Molecular Weight Information Research Articles

MS-Based Analytical Techniques: Advances in Spray-Based Methods and EI-LC-MS Applications.

Mass spectrometry is the most powerful technique for the detection and identification of organic compounds. It can provide molecular weight information and a wealth of structural details that give a unique fingerprint for each analyte. Due to these characteristics, mass spectrometry-based analytical methods are showing an increasing interest in the scientific community, especially in food safety, environmental, and forensic investigation areas where the simultaneous detection of targeted and nontargeted compounds represents a key factor. In addition, safety risks can be identified at the early stage through online and real-time analytical methodologies. In this context, several efforts have been made to achieve analytical instrumentation able to perform real-time analysis in the native environment of samples and to generate highly informative spectra. This review article provides a survey of some instrumental innovations and their applications with particular attention to spray-based MS methods and food analysis issues. The survey will attempt to cover the state of the art from 2012 up to 2017.

Study on Chemical Profile and Neuroprotective Activity of Myrica rubra Leaf Extract.

The chemical profile of Myrica rubra (a native species in China) leaf extract was investigated by UPLC-PDA-HRMS, and the neuroprotective activity of two characteristic constituents, myricanol and myricetrin, was evaluated with N2a cells using H2O2-inducedoxidative challenge through a series of methods, e.g., MTT assay, ROS assay and [Ca2+]i assay. Among the 188 constituents detected in the extract of Myrica rubra leaf, 116 were identified definitely or tentatively by the comprehensive utilization of precise molecular weight and abundant multistage fragmentation information obtained by quadrupole orbitrap mass spectrometry. In addition, 14 potential new compounds were reported for the first time. This work established an example for the research of microconstituents in a complex analyte and revealed that suppression of H2O2-induced cytotoxicity in N2a cells was achieved by the pretreatment with myricanol. The evidence suggested myricanol may potentially serve as a remedy for prevention and therapy of neurodegenerative diseases induced by oxidative stress.

Triacylglycerol compositions of sunflower, corn and soybean oils examined with supercritical CO2 ultra-performance convergence chromatography combined with quadrupole time-of-flight mass spectrometry

A supercritical CO2 ultra-performance convergence chromatography (UPC2) system was utilized with a quadrupole time-of-flight mass spectrometry (Q-TOF MS) to examine the triacylglycerol compositions of sunflower, corn and soybean oils. UPC2 provided an excellent resolution and separation for the triacylglycerols, while the high performance Q-TOF MS system was able to provide the molecular weight and fragment ions information for triacylglycerol compound characterization. A total of 33 triacylglycerols were identified based on their elementary compositions and MS2 fragment ion profiles, and their levels in the three oils were estimated. The combination of UPC2 and Q-TOF MS may determine triacylglycerol compositions for oils and fats, and provide sn-position information for fatty acids, which may be important for food nutritional value and stability.

Study on glyco-modification of endostatin-derived synthetic peptide endostatin2 (ES2) by soluble chitooligosaccharide

Soluble O-(2-hydroxyl)propyl-3-trimethyl ammonium chitooligosaccharide chloride (HTCOSC) was covalently conjugated to the 11-amino-acid peptide derived from amino terminus of endostatin (endostatin2, ES2, IVRRADRAAVP) to overcome its poor stability, low cell affinity and instable activity. Nuclear magnetic resonance spectroscopy and mass spectrometry was used to study the structure and molecular weight information. The anti-angiogenic activities were evaluated using cell counting Kit-8 assay, flow cytometry assay, wounding migration assay, transwell migration assay, chicken chorioallantoic membrane (CAM) assay and zebra fish angiogenesis assay. In contrast with ES2, the novel carbohydrate-polymer HTCOSC-ES2 displayed improved heat stability, higher cell affinity, better inhibition on endothelial cell proliferation, tube formation, 2-dimensional and 3-dimensional migration in vitro. According to the evaluation in CAM and zebra fish, HTCOSC-ES2 also displayed better anti-angiogenic activity than ES2 in vivo. These results indicate that HTCOSC has good properties as potential candidate for protein/peptide modifier and HTCOSC-ES2 has good potential in angiogenesis related diseases treatment.

Mass spectral studies on vinylic degradation products of sulfur mustards under gas chromatography/mass spectrometry conditions.

