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František Tureček - One of the best experts on this subject based on the ideXlab platform.
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near uv photoDissociation of tryptic peptide cation radicals scope and effects of amino acid residues and radical sites
Journal of the American Society for Mass Spectrometry, 2017Co-Authors: Huong Thanh Nguyen, František TurečekAbstract:Peptide cation-radical fragment ions of the z-type, [●AXAR+], [●AXAK+], and [●XAR+], where X = A, C, D, E, F, G, H, K, L, M, N, P, Y, and W, were generated by electron transfer Dissociation of peptide dications and investigated by MS3-near-ultraviolet photoDissociation (UVPD) at 355 nm. Laser-pulse dependence measurements indicated that the ion populations were homogeneous for most X residues except phenylalanine. UVPD resulted in Dissociations of backbone CO─NH bonds that were accompanied by hydrogen atom transfer, producing fragment ions of the [yn]+ type. Compared with collision-induced Dissociation, UVPD yielded less side-chain Dissociations even for residues that are sensitive to radical-induced side-chain bond cleavages. The backbone Dissociations are triggered by transitions to second (B) excited electronic states in the peptide ion R-CH●-CONH- chromophores that are resonant with the 355-nm photon energy. Electron promotion increases the polarity of the B excited states, R-CH+-C●(O–)NH-, and steers the reaction to proceed by transfer of protons from proximate acidic Cα and amide nitrogen positions.
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Photoleucine Survives Backbone Cleavage by Electron Transfer Dissociation. A Near-UV PhotoDissociation and Infrared Multiphoton Dissociation Action Spectroscopy Study
Journal of The American Society for Mass Spectrometry, 2016Co-Authors: Christopher J. Shaffer, Aleš Marek, Jonathan Martens, Jos Oomens, František TurečekAbstract:We report a combined experimental and computational study aimed at elucidating the structure of N -terminal fragment ions of the c type produced by electron transfer Dissociation of photo-leucine (L*) peptide ions GL*GGKX. The c _ 4 ion from GL*GGK is found to retain an intact diazirine ring that undergoes selective photoDissociation at 355 nm, followed by backbone cleavage. Infrared multiphoton Dissociation action spectra point to the absence in the c _ 4 ion of a diazoalkane group that could be produced by thermal isomerization of vibrationally hot ions. The c _ 4 ion from ETD of GL*GGK is assigned an amide structure by a close match of the IRMPD action spectrum and calculated IR absorption. The energetics and kinetics of c _ 4 ion Dissociations are discussed. Graphical Abstract ᅟ
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Electron Transfer Reduction of the Diazirine Ring in Gas-Phase Peptide Ions. On the Peculiar Loss of [NH_4O] from Photoleucine
Journal of The American Society for Mass Spectrometry, 2015Co-Authors: Aleš Marek, Robert Pepin, Christopher J. Shaffer, Kristina Slováková, Kenneth J. Laszlo, Matthew F. Bush, František TurečekAbstract:Electron transfer to gas-phase peptide ions with diazirine-containing amino acid residue photoleucine (L*) triggers diazirine ring reduction followed by cascades of residue-specific radical reactions. Upon electron transfer, substantial fractions of (GL*GGR +2H)^+● cation-radicals undergo elimination of [NH_4O] radicals and N_2H_2 molecules from the side chain. The side-chain Dissociations are particularly prominent on collisional activation of long-lived (GL*GGR +2H)^+● cation-radicals formed by electron transfer Dissociation of noncovalent peptide-18-crown-6-ether ion complexes. The ion Dissociation products were characterized by multistage tandem mass spectrometry (MS^n) and ion mobility measurements. The elimination of [NH_4O] was elucidated with the help of ^2H, ^15 N, and ^18O-labeled peptide ions and found to specifically involve the amide oxygen of the N -terminal residue. The structures, energies, and electronic states of the peptide radical species were elucidated by a combination of near-UV photoDissociation experiments and electron structure calculations combining ab initio and density functional theory methods. Electron transfer reaching the ground electronic states of charge reduced (GL*GGR +2H)^+● cation-radicals was found to reduce the diazirine ring. In contrast, backbone N − C_α bond Dissociations that represent a 60%–75% majority of all Dissociations because of electron transfer are predicted to occur from excited electronic states. Graphical Abstract ᅟ
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kinetic ion thermometers for electron transfer Dissociation
Journal of Physical Chemistry B, 2015Co-Authors: Robert Pepin, František TurečekAbstract:Peptide fragment ions of the z-type were used as kinetic ion thermometers to gauge the internal energy of peptide cation-radicals produced by electron transfer in the gas-phase. Electron transfer Dissociation (ETD)-produced z2 ions containing the leucine residue, z2(Leu-Lys) and z2(Leu-Arg), were found to undergo spontaneous Dissociation by loss of C3H7 that was monitored by time-resolved kinetic measurements on the time scale of the linear ion trap mass spectrometer. Kinetic modeling of the Dissociations, including collisional cooling and product loss by neutralization, provided unimolecular rate constants for Dissociation that were converted to the z ion internal energies using RRKM theory. The internal energy of z2(Leu-Lys) and z2(Leu-Arg) fragment ions was found to decrease with the increasing size of the precursor peptide ion, indicating vibrational energy partitioning between the ion and neutral fragments and ergodic behavior. The experimentally determined excitation in the peptide cation-radicals u...
