Characterization of styrene/methyl methacrylate/n-butyl acrylate terpolymer with Kendrick mass defect analysis in electrospray ionization-ion mobility spectrometry-mass spectrometry.

RATIONALE: Synthesis of copolymer is one of the major approaches to establish sophisticated polymers. In copolymer analysis in mass spectrometry (MS), an increase in the number of monomer unit species and/or the polymer molecular weight results in complex mass spectra, and a method is required to solve this problem. METHODS: In this study, electrospray ionization-ion mobility spectrometry-mass spectrometry was employed to analyze styrene/methyl methacrylate/n-butyl acrylate (St/MMA/nBA) terpolymers via Kendrick mass defect (KMD) analysis. An expanded Fourier transform-based noise reduction method for the copolymer was developed to improve the decrease in the signal/noise ratio observed in the higher m/z region. RESULTS: Low-mass terpolymers (0.7 kDa) were identified by comparing the observed and theoretical results using a two-dimensional KMD plot. For the 1.5 kDa terpolymer, the signal overlap, of which KMD value was not matched with the theoretical one, was interpreted by the shift from the theoretical value in the KMD plot. For the 3.0 kDa terpolymers, the compositional candidates were determined by the prediction based on the compositional information of low-mass terpolymers previously analyzed. The 4.5 kDa terpolymer was interpreted after the expanded noise filtering. CONCLUSIONS: The terpolymers, whose molecular weight was up to 4.5 kDa, were successfully characterized at a molecular level. The dependency of the St/MMA/nBA composition on molecular weight was observed; that is, the nBA content decreased with an increase in the molecular weight.

End group analysis of poly(methylmethacrylate)s using the most abundant peak in electrospray ionization-ion mobility spectrometry-tandem mass spectrometry and Fourier transform-based noise filtering.

RATIONALE: We recently developed the characterization method for synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization-ion mobility spectrometry-tandem mass spectrometry, in which the m/z value of the most abundant peak was used for characterization. However, the identification of the most abundant peak from the isotopic peaks was often difficult due to the background noise. METHODS: Here, we employed a noise reduction method using Fourier transform (FT) filtering. In the power spectrum obtained using FT of the mass spectrum of the multiple charged analytes, the significant signals in the low-frequency region and at frequency z are observed for the analytes of z charges. When the signals in both regions were used for inversed FT (i.e., the signals in other regions were zero padded), a noise-filtered mass spectrum was obtained. RESULTS: In the analysis of poly(methylmethacrylate)s weighing 13-17 kDa, mass spectra without noise filtering with relatively high-intensity noise (than signal) were complicated to identify the most abundant peak. On the contrary, the most abundant peak was clearly identified from the mass spectra after FT-based noise filtering, and end group composition was estimated successfully. CONCLUSIONS: The proposed FT-based noise filtering for the mass spectrum is effective to characterize multiply charged synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization-ion mobility spectrometry-tandem mass spectrometry.

Characterizing chain-end structures formed during initiation reactions of radical polymerization for MMA-St-BA terpolymer using pyrolysis-gas chromatography/atmospheric pressure chemical ionization high-resolution time-of-flight mass spectrometry.

RATIONALE: Analyzing polymer end groups using pyrolysis (Py) gas chromatography/mass spectrometry (GC/MS) in multi-component polymer samples is not an easy task because of the insufficient sensitivity, selectivity, and mass resolution of conventional Py-GC/MS systems. METHODS: A new Py-GC/MS system using an atmospheric pressure chemical ionization (APCI) source combined with high-resolution time-of-flight mass spectrometry (TOFMS) was used for end-group analysis of a methyl methacrylate (MMA)-styrene (St)-butyl acrylate (BA) terpolymer (P (MMA-St-BA)), which was radically polymerized using 2,2'-azobis(2-methylbutyronitrile) (AMBN) as an initiator. RESULTS: Five possible pyrolyzates, comprising an AMBN fragment and a monomer unit, formed during the initiation reactions from one of the three types of end groups, were selectively detected and exclusively identified in their respective extracted ion chromatograms for molecule-related ions, such as M+ and [M + H]+ , with a narrow mass window of ±2 milli m/z units. CONCLUSIONS: It was demonstrated that Py-APCI-TOFMS is a powerful technique to characterize in detail the complex end groups in multi-component polymer samples, because of the soft ionization nature of APCI and the high mass resolution of TOFMS.

