Growth of Highly Oriented (VNbMoTaW)S2 Layers.

Compositional tunability, an indispensable parameter for modifying the properties of materials, can open up new applications for van der Waals (vdW) layered materials such as transition-metal dichalcogenides (TMDCs). To date, multielement alloy TMDC layers are obtained via exfoliation from bulk polycrystalline powders. Here, we demonstrate direct deposition of high-entropy alloy disulfide, (VNbMoTaW)S2, layers with controllable thicknesses on free-standing graphene membranes and on bare and hBN-covered Al2O3(0001) substrates via ultra-high-vacuum reactive dc magnetron sputtering of the VNbMoTaW target in Kr and H2S gas mixtures. Using a combination of density functional theory calculations, Raman spectroscopy, X-ray diffraction, scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, we determine that the as-deposited layers are single-phase, 2H-structured, and 0001-oriented (V0.10Nb0.16Mo0.19Ta0.28W0.27)S2.44. Our synthesis route is general and applicable for heteroepitaxial growth of a wide variety of TMDC alloys and potentially other multielement alloy vdW compounds with the desired compositions.

Discrimination of Aspartic and Isoaspartic Acid Residues in Peptides by Tandem Mass Spectrometry with Hydrogen Attachment Dissociation.

Long-lived proteins undergo chemical modifications that can cause age-related diseases. Among these chemical modifications, isomerization is the most difficult to identify. Isomerization often occurs at the aspartic acid (Asp) residues. In this study, we used tandem mass spectrometry equipped with a newly developed ion activation method, hydrogen attachment dissociation (HAD), to analyze peptides containing Asp isomers. Although HAD preferentially produces [cn + 2H]+ and [zm + 2H]+ via N-Cα bond cleavage, [cn + 58 + 2H]+ and [zm - 58 + 2H]+ originate from the fragmentation of the isoAsp residue. Notably, [cn + 58 + 2H]+ and [zm - 58 + 2H]+ could be used as diagnostic fragment ions for the isoAsp residue because these fragment ions did not originate from the Asp residue. The detailed fragmentation mechanism was investigated by computational analysis using density functional theory. According to the results, hydrogen attachment to the carbonyl oxygen in the isoAsp residue results in the Cα-Cß bond cleavage. The experimental and theoretical joint study indicates that the present method allows us to discriminate Asp and isoAsp residues, including site identification of the isoAsp residue. Moreover, we demonstrated that the molar ratio of peptide isomers in the mixture could be estimated from their fragment ion abundance. Therefore, tandem mass spectrometry with HAD is a useful method for the rapid discrimination and semiquantitative analysis of peptides containing isoAsp residues.

ADAMTS4 is involved in the production of the Alzheimer disease amyloid biomarker APP669-711.

Amyloid-ß (Aß) deposition in the brain parenchyma is one of the pathological hallmarks of Alzheimer disease (AD). We have previously identified amyloid precursor protein (APP)669-711 (a.k.a. Aß(-3)-40) in human plasma using immunoprecipitation combined with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (IP-MALDI-MS). Furthermore, we found that the level of a composite biomarker, i.e., a combination of APP669-711/Aß1-42 ratio and Aß1-40/Aß1-42 ratio in human plasma, correlates with the amyloid PET status of AD patients. However, the production mechanism of APP669-711 has remained unclear. Using in vitro and in vivo assays, we identified A Disintegrin and Metalloproteinase with a Thrombospondin type 1 motif, type 4 (ADAMTS4) as a responsible enzyme for APP669-711 production. ADAMTS4 cleaves APP directly to generate the C-terminal stub c102, which is subsequently proteolyzed by γ-secretase to release APP669-711. Genetic knockout of ADAMTS4 reduced the production of endogenous APP669-711 by 30% to 40% in cultured cells as well as mouse plasma, irrespectively of Aß levels. Finally, we found that the endogenous murine APP669-711/Aß1-42 ratio was increased in aged AD model mice, which shows Aß deposition as observed in human patients. These data suggest that ADAMTS4 is involved in the production of APP669-711, and a plasma biomarker determined by IP-MALDI-MS can be used to estimate the level of Aß deposition in the brain of mouse models.

Association between suicide attempts and pediatric OHCA survival during the COVID-19 pandemic: Japanese cohort study.

