bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas‐phase reactions of transition metal carbonyl anions and atomic metal anions with nitrous oxide and dioxygen: Oxygen atom transfer and ligand exchange in reactions with nitrous oxide
Authors: van den Berg Klaas Jan , Ingemann Steen , Nibbering Nico M. M. , Gregor Ian K. 
Published: May 2005

AbstractThe gas‐phase reactions of a series of metal carbonyl anions M(CO) (M=Cr, n=2–5; M=Mn, n=1–5; M=Fe, n=1–4) with nitrous oxide and dioxygen have been studied by use of Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometry. With nitrous oxide, most of the metal carbonyl ions react by oxygen atom transfer leading to oxo‐metal anions and oxo‐metal carbonyl anions. The Cr− and Fe− ions also react relatively easily with nitrous oxide by oxygen atom abstraction to form CrO− and FeO−, respectively. Experiments with N15NO reveal that loss of a CO molecule from a collision complex is a significant ligand exchange channel for the Mn(CO), Mn(CO) and Fe(CO) ions. The nitrous oxide molecule remains intact in the resultant product ions, M(CO)n(N2O)− with M=Mn, n=2 and 3; and M=Fe, n=2. The losses of 15NN and 15NN + CO in the collision‐induced dissociations of the Mn(CO)3(N15NO)− ions, in combination with the relatively facile occurrence of oxygen atom transfer, are taken to mean that coordination of the metal centre to the oxygen atom is preferred over bond formation to the terminal nitrogen atom of the nitrous oxide molecule. The metal carbonyl anions react readily with dioxygen to form mainly oxo‐metal ions as well as oxo‐ and dioxo‐metal carbonyl anions in relative yields which depend on the nature of the metal and the number of CO ligands in the reactant ion.
Investigation of mammalian lignan precursors in flax seed: First evidence of secoisolariciresinol diglucoside in two isomeric forms by liquid chromatography/mass spectrometry
Authors: Bambagiotti‐Alberti Massimo , Coron Silvia A. , Ghiara Caterina , Moneti Gloriano , Raffaelli Andrea , Traldi P. 
Published: May 2005

AbstractA strong research effort has been devoted in recent years to the mammalian lignans enterolactone and enterodiol because of their claimed protective effects against breast and colon cancer. Some plant lignans appear to be precursors of these molecules. This paper reports a novel identification procedure for one of these precursors, the secoisolariciresinol diglucoside, in the extracts of defatted flax‐seed meal. The procedure is based on high‐performance liquid chromatography coupled with either ionspray or continuous‐flow fast‐atom bombardment mass spectrometry. The application of these techniques allowed the identification in flax seed of two isomeric forms of this precursor for the first time. The isomers are reasonably the two diastereoisomers, due to the two equivalent stereogenic centers present in the molecule.
Role of coulomb energy in promoting collisionally activated dissociation of multiply charged peptides formed by electrospray ionization
Authors: Ishikawa Keiichiro , Nishimura Toshihide , Koga Yoshinori , Niwa Yoshio 
Published: May 2005

AbstractElectrospray ionization tandem quadrupole mass spectrometry has been applied to a series of lysine‐substituted octaalanines and some naturally occurring peptides containing more than two basic amino acid residues. Unusually high fragmentation efficiency along with site‐specific cleavages at the outer side of and remote from basic residues were observed for collisionally activated dissociation spectra of multiply charged peptides (MCP) with basic residues in close proximity. It was suggested that Coulomb energy (CE) rather than Coulomb repulsion (CR) was responsible for promoting fragmentation of the MCP studied. A possible fragmentation mechanism of MCP is proposed, in which the conversion of CE into internal vibrational energy was brought about by intramolecular proton migration in the presence of CR between charged sites.
Plasma desorption mass spectrometry of two synthetic sarafotoxins: Side reactions and characterization of the intermediates
Authors: Lamthanh Hung , Deprun Claude , Beyec Yvon Le 
Published: May 2005