Frequency division multiplex HPLC-MS for simultaneous analyses.

Multiplex high-performance liquid chromatograph-mass spectrometry (HPLC-MS), in which multiple HPLCs and one MS are hyphenated, is an approach for high throughput analysis in HPLC-MS. A general multiplex HPLC-MS method employs a column-switching technology, and only one HPLC is connected to one MS at a time. In the present study, we propose a novel multiplex HPLC-MS system for simultaneous HPLC-MS analyses. In this study, multiple HPLCs are hyphenated with one MS without a column-switching mechanism, and a mixed-chromatogram is observed by the MS. Here, we employ a frequency division multiplexing (FDM) technique used in communication engineering to extract any chromatogram from the mixed-chromatogram. When a modulator (chopper or ion-gate type) is set between each ion source and the MS, each modulator blocks each sample stream with an individual frequency. In theory, each chromatogram can be extracted from the mixed-chromatogram via a signal processing based on a Fourier transform (FT), frequency-based signal extraction, and reversed FT. In the actual experiment, two HPLCs are hyphenated with one MS (2HPLC-1MS). The use of chopper type modulators leads to the extraction and restoration of each chromatogram from the mixed-chromatogram. However, each restored-chromatogram involves signal interference. On the other hand, the ion-gate modulation system successfully resulted in restored-chromatograms without interference. The potential of the novel multiplex HPLC-MS system based on FDM is confirmed with respect to the simultaneous and continuous analyses of plural samples.

Electrospray ionization-ion mobility spectrometry-high resolution tandem mass spectrometry with collision-induced charge stripping for the analysis of highly multiply charged intact polymers.

Polymers with large molecular weight are difficult to interpret using electrospray ionization-mass spectrometry (ESI-MS) due to the generation of various highly multiply charged analytes. Although ESI-ion mobility spectrometry (IMS)-MS is effective in reducing the complexity of the mass spectrum, this approach is insufficient for analyzing highly multiply charged polymers. In this study, we propose a method combining tandem mass spectrometry (quadrupole and high-resolution time-of-flight MS, QMS/TOFMS), IMS, and collision-induced charge stripping (CICS) for analyzing large intact polymers (∼40 kDa), which are highly multiply charged. The number of charges can be estimated from a Fourier transform power spectrum of a mass spectrum when the charge number is less than approximately 20. Interpretations of the spectra of poly(ethylene oxide)s (PEOs) weighing 20 kDa, poly(methyl methacrylate)s weighing 22 kDa, and methoxy-PEO-maleimide weighing 40 kDa were successfully demonstrated with isotope level and polymerization degree level separations, respectively. In the proposed method, a mixture can be analyzed for relatively small (a few kDa) and large (a few tens of kDa) polymers simultaneously without any sample pretreatment.

Hydrogen Bonding Environments in the Photocycle Process around the Flavin Chromophore of the AppA-BLUF domain.

Three kinds of photochemical reactions are known in flavins as chromophores of photosensor proteins, reflecting the various catalytic reactions of the flavin in flavoenzymes. Sensor of blue light using the flavin FAD (BLUF) domains exhibit a unique photoreaction compared with other flavin-binding photoreceptors in that the chromophore does not change its chemical structure between unphotolyzed and intermediate states. Rather, the hydrogen bonding environment is altered, whereby the conserved Gln and Tyr residues near FAD play a crucial role. One proposal for this behavior is that the conserved Gln changes its chemical structure from a keto to an enol. We applied light-induced difference Fourier transform infrared (FTIR) spectroscopy to AppA-BLUF. The spectra of AppA-BLUF exhibited a different feature upon 15N-Gln labeling compared with the previously reported spectra from BlrB, a different BLUF domain. The FTIR signals were interpreted from quantum mechanics/molecular mechanics (QM/MM) calculation as the keto-enol tautomerization and rotation of the Gln63 side chain in the AppA-BLUF domain. The former was consistent with the result from BlrB, but the latter was not uniquely determined by the previous study. QM/MM calculation also indicated that the infrared signal shape is influenced depending on whether a Trp side chain forms a hydrogen bond with the Gln side chain. FTIR spectra and QM/MM simulations concluded that Trp104 does not flip out but is maintained in the intermediate state. In contrast, our data revealed that the Trp residue at the corresponding position in BlrB faces outward in both states.

