The acidity of chloro-substituted benzenes: a comparison of gas phase, ab initio, and kinetic data

The deprotonation energies of benzene, chlorobenzene, all di-, tri-, tetrachlorobenzenes, and pentachlorobenzene have been determined in the gas phase using a Fourier transform ion cyclotron resonance mass spectrometer. The values measured differ only slightly, though significantly, from the corresponding data for oligofluorobenzenes. The heavier halogen acidifies orthopositions slightly less and meta-positions slightly more than fluorine does. Moreover, the contributions of three or more chloro substituents are not perfectly additive. In fact the accumulation attenuates the contributions somewhat. Quantum chemical calculations at the MP2/6-311+G* level reproduce the gas-phase acidities fairly well, but reveal special effects when extended to experimentally not observable benzenides carrying the halogens at anion-remote positions. Competition experiments have been performed to assess the relative reactivity of nine oligochlorobenzenes towards sec-butyllithium in tetrahydrofuran at -100 degrees C. An almost exact linear correlation between logarithmic rates and gas-phase acidities has been found.

Methodology for the development of a drug library based upon collision-induced fragmentation for the identification of toxicologically relevant drugs in plasma samples

The possibility of creating a robust mass spectral library with use of high-performance liquid chromatography-atmospheric pressure-electrospray ionization (HPLC-AP-ESI) for the identification of drugs misused in cases of clinical toxicology has been examined. Factors reported as influencing the fragmentation induced by "source transport region collision induced dissociation" (CID) have been tested in this study (i.e. solvent, pH, different acids or buffer salts and their concentration, different organic modifiers and the modifier concentration). The tests performed on a few "model drugs" were analysed with use of two different single quadrupole instruments. The large number of mass spectra obtained appears to be affected by the mobile phase conditions to only a minor extent. This also holds for the mass spectra obtained at two different instruments (laboratories). Subsequently breakdown curves have been measured for about 20 randomly chosen drugs by variation of the kinetic energy of their ions in the CID zone through changing the fragmenter voltage. These breakdown curves were used to optimize the fragmenter voltage for each drug. The optimized fragmenter voltages were then applied by use of a variably ramped fragmenter voltage to acquire mass spectra for the library. The chromatographic separations were run on a Zorbax Stable bond column using a 10-mM ammonium formate-acetonitrile gradient method. Spiked blank serum and patient samples with a total of 40 different drugs were extracted with use of a standard basic liquid-liquid extraction (LLE) method. A search of significant peaks in the chromatogram by application of the developed mass spectral library is shown to result in a more than 95% positive identification. reserved.

Convergent synthesis of noncovalent metallodendrimers containing hydrophobic dendrons at the periphery

The noncovalent synthesis of "layer-block" metallodendrimers containing hydrophobic shells of covalent dendritic wedges at the periphery is described. Starting from first- and second-generation Fréchet wedges having phosphines at their focal point, convergent dendritic growth yields third- and fourth-generation metallodendrimers in which the coordination of nitriles, pyridines, and phosphines to SCS Pd(II) pincers is used as the assembly motif. In this convergent growth, the number of terminal hydrophobic phosphine wedges increases with generation. The solubility of the dendritic structures in apolar organic solvents such as chloroform and dichloromethane increases accordingly, in contrast to previously reported metallodendrimers. All dendritic structures were characterized by (1)H and (31)P NMR spectroscopy, elemental analysis, and MALDI-TOF mass spectrometry.

A study of light-induced proton transfer from gas phase (radical) cations to reference bases. Bracketing of proton transfer from excited ions and associated reaction kinetics

By use of Fourier transform ion cyclotron resonance, it is shown that protonated naphthalene when excited with laser light of 488 nm is more reactive in proton transfer to reference bases than in its ground state. The excitation leads to reaction with bases for which proton transfer in the ground state is endothermic up to a detected maximum of 60 kJ/mol. For indene radical cations excited at 514.5 nm, it is shown that the rate constant for proton transfer to 3-pentanone is either about 10 or about 100 times lower than the rate constant for relaxation by collisions with 3-pentanone. From the energy deposited in the ions, 0.5-0.6 eV is available for proton transfer to a base which seems reasonable when taking into account a complete randomization of the initially deposited energy.

