Distinct Fragmentation Pathways Research Articles

Relaxation of the 2a1 ionized water dimer: An interplay of intermolecular Coulombic decay (ICD) and proton transfer processes.

This article investigates the relaxation dynamics of the ionized 2a1 state of a water molecule within a water dimer. The study was motivated by findings from two previous pieces of research that focused on the relaxation behaviors of the inner-valence ionized water dimer. The present study discloses an observation indicating that water dimers display specific fragmentation patterns following inner-valence ionization, depending on the position of the vacancy. Vacancies were created in the 2a1 state of the proton-donating water molecule (PDWM) and proton-accepting water molecule (PAWM). Utilizing Born-Oppenheimer molecular dynamics simulations, the propagation of the 2a1 ionized state was carried out for both scenarios. The results revealed proton transfer occurred when the vacancy resided in the PDWM, accompanied by the closing of decay channels for O-H bond distance (RO-H) > 1.187Å (matching Richter et al.'s findings). Conversely, when vacancy was on PAWM, we observed no closing of decay channels (aligning with Jahnke et al.'s findings). This difference translates to distinct fragmentation pathways. In PDWM cases, 2a1 state ionization leads to H3O+ -OH• formation. In contrast, PAWM vacancies result in decay pathways leading to H2O+-H2O+ products.

Kinetic parameters for H abstraction from the serine amino acid molecule

The Serine compound signifies an important model entity of polar amino acids species in various categories of biomass. The presence of adjacent amino and hydroxyl groups is expected to afford this molecule distinct fragmentation pathways. Comprehending the decomposition chemistry of serine (and other amino acids) is of a crucial important in the pursuit to minimize emission of notorious nitrogen-bearing species during thermal treatment of biomass. This contribution provides thermo-kinetic parameters for H abstraction from the five distinct sites in the serine molecule; namely amine’s, secondary’s, hydroxyl’s, and α CH hydrogen atoms by the abundant radical species in the pyrolytic/oxidative environments (H, CH3, NH2, OH, and HO2). For all considered radicals, it is illustrated that reactions of these five radicals predominantly ensue through abstraction of the α CH’s hydrogen atoms. Nonetheless, computed reaction rate constants also disclose that abstraction from the secondary’s H site becomes important as the temperature increases. Outcomes provided herein could be deployed in formulating robust kinetic models that account for the nitrogen transformation chemistry in energy recovery of biomass.

Distinct Fragmentation Pathways of Anticancer Drugs Induced by Charge-Carrying Cations in the Gas Phase.

With the growth of the pharmaceutical industry, structural elucidation of drugs and derivatives using tandem mass spectrometry (MS2) has become essential for drug development and pharmacokinetics studies because of its high sensitivity and low sample requirement. Thus, research seeking to understand fundamental relationships between fragmentation patterns and precursor ion structures in the gas phase has gained attention. In this study, we investigate the fragmentation of the widely used anticancer drugs, doxorubicin (DOX), vinblastine (VBL), and vinorelbine (VRL), complexed by a singly charged proton or alkali metal ion (Li+, Na+, K+) in the gas phase. The drug-cation complexes exhibit distinct fragmentation patterns in tandem mass spectra as a function of cation size. The trends in fragmentation patterns are explicable in terms of structures derived from ion mobility mass spectrometry (IM-MS) and theoretical calculations. Graphical Abstract ᅟ.

Fragmentation reactions of an (n = 4–8) ions containing only alanine residues

A detailed study of the fragmentation reactions of an (n=4–8) ions containing only Ala residues has been carried out using collisional activation on an electrospray/QqToF instrument. Two distinct fragmentation pathways are observed. One, which we have called the “imine” pathway, involves initial elimination of an imine (an→bn−1) followed by elimination of Ala residues (bn−1→bn−2, etc.). This pathway most likely involves the protonated substituted imine R2C(O)NH+CHR1. The second pathway, which we have called the “amide” pathway, involves initial elimination of NH3 to form an an* ion followed by elimination of Ala residues to form a series of a* ions (an*→an−1*→an−2*, etc.). This latter reaction sequence begins from a protonated C-terminal amide which has been identified by IRMPD studies as the major species present for the A-A-A-A a4 ion (Bythell et al., 2010). The present results strongly indicate that the larger an ions fragment in a manner similar to that elucidated for the all-Ala a4 ion and that the “amide” pathway is the dominant fragmentation channel for all the an ions studied in the present work.

