bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactions in the mass spectrometry of a hydride meisenheimer complex of 2,4,6‐trinitrotoluene (TNT)
Authors: Yinon Jehuda , Johnson Jodie V. , Bernier Ulrich R. , Yost Richard A. , Mayfield Howard T. , Mahone William C. , Vorbeck Claudia 
Published: May 2005

AbstractA hydride Meisenheimer complex of 2,4,6‐trinitrotoluene (TNT) (TNTH−) was synthesized using tetramethylammonium octahydroborate. TNT and TNTH− (as the tetramethylammonium salt) were analyzed by direct exposure probe mass spectrometry using electron impact (EI), chemical ionization (CI) and negative‐ion chemical ionization (NCI). For further identification, the ions of the mass spectra were investigated using tandem mass spectrometry with collision‐induced dissociation (CID). Although the EI mass spectra of both compounds were similar, the CID mass spectra of the ions at m/z 227 (M+ of TNT) of the two compounds showed large differences in daughter ion abundances. A major difference between the two compounds also appeared in their CI methane mass spectra. Two abundant ions, at m/z 183 and 198, appeared only in the CI mass spectrum of TNNH−. CID parent ion scans showed that the origin of these two ions was not the m/z 227 ion. We suggest that these ions are formed by chemical reactions of the complex on the surface of the heated probe tip, followed by ionization. These reactions, probably a reduction process forming m/z 198 and hydrolysis forming m/z 183, occur preferentially in TNTH−, the already reduced form of TNT. Formation of the ions at m/z 183 and 198 was also observed in the liquid chromatography particle beam CI mass spectrum of TNTH−.
Reactivity of [C3H8N]+ ions: A combined Fourier transform ion cyclotron resonance and molecular orbital approach
Authors: Bouchoux G. , Penaud‐Berruyer F. , Tortajada J. 
Published: May 2005

AbstractThe unimolecular dissociations of the two isomeric ions, [CH3 CH2 CHNH2]+, 1, and [CH3 CH2 NHCH2]+, 2, were re‐examined. Molecular orbital calculations (MP2/6–311 + G**//HF/6–31G* + ZPE level) were used to characterize the corresponding potential energy profiles and, in order to understand the various kinetic effects observed, RRKM calculations were also undertaken. The experimental picture was completed by a Fourier transform ion cyclotron resonance mass spectrometry investigation on the system [CH2CHCH2]+ + NH3. A prominent result is that the elimination of an ethene molecule from metastable ions 1 and 2 occurs via two ion‐neutral complexes involving [CH2 NH2]+ and C2H4 species. In the former case, this intermediate structure looks like a corner protonated cyclopropylamine. In the latter, the data confirm the earlier proposal of Bowen et al. that the reaction is mediated by a proton‐bound complex [C2H4 …︁H…︁NHCH2]+.
Gas‐phase nucleophilic reactions in tetraalkoxysilanes
Authors: da Silva Maria Lucia Pereira , Riveros José M. 
Published: May 2005

AbstractThe gas‐phase reactions of F−, OH−·, OH−, EtO−, NH and EtNH− with Si(OEt)4 were investigated by Fourier transform ion cyclotron resonance in order to probe the intrinsic reactivity of substrates used in plasma chemical vapour deposition. Isotopic data and the nature of the product ions suggest that reactions proceed primarily by attack of the nucleophile on the silicon centre. The ensuing chemistry can be explained by the fragmentation pathways available to the [XSi(OR)4]− intermediate, which includes alkoxide displacement, internal nucleophilic displacement and cyclic elimination of ethylene in the ethoxy case. Pentacoordinated adducts are observed in the reactions with F− and in the symmetric alkoxide/tetraalkoxysilane reactions. The reaction of F− with Si(OMe)4 is also shown to produce a perplexing ion of unknown structure and identified as [FSi(OMe)2(OCH2)]−.
Electron impact mass spectrometry of monocyclic and spirocyclic oxyphosphorane compounds
Authors: Chen Xin , Zhao Yufen , Fu Hua , Wang Jingzun 
Published: May 2005

AbstractThe electron impact ionizatio (EI) mass spectral (EIMS) fragmentations of a series of monocyclic and spirocyclic oxyphosphorane compounds were investigated. The results showed that the EIMS of such compounds exhibited very characteristic fragmentation patterns, which could provide a useful tool for the structural assignment of other pentacovalent phosphorus compounds.
Generation and fragmentation of didehydronaphthalene radical cations under electron impact
Authors: Bromfield Sean M. , Dyall Leonard K. 
Published: May 2005