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Collision-Induced Dissociation of Diazirine-Labeled Peptide Ions. Evidence for Brønsted-Acid Assisted Elimination of Nitrogen
Journal of The American Society for Mass Spectrometry, 2014Co-Authors: Aleš Marek, František TurečekAbstract:Gas-phase Dissociations were investigated for several peptide ions containing the Gly-Leu* N-terminal motif where Leu* was a modified norleucine residue containing the photolabile diazirine ring. Collisional activation of gas-phase peptide cations resulted in facile N_2 elimination that competed with backbone Dissociations. A free lysine ammonium group can act as a Brønsted acid to facilitate N_2 elimination. This Dissociation was accompanied by insertion of a lysine proton in the side chain of the photoleucine residue, as established by deuterium labeling and gas-phase sequencing of the products. Electron structure calculations were used to provide structures and energies of reactants, intermediates, and transition states for Gly-Leu*-Gly-Gly-Lys amide ions that were combined with RRKM calculations of unimolecular rate constants. The calculations indicated that Brønsted acid-catalyzed eliminations were kinetically preferred over direct loss of N_2 from the diazirine ring. Mechanisms are proposed to explain the proton-initiated reactions and discuss the reaction products. The non-catalyzed diazirine ring cleavage and N_2 loss is proposed as a thermometer Dissociation for peptide ion Dissociations. Fig. a ᅟ
Gilles Flamant - One of the best experts on this subject based on the ideXlab platform.
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thermal Dissociation of compressed zno and sno2 powders in a moving front solar thermochemical reactor
Aiche Journal, 2011Co-Authors: Marc Chambon, Stéphane Abanades, Gilles FlamantAbstract:The high-temperature thermal Dissociation reaction of ZnO and SnO2 was investigated, as part of a two-step thermochemical water-splitting cycle for H2 production. A lab-scale solar reactor (1 kW) was designed, built, and operated for continuous Dissociation of volatile oxides under reduced pressure. In this reactor, compressed oxide powders placed in a vertical ceramic cavity are irradiated by highly concentrated solar energy. The reactor design allows moving the reaction front for achieving continuous reactant feeding. ZnO and SnO2 thermal Dissociations were successfully performed at about 1900 K, with the recovery of up to 50% of products as nanopowders with high specific surface area (in the range 20–60 m2/g) and with mass fractions of reduced species up to 48 wt % for Zn and 72 wt % for SnO. The performed O2 measurements confirmed the kinetics of ZnO Dissociation and gave an activation energy of 380 ± 16 kJ/mol, based on an ablation regime of the ZnO surface. © 2010 American Institute of Chemical Engineers AIChE J, 2011
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Thermal Dissociation of compressed ZnO and SnO2 powders in a moving‐front solar thermochemical reactor
Aiche Journal, 2010Co-Authors: Marc Chambon, Stéphane Abanades, Gilles FlamantAbstract:The high-temperature thermal Dissociation reaction of ZnO and SnO2 was investigated, as part of a two-step thermochemical water-splitting cycle for H2 production. A lab-scale solar reactor (1 kW) was designed, built, and operated for continuous Dissociation of volatile oxides under reduced pressure. In this reactor, compressed oxide powders placed in a vertical ceramic cavity are irradiated by highly concentrated solar energy. The reactor design allows moving the reaction front for achieving continuous reactant feeding. ZnO and SnO2 thermal Dissociations were successfully performed at about 1900 K, with the recovery of up to 50% of products as nanopowders with high specific surface area (in the range 20–60 m2/g) and with mass fractions of reduced species up to 48 wt % for Zn and 72 wt % for SnO. The performed O2 measurements confirmed the kinetics of ZnO Dissociation and gave an activation energy of 380 ± 16 kJ/mol, based on an ablation regime of the ZnO surface. © 2010 American Institute of Chemical Engineers AIChE J, 2011
Bernhard H Schlegel - One of the best experts on this subject based on the ideXlab platform.