Sulfur mustards are a class of vesicant chemical warfare agents that rapidly degrade in environmental samples. The most feasible degradation products of sulfur mustards are chloroethyl vinylic compounds and divinylic compounds, which are formed by the elimination of one and two HCl molecules from sulfur mustards, respectively. The detection and characterization of these degradation products in environmental samples are an important proof for the verification of sulfur mustard usage. In this study, we synthesized a set of sulfur mustard degradation products, i.e., divinylic compounds (1-7) and chloroethyl vinylic compounds (8-14), and characterized using gas chromatography/mass spectrometry (GC/MS) under electron ionization (EI) and chemical ionization (CI) (methane) conditions. The EI mass spectra of the studied compounds mainly included the fragment ions that resulted from homolytic cleavages with or without hydrogen migrations. The divinylic compounds (1-7) showed [M-SH](+) ions, whereas the chloroethylvinyl compounds (8-14) showed [M-Cl](+) and [M-CH2CH2Cl](+) ions. Methane/CI mass spectra showed [M+H](+) ions and provided molecular weight information. The GC retention index (RI) values were also calculated for the studied compounds. The EI and CI mass spectral data together with RI values are extremely useful for off-site analysis for the verification of the chemical weapons convention and also to participate in official Organization for the Prohibition of Chemical Weapons proficiency tests.

Efficient fabrication of polymer nanoparticles via sonogashira cross‐linking of linear polymers in dilute solution

ABSTRACTThe synthesis of single‐chain nanoparticles by palladium‐catalyzed Sonogashira coupling between a terminal alkyne and a di‐halo aryl cross‐linker is reported. Statistical copolymers with trimethylsilyl protected alkyne groups pendent to the linear methacrylate back bones were synthesized using reversible addition‐fragmentation chain transfer polymerization post polymerization de‐protection providing terminal alkyne functionalized linear polymer chains. These linear polymer chains were intramolecularly cross‐linked via bifunctional cross‐linkers. The resulting well‐defined covalently bonded nanoparticles were characterized via triple‐detection size exclusion chromatography where MALS detector provided molecular weight information and viscometric detection characterizes particle size and conformations. The particle size could be readily tuned through polymer molecular weight and by degree of cross‐linking. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 209–217

Fabrication and Characterization of Polysaccharide Ion Gels with Ionic Liquids and Their Further Conversion into Value-Added Sustainable Materials

A review of the fabrication of polysaccharide ion gels with ionic liquids is presented. From various polysaccharides, the corresponding ion gels were fabricated through the dissolution with ionic liquids. As ionic liquids, in the most cases, 1-butyl-3-methylimidazolium chloride has been used, whereas 1-allyl-3methylimidazolium acetate was specifically used for chitin. The resulting ion gels have been characterized by suitable analytical measurements. Characterization of a pregel state by viscoelastic measurement provided the molecular weight information. Furthermore, the polysaccharide ion gels have been converted into value-added sustainable materials by appropriate procedures, such as exchange with other disperse media and regeneration.

Phylogenetic Tree Generation using Different Scoring Methods

Data Mining is a branch of knowledge discovery in the field of research and development. The biological data is available in different formats and is comparatively more complex. Knowledge discovery from these large and complex databases is the key problem of this era. Data mining and machine learning techniques are needed which can scale to the size of the problems and can be customized to the application of biology. Hierarchical Clustering is the one of the main techniques for data mining. Phylogeny is the evolutionary history for a set of evolutionary related species. One approach on determining the evolutionary histories of a dataset are scoring based methods. There are number of different distance based methods of which two are details with here: the UPGMA (Unweighted Pair Group Method using Arithmetic average) and Neighbor Joining. A method for construction of distance based phylogenetic tree using hierarchical clustering is proposed and implemented on different rice varieties. The sequences are downloaded from NCBI databank. Evolutionary distances are calculated using jukes cantor distance method. Multiple sequence alignment is applied on different datasets. Trees are constructed for different datasets from available data using both the distance based methods and pruning technique. SNAP calculates synonymous and nonsynonymous substitution rates based on a set of codon aligned nucleotide sequences. The DNA Multiple sequences to calculate the GC content of eukaryotes, molecular weight, melting temperature and tree information. Extractions of closely related varieties are performed by applying threshold condition. Then, final tree is constructed using these closely related rice varieties.

Preparation, chemical, and thermal characterization of nylon 4/6 copolymers by anionic ring opening polymerization of 2-Pyrrolidone and ε-Caprolactam

Nylon 4/6 copolymers based on 2-pyrrolidone (C4) and e-caprolactam (C6) were synthesized and characterized as part of ongoing efforts to develop thermally stable, melt-processable 2-pyrrolidone (C4) based Nylons. Copolymers of various compositions were synthesized at between 50 and 100 °C via the anionic ring opening polymerization of C4 and C6 using a potassium tert-butoxide catalyst and a benzoyl chloride initiator. The polymers were characterized by NMR spectroscopy, DSC, TGA, GPC, intrinsic viscosity measurements, and X-ray scattering (SAXS and WAXS). Their chemical compositions and sequence distributions were obtained by 1H- and 13C-NMR spectroscopies, respectively. X-ray scattering was used to investigate the lamellar morphologies and the crystal structures of solvent cast films of the copolymers. WAXS revealed the presence of α-phase crystals in the copolymers. TGA data coupled with molecular weight and sequence distribution information indicated that the polymers’ thermal stability depended on both their chemical composition and their sequence distribution.

