bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ionization energies of homologous organic compounds and correlation with molecular size
Authors: Holmes J. L. , Lossing F. P. 
Published: May 2005

AbstractThe empirical relationship IE ∝︁ 1/n, between the ionization energy (IE) and molecular size (as represented by the number of atoms, n) in homologous series of organic compounds has been confirmed for n‐alkanes, alkyl halides, cyclic ethers and alkyl‐subsiituted cycloalkanes. For each series, the plot of IE vs. 1/n produces a line of characteristic slope. The only exception is the cycloalkanes themselves, whose IE values (from C3 to C8) are closely similar. The possible relationship between the IE, the polarizability of the molecules and the energy of the highest occupied molecular orbital is briefly discussed.
Formation of charged clusters during electrospray ionization of organic solute species
Authors: Meng Chin Kai , Fenn John B. 
Published: May 2005

AbstractElectrospray dispersion of solutions into a bath gas can produce solute ions with many charges per molecule. In contrast to such multiple charging, it can also result in ‘fractional charging’ by which cluster ions are formed with more than one solute molecule per charge. Examples of such fractional charging or clustering are presented and discussed. In the case of arginine solutions, which are reported in some detail, ion masses corresponding to clusters containing as many as 24 solute molecules and up to four charges were identified. The number and size of these cluster ions increased markedly with increase in the initial solute concentration. When co‐solutes consisting of acids, salts or bases were present, at up to millimolar concentrations in the initial solution, clustering was often strongly suppressed, especially by strong acids and their salts. This clustering phenomenon not only provides insight into the chemistry of solute precipitation in solution, but also offers a means of producing new kinds of clusters for experimental studies.
Mass spectra of 2‐ and/or 6‐alkyl‐3‐hydroxypyridines
Authors: Lin Shaw‐Tao , Tien Ling‐Ling , Kuo Yueh‐Hsiung , Shih Kae‐Shyang 
Published: May 2005

AbstractThe mass spectra of 2‐ and/or 6‐aIkyI‐3‐hydroxypyridines were measured. The fragmentation processes include the loss of 1, 28 and 29 u and RCN from the molecular ions. Among the characteristic ions, the [M – 1]+ ions are the base peak for all of the ethyl‐containing pyridines. According to a labelling study, the hydrogen on the β‐caroon is the major contributor to the formation of [M – 1]+.
Electron impact ionization mass spectrometry and tandem mass spectrometry of phenylalkylpyridazines
Authors: Pittenauer Ernst , Allmaier Günter , Schmid Erich R. , Stanek Wolfgang , Heinisch Gottfried 
Published: May 2005

AbstractThe mass spectrometric fragmentation behaviour of pyridazine and four monosubstituted derivatives containing a pbenylalkyl side‐chain (3‐ and 4‐benizylpyridazine, 3‐ and 4‐(2‐pbenylethyl)pyridazine) was investigated. In the electron impact ionization mess spectra of the 3‐substituted compounds abundant [M – H]+ peaks are observed. This allows a clear distinction between 3‐ and 4‐substituted pyridazines, as the spectra of the latter isomers show only very weak [M – H]+ signals. The stability of [M – H]+ ions derived from 3‐alkylpyridazines (deduced from only the very low abundance of further fragment ions) gives strong evidence for a cyclic structure of these ions. One fragmentation pathway typical of the parent pyridazine, the [M ‐ N2] fragmentation, was not detectable with any of the phenylalkylpyridazines investigated. Instead, loss of HCN, H3CN+ and N2H+ was observed. An interesting fragmentation, observed with 3‐(2‐phenylethyl)pyridazine, is the loss of +CH3 from the molecular ion and also from the [M – H]+ ion.
Stereochemical effects in mass spectrometry. Part 10‐reaction mass spectrometry of cyclic glycols and monosaccharides with methylene chloride as reagent gas
Authors: Tu Ya‐Ping , Yang Guan‐Yu , Liu Yu‐Hua , Chen Shao‐Nong , Chen Yao‐Zu 
Published: May 2005

AbstractThe reaction mass spectrometry of cyclic glycols and monosaccharides with methylene chloride as reagent was studied. In the presence of ammonia, it was found that methylene chloride reacted stereoselectively with the quasi‐molecular ions of cyclic glycols and monosaccharides to form characteristic ions, by comparison of the relative abundances of which the stereoisomers of cyclopentane‐l,2‐diols and cyclohexane‐l,2‐diols and some monosaccharides could be definitely distinguished.
Electron impact mass spectra of 5,5‐bis(carboethoxy)‐1,3‐dioxanes
Authors: Horn Mihai , Mager Sorin , Palibroda Nicolae , Culea Monica 
Published: May 2005