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Dissociation of h2nch dication in a strong laser field
Journal of Physical Chemistry A, 2011Co-Authors: Jia Zhou, Bernhard H SchlegelAbstract:Ab initio classical molecular dynamics calculations have been used to simulate the Dissociation of H(2)NCH(2+) in a strong laser field. The frequencies of the continuous oscillating electric field were chosen to be ω = 0.02, 0.06, and 0.18 au (2280, 760, and 253 nm, respectively). The field had a maximum strength of 0.03 au (3.2 × 10(13) W cm(-2)) and was aligned with the CN bond. Trajectories were started with 100 kcal/mol of vibrational energy above zero point and were integrated for up to 600 fs at the B3LYP/6-311G(d,p) level of theory. A total of 200 trajectories were calculated for each of the three different frequencies and without a field. Two Dissociation channels are observed: HNCH(+) + H(+) and H(2)NC(+) + H(+). About one-half to two-thirds of the H(+) Dissociations occurred directly, while the remaining indirect Dissociations occurred at a slower rate with extensive migration of H(+) between C and N. The laser field increased the initial Dissociation rate by a factor of ca. 1.4 and decreased the half-life by a factor of ca. 0.75. The effects were similar at each of the three frequencies. The HNCH(+) to H(2)NC(+) branching ratio decreased from 10.6:1 in the absence of the field to an average of 8.4:1 in the laser field. The changes in the rates and branching ratios can be attributed to the laser field lowering the reaction barriers as a result of a difference in polarizability of the reactant and transition states.
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ab initio classical trajectory study of the Dissociation of neutral and positively charged methanimine ch2nhn n 0 2
Journal of Physical Chemistry A, 2009Co-Authors: Jia Zhou, Bernhard H SchlegelAbstract:The structures and energetics of the reactants, intermediates, transition states, and products for the Dissociation of methanimine neutral, monocation, dication, and trication were calculated at the CBS-APNO level of theory. The Dissociations of the neutral, monocation, and dication were studied by ab initio direct classical trajectory calculations at the B3LYP/6-311G(d,p) level of theory. A microcanonical ensemble using quasiclassical normal mode sampling was constructed by distributing 200, 150, and 120 kcal/mol of excess energy above the local minima of the neutral, singly, and doubly charged species, respectively. Many of the trajectories dissociate directly to produce H+, H atom, or H2. However, for a fraction of the cases, substantial migration of the hydrogen occurs within the molecule before Dissociation. The preferred Dissociation product for the neutral and the monocation is hydrogen atom. Elimination of H2 was seen in 20% of the trajectories for the neutral and in 5% of the trajectories for the...
Andras Bodi - One of the best experts on this subject based on the ideXlab platform.
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From iron pentacarbonyl to the iron ion by imaging photoelectron photoion coincidence.
Journal of Physical Chemistry A, 2013Co-Authors: Eileen M. Russell, James P. Kercher, Balint Sztaray, Elvis Cudjoe, Michael E. Mastromatteo, Andras BodiAbstract:The Dissociation dynamics of internal energy selected iron pentacarbonyl cations, Fe(CO)5+, have been investigated using the imaging photoelectron photoion coincidence (iPEPICO) spectrometer at the Swiss Light Source. The molecular ion loses all five carbonyl ligands in sequential Dissociations in the 8.5–20 eV photon energy range. The Fe(CO)5+ parent ion is metastable at the onset of the first Dissociation reaction on the time scale of the experiment. The slightly asymmetric and broad daughter ion time-of-flight distributions indicate parent ion lifetimes in the microsecond range, and are used to obtain an experimental Dissociation rate curve. Further carbonyl losses were found to be fast at threshold. The fractional parent and daughter ion abundances as a function of the photon energy, that is, breakdown diagram, as well as the Dissociation rates for the first CO loss were modeled using the statistical Rice–Ramsperger–Kassel–Marcus (RRKM) and statistical adiabatic channel model (SSACM) theories. The exc...