International Mass Spectrometry Society (IMSS)

This paper gives a brief description of the recently formalized International Mass Spectrometry Society (IMSS). It is presented here in order to increase awareness of the opportunities for collaboration in mass spectrometry in an international context. It also describes the recent 15th International Mass Spectrometry Conference, held August/September 2000, in Barcelona. Each of the authors is associated with the IMSS. The 15th Conference, which covers all of mass spectrometry on a triennial basis, was chaired by Professor Emilio Gelpi of the Instituto de Investigaciones Biomedicas, Barcelona. The outgoing and founding President of the IMSS is Professor Graham Cooks, Purdue University, and the incoming President is Professor Nico Nibbering, University of Amsterdam. Similar material has been provided to the Editors of other journals that cover mass spectrometry.

Ag+ labeling: a convenient new tool for the characterization of hydrogen-bonded supramolecular assemblies by MALDI-TOF mass spectrometry

Herein we describe our results on the characterization of a wide variety of different hydrogen-bonded assemblies by means of a novel matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) technique with Ag+ labeling. The labeling technique with Ag+ ions is extremely mild and provides a nondestructive way to generate charged assemblies that can be detected by mass spectrometry. Up to now more than 25 different single (1(3).2(3)), double (3(3).2(6)), and tetrarosettes (4(3).2(12)) have been successfully characterized by the use of this method. The success of the method entirely depends on the presence of a suitable binding site for the Ag+ ion. A variety of functionalities has been identified that provide strong binding sites for Ag+, either acting in a cooperative way (pi-arene and pi-alkene donor functionalities) or individually (cyano and crown ether functionalities). The method works well for assemblies with molecular weights between 2,000 and 8,000 Da, and most likely far beyond this limit.

In-source decay of hyperbranched polyesteramides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Hyperbranched polyesteramides (DA2), prepared from hexahydrophthalic anhydride (D) and diisopropanolamine (A) have been characterized, by use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), field desorption (FD)-MS, and electrospray ionization (ESI)-MS. MALDI of polyesteramides produces protonated molecules. The spectra show a complex chemical composition distribution and end-group distribution which are mainly composed of two series of homologous oligomers DnA(n)+1 - mH2O and DnA(n) - mH2O, where m = 1-2. Signals from protonated molecules DnAn+1 and DnAn are almost absent in the MALDI spectrum, whereas these ions are responsible for the base peak of DnA(n)+1 - mH2O and DnA(n) - mH2O (m = 1-2) clusters in the ESI spectrum. The absence of -OH end-groups signals in the MALDI spectrum is due to a metastable decay of protonated DnA(n)+1 and DnAn ions in the ion source of the MALDI mass spectrometer prior to ion extraction. In-source decay results in the formation of protonated lower DnA(n)+1 - mH2O and DnA(n) - mH2O oligomers and their corresponding neutrals, leading to wrong conclusions concerning the relative end-group distribution as a function of the degree of polymerization and the chemical composition.

Peptide bond formation in gas-phase ion/molecule reactions of amino acids: a novel proposal for the synthesis of prebiotic oligopeptides

There is a general fascination with regard to the origin of life on Earth. There is an intriguing possibility that prebiotic precursors of life occurred in the interstellar space and were then transported to the early Earth by comets, asteroids and meteorites. It is probable that some part of the prebiotic molecules may have been generated by gas-phase ion/molecule reactions. Here we show experimentally that gaseous ion/molecule reactions of the amino acids, Glu and Met, may promote the synthesis of protonated dipeptides such as (Glu-Glu)H(+) and (Glu-Met)H(+) and their chemical growth to larger protonated peptides.