Dissociation behavior of a bifunctional tempo-active ester reagent for peptide structure analysis by free radical initiated peptide sequencing (FRIPS) mass spectrometry.

We have synthesized a homobifunctional active ester cross-linking reagent containing a TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy) moiety connected to a benzyl group (Bz), termed TEMPO-Bz-linker. The aim for designing this novel cross-linker was to facilitate MS analysis of cross-linked products by free radical initiated peptide sequencing (FRIPS). The TEMPO-Bz-linker was reacted with all 20 proteinogenic amino acids as well as with model peptides to gain detailed insights into its fragmentation mechanism upon collision activation. The final goal of this proof-of-principle study was to evaluate the potential of the TEMPO-Bz-linker for chemical cross-linking studies to derive 3D-structure information of proteins. Our studies were motivated by the well documented instability of the central NO-C bond of TEMPO-Bz reagents upon collision activation. The fragmentation of this specific bond was investigated in respect to charge states and amino acid composition of a large set of precursor ions resulting in the identification of two distinct fragmentation pathways. Molecular ions with highly basic residues are able to keep the charge carriers located, i.e. protons or sodium cations, and consequently decompose via a homolytic cleavage of the NO-C bond of the TEMPO-Bz-linker. This leads to the formation of complementary open-shell peptide radical cations, while precursor ions that are protonated at the TEMPO-Bz-linker itself exhibit a charge-driven formation of even-electron product ions upon collision activation. MS(3) product ion experiments provided amino acid sequence information and allowed determining the cross-linking site. Our study fully characterizes the CID behavior of the TEMPO-Bz-linker and demonstrates its potential, but also its limitations for chemical cross-linking applications utilizing the special features of open-shell peptide ions on the basis of selective tandem MS analysis.

Characterization of multiple fragmentation pathways initiated by collision‐induced dissociation of multifunctional anions formed by deprotonation of 2‐nitrobenzenesulfonylglycine

The correlation of anion structure with the fragmentation behavior of deprotonated nitrobenzenesulfonylamino acids was investigated using tandem mass spectrometry, isotopic labeling and computational methods. Four distinct fragmentation pathways resulting from the collision-induced dissociation (CID) of deprotonated 2-nitrobenzenesulfonylglycine (NsGly) were characterized. The unusual loss of the aryl nitro substituent as HONO was the lowest energy process. Subsequent successive losses of CO, HCN and SO2 indicated that an ortho cyclization reaction had accompanied loss of HONO. Other pathways involving rearrangement of the ionized sulfonamide group, dual bond cleavage and intramolecular nucleophilic displacement were proposed to account for the formation of phenoxide, arylsulfinate and arylsulfonamide product ions at higher collision energies. The four distinct fragmentation pathways were consistent with precursor-product relationships established by CID experiments, isotopic labeling results and the formation of analogous product ions from 2,4-dinitrobenzenesulfonylglycine and the Ns derivatives of alanine and 2-aminoisobutyric acid. The computations confirmed a low barrier for ortho cyclization with loss of HONO and feasible energetics for each reaction step in the four pathways. Computations also indicated that three of the fragmentation pathways started from NsGly ionized at the carboxyl group. Overall, the pathways identified for the fragmentation of the NsGly anion differed from processes reported for anions containing a single functional group, demonstrating the importance of functional group interactions in the fragmentation pathways of multifunctional anions.

Characterisation of polyacetylenes isolated from carrot (Daucus carota) extracts by negative ion tandem mass spectrometry

The potential use of negative electrospray ionisation mass spectrometry (ESI-MS) in the characterisation of the three polyacetylenes common in carrots (Daucus carota) has been assessed. The MS scans have demonstrated that the polyacetylenes undergo a modest degree of in-source decomposition in the negative ionisation mode while the positive ionisation mode has shown predominantly sodiated ions and no [M+H](+) ions. Tandem mass spectrometric (MS/MS) studies have shown that the polyacetylenes follow two distinct fragmentation pathways: one that involves cleavage of the C3-C4 bond and the other with cleavage of the C7-C8 bond. The cleavage of the C7-C8 bond generated product ions m/z 105.0 for falcarinol, m/z 105/107.0 for falcarindiol, m/z 147.0/149.1 for falcarindiol-3-acetate. In addition to these product ions, the transitions m/z 243.2 → 187.1 (falcarinol), m/z 259.2 → 203.1 (falcarindiol), m/z 301.2 → 255.2/203.1 (falcarindiol-3-acetate), mostly from the C3-C4 bond cleavage, can form the basis of multiple reaction monitoring (MRM)-quantitative methods which are poorly represented in the literature. The 'MS(3) ' experimental data confirmed a less pronounced homolytic cleavage site between the C11-C12 bond in the falcarinol-type polacetylenes. The optimised liquid chromatography (LC)/MS conditions have achieved a baseline chromatographic separation of the three polyacetylenes investigated within 40 min total run-time.