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Comparing femtosecond multiphoton dissociative ionization of tetrathiafulvene with imaging photoelectron photoion coincidence spectroscopy.
Journal of Physical Chemistry A, 2013Co-Authors: Paul M Mayer, David Staedter, Valérie Blanchet, Patrick Hemberger, Andras BodiAbstract:In this paper we describe femtosecond photoionization and the imaging photoelectron photoion coincidence spectroscopy of tetrathiafulvene, TTF. Femtosecond photoionization of TTF results in the absorption of up to twelve 808 nm photons leading to ion internal energies up to 12.1 eV as deduced from the photoelectron spectrum. Within this internal energy a variety of Dissociation channels are accessible. In order to disentangle the complex ionic Dissociation, we utilized the imaging photoelectron photoion coincidence (iPEPICO) technique. Above the Dissociation threshold, iPEPICO results show that the molecular ion (m/z = 204) dissociates into seven product ions, six of which compete in a 1.0 eV internal energy window and are formed with the same appearance energy. Ab initio calculations are reported on the possible fragment ion structures of five Dissociation channels as well as trajectories showing the loss of C2H2 and C2H2S from high internal energy TTF cations. A three-channel Dissociation model is used to fit the PEPICO data in which two Dissociation channels are treated as simple Dissociations (one with a reverse barrier), while the rest involve a shared barrier. The two lower energy Dissociation channels, m/z = 146 and the channel leading to m/z = 178, 171, 159, 140, and 127, have E0 values of 2.77 ± 0.10 and 2.38 ± 0.10 eV, respectively, and are characterized by ΔS(‡)(600 K) values of -9 ± 6 and 1 ± 6 J K(-1) mol(-1), respectively. Competing with them at higher internal energy is the cleavage of the central bond to form the m/z = 102 fragment ion, with an E0 value of 3.65 ± 0.10 eV and ΔS(‡)(600 K) = 83 ± 10 J K(-1) mol(-1).
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Modeling unimolecular reactions in photoelectron photoion coincidence experiments
Journal of Mass Spectrometry, 2010Co-Authors: Balint Sztaray, Andras Bodi, Tomas BaerAbstract:A computer program has been developed to model and analyze the data from photoelectron photoion coincidence (PEPICO) spectroscopy experiments. This code has been used during the past 12 years to extract thermochemical and kinetics information for almost a hundred systems, and the results have been published in over forty papers. It models the dissociative photoionization process in the threshold PEPICO experiment by calculating the thermal energy distribution of the neutral molecule, the energy distribution of the molecular ion as a function of the photon energy, and the resolution of the experiment. Parallel or consecutive Dissociation paths of the molecular ion and also of the resulting fragment ions are modeled to reproduce the experimental breakdown curves and time-of-flight distributions. The latter are used to extract the experimental Dissociation rates. For slow Dissociations, either the quasi-exponential fragment peak shapes or, when the mass resolution is insufficient to model the peak shapes explicitly, the center of mass of the peaks can be used to obtain the rate constants. The internal energy distribution of the fragment ions is calculated from the densities of states using the microcanonical formalism to describe consecutive Dissociations. Dissociation rates can be calculated by the RRKM, SSACM or VTST rate theories, and can include tunneling effects, as well. Isomerization of the dissociating ions can also be considered using analytical formulae for the Dissociation rates either from the original or the isomer ions. The program can optimize the various input parameters to find a good fit to the experimental data, using the downhill simplex algorithm. Copyright © 2010 John Wiley & Sons, Ltd.