Dimethyl ether chemical ionization of arylalkylamines

The gas-phase reactions of dimethyl ether (DME) ions with a number of biologically active arylalkylamines of the general formula R(1)R(2)C(6)H(3)CHR(3)(CH(2))(n)NR(4)R(5), where R(1) = H or OH, R(2) = H, F, NO(2), OH or OCH(3), R(3) = H or OH, R(4) and R(5) = H or CH(3), have been studied by means of chemical ionization mass spectrometry. Under the experimental conditions used, the most abundant DME ion is the methoxymethyl cation (CH(3)OCH(2)(+), m/z 45). The unimolecular metastable decompositions of the [M + 45](+), [M + 13](+) and [M + 15](+) adducts formed have been interpreted in terms of the initial site of reaction with the amines and the presence of different functional groups in the molecule. This has permitted establishment of general fragmentation patterns for the adducts, and their correlation with structural features of the molecules. The main site of reaction of the ion CH(3)OCH(2)(+) with the amines seems to be the amino group, particularly if the amine is primary, although a competition with attack on the aromatic ring and especially on the benzylic hydroxy group is observed. In a few cases the reaction mechanisms have been elucidated through the use of deuterated amines obtained by H/D exchange with D(2)O.

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.

High-performance liquid-chromatographic-atmospheric-pressure chemical-ionization ion-trap mass-spectrometric identification of isomeric C6-hydroxy and C20-hydroxy metabolites of methylprednisolone in the urine of patients receiving high-dose pulse therapy

Fourteen metabolites of methylprednisolone have been analysed by gradient-elution high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS). The compounds were separated on a Cp Spherisorb 5 microm ODS column connected to a guard column packed with pellicular reversed phase. The mobile phase was an acetonitrile- 1.0% aqueous acetic acid gradient at a flow rate of 1.5 mL min(-1) The analysis gave a complete picture of parent drug, prodrugs and metabolites, and the alpha/beta stereochemistry was resolved. The short (1-2 h) elimination half-life of methylprednisolone is explained by extensive metabolism. The overall picture of the metabolic pathways of methylprednisolone is apparently simple-reduction of the C20 carbonyl group and further oxidation of the C20,C21 side chain (into C21COOH and C20COOH), in competition with or in addition to oxidation at the C6 position.

Chemical ionization of phenyl n-propyl ether and methyl substituted analogs: Propene loss initiated by competing proton transfer to the oxygen atom and the aromatic ring

The mechanism of propene loss from protonated phenyl n-propyl ether and a series of mono-, di-, and trimethylphenyl n-propyl ethers has been examined by chemical ionization (CI) mass spectrometry in combination with tandem mass spectrometry experiments. The role of initial proton transfer to the oxygen atom and the aromatic ring, respectively, has been probed with the use of deuterated CI reagents, D2O, CD3OD, and CD3CN (given in order of increasing proton affinity), in combination with deuterium labeling of the β position of the n-propyl group or the phenyl ring. The metastable [M + D](+) ions of phenyl n-propyl ether-formed with D2O as the CI reagent-eliminate C3H5D and C3H6 in a ratio of 10:90, which indicates that the added deuteron is incorporated to a minor extent in the expelled neutral species. In the experiments with CD3OD as the CI reagent, the ratio between the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of phenyl n-propyl ether is 18:82, whereas the ratio becomes 27:73 with CD3CN as the reagent. A similar trend in the tendency to expel a propene molecule that contains the added deuteron is observed for the metastable [M + D](+) ions of phenyl n-propyl ether labeled at the β position of the alkyl group. Incorporation of a hydrogen atom that originates from the aromatic ring in the expelled propene molecule is of negligible importance as revealed by the minor loss of C3H5D from the metastable [M + H](+) ions of C6D5OCH2CH2CH3 irrespective of whether H2O, CH3OH, or CH3CN is the CI reagent. The combined results for the [M + D](+) ions of phenyl n-propyl ether and deuterium-labeled analogs are suggested to be in line with a model that assumes that propene loss occurs not only from species formed by deuteron transfer to the oxygen atom, but also from ions generated by deuteron transfer to the ring. This is substantiated by the results for the methyl-substituted ethers, which reveal that the position as well as the number of methyl groups bonded to the ring exert a marked effect on the relative importances of the losses of C3H5D and C3H6 from the metastable [M + D](+) ions of the unlabeled methyl-substituted species.