AbstractThe electron impact mass spectra of disubstituted naphthalenes (chloronitro, acetylnitro, dibromo and dinitro derivatives) and of two naphthalenedicarboxylic anhydrides were studied under high resolution and by means of linked (B/E) scans. They all generate didehydronaphthalene radical cation, C10H, in most cases with a very high abundance, so that a convenient route to these interesting species is provided. These isomeric ions were all seen to lose the same fragments, namely C2H2, C2H4, C3H3, C4H2, or C2H2 + C2H2. In three instances, mass‐analysed ion kinetic energy spectrometric (MIKES) and collisional activation/MIKES experiments were carried out and no differences in fragmentation behaviour were detected. Hence these isomeric C10H6+˙ ions achieve some common structure either before or during the fragmentation.
Dissociation of meta‐stable ions in mass spectrometers with release of internal energy
Authors: Beynon J. H. , Saunders R. A. , Williams A. E. 
Published: May 2005

AbstractCertain of the “meta‐stable peaks” in mass spectra are abnormally wide. This extra width is shown to be associated with release of kinetic energy during fragmentation. Methods are presented for measuring this energy release and values are given for various transitions in the spectra of aromatic nitro compounds.
Collisional activation spectra of organic ions
Authors: McLafferty F. W. , Bente P. F. , Kornfeld Richard , Tsai Shih‐Chuan , Howe Ian 
Published: May 2005

AbstractCollision with neutral molecules is shown to provide a convenient method of adding internal energy to ions in a field‐free drift region of the mass spectrometer. The effects on this process of ion accelerating potential, target gas pressure and identity, and precursor ion internal energy and mass have been investigated to optimize experimental conditions. Such collisions cause ion decompositions whose activation energies cover a broad range; for a particular ion such decompositions can be viewed as its “collisional activation (CA) spectrum.” CA spectra, which can be obtained for each ion in the normal mass spectrum, and which appear to follow the predictions of the quasi equilibrium theory, show many more of the possible unimolecular ion decomposition reactions for an ion than do unimolecular metastables, and thus provide valuable information for ion reaction mechanisms and molecular structure determination. Collisional activation can sometimes yield ion energies which are relatively inaccessible by electron impact. The precursor ion internal energy has a negligible effect on the ion's CA spectrum except for product ions formed through the processes of lowest activation energy. Thus, CA spectra should also be valuable for the characterization of ion structures.
Relative carbonyl isocyanate cation [OCNCO]+ affinities of pyridines determined by the kinetic method using multiple‐stage (MS3) mass spectrometry
Authors: Yang Sheng Sheng , Chen Guodong , Ma Shuguang , Cooks R. Graham , Gozzo Fabio C. , Eberlin Marcos N. 
Published: May 2005

AbstractIon‐molecule reactions in a pentaquadrupole mass spectrometer are used to generate cluster ions in which neutral pyridine molecules are bound to a linear polyatomic cation, [OCNCO]+. The dimeric adduct, viz. Py1[OCNCO]+Py2 where Py1 and Py2 represent substituted pyridines, formed upon reaction of mass‐selected [OCNCO]+ with a mixture of pyridines, has a loosely bound structure, as suggested by triple stage mass spectrometric (MS3) experiments. Dimeric adducts comprised of meta‐ and/or para‐substituted pyridines (unhindered pyridines) display an excellent linear correlation between the fragment ion abundance ratio ln [Py1[OCNCO]+/Py2[OCNCO]+] and the proton affinity difference of the pyridines. On the assumption that the effective temperature of the [OCNCO]+ ‐bound dimers is similar to that of the corresponding Cl+‐bound dimers, [OCNCO]+ affinities of the substituted pyridines relative to pyridine are estimated to be 3‐MePy 2.3, 4‐MePy 3.2, 3‐EtPy 3.5, 4‐EtPy 4.1, 3,5‐diMePy 4.9 and 3,4‐diMePy 5.6 kcal mol−1 (1 kcal = 4.184 kJ). A linear relationship between the relative [OCNCO]+ cation affinity and the relative proton affinity (PA) is derived as relative [OCNCO]+ affinity (kcal mol−1) = 0.96 ΔPA, using the assumed effective temperature of 555 K. Dimers consisting of ortho‐substituted pyridines display substantial steric effects between the ortho‐substituted alkyl group and the central [OCNCO]+ cation. A set of gas‐phase steric parameters (Sk) is determined and steric effects are ordered 2‐MePy (‐1.39) <2,5‐diMePy (‐3.02) < 2,4‐diMePy (‐3.15) < 2,3‐diMePy ( −3.29) < 2,6‐diMePy (‐5.09) < 2,4,6‐triMe (‐6.13). A greater steric effect is experienced in the [OCNCO]+ system than in the corresponding Cl+ system, owing to the larger central ion in Py[OCNCO]+ Py. Structural and electronic information regarding the bond angles, bond lengths and charge density distributions in [OCNCO]+, Py[OCNCO]+ and Py[OCNCO]Py+ was obtained from ab initio calculations. The calculations show that [OCNCO]+ is linear with high positive charge densities on the carbon atoms. The calculations also reveal that the Py[OCNCO]+ monomer is a planar ion with the nitrogen atom of pyridine bound to a carbon atom of the [OCNCO]+ cation, and that the Py[OCNCO]Py+ dimer is a symmetrical ion in which the nitrogen atoms on the pyridine molecules bind to the carbon atoms of the central cluster ion, [OCNCO]+.
In vivo metabolism of substance P in rat striatum utilizing microdialysis/liquid chromatography/micro‐electrospray mass spectrometry
Authors: Andrén Per E. , Caprioli Richard M. 
Published: May 2005

