The Experts below are selected from a list of 1125 Experts worldwide ranked by ideXlab platform
John L Holmes - One of the best experts on this subject based on the ideXlab platform.
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neutralization reionization Mass Spectrometry applied to organometallic and coordination chemistry update 1994 1998
Mass Spectrometry Reviews, 1999Co-Authors: Dmitri V Zagorevskii, John L HolmesAbstract:This review presents the results from the last 5 years on neutralization–reionization Mass Spectrometry (NRMS) studies of metal-containing ions. The results for silicon- and phosphorus-containing species are also discussed. The major aim of NRMS experiments is to generate (in the gas phase) neutrals that cannot be easily produced and/or detected in other experimental conditions. A variety of elusive complexes of coordinatively unsaturated and saturated metal(s), including important reaction intermediates, have been produced by collisional neutralization of their positively or negatively charged counterparts in the Mass spectrometer. The detection of these species helps in understanding the mechanisms of reactions in the gas and condensed phases (interstellar chemistry, catalytic transformations, reactions on surfaces, etc.). The reviewed period of time has been characterized by the development of new experimental techniques. These techniques allow studying stability, electronic structure, and reactivity of selected molecules and radicals. The review provides a complete list of metal-, Si-, and P-containing ions that have been studied by using NRMS and related methods prior to 1999. © 1999 John Wiley & Sons, Inc., Mass Spec Rev 18: 87–118, 1999
Helmut Schwarz - One of the best experts on this subject based on the ideXlab platform.
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gas phase generation and characterization of methyl and dimethylsilylene and their cations by collisional activation and neutralization reionization Mass Spectrometry
ChemInform, 1994Co-Authors: R Srinivas, Diethard K Bohme, Helmut SchwarzAbstract:Results of Mass spectrometric measurements are reported which characterize the chemical bonding in the radical cations (CH 3 SiH) .+ and (CH 3 ) 2 Si .+ and provide evidence for the existence of the corresponding neutral silylene molecules CH 3 SiH and (CH 3 ) 2 Si in the gas phase. The experiments were performed with a modified four-sector ZAB Mass spectrometer with a BEBE configuration and collision cells mounted in the intermediate field-free regions B(1)/E(1), E(1)/B(2), and B(2)E(2). Observed collisional activation (CA) Mass spectra of the ions [H 4 ,C,Si] + and [H 6 ,C 2 ,Si] + generated from electron impact of tetramethylsilane and other precursors and CA/CA spectra of the [C,H 3 ,Si] + derived from them are most compatible with the connectivities CH 3 SiH .+ and (CH 3 ) 2 Si .+
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gas phase generation and structural characterization of h2 c o si bul and h2 c o si by collisional activation and neutralization reionization Mass Spectrometry and theory evidence for the distonic ion h2c bul o si and the biradical ch2osi
Journal of the American Chemical Society, 1992Co-Authors: R Srinivas, Diethard K Boehme, Jan Hrusak, Detlef Schroeder, Helmut SchwarzAbstract:Results of laboratory measurements and theoretical investigations are reported which provide evidence for the stability of the distonic ion 'CH,OSi+ and which show that the biradical species 'CH20Si' may be generated by the neutralization of the distonic ion in the gas phase. The measurements were made using collisional-activation and Neutralization-Reionization Mass Spectrometry. Ions of the type (H,, C, 0, Si)" were generated by electron-impact ionization of Si(OCH3), at 70 eV. Observed collisional-activation (CA) Mass spectra of these ions at 8-keV translational energy are most compatible with the connectivity 'CH,OSi+. Neutralization-Reionization (NRMS) experiments with this distonic ion suggest an identical connectivity for the corresponding neutral species. The experimental findings are complemented by ab intio MO studies (MP2/6- 3lGS*//MP2/6-31G** +ZPVE) which predict that the heavy-atom backbone of both the distonic ion and the biradical neutral are linear and that they have very similar bond lengths. They also provide useful information on the energetics of the unimolecular decompositions of the distonic ion and the energetics and structures of many of its isomers.
Dmitri V Zagorevskii - One of the best experts on this subject based on the ideXlab platform.