Screening of seized emerging drugs by ultra-high performance liquid chromatography with photodiode array ultraviolet and mass spectrometric detection

The use of psychoactive “designer drugs” has increased rapidly due to their varying and sometimes ambiguous legal status and their ready access via the Internet and at local “headshops.” A quick screening method for samples containing these substances, using ultra-high performance liquid chromatography with photodiode array UV and mass spectrometric detection (UHPLC-PDA/UV–MS), is presented. The method enables the screening of a variety of samples containing emerging/reemerging drugs, including β-keto phenethylamines (cathinone derivatives), synthetic cannabinoids/cannabimimetics, and phenethylamine derivatives. The use of dual detectors not only provides molecular weight information but also differentiates the drugs by their categories and in some cases even their sub-categories. Moreover, ring positional isomers of cathinone and phenethylamine derivatives can be easily differentiated by their retention times and UV spectra.

Molecular structures of the constituents of pyrene pitches

The main dimeric species present in pyrene pitches produced via both catalytic (with AlCl3) and thermal polymerization of pure pyrene have been identified. Characterization of these species was performed by first isolating dimer-rich pitch fractions either by semi-continuous supercritical extraction (SCE) with N-methyl pyrrolidine–toluene mixtures or by solvent extraction with dichloromethane. These fractions were then separated into their individual species via reverse-phase high performance liquid chromatography (RP-HPLC). Molecular weight and structure information of the eluted species was obtained by a combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI) and UV–vis spectroscopy. By following this strategy, two alternant (i.e., six-membered ring) pyrene dimer isomers, dinaphtho[2,1,8,7-defg:2′,1′,8′,7′-opqr]pentacene and dinaphtho[2,1,8,7-defg:2′,1′,8′,7′-ijkl]pentaphene, were found in both the catalytically and thermally produced pitches. Non-alternant (i.e., containing a connecting five-membered ring) pyrene dimer isomers (cyclopenta[1,2,3-cd:4,5-e′]dipyrene and cyclopenta[1,2-a:3,4,5-c′d′]dipyrene) were also found in both pitches. Interestingly, small amounts of methylated monomeric and oligomeric species (e.g., methyl and dimethyl pyrene; methyl and dimethyl pyrene dimer, etc.) were detected in the catalytically produced pitch, but were completely absent in both the starting monomer and in the thermally produced pitch. These results indicate that the main difference between the two polymerization methods are the AlCl3-induced methylation reactions that occur simultaneously to dehydrogenative condensation reactions.

Identification of constituents in Suanzaoren tang by LC-Q-TOF-MS and LC-IT-MS

LC-Q-TOF-MS and LC-IT-MS in positive and negative ion mode were applied to simultaneously characterize the constituents in Suanzaoren tang. Analysis was performed on an Agilent Zorbax SB-C18, Rapid Resolution HT column(4.6 mmx 50 mm, 1. 8 micro m) with gradient elution of acetonitrile(A) -aqueous solution containing 0. 05% formic acid(B) at a flow rate of 0. 6 mL min(-1) and the column temperature was 30 degreesC. By comparing MS fragmentation, accurate molecular weight, literature date and standard compounds information, a total of48 compounds were successfully identified or speculated. The origins of these compounds were assigned to the corresponding Chinese medicine. Thirty-one compounds were reported in Suanzaoren tang for the first time. LC-Q-TOF-MS combined with LC-IT-MS is a simple and rapid tool for the identification of constituents of Suanzaoren tang, and the results could provide evidence for the research on quality combined and effective constituents of Suanzaoren tang.