AbstractIn vivo microdialysis in combination with liquid chromatography/micro‐electrospray mass spectrometry was used to study the metabolism of substance P in rat brain. A microdialysis probe was used both to introduce substance P into the brain and to collect metabolic products. Unilateral infusions of 25 and 50 pmol μl−1 substance P, or isotopically labeled [D8‐Phe8] substance P, at flow rates of 0.3 μl min−1, were made through the microdialysis probe implanted in the striatum of anesthetized rats. The metabolic products were analyzed by on‐line mass spectrometry and the results showed that substance P, an 11 amino acid residue polypeptide, was metabolized in the striatum to form N‐terminal fragments 1–9, 1–8 and 1–7; C‐terminal fragments 3–11, 5–11, 6–11, 7–11 and 8–11; and internal fragments 4–8, 6–10 and 7–10. The concentrations of these metabolites in dialysates were measured in order to compare the relative importance of several possible metabolic degradative pathways.
Ultrahigh‐resolution matrix‐assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectra of peptides
Authors: Paša‐Tolić Ljiljana , Huang Yulin , Guan Shenheng , Kim Hyun Sik , Marshall Alan G. 
Published: May 2005

AbstractQuasimolecular peptide [M + H]+ions are generated by matrix‐assisted (2,5‐dihydroxybenzoic acid/D‐fructose) laser desorption/ionization (frequency‐tripled Nd: YAG at 355 nm) from leucine enkephalin, bradykinin, the non‐apeptide Arg–Leu–Cys–Ile–Phe–Ser–Cys–Phe–Arg, angiotensin I, bovine insulin chain B and some of their deuterated derivatives. The ions are cooled and axialized by azimuthal quadrupolar irradiation in the presence of argon collision gas in the ‘source’ compartment of a dual cubic Penning trap. Following ion transfer to the low‐pressure ‘analyzer’ trap, ultrahigh FT‐ICR mass resolving power is obtained for protonated oligopeptide quasimolecular [M + H]+ions: e.g.m/Δm50%≈ 1 500 000 for bradykinin (m/z≈ 1060) after frequency drift correction and 100 000 for insulin B‐chain, in which Δm50%is the magnitude‐mode peak full width at half‐maximum peak height. These results constitute the highest mass resolving power yet demonstrated for internally‐generated MALDI ions at 3 T, and compare favorably with results obtained at much higher‐magnetic field with externally‐generated ions. High mass resolution is important for resolving adducts and chemical modifications of a peptide or protein and (as demonstrated here) for facile determination of the degree of deuteration from an H/D exchange experiment. Limitations to FT‐ICR mass resolving power by Coulombic ion–ion interactions at high ion density in the trap are demonstrated experimentally and discussed.
Ion–molecule reactions of C60Rh+ with CH3X, C6H5X(X = Cl, Br, I) and CH2I2
Authors: Kan Steven Z. , Xu Young C. , Byun Yong G. , Freiser Ben S. 
Published: May 2005

