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91.
应用串联质谱的碰撞诱导解离和联动扫描技术,研究了2,5-双(4-羟基苯亚甲基)环戊酮的质谱解离特征,提供了双电荷离子存在的实验证据。进一步对双电荷离子(m/z146)的碰撞诱导解离碎裂进行了讨论。 相似文献
92.
Huakuan Lin Shourong Zhu Appolin Bave Kondiano Xuncheng Su Fuping Kou Yunti Chen 《Polyhedron》1998,17(25-26)
The kinetics of the acid dissociation of copper(II) complexes of novel C-functionalized macrocyclic dioxotetraamines has been studied by means of a stopped-flow spectrophotometer. The acid dissociation rate follows the law Vd = CcomkK1K2H 2/(1+K1H+K1K2H 2). From the experimental facts we have obtained, the dissociation kinetics are interpreted by a mechanism involving the negatively charged carbonyl oxygen of the complex being rapidly protonated in a pre-equilibrium step, the rate-determining step being intramolecular hydrogen (enolic tautomer) migration (to imine nitrogen). The dissociation rate reached a plateau in the strongly acidic solution. By means of temperature coefficient method, ΔH φ, ΔS φ of the pre-equilibrium step and ΔH ≠, ΔS≠ of the rate-determining step were obtained. The results of 13-membered macrocyclic dioxotetraamines have been discussed. The influence of the substituents to the acid dissociation rates has also been discussed. The Bronsted type linear free energy relationships do also exist in these C-functionalized dioxotetraamine copper(II) complexes. 相似文献
93.
Uncovering the Stoichiometry of Pyrococcus furiosus RNase P,a Multi‐Subunit Catalytic Ribonucleoprotein Complex,by Surface‐Induced Dissociation and Ion Mobility Mass Spectrometry 下载免费PDF全文
Xin Ma Lien B. Lai Stella M. Lai Akiko Tanimoto Prof. Mark P. Foster Prof. Vicki H. Wysocki Prof. Venkat Gopalan 《Angewandte Chemie (International ed. in English)》2014,53(43):11483-11487
We demonstrate that surface‐induced dissociation (SID) coupled with ion mobility mass spectrometry (IM‐MS) is a powerful tool for determining the stoichiometry of a multi‐subunit ribonucleoprotein (RNP) complex assembled in a solution containing Mg2+. We investigated Pyrococcus furiosus (Pfu) RNase P, an archaeal RNP that catalyzes tRNA 5′ maturation. Previous step‐wise, Mg2+‐dependent reconstitutions of Pfu RNase P with its catalytic RNA subunit and two interacting protein cofactor pairs (RPP21?RPP29 and POP5?RPP30) revealed functional RNP intermediates en route to the RNase P enzyme, but provided no information on subunit stoichiometry. Our native MS studies with the proteins showed RPP21?RPP29 and (POP5?RPP30)2 complexes, but indicated a 1:1 composition for all subunits when either one or both protein complexes bind the cognate RNA. These results highlight the utility of SID and IM‐MS in resolving conformational heterogeneity and yielding insights on RNP assembly. 相似文献
94.
Competitive homolytic and heterolytic decomposition pathways of gas‐phase negative ions generated from aminobenzoate esters 下载免费PDF全文
Hanxue Xia Yong Zhang Julius Pavlov Freneil B. Jariwala Athula B. Attygalle 《Journal of mass spectrometry : JMS》2016,51(3):245-253
An alkyl‐radical loss and an alkene loss are two competitive fragmentation pathways that deprotonated aminobenzoate esters undergo upon activation under mass spectrometric conditions. For the meta and para isomers, the alkyl‐radical loss by a homolytic cleavage of the alkyl‐oxygen bond of the ester moiety is the predominant fragmentation pathway, while the contribution from the alkene elimination by a heterolytic pathway is less significant. In contrast, owing to a pronounced charge‐mediated ortho effect, the alkene loss becomes the predominant pathway for the ortho isomers of ethyl and higher esters. Results from isotope‐labeled compounds confirmed that the alkene loss proceeds by a specific γ‐hydrogen transfer mechanism that resembles the McLafferty rearrangement for radical cations. Even for the para compounds, if the alkoxide moiety bears structural motifs required for the elimination of a more stable alkene molecule, the heterolytic pathway becomes the predominant pathway. For example, in the spectrum of deprotonated 2‐phenylethyl 4‐aminobenzoate, m/z 136 peak is the base peak because the alkene eliminated is styrene. Owing to the fact that all deprotonated aminobenzoate esters, irrespective of the size of the alkoxy group, upon activation fragment to form an m/z 135 ion, aminobenzoate esters in mixtures can be quantified by precursor ion discovery mass spectrometric experiments. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
95.
Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking 下载免费PDF全文
B. Sc. Zongyuan Liu Dr. David C. Grinter Dr. Pablo G. Lustemberg Dr. Thuy‐Duong Nguyen‐Phan Dr. Yinghui Zhou B. Sc. Si Luo Dr. Iradwikanari Waluyo Dr. Ethan J. Crumlin Dr. Dario J. Stacchiola Prof. Jing Zhou Dr. Javier Carrasco Prof. H. Fabio Busnengo Dr. M. Verónica Ganduglia‐Pirovano Dr. Sanjaya D. Senanayake Prof. José A. Rodriguez 《Angewandte Chemie (International ed. in English)》2016,55(26):7455-7459
Ni‐CeO2 is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO2 at temperatures as low as 300 K, generating CHx and COx species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CHx or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way. 相似文献
96.
《Angewandte Chemie (International ed. in English)》2017,56(42):13041-13046
Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO2) surfaces indicate that metal–oxide interactions can play a very important role for the activation of methane and its reforming with CO2 at relatively low temperatures (600–700 K). Among the systems examined, Co/CeO2(111) exhibits the best performance and Cu/CeO2(111) has negligible activity. Experiments using ambient pressure X‐ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO2(111) at temperatures as low as 300 K—generating CHx and COx species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co2+/CeO2(111), and to only 0.05 eV on Co0/CeO2−x (111). At 700 K, under methane dry reforming conditions, CO2 dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CHx formed on the Co0/CeO2−x (111) catalyst recombines to yield ethane or ethylene. 相似文献
97.
Relationships have been established between the average conversion degree and the dissociation time for polydisperse granular
material, taking its grain size distribution into account. It has been checked in which cases the kinetic curves obtained
by a numerical solution can be described in terms of KEKAM equation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
98.
99.
The temperature dependences of the equilibrium constants of two chain reversible reactions in quinonediimine (quinonemonoimine)—2,5-dichlorohydroquinone
systems in chlorobenzene were studied. The enthalpy of equilibrium of the reversible reaction of quinonediimine with 4-hydroxydiphenylamine
was estimated from these data (ΔH = − 14.4±1.6 kJ mol−1) and a more accurate value of the N-H bond dissociation energy in the 4-anilinodiphenylaminyl radical was determined (D
NH = 278.6±3.0 kJ mol−1). A chain mechanism was proposed for the reaction between quinonediimine and 2,5-dichlorohydroquinone, and the chain length
was estimated (ν = 300 units) at room temperature. Processing of published data on the rate constant of the reaction of styrylperoxy
radicals with 2,5-dichlorohydroquinone in the framework of the intersecting parabolas method gave the O-H bond dissociation
energy in 2,5-dichlorohydroquinone: D
OH = 362.4±0.9 kJ mol−1. Taking into account these data, the O-H bond dissociation energy in the 2,5-dichlorosemiquinone radical was found: D
OH = 253.6±1.9 kJ mol−1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1661–1666, October, 2006. 相似文献
100.
Fragmentation of intra-peptide and inter-peptide disulfide bonds of proteolytic peptides by nanoESI collision-induced dissociation 总被引:1,自引:0,他引:1
Mormann M Eble J Schwöppe C Mesters RM Berdel WE Peter-Katalinić J Pohlentz G 《Analytical and bioanalytical chemistry》2008,392(5):831-838
Characterisation and identification of disulfide bridges is an important aspect of structural elucidation of proteins. Covalent
cysteine-cysteine contacts within the protein give rise to stabilisation of the native tertiary structure of the molecules.
Bottom-up identification and sequencing of proteins by mass spectrometry most frequently involves reductive cleavage and alkylation
of disulfide links followed by enzymatic digestion. However, when using this approach, information on cysteine-cysteine contacts
within the protein is lost. Mass spectrometric characterisation of peptides containing intra-chain disulfides is a challenging
analytical task, because peptide bonds within the disulfide loop are believed to be resistant to fragmentation. In this contribution
we show recent results on the fragmentation of intra and inter-peptide disulfide bonds of proteolytic peptides by nano electrospray
ionisation collision-induced dissociation (nanoESI CID). Disulfide bridge-containing peptides obtained from proteolytic digests
were submitted to low-energy nanoESI CID using a quadrupole time-of-flight (Q-TOF) instrument as a mass analyser. Fragmentation
of the gaseous peptide ions gave rise to a set of b and y-type fragment ions which enabled derivation of the sequence of the
amino acids located outside the disulfide loop. Surprisingly, careful examination of the fragment-ion spectra of peptide ions
comprising an intramolecular disulfide bridge revealed the presence of low-abundance fragment ions formed by the cleavage
of peptide bonds within the disulfide loop. These fragmentations are preceded by proton-induced asymmetric cleavage of the
disulfide bridge giving rise to a modified cysteine containing a disulfohydryl substituent and a dehydroalanine residue on
the C-S cleavage site. 相似文献