5-Hydroxy-2-methylpyridine Isolated from Cigarette Smoke Condensate Aggravates Collagen-Induced Arthritis in Mice.

The risk of rheumatoid arthritis (RA) is linked to environmental and genetic factors. Cigarette smoking is an established environmental risk factor for the disease that contributes to its development and severity. Previously, we found that cigarette smoke condensate (CSC), both mainstream and sidestream, aggravates collagen type II-induced arthritis (CIA), which was observed following either intraperitoneal inoculation or nasal exposure. In the present study, we aimed to identify the compound in CSC, which aggravates CIA. By sequential fractionation and analysis, extraction with water/ether in different pH values, silica gel column chromatography, TLC, octadecyl silica (ODS) HPLC, GC/MS, and NMR, the active compound was identified as 5-hydroxy-2-methylpyridine (5H2MP). Its isomer 2-hydroxy-3-methylpyridine, but not 3-hydroxy-2-methylpyridine, was also active. 5H2MP was not mutagenic, and did not exhibit aryl hydrocarbon receptor-dependent activity. Our data help clarify the mechanism underlying the pathogenic effects of cigarette smoking on RA.

Effect of surfactant species and electrophoretic medium composition on the electrophoretic behavior of neutral and water-insoluble linear synthetic polymers in nonaqueous capillary zone electrophoresis.

We have recently demonstrated the separation of neutral and water-insoluble linear synthetic polymers in nonaqueous capillary zone electrophoresis (NACZE) using a cationic surfactant of cetyltrimethylammonium chloride (CTAC). In this study, eight ionic surfactants were investigated for the separation of four synthetic polymers (polystyrene, polymethylmethacrylates, polybutadiene, and polycarbonate); only three surfactants (CTAC, dimethyldioctadecylammonium bromide, and sodium dodecylsulfate) caused their separation. The order of the interaction between the polymers and the surfactants depended on both the surfactant species and the composition of the electrophoretic medium. Their investigation revealed that the separation is majorly affected by the hydrophobic interactions between the polymers and the ionic surfactants. In addition, the electrophoretic behavior of polycarbonate suggested that electrostatic interaction also affects the selectivity of the polymers.

High Performance Liquid Chromatography at -196 °C.

Ultralow temperature high-performance liquid chromatography (HPLC) was developed using a liquefied gas as the mobile phase. HPLC separation of low molecular weight alkanes at -196 °C with liquid nitrogen mobile phase was successfully achieved, whereas their GC separation at -196 °C using helium gas mobile phase failed to elute the analytes due to strong adsorption. Prior to the further study of HPLC at -196 °C, the effect of column temperature on the chromatographic behavior was investigated, and it was found that the retention of analytes drastically increased when the column temperature was over the boiling point of the mobile phase. As the study of retention control in HPLC at -196 °C, the mobile phases of nitrogen and methane mixtures were investigated. The addition of methane to the nitrogen mobile phase suppressed the retention of the analytes (tetra-deuterated methane, ethane, and propane), that is, the retention on HPLC at ultralow temperature could be controlled by the mobile phase composition, akin to the typical retention in HPLC. The selectivity toward the n- and iso-alkane in HPLC at -196 °C was altered compared with that in GC separation at room temperature. A significant enhancement of retention of alkanes compared with alkanes were observed in HPLC at -196 °C.

Organically modified titania having a metal catalyst: a new type of liquid-phase hydrogen-transfer photocatalyst working under visible light irradiation and H2-free conditions.

Organically modified titania having a metal catalyst (OMTC), 2,3-dihydroxynaphthalene-modified titania having palladium metal, successfully worked as a hydrogen-transfer (C[double bond, length as m-dash]C hydrogenation) photocatalyst in the presence of triethanolamine as the hydrogen source under visible light irradiation and hydrogen-free conditions.