BACKGROUND: Suicide is a leading cause of death in children. The COVID-19 pandemic might change the characteristics, causes (medical, suicidal, accidental, and other non-medical), and outcomes of pediatric OHCA. This study aimed to investigate the impact of pediatric OHCA in age, location, and quarantine-related movement restriction subgroups. METHODS: Combining the nationwide OHCA registry with the emergency medical service transportation database, we created a database with detailed information on 7657 non-neonatal, pediatric OHCA cases. RESULTS: The pandemic period did not significantly alter neurologically favorable 1-month survival compared to pre-pandemic 4 years (95% confidence interval 0.73-1.00). However, the survival rate significantly decreased in the following subgroups of OHCA: school-age (0.62-0.96), outside of school or home (0.52-0.96), and cases where no quarantine-related movement restrictions were applied (0.68-0.97). There was a prominent increase in the proportion of suicide-related OHCA in these subgroups: from 30.3 to 38.1% (1.22-1.64), from 10.2 to 15.9% (1.21-2.28), and from 12.5 to 17.8% (1.30-1.77), respectively. CONCLUSION: The COVID-19 pandemic did not significantly alter neurologically favorable 1-month survival. However, it led to worsened survival in subgroups with higher suicide attempt rates. Prevention of suicide is likely essential in the assurance of children's lives during the pandemic. IMPACT: This cohort study found that during the 2020/2021 pandemic, neurologically favorable survival decreased in school-age out-of-hospital cardiac arrest (OHCA) cases, those not subject to quarantine-related movement restrictions, and those in locations outside of school or home. Within these three subgroups, there was a notable rise in OHCA cases related to suicide, historically known to be more challenging to manage successfully. However, survival rates for overall OHCA and medically related OHCA cases remained unchanged throughout the pandemic. Preventive measures for suicide attempts may be necessary to improve the overall survival of pediatric OHCA during the pandemic.

High performance plasma amyloid-ß biomarkers for Alzheimer's disease.

To facilitate clinical trials of disease-modifying therapies for Alzheimer's disease, which are expected to be most efficacious at the earliest and mildest stages of the disease, supportive biomarker information is necessary. The only validated methods for identifying amyloid-ß deposition in the brain-the earliest pathological signature of Alzheimer's disease-are amyloid-ß positron-emission tomography (PET) imaging or measurement of amyloid-ß in cerebrospinal fluid. Therefore, a minimally invasive, cost-effective blood-based biomarker is desirable. Despite much effort, to our knowledge, no study has validated the clinical utility of blood-based amyloid-ß markers. Here we demonstrate the measurement of high-performance plasma amyloid-ß biomarkers by immunoprecipitation coupled with mass spectrometry. The ability of amyloid-ß precursor protein (APP)669-711/amyloid-ß (Aß)1-42 and Aß1-40/Aß1-42 ratios, and their composites, to predict individual brain amyloid-ß-positive or -negative status was determined by amyloid-ß-PET imaging and tested using two independent data sets: a discovery data set (Japan, n = 121) and a validation data set (Australia, n = 252 including 111 individuals diagnosed using 11C-labelled Pittsburgh compound-B (PIB)-PET and 141 using other ligands). Both data sets included cognitively normal individuals, individuals with mild cognitive impairment and individuals with Alzheimer's disease. All test biomarkers showed high performance when predicting brain amyloid-ß burden. In particular, the composite biomarker showed very high areas under the receiver operating characteristic curves (AUCs) in both data sets (discovery, 96.7%, n = 121 and validation, 94.1%, n = 111) with an accuracy approximately equal to 90% when using PIB-PET as a standard of truth. Furthermore, test biomarkers were correlated with amyloid-ß-PET burden and levels of Aß1-42 in cerebrospinal fluid. These results demonstrate the potential clinical utility of plasma biomarkers in predicting brain amyloid-ß burden at an individual level. These plasma biomarkers also have cost-benefit and scalability advantages over current techniques, potentially enabling broader clinical access and efficient population screening.

Highly Efficient Light Helicity Detection of Enantiomers by Chiral Metal-Organic Framework Thin Films.

The potential of chiral metal-organic frameworks (MOFs) for circularly polarized (CP) optics has been largely unexplored. Herein, we have successfully deposited monolithic and highly oriented chiral MOF thin films prepared by a layer-by-layer method (referred to as surface-coordinated MOF thin films, SURMOF) to fabricate CP photodetection devices and distinguish enantiomers. The helicity-sensitive absorption induced by a pair of enantiopure oriented SURMOF was found to be excellent, with an anisotropy factor reaching 0.41. Moreover, the chiral SURMOFs exhibited a pronounced difference in the uptake of the l- and d-tryptophan enantiomers. To demonstrate the potential of these novel MOF thin films for chirality analysis, we fabricated a portable sensor device that allows for chiral recognition by monitoring the photocurrent signals. Our findings not only introduce a new concept of using chiral building blocks for realizing direct CP photodetectors but also provide a blueprint for novel devices in chiral optics.