AbstractThe gas‐phase ion‐molecule chemistry of exohedrally bound C60Rh+ with CH3X, C6H5X (X = Cl, Br, and I) and CH2I2 is studied using Fourier transform ion cyclotron resonance mass spectrometry. Reactions with CH3I and CH2I2 yield the buckminsterfullerene derivatives, C60CH3+ and C60CH2+, respectively. Energy resolved collisional activation experiments on these two product ions indicate that the methylene group is more strongly bound to C60 than the methyl group. This is consistent with methylene being bound by two carbon‐carbon bonds to C60, while methyl is bound by a single carbon‐carbon bond. Unlike CH3I, CH3Cl and CH3Br react with C60Rh+ in a stepwise fashion to yield C60Rh(CH2)n+ (n = 1 − 3). Interestingly, C60Rh(CH2)2,3+ are shown to be isomers of C60RhX+ (X = ethene, propene), possibly with a carbon‐carbon bond formed with C60. Products containing more than three CH2 moieties were not observed. Reactions of C60Rh+ with C6H5X(X = Cl, Br, and I) yield C60Rh(C6H4)n+ (n = 1, 2), in a stepwise fashion via losses of HX. C60Rh(C6H4)2+ is unreactive with C6H5X. Again, indirect evidence for CC bond formation to C60 is obtained. Consistent with previous observations on C60Fe+ C60Co+, the Rh+–C60 bond energy is found to fall between those of Rh+–propene and Rh+–benzene, due to the alkene behavior of C60.
Space‐charge effects and ion distribution in plasma source mass spectrometry
Authors: Li Gangqiang , Duan Yixiang , Hieftje Gary M. 
Published: May 2005

AbstractSpace‐charge effects appear to be key in understanding ion‐transport processes in plasma‐source mass spectrometry. Both theoretical calculations and experimental measurements demonstrate that space charge influences ion transport between the plasma source and mass analyzer. In a theoretical analysis, both drift space and accelerating space in the interface have been considered and preliminary conclusions have been drawn concerning space‐charge repulsion and ion‐beam divergence in those regions. In the experimental work, spatial patterns of sample deposition on the third stage vacuum orifice plate were recorded while using a microwave plasma source. To measure these patterns, a stainless‐steel target was used to cover the orifice and both x‐ray fluorescence microanalysis and scanning electron microscopy (SEM) were used to examine the sample material deposited on it. The resulting spatial maps show that analyte deposition is somewhat element‐dependent in a way that is correlated with analyte atomic mass. These findings can be explained on the basis of space‐charge theory.
Simultaneous measurement of fluphenazine and [2H4]fluphenazine in plasma using solids probe tandem mass spectrometry
Authors: Hadad S. , Edom R. , McKay G. , Hawes E. M. , Midha K. K. 
Published: May 2005

AbstractA procedure which utilizes the specificity of tandem mass spectrometry was developed for the simultaneous quantification of fluphenazine and its stable isotopomer, [2H4] fluphenazine, in 1 ml plasma samples, after low oral doses of this antipsychotic agent. The unlabeled and the deuterium labeled‐drug were isolated by a selective extraction procedure, derivatized and analyzed under electron impact ionization via the direct insertion probe of a tandem mass spectrometer. Selected reaction monitoring of the low‐energy collision‐induced dissociation of analogous major fragment ions to their respective product ions conferred the necessary specificity to allow direct analysis of plasma extracts without the need for a chromatographic separation step. Calibration graphs constructed from spiked blank plasma were linear over the range 25–1000 pg ml−1 for each isotopomer, with an overall coefficient of variation of 4.82% and 4.72% for fluphenazine and [2H4] fluphenazine, respectively. The limit of detection was 5 pg ml−1 when 1 ml of plasma was used. The described procedure provided sufficient sensitivity and selectivity such that plasma concentrations of fluphenazine and [2H4] fluphenazine could be followed in schizophrenic patients for 24 h after the simultaneous administration of single oral doses that contain 5 mg each of fluphenazine dihydrochloride and its deuterated isotopomer, [2H4] fluphenazine dihydrochloride. Endogeneous plasma constituents and known metabolites of fluphenazine did not interfere in the assay. Virtually superimposable plasma concentration versus time profiles were obtained, demonstrating that the deuterated isotopomer has no significant isotopic effect.
Comparison of thermospray and electrospray for the analysis of the conjugates of androgen receptor antagonist zanoterone
Authors: Stack Robert F. , Rudewicz Patrick J. 
Published: May 2005

