Fragmentation Of Molecular Ions Research Articles

ISOLATION AND IDENTIFICATION OF ANTIOXIDANT COMPOUNDS FROM METHANOL EXTRACT OF SAPPAN WOOD (Caesalpinia sappan)

Sappan wood extract (Caesalpinia sappan) provides better antioxidant properties than ascorbic acid. Empirically, Sappan wood is often used as traditional medicine. To support the utilization of Sappan wood, the isolation and identification of active antioxidant compounds from the methanol extract of Sappan wood had been conducted from this study. Extraction was performed with maceration and evaporation methods. The spots of active antioxidant compounds in TLC-DPPH observations were isolated using liquid vacuum chromatography to obtain two pure compounds. The results of the LC-MS/MS identification of the two compounds, respectively, exhibited peak fragmentation of molecular ions at m/z 271.09, 257.15, 167.03, 151.06, 123.12, and 104.06 at the retention time of 6.35 minutes which were translated as Alpinetine and peak fragmentation of molecular ion at m/z 287.09, 177.06, 164.05, 123.04 and 110.04 at a retention time of 5.75. minutes which were translated as 3-Deoxysappanone B. The antioxidant activity quantitatively showed that Alpinetine and 3-Deoxysappanone B were capable of scavenging DPPH radicals with IC50 values ​​of 20.11 M and 15.28 M, respectively.

ISOLATION AND IDENTIFICATION OF ANTIOXIDANT COMPOUNDS FROM METHANOL EXTRACT OF SAPPAN WOOD (Caesalpinia sappan)

Sappan wood extract (Caesalpinia sappan) provides better antioxidant properties than ascorbic acid. Empirically, Sappan wood is often used as traditional medicine. To support the utilization of Sappan wood, the isolation and identification of active antioxidant compounds from the methanol extract of Sappan wood had been conducted from this study. Extraction was performed with maceration and evaporation methods. The spots of active antioxidant compounds in TLC-DPPH observations were isolated using liquid vacuum chromatography to obtain two pure compounds. The results of the LC-MS/MS identification of the two compounds, respectively, exhibited peak fragmentation of molecular ions at m/z 271.09, 257.15, 167.03, 151.06, 123.12, and 104.06 at the retention time of 6.35 minutes which were translated as Alpinetine and peak fragmentation of molecular ion at m/z 287.09, 177.06, 164.05, 123.04 and 110.04 at a retention time of 5.75. minutes which were translated as 3-Deoxysappanone B. The antioxidant activity quantitatively showed that Alpinetine and 3-Deoxysappanone B were capable of scavenging DPPH radicals with IC50 values ​​of 20.11 M and 15.28 M, respectively.

Fragmentation of 2,5-diketopiperazine cyclic dipeptide ions

The mechanism of radiation damage to 2,5-diketopiperazine (DKP, C4H6N2O2) molecules in the gas phase upon interaction with He2+ ions with an energy Ep = 4 keV/u has been investigated. The relative cross sections of various elementary processes occurring in single collisions of DKP with ions have been measured for the first time. The channels of fragmentation processes of singly charged ions have been studied experimentally. The DFT method was used to calculate the geometry of molecules and singly charged DKP ions, as well as the energies of the main experimentally observed channels of fragmentation of these ions. Keywords: electron capture, dipeptides, molecular ion fragmentation.

Pyrotinib in vitro metabolite profiling via rat, dog and human hepatocytes using liquid chromatography-quadrupole/orbitrap mass spectrometry.