AbstractElectron impact‐induced fragmentations of 2‐substituted 5,5‐bis(carboethoxy)‐l,3‐dioxanes were studied by exact mass measurements and metastable ion analysis. The substituent R on C(2) of the heterocyclic ring has little influence on the principal cleavage reactions. Elimination of CH2O/CO and C2H4O/C2H4/C2H5OH are common fragmentations for ions containing the 1,3‐dioxane moiety or the OC2H5 group, respectively. The abundant ions at m/z 173 and 127 serve as structural probes for the class of compounds studied. Primary fragmentations implying the ester function are of little importance.
Dithia[3.3 ]phanes. 4—mass spectrometry of some dithia[3.3]‐naphthalenophanes1
Authors: Kus̀ Piotr 
Published: May 2005

AbstractThe mass spectral fragmentation of 23 dithia [3.3]naphthalenophanes is discussed. The most characteristic species for these compounds are the M+ ion and ions at m/z 115, 135 (or 136), 141, 155 (or 154) and 185.
Reactions of ions of iron and cobalt acetylacetonates with macrocyclic thioiurea derivatives in the gas phase
Authors: Zagorevskii D. V. , Nekrasov Yu. S. , Timofeev O. S. , Gren' A. I. 
Published: May 2005

AbstractIon‐molecule reactions of (acac)2M+ ions (M = Fe, Co) with macrocyclic thiourea derivatives (L) were studied. The formation of acacML+ and acacM(L – H)+ were observed. AcacM(L – H)+ ions arise from loss of the hydrogen atom of the NH group. The ion peak intensity ratios, Z = [acacML+]/[acacM(L – H)+], for M = Co are higher than those for M = Fe, in accordance with the easier reduction of Co(III) to Co(II) than that of Fe(III) to Fe(II). It is proposed that the metal‐containing ions preferentially attack the thiourea fragment of the macro‐cycles studied.
Mass spectrometry of π‐complexes of transition metals 38—keto‐enol tautomerization of molecular ions of acetyl‐ and propionyl‐ferrocenes in the gas phase
Authors: Zagorevskii Dmitrii V. , Volkova Tatyana V. , Yakushin Sergey O. , Antipov Boris G. , Nekrasov Yurii S. 
Published: May 2005

AbstractFragmentation of the acetyl‐ and propionyl‐ferrocenes under electron impact together with the rupture of CCO bonds, characteristic of ketones, also includes elimination of water and migration of the OH group to the central metal atom, which is due to keto‐enol tautomerization of the acyl group in molecular or fragment ions.
On‐target deuteration technique in time‐of‐flight 252Cf plasma desorption mass spectrometry
Authors: Bondarenko P. V. , Zubarev R. A. , Knysh A. N. , Rozynov B. V. 
Published: May 2005

AbstractA new on‐target deuteration technique in plasma desorption mass Spectrometry (PDMS) is proposed, involving replacing labile hydrogen atoms in a molecule with deuterium atoms. This technique is very simple and allows direct comparison of spectra before and after deuteration for the same probe. The utility of the deuteration procedure in PDMS has been demonstrated in obtaining additional information on the structure of a molecule and its fragments and on the mechanism of quasi‐molecular ion formation.
Mass spectral study of substituted methyl (E)‐and (Z)‐cinnamates under 1,2‐dibromoethane chemical ionization
Authors: Vairamani M. , Saraswathi M. , Rao G. K. Viswanadha 
Published: May 2005

AbstractDibromoethane chemical ionization mass spectra of ten pairs of methyl (E)‐ and (Z)‐cinnamates were studied. C2H4Br+ ion forms stable adducts with E‐isomers and the adducts of Z‐isomers show preferential loss of methanol. The observed results suggest that the probability of ring alkylation is greater than with the carbonyl group.
Behaviour of isomeric methyl ethyl and ethyl methyl halosuccinates under electron impact. Elimination of a halogen atom by a multi‐step mechanism
Authors: Bornstein D. , Mandelbaum A. , Vidavsky I. , Domon B. , Mueller D. , Richter W. J. 
Published: May 2005