Fast fixing and comprehensive identification to help improve real-time ligands discovery based on formaldehyde crosslinking, immunoprecipitation and SDS-PAGE separation

BackgroundFast Fixation is necessary to study real-time protein-protein interactions under physiological conditions. Fast formaldehyde cross-linking can fix transient and weak protein interactions, thereby reducing the number of false negatives but producing great complexity. To reduce this complexity, immunoaffinity purification can Fish out complexes that include particular target proteins, but affinity-based co-purification has a limited capacity to eliminate nonspecific binding to beads and/or antibodies. To Filter out these complexes, SDS-PAGE is used to disrupt non-covalent bonds, thereby eliminating uncross-linked complexes and simultaneously providing molecular weight information for identification.ResultsWe described a 4 F strategy to help improve real-time ligands discovery based on formaldehyde crosslinking, immunoprecipitation and SDS-PAGE separation: Fast Fix, Fish, and Filter, using albumin interactome as an example. The use of gel excision without staining makes this strategy comprehensive and sensitive. The target protein must be identified in the same slice as its ligands. The ligands must be identified in slices for the experimental group but not in the corresponding control slices. Only proteins that appear in the range of molecular weights equal to or greater than the sum of the proteins’ theoretical molecular weights, together with the target, are considered ligands. In this study, 5 s of cross-linking with 10% formaldehyde was achieved in human blood. The use of this strategy identified 35 ligands for albumin. Comparison with four major previous studies of the albuminome revealed that 68.57% of the 35 ligands identified in our study were identified in these other studies.ConclusionsFast cross-linking was achieved. The 4 F strategy can be used to identify real-time in situ interactions without prior intervention and to comprehensively identify ligands of particular target proteins with fewer false positives.

Molecular weight sensing properties of ionic liquid-polymer composite films: theory and experiment

Simultaneous measurements of two output signals from an ionic liquid–polymer composite-based QCM sensor provide molecular weight information on vapor analytes.

Qualitative Gas Chromatography–Mass Spectrometry Analyses Using Amines as Chemical Ionization Reagent Gases

Ammonia is a very useful chemical ionization (CI) reagent gas for the qualitative analyses of compounds by positive ion gas chromatography-mass spectrometry (GCMS). The gas is readily available, inexpensive, and leaves no carbon contamination in the MS source. Compounds of interest to our laboratory typically yield abundant protonated or ammoniated species, which are indicative of a compound's molecular weight. Nevertheless, some labile compounds fragment extensively by substitution and elimination reactions and yield no molecular weight information. In these cases, a CI reagent gas mixture of methylamine in methane prepared dynamically was found to be very useful in obtaining molecular weight data. Likewise, deuterated ammonia and deuterated methylamine are useful CI reagent gases for determining the exchangeable protons in organic compounds. Deuterated methylamine CI reagent gas is conveniently prepared by dynamically mixing small amounts of methylamine with excess deuterated ammonia.

Formation of nitro-PAHs from the heterogeneous reaction of ambient particle-bound PAHs with N2O5/NO3/NO2.

Reactions of ambient particles collected from four sites within the Los Angeles, CA air basin and Beijing, China with a mixture of N2O5, NO2, and NO3 radicals were studied in an environmental chamber at ambient pressure and temperature. Exposures in the chamber system resulted in the degradation of particle-bound PAHs and formation of molecular weight (mw) 247 nitropyrenes (NPYs) and nitrofluoranthenes (NFLs), mw 273 nitrotriphenylenes (NTPs), nitrobenz[a]anthracenes (NBaAs), nitrochrysene (NCHR), and mw 297 nitrobenzo[a]pyrene (NBaP). The distinct isomer distributions resulting from exposure of filter-adsorbed deuterated fluoranthene to N2O5/NO3/NO2 and that collected from the chamber gas-phase suggest that formation of NFLs in ambient particles did not occur by NO3 radical-initiated reaction but from reaction of N2O5, presumably subsequent to its surface adsorption. Accordingly, isomers known to result from gas-phase radical-initiated reactions of parent PAHs, such as 2-NFL and 2- and 4-NPY, were not enhanced from the exposure of ambient particulate matter to N2O5/NO3/NO2. The reactivity of ambient particles toward nitration by N2O5/NO3/NO2, defined by relative 1-NPY formation, varied significantly, with the relative amounts of freshly emitted particles versus aged particles (particles that had undergone atmospheric chemical processing) affecting the reactivity of particle-bound PAHs toward heterogeneous nitration. Analyses of unexposed ambient samples suggested that, in nighttime samples where NO3 radical-initiated chemistry had occurred, heterogeneous formation of 1-NPY on ambient particles may have contributed to the ambient 1-NPY concentrations at downwind receptor sites. These results, together with observations that 2-NFL is consistently the dominant particle-bound nitro-PAH measured in ambient atmospheres, suggest that for PAHs that exist in both the gas- and particle-phase, the heterogeneous formation of particle-bound nitro-PAHs is a minor formation route compared to gas-phase formation.

