Loss Of HCN Research Articles

Tandem mass spectrometry of homologous 3-hydroxyfurazan and nitrile amino acids: Analysis of cooperative interactions and fragmentation processes.

The assignment of structure by tandem mass spectrometry (MS/MS) relies on the interpretation of the fragmentation behavior of gas-phase ions. Mass spectra were acquired for a series of heterocyclic mimetics of acidic amino acids and a related series of nitrile amino acids. All amino acids were readily protonated or deprotonated by electrospray ionization (ESI), and distinctive fragmentation processes were observed when the ions were subjected to collision-induced dissociation (CID). The deprotonated heterocycles showed bond cleavages of the 3-hydroxyfurazan ring with formation of oxoisocyanate and the complementary deprotonated nitrile amino acid. Further fragmentation of the deprotonated nitrile amino acids was greatly dependent on the length of the alkyl nitrile side chain. Competing losses of CO2 versus HCN occurred from α-cyanoglycinate (shortest chain), whereas water was lost from 2-amino-5-cyanopentanoate (longest chain). Interestingly, loss of acrylonitrile by a McLafferty-type fragmentation process was detected for 2-amino-4-cyanobutanoate, and several competing processes were observed for β-cyanoalanate. In one process, cyanide ion was formed either by consecutive losses of ammonia, carbon dioxide, and acetylene or by a one-step decarboxylative elimination. In another, complementary ions were obtained from β-cyanoalanate by loss of acetonitrile or HN=CHCO2H. Fragmentation of the protonated 3-hydroxyfurazan and nitrile amino acids resulted in the cumulative loss (H2O + CO), a loss that is commonly observed for protonated aliphatic α-amino acids. Overall, the distinct fragmentation behavior of the multifunctional 3-hydroxyfurazan amino acids correlated with the charged site, whereas fragmentations of the deprotonated nitrile amino acids showed cooperative interactions between the nitrile and the carboxylate groups.

Crystal structures, electron spin resonance, and thermogravimetric analysis of three mixed-valence copper cyanide polymers.

The crystal structures of three mixed-valence copper cyanide alkanolamine polymers are presented, together with thermogravimetric analysis (TGA) and electron spin resonance (ESR) data. In all three structures, a CuII moiety on a crystallographic center of symmetry is coordinated by two alkanolamines and links two CuICN chains via cyanide bridging groups to form diperiodic sheets. The sheets are linked together by cuprophilic CuI-CuI interactions to form a three-dimensional network. In poly[bis(μ-3-aminopropanolato)tetra-μ-cyanido-dicopper(I)dicopper(II)], [Cu4(CN)4(C3H8NO)2]n, 1, propanolamine bases have lost their hydroxyl H atoms and coordinate as chelates to two CuII atoms to form a dimeric CuII moiety bridged by the O atoms of the bases with CuII atoms in square-planar coordination. The ESR spectrum is very broad, indicating exchange between the two CuII centers. In poly[bis(2-aminopropanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu3(CN)4(C3H9NO)2]n, 2, and poly[bis(2-aminoethanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu3(CN)4(CH7NO)2]n, 3, a single CuII atom links the CuICN chains together via CN bridges. The chelating alkanolamines are not ionized, and the OH groups form rather long bonds in the axial positions of the octahedrally coordinated CuII atoms. The coordination geometries of CuII in 2 and 3 are almost identical, except that the Cu-O distances are longer in 2 than in 3, which may explain their somewhat different ESR spectra. Thermal decomposition in 2 and 3, but not in 1, begins with the loss of HCN(g), and this can be correlated with the presence of OH protons on the ligands in 2 and 3, which are not present in 1.

Structural analysis of C8H6˙+ fragment ion from quinoline using ion-mobility spectrometry/mass spectrometry.

This study investigated the structures of fragment ions derived from the quinoline (C9H7N) radical cation using ion-mobility spectrometry and mass spectrometry. Ion mobility and mass analysis revealed that C8H6˙+ is the primary dissociation product resulting from the loss of HCN during collision-induced dissociation of the quinoline radical cation. The reduced mobility (K0) of the C8H6˙+ fragment product in helium gas was measured over a range of reduced electric fields (E/N = 20.8-27.4 Td) at room temperature. The experimental K0 values indicated that C8H6˙+ is a mixture of phenylacetylene and pentalene radical cations. Furthermore, quantum chemical calculations revealed two potential energy surfaces delineating the loss of HCN from the quinoline radical cation to form phenylacetylene radical cations.