Fragmentation Dynamics ofCO23+Investigated by Multiple Electron Capture in Collisions with Slow Highly Charged Ions

Fragmentation of highly charged molecular ions or clusters consisting of more than two atoms can proceed in a one step synchronous manner where all bonds break simultaneously or sequentially by emitting one ion after the other. We separated these decay channels for the fragmentation of CO(2)(3+) ions by measuring the momenta of the ionic fragments. We show that the total energy deposited in the molecular ion is a control parameter which switches between three distinct fragmentation pathways: the sequential fragmentation in which the emission of an O(+) ion leaves a rotating CO(2+) ion behind that fragments after a time delay, the Coulomb explosion and an in-between fragmentation--the asynchronous dissociation. These mechanisms are directly distinguishable in Dalitz plots and Newton diagrams of the fragment momenta. The CO(2)(3+) ions are produced by multiple electron capture in collisions with 3.2 keV/u Ar(8+) ions.

Imaging studies of the photodissociation of H2S+ cations. I. Illustrations of the role of nuclear spin

Ion imaging methods have been used to study the dynamics of H(2)(D(2)) molecular elimination from H(2)S(+)(D(2)S(+)) cations following photoexcitation to the A(2)A(1) state in the wavelength range 300<lambda<360 nm. Ground (X (2)B(1)) state parent ions were formed by multiphoton ionization of a jet cooled H(2)S(D(2)S) sample, resonance enhanced at the two photon energy by the v=0 level of the (1)A(2)(... 2b(1) (1)4pb(2)(1)) Rydberg state. This Rydberg excited state predissociates sufficiently slowly that the 2+1 resonance enhanced multiphoton ionization (REMPI) spectrum shows resolved rovibronic structure, thereby allowing full quantum state selectivity at this intermediate stage of the cation preparation process. Analysis of the S(+) ion images following one photon excitation of the resulting H(2)S(+)(D(2)S(+)) cations shows that these fragments are formed in their ground (4)S state, and that the H(2)(D(2)) cofragments are formed predominantly (if not exclusively) in rotational states with either odd or even J rotational quantum number--depending on the chosen REMPI preparation wavelength. This striking specificity for forming ortho- or para-H(2)(D(2)) products can be traced back to the state selectivity introduced in the REMPI preparation step. In the case of H(2)S, therefore, the nuclear spin symmetry of the two equivalent H nuclei in ortho-H(2)S (and H(2)S(+)) carries through into ortho-H(2) products, and para-H(2)S molecules map into para-H(2) fragments, surviving photoionization of the Rydberg state, photolysis of the resulting parent cation, and two subsequent radiationless transitions during the evolution from the photoexcited (A(2)A(1) state) cation through to S((4)S)+H(2) products. We identify two distinct fragmentation pathways. One, which we term route I, involves nonadiabatic (Renner-Teller) coupling to the X state at near linear configurations and subsequent (spin-orbit induced) coupling to the repulsive (4)A(2) potential energy surface (PES) at smaller bond angles. This process operates throughout the photolysis wavelength range investigated and yields rotationally "cool" and vibrationally "cold" H(2) products. The second (route II) shows a long wavelength threshold lambda approximately 335 nm, and gradually becomes dominant as the photolysis wavelength is reduced. Route II dissociation involves vibronically facilitated nonadiabatic transfer from the A to the B(2)B(2) state, followed by spin-orbit induced transfer to the (4)A(2) PES; the route II fragmentation dynamics results in H(2) products carrying higher levels of rotational and vibrational excitation.