Variation in the chromatographic, material, and chemical characteristics of methacrylate-based polymer monoliths during photoinitiated low-temperature polymerization.

Both the separation behavior and the structure of a polymer monolith column depends on both the reaction solution composition and the polymerization conditions. In photoinitiated low-temperature polymerization, polymerization temperature, irradiation intensity, and polymerization time were key factors to control the monolith characteristics. In this study, the effect of polymerization time on the chromatographic, material, and chemical characteristics of poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths was studied using pyrolysis-gas chromatography, Raman spectroscopy, inverse size exclusion chromatography, scanning electron microscopy, and chromatographic methods. Both butyl methacrylate and ethylene dimethacrylate monomers were incorporated into the monolith as the polymerization time increased, and it resulted in increases in both the flow resistance (decrease in both permeability and total/through pore porosities) and retention factors. The longer polymerization time led to lower relative amounts of free methacrylate functional groups in the monolith, i.e. cross-linking was enhanced. The increase of the polymerization time from 8 to 12 min significantly reduced the separation efficiency for the retained analyte, whereas an increase in the fraction of the mesoporosity was observed.

Chromatographic behavior of small organic compounds in low-temperature high-performance liquid chromatography using liquid carbon dioxide as the mobile phase.

Low-temperature high-performance liquid chromatography, in which a loop injector, column, and detection cell were refrigerated at -35ºC, using liquid carbon dioxide as the mobile phase was developed. Small organic compounds (polyaromatic hydrocarbons, alkylbenzenes, and quinones) were separated by low-temperature high-performance liquid chromatography at temperatures from -35 to -5ºC. The combination of liquid carbon dioxide mobile phase with an octadecyl-silica (C18 ) column provided reversed phase mode separation, and a bare silica-gel column resulted in normal phase mode separation. In both the cases, nonlinear behavior at approximately -15ºC was found in the relationship between the temperature and the retention factors of the analytes (van't Hoff plots). In contrast to general trends in high-performance liquid chromatography, the decrease in temperature enhanced the separation efficiency of both the columns.

Analyte zone sharpening in pressurized capillary electrochromatography based on electrophoretic migration under a heterogeneous field.

Significant peak width reductions, or peak height enhancements, of angiotensins were observed when a high voltage was applied to hydrophilic interaction pressurized capillary electrochromatography using gradient elution with mobile phases containing perchloric acid. The investigation using a contactless conductivity detector revealed that perchloric acid was adsorbed on the surface of the stationary phase, when the acetonitrile content in the mobile phase was high, and released from the stationary phase by increasing the water content during a gradient procedure. The released perchloric acid formed a highly concentrated zone moving from the column inlet to the outlet. The electrochromatographic behavior of the analytes, primarily electrophoretic migration, was changed in this zone. As a consequence of the significant variation in migration velocity of the analytes, the sample band width was reduced similar fashion to on-capillary concentration in capillary electrophoresis. Using this result, the reduction of band width and enhancement in separation efficiency was demonstrated in reversed-phase pressurized electrochromatography, in which the conductivity of the mobile phase was significantly altered using a step gradient. The resolution between benzoic acid and 1-naphthalene sulfonic acid was successfully improved from 2.7 to 4.3 by using the band width reduction method based on field-amplified stacking.

Characterization of balsam sulfide via pyrolysis-gas chromatography-mass spectrometry/sulfur chemiluminescence detection and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Balsam sulfide, produced by the reaction of turpentine/rosin and sulfur, has been used as one of the raw materials of liquid gold to decorate ceramics and tableware with thin gold film for more than 100 years. The characterization of balsam sulfide is still insufficient because of its compositional complexity. In this study, balsam sulfide was characterized using pyrolysis-gas chromatography (Py-GC)-mass spectrometry (MS) and Py-GC with sulfur chemiluminescence detection (SCD) as well as matrix-assisted laser desorption/ionization time-of-flight MS (MALDI-TOFMS). Py-GC-MS/SCD analyses of balsam sulfide and its model samples revealed that the low molecular weight reaction products were mainly composed of compounds of one α-pinene unit reacted with 1-3 sulfur atoms. In the analysis of the high molecular weight components by MALDI-TOFMS, the products of two or three α-pinene units crosslinked by sulfur atoms were observed. It was found that dehydrogenation reaction proceeded gradually with the increase in the reaction time.