Discriminating alkylbenzene isomers with tandem mass spectrometry using a dielectric barrier discharge ionization source.

Soft ambient ionization sources generate reactive species that interact with analyte molecules to form intact molecular ions, which allows rapid, sensitive, and direct identification of the molecular mass. We used a dielectric barrier discharge ionization (DBDI) source with nitrogen at atmospheric pressure to detect alkylated aromatic hydrocarbon isomers (C8 H10 or C9 H12 ). Intact molecular ions [M]•+ were detected at 2.4kVpp , but at increased voltage (3.4 kVpp ), [M + N]+ ions were formed, which could be used to differentiate regioisomers by collision-induced dissociation (CID). At 2.4 kVpp , alkylbenzene isomers with different alkyl-substituents could be identified by additional product ions: ethylbenzene and -toluene formed [M-2H]+ , isopropylbenzene formed abundant [M-H]+ , and propylbenzene formed abundant C7 H7 + . At an operating voltage of 3.4 kVpp , fragmentation of [M + N]+ by CID led to neutral loss of HCN and CH3 CN, which corresponded to steric hindrance for excited state N-atoms approaching the aromatic ring (C-H). The ratio of HCN to CH3 N loss (interday relative standard deviation [RSD]< 20%) was distinct for ethylbenzene and ethyltoluene isomers. The greater the number of alkyl-substituents (C-CH3 ) and the more sterically hindered (meta > para > ortho) the aromatic core, the greater the loss of CH3 CN relative to HCN was.

Threshold photoelectron spectroscopy and dissociative photoionization of benzonitrile.

The threshold photoionization and dissociative ionization of benzonitrile (C6H5CN) were studied using double imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy at the Vacuum Ultraviolet (VUV) beamline of the Swiss Light Source (SLS). The threshold photoelectron spectrum was recorded from 9.6 to 12.7 eV and Franck-Condon simulations of ionization into the ionic ground state, X̃+, as well as the B̃+ and C̃+ states were performed to assign the observed vibronic structures. The adiabatic ionization energies of the X̃+, B̃+ and C̃+ states are determined to be (9.72 ± 0.02), (11.85 ± 0.03) and, tentatively, (12.07 ± 0.04) eV, respectively. Threshold ionization mass spectra were recorded from 13.75 to 19.75 eV and the breakdown diagram was constructed by plotting the fractional abundances of the parent ion and ionic dissociation products as a function of photon energy. The seven lowest energy dissociative photoionization channels of benzonitrile were found to yield CN˙ + c-C6H5+, HCN + C6H4˙+, C2H4 + HC5N˙+, HC3N + C4H4˙+, H2C3N˙ + C4H3+, CH2CHCN + C4H2˙+ and H2C4N˙ + c-C3H3+. HCN loss from the benzonitrile cation is the dominant dissociation channel from the dissociation onset of up to 18.1 eV and CH2CHCN loss becomes dominant from 18.1 eV and up. We present extensive potential energy surface calculations on the C6H5CN˙+ surface to rationalize the detected products. The breakdown diagram and time-of-flight mass spectra are fitted using a Rice-Ramsperger-Kassel-Marcus statistical model. Anchoring the fit to the CBS-QB3 result (3.42 eV) for the barrier to HCN loss, we obtained experimental dissociation barriers for the products of 4.30 eV (CN loss), 5.53 eV (C2H4 loss), 4.33 eV (HC3N loss), 5.15 eV (H2C3N loss), 4.93 eV (CH2CHCN loss) and 4.41 eV (H2C4N loss). We compare our work to studies of the electron-induced dissociative ionization of benzonitrile and isoelectronic phenylacetylene (C8H6), as well as the VUV-induced dissociation of protonated benzonitrile (C6H5CNH+). Also, we discuss the potential role of barrierless association reactions found for some of the identified fragments as a source of benzonitrile(˙+) in interstellar chemistry and in Titan's atmosphere.