The bimolecular hydrogen-deuterium exchange behavior of protonated alkyl dipeptides in the gas phase

As part of an ongoing characterization of the intrinsic chemical properties of peptides, thermal hydrogen-deuterium exchange has been studied for a series of fast-atom-bombardment-generated protonated alkyldipeptides and related model compounds in the reaction with D2O, CH3OD, and ND3 in a Fourier transform ion cyclotron resonance mass spectrometer. Despite the very large basicity difference between the dipeptides and the D2O and CH3OD exchange reagents, efficient exchange of all active hydrogen atoms occurs. From the kinetic data it appears that exchange of the amino, amide, and hydroxyl hydrogens proceeds with different efficiencies, which implies that the proton in thermal protonated dipeptides is immobile. The selectivity of the exchange at the different basic sites is governed by the nature of both the dipeptide and the exchange reagent. The results indicate that reversible proton transfer in the reaction complexes, which effectuates the deuterium incorporation, is assisted by formation of multiple hydrogen bonds between the reagents. Exchange is considered to proceed via the intermediacy of different competing intermediate complexes, each of which specifically leads to deuterium incorporation at different basic sites. The relative stabilization of the competing intermediate complexes can be related to the relative efficiencies of deuterium incorporation at different basic sites in the dipeptide. For all protonated dipeptides studied, the exchange in the reaction with ND3 proceeds with unit efficiency, whereas all active hydrogen atoms are exchanged equally efficiently. Evidently specific multiple hydrogen bond formations are far less important in the reversible proton transfers with the relatively basic ammonia, which allows effective randomization of all active hydrogen atoms in the reaction complexes.

Gas phase bimolecular chemistry of isomeric C3H 6Br (+) cations

The gas phase chemistry of C3H6Br(+) cations generated via low energy electron impact on various dibromopropanes has been studied by using Fourier transform ion cyclotron resonance mass spectrometry. Neutral substrate molecules that have been selected to probe the bimolecular reactivity of the C3H6Br(+) isomers are ammonia, methylamine, trimethylamine, cis-butene, and 2, 3-dimethyl-2-butene. At least three different isomers are characterized on the basis of their different reactivity toward the various substrate molecules. It is suggested that these isomers have (a) the 2-bromo-2-propyl cation structure, (b) the propylenebromomum ion structure, and (c) the cyclic four-membered trimethylenebromonium ion structure. The 2-bromo-2-propyl cations react predominantely via proton transfer. This reaction is hampered for the propylenebromonium ions, which react mainly as electrophiles or bromanyl cation donors. Cyclic trimethylenebromoruum ions react predominantly via adduct formation, even under low pressure conditions, which implies that tturd body collisions are not the only stabilization mechanism.

Formation and characterization of the sulfur-containing distonic radical anion, [Formula: see text], in the gas phase, in the gas phase

The reactions of the atomic oxygen radical anion O(-) with CH3-S-CH2-CN m the gas phase have been examined with Fourier transform ion cyclotron resonance in combination with tandem mass spectrometric experiments performed with a double-focusing quadrupole hybrid instrument. Deuterium labeling has revealed that the O(-) ion reacts with CH3-S-CH2-CN by proton abstraction from the methylene group as well as by competing 1,1- and 1,3-H 2 (+) abstractions to afford isomeric radical anions. High kinetic energy (8 keV) collision-induced charge reversal experiments indicate that the 1,1-H 2 (+.) -abstraction leads to a [Formula: see text] carbene ion, whereas the 1,3-H 2 (+) abstraction yields a novel sulfur-containing distonic radical anion, which is formulated as [Formula: see text].

Insertion reactions of metal carbonyl anions with methyl formate in the gas phase as revealed by (13)C- and D-labeling

