Analysis of cyanoacrylate ultraviolet absorbers using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry: influence of fragmentor voltage and solvent on ionization and fragmentation behaviors

Ionization efficiencies and fragmentation patterns of cyanoacrylate ultraviolet (UV) absorbers, Uvinul 3035 and Uvinul 3039, were studied using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS). Solvent effect on the ionization efficiencies was investigated using methanol, ethanol, acetone, and chloroform. The fragmentation patterns were also investigated by varying the fragmentor voltage. Solvated ions, the [M+H + solvent](+) of methanol, ethanol, and acetone were detected, but the [M+H + chloroform](+) ion was not observed. For Uvinul 3039 in chloroform, the [M+CHCl(2)](+) ion was detected instead of the solvated ion. Relative abundance of the solvated ion was decreased by increasing the fragmentor voltage. Fragment ions of m/z 250, 232, and 204 were detected and their abundance increased with an increase in the fragmentor voltage. The m/z 250 ion can be accounted for by a McLafferty rearrangement. The fragment ions of m/z 232 and 204 were formed not only by subsequent fragmentations of the m/z 250 ion, but also by ion-molecule reactions of solvent ion and neutral analyte.     

Electrospray ionization mass spectrometry of ginsenosides

Ginsenosides R(b1), R(b2), R(c), R(d), R(e), R(f), R(g1), R(g2) and F(11) were studied systematically by electrospray ionization mass spectrometry in positive- and negative-ion modes with a mobile-phase additive, ammonium acetate. In general, ion sensitivities for the ginsenosides were greater in the negative-ion mode, but more structural information on the ginsenosides was obtained in the positive-ion mode. [M + H](+), [M + NH(4)](+), [M + Na](+) and [M + K](+) ions were observed for all of the ginsenosides studied, with the exception of R(f) and F(11), for which [M + NH(4)](+) ions were not observed. The signal intensities of [M + H](+), [M + NH(4)](+), [M + Na](+) and [M + K](+) ions varied with the cone voltage. The highest signal intensities for [M + H](+) and [M + NH(4)](+) ions were obtained at low cone voltage (15-30 V), whereas those for [M + Na](+) and [M + K](+) ions were obtained at relatively high cone voltage (70-90 V). Collision-induced dissociation yielded characteristic positively charged fragment ions at m/z 407, 425 and 443 for (20S)-protopanaxadiol, m/z 405, 423 and 441 for (20S)-protopanaxatriol and m/z 421, 439, 457 and 475 for (24R)-pseudoginsenoside F(11). Ginsenoside types were identified by these characteristic ions and the charged saccharide groups. Glycosidic bond cleavage and elimination of H(2)O were the two major fragmentation pathways observed in the product ion mass spectra of [M + H](+) and [M + NH(4)](+). In the product ion mass spectra of [M - H](-), the major fragmentation route observed was glycosidic bond cleavage. Adduct ions [M + 2AcO + Na](-), [M + AcO](-), [M - CH(2)O + AcO](-), [M + 2AcO](2-), [M - H + AcO](2-) and [M - 2H](2-) were observed at low cone voltage (15-30 V) only.     

Electrospray and chemical ionization mass spectrometry of di-n-butyl sulfate. Unimolecular chemistry of its protonated form and quantification method by liquid chromatography/electrospray ionization tandem mass spectrometry

Di-n-butyl sulfate (DNBS) has been studied by electrospray (ESI) and chemical (CI) ionization mass spectrometry. The use of methanol as solvent in electrospray ionization allows observation of relatively abundant [DNBS + CH(3)OH + H](+) ions (m/z 243) which upon collision dissociate to [DNBS + H](+) ions (m/z 211). In both ESI and CI experiments, it is found that [DNBS + H](+) ions lead to m/z 113 daughter ions. The composition of this m/z 113 fragment ion and its mechanism of formation have been established by high resolution measurements and CID-MIKE experiments. An 'internal substitution' reaction involving an ion-neutral intermediate is proposed to explain the formation of a [C(8)H(17)](+) ion (m/z 113) by loss of a H(2)SO(4) molecule. Finally, a LC/ESI-MS/MS quantification method is proposed in which a detection limit of di-n-butyl sulfate in the ppm range is obtained. It is suggested that the quantification method might be extended to higher dialkyl sulfates. Copyright 2000 John Wiley & Sons, Ltd.     