Composition of Two Local Cassava Varieties and the Effect of Processing on their Hydrocyanic Acid Content and Nutrient Digestibility by the Rat

Two common Nigerian cassava varieties Were subjected to proximate analysis with a view to assessing the relative potential nutrient composition of the roots, stems, leaves and seeds. The results obtained showed that the leaves, seeds and stems in that order are much richer than the roots in protein but higher in crude fibre. There was a relationship between the crude protein contents of the roots and stem and the hydrocyanic acid (HCN) content of the plant while that of the leaves and seeds did not appear to follow the same trend. HCN of the bitter cassava variety was considerably higher in the whole tuber, pulp and peel than in the sweet strain, sundrying and ensiling resulted in appreciable losses of HCN. Grated root lost about half its HCN content within six hours while stored whole roots showed a rapid decline in HCN from the fifth day after harvest. Apparent digestibility coefficients (A.D.C.) of the major nutrients of cassava roots were not significantly (P &lt;0.05) affected by the processes of boiling or sundrying.

Detrusor Underactivity as an HCN-Mediated Failure of Resilience in Aging

Sympathetic relaxation of the bladder wall permits low pressure urine storage and allows central regulation of afferent sensitivity to volume. Impaired regulation of volume sensitivity has been linked to symptoms of underactive bladder and cystometric detrusor underactivity. Hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels) are mediators of sympathomimetic-induced detrusor relaxation in young mouse bladder tissue, however in bladder strips from old female mice, HCN blockade enhanced age-diminished isoproterenol-induced relaxation. We therefore hypothesized that loss of HCN would compromise cystometric function and enhance sympathomimetic responses in old mice. Male HCN1 KO mice (20-22 mo) and their WT littermates underwent pressure-flow cystometry under urethane anesthesia to assess urinary performance at the level of the autonomic nervous system in the absence of cortical control. Following cystometry, bladders were harvested and pharmacomyography was performed on bladder strips to determine tissue-level changes in the absence of CNS input. All mice responded to continuous-fill cystometry by establishing regular filling/voiding cycles. HCN KO mice function showed discrete changes in volume sensitivity vs. WT. Bladder strip studies showed minimal response to isoproterenol regardless of HCN status, and no significant differences in response to carbachol based on HCN status. We conclude that HCN status impacts the brainstem-bladder reflexic control over urine storage/voiding, but not by regulating bladder wall tensions during filling. The absence of HCN influence on the loss of end-organ responsiveness to sympathetic control in old mice points to an increasing dependency on central control mechanisms with aging.

Photoredox chemistry in the synthesis of 2-aminoazoles implicated in prebiotic nucleic acid synthesis.

Prebiotically plausible ferrocyanide-ferricyanide photoredox cycling oxidatively converts thiourea to cyanamide, whilst HCN is reductively homologated to intermediates which either react directly with the cyanamide giving 2-aminoazoles, or have the potential to do so upon loss of HCN from the system. Thiourea itself is produced by heating ammonium thiocyanate, a product of the reaction of HCN and hydrogen sulfide under UV irradiation.

Spectroscopic identification of fragment ions of DNA/RNA building blocks: the case of pyrimidine.

Pyrimidine (Pym, 1,3-diazine, 1,3-diazabenzene) is an important N-heterocyclic building block of nucleobases. Understanding the structures of its fragment and precursor ions provides insight into its prebiotic and abiotic synthetic route. The long-standing controversial debate about the structures of the primary fragment ions of the Pym+ cation (C4H4N2+, m/z 80) resulting from loss of HCN, C3H3N+ (m/z 53), is closed herein with the aid of a combined approach utilizing infrared photodissociation (IRPD) spectroscopy in the CH and NH stretch ranges (νCH/NH) and density functional theory (DFT) calculations. IRPD spectra of cold Ar/N2-tagged fragment ions reveal that the C3H3N+ population is dominated by cis-/trans-HCCHNCH+ ions (∼90%) along with a minor contribution of the most stable H2CCCNH+ and cis-/trans-HCCHCNH+ isomers (∼10%). We also spectroscopically confirm that the secondary fragment resulting from further loss of HCN, C2H2+ (m/z 26), is the acetylene cation (HCCH+). The spectroscopic characterization of the identified C3H3N+ isomers and their hydrogen-bonded dimers with Ar and N2 provides insight into the acidity of their CH and NH groups. Finally, the vibrational properties of Pym+ in the 3 μm range are probed by IRPD of Pym+-(N2)1-2 clusters, which shows a high π-binding affinity of Pym+ toward a nonpolar hydrophobic ligand. Its νCH spectrum confirms the different acidity of the three nonequivalent CH groups.