Borazine Promoted Growth of Highly Oriented Thin Films.

We report on a phenomenon, where thin films sputter-deposited on single-crystalline Al2O3(0001) substrates exposed to borazine─a precursor commonly used for the synthesis of hexagonal boron nitride layers─are more highly oriented than those grown on bare Al2O3(0001) under the same conditions. We observed this phenomenon in face-centered cubic Pd, body-centered cubic Mo, and trigonal Ta2C thin films grown on Al2O3(0001). Interestingly, intermittent exposure to borazine during the growth of Ta2C thin films on Ta2C yields better crystallinity than direct deposition of monolithic Ta2C. We attribute these rather unusual results to a combination of both enhanced adatom mobilities on, and epitaxial registry with, surfaces exposed to borazine during the deposition. We expect that our approach can potentially help improve the crystalline quality of thin films deposited on a variety of substrates.

Hot Hydrogen Atom Irradiation of Protonated/Deprotonated Peptide in an Ion Trap Facilitates Fragmentation through Heated Radical Formation.

Tandem mass spectrometry with fragmentation involving the reaction with hydrogen atoms is expected to be useful for the analysis of peptides and proteins. In general, hydrogen atoms preferentially react with odd-electron radicals. The attachment of hydrogen atoms to even-electron peptide ions is barely observed because of their low reaction rate. To date, only the methodology developed by our group has successfully induced the fragmentation of even-electron peptide ions by reacting with hydrogen atoms. In the present study, we focused on the temperature of the peptide ions and hydrogen atoms in an ion trap mass spectrometer to understand the mechanism of the corresponding reaction. Because the reaction between even-electron peptide ions and hydrogen atoms has a significant transition state barrier, the use of hot hydrogen atoms is required to initiate the reaction. The reaction contributes to increase the internal energy of the resultant peptide radicals because the heat of reaction and kinetic energy of the hydrogen atom are converted to the internal energy of the product. The resultant oxygen- and carbon-centered peptide radicals undergo radical-induced fragmentation with sub-picosecond and sub-millisecond time scales, respectively.

Self-Organized Growth of 111-Oriented (VNbTaMoW)N Nanorods on MgO(001).

Refractory high-entropy alloy nitride, (VNbTaMoW)N, layers are grown on single-crystalline MgO(001) via ultrahigh vacuum direct current magnetron sputtering of a VNbTaMoW target in Kr/N2 gas mixtures at 1073 K. X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive X-ray spectroscopy characterizations revealed the formation of B1-structured, 111-textured (V0.21Nb0.18Ta0.19Mo0.21W0.21)N1.05 with lattice parameter a = 0.4249 nm. The alloy nitride film exhibits dense columnar microstructure near the substrate-film interface with coherent 001 grain growth limited to a few tens of nanometers, followed by an outgrowth of quasi one-dimensional nanorods with 3-fold symmetric facets. We attribute the self-organized growth of rather unusual 111-textured nanorods on isostructural MgO(001) to kinetic limitations of the sputter-deposition process exacerbated by the sluggish diffusion of the multicomponent adspecies and the preferential growth of {111} crystals.

SIG-1451, a Novel, Non-Steroidal Anti-Inflammatory Compound, Attenuates Light-Induced Photoreceptor Degeneration by Affecting the Inflammatory Process.

Age-related macular degeneration is a progressive retinal disease that is associated with factors such as oxidative stress and inflammation. In this study, we evaluated the protective effects of SIG-1451, a non-steroidal anti-inflammatory compound developed for treating atopic dermatitis and known to inhibit Toll-like receptor 4, in light-induced photoreceptor degeneration. SIG-1451 was intraperitoneally injected into rats once per day before exposure to 1000 lx light for 24 h; one day later, optical coherence tomography showed a decrease in retinal thickness, and electroretinogram (ERG) amplitude was also found to have decreased 3 d after light exposure. Moreover, SIG-1451 partially protected against this decrease in retinal thickness and increase in ERG amplitude. One day after light exposure, upregulation of inflammatory response-related genes was observed, and SIG-1451 was found to inhibit this upregulation. Iba-1, a microglial marker, was suppressed in SIG-1451-injected rats. To investigate the molecular mechanism underlying these effects, we used lipopolysaccharide (LPS)-stimulated rat immortalised Müller cells. The upregulation of C-C motif chemokine 2 by LPS stimulation was significantly inhibited by SIG-1451 treatment, and Western blot analysis revealed a decrease in phosphorylated I-κB levels. These results indicate that SIG-1451 indirectly protects photoreceptor cells by attenuating light damage progression, by affecting the inflammatory responses.