AbstractSarafotoxins (SRTXs) form a family of toxic and potent vasoconstrictor peptides of 21 amino acids and two disulfide bonds. They are present in the venom of the burrowing asp Atractaspis engaddensis. We have made two derivatives of the amino acid sequence of SRTX‐b, one of the most potent isotoxins, in the solid phase. First, we replaced Ser2 by Thr, to investigate whether, as previously postulated, this change is responsible for the weak activities of SRTXs c and d. Secondly, we replaced Ser2, Asp18 and Val19 respectively by Thr, Gly and He, with a view to generating SRTX‐e whose amino acid sequence was deduced from cDNA.Solid‐phase peptide synthesis (SPPS) was performed according to the tert‐butyloxycarbonyl strategy and the disulfides were paired sequentially using a selective chemistry. The disulfide 1–15 was formed by oxidation of cysteines1,15 with ferricyanide, whereas disulfide 3–11 was made by iodine oxidation of Acm‐blocked cysteines3,11. By plasma desorption mass spectrometry (PDMS), we monitored all possible side reactions that occurred during the synthesis. We thus observed a benzyl shift in mass spectra when aspartic and glutamic acid side chains were protected by a benzyl group during the SPPS. This could be circumvented by using instead, a cyclohexyl protecting group. We also noted the oxidation of the methionine and the tryptophan side chain (formation of methionine sulfoxide and oxindole ring of tryptophan) to a small extent during the cleavage peptide/solid phase oxidation of the methionine side chain during the formation of the disulfide 1–15 by ferricyanide. These known side reactions could be avoided by using a mixture of scavengers (ethanedithiol, dimethylsulfide, thioanisole, m‐cresol and skatole) and by shortening the ferricyanide oxidation time to one hour. The sequential disulfied bond formation starting from the linear peptide (mono‐disulfied and bi‐disulfide) was also monitored by PDMS. PDMS therefore proved to be a sensitive analytical method for the measurement of the molecular weights of synthetic or natural peptides (SRTX peptides in this application) in the field of peptide and protein chemistry.
Matrix‐free desorption of biomolecules using massive cluster impact
Authors: Shannon Cornett D. , Lee Terry D. , Mahoney John F. , Todd P. J. 
Published: May 2005

AbstractMassive‐cluster impact (MCI) ionization was found to be capable of producing high secondary‐ion yields from biological samples without the use of a liquid matrix. Dry samples of molecules as large as cytochrome c were observed to be efficiently desorbed without significant fragmentation by the MCI beam of glycerol clusters. In addition, signals from protonated molecules retained a significant proportion of their initial intensity even after several minutes exposure to the primary beam. It was determined that these remarkable phenomena are not the result of the build‐up of a layer of glycerol caused by the cluster bombardment.
Peptide fingerprints after partial acid hydrolysis: Analysis by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Knierman Michael D. , Coligan John E. , Parker Kenneth C. , Chait B. T. 
Published: May 2005

AbstractA method is described by which a sequence‐dependent peptide fingerprint can be rapidly obtained upon partial hydrolysis of peptides with hydrochloric acid and subsequent analysis by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). When synthetic peptides are treated with 3M HCI for 5 min at 110°C, amino acids are released in turn from the C‐terminus or, depending on the peptide, from the N‐terminus. Sequence information can be deduced by identifying the amino acid whose mass corresponds to the difference in MW between the major hydrolysis products, beginning from the MW of the starting peptide. A similar pattern exclusively from the C‐terminus has been obtained using pentafluoropropionic acid as a hydrolyzing agent (Tsugita et al. Eur. J. Biochem. 206, 691 (1992)), but required longer hydrolysis time and more handling prior to analysis. The technique we have developed could be used to obtain a sequence‐dependent ‘fingerprint’ for a peptide cheaply and rapidly, starting with picomole amounts of peptide, because the hydrolysate can be directly analyzed by MALDI. This methodology might be especially useful for confirming the identity of peptides during peptide mapping.
The unimolecular dissociation of the molecular ion of acetophenone induced by thermal radiation
Authors: Sena Marcelo , Riveros José M. , Nibbering N. M. M. 
Published: May 2005

AbstractThe molecular ion of acetophenone is shown to undergo unimolecular dissociation to the benzoyl cation in an ICR cell at low pressures and in the vicinity of 333 K with rate constants in the range of 2 to 4 s−1. Pressure and temperature dependence of this process reveal that the process is primarily induced by absorption of thermal radiation driving ions to energies above the dissociation limit. Collisional effects also enhance this dissociation by a mechanism that attempts to restore a full Boltzmann distribution of the molecular ions.
Electrospray mass spectrometry for the characterization of the purity of natural and modified oligodeoxynucleotides
Authors: Deroussent Alain , Le Caer Jean‐Pierre , Rossier Jean , Gouyette Alain 
Published: May 2005