Differential EI fragmentation pathways for peracetylated C‐glycoside ketones as a consequence of bicyclic ketal ring structures

Several C-glycoside ketones and peracetylated C-glycoside ketones have been synthesized from 13 structurally-diverse aldoses sugars (including isotope labeled [1-(13)C]Glc, [U-(13)C]Glc, and [6, 6'-(2)H(2)]Glc) via an aqueous-based Knoevanagel condensation with aliphatic 1,3-diketones. Sodium adduct molecular ions observed by MALDI-TOF MS confirmed that the reactions are essentially quantitative, and that the acetylation products are the expected peracetylated C-glycoside ketones, rather than cyclized ketofurans. Analysis of the peracetylated C-glycoside ketones by gas chromatography-EI-MS show characteristic fragment ions that have been assigned to four distinct fragmentation pathways. Peracetylated aldohexose-, aldopentose-, and 6-deoxyaldohexose-C-glycoside ketones fragment via gas phase furanoid intermediates. These data, and DFT calculations, indicate that the furanoid intermediates arise because the peracetylated C-glycoside ketones adopt a bicyclic structure containing a 5-member ketal ring. This ketal ring is the precursor of the furanoid rings in the gas phase. The 2-deoxyhexose-C-glycoside ketones are unable to form an intramolecular 2-ketal bond, and therefore undergo ion fragmentations via nonfuranoid pathways.

Generation of Gas-Phase VO2+, VOOH+, and VO2+−Nitrile Complex Ions by Electrospray Ionization and Collision-Induced Dissociation

Cationic metal species normally function as Lewis acids, accepting electron density from bound electron-donating ligands, but they can be induced to function as electron donors relative to dioxygen by careful control of the oxidation state and ligand field. In this study, cationic vanadium(IV) oxohydroxy complexes were induced to function as Lewis bases, as demonstrated by addition of O2 to an undercoordinated metal center. Gas-phase complex ions containing the vanadyl (VO2+), vanadyl hydroxide (VOOH+), or vanadium(V) dioxo (VO2+) cation and nitrile (acetonitrile, propionitrile, butyronitrile, or benzonitrile) ligands were generated by electrospray ionization (ESI) for study by multiple-stage tandem mass spectrometry. The principal species generated by ESI were complexes with the formula [VO(L)n]2+, where L represents the respective nitrile ligands and n=4 and 5. Collision-induced dissociation (CID) of [VO(L)5]2+ eliminated a single nitrile ligand to produce [VO(L)4]2+. Two distinct fragmentation pathways were observed for the subsequent dissociation of [VO(L)4]2+. The first involved the elimination of a second nitrile ligand to generate [VO(L)3]2+, which then added neutral H2O via an association reaction that occurred for all undercoordinated vanadium complexes. The second [UO(L)4]2+ fragmentation pathway led instead to the formation of [VOOH(L)2]+ through collisions with gas-phase H2O and concomitant losses of L and [L+H]+. CID of [VOOH(L)2]+ caused the elimination of a single nitrile ligand to generate [VOOH(L)]+, which rapidly added O2 (in addition to H2O) by a gas-phase association reaction. CID of [VONO3(L)2]+, generated from spray solutions created by mixing VOSO4 and Ba(NO3)2 (and precipitation of BaSO4), caused elimination of NO2 to produce [VO2(L)2]+. CID of [VO2(L)2]+ produced elimination of a single nitrile ligand to form [VO2(L)]+, a V(V) analogue to the O2-reactive V(IV) species [VOOH(L)]+; however, this V(V) complex was unreactive with O2, which indicates the requirement for an unpaired electron in the metal valence shell for O2 addition. In general, the [VO2(L)2]+ species required higher collisions energies to liberate the nitrile ligand, suggesting that they are more strongly bound than the [VOOH(L)2]+ counterparts.

Tandem mass spectrometric analysis of distinct fragmentation patterns to [M+Na]/z and [M+H]/z of dendritic Al(III) and Zn(II) quinolates.

The synthesis of two novel dendritic aluminum and zinc quinolates, which are soluble in common solvents, was monitored effectively by positive ion electrospray ionization mass spectrometry (ESI-MS). Through tandem mass spectrometric analysis of the complexes, distinct fragmentation pathways for sodium adduct molecular ion [M+Na]+ and protonated molecular ion [M+H]+ were observed.

Coumarins VIII: Mass Spectra of Lomatin and Some of Its Derivatives

The fragmentation behavior of lomatin and certain of its derivatives has been studied. Two distinct fragmentation pathways have been observed, one leading to aromatization of the chroman ring and the other leading to its fission. These findings are in complete agreement with the observations of other workers. Probable fragmentation mechanisms have been proposed.