Pyrotinib is an irreversible EGFR/HER2 inhibitor that has shown antitumor activity and tolerance in the treatment of breast cancer. Studies focused on its metabolic pathways and major metabolites are insufficient. In the evaluation of drug safety and therapeutic use, metabolite characterization is critical. The metabolism of pyrotinib in vitro was studied utilizing rat, dog and human hepatocytes in this study. Pyrotinib (10 μM) was incubated with hepatocytes in Williams' E medium. The metabolites were examined and profiled using ultrahigh-performance liquid chromatography coupled with quadrupole/orbitrap high-resolution mass spectrometry. The metabolite structures were deduced by comparing their precise molecular weights, fragment ions and retention times with those of the parent drug. A total of 16 metabolites, including 6 novel ones, were discovered and structurally described under the present conditions. Oxidation, demethylation, dehydrogenation, O-dealkylation and glutathione (GSH) conjugation were all involved in the metabolism of pyrotinib in hepatocytes. The most predominant metabolic route was identified as GSH conjugation (M5). This study generated valuable metabolite profiles of pyrotinib in several species, which will aid in the understanding of the drug's disposition in various species and in evaluating the contribution of metabolites to overall effectiveness and toxicity of pyrotinib.

Measuring Electronic Structure of Multiply Charged Anions to Understand Their Chemistry: A Case Study on Gaseous Polyhedral closo-Borate Dianions.

Research on multiply charged anions (MCAs) in the gas phase has been intensively performed during the past decades, mainly to understand fundamental molecular physics phenomena, for example, intramolecular Coulomb repulsion and existence of the repulsive Coulomb barrier. However, the relevance of these investigations with respect to understanding MCAs' chemistry appears often vague. Here, we discuss how insights into the electronic structure obtained from negative ion photoelectron spectroscopy (NIPES) combined with theoretical calculations and collision-induced dissociation can provide a fundamental understanding of the intrinsic chemical reactivity of MCAs and their fragments. This is exemplified in our studies on polyhedral closo-borate dianions [BnXn]2- (n = 6, 10, 11, 12; X = H, F-I, CN) and their fragment ions. For example, the rational design of closo-borate dianions with specific electronic properties is described, which leads to generating highly reactive fragments. Depending on the dianionic precursor, these fragments are tuned to either bind noble gases effectively or activate small molecules like CO and N2. The intrinsic electronic properties of closo-borate dianions are further compared to their electrochemistry in solutions, revealing solvent effects on the redox potentials. Neutral host molecules such as cyclodextrins are found to bind strongly to [BnXn]2-, and gas phase NIPES provides insights into the intrinsic host-guest interactions. Finally, outlooks including the direct NIPES of molecular fragment ions that cannot be generated in the condensed phase and their utilization in preparative mass spectrometry are discussed.

High-Throughput Identification of Organic Compounds from Polygoni Multiflori Radix Praeparata (Zhiheshouwu) by UHPLC-Q-Exactive Orbitrap-MS.

Polygoni Multiflori Radix Praeparata (PMRP), as the processed product of tuberous roots of Polygonum multiflorum Thunb., is one of the most famous traditional Chinese medicines, with a long history. However, in recent years, liver adverse reactions linked to PMRP have been frequently reported. Our work attempted to investigate the chemical constituents of PMRP for clinical research and safe medication. In this study, an effective and rapid method was established to separate and characterize the constituents in PMRP by combining ultra-high performance liquid chromatography with hybrid quadrupole-orbitrap mass spectrometry (UHPLC-Q-Exactive Orbitrap-MS). Based on the accurate mass measurements for molecular and characteristic fragment ions, a total of 103 compounds, including 24 anthraquinones, 21 stilbenes, 15 phenolic acids, 14 flavones, and 29 other compounds were identified or tentatively characterized. Forty-eight compounds were tentatively characterized from PMRP for the first time, and their fragmentation behaviors were summarized. There were 101 components in PMRP ethanol extract (PMRPE) and 91 components in PMRP water extract (PMRPW). Simultaneously, the peak areas of several potential xenobiotic components were compared in the detection, which showed that PMRPE has a higher content of anthraquinones and stilbenes. The obtained results can be used in pharmacological and toxicological research and provided useful information for further in vitro and in vivo studies.