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neutralization reionization Mass Spectrometry applied to organometallic and coordination chemistry update 1994 1998
Mass Spectrometry Reviews, 1999Co-Authors: Dmitri V Zagorevskii, John L HolmesAbstract:This review presents the results from the last 5 years on neutralization–reionization Mass Spectrometry (NRMS) studies of metal-containing ions. The results for silicon- and phosphorus-containing species are also discussed. The major aim of NRMS experiments is to generate (in the gas phase) neutrals that cannot be easily produced and/or detected in other experimental conditions. A variety of elusive complexes of coordinatively unsaturated and saturated metal(s), including important reaction intermediates, have been produced by collisional neutralization of their positively or negatively charged counterparts in the Mass spectrometer. The detection of these species helps in understanding the mechanisms of reactions in the gas and condensed phases (interstellar chemistry, catalytic transformations, reactions on surfaces, etc.). The reviewed period of time has been characterized by the development of new experimental techniques. These techniques allow studying stability, electronic structure, and reactivity of selected molecules and radicals. The review provides a complete list of metal-, Si-, and P-containing ions that have been studied by using NRMS and related methods prior to 1999. © 1999 John Wiley & Sons, Inc., Mass Spec Rev 18: 87–118, 1999
R Srinivas - One of the best experts on this subject based on the ideXlab platform.
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gas phase generation and characterization of methyl and dimethylsilylene and their cations by collisional activation and neutralization reionization Mass Spectrometry
ChemInform, 1994Co-Authors: R Srinivas, Diethard K Bohme, Helmut SchwarzAbstract:Results of Mass spectrometric measurements are reported which characterize the chemical bonding in the radical cations (CH 3 SiH) .+ and (CH 3 ) 2 Si .+ and provide evidence for the existence of the corresponding neutral silylene molecules CH 3 SiH and (CH 3 ) 2 Si in the gas phase. The experiments were performed with a modified four-sector ZAB Mass spectrometer with a BEBE configuration and collision cells mounted in the intermediate field-free regions B(1)/E(1), E(1)/B(2), and B(2)E(2). Observed collisional activation (CA) Mass spectra of the ions [H 4 ,C,Si] + and [H 6 ,C 2 ,Si] + generated from electron impact of tetramethylsilane and other precursors and CA/CA spectra of the [C,H 3 ,Si] + derived from them are most compatible with the connectivities CH 3 SiH .+ and (CH 3 ) 2 Si .+
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gas phase generation and structural characterization of h2 c o si bul and h2 c o si by collisional activation and neutralization reionization Mass Spectrometry and theory evidence for the distonic ion h2c bul o si and the biradical ch2osi
Journal of the American Chemical Society, 1992Co-Authors: R Srinivas, Diethard K Boehme, Jan Hrusak, Detlef Schroeder, Helmut SchwarzAbstract:Results of laboratory measurements and theoretical investigations are reported which provide evidence for the stability of the distonic ion 'CH,OSi+ and which show that the biradical species 'CH20Si' may be generated by the neutralization of the distonic ion in the gas phase. The measurements were made using collisional-activation and Neutralization-Reionization Mass Spectrometry. Ions of the type (H,, C, 0, Si)" were generated by electron-impact ionization of Si(OCH3), at 70 eV. Observed collisional-activation (CA) Mass spectra of these ions at 8-keV translational energy are most compatible with the connectivity 'CH,OSi+. Neutralization-Reionization (NRMS) experiments with this distonic ion suggest an identical connectivity for the corresponding neutral species. The experimental findings are complemented by ab intio MO studies (MP2/6- 3lGS*//MP2/6-31G** +ZPVE) which predict that the heavy-atom backbone of both the distonic ion and the biradical neutral are linear and that they have very similar bond lengths. They also provide useful information on the energetics of the unimolecular decompositions of the distonic ion and the energetics and structures of many of its isomers.
Fred W Mclafferty - One of the best experts on this subject based on the ideXlab platform.