Gas-Phase Peptide Fragmentation Induced by Hydrogen Attachment, from Principle to Sequencing of Amide Nitrogen-Methylated Peptides.

Tandem mass spectrometry (MS/MS) with radical-based fragmentation was developed recently, which involves the reaction of hydrogen atoms and peptides in a process called hydrogen attachment/abstraction dissociation (HAD). HAD mainly produces [cn + 2H]+ and [zm + 2H]+ via hydrogen attachment to the carbonyl oxygen on the peptide backbone. In addition, HAD often generates [an + 2H]+ and [xm + 2H]+. To explain the formation of [an + 2H]+ and [xm + 2H]+, hydrogen attachment to the carbonyl carbon atom on the peptide backbone is proposed to initiate Cα-C bond cleavage. The resultant hydrogen-abundant oxygen-centered radical intermediate undergoes radical-induced dissociation to give [an + H]+• and [xm + 2H]+. Subsequently, [an + 2H]+ was produced by the reaction of [an + H]+• and a hydrogen atom. The fragment ions formed by the cleavage of N-Cα and Cα-C bonds are observed in the HAD-MS/MS spectra, and the mass differences of these fragment ions correspond to the mass of peptide bonds. Consequently, HAD-MS/MS allows the identification of post-translational modifications on the peptide backbone. In addition, HAD-MS/MS provides a consecutive series of [cn + 2H]+ and [an + 2H]+ as the N-terminal fragments, as well as [zm + 2H]+ and [xm + 2H]+, which enables the sequencing of peptides with post-translational modification, including the discrimination of modifications on the side chain and backbone.

Lactone-Driven Ester-to-Amide Derivatization for Sialic Acid Linkage-Specific Alkylamidation.

Sialic acid attached to nonreducing ends of glycan chains via different linkages is associated with specific interactions and physiological events. Linkage-specific derivatization of sialic acid is of great interest for distinguishing sialic acids by mass spectrometry, specifically for events governed by sialyl linkage types. In the present study, we demonstrate that α-2,3/8-sialyl linkage-specific amidation of esterified sialyloligosaccharides can be achieved via an intramolecular lactone. The method of lactone-driven ester-to-amide derivatization for sialic acid linkage-specific alkylamidation, termed LEAD-SALSA, employs in-solution ester-to-amide conversion to directly generate stable and sialyl linkage-specific glycan amides from their ester form by mixing with a preferred amine, resulting in the easy assignments of sialyl linkages by comparing the signals of esterified and amidated glycan. Using this approach, we demonstrate the accumulation of altered N-glycans in cardiac muscle tissue during mouse aging. Furthermore, we find that the stability of lactone is important for ester-to-amide conversion based on experiments and density functional theory calculations of reaction energies for lactone formation. By using energy differences of lactone formation, the LEAD-SALSA method can be used not only for the sialyl linkage-specific derivatization but also for distinguishing the branching structure of galactose linked to sialic acid. This simplified and direct sialylglycan discrimination will facilitate important studies on sialylated glycoconjugates.

Sequencing of Sulfopeptides Using Negative-Ion Tandem Mass Spectrometry with Hydrogen Attachment/Abstraction Dissociation.

Tandem mass spectrometry (MS/MS) with radical-based fragmentation involving the attachment or abstraction of hydrogen to peptides, in a process called hydrogen attachment/abstraction dissociation (HAD), has been recently developed. HAD-MS/MS is considered a useful method for the analysis of proteins with post-translational modification (PTM) because of its ability to determine the PTM site on proteins. In the present investigation, we analyzed highly acidic sulfopeptides and sulfoprotein digests using negative-ion HAD-MS/MS combined with matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI). In general, MALDI and ESI produced singly and multiply charged peptides, respectively. HAD of singly deprotonated sulfopeptides preferentially produced fragment ions with sulfonation, whereas both sulfonated and nonsulfonated fragment ions were observed in the HAD-MS/MS spectrum of multiply deprotonated sulfopeptides. A comparison of the MALDI and ESI HAD-MS/MS spectra allows the discrimination of sulfonated and nonsulfonated fragments, which would be helpful in performing de novo sequencing of sulfopeptides. In addition, the combination of ESI-based HAD-MS/MS and liquid chromatography (LC) allows the analysis of sulfopeptides present in protein digests. LC-ESI-MS/MS with HAD is a potentially useful method for sulfoproteomic application.