Metabolism and Tissue Distribution of Chelerythrine and Effects of Macleaya Cordata Extracts on Liver NAD(P)H Quinone Oxidoreductase

Background: Macleaya cordata (Willd.) (Papaveraceae) is listed as a feed additive in animal production by the European Food Authority.Methods: The metabolites of chelerythrine in rats were measured in vitro and in vivo by rapid and accurate high-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry (HPLC/QqTOF-MS). The structures of CHE metabolites were elucidated by comparing their changes in accurate molecular masses and fragment ions with those of parent ion or metabolite. The metabolic enzymes that were involved in chelerythrine reduction were investigated using an inhibition method. The tissue distribution of chelerythrine and the effects on NQO1 following intragastric administration with M. cordata extracts in rats were examined.Results: A total of twelve metabolites of chelerythrine were characterized by this approach in rat liver S9 and in vivo. The reduction of the iminium bond of chelerythrine and subsequent O-demethylation was the main metabolic pathway of chelerythrine in rat liver S9 while the reduction of the iminium bond of chelerythrine was the main metabolic pathway of chelerythrine in rats in vivo. After the rats were given intragastric administration, the low concentration residues of sanguinarine and chelerythrine in different rat tissues were found at 48 h after the last dose, suggesting that both compounds could be widely distributed in tissues. The results also indicated that XO, NQO1, NQO2, and carbonyl reductase are involved in chelerythrine reduction. Macleaya cordata extracts treated female and male rats, respectively, showed different responses, inhibiting NQO1 activity in males, but inducing NQO1 activity in females. Chelerythrine had a weak impact on NQO1 activity, but sanguinarine inhibited NQO1 activityConclusion: Through studying the effects of cytosolic reductase inhibitors on chelerythrine reduction and the impact of chelerythrine and sanguinarine on the activity of NQO1 in vitro and in vivo, we clarified the potential drug interaction of Macleaya cordata extract in clinical application, so as to provide theoretical guidance for clinically safe medication. In addition, it provided a reference basis for the metabolic mechanism of chelerythrinein rats.

Improved TGA-MS measurements for evolved gas analysis (EGA) during pyrolysis process of various biomass feedstocks. Syngas energy balance determination

This paper provides in-depth knowledge about the evolved gas analysis interpretation via newly proposed semi-quantitative approach, arising from thermogravimetric analysis (TGA) – mass spectrometry (MS) coupled measurements, for studying pyrolysis behavior of three kinds of biomass waste materials (spent coffee grounds, beech sawdust and wheat straw). TGA – MS coupling allows accurate correlation between molecular ion peak and fragment peaks to the corresponding mass loss rates from derivative thermogravimetry curves. Within proposed semi-quantitative analysis, MS spectra were interpreted through the comparative analysis of compounds fragments and of the compound itself, where the single atomic mass unit was identified by multiple compounds exhibition. It was shown that by this procedure which involves overlapping multiple curves supervising, the identification of gases in volatiles complex scheme becomes more simplified. By setting up semi-quantitative formulas, easy and reliable calculations of gaseous products yield and syngas energy capacities are possible to achieve. The H2/CO ratio derived from the proposed method for wood waste product (sawdust) is in an excellent agreement with H2/CO ratio for sawdust syngas production, in fuel reactor for biomass gasification and H2 production.

Metabolomics-based profiling with chemometric approach to identify bioactive compounds in Salacca zalacca fruits extracts and in silico molecular docking