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0 SMALL CARBON CLUSTERS (C,, 0, C,,+ C,,) FROM ACYCLIC AND CY ~ < PRECURSORS. Neutralization-Reionization Mass Spectrometry AND THEORY
2016Co-Authors: Aberra Fura, Frantisek Turecek, Fred W MclaffertyAbstract:• Abstract: Ab initio calculations of isomeric carbon clusters Cn° % and Cn', n = 2-4, yield structures and energies similar to previous reports, although five (not two) C4 ÷ structures have local energy minima. Dissociative ionization of structurally varied precursors 7as used to prepare C3 and C4 ionic and neutral isomers; however, their Mass spectra from collisionally activated dissociation (CAD) and Neutralization-Reionization (NR) under a wide variety of conditions are indistinguishable, indicating only one isomer or the same mixture of isomers. Likewise, CAD and NR spectra of C4 ÷ and C40 from 1"CH 2=CHCH=1 3CH2 and C3+ and C30 from CH2=13CHCH 3 show complete 13C / 12C scrambling. CAD cross sections are consistent with C4+- C6÷ ions as mainly linear isomers and C7 ÷ ions from cyclic precursors as mainly cyclic. Product abundances from the unimolecular dissociation of Cn0, Cn-, and Cn ÷ allow the selection of thermodynamic data that should be of higher relative accuracy, such as 11.4 eV for the C3 ionization energy from reported values of 10.0-13.0 eV
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electron capture dissociation of multiply charged protein cations a nonergodic process
Journal of the American Chemical Society, 1998Co-Authors: Roman A Zubarev, Neil L Kelleher, Fred W MclaffertyAbstract:Neutralization-Reionization Mass Spectrometry (MS)1 is of unique value for preparing and characterizing highly reactive and unstable neutral species, such as the intermediate in the dissociative-recombination reaction H3O + ef H2O + H + 6.4 eV.2 Following an earlier suggestion,3 using neutralization accompanying surface-induced dissociation (SID)4 to form an unstable site did not yield new cleavage reactions5 in multiply charged protein cations from electrospray ionization (ESI) with Fourier transform (FT) MS.6 Serendipitously, we now find that one or more charges on such protein cations can be neutralized with low-energy electrons to cause specific cleavage of the amine bond to form c, z products,7 in contrast to the amide cleavage b, y products formed by collisionally activated dissociation (CAD),8 infrared multiphoton (IRMPD)9 and UV10 photodissociation, 70 eV electron impact excitation,11 and SID.5 The b, y products are formed by the lowest energy backbone cleavage of ESI protein ions.6-9 An attempt to cleave stronger bonds using high-energy (6.4 eV) 193 nm photons gave mainly b, y products for 2 kDa protein ions,10 but for 2.8 and 8.6 kDa protein ions12 gave small yields of c, z amine bond cleavage products not previously observed. In this further investigation, extra electrodes were placed outside the ion cell electrodes that trap the positively charged ions. With the outside electrodes at +9 V,13 extensive 193 nm laser irradiation of SWIFT-selected14 (M + 11H)11+ ubiquitin ions (8.6 kDa) only produces b, y, not c, z, ions. However, with the outside electrodes at -1 V, the c, z products are formed along with 10+ molecular ions; unexpectedly, these are mainly (M + 11H)10+• ions (Figure 1d), 1 Da heavier than the (M + 10H)10+ ions formed by ESI (Figure 1c). The 4+ mellitin ion spectrum measured under the same conditions (Figure 1b) similarly contains (M + 4H)3+•, consistent with capture of secondary electrons formed by the 193 nm photons impinging on metal surfaces and trapped by the -1 V electrodes: (M + 4H)4+ + ef (M + 4H)3+•.15 Electrons were produced instead (no laser) by a conventional heated filament source outside the FTMS magnet opposite the ESI source.11 With a 10-5 Torr Ar pulse for ecooling (energy < 0.2 eV; an SF6 pulse lowered the efficiency), the 11+ ions of ubiquitin gave a spectrum that showed c, z cleavage of 50 out of 75 backbone positions; CAD8/IRMPD9 gave b, y cleavage of eight of these positions plus seven others. Cooled electrons plus the 15+ ions of FeIII equine cytochrome c16 produced (Figure 2) c, z fragment ions from cleavages at all but 40 of the 103 possible backbone sites (e.g., N-terminal side of Pro, none; of Ile, Leu, Val, few); CAD produces b, y cleavages (total 19) at eight additional sites. The 21+ apomyoglobin ions (17 kDa) yielded 33 c, z cleavages, but the 34+ ions of bovine carbonic anhydrase (29 kDa) as yet has given only 33+, 32+, and 31+ molecular ions. Electron capture dissociation (ECD)1-3 rationalizes these results. The capture cross section should be proportional to the ionic charge squared, consistent with the minimal secondary fragmentations to produce internal ions and the predominance of cleavages in the central∼70% of the protein chain. Charge values and Masses17 of the complementary product ions are consistent with dissociation after ecapture, such as c39/z37 from the 76-residue ubiquitin 11+ ions and c69/z35 from the 104residue cytochrome c 15+ ions. The most favored protonation sites are the side chains of Lys, Arg, and His;18 neutralization to form hypervalent species1-3 at Lys and Arg would account for ions (Figure 2) representing losses of 17, 44, and 59 Da from (M + nH)(n-x)+ (eq 1; neutralization of protonated His gives a more stable radical site).