Coupling Isoelectric Focusing Gel Electrophoresis to Mass Spectrometry by Electrostatic Spray Ionization

Gel electrophoresis has been used for decades as a high-resolution separation technique for proteins and protein isomers but has been limited in the coupling with MS because of low throughput and poor automaticity compared with LC-MS. In this work, we have developed an ambient ionization strategy, electrostatic spray ionization, for in situ ionization of proteins or peptides inside a surfactant-free polyacrylamide gel. The samples can be first separated by isoelectric focusing in a gel and then quickly in situ detected by scanning the gel with the electrostatic spray ionization mass spectrometry. With this strategy, nanograms of proteins or peptides inside a band are enough to be ionized for MS detection. This method for protein/peptide spots visualization is sensitive, providing sample molecular weight information while avoiding spot staining and chemical extraction procedures that can introduce contaminants and sample loss. Proof-of-principle results have demonstrated that the electrostatic spray ionization can produce sample ions from a complex background, and with a spatial resolution matching the isoelectric focusing, it is therefore a good choice to couple directly isoelectric focusing gel electrophoresis with mass spectrometry.

Fast Fix, Fish and Filter, 4Facts strategy to identify real time protein‐protein interactions in situ with few false positives

To study dynamic protein‐protein interactions in physiological state, Fast Fix is essential. Formaldehyde cross‐linking can fix the transient and weak protein interactions, but produces great complexity. To reduce the complexity, immunoaffinity purification can Fish complexes of the target protein, but co‐purification by affinity has limited ability in eliminating the nonspecific interactions of beads and antibodies. To Filter the complexes, SDS‐PAGE was used to disrupt non‐covalent bonds thereby eliminated uncross‐linked complexes and at the same time provided molecular weight information for quality control of identified complexes. Only proteins appeared in ranges with molecular weight higher than the sum of their theoretic molecular weights were considered ligands in situ. This strategy tried to combine the advantages of above methods. Proteins which have post‐translational modification can also show up in gels at much higher than that of potential complexes. So the corresponding control was used to eliminate this possibility. In the present study, human blood was added to10% formaldehyde to cross‐link with ligands for five seconds, complexes of albumin and transferrin were purified using their antibodies respectively, then separated in SDS‐PAGE and analyzed by LC‐MS/MS. Proteins identified were further filtered by molecular weight information. Application of this strategy in human blood generated 33 and 24 ligands for albumin and transferrin respectively. Comparing with three previous major albuminome studies, 30% of 33 ligands in our study were also identified in other studies. But only around 15% of their ligands in each of three studies were identified in our study. This 4facts strategy can be used to reveal real time transient and weak protein interactions in situ with less false positives.

Effect of hydrogen peroxide on the UCST behavior of PMMA in the modified dispersion polymerization

The effect of hydrogen peroxide on the formation of molecular weight of poly(methyl methacrylate) (PMMA) in the modified dispersion polymerization using a co-solvent of methanol/water and methanol/hydrogen peroxide aqueous solution was studied. The variables included the molecular weight upon the concentration of initiator and hydrogen peroxide, solubility upon molecular weight and temperature, particle size upon cooling rate, and reversible temperature responsive behavior upon thermal history. The relationship between the temperature and PMMA particle size showed reversible temperature-responsive behavior upon the heating and cooling processes. As a result, hydrogen peroxide was confirmed to act as a co-initiator in reducing the molecular weight of PMMA, a good co-solvent with methanol by improving the solubility and inducing the upper critical solution temperature behavior, and a stabilizer in forming stable particles upon cooling. Open image in new window

Molecular Weight Distributions of Polymer Solutions: Combination of Field Flow Fractionation (FFF) and Analytical Ultracentrifugation (AUC)

Molecular weight, distribution, as well as other molecular characteristics are important drivers in determining the potential behaviors and hence applications of polymeric materials. Out of different methods available for the determination of molecular weight and its distribution, field flow fractionation (FFF) provides absolute molecular weight values and accurate molecular weight distributions. Analytical ultracentrifugation (AUC), on the other hand, relies on the exact density of the polymer materials in solution to determine the accurate molecular weight and its distribution and in the absence of knowledge of exact density, AUC is less accurate than the FFF method. However, combination of the two methods can be achieved to gain insights into the other molecular characteristics of swollen polymer chains. One such example is the determination of the exact density of the swollen polymer chains by the incorporation of the molecular weight information from FFF into AUC analysis. Based on the comparison of the optimized polymer chain density with the bulk density, it was observed that the polyacrylic acid and polyacrylamide chains were swollen in the range of 27 to 29%. Moreover, the FFF and AUC can also complement each other in enhancing the range of characterization possible with the two methods when used separately.