Comparative Glycomic Analysis of Sialyl Linkage Isomers by Sialic Acid Linkage-Specific Alkylamidation in Combination with Stable Isotope Labeling of α2,3-Linked Sialic Acid Residues.

Sialic acids form the terminal sugars in glycan chains on glycoproteins via α2,3, α2,6, or α2,8 linkages, and structural isomers of sialyl linkages play various functional roles in cell recognition and other physiological processes. We recently developed a novel procedure based on sialic acid linkage-specific alkylamidation via lactone ring opening (aminolysis-SALSA). Herein, we have investigated an isotope labeling of α2,3-linked sialic acid residues (iSALSA) using amine hydrochloride salts. One limitation of SALSA using amine hydrochloride salts may be solved by adding only tert-butylamine (t-BA) as an acid scavenger, and comparative and quantitative glycomic analyses can be performed using iSALSA. We also developed quantitative glycomic analysis using dual isotope-labeled glycans by derivatizing with aminooxy-functionalized tryptophanylarginine methyl ester (aoWR) and iSALSA at the reducing and nonreducing end, respectively. Furthermore, we demonstrate that the amount of α2,3-linked sialoglycans in serum are altered during liver fibrosis using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and liquid chromatography MS (LC/MS) analyses. We revealed that the ratio of A33,6,6 to A3F3,6,6 was gradually decreased along with liver fibrosis progression. Therefore, these glycan alterations are potential diagnostic markers of nonalcoholic steatohepatitis (NASH) fibrosis progression.

Late-Onset Circulatory Collapse and Risk of Cerebral Palsy in Extremely Preterm Infants.

OBJECTIVE: To investigate whether the development of postnatal, late-onset refractory hypotension, referred to as late-onset circulatory collapse, was associated with an increased risk of developing cerebral palsy (CP) at 3 years of age in extremely preterm infants. METHODS: In this historical cohort study, infants who were born at 22-27 weeks of gestation from 2008 to 2012 in the Neonatal Research Network of Japan were eligible. The study sample consisted of 3474 infants (45.6% of 7613 potentially eligible infants) who were evaluated at 36-42 months of age. Late-onset circulatory collapse was defined as a clinical diagnosis of late-onset circulatory collapse requiring treatment with corticosteroids. We compared the neurodevelopmental outcomes between infants with and without late-onset circulatory collapse. RESULTS: Late-onset circulatory collapse was diagnosed in 666 of the infants studied. Infants with late-onset circulatory collapse had a higher incidence of CP than those without late-onset circulatory collapse (18.0% vs 9.8%; P < .01). In multivariable logistic analysis, late-onset circulatory collapse was independently associated with CP (aOR, 1.52; 95% CI, 1.13-2.04) and developmental quotient score of <50 (OR, 1.83; 95% CI, 1.23-2.72). CONCLUSIONS: Late-onset circulatory collapse may be a relatively common event occurring in extremely preterm infants and an independent risk factor for CP at 3 years of age.

Hydrogen atom attachment to histidine and tryptophan containing peptides in the gas phase.

In this study, we use a combination of tandem mass spectrometry and hydrogen radical-mediated fragmentation techniques to analyze the sequence of peptides. We focus on fragmentation induced by the attachment of hydrogen atoms to the histidine and tryptophan residue side-chains in the peptide that occurs in the gas-phase. The hydrogen atom attached to the imidazole and indole rings in the histidine and tryptophan residues, respectively, and the resulting intermediate experienced Cα-Cß bond cleavage. The detailed fragmentation mechanism is investigated by computational analysis using density functional theory. According to the results, hydrogen attachment occurs at the C-5 position in histidine and at the C-2 position in the tryptophan, which has a lower activation energy compared with the other positions and the resulting intermediate radicals yielded fragments due to Cα-Cß bond cleavage. For the peptides that contain the histidine and tryptophan residues, cleavages in the Cα-Cß and N-Cα bonds occurred independently. Therefore, the method presented in this study is applicable when analyzing peptides that contain histidine and tryptophan residues.

Hydrogen attachment dissociation of peptides containing disulfide bonds.