School of Chemistry, University of New South Wales, Kensington, Australia Institute of Mass Spectrometry, University of Amsterdam, Nieuwe Achtergracht The gas-phase reactions of coordinatively unsaturated metal carbonyl anions (M(CO) n (-) , M=Cr, Mn, Fe, Co; n=0-3 and Co(CO)nNO(-), n=0-2) with unlabeled and D- and (13)C-labeled methyl formate have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The reactions proceed in most instances by loss of one or more CO molecules from the collision complex. In the reactions of the dicarbonyl and tricarbonyl anions with H(13)COOCH3, part of the eliminated carbon monoxide molecules contain the label revealing the occurrence of initial insertion of the metal center into the bonds adjacent to the carbonyl function of the substrate with formation of five- or six-coordinate intermediates, respectively. In addition, the MnCCO) 3 (-) , Fe(CO) 2 (-) , and CoCCO) 2 (-) ions react by the loss of methanol and a [C,H2,O] neutral species. The D- and (13)C-labeling show that methanol is expelled in a reductive elimination from a five- or six-coordinate species, whereas the [C,H2,O] loss is a more complex process possibly involving the competing losses of formaldehyde and CO + H2. In the reaction of Fe(CO) 3 (-) with H 13 (13) COOCH3, a facile consecutive exchange of all three CO ligands of the reactant ion for (13)CO is observed. This novel reaction appears to involve initial insertion into the H(13)CO-OCH3-bond followed by facile hydrogen shifts from the formyl ligand to a CO Hgand prior to the loss of unlabeled methyl formate.

On the stabilization of carbanions by adjacent phenyl, cyano, methoxy-carbonyl, and nitro groups in the gas phase

Institute of Mass Spectrometry, University of Amsterdam, Amsterdam, The Netherlands By using the method of Fourier transform ion cyclotron resonance mass spectrometry, substituent stabilization energies of homologous series of cycloalkyl carbanions, Ξ-c-CnH2n-2 (n = 3, 4, 5, 6, 7) with π-accepting substituents (Ξ = Ph, CN, COOMe, NO2) have been determined experimentally in the gas phase as the difference between the proton affinity of the substituted and corresponding unsubstituted (Ξ = H) cycloalkyl carbanions.The stabilization energy data have been analyzed in terms of Taft's parametrization of polarizability, field/inductive, and resonance effects. The linear regression analyses show excellent correlations within the ΞCH2 (-) Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7), and Ξ-c-C3H4 (-) carbanion series, from which it appears that the contributions of polarizability effects are independent of the above type of carbanions and only depend on the nature of the substituent.Further, it follows that inductive stabilization is more effective in the substituted methyl, ΞCH2 (-), than in the substituted cycloalkyl, Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7) carbanions. This result suggests that inductive stabilization is counteracted by the electron releasing effect of alkyl groups.Resonance stabilization is significantly more effective in the substituted cycloalkyl, Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7), than in the substituted methyl, ΞCH2 (-), carbanions, which suggests that m contrast to inductive stabilization, resonance stabilization is assisted by the electron releasing effect of alkyl groups.Finally, it appears that substitutent stabilization in the geometrically restricted substituted cyclopropyl carbanions, Ξ-c-C3H4 (-), is dramatically less effective than in the corresponding geometrically unrestricted larger substituted cycloalkyl carbanions, Ξ-c-CnH2n-2 (-) (n = 4, 5, 6, 7). The linear regression analyses of the substituted cycloalkyl carbanions indicate that reduction of the stabilization energy is caused not exclusively by a geometrically hindered resonance stabilization, but also to a smaller extent by a less efficient inductive stabilization in the substituted cyclopropyl carbanions.

Verification of the position of the phosphate group in some synthetic phosphopeptides by fast-atom bombardment and tandem mass spectrometry

Some synthetically obtained linear and cyclic phosphopeptides of low molecular weight have been studied by fast-atom bombardment and tandem mass spectrometry to verify the position of the phosphate group in these compounds. Based upon the occurrence/non-occurrence of loss of phosphoric acid from low abundance fragment ions induced by low- and high-energy collisions with target gases, it is shown that the position of the phosphate group in the phosphopeptides studied can be determined unequivocally.