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Threshold photoelectron photoion coincidence studies of parallel and sequential Dissociation reactions
Physical Chemistry Chemical Physics, 2005Co-Authors: Tomas Baer, Alexsandre F. Lago, James P. Kercher, Christopher Skull, Andras Bodi, Balint Sztaray, Don PalathinkalAbstract:Recent advances in threshold photoelectron photoion coincidence (TPEPICO) make possible the analysis of several parallel and sequential Dissociations of energy selected ions. The use of velocity focusing optics for the simultaneous collection of threshold and energetic electrons not only improves the resolution, but also permits subtraction of coincidences associated with “hot” electrons, thereby yielding TPEPICO data with no contamination from “hot” electrons. The data analysis takes into account the thermal energy distribution of the sample and uses statistical theory rate constants and energy partitioning in Dissociation reactions to model the time of flight distributions and the breakdown diagram. Examples include CH2BrCl and P(C2H5)3. Of particular interest is the ability to extract error limits for rate constants and Dissociation energies.
Jia Zhou - One of the best experts on this subject based on the ideXlab platform.
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Dissociation of h2nch dication in a strong laser field
Journal of Physical Chemistry A, 2011Co-Authors: Jia Zhou, Bernhard H SchlegelAbstract:Ab initio classical molecular dynamics calculations have been used to simulate the Dissociation of H(2)NCH(2+) in a strong laser field. The frequencies of the continuous oscillating electric field were chosen to be ω = 0.02, 0.06, and 0.18 au (2280, 760, and 253 nm, respectively). The field had a maximum strength of 0.03 au (3.2 × 10(13) W cm(-2)) and was aligned with the CN bond. Trajectories were started with 100 kcal/mol of vibrational energy above zero point and were integrated for up to 600 fs at the B3LYP/6-311G(d,p) level of theory. A total of 200 trajectories were calculated for each of the three different frequencies and without a field. Two Dissociation channels are observed: HNCH(+) + H(+) and H(2)NC(+) + H(+). About one-half to two-thirds of the H(+) Dissociations occurred directly, while the remaining indirect Dissociations occurred at a slower rate with extensive migration of H(+) between C and N. The laser field increased the initial Dissociation rate by a factor of ca. 1.4 and decreased the half-life by a factor of ca. 0.75. The effects were similar at each of the three frequencies. The HNCH(+) to H(2)NC(+) branching ratio decreased from 10.6:1 in the absence of the field to an average of 8.4:1 in the laser field. The changes in the rates and branching ratios can be attributed to the laser field lowering the reaction barriers as a result of a difference in polarizability of the reactant and transition states.
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Ab initio classical trajectory study of the Dissociation of neutral and positively charged methanimine (CH2NHn+ n = 0-2).
Journal of Physical Chemistry A, 2009Co-Authors: Jia Zhou, H. Bernhard SchlegelAbstract:The structures and energetics of the reactants, intermediates, transition states, and products for the Dissociation of methanimine neutral, monocation, dication, and trication were calculated at the CBS-APNO level of theory. The Dissociations of the neutral, monocation, and dication were studied by ab initio direct classical trajectory calculations at the B3LYP/6-311G(d,p) level of theory. A microcanonical ensemble using quasiclassical normal mode sampling was constructed by distributing 200, 150, and 120 kcal/mol of excess energy above the local minima of the neutral, singly, and doubly charged species, respectively. Many of the trajectories dissociate directly to produce H+, H atom, or H2. However, for a fraction of the cases, substantial migration of the hydrogen occurs within the molecule before Dissociation. The preferred Dissociation product for the neutral and the monocation is hydrogen atom. Elimination of H2 was seen in 20% of the trajectories for the neutral and in 5% of the trajectories for the...
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ab initio classical trajectory study of the Dissociation of neutral and positively charged methanimine ch2nhn n 0 2
Journal of Physical Chemistry A, 2009Co-Authors: Jia Zhou, Bernhard H SchlegelAbstract:The structures and energetics of the reactants, intermediates, transition states, and products for the Dissociation of methanimine neutral, monocation, dication, and trication were calculated at the CBS-APNO level of theory. The Dissociations of the neutral, monocation, and dication were studied by ab initio direct classical trajectory calculations at the B3LYP/6-311G(d,p) level of theory. A microcanonical ensemble using quasiclassical normal mode sampling was constructed by distributing 200, 150, and 120 kcal/mol of excess energy above the local minima of the neutral, singly, and doubly charged species, respectively. Many of the trajectories dissociate directly to produce H+, H atom, or H2. However, for a fraction of the cases, substantial migration of the hydrogen occurs within the molecule before Dissociation. The preferred Dissociation product for the neutral and the monocation is hydrogen atom. Elimination of H2 was seen in 20% of the trajectories for the neutral and in 5% of the trajectories for the...