AbstractElectrospray ionization mass spectrometry is an accurate and sensitive analytical method to characterize the purity of oligodeoxynucleotides being tested for pharmacological studies. We report the preparation procedure (‘desalting’) of natural and modified oligodeoxynucleotides (ODNs) and their analysis by negative‐ion electrospray mass spectrometry. We evaluate the sensitivity and the accuracy of the method for two antisense ODN sequences. Mass analysis of the 25‐mer phosphorothioate can be performed to within 0.001% accuracy (standard error of 0.05 Da) for a sample concentration of 12 pmol/μL. In addition, the adduct ion and the failure sequence can be identified to characterize the antisense ODN.
Formation of protonated phosphonates in the ion‐trap mass spectrometer under electron impact conditions
Authors: Méchin N. , Plomley J. , March R. E. , Blasco T. , Tabet J.‐C. 
Published: May 2005

AbstractThe gas‐phase behaviour of organophosphorus compounds such as diethylmethylphosphonate towards electron impact (EI) ionization occurring in a quadrupole ion‐trap instrument is investigated. If all ions observed in conventional EI mass spectra are detected, ion/molecule reactions are seen to occur leading to formation of protonated molecules and adduct ions such as 2M+· and [2M + H]+. The keto‐to‐enol‐like isomerization of the molecular M+· ion seems to favour proton transfer to neutral M species and a “self chemical ionization” ion is observed with corresponding fragment ions.
Stereospecific decompositions induced by low‐energy collision‐induced dissociation of MH+ ions of epimeric alkaloids
Authors: Grégoire S. , Dugat D. , Fournier F. , Gramain J.‐C. , Tabet J.‐C. 
Published: May 2005

AbstractSeveral studies have investigated stereochemical effects observed in the electron ionization and low‐energy collision‐induced dissociation (CID) mass spectra of molecular ions from synthetic and natural alkaloids. More recently, it has been shown that low‐collision‐energy CID spectra of protonated epimeric alkaloids can yield additional information. For instance, three epimeric tetracyclic alkaloids studied in the present work are characterized by different cis/trans ring junction geometries and by different configurations of the ethyl group linked to the C‐ring. Low‐energy collisional spectra of the epimeric MH+ ions show large differences depending both on the ring junction geometry and the stereochemistry of the side chain. Interpretation of certain specific processes invokes ion‐dipole formation, allowing internal electron transfer. Consecutive decompositions have also been scrutinized.
Sequencing of hydrophobic peptides as lithiated adducts using liquid secondary‐ion mass spectrometry without tandem mass spectrometry
Authors: Becchi M. , Rebuffat S. , Dugast J‐Y. , Hlimi S. , Bodo B. , Molle G. 
Published: May 2005

AbstractLithium cationized hydrophobic peptides in the molecular weight range 1900–2650 Da have been studied by liquid secondary‐ion mass spectrometry. The mass spectra exhibit characteristic lithiated sequence ions. N‐terminal [an+LiH]+ and [dn+LiH]+ ions together with limited C‐terminal [ypro+Li+H]+ ions lead to an easy sequencing of the peptides studied, without the need for tandem mass spectrometry.
Particle size distribution is not the major factor explaining variable analyte transmission efficiency in liquid chromatography/particle beam/mass spectrometry
Authors: Wilkes Jon G. , Zarrin Fahimeh , Lay Jackson O. , Vestal Marvin L. 
Published: May 2005

AbstractWe characterized the particle size distribution and the analyte transmission efficiency of a liquid chromatography/particle beam/mass spectrometry (LC/PB/MS) system as a function of experimental variations normally used to optimize the LC/PB/MS system. The particle size distribution was evaluated using an electrical differential mobility particle sizer (DMPS) and both the DMPS and the mass spectrometer were used to evaluate transmission. The latter results were correlated to provide evidence related to mechanisms which contribute to poor sample transmission. Addition of ammonium acetate buffer did not increase the aerosol particle riean diameter. However, it did lead to significant increases in caffeine transmission efficiency observed in both the DMPS and the mass spectrometer. Our results were interpreted to suggest a possible electrostatic cause for quantitative anomalies in LC/PB/MS rather than simple mass discrimination in the particle beam momentum separator.
Fast‐atom bombardment mass spectrometry of some pharmacologically relevant anthraquinone derivatives
Authors: Maccioni Elias , Delogu Giovanna , Podda Gianni , Palumbo Manlio , Zagotto Giuseppe , Seraglia Roberta , Traldi Pietro 
Published: May 2005