Gas-phase reactions between O(-.) and C 6H 5F: On the acidity of fluorobenzene and 1,4-difluorobenzene

The gas-phase reactions of negative ions (O(-.), NH 2 (-) , C2H5NH(-), (CH3)2N(-), C6H 5 (t-) , and CH3SCH 2 (-) ) with fluorobenzene and 1,4-difluorobenzene have been studied with Fourier transform ion cyclotron resonance mass spectrometry. The O(-.) ion reacts predominantly by (1) proton abstraction, (2) formal H 2 (+.) abstraction, and (3) attack on an unsubstituted carbon atom. In addition to these processes, attack on a fluorine bearing carbon atom yielding F(-) and C6H4FO(-) ions occurs with 1,4-difluorobenzene. Site-specific deuterium labeling reveals the occurrence of competing 1,2-, 1,3-, and 1,4-H 2 (+.) abstractions in the reaction of O(-.) with fluorobenzene. Attack of the O(-.) ion on the 3- and 4-positions in fluorobenzene with formation of the 3- and 4-fluorophenoxide ions, respectively, is preferred to reaction at the 2-position, as indicated by the relative extent of loss of a hydrogen and a deuterium atom in the reactions with labeled fluorobenzenes. The NH 2 (-) , C2H5NH(-), (CH3)2N(-), C6H 5 (-) , and CH3SCH 2 (-) anions react with fluoroberuene and 1,4-difluorobenzene only by proton abstraction. The relative importance of H(+) and D(+) abstraction in the reaction of these anions with labeled fluorobenzenes indicates that the 2-position in fluorobenzene is more acidic than the 3- and 4-positions, suggesting that the literature value of the gas-phase acidity of this compound (ΔH acid (o) = 1620 ± 8 kJ mol(-1)) refers to the former site. Based on the occurrence of reversible proton transfer between the CH3O(-) ion and 1,4-difluorobenzene, the ΔH acid (o) of this compound is redetermined to be 1592 ± 8 kJ mol(-1).

Gas-phase ion-molecule reactions of the CH3O (+) cation

The methoxy cation, CH30(+), formed by collision-induced charge reversal of methoxr anions with a kinetic energy of 8 keY, has been differentiated from the isomenric CH2OH(+) ion by performing low kinetic energy ion-molecule reactions In the radiofrequency-only quadrupole of a reverse-geometry double-focusing quadrupole hybrid mass spectrometer. The methoxy cation reacts with CH3SH, CH3-CH=CH2, (CH3)2O, and CH3CH2Cl by electron transfer, whereas the CH2OH(+) ion reacts by proton transfer with these substrates.

On the structure of protonated methane

Results of a Fourier transform-ion cyclotron resonance study are reported concerning the reactivity of protonated perdeuteromethane and deuteronated methane, generated under varying pressure conditions in an external chemical ionization ion source, toward ammonia. The competition between proton and deuteron transfer from both protonated perdeuteromethane and deuteronated methane to ammonia exhibits chemically distinguishable hydrogens. The chemical behavior of protonated methane appears to be compatible with the theoretically predicted stable structure with Cs symmetry, involving a three-center two-electron bond associating two hydrogens and the carbon atom. Interconversion of this structure due to exchange between one of these hydrogens and one of the three remaining hydrogens appears to be a fast process that is induced by interactions with the chemical ionization gas.

Interaction of myeloperoxidase with diclofenac. Inhibition of the chlorinating activity of myeloperoxidase by diclofenac and oxidation of diclofenac to dihydroxyazobenzene by myeloperoxidase

The chlorinating activity of myeloperoxidase, isolated from human polymorphonuclear neutrophils, was inhibited by the non-steroidal anti-inflammatory drug diclofenac (Voltaren). The concentration of diclofenac needed for 50% inhibition was 20 microM, a value comparable with IC50 values found for other drugs. Diclofenac did not react with HOCl nor with H2O2 but was oxidized in the presence of myeloperoxidase and H2O2 to an orange-coloured unstable product. The rate of oxidation was proportional to the enzyme concentration and to the concentration of diclofenac. but independent of the H2O2 concentration. Presumably both Compound I and Compound II, two intermediates formed during the reaction cycle of myeloperoxidase with H2O2 are able to oxidize diclofenac. In these redox reactions, the active short-living Compound I is reduced to Compound II, thereby inhibiting the chlorinating activity of the enzyme. Analysis by Fast Atom Bombardment mass spectrometry showed that in the presence of H2O2 myeloperoxidase oxidizes diclofenac to dihydroxyazobenzene.