Evaluation of interactions between metal ions and nonionic surfactants in high-concentration HCl using low-pressure high-performance liquid chromatography with low-flow-resistance polystyrene-based monolithic column.

A method for evaluating the interactions between metal ions and nonionic surfactants in aqueous solutions containing high-concentration HCl, using gas pressure-driven low-pressure high-performance liquid chromatography (LP-HPLC) as a highly acid-resistant HPLC system, was developed. To construct the LP-HPLC for this purpose, poly(styrene-co-divinylbenzene)-based low-flow-resistance monolithic columns tolerant to highly acidic conditions were prepared using low-conversion thermal polymerization. Thermal polymerization at 65 °C for 1.5 h (monomer conversions, 33% for styrene and 59% for divinylbenzene) allowed preparation of a column with both high separation efficiency (around 60,000 plates m(-1) for alkylbenzenes) and a quite low back pressure of 0.14 MPa at a linear flow rate of 1 mm s(-1) (2.8 × 10(-13) m(2) in permeability). The base column prepared under the above conditions was coated with a nonionic surfactant, polyoxyethylene nonylphenyl ether (PONPE, average oxyethylene unit numbers (n) = 3, 7.5, 15, and 20), and used for evaluation of the interactions between PONPEs and metal ions in 6 M HCl. The interactions between PONPEs and Au(III), Ga(III), Fe(III), Zn(II), and Cu(II) were successfully evaluated using both breakthrough and chromatographic methods. Furthermore, a study of the effect of the polyoxyethylene (POE) chain length revealed that the use of PONPE with the longer POE moiety enhanced the magnitude of the interaction together with the increase in the amount of oxyethylene (OE) units coated on the monolith. Moreover, the interactions of metal ions with a single OE unit were almost constant in the range of n = 7.5-20, whereas the suppression of the interaction between Au(III) with the shortest PONPE chain (n = 3) was also observed.

Simultaneous separation of water- and fat-soluble vitamins in isocratic pressure-assisted capillary electrochromatography using a methacrylate-based monolithic column.

A method of simultaneous separation of water- and fat-soluble vitamins using pressure-assisted CEC with a methacrylate-based capillary monolithic column was developed. In the proposed method, water-soluble vitamins were mainly separated electrophoretically, while fat soluble-ones were separated chromatographically by the interaction with a methacrylate-based monolith. A mixture of six water-soluble and four fat-soluble vitamins was separated simultaneously within 20 min with an isocratic elution using 1 M formic acid (pH 1.9)/acetonitrile (30:70, v/v) containing 10 mM ammonium formate as a mobile phase. When the method was applied to a commercial multivitamin tablet and a spiked one, the vitamins were successfully analyzed, and no influence of the matrix contained in the tablet was observed.

Analysis of polyisoprene oligomers via in situ silver nanoparticle formation on thin-layer chromatography plate using matrix-assisted laser-induced desorption/ionization mass spectrometry.

The direct mass spectrometry (MS) detection of polyisoprene (PI) oligomers on a thin-layer chromatography (TLC) plate using matrix-assisted laser-induced desorption/ionization (MALDI) with silver trifluoroacetate as the cationization reagent was investigated. The spots of PI oligomers and silver trifluoroacetate on the TLC plate resulted in brown materials after UV laser irradiation. It was suggested that silver trifluoroacetate yielded Ag nanoparticles as brown materials after heating via laser irradiation. The nanoparticles behaved as an inorganic matrix and a source of Ag+ adduct in the analysis of PI oligomers. The use of organic matrices together with silver trifluoroacetate reduced the signal intensity of PI oligomers on MALDI-MS on a TLC plate. The separation of PI oligomers (polymerization degree, n = 5-11) by TLC resulted in a single elliptical spot without a clear separation after the chromatographic procedure. However, in MS imaging, differences in migration lengths based on degrees of polymerization were clearly observed and the degrees of polymerization were identified without comparison with standards.

Pyrolysis-GC-MS analysis of ingested polystyrene microsphere content in individual Daphnia magna.