AbstractThe mass spectrometric behaviour of some anthraquinone derivatives has been studied by fast‐atom bombardment ionization. For all the compounds under study, a retrosynthetic process, consisting in the cleavage of the NHCO bond with hydrogen rearrangement, has been detected. This decomposition pathway leads to the formation of the protonated molecule of 1,4‐diaminoanthraquinone or to the 1‐amino‐4,5,8‐trihydroxy‐anthraquinone, representing the basic synthetic elements of the compounds under investigation.
Matrix‐assisted laser desorption and fast‐atom bombardment mass spectrometry of water‐soluble phthalocyanines and their carboxyl derivatives
Authors: Shankai Zhao , Feng Zhong , Weide He , Zhongping Yao , Hanhui Wen 
Published: May 2005

AbstractAluminium phthalocyanine and copper, nickel and zinc 4,4′,4″,4‴‐tetra carboxyl phthalocyanines have been studied by matrix‐assisted laser desorption ionization(MALDI) and fast‐atom bombardment(FAB) mass spectrometry. Aluminium phthalocyanines can be analysed by both FAB and MALDI with promising results but FAB provides more fragment information. The carboxyl derivatives are less volatile than the unsubstituted compounds and their mass spectra cannot be obtained by FAB, but can be obtained by MALDI with good results.
Peptide mapping of recombinant human parathyroid hormone by enzymatic digestion and subsequent fast‐atom bombardment mass spectrometry
Authors: Nabuchi Yoshiaki , Kuboniwa Hitoshi , Takasu Hisashi , Asoh Yoshinori , Ushio Hidetoshi 
Published: May 2005

AbstractPeptide maps of recombinant human parathyroid hormone (rhPTH) were determined by both trypsin and V‐8 protease digestion with subsequent fast‐atom bombardment mass spectrometry (FAB‐MS). Coverage of the sequence was 85% when using trypsin and 90% when using V‐8 protease. Five rhPTH variants that were recombinantly produced as models of Asn deamidated type degradation products were measured, and molecular weight differences between their respective deamidated peptide fragments were completely detected. In the V‐8 protease digests of some variants, characteristic peptide ions caused by the deamidation were observed and this greatly facilitated the assignment and recognition of the deamidated position. Our data suggest that FAB‐mapping of rhPTH via the protease digestion methods used, appears to have great potential for structural investigations of the peptide.
Reduction phenomenon in frit fast‐atom bombardment mass spectrometry
Authors: Aubagnac Jean‐Louis , Gilles Isabelle , Lazaro René , Claramunt Rosa‐Maria , Gosselin Gilles , Martinez Jean 
Published: May 2005

AbstractThe reduction phenomenon of polar compounds that has already been described in fast‐atom bombardment (FAB) mass spectrometry also occurs in frit‐FAB mass spectrometry.
Compact Wien filter/magnetic sector double‐focusing mass spectrometer
Authors: Ioanoviciu Damaschin , Cuna Cornel 
Published: May 2005

AbstractA compact Wien filter/magnetic deflector, double‐focusing mass spectrometer was constructed and tested. The Wien filter is sited inside the gap common with the magnetic deflector. The instrument first‐order ion‐optical parameters and the second‐order aberration coefficients are given. A brief description of the instrument is followed by the experimental results obtained on a methane sample. Jon currents of 1.6 × 10−8 A were collected at a resolution of 170 for a main path radius of 56 mm.
Influence of the laser beam direction on the molecular ion ejection angle in matrix‐assisted laser desorption/ionization
Authors: Aksouh Farouk , Chaurand Pierre , Deprun Claude , Della‐Negra Serge , Beyec Yvon Le , Hoyes John , Pinho Roberto Rosas 
Published: May 2005

AbstractAngular intensity distribution of molecular ions ejected in matrix‐assisted laser desorption/ionization (MALDI) have been measured for two symmetrical positions of the laser beam with respect to the sample surface normal (+60° and −60°). It is shown that the molecular ions are ejected in the direction opposite to the incident laser beam with an average angle of ∼30° which does not depend on the molecular weight in the mass range m/z = 1000 to 25 000. Experiments were performed with the matrix α‐cyano4‐hydroxy‐cinnamic acid.
7‐Deaza purine bases offer a higher ion stability in the analysis of dna by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Kirpekar F. , Nordhoff E. , Kristiansen K. , Roepstorff P. , Hahner S. , Hillenkamp F. 
Published: May 2005