The role of distonic ions in the formation of CH3NH 3 (+) and (CH 3) 2NH 2 (+) from the molecular ions of octopamine and synephrine

It is shown by mass-analyzed ion kinetic energy spectrometry that the metastably decomposing molecular ions of octopamine (p-HOC6H4CH(OH)CH2NH2) and synephrine (p-HOC6H4CH(OH)CH2NHCH3) yield only protonated methylamine and dimethylamine, respectively, as product ions. From deuterium labeling and variation of the internal energy of the molecular ions, experimental support has been obtained that these product ions are generated via the occurrence of a distonic ion-neutral complex. In the case of octopamine, this complex would consist of a nitrogen-protonated aminomethyl radical and p-hydroxylbenzaldehyde in which the former species abstracts the aldehydic or phenolic hydrogen atom from the latter to give protonated dimethylamine.

FAB and tandem mass spectrometry for endorphin- and ACTH peptides of molecular weight to 2000

Four beta-endorphins (beta-endorphin 6-17, 2-17, 1-16, and 1-17) and two adrenocorticotropic hormone (ACTH) peptides (ACTH 1-10 and (1-16)-NH2) were studied by using fast atom bombardment coupled with tandem mass spectrometry. The capability to reproduce metastable ion and collisionally activated decomposition spectra on two different commercial sector mass spectrometers in two different laboratories was found to be acceptable (deviations in relative abundance are less than +/- 50%). The endorphin peptides fragment metastably or upon collisional activation to give abundant B-series ions as well as Y-series ions, whereas Y-series ions are the principal ionic species produced upon the desorption by fast atom bombardment. The ACTH peptides also fragment to give Y-series ions, but of relatively low abundance compared to those from the endorphins. For both sets of peptides, high-energy collisionally activated decomposition and metastable ion decomposition daughter ion spectra are precise, structurally informative--even for peptides up to m/z 2000--and complementary to spectra of daughter ions produced by desorption ionization alone.

Mass spectrometric analysis of fluorescent products originating from the molybdenum cofactor

Mass spectra of 4 fluorescent HPLC fractions originating from the molybdenum cofactor in xanthine oxidase extracts have been obtained with the method of field desorption (FD). The most polar fraction contains compounds which show peaks in the M/Z = 110-230 and M/Z = 580-750 range. Two other fractions exhibit in the FD spectra peaks at M/Z = 1,113 and M/Z = 886, respectively. Both corresponding compounds contain at most 24 C atoms and lack S, Mo, Cl and Br, as judged from the isotopic pattern. The most apolar fluorescent compound, which could be isolated only from xanthine oxidase extracts prepared in the absence of phosphate, has been identified as a species with a molecular weight around 482.

2-Mercaptoethanesulfonate-cysteine disulfide excretion following the administration of 2-mercaptoethanesulfonate--a pitfall in the diagnosis of sulfite oxidase deficiency

In the urine of a neonate with respiratory insufficiency and convulsions a positive sulfite reaction was found, which is suggestive of sulfite oxidase deficiency. The nitroprusside reaction also was positive. More detailed investigations showed that both tests were positive due to the administration of 2-mercaptoethanesulfonate, a mucolytic drug. The patient's urine contained an acidic amino acid with a column chromatographic behaviour like S-sulfocysteine. The high-voltage electrophoretic mobility was slightly different. This compound was isolated from the urine and identified as the mixed disulfide of 2-mercaptoethanesulfonate and cysteine. Its identity was proven with field desorption mass spectrometry, a technique which is suitable for the analysis of sulfonic acid derivatives.

An emission-controlled field desorption and electron impact spectrometry study of some N-substituted propane and butane sultams

It is shown that the production of field desorption mass spectra with an emission-controlled emitter heating device is a useful tool in obtaining information about molecular structures. Since the structurally significant signals are sometimes missing in the corresponding electron impact spectra but not in the field desorption spectra the use of field desorption mass spectrometry appears to be more advantages. This will be especially true for substances that are thermally labile, unvolatile or unstable upon electron impact (both at high and low electron energy), the latter being the case for some of the compounds presently investigated which are derivatives of a drug with antitumour and antiepileptic effects. Further, emission-controlled desorption improves the reproducibility of the spectra obtained and thus appears to be a prerequisite for quantification in biomedical and pharmacokinetic studies.