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Molecule Reactions (molecule + reaction)
Selected AbstractsIon,Molecule Reactions in Helium Nanodroplets Doped with C60 and Water Clusters,ANGEWANDTE CHEMIE, Issue 47 2009Stephan Denifl Dr. Weltraumchemie: Die Bindung zwischen C60+ und (H2O)4 in einem geladenen Komplex aus C60 und dem H2O-Tetramer in Heliumnanotröpfchen (siehe Bild) ist überraschend schwach. Doppelt geladene C602+ -Intermediate könnten durch Ladungstransfer mit He+ entstehen; sie können Ion-Molekül-Reaktionen auslösen, die bei der Molekülsynthese in interstellaren Wolken und im Sonnennebel eine Rolle spielen könnten. [source] Radical,Molecule Reactions for Aromatic Growth: A Case Study for Cyclopentadienyl and Acenaphthylene.CHEMINFORM, Issue 3 2007Dong Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Dimerization of ionized 4-(methyl mercapto)-phenol during ESI, APCI and APPI mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2009Lianming Wu Abstract A novel ion/molecule reaction was observed to occur under electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo ionization (APPI) conditions, leading to dimerization of ionized 4-(methyl mercapto)-phenol followed by fast H· loss. The reaction is particularly favored during ESI, which suggests that this ion/molecule reaction can occur both in the solution inside the ESI-charged droplets and in the gas-phase environment of most other atmospheric pressure ionization techniques. The dimerization reaction is inherent to the electrolytic process during ESI, whereas it is more by ion/molecule chemistry in nature during APCI and APPI. From the tandem mass spectrometry (MS/MS) data, accurate mass measurements, hydrogen/deuterium (H/D) exchange experiments and density functional theory (DFT) calculations, two methyl sulfonium ions appear to be the most likely products of this electrophilic aromatic substitution reaction. The possible occurrence of this unexpected reaction complicates mass spectral data interpretation and can be misleading in terms of structural assignment as reported herein for 4-(methyl mercapto)-phenol. Copyright © 2009 John Wiley & Sons, Ltd. [source] Gas-Phase Chemistry of Vanadium Oxide Cluster Cations VmOn+ (m = 1,4; n = 1,10) with Water and Molecular OxygenEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2008Sandra Feyel Abstract Bare vanadium oxide cluster cations VmOn+ (m = 1,4; n =1,10) generated by electrospray ionization are investigated with respect to their reactivity toward water and molecular oxygen by using mass spectrometric techniques. Besides ion hydration, the ion/molecule reactions of VmOn+ with oxygen-labeled water (H218O) also lead to 16O/18O exchange reactions of the vanadium oxide clusters cations. Although the probability of degenerate 16O/18O exchange between VmOn+ and water is fairly high for the cluster cations with a medium valence state of vanadium, oxygen-atom exchange reactions between VmOn+ and 18O2 can only be accomplished by VO+, V3O6+, and V4O8+. Particularly interesting is the fact that not only oxygen atoms from vanadyl units are exchanged in the cluster cations, but bridging oxygen atoms are also most likely involved in the processes. Other reaction channels for the interaction of VmOn+ cluster cations with molecular oxygen are reported as well, such as oxidative degradation of the low-valent cluster cations upon collision with O2 and formation of association complexes for the high-valent cluster cations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Screening of organic nitrate explosives: selective ion/molecule reactions for the diagnostic ion NO2+JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 11 2005Liliane Girotto Cabrini [source] Adiabatic decoupling of the reaction coordinateINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2008J. C. Lorquet Abstract When the dynamics is constrained by adiabatic invariance, a reactive process can be described as a one-dimensional motion along the reaction coordinate in an effective potential. This simplification is often valid for central potentials and for the curved harmonic valley studied in the reaction path Hamiltonian model. For an ion,molecule reaction, the action integral ,P,, = (1/2,),P,d, is an adiabatic invariant. The Poisson bracket of ,P,,2 with Hamiltonians corresponding to a great variety of long-range electrostatic interactions is found to decrease with the separation coordinate r, faster than the corresponding potential. This indicates that the validity of the adiabatic approximation is not directly related to the shape of the potential energy surface. The leading role played by the translational momentum is accounted for by Jacobi's form of the least action principle. However, although the identification of adiabatic regions by this procedure is limited to a specific range of coordinate configurations, equivalent constraints must persist all along the reaction coordinate and must operate during the entire reaction, as a result of entropy conservation. The study of the translational kinetic energy released on the fragments is particularly appropriate to detect restrictions on energy exchange between the reaction coordinate and the bath of internal degrees of freedom. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Possible molecular hydrogen formation mediated by the radical cations of anthracene and pyreneJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2003Mutsumi Hirama Abstract Hydrogen molecules cannot be formed readily by the association of gaseous hydrogen atoms. Possible H2 formation mediated by the radical cations of typical polycyclic aromatic hydrocarbons (PAHs), anthracene and pyrene, was studied at the B3LYP/6-31G** level of theory. We presumed that H2 is formed by way of two elementary reactions: the addition of an H atom to a PAH molecular cation, and the H abstraction from the resulting monohydro-PAH cation (i.e., arenium ion) by a second H atom to yield H2. The first reaction takes place without any activation energy. The second reaction is also predicted to proceed along almost barrierless pathways, although it is far from being a typical ion,molecule reaction. There is a possibility that these reactions might constitute one of the mechanisms for H2 formation in extremely cold interstellar space. Deuterium enrichment in PAH cations is possibly accompanied by such H2 formation because deuteration lowers the energies of polyatomic PAH cations appreciably. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1378,1382, 2003 [source] Noncovalent dimerization of paclitaxel in solution: Evidence from electrospray ionization mass spectrometryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2002Sarah A. Lorenz Abstract Paclitaxel, a unique antimitotic chemotherapy agent that inhibits cell division by binding to microtubules and prevents them from "depolymerizing," has received widespread interest because of its efficacy in fighting certain types of cancer, including breast and ovarian cancer. Paclitaxel undergoes aggregation at millimolar concentrations in both aqueous media and solvents of low polarity (mimicking hydrophobic environments). Its aggregation may have impact on its aqueous stability and its ability to stabilize microtubules. Here, we investigated the dimerization phenomenon of paclitaxel by electrospray ionization mass spectrometry (ESI-MS). Paclitaxel dimers were stable in solutions of acetonitrile/aqueous ammonium acetate (80/20) and aqueous sodium acetate/acetonitrile (92/8 or 95/5) at various pH values. Additional experiments using solution-phase hydrogen/deuterium exchange were employed to ascertain whether or not the observed dimers were formed in solution or as an artifact of the ESI process by ion,molecule reaction. The evidence supports formation of the dimer in solution, and the approach used can be extended to investigation of other types of drug,drug interactions. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:2057,2066, 2002 [source] Gas-Phase Reactivity of Metavanadate [VO3], towards Methanol and Ethanol: Experiment and TheoryCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2007Tom Waters Dr. Abstract The gas-phase reactivity of the metavanadate anion [VO3], towards methanol and ethanol was examined by a combination of ion,molecule reaction and isotope labelling experiments in a quadrupole ion-trap mass spectrometer. The experimental data were interpreted with the aid of density functional theory calculations. [VO3], dehydrated methanol to eliminate water and form [VO2(,2 -OCH2)],, which features an [,2 - C,O -OCH2]2, ligand formed by formal removal of two protons from methanol and which is isoelectronic with peroxide. [VO3], reacted with ethanol in an analogous manner to form [VO2(,2 -OCHCH3)],, as well as by loss of ethene to form [VO2(OH)2],. The calculations predicted that important intermediates in these reactions were the hydroxo alkoxo anions [VO2(OH)(OCH2R)], (R: H, CH3). These were predicted to undergo intramolecular hydrogen-atom transfer to form [VO(OH)2(,1 -OCHR)], followed by ,1 - O,,2 - C,O rearrangements to form [VO(OH)2(,2 -OCHR)],. The latter reacted further to eliminate water and generate the product [VO2(,2 -OCHR)],. This major product observed for [VO3], is markedly different from that observed previously for [NbO3], containing the heavier Group,5 congener niobium. In that case, the major product of the reaction was an ion of stoichiometry [Nb, O3, H2], arising from the formal dehydrogenation of methanol to formaldehyde. The origin of this difference was examined theoretically and attributed to the intermediate alkoxo anion [NbO2(OH)(OCH3)], preferring hydride transfer to form [HNbO2(OH)], with loss of formaldehyde. This contrasts with the hydrogen-atom-transfer pathway observed for [VO2(OH)(OCH3)],. [source] Toward a reduction of the bimolecular reaction model for titan's ionosphereINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2008Nathalie Carrasco The aim of this paper is to highlight the skeletal chemistry responsible for the rich ionospheric chemistry observed in Titan's atmosphere. The present database is represented by about 700 ion,molecule reactions, which are not all important to describe the system. Our criterion to reduce the list of reactions is to reproduce a reference mass spectrum within its uncertainties. This reference mass spectrum is obtained with the complete reaction database and with neutral densities optimized for the INMS mass spectrum measured at 1200 km during the T5 flyby. We compared two mechanism reduction methods, brute force screening and global sensitivity analysis. The analysis of the residual scheme with only 35 bimolecular reactions highlights several patterns, concerning in particular ionic growth processes and introduction of nitrogen to the ionic species. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 699,709, 2008 [source] Ion chemistry in germane/fluorocompounds gaseous mixtures: a mass spectrometric and theoretical studyJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2008Paola Antoniotti Abstract The ion,molecule reactions occurring in GeH4/NF3, GeH4/SF6, and GeH4/SiF4 gaseous mixtures have been investigated by ion trap mass spectrometry and ab initio calculations. While the NFx+ (x = 1,3) react with GeH4 mainly by the exothermic charge transfer, the open-shell Ge+ and GeH2+ undergo the efficient F-atom abstraction from NF3 and form GeF+ and FGeH2+ as the only ionic products. The mechanisms of these two processes are quite similar and involve the formation of the fluorine-coordinated complexes GeFNF2+ and H2GeFNF2+, their subsequent crossing to the significantly more stable isomers FGeNF2+ and FGeH2NF2+, and the eventual dissociation of these ions into GeF+ (or FGeH2+) and NF2. The closed-shell GeH+ and GeH3+ are instead much less reactive towards NF3, and the only observed process is the less efficient formation of GeF+ from GeH+. The theoretical investigation of this unusual H/F exchange reaction suggests the involvement of vibrationally-hot GeH+. Passing from NF3 to SF6 and SiF4, the average strength of the MF bond increases from 70 to 79 and 142 kcal mol,1, and in fact the only process observed by reacting GeHn+ (n = 0,3) with SF6 and SiF4 is the little efficient F-atom abstraction from SF6 by Ge+. Irrespective of the experimental conditions, we did not observe any ionic product of GeN, GeS, or GeSi connectivity. This is in line with the previously observed exclusive formation of GeF+ from the reaction between Ge+ and CF compounds such as CH3F. Additionally observed processes include in particular the conceivable formation of the elusive thiohypofluorous acid FSH from the reaction between SF+ and GeH4. Copyright © 2008 John Wiley & Sons, Ltd. [source] Gas-phase ion chemistry in the ternary SiH4,C3H6,PH3 systemJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2002Stefania Calderan Abstract Propene,phosphine and the silane,propene,phosphine gaseous mixtures were studied by ion trap mass spectrometry. For the binary mixture the variation of ion abundances under different partial pressures and the mechanisms of ion,molecule reactions are reported. Moreover, the rate constants of the main processes were measured and compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane,propene,phosphine mixture the mechanisms of formation of ion clusters were elucidated, but the complexity of the system and the low abundances of the ions usually isolated by successive steps prevented the determination of rate constants. The hydrogenated ternary ions are mainly formed by reactions of ions with propene, whereas a minor contribution comes from reactions of ions with phosphine. The ions show very low reactivity with silane. The formation processes of these species are discussed in relation to their possible role as precursors of amorphous silicon carbides doped