Salak (Salacca zalacca) is well-known as snake fruit and it is immensely studied for its antioxidative and antidiabetic active metabolites throughout the southeast Asian countries. However, there are many remaining unidentified metabolites due to very low abundance and natural variation, which need to be further explored. Nowadays mass spectrometry (MS/MS) facilitates the tentative identification of unknown compounds in the crude herbal extracts. This study described the metabolite profiling of hydroalcoholic extracts of S. zalaccaanalysed by LC-QTOF-MS/MS. The 60% ethanolic extract exhibited the highest α-glucosidase inhibition and ferric reducing antioxidant power activities with IC50 of 15.94 µg/mL and 78.13 μg AAE/g, respectively. Multivariate data analysis (MVDA) by an orthogonal partial least-squares (OPLS) algorithm was conducted to correlate the α-glucosidase inhibition activity with the LC- QTOF-MS data. A total of 4 compounds were reported for first time in this fruit and identified based on the molecular mass and fragment ions. LC-QTOF-MS analysis indicated the presence of carexane I, 5-phenoxytetrazol-1-yl)-2,3,5,6-hexahydrofurofuran-3-ethylurea, 3-acetylphenoxy)-N-[(2)-1-amino-4-methyl-1-oxopentan-2-yl]-4,5-dihydroxycyclohexene-1-carboxamide and Ethyl 4-[5-methyl-2-oxo-1′,2′,5′,6′,7′,7′a-hexahydro-1H-spiro[indole-3,3′-pyrrolizine]-2′-ylamido] benzoate. Molecular docking of those compounds with the α–glucosidase enzyme was performed to confirm their antidiabetic potential. These bioactive compounds could be suggested as α-glucosidase inhibitors and functional food additives.

Hydrogen transfer-induced S-C rearrangement in the molecular ion of thioanisole derivatives with site-specificity.

In this study, the gas-phase fragmentations of molecular ions of thioanisole derivatives were investigated using electron ionization mass spectrometry (EI-MS). In the EI-MS spectrum, a characteristic fragment ion [M - SH]+ was observed. The same result with the molecular ion of 3-aminothioanisole was enhanced, while the same phenomenon was not obvious in the EI-MS spectra of 2- or 4-aminothioanisole. To explain the fragmentation, we proposed a mechanism that involved the hydrogen transfer-induced S-C rearrangement with 3 pathways. Substituent effect results, deuterium-labelled experiments and density functional theory (DFT) calculations also confirmed the proposed mechanism.

High Performance Liquid Chromatography–Quadrupole Time-of-Flight Mass Spectrometry Based Metabolomic Detection of Non-Volatile Components of Different Chemotype of Cinnamomum camphora

A liquid chromatography−quadrupole time-of-flight mass spectrometry (LC−QTOF/MS) based plant metabolomics approach was established to investigate the metabolic profiles of the Cinnamomum camphora leaves of four different areas. The LC−QTOF/MS data were subjected to principal component analysis (PCA) and orthogonal partial least squared discrimination analysis (OPLS-DA) to find the potential characteristic components of C. camphora leaves from the four areas in a quick way. C. camphora leaves from different areas could be separated into four different groups chemically according to the PCA scores. The chemical constituents in C. camphora leaves from four areas were obviously different. The potential markers were identified by comparison with the reference compounds or were tentatively assigned by matching the retention time, empirical molecular formula and fragment ions with those of the published compounds of C. camphora leaves. The proposed analytical method is fast, accurate and reliable for differentiating C. camphora leaves from different areas. Moreover, this study supplied a new method for the quality evaluation of other medicinal materials.

Reduction Reactions in the Ion Source in Electron Ionization Mass Spectrometry

Theoretically, electron ionization mass spectra should contain exclusively peaks of ions due to the monomolecular fragmentation of molecular ions. However, spectra of aromatic compounds with halogen atoms and nitro groups contain ion peaks with the composition not consistent with this postulate. Based on a detailed study of such ions by high-resolution mass spectrometry, we showed that their formation is associated with the reduction of the initial molecules at the metal walls of the ion source before their ionization. As a result, products of the reduction reaction of the corresponding composition are ionized. Nitro compounds are reduced to the corresponding amines, while halogenated compounds lose the halogen atom, turning into unsubstituted substrates. Water molecules on the metal surface of the ion source act as reduction agents. This process does not depend on the geometry of the source and proceeds in any mass spectrometer.