Differentiation of a pair of diastereomeric tertiarybutoxycarbonylprolylproline ethyl esters by collision-induced dissociation of sodium adduct ions in electrospray ionization mass spectrometry and evidence for chiral recognition by ab initio molecular orbital calculations

The fragmentation of the sodium adduct ions for tert-butoxycarbonyl-L-prolyl-L-proline ethyl ester (Boc-L-Pro-L-Pro-OEt) was compared with that for Boc-D-Pro-L-Pro-OEt in positive-ion electrospray ionization (ESI) mass spectrometry. In the collision-induced dissociation (CID) mass spectra of the [M + Na](+) ions, the abundance of the [M + Na - C(CH(3))(3) + H](+) ion, which is due to the loss of a tert-butyl group from the [M + Na](+) ion for Boc-D-Pro-L-Pro-OEt, was about eight times higher than that for Boc-L-Pro-L-Pro-OEt. In addition, in the CID spectra of the sodium adduct fragment ion ([M + Na - Boc + H](+)), the abundance of the [M + Na - Boc - prolylresidue + H](+) ion, which is due to the loss of prolyl residue from the [M + Na - Boc + H](+) ion for Boc-L-Pro-L-Pro-OEt, was about five times higher than that for Boc-D-Pro-L-Pro-OEt. These results indicate that Boc-L-Pro-L-Pro-OEt was distinguished from Boc-D-Pro-L-Pro-OEt by the CID mass spectra of the sodium adduct ions in ESI mass spectrometry. The optimized geometries of the [M + Na](+) and the [M + Na - Boc + H](+) ions calculated by ab initio molecular orbital calculations suggest that the chiral recognition of these diastereomers was due to the difference of the orientation of a sodium ion to the oxygen and nitrogen atoms in dipeptide derivatives, and to the difference of the total energies between them.     

Unimolecular metastable decompositions of gem-dimethoxyalkanes (RR'C(OCH(3))(2)) upon electron impact. I. Dimethoxymethane and 1, 1-dimethoxyethane

The unimolecular metastable decompositions of dimethoxymethane (CH(2)(OCH(3))(2), 1) and 1,1-dimethoxyethane (CH(3)CH(OCH(3))(2), 2) upon electron impact have been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry, collision-induced dissociation (CID) spectrometry and D-labeling techniques. Both molecular ions are formed at extremely low abundance. Sequential transfers of a methyl group and a hydrogen atom to an ether oxygen are observed during the decomposition of [M - H](+) ions from 1 and 2. The [M - H](+) ion from 2 also decomposes into the m/z 43 ion by the loss of dimethyl ether. Almost complete hydrogen exchange is observed prior to the loss of CH(4) from the m/z 45 ion ([M - OCH(3)](+)) of 1. The m/z 59 ions ([M - OCH(3)](+)) of 2 decompose competitively into the m/z 31 and 29 ions by the losses of C(2)H(4) and CH(2)O, respectively. The former loss occurs via two different fragmentation pathways. The relative abundances of the ions in the MIKE spectra increase with decreases in the total heat of formation (Sigma DeltaH(f)) of the ion plus the neutral fragment. Copyright 2000 John Wiley & Sons, Ltd.     

Mass spectral study of Boc-carbo-beta3-peptides: differentiation of two pairs of positional and diastereomeric isomers