Statistical process in nitrogen containing naphthalene derivatives in collision with fast electrons and protons

SynopsisThe effect of nitrogen substitution and isomerization in naphthalene under swift charged particle collision is investigated. The ratios of single ionization to capture cross-section are measured for the case of naphthalene and two of its nitrogen-containing derivatives. The propensity of HCN loss in quinoline and isoquinoline is shown to alter systematically from evaporation dominated to randomization dominated process in the case of monocation. The influence of plasmon excitation process in polycyclic aromatic nitrogen heterocycles (PANHs) is identified for the first time.

Fragmentation processes of ionized 5-fluorouracil in the gas phase and within clusters

We have measured mass spectra for positive ions produced from neutral 5-fluorouracil by electron impact at energies from 0 to 100 eV. Fragment ion appearance energies of this (radio-)chemotherapy agent have been determined for the first time and we have identified several new fragment ions of low abundance. The main fragmentations are similar to uracil, involving HNCO loss and subsequent HCN loss, CO loss, or FCCO loss. The features adjacent to these prominent peaks in the mass spectra are attributed to tautomerization preceding the fragmentation and/or the loss of one or two additional hydrogen atoms. A few fragmentions are distinct for 5-fluorouracil compared to uracil, most notably the production of the reactive moiety CF+. Finally, multiphoton ionization mass spectra are compared for 5-fluorouracil from a laser thermal desorption source and from a supersonic expansion source. The detection of a new fragment ion at 114 u in the supersonic expansion experiments provides the first evidence for a clustering effect on the radiation response of 5-fluorouracil. By analogy with previous experiments and calculations on protonated uracil, this is assigned to NH3 loss from protonated 5-fluorouracil.

Why Do Large Ionized Polycyclic Aromatic Hydrocarbons Not Lose C2H2?

The reaction mechanisms for the loss of C2H2 from the ions of anthracene, phenanthrene, tetracene, and pyrene were calculated at the B3-LYP/6-311++G(2d,p) level of theory and compared to that previously published for ionized naphthalene. A common pathway emerged involving the isomerization of the molecular ions to azulene-containing analogues, followed by the contraction of the seven-member ring into a five- and four-member fused ring system, leading to the cleavage of C2H2. The key transition state was found to be for this last process, and its relative energy was consistent going from naphthalene to tetracene. That for pyrene, though, was significantly higher due to the inability of the azulene moiety to achieve a stable conformation because of the presence of the three fused rings. Thus, C2H2 loss is discriminated against in pericondensed PAHs. For catacondensed PAHs, C2H2 loss also drops in relative abundance as the PAH gets larger due to the increase in the number of available hydrogen atoms, increasing the rate constant for H atom loss over that for C2H2 loss as PAH size increases. The unimolecular reactions of four cyano-substituted polycyclic aromatic hydrocarbon (PAH) ions were also probed as a function of collision energy by collision-induced dissociation tandem mass spectrometry. As the size of the ring system increases, HCN loss decreases in importance relative to other processes (H and C2H2 loss). 9-Cyanophenanthrene ions were chosen for further exploration by theory and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. The calculated reaction pathway and energetics for C2H2 loss were consistent with those found above. The calculations suggest that larger PAHs of interest in the interstellar environment will behave independently of a CN substituent.

Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine.

Flavin chromophores play key roles in a wide range of photoactive proteins, but key questions exist in relation to their fundamental spectroscopic and photochemical properties. In this work, we report the first gas-phase spectroscopy study of protonated alloxazine (AL∙H+), a model flavin chromophore. Laser photodissociation is employed across a wide range (2.34–5.64 eV) to obtain the electronic spectrum and characterize the photofragmentation pathways. By comparison to TDDFT quantum chemical calculations, the spectrum is assigned to two AL∙H+ protomers; an N5 (dominant) and O4 (minor) form. The protomers have distinctly different spectral profiles in the region above 4.8 eV due to the presence of a strong electronic transition for the O4 protomer corresponding to an electron-density shift from the benzene to uracil moiety. AL∙H+ photoexcitation leads to fragmentation via loss of HCN and HNCO (along with small molecules such as CO2 and H2O), but the photofragmentation patterns differ dramatically from those observed upon collision excitation of the ground electronic state. This reveals that fragmentation is occurring during the excited state lifetime. Finally, our results show that the N5 protomer is associated primarily with HNCO loss while the O4 protomer is associated with HCN loss, indicating that the ring-opening dynamics are dependent on the location of protonation in the ground-state molecule.