Chemical Imaging of Fingerprint on RMB Banknotes Using Time-of-Flight Secondary Ion Mass Spectrometry

The development of latent fingerprints on long-circulated RMB banknotes has been one of the challenging task in forensic science research. In this work, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to perform chemical imaging of latent fingerprints on the surface of the substrate due to its advantages such as in-situ, quasi-nondestructive, high-throughput, simultaneous analysis of multi-components and high spatial resolution. The developing effect of TOF-SIMS was firstly compared with that of several traditional methods, and the reasons for the unique advantages of TOF-SIMS were discussed. Its applicability was further discussed from the perspective of universality, sensitivity and fingerprint three-level feature acquisition capability. Finally, exogenous substances in fingerprints were also analyzed by using this technology to detect the molecular ions (m/z 92.06) and fragment ion peaks (m/z 43.02) of glycerol in the moisture lotion and developed clear fingerprint images. Preliminary research results showed that TOF-SIMS technology could provide an effective method for the development of latent fingerprints on long-circulated RMB banknotes and was expected to be used for the detection of substances in fingerprints on the surface of various substrates.

Microsecond pulsed glow discharge in copper hollow cathode reveals a new approach to ionization and determination of volatile organic compounds

Recently glow discharge (GD) mass spectrometry, which is conventionally used to analyze solid samples, was successfully applied for ionization and the subsequent determination of volatile organic compounds (VOCs). In the present study, the possibility of direct determination of VOCs in ambient air using time-of-flight mass spectrometry with microsecond pulsed discharge in a copper hollow cathode was considered for the first time. The discharge cell of the mass spectrometer was modified for the direct analysis of gaseous samples by the introduction of a quartz capillary into the argon input channel. Various classes of compounds (aromatic and aliphatic hydrocarbons and derivatives of carboxylic acids) were studied. Particular attention was paid to the ionization mechanisms of VOCs. New mechanisms of chemical and electron ionization, resulting in the formation of associate ions with cathode material (copper) – CuM+, were demonstrated and implemented. Alternative mechanisms of organic compounds ionization in GD may be related to Penning process and proton transfer reactions. These processes are mainly responsible for the formation of molecular and protonated molecular ions. The relative contribution of all these mechanisms can be adjusted by operating parameters. In general, an extremely low degree of fragmentation of molecular ions or associates was observed. Due to its isotopic structure (only two isotopes 63Cu and 65Cu with comparable abundances), the use of copper as cathode material additionally increases the reliability of VOC identification in the form of their CuM+ associates. Such association shifts the detected ions to the region of large masses with fewer interferences and noise related to scattered ions.

Triacylglycerols and Fatty Acid Compositions of Cucumber, Tomato, Pumpkin, and Carrot Seed Oils by Ultra-Performance Convergence Chromatography Combined with Quadrupole Time-of-Flight Mass Spectrometry.

The triacylglycerol (TAG) compositions of cucumber, tomato, pumpkin, and carrot seed oils were analyzed using ultra-performance convergence chromatography (UPC2) combined with quadrupole time-of-flight mass spectrometry (Q-TOF MS). A total of 36, 42, 39, and 27 different TAGs were characterized based on their Q-TOF MS accurate molecular weight and MS2 fragment ion profiles in the cucumber, tomato, pumpkin, and carrot seed oils, respectively. Generally, different vegetable seed oils had different TAGs compositions. Among the identified fatty acids, linoleic acid was the most abundant fatty acid in cucumber, tomato, and pumpkin seed oils and the second most abundant in carrot seed oil with relative concentrations of 54.48, 48.69, 45.10, and 15.92 g/100 g total fatty acids, respectively. Oleic acid has the highest concentration in carrot seed oil and the second highest in cucumber, tomato, and pumpkin seed oils, with relative concentrations of 78.97, 18.57, 27.16, and 33.39 g/100 g total fatty acids, respectively. The chemical compositions of TAGs and fatty acids could promote understanding about the chemical profiles of certain vegetable seed oils, thus improving the potential ability to select appropriate oils with specific functions and a high nutritional value and then develop functional foods in the future.