AbstractThe use of both pneumatically‐assisted ionspray (IS) and thermospray (TS) in liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the determination of the biotransformation pathways of zanoterone in humans is described. After administration of a single oral dose of [14C] zanoterone, 16% of the dose was excreted as four metabolites in urine. Initially TS LC‐MS/MS analysis indicated the presence of monohydroxylated metabolites; however, their high‐performance liquid chromatographic (HPLC) retention times indicated more polar structures. These conflicting results led to IS experiments, in which abundant molecular ions were obtained for all four metabolites, identifying them as either glucuronide or sulfate conjugates. A contour plot of the data from an IS neutral loss experiment revealed the presence of a minor metabolite not observed in either HPLC–flow scintillation or TS LC‐MS experiments. These data demonstrate the advantages of IS LC‐MS/MS for the analysis of drug conjugates.
Studies on the distribution of oligodeoxynucleotide charge states in the gas phase by ion spray mass spectrometry
Authors: Tong Xinchun , Henion Jack , Ganem Bruce 
Published: May 2005

AbstractThe naturally occurring purine and pyrimidine heterocycles found in nucleic acids differ significantly in their basicity. To investigate whether such differences may provide useful mass spectrometric information about nucleic acid sequence and/or composition, the distribution of charge states in a series of oligodeoxynucleotide gas‐phase ions was studied by ion spray mass spectrometry (MS). Hexadeoxynucleotides of adenosine, cytidine, guanosine and thymidine were evaluated over the pH range 2.6–7.0 using negative‐ion MS. A significant reduction in the maximum charge state was noted for d(pA)6, d(pC)6 and d(G)6 at low pH, while the maximum charge state observed for d(pT)6 was independent of pH. These effects displayed a good correlation with the pKa values of the respective nucleoside bases. The findings suggest that charge‐state reduction probably resulted from internal charge neutrazation by gas‐phase protonation of the nucleoside base.
Structural characterization of naturally occurring pteridines by laser desorption Fourier transform mass spectrometry
Authors: Hettich Robert L. , Jacobson K. Bruce 
Published: May 2005

AbstractDetailed structural information can be obtained without derivatization for a variety of naturally occurring pteridines by using laser desorption Fourier transform mass spectrometry. Laser desorption provides a soft ionization technique for these non‐volatile compounds and generates characteristic positive and negative ions. The positive‐ion spectra usually consist of [M + Na]+ and [M + K]+ ions, whereas the negative‐ion spectra reveal [M – H]− ions and fragment ions. Collison‐induced dissociation experiments were used to probe the fragmentation pathways of these negative ions. The fragmentation observed for negative ions supports known resonance structures and provides detailed structural information which can be used to differentiate isomers, such as L‐sepiapterin, L‐biopterin, and L‐primapterin (sometimes referred to as 7‐biopterin). However, optical isomers, such as monapterin and neopterin, cannot be resolved by differences in fragmentation alone. Twenty‐three compounds that are pterins or related structures were characterized.
Regioselectivity of dechlorination of DDT and its metabolites in mass spectrometry
Authors: Lépine François L. , Milot Sylvain , Mamer Orval A. 
Published: May 2005

AbstractDDT and several of its metabolites were synthesized with their aromatic chlorines enriched with 37Cl. The mass spectra of these compounds were recorded under electron impact and under methane positive‐ion and electroncapture negative‐ion chemical ionization. The regioselectivity of the dechlorination reactions was determined by measurement of the relative proportions of the unlabeled aliphatic versus the labeled aromatic chlorines in the various fragment ions observed. For all the α,β‐unsaturated compounds studied under electron impact ionization, the regioslectivity is small, as both the aromatic and the aliphatic chlorines are lost. Under positive‐ion chemical ionization, the dechlorination is highly regioselective, the aliphatic chlorines being almost exclusively lost. Under electron‐capture negative‐ion chemical ionization, the regioselectivity is also very high and the reactivity of the various chlorines is often controlled by the position of the aromatic chlorines.
Analysis of benzannelated thiophene derivatives by negative‐ion chemical ionization using oxygen as a reagent gas
Authors: Drabner G. , Budzikiewicz H. 
Published: May 2005

AbstractUnder the conditions of negative‐ion chemical ionization with O2 as a reagent gas [NCI(O2)], thiophene derivatives suffer surface‐catalysed oxidative degradation with subsequent ionization of the resulting species. These degradation reactions are to some extent structure specific and thus may be used for the localization of rings and/or substituents. It is advisable, however, to combine NCI(O2) with either electron impact ionization or positive ion CI. The latter ionization methods yield abundant M+· ions but hardly any structure‐specific fragments, whereas with NCI(O2) the determination of the molecular mass may be difficult owing to the competing oxidation reactions.