HCN as a Mediator of Urinary Homeostasis: Age-Associated Changes in Expression and Function in Adrenergic Detrusor Relaxation

The Hyperpolarization activated, cyclic nucleotide gated (HCN) channel is a candidate mediator of neuroendocrine influence over detrusor tonus during filling. In other tissues, HCN loss with aging is linked to declines in rhythmicity and function. We hypothesized that HCN has an age-sensitive expression profile and functional role in adrenergic bladder relaxation. HCN was examined in bladders from young (2-6 months) and old (18-24 months) C57BL/6 female mice, using qRT-PCR, RNAScope, and Western blots. Isometric tension studies were conducted using bladder strips from young wild-type (YWT), old wild-type (OWT), and young HCN1 knock-out (YKO) female mice to test the role HCN in effects of β-adrenergic stimulation. Hcn1 is the dominant HCN isoform RNA in the mouse bladder wall, and is diminished with age. Location of Hcn RNA within the mouse bladder wall is isoform-specific, with HCN1 limited to the detrusor layer. Passively-tensioned YWT bladder strips are relaxed by isoproterenol in the presence of HCN function, where OWT strips are relaxed only in the presence of HCN blockade. HCN has an age-specific expression and function in adrenergic detrusor relaxation in mouse bladder strips.

Synthesis, spectroscopic and electrochemical characterization of secnidazole esters

We report a low-cost, less toxic to environment and simple method for the esterification of secnidazole. This is first comprehensive structural characterization of novel secnidazole esters by the spectroscopic and electrochemical methods. The important EIMS fragmentation analysis showed unique contribution of heteroatom bonds explained by the fragmentation patterns. These peaks originate from the loss of single electron, loss of HCN, M-O, M-NO, M-NO2, M-C7H10N3O3, and M-C8H10N3O4. The comparison of 13C NMR predicted values with the experimental values showed that ChemBioDraw Ultra 14.0 has advantage of predicting aromatic (sp2) carbons, while MestReNova 6.1 predicts sp3 hybrid carbons more accurately. The electrochemical properties indicated an irreversible oxidation process and reversible reduction process in these ester molecules similar to the parent secnidazole.

Mechanistic investigation of charge-remote and charge-driven fragmentation processes in 2,5-diphenyl-3,4-ethylenedioxythiophene diamidines.

Diphenylfuran diamidines represent an important class of DNA minor groove binders of high therapeutic interest as antitumor and antibacterial agents. This study aimed to investigate fragmentation patterns in mass spectra of four diamidine derivatives with significant antitumor activity, in order to gain more insight into the structures and stability of their putative biological metabolites. Compounds were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) using low-energy collision-induced dissociation (CID). Density functional theory calculations were performed to confirm the main fragmentation paths. The most abundant ion present in mass spectra is the doubly protonated molecule, whereas singly protonated molecules are present to a lesser extent. In the simplest compound, 2,5-bis(4-amidinophenyl)-3,4-ethylenedioxythiophene, the main fragmentation path was loss of ammonia, followed by loss of HCN where possible. The fragmentation of the N-alkyl derivatives (N-isopropyl-, N-isobutyl-, N-cyclopentyl-) includes competition between loss of alkene and the corresponding amine, followed by loss of another alkene and formation of fragment ions present in the pathway of the parent compound. The primary sites of fragmentations of investigated compounds are amidine groups, while breaking the core 3,4-ethylenedioxythiophene ring system does not take place. Fragmentation of the singly protonated molecule [M+H](+) occurs primarily on the charged side of the molecule, but a charge-remote process is energetically viable. The fragmentation mechanism of the alkyl derivatives revealed that singly and doubly protonated molecules cleave to the singly and doubly protonated molecules of the parent compound. Once formed, they are gradually transformed into nitrile. Copyright © 2016 John Wiley & Sons, Ltd.

Dissociation mechanism of the 3-hydroxypyridine radical cation: A computational study.