AbstractOligodeoxynucleotides which contain 7‐deaza analogues of the normal purine nucleotides have been synthesized both enzymatically and chemically. When subjected to matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) analysis, the modified samples offer both higher stability and increased sensitivity compared to otherwise identical unmodified Oligodeoxynucleotides. In view of these observations, models for the fragmentation of oligodeoxynucleotides in MALDI‐MS with positive ion detection mode are presented. Additionally, the potential use of 7‐deaza purine nucleotides in the MALDI‐MS analysis of DNA sequencing reactions is discussed.
Examination of recombinant truncated mature human fibroblast collagenase by mass spectrometry: Identification of differences with the published sequence and determination of stable isotope incorporation
Authors: Chowdhury Swapan K. , Eshraghi Jamshid , Gonyea George , Brake Patricia G. , Vavra Karen J. , Banks Tracey , Falvo Joseph , Wahl Robert , Chait Brian T. , Vestal Christina H. 
Published: May 2005

AbstractHuman fibroblast collagenase belongs to a family of matrix metalloproteinases which have been implicated in a number of connective tissue disorders ranging from rheumatoid arthritis to tumor invasion. To examine the active site of this enzyme by biophysical studies, a 19 kDa recombinant truncated mature collagenase (mCL‐t) was prepared. Electrospray ionization (ESI) and matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry have been utilized for the characterization of mCL‐t. The molecular weights measured by these techniques identified the presence of two closely related protein components separated by approximately 100 Da. Edman sequence analysis demonstrated that the two protein components differ from each other by an amino terminal valine, consistent with the mass spectrometric data. In addition, the molecular weight of mCL‐t determined by mass spectrometry did not agree with that calculated from the reported sequence. To identify the origin of this discrepancy, the DNA sequence of the mCL‐t clone was examined. Several differences were noted between the DNA sequence of mCL‐t and the published collagenase gene sequence. When these differences were taken into account, the measured molecular weights were found to be in good agreement with that calculated for the modified sequence. In separate experiments, both ESI and MALDI mass spectrometry have been used to determine molecular weights of mCL‐t samples enriched with stable isotopes 15N and (15N+13C). The measured molecular weights demonstrated a 97% (15N) and 99% (15N+13C) incorporation of labeled isotopes in the two samples.
Mass spectrometry of phosphorus‐containing acids chemisorbed on a disperse silica surface
Authors: Bogatyr'ov Viktor M. , Pokrovskiy Valeriy A. 
Published: May 2005

AbstractThermal transformations of phosphorus and phosphoric acid were studied on a pyrogenic silica surface. Complete binding of phosphoric acid with the surface was observed as a result of thermal vacuum treatment. Oxidation‐reduction disproportion reactions in the samples containing phosphorus acid resulted in removal of molecular phosphorus in two stages which were attributed to disproportion of phosphorus atoms in the surface monolayer (high‐temperature stage) and in the bulk layers (low‐temperature stage).
Biosynthesis of melanin from dopamine. An investigation of early oligomerization products
Authors: Bertazzo Antonella , Costa Carlo , Allegri Graziella , Seraglia Roberta , Traldi Pietro 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization (MALDI) and fast‐atom bombardment (FAB) mass spectrometry experiments were applied to the study of the early stages of the oligomerization reaction of dopamine with mushroom tyrosinase. Ultrafiltration was employed to remove the enzyme at various reaction times, to prevent possible attachment of the protein to the highly reactive intermediates. Two sets of five samples each, obtained at different reaction times, in one case immediately lyophilized and in the other left to react under an oxygen stream for 24 h before lyophilization, were compared. FAB showed the presence of various species and of these, that at m/z 305 increased in abundance with reaction time in the immediately lyophilized set of samples only. Accurate mass measurements and tandem mass spectrometric experiments indicated the structure of a dopamine protonated dimer for this ion. MALDI measurements showed that all samples were composed of clusters of oligomers differing in degree of oligomerization. Oligomerization increases with reaction time, resulting in the formation of species at 2643–2911 Da. These clusters in turn were formed of species with a different degree of oxidation, detected in both sets of samples.