases, P = 0.35; initial versus advanced stage, P = 0.37). Conclusions: The expression of HA was found to be slightly lower in tumor tissue than in colorectal non-neoplastic mucosa, although this difference was not statistically significant. This finding probably influenced the lower expression of HA in tumor tissue than in colorectal non-neoplastic mucosa. Compared to normal tissues, HA levels are significantly increased in the tumor tissues unless they exhibit lymph node metastasis. Otherwise, the expression of HA in tumor tissue did not correlated with the other clinicopathological parameters.

Spatial effects on electrospray ionization response

The position of the spray-head, the solvent, and a variety of additional instrumental parameters were independently adjusted during electrospray ionization mass spectrometric (ESI-MS) analysis of an equimolar mixture of two different ions. These parameters were found to have drastic effects on the distribution of signal intensity from one ion to another, and therefore the resulting usefulness of acquired spectra. The analytes studied were bis(triphenylphosphine)iminium (PPN) chloride and tetramethylammonium (TMA) chloride, two chemically distinct ions. The use of these two ions in a test solution yielded information regarding ESI probe spatial effects for two very different analytes, while probing the issue of sampling efficiency. Each experimental parameter was individually adjusted prior to rastering the spray head across the operational plane in order to observe how adjustment to a particular parameter affects analyte signal in relation to the distance from the MS aperture. Following acquisition, the intensities of both ions were plotted as ion contour maps demonstrating the intensity change with respect to capillary position in relation to the mass spectrometer aperture. The sharp contrast in ion intensity, and even differential ion activity, with relatively minor instrument changes (such as temperature programming, gas flow rates and solvent choice) clearly demonstrates the importance of finding the “sweet spot” for the ESI spray head, especially when signal intensity and a quality analysis are key.

Identification of proteins interacting with protein kinase C-δ in hyperthermia-induced apoptosis and thermotolerance of Tca8113 cells.

The purpose of the present study was to investigate the differential proteins that interact with protein kinase C‑δ (PKC‑δ) in hyperthermia‑induced apoptosis as well as thermotolerance in Tca8113 cells, and furthermore, to investigate the mechanisms of these processes in tumor cells. Activation of PKC‑δ was previously indicated to be involved in the heat sensitivity and thermal resistance of tongue squamous carcinoma cells. Tca8113 cell apoptosis was induced by incubation at 43˚C for 80 min and the thermotolerant Tca8113 cells (TT‑Tca8113) were generated through a gradient temperature‑elevating method. The apoptotic rate of the cells was determined by flow cytometry, while cleavage and activation of PKC‑δ were analyzed by western blot analysis. The proteins that interacted with PKC‑δ in the Tca8113 and TT‑Tca8113 cells were identified by co‑immunoprecipitation coupled with mass spectrometry. Co‑immunoprecipitation analysis followed by electrospray ionization mass spectrometric analysis were utilized to identify the pro‑ and anti‑apoptotic proteins that interacted with PKC‑δ. Significant cell apoptosis was observed in Tca8113 cells following hyperthermia, and the apoptotic rate was significantly higher than that in the control group (P<0.05). Marked PKC‑δ cleavage fragmentation was also identified. By contrast, the apoptotic rate of the TT‑Tca8113 cells was not significantly increased following hyperthermia and no PKC‑δ cleavage fragmentation was observed. Among the proteins interacting with PKC‑δ, 39 were found to be involved in the promotion of apoptosis and 16 in the inhibition of apoptosis of Tca8113 cells; these proteins were known to be involved in the regulation of cell proliferation, apoptosis, transcription and intracellular protein transport. The results of the present study provided evidence that PKC‑δ is a crucial factor in the heat sensitivity and thermal resistance of tongue squamous carcinoma cells and elucidated the underlying molecular basis, which may aid in the improvement of hyperthermic cancer treatments.

Development of amino acid derivatization reagents for liquid chromatography electrospray ionization mass spectrometric analysis and ionization efficiency measurements

Derivatization is one of the most common ways for improving chromatographic separation and sensitivity for LC-ESI-MS analysis. The aim of this work was to design new derivatization reagents for LC-ESI-MS analysis of amino acids which would (1) provide good reversed phase chromatographic separation, (2) most importantly, provide low detection limits, (3) be easily synthesized, (4) produce derivatives which are less susceptible to matrix influences and (5) have convenient derivatization procedure with stable derivatives suitable for automatization. In the current work two new LC-ESI-MS compatible derivatization reagents have been designed and synthesized, dibenzyl ethoxymethylene malonate (DBEMM) and benzyl ethyl ethoxymethylene malonate (EBEMM). The DBEMM meets all the goals set with instrumental detection limits as low as 1 femtomole for amino acids and 40 attomole for selenoamino acids.

Cellulose Conversion to Sugar Alcohol by Solution Plasma Processing

ABSTRACTCellulose was selectively converted to sugar alcohols (sorbitol and mannitol) over a supported-metal catalyst ruthenium on carbon (Ru/C) by the application of plasma in cellulose aqueous suspension. Generally, conversion of cellulose to sugar alcohol should be done under H2 pressure and high temperature. The goal of using solution plasma process (SPP) in this study is to initiate “self-hydrogenation” by reactive hydrogen species generated from the plasma due to dissociation of water medium. The sugar alcohols were produced at room temperature and atmospheric pressure. Electrospray ionization mass spectrometric analysis indicates that the SPP is a potent tool to promote the conversion of cellulose to sugar alcohols.

Lipase ligands in Nelumbo nucifera leaves and study of their binding mechanism.

Lotus (Nelumbo nucifera) leaves have been widely used in weight-loss foods to prevent obesity in China. In this work, a facile procedure based on ligand fishing was developed to isolate and identify lipase inhibitors present in lotus leaves. Highly stable and active lipase-Fe3O4 superparamagnetic nanoparticle conjugates (LMNPs) were prepared and used as baits. Two flavonoids in lotus leaf extract were found to bind to the baits and were identified as quercetin-3-O-β-d-arabinopyranosyl-(1→2)- β-d-galactopyranoside (1) and quercetin-3-O-β-d-glucuronide (4) based on electrospray ionization-mass spectrometric analyses. Their 50% inhibitory concentrations on lipase (IC50) were 52.9 ± 3.2 and 17.1 ± 1.5 μg/mL, respectively. In addition, they were found to significantly quench the fluorescence of lipase, suggesting their strong affinities with this enzyme, which was further evidenced by molecular docking. Ligand fishing based on LMNPs shows great power for fast screening and identification of lipase inhibitors present in edible and medicinal plants.