Identification of Synthetic Organic Pigments (SOPs) Used in Modern Artist's Paints with Secondary Ion Mass Spectrometry with MeV Ions.

This work reports on the first systematic study using secondary ion mass spectrometry with MeV ions (MeV-SIMS) for analysis of synthetic organic pigments (SOPs) that can be usually found in modern and contemporary art paints. In order to prove the applicability of the method to different chemical classes of SOPs, 17 pigments were selected for the analyses. The focus was on blue and green phthalocyanines, yellow and red (naphthol AS) azo pigments, red quinacridone, anthraquinone, and diketopyrrolo-pyrrole pigments. Since there are no reference spectra available for this technique, pure pigment powders were measured first to create a database. Simple two-component paint systems were also prepared for testing purposes by mixing synthetic organic pigments with alkyd and acrylic binders. Commercial paints that contain the SOPs with identical C.I. numbers as in the prepared two-component samples were analyzed. All pigments were successfully identified in commercial products in the MeV-SIMS mass spectra through molecular and larger specific fragment ion peaks in the positive-ion mode. The main advantages of MeV-SIMS over other techniques used in SOPs identification, like pyrolysis gas chromatography mass spectrometry (Py-GC/MS), direct-temperature resolved mass spectrometry (DTMS), and laser desorption ionization mass spectrometry (LDIMS), can be summarized as follows: (i) pigments and binders can be detected simultaneously in the same mass spectrum acquired over a short measurement time (up to 500 s), (ii) only small sample flakes are required for the measurements, which are analyzed without any chemical treatment prior to the analyses, (iii) samples are not consumed during the analyses and can be reused for other measurements, e.g., multielemental analysis by other ion beam analysis (IBA) techniques, such as particle-induced X-ray emission (PIXE). Compared to, e.g., Raman spectroscopy, the significant benefit of MeV-SIMS is the exact identification of the SOPs in the paints even if pigments of similar structures are measured.

Mass spectral fragmentation of perfluoroacyl derivatives of half nitrogen mustards for their detection by gas chromatography/mass spectrometry.

Analytical methods for the detection and identification of half nitrogen mustards (halfNMs), i.e., partially hydrolyzed products of nitrogen mustards (pHpNMs), using silyl derivatives are often associated with low sensitivity and selectivity. In order to overcome these limitations, the derivatization of halfNMs was performed using perfluoroacylation. Two efficient derivatization techniques using trifluoroacetyl (TFA) and heptafluorobutyryl (HFB) groups were developed for the unambiguous identification of halfNMs. A mass spectral database was generated by performing gas chromatography/electron ionization mass spectrometry (GC/EI-MS) and gas chromatography/positive chemical ionization mass spectrometry (GC/PCI-MS). The fragmentation pathways were studied by tandem mass spectrometry (MS/MS) in both EI and PCI mode. The EI-MS spectra of the TFA and HFB derivatives of halfNMs contain intense molecular ions and fragment ions, thus making perfluoroacylation preferable to silylation. In addition, the background-free chromatogram obtained using these derivatives provides unambiguous identification of these compounds in blind samples. The structures of the fragment ions were postulated, and the sources of significant ions were traced by performing MS/MS precursor ion scans. In the PCI-MS spectra, along with the protonated molecule, significant peaks due to neutral losses of HF, HCl, CH3 Cl and CF3 COOH were observed. This is the first report of the elucidation of the fragmentation pathways of perfluoroacyl derivatives of halfNMs. The complementary GC/PCI-MS and GC/PCI-MS/MS data will be helpful in the identification of unknown metabolites in a fast and reliable fashion.