A combination of tandem mass spectrometry (MS/MS) and hydrogen attachment dissociation (HAD) is a useful method for peptide sequence analysis. In this study, gas-phase fragmentation induced by the attachment of hydrogen to peptides containing disulfide bonds was investigated. Hydrogen attachment induced the cleavage of either the disulfide or N-Cα bond, which competitively occurred during HAD. The disulfide bond cleavage proceeded through an intermediate, which contains a thiyl radical (-S˙) and a thiol group (-SH). In contrast, N-Cα bond cleavage produced an intermediate containing an enol-imine group and α-carbon radical. The intermediate α-carbon radical then attacked the disulfide bond, resulting in a cyclic [z]+ fragment. The counterpart, [c + H]+˙ with a thiyl radical underwent further hydrogen attachment, producing [c + 2H]+. Because both disulfide and N-Cα bonds were cleaved by a single hydrogen attachment event, HAD-MS/MS can provide sequence information for the backbone region in the disulfide loop.

Classification of Cutibacterium acnes at phylotype level by MALDI-MS proteotyping.

Cutibacterium acnes is a major commensal human skin bacteria. It is a producer of propionic acids that maintain skin acidic pH to inhibit the growth of pathogens. On the other hand, it is also associated with diseases such as acne vulgaris and sarcoidosis. C. acnes strains have been classified into six phylotypes using DNA-based approaches. Because several characteristic features of C. acnes vary according to the phylotype, the development of a practical method to identify these phylotypes is needed. For rapid identification of phylotypes for C. acnes strains, a matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) fingerprinting technique has been applied; however, some phylotypes have not been discriminated. We developed a high-throughput protein purification method to detect biomarker proteins by ultrafiltration. MALDI-MS proteotyping using profiling of identified biomarker peaks was applied for the classification of 24 strains of C. acnes, and these were successfully classified into the correct phylotypes. This is a promising method that allows the discrimination of C. acnes phylotypes independent of a DNA-based approach.

De Novo Sequencing of Tryptic Phosphopeptides Using Matrix-Assisted Laser Desorption/Ionization Based Tandem Mass Spectrometry with Hydrogen Atom Attachment.

Phosphorylation is the most abundant protein modification, and tandem mass spectrometry (MS/MS) with radical-based fragmentation techniques has proven to be a promising method for phosphoproteomic applications, owing to its ability to determine phosphorylation sites on proteins. The radical-induced fragmentation technique involves the attachment or abstraction of hydrogen to peptides in an ion trap mass spectrometer, in a process called hydrogen attachment/abstraction dissociation (HAD), which has only been recently developed. In the present investigation, we have analyzed model phosphopeptides and phosphoprotein digests using HAD-MS/MS, combined with matrix-assisted laser desorption/ionization (MALDI), in order to demonstrate the usefulness of the HAD-MS/MS-based analytical method. The tryptic peptides were categorized as arginine- and lysine-terminated peptides, and MALDI HAD-MS/MS is found to facilitate the sequencing of arginine-terminated tryptic peptides, because of the selective observation of C-terminal side fragment ions. In contrast, MALDI HAD-MS/MS of lysine-terminated tryptic peptides produced both N- and C-terminal side fragments, such that the mass spectra were complex. The guanidination of peptide converted lysine into homoarginine, which facilitated the interpretation of MALDI HAD-MS/MS mass spectra. The present method was useful for de novo sequencing of tryptic phosphopeptides.

Tandem Mass Spectrometry of Peptide Ions by Microwave Excited Hydrogen and Water Plasmas.

A thermal cracking cell that served as the atomic hydrogen source for hydrogen attachment/abstraction dissociation (HAD) analysis has an intrinsic problem to produce a beam of atoms reactive against heated tungsten capillary. A plasma excited by 2.45 GHz microwave discharge can deliver reactive species to a quadrupole ion trap confining analyte ions without excessive heating of the radical source components. The radical (H•) production performance of the developed source was evaluated by optical emission spectroscopy and H• attachment reaction to fullerene ions. The source exhibited the H• attachment rate as high as a thermal cracking source forming H• in the high temperature tungsten capillary to induce fragmentation processes preserving post-translational modifications. Water vapor was introduced to the source to confirm the stability to generate oxygen containing radicals, which were found present in the water vapor plasma together with atomic hydrogen. Injection of radicals from a water vapor plasma successfully dissociated peptide ions to c-/z- and a-/x-type ions as the case of HAD induced by a thermal cracking cell.