A mass spectral study of a series of new Boc-C-linked carbo-beta(3)-peptides prepared from C-linked carbo-beta(3)-amino acids (Caa) was carried out using liquid secondary ion mass spectrometry (LSIMS), electrospray ionization (ESI) and tandem mass spectrometry. Using the nomenclature of Roepstorff and Fohlman, the positive ion high- and low energy collision-induced dissociation (CID) of [M + H - Boc + H](+) ions of the peptides produce both N- and C-terminus ions, y(n) (+) and b(n) (+) ions, with high abundance and other ions of low abundance. Further, characteristic fragment ions of carbohydrate moiety are observed. In contrast to the CID of protonated peptide acids, the CID of [M - H](-) ions of the beta(3)-peptide acids do not give b(n)(-) ions and show abundant z(n)(-) and c(n) (-) ions which are insignificant in the former. Two pairs of positionally isomeric Boc-carbo-beta(3)-dipeptides were differentiated by the CID of [M + H](+) ions in LSIMS and ESIMS. The fragment ion [M + H - C(CH(3))(3) + H](+) formed from [M + H](+) by the loss of 2-methylprop-2-ene is relatively more abundant in the dipeptide Boc-NH-beta-hGly-Caa(S)-OCH(3) (14) containing the sugar moiety at the C-terminus whereas it is insignificant in Boc-NH-Caa(S)-beta-hGly-OCH(3) (13), which has the sugar moiety at the N-terminus. Similarly, two pairs of diastereomeric dipeptides were distinguished by the high- and low-energy CID of [M + H](+) ions. The loss of 2-methylprop-2-ene is more pronounced for Boc-NH-Caa(R)-beta-hGly-OCH(3) (17) and Boc-NH-Caa(R)-Caa(S)-OCH(3) (18) isomers whereas it is insignificant for Boc-NH-Caa(S)-beta-hGly-OCH(3) (13) and Boc-NH-Caa(S)-Caa(S)-OCH(3) (2) isomers. This was attributed to a favorable configuration of the carbohydrate moiety favoring the 'H' migration involved in the loss of 2-methylprop-2-ene from the [M + H](+) ions of isomers 17 and 18 compared with the unfavorable configuration of the carbohydrate moiety in isomers 13 and 2.     

Side-chain radical losses from radical cations allows distinction of leucine and isoleucine residues in the isomeric peptides Gly-XXX-Arg

Sequencing of peptides via low-energy collision-induced dissociation of protonated peptides typically yields b(n) and y(n) sequence ions. The isomeric residues leucine and isoleucine rarely can be distinguished in these experiments since they give b(n) and y(n) sequence ions of the same m/z. Siu's pioneering work on electrospray ionization of copper complexes of peptides (Chu IK, Rodriquez CF, Lau TC, Hopkinson AC, Siu KWM. J. Phys. Chem. B 2000; 104: 3393) provides a way of forming radical cations of peptides in the gas phase. This method was used to generate M(+ small middle dot) ions of the two isomeric peptides Gly-Leu-Arg and Gly-Ile-Arg in order to compare their fragmentation reactions. Both radical cations fragment to give even electron y(2) and y(1) sequence ions as well as side-chain radical losses of CH(3) and CH(3)CH(2) for isoleucine and (CH(3))(2)CH for leucine. In contrast the [M + H](+) and [M + 2H](2+) ions do not allow distinction between the isomeric leucine and isoleucine peptides.     

Observation of Na(+)-bound oligomers of quercetin in the gas phase

While developing a liquid chromatography/tandem mass spectrometry method for the analysis of the flavonoid quercitin, it was observed that quercetin (3,3',4',5,7-pentahydroxyflavone) exhibited clustering in both the positive and negative ion mode. Two series of positive ion clusters were observed; the first series corresponds to singly charged [2M + Na](+) at m/z 627.2 to [13M + Na](+) at m/z 3947.5, while the second series corresponds to doubly charged [7M + 2Na](2+) at m/z 1080.4 to [25M + 2Na](2+) at m/z 3798.5. In the negative ion mode, the behavior of quercetin parallels that of apigenin (4',5,7-trihydroxyflavone) in that [M + NO(3)](-), [2M + NO(3)](-), and [3M + NO(3)](-) were observed at m/z 364.1, 666.0, and 968.9, respectively; in addition, quercitin clusters with chloride ions ([2M + Cl](-) at m/z 638.9 and [3M + Cl](-) at m/z 940. 9) were observed. The results of tandem mass spectrometric examination of several cluster ions are reported.     