Inhibitory Effect and Mechanism of Action of Quercetin and Quercetin Diels-Alder anti-Dimer on Erastin-Induced Ferroptosis in Bone Marrow-Derived Mesenchymal Stem Cells

In this study, the anti-ferroptosis effects of catecholic flavonol quercetin and its metabolite quercetin Diels-Alder anti-dimer (QDAD) were studied using an erastin-treated bone marrow-derived mesenchymal stem cell (bmMSCs) model. Quercetin exhibited higher anti-ferroptosis levels than QDAD, as indicated by 4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid (C11-BODIPY), 2′,7′-dichlorodihydrofluoroscein diacetate (H2DCFDA), lactate dehydrogenase (LDH) release, cell counting kit-8 (CCK-8), and flow cytometric assays. To understand the possible pathways involved, the reaction product of quercetin with the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH●) was measured using ultra-performance liquid-chromatography coupled with electrospray-ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC-ESI-Q-TOF-MS). Quercetin was found to produce the same clusters of molecular ion peaks and fragments as standard QDAD. Furthermore, the antioxidant effects of quercetin and QDAD were compared by determining their 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical-scavenging, Cu2+-reducing, Fe3+-reducing, lipid peroxidation-scavenging, and DPPH●-scavenging activities. Quercetin consistently showed lower IC50 values than QDAD. These findings indicate that quercetin and QDAD can protect bmMSCs from erastin-induced ferroptosis, possibly through the antioxidant pathway. The antioxidant pathway can convert quercetin into QDAD—an inferior ferroptosis-inhibitor and antioxidant. The weakening has highlighted a rule for predicting the relative anti-ferroptosis and antioxidant effects of catecholic flavonols and their Diels-Alder dimer metabolites.

A unified statistical RRKM approach to the fragmentation and autoneutralization of metastable molecular negative ions of hexaazatrinaphthylenes.

For the compounds promising for use as n-type semiconductors in organic electronics and energy storage devices, hexaazatrinaphthylene (HATNA) and its derivative hexamethoxy-hexaazatrinaphthylene (HMHATA), the monomolecular processes occurring under the exposure of molecules to low-energy (0-15 eV) free electrons were studied by means of resonant electron capture negative ion mass spectrometry. Resonant electron attachment results in the formation of eminently long-lived molecular negative ions (MNIs) in an abnormally wide range of incident electron energy (Ee) from 0 to 5-7 eV. For both compounds, this observation serves as an indication of the strong electron-accepting properties and high stability of MNIs against electron autodetachment. A weak yield of the only fragment NIs, dehydrogenated anions, was detected for HATNA at Ee > 6 eV. MNIs of HMHATA are less stable to dissociative decay because of the presence of weakly bound terminal substituents. This is evidenced by the mass spectral observation of intense fragmentation occurring above Ee≈ 1 eV and leading to a loss of up to 3 methyl groups as the Ee increases. A series of metastable NI peaks observed in the mass spectra testify to the delayed and sequential nature of fragmentation. Based on the principles of statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory, the theoretical model of dissociative decay of NIs was developed and then adopted to quantify the rates of ground-state anion decay via electron autodetachment. The experimentally measured electron autodetachment lifetimes and fragmentation rates were best reproduced by the model at molecular adiabatic electron affinities preset to 2.15 eV for HATNA and 1.88 eV for HMHATA, in reasonable agreement with the quantum chemical DFT PBE/3ζ predictions.

Resonance Electron Capture by Cysteine and N-Acetylcysteine Molecules

Processes of the formation of negative ions during the resonance electron capture by molecules of cysteine and its N-substituted derivative are studied. The ion structures in the energy region <4 eV are identified. It is found that in acetylcysteine, the additional channels of molecular ion fragmentation are associated with the cleavage or destruction of the substituent. It is suggested that some processes may be associated with the antioxidant, antitoxic, radioprotective and mucolytic properties of the compounds.