The potential energy surface (PES) for the losses of CO and HCN from the 3-hydroxypyridine radical cation (3-HP(+•)) and for the isomerizations to 2- and 4-HP(+•) was determined from G3//B3LYP calculations. The overall activation energies are similar for six dissociation channels to form the radical cations of CH(2)=CHCH=N=CH, 1-H, 2-H, and 3-H pyrrole by the loss of CO and to form the radical cations of CH(2)=CHCH=C=O and furan by the loss of HCN. A kinetic analysis based on the obtained PES shows that the acyclic C(4)H(5)N(+•) and C(4)H(4)O(+•) ions are the main products formed by the losses of CO and HCN, respectively.

Dissociative photoionization of quinoline and isoquinoline.

Two nitrogen-containing polycyclic aromatic hydrocarbon isomers of C9H7N composition, quinoline, and isoquinoline have been studied by imaging photoelectron photoion coincidence spectroscopy at the VUV beamline of the Swiss Light Source. High resolution threshold photoelectron spectra have been recorded and are interpreted applying a Franck-Condon model. Dissociative ionization mass spectra as a function of the parent ion internal energy are analyzed with the use of breakdown diagrams. HCN loss and H loss are the dominant dissociation paths for both C9H7N(•+) isomers at photon energies below 15.5 eV. Computed C9H7N(•+) potential energy surfaces suggest that the lowest energy path leading to HCN-loss yields the benzocyclobutadiene cation. A statistical model is used to fit the breakdown diagram and-to account for the kinetic shift-the time-of-flight mass spectra that reveal the dissociation rates. We have derived appearance energies of 11.9 ± 0.1 (HCN loss) and 12.0 ± 0.1 (H loss), as well as 11.6 ± 0.2 (HCN loss) and 12.1 ± 0.2 (H loss) eV, for the dissociative ionization of quinoline and isoquinoline, respectively. The results are compared to a recent study on the dissociative ionization of naphthalene. Implications for the formation and destruction of nitrogenated PAHs in the interstellar medium and in Titan's atmosphere are highlighted.

Synthesis, crystal structure, structural characterization and in vitro antimicrobial activities of 1-methyl-4-nitro-1H-imidazole

We report new reaction conditions (less corrosive reagents) for the regio-specific synthesis, spectroscopic properties, crystal structure, antimicrobial activities and MICs of 1-methyl-4-nitro-1H-imidazole (I). For structure confirmation, X-ray crystallography was performed using crystals obtained from chloroform and hexane (1:1). The structure of the compound (I) was further characterized by FTIR, 1H NMR, 13C NMR and EIMS. Important peaks appearing in the EIMS, at the m/z=127, 111, 97, 81, and 54 arise due to the loss of single electron, loss of O, NO, NO2, and loss of NO2 & HCN respectively. The high intensity peak in the EIMS at m/z=42 arises due to the loss of NO, CO and HCN from the molecular ion. The correct 1H NMR (400MHz, CDCl3) of (I) shows peaks at 7.76 (ArH, HCN), 7.42 (ArH, HCC), and 3.82 (N–CH3)ppm. Further structural studies showed that the driving force for crystallization (self-assembly) and hydrogen bonding (C–H…O–NO, 2.57Å) originates from the partial negative oxygen of the nitro (NO2) group at one end and the partial positive hydrogen (N–CH3) at another corner of the molecule. Biological assay against many (13) microorganisms and fungi showed that the title compound (I) is moderately active against Gram (+), Gram (−) bacteria and fungi.

Decarbonylation of the 2-Hydroxypyridine Radical Cation: A Computational Study

The potential energy surface (PES) for the dissociation of the 2-hydroxypyridine (2-HP) radical cation was determined from G3//B3LYP calculations, including the loss of CO, HCN, and HNC. The formation of the 1Hpyrrole radical cation by decarbonylation through a more stable tautomer, the 2-pyridone (2-PY) radical cation, was the most favorable dissociation pathway. Kinetic analysis by the Rice-Ramsperger-Kassel-Marcus model calculations was carried out based on the obtained PES. It is proposed that the dissociation occurs after a rapid tautomerization to 2-PY + , and that most of the ions generated by ionization of 2-HP have the structure of 2PY + at equilibrium above the tautomerization barrier.