Structural characterization of glycoporphyrins by electrospray tandem mass spectrometry

Porphyrin derivatives having a galactose or a bis(isopropylidene)galactose structural unit, linked by ester or ether bonds, were characterized by electrospray tandem mass spectrometry (ES-MS/MS). The electrospray mass spectra of these glycoporphyrins show the corresponding [M + H](+) ions. For the glycoporphyrins with pyridyl substituents and those having a tetrafluorophenyl spacer, the doubly charged ions [M + 2H](2+) were also observed in ES-MS with high relative abundance. The fragmentation of both [M + H](+) and [M + 2H](2+) ions exhibited common fragmentation pathways for porphyrins with the same sugar residue, independently of the porphyrin structural unit and type of linkage. ES-MS/MS of the [M + H](+) ions of the galactose-substituted porphyrins gave the fragment ions [M + H - C(2)H(4)O(2)](+), [M + H - C(3)H(6)O(3)](+), [M + H - C(4)H(8)O(4)](+) and [M + H - galactose residue](+). The fragmentation of the [M + 2H](2+) ions of the porphyrins with galactose shows the common doubly charged fragment ions [porphyrin + H](2+), [M + 2H - C(2)H(4)O(2)](2+), [M + 2H - C(4)H(8)O(4)](2+), [M + 2H - galactose residue](2+) and the singly charged fragment ions [M + H - C(3)H(6)O(3)](+) and [M + H - galactose residue](+). The fragmentation of the [M + H](+) ions of glycoporphyrins with a protected galactosyl residue leads mainly to the ions [M + H - CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2) - CO](+), [M + H - C(10)H(16)O(4)](+) and [M + H - protected galactose](+). The doubly charged ions [M + 2H](2+) fragment to give the doubly charged ions [porphyrin + H](2+) and the singly charged ions [M + H - protected galactose residue](+) and [M + H - CO(CH(3))(2)](+). For the porphyrins where the sugar structural unit is linked by an ester bond, [M + 2H](2+), ES-MS/MS showed a major and typical fragmentation corresponding to combined loss of a sugar structural unit and further loss of water, leading to the ion [M + 2H - sugar residue - H(2)O](2+), independently of the structure of the sugar structural unit. These results show that ES-MS/MS can be a powerful tool for the characterization of the sugar structural unit of glycoporphyrins, without the need for chemical hydrolysis.     

Phase behaviour and conductivity study of electrolytes in supercritical hydrofluorocarbons

The purpose of this work was to characterise supercritical hydrofluorocarbons (HFC) that can be used as solvents for electrodeposition. The phase behaviour of CHF(3), CH(2)F(2), and CH(2)FCF(3) containing [NBu(n)(4)][BF(4)], [NBu(n)(4)][B{3,5-C(6)H(3)(CF(3))(2)}(4)] and Na[B{3,5-C(6)H(3)(CF(3))(2)}(4)] was studied and the conditions for forming a single supercritical phase established. Although all three HFCs are good solvents for [NBu(n)(4)][BF(4)] the results show that the CH(2)F(2) system has the lowest p(r) for dissolving a given amount of [NBu(n)(4)][BF(4)]. The solubility of Na[B{3,5-C(6)H(3)(CF(3))(2)}(4)] in CH(2)F(2) was found to be unexpectedly high. Studies of the phase behaviour of CH(2)F(2) containing [NBu(n)(4)][BF(4)] and [Cu(CH(3)CN)(4)][BF(4)] showed that the copper complex was unstable in the absence of CH(3)CN. For CHF(3), [Cu(hfac)(2)] was more soluble and more stable than [Cu(CH(3)CN)(4)][BF(4)] and only increased the phase-separation pressure by a moderate amount. Studies of the conductivity of [NBu(n)(4)][B(C(6)F(5))(4)], [NBu(n)(4)][B{3,5-C(6)H(3)(CF(3))(2)}(4)], [NR(f)Bu(n)(3)][B{3,5-C(6)H(3)(CF(3))(2)}(4)] (R(f) = (CH(2))(3)C(7)F(15)), and Na[B{3,5-C(6)H(3)(CF(3))(2)}(4)] were carried out in scCH(2)F(2). The results show that these salts are more conducting than [NBu(n)(4)][BF(4)] under the same conditions although the increase is much less significant than that reported in previous work in supercritical CO(2) + CH(3)CN. Consequently, either [NBu(n)(4)][BF(4)] or the corresponding BARF salts would be suitable background electrolytes for electrodeposition from scCH(2)F(2).     