with phosphorus obtained by deposition from properly activated silane,propene,phosphine mixtures. Copyright © 2001 John Wiley & Sons, Ltd. [source] Formation and photodissociation of M+,C6H6 (M+ = V+ and Ta+) and Ta+,C6H4 complexes in a time-of-flight mass spectrometerJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2001Hsiu-Fang Lee Abstract A series of cyclic hydrocarbons were introduced to react with V+ and Ta+ using a pulsed beam expansion source in a time-of-flight mass spectrometer. The third-row metal Ta+ displayed high reactivity in dehydrogenation to form benzyne complexes, whereas benzene complexes were the terminal products for V+. M+,C6H6 (M+ = V+ and Ta+) and Ta+,C6H4 were selected to perform the photodissociation experiments. In contrast to the V+ fragment formation via simple cleavage of the V+,C6H6 bond, a photoinduced loss of C2H2 occurred in both the Ta+,C6H6 and Ta+,C6H4 complexes. Plausible explanations involved in the formation of Ta+,C6H6 and Ta+,C6H4 complexes are given for observing such photo-induced dissociation. The observed photodissociation in Ta+,C6H6 is analogous to the dissociative process previously investigated in metal ion,molecule reactions. The photodissociation spectrum of Ta+,C6H4 was obtained by recording the appearance of Ta+,C4H2 as a function of wavelength and yielded a dissociation energy of 91 ± 1 kcal mol,1. Copyright © 2001 John Wiley & Sons, Ltd. [source] Solvation of acylium fragment ions in electrospray ionization quadrupole ion trap and Fourier transform ion cyclotron resonance mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2001Ziqiang Guan Abstract In electrospray ionization (ESI) quadrupole ion trap and Fourier transform ion cyclotron resonance mass spectrometry, certain fragment ions (e.g. acylium ions) generated either during the ion transportation process (in the source interface region) or in the ion trap are found to undergo ion,molecule reactions with ESI solvent molecules (water, acetonitrile and aliphatic alcohols) to form adduct species. These unexpected solvated fragment ions severely complicate the interpretation of mass spectrometic data. High-resolution accurate mass measurements are important in establishing the elemental compositions of these adduct species and preventing erroneous data interpretation. Copyright © 2001 John Wiley & Sons, Ltd. [source] Micro-Hydration of the MgNO3+ Cation in the Gas PhaseCHEMPHYSCHEM, Issue 11 2007Barbara Jagoda-Cwiklik Dr. Abstract Coordination complexes of the magnesium nitrate cation with water [MgNO3(H2O)n]+ up to n=7 are investigated by experiment and theory. The fragmentation patterns of [MgNO3(H2O)n]+ clusters generated via electrospray ionization indicate a considerable change in stability between n=3 and 4. Further, ion,molecule reactions of mass-selected [MgNO3(H2O)n]+ cations with D2O reveal the occurrence of consecutive replacement of water ligands by heavy water, and in this respect the complexes with n=4 and 5 are somewhat more reactive than their smaller homologs with n=1,3 as well as the larger clusters with n=6 and 7. For the latter two ions, the theory suggests the existence of isomers, such as complexes with monodentate nitrato ligands as well as solvent-separated ion pairs with a common solvation shell. The reactions observed and the ion thermochemistry are discussed in the context of ab initio calculations, which also reveal the structures of the various hydrated cation complexes. [source] Isomer differentiation by combining gas chromatography, selective self-ion/molecule reactions and tandem mass spectrometry in an ion trap mass spectrometerRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2003Hui-Fen Wu This study presents a novel, simple and rapid procedure for isomer differentiation by combining gas chromatography (GC), a selective self-ion/molecule reaction (SSIMR) and tandem mass spectrometry (MS/MS) in an ion trap mass spectrometer (ITMS). SSIMR product ions were produced from four isomers. For aniline, SSIMR induces the formation of the molecular ion, [M+H]+, [M+CH]+, adduct ions of fragments ([M+F]+, where F represents fragment ions) and [2MH]+. 2 and 3-Picoline produce [M+H]+, [2MH]+ and [M+F]+, while 5-hexynenitrile produces [M+H]+, [M+F]+ and [2M+H]+ ions. The proposed method provides a relatively easy, rapid and efficient means of isomer differentiation via a SSIMR in the ITMS. Typically, isomer differentiation can be achieved within several minutes. The superiority of the SSIMR technique for isomer differentiation over electronic ionization (EI) is also demonstrated. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||