Microplastic (MP) pollution in the aquatic environment is a cause for increasing concern. However, analyzing MPs ingested by small organisms, such as zooplankton, is difficult because of the low content and small size of the ingested MPs. We attempted to determine the content of ingested MPs in individual zooplankton using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). To establish zooplankton model of MP ingestion, individual Daphnia magna were cultivated separately in microplate cells with polystyrene (PS) microspheres (10 µm in diameter, 245,000 particles, 135 µg) under different conditions. To prepare calibration curves for determining ingested PS content, approximately 100-150 µg of commercially available Daphnia-based powdered fish food, roughly corresponding to the weight of a single D. magna organism, was mixed with PS microspheres (0.005-26 µg) and analyzed using Py-GC-MS at 600 °C. In the resulting pyrograms, peaks of the styrene monomer and trimer from PS were detected, and linear relationships were obtained between the relative peak area and the amount of added PS. Finally, the cultivated zooplankton were individually subjected to Py-GC-MS analysis, and the ingested PS content in each zooplankton was successfully determined. Individual zooplankton cultured with PS in the absence of food ingested 2.3-7.9 µg of PS particles, whereas that in the presence of food (Chlorella vulgaris) ingested only 0.1-0.2 µg of PS particles. This result suggests that zooplankton might preferentially ingest ordinary food when both food and MPs are present, although further systematic studies are necessary to validate this observation.

Large-volume sample on-line concentration of angiotensins in non-aqueous capillary electrophoresis.

A single step on-line concentration and separation method for peptides in non-aqueous capillary electrophoresis was developed. ACN containing 50 mM tetraethylammonium perchlorate was used as the electrophoretic medium; angiotensins I-IV were separated as a result of the differences in the magnitudes of their interactions with perchlorate anions. When the sample solution (ACN containing 0.5% trifluoroacetic acid and angiotensins) was injected as a large-volume plug, the analytes were concentrated at the inlet end of the capillary by both sweeping and stacking mechanisms; the separation procedure then started automatically without any operations such as polarity change. It was found that the concentration of analytes, injection period, and concentration of tetraethylammonium perchlorate in the electrophoretic medium were important factors for both separation and concentration efficiencies. The angiotensins were concentrated and separated with the large-volume injection of up to 80% of the effective capillary length.

Inverse Hydrogen-Bonding Change Between the Protonated Retinal Schiff Base and Water Molecules upon Photoisomerization in Heliorhodopsin 48C12.

Heliorhodopsin (HeR) is a new class of the rhodopsin family discovered in 2018 through functional metagenomic analysis (named 48C12). Similar to typical microbial rhodopsins, HeR possesses seven transmembrane (TM) α-helices and an all-trans-retinal covalently bonded to the lysine residue on TM7 via a protonated Schiff base. Remarkably, the HeR membrane topology is inverted compared with that of typical microbial rhodopsins. The X-ray crystal structure of HeR 48C12 was elucidated after the first report on a HeR variant from Thermoplasmatales archaeon SG8-52-1, which revealed the water-mediated hydrogen-bonding network connected to the Schiff base region in the cytoplasmic side. Herein, low-temperature light-induced FTIR spectroscopic analyses of HeR 48C12 and 15N isotopically labeled proteins were used to elucidate the structural changes during retinal photoisomerization. N-D stretching vibrations of the protonated retinal Schiff base (PRSB) at 2286 and 2302 cm-1 in the dark state, and 2239 and 2252 cm-1 in the K intermediate were observed. The frequency changes indicated that the hydrogen bond of PRSB strengthens upon photoisomerization in HeR. Moreover, O-D stretching vibration frequencies of the internal water molecules indicate that the hydrogen-bonding strength decreases concomitantly. Therefore, the PRSB hydrogen bond responds to photoisomerization in an opposite way to the hydrogen-bonding network involving water molecules. No frequency changes of the indole N-H or N-D stretching vibrations of tryptophan residues were observed upon photoisomerization, suggesting that all tryptophan residues in the HeR 48C12 maintained the hydrogen-bonding strengths in the K intermediate. These results provide insights into the molecular mechanism of the energy storage and propagation upon retinal photoisomerization in HeR.