Separation, determination and identification of the diastereoisomers of podophyllotoxin and its esters by high-performance liquid chromatography/tandem mass spectrometry

A rapid and stable high-performance liquid chromatography-diode array detection (HPLC-DAD) and a high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI/MS/MS) method were developed and validated for the separation, determination, and identification of eight pairs of diastereoisomers of podophyllotoxin and its esters at C-2 position. The separation was carried out on BDS Hypersil C18 column with CH3OH-CH3CN-H2O as the mobile phase in a gradient program. Interestingly, every 2alpha-H compound migrated before its corresponding 2beta-H epimer under optimum conditions. Also, the [M+NH(4)](+) of all eight pairs of compounds was observed in the HPLC-ESI/MS spectra. The characteristic elimination from the precursor protonated ions and the product ions at m/z 397, 313, 282, and 229 were the common diagnostic masses. The ion ratios of relative abundance [M-ROH+H](+) (ion 397) to [M+NH(4)](+), [A+H](+) (ion 313) to [M-ROH+H](+), and [M-ROH-ArH+H](+) (ion 229) to [M-ROH+H](+) in the ESI/MS/MS spectra of each pair of diastereoisomers of the lignans specifically exhibited a stereochemical effect. Thus, by using identical sample solutions and chromatographic conditions (including the same columns and gradient programs), the combination of DAD and MS/MS data permitted the separation and identification of the eight pairs of diastereoisomers of the podophyllotoxin and its esters in the mixture. The method could be used in rapidly identifying the purity and monitoring of the epimerization of 2-H of podophyllotoxin and its analogues from natural products, chemical reactions, and pharmaceutical metabolism.     

Electrospray ionization tandem mass spectrometric study on the effect of N-terminal beta- and gamma-carbo amino acids on fragmentation of GABA-hybrid peptides

The fragmentations of protonated and deprotonated ions of a new class of N-blocked hybrid Boc-carbopeptides containing repeats of gamma-Caa/gammaAbu- and beta-Caa/gammaAbu- (Caa==C-linked carbo gamma(4)-/beta(3)- amino acids derived from D-xylose, gammaAbu = gamma-aminobutyric acid) have been studied using electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS). MS/MS of a pair of these protonated diastereomers produces distinct fragmentation of the Boc group. The formation of [M + H-56](+) corresponding to loss of isobutylene is more pronounced for Boc-NH-(R)-gamma-Caa-gammaAbu-OH (2) whereas it is of low abundance for Boc-NH-(S)-gamma-Caa-gammaAbu--OH (1). Similarly, MS(2) of [M--H](-) of 2 produces an abundant [M--H--C(CH(3))(3)OH--CO(2)](-) ion, which is absent for its diastereomeric isomer 1. From this, it can be suggested that MS/MS of N-blocked Boc-protected carbopeptides may be helpful in distinguishing the stereochemistry of the N-terminus Caa. MS(3) of [M + H-Boc + H](+) ions of peptides with a gamma-amino acid (gamma-Caa/gammaAbu) at the N-terminus produces only abundant y(n) (+) ions. On the other hand, characteristic fragmentations involving the peptide backbone (b(n) (+) and y(n) (+)) and the side chain are seen when beta-Caa is at the N-terminus of the peptides. MS(3) of the [M--H--C(CH(3))(3)OH](-) ion of peptides containing gamma-Caa/gammaAbu at the N-terminus gave y(n) (-) and [M--H--C(CH(3))(3)OH--CO(2)](-) ions, whereas the presence of beta-Caa at the N-terminus yielded predominantly [M--H--C(CH(3))(3)OH--HNCO](-). Thus, on the basis of our previous study and that presented here we propose that the fragmentation of these hybrid carbopeptides is highly influenced by the type