AbstractThe electron impact mass spectra of isomeric methyl ethyl and ethyl methyl halosuccinates (X = Cl and Br) are surprisingly different. Only the isomers with the ethyl group remote from the halogen give rise to [M ‐ X]+ ions. A low‐energy collision‐induced dissociation study of deuterium‐labelled analogues of the former isomers indicates that the [M ‐ X]+ ions are mixtures of protonated methyl ethyl maleate (major component, > 85%) and fumarate, and the loss of the halogen atom is a multi‐step process including at least two specific hydrogen transfers. Migration of a β‐hydrogen atom to the carbonyl oxygen within the ethoxycarbouyl group produces a primary radical site in a distonic intermediate which, by subsequent abstraction of a hydrogen atom from C(3), triggers the ejection of X from C(2) with concomitant double bond formation. Whereas in the other isomer an [M ‐ X]+ ion is absent or negligible, a characteristic double loss of C2H4 and CO2 is observed.
Field desorption mass spectrometry, fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry of echinacoside, the main caffeoyl‐glycoside from Echinacea angustifolia roots (Asteraceae)
Authors: Facino Roberto Maffei , Sparatore Anna , Carini Marina , Gioia Bruno , Arlandini Emanuele , Franzoi Luigi 
Published: May 2005

AbstractThe mass spectral fragmentation of echinacoside, a pharmacologically active caffeoyl‐glycoside isolated from Echinacea angustifolia roots, has been investigated using different soft‐ionization techniques, field desorption and fast atom bombardment (positive and negative ions) mass Spectrometry. Both ionization modes are successful in molecular mass determination and furnish approximately equivalent structural information. A fast atom bombardment tandem mass spectrometry approach (negative ions) was developed for the study of the fragmentation pathways and for the detection of echinacoside in crude plant extracts. The results demonstrate the usefulness of this technique for the rapid search of this important caffeoyl‐glucoside directly in natural complex matrices.
Gas chromatographic/mass spectrometric identification of some organic compounds and odours in poultry wastes
Authors: Sturaro Alberto , Parvoli Giorgio , Doretti Lucio , Daolio Sergio 
Published: May 2005

AbstractAir and waste samples coming from poultry breeding farms have been analysed by means of thermal desorption coupled to the gas chromatographic/mass spectrometric technique. The solid samples not only showed the presence of organic compounds such as acids, sulphides, benzopyrroles and phenols originated by anaerobic biotransfor‐mation of the natural products, but also the occurrence of anti‐oxidant substances: 2,6‐di‐tert‐butylcresol, 2,6‐di‐tert‐butylphenol and two of their oxidation derivatives. In the air, four artificial benzoquinones were detected, two of which had already been identified in the solid waste. In this work, the mechanism by which oxidized compounds are formed, is suggested.
Fragment‐molecule adduct ion formation in the mass spectra of cyclic N‐acetylamines and related nitramines
Authors: Burrows Elizabeth P. 
Published: May 2005

AbstractMass spectra of seven related N‐heterocyclics, introduced by direct exposure probe, were determined in electron impact (EI) and positive‐ and negative‐ion chemical ionization (PCI and NCI) modes. Proton adducts were the predominant molecular ion species in the EI and PCI modes. In addition, a variety of fragment–molecule adduct ions were observed for each compound in one or more of the modes. The propensity of 1,3,5‐trinitrohexahydro‐1,3,5‐triazine for fragment–molecule adduct formation was high in all three ionization modes. Fragmentation processes were documented by collision‐induced dissociation experiments.
Improved metal vapor neutralization and resolution in neutralization‐reionization mass spectrometry
Authors: Drinkwater Donald E. , Fura Aberra , Zhang Mei‐Yi , McLafferty Fred W. 
Published: May 2005

AbstractIncreased differential pumping improves the simultaneous sequential operation of ion‐beam neutralization, neutral dissociation, neutral product ionization, and ion product dissociation for neutralization‐reionization (NR) mass spectrometry. Following Porter's developments for neutralized ion‐beam spectroscopy, instrument modifications allow a wider variety of metals (vaporization up to 800 °C) to be used for neutralization and eliminate multiplier instabilities seen previously using neutralization metals such as sodium. Irreproducibility of recovered precursor ion signals using metal vapors of low ionization potential has been traced to mercury background. Double focusing of the ionized neutral beam yields NR mass spectra of the highest resolution yet reported.
Comparative electron impact mass spectra of new 5‐benzylidene‐4,5‐dihydro‐(2H)‐pyridazin‐3‐ones and 4‐benzylidene‐4,5‐dihydrooxazin‐6‐ones
Authors: Chabard Jean‐Louis , Taoufik Jamal , Couquelet Jacques , Tronche Pierre 
Published: May 2005

AbstractElectron impact mass spectra are reported for a series of 5‐benzylidene‐4,5‐dihydro‐(2H)‐pyridazin‐3‐ones and 4‐benzylidene‐4,5‐dihydrooxazin‐6‐ones.
Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses
Authors: Peltier John M. , Smith Richard W. , Maclean David B. , Szarek Walter A. 
Published: May 2005

AbstractThe ammonia desorption chemical ionization (NH3‐DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non‐reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [M + NH4 – 42]+ ion is not formed direct from [M + NH4]+ by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH4+. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH3CO to afford neutral species which complex with NH4+. The structures of the ions resulting from H transfer have been inferred by comparison of their mass‐analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [M + NH4]+ ions of compounds of established structure. A ring fragmentation reaction of 1, 2 and 3 is reported.
Methylene chloride chemical ionization of fumaric and maleic acids and their esters
Authors: Tu Ya‐Ping , Liu Ya‐Qin , Yang Guan‐Yu 
Published: May 2005

AbstractThe chemical ionization (CI) mass spectrometry of fumaric and maleic acids and their esters with methylene chloride as reagent gas is described. The introduction of methylene chloride to the CI(CH4) plasma led to the formation of new characteristic ions in addition to the protonation and the subsequent fragmentation, revealing diagnostic information on the configuration of geometrical isomers. The new characteristic ions have been found to arise from the addition of the reactant ion of methylene chloride, [CH2Cl]+, to the substrates and, for higher dialkyl esters, from the further McLafferty rearrangement of the adduct ion [M + CH2Cl]+.
Study of the reactions and reaction mechanisms of phosphine (Ph3P) and of phosphite ((PhO)3P) with sulphur (S8)
Authors: Zhang Haiying , Peng Jiarou , Peng Shiqi , Wu Guowang , Dai Duenhua , Zhu Guozheng 
Published: May 2005

AbstractThe reactions of sulphur with phosphine and phosphite were investigated by low‐energy electron impact mass spectrometry and fast atom bombardment mass spectrometry. A previously reported mechanism of the Ph3P–S8 reaction was supported and a possible mechanism for the (PhO)3P–S8 reaction is proposed.
Mass spectral study of derivatives of 2‐aryloxy‐2‐methylpropanoicacids
Authors: Vairamani M. , Kumar K. V. Siva , Rao G. K. Viswanadha 
Published: May 2005

AbstractElectron impact mass spectra are reported for series of 2‐aryloxy‐2‐methylpropanoic acids, 2‐aryloxy‐2‐methylpropanamides and N‐phenyl‐2‐aryloxy‐2‐methylpropanamides. Fragmentation mechanisms are discussed on the basis of deuterium labelling, meastable ions and accurate mass measurements.
Gas‐phase chemistry of the methyl carbamate radical cation, H2NCOOCH. II—A test case for ion structure assignment
Authors: McGibbon Graham A. , Kingsmill Carol A. , Terlouw Johan K. , Burgers Peter C. 
Published: May 2005

AbstractThe unimolecular chemistry of the methyl carbamate radical cation, H2NCOOCH, 1, has been further investigated by a combination of mass spectrometry‐based experiments (metastable ion (MI), collisional activation (CA), collision‐induced dissociative ionization (CIDI), neutralization‐reionization (NR) Spectrometry and 2H labelling) and ab initio molecular orbital calculations, executed at the MP3/6–31G*//4–31G level of theory and corrected for zero‐point vibrational energies. Apart from the previously located maxima, i.e. H2NCOOCH3+·, 1, the distonic ion H2NC(OH)OCH3+·, 2, hydrogen‐bridged ions [H2NCO…︁ H…︁OCH2]+·, 5, and [H2NCHO…︁…︁H…︁OCH]+·, 7, there exist at least two other equilibrium structures, viz. the iminol ion HNC(OH)OCH, la, and the hydrogen‐bridged species [H2CO…︁H…︁N(H)COH], 6a, which is closely related to ion 5. Although the iminol ion la lies only 30 kJ mol−1 above 1, our calculations indicate that the barriers for its formation either directly from ionized methyl carbamate 1 via a 1,3‐hydrogen shift or indirectly via 1,4‐hydrogen shifts from the distonic ion 2 are too high to allow the iminol ion to be involved in the unimolecular chemistry of ionized methyl carbamate. This explains the earlier observation that there are no H‐D exchange reactions prior to decomposition of ionized labelled methyl carbamate, in contrast to the related ion methyl acetate. However, attempts to generate the iminol ion by loss of CH3CN from CH3CHNNHCOOCH3 produced the more stable distonic ion 2 instead, but it proved very difficult to assign its structure unequivocally because 2 can rapidly interconvert with 1 and so virtually identical dissociation characteristics ensue. Only by integration of results obtained from many experiments and from ab initio calculations could structure 2 be assigned. The distonic ion 2 can undergo two transformations: after stretching of the COCH2 bond the incipient formaldehyde can migrate within the electrostatic field of ionized hydroxyaminocarbene to the OH end to generate 5, but it can also migrate to the NH end to generate 6a. This explains the previous puzzling observation that H2NCOOCD forms both CD2OD· and CD2OH· in CA and NR experiments. The calculations and experiments indicate that, although the ion is exceedingly difficult to characterize, the distonic ion 2 is the key intermediate for all the observed dissociations of methyl carbamate.
Suppression of matrix ions in ultraviolet laser desorption: Scanning electron microscopy and raman spectroscopy of the solid samples
Authors: Chan T‐W. Dominic , Colburn A. W. , Derrick Peter J. , Gardiner Derek J. , Bowden Michael 
Published: May 2005

AbstractSuppression of low‐mass ion peaks in matrix‐assisted ultraviolet laser desorption has been found to occur at low matrix‐to‐analyte molar ratios when using nicotinic acid as matrix, independent of the angle of illumination. Microscopic Raman scattering spectroscopy has been employed to investigate the matrix–analyte solid‐state composition. The matrix‐to‐analyte molar ratios employed in preparing the solutions are reliable guides to the relative amounts of matrix and analyte molecules in the solid crystals, given the method of sample preparation employed involving drying under a stream of nitrogen. A qualitative model based on the proton supply‐and‐demand argument is tentatively proposed to explain the suppression phenomenon.
Advantages of high‐resolution and high‐mass range magnetic‐sector mass spectrometry for electrospray ionization
Authors: Chapman John R. , Gallagher Richard T. , Barton E. C. , Curtis Jonathan M. , Derrick Peter J. 
Published: May 2005

AbstractElectrospray ionization (ESI) mass spectra have been measured on a magnetic‐sector double‐focusing mass spectrometer for a number of proteins and peptides. It is pointed out how in theory raising the mass resolution of a mass spectrometer from 800–1000 to 2400–3000 significantly increases the precision with which the envelope of isotopic peaks of a protein ion (or other organic ion) can be defined, particularly at higher masses. Better definition of the isotopic envelope ought to lead to higher precision in the experimental determination of molecular mass, which has been demonstrated. It is shown how ESI mass spectra of high‐mass molecules are significantly less congested at higher m/z values, so that for these molecules (RMM > 40 000) there is an advantage in being able to record peaks at higher m/z values (m/z > 2000) representing ions with fewer charges. Fragmentation of a small peptide in the ESI source has been found to provide sequence information.
Identification of aminophospholipid stereomers by positive‐ion fast atom bombardment combined with collisional activation mass‐analysed ion kinetic energy analysis and high‐performance liquid chromatography
Authors: Chen Su , Menon Giampaolo , Traldi Pietro 
Published: May 2005

AbstractTwo methods for the identification of aminophospholipid stereomers are described. After a chemical derivatization, 9‐fluorenylmethoxycarbonyl derivatives of diacyl‐sn‐2‐ and diacyl‐sn‐3‐phosphoserine and diacyl‐sn‐2‐ and diacyl‐sn‐3‐phosphoethanolamine can be characterized by positive‐ion fast atom bombardment combined with collisional activation mass‐analysed ion kinetic energy analysis based on the differentiation of relative abundances [M + H + diethanolamine − 89]+ and [M + H]+ fragments derived from [M + H + diethanolamine]+ ions, the protonated solvated molecules, and normal phase high‐performance liquid chromatography on the basis of different elution times of the derivatives of the aminophospholipid stereomers on an aminopropyl‐bonded column.
Contribution of mass spectrometric techniques to the structure elucidation of antibiotic GE2270A, a novel inhibitor of bacterial protein synthesis
Authors: Colombo L. , Tavecchia P. , Selva E. , Gallo G. G. , Zerilli L. F. 
Published: May 2005

AbstractGE2270A is a novel antibiotic active against Gram‐positive bacteria and anaerobes. Its structure originates from a peptidic backbone, the amino acids of which have been modified to produce a macrocycle and a side‐chain. It contains a heterocyclic chrornophonc system, a number of thiazoleamino acids and three unmodified natural amino acids. The structure [relative molecular mass (RMM) 1289] was determined using various spectroscopic techniques, of which fast atom bombardment mess spectrometry, gas chromatography/mass spectrometry, desorption chemical ionization mass spectrometry and fast atom bombardment tandem mass spectrometry played an important role. The mass spectrometric approach was applied to the intact molecule and to the various hydrolysis products, including the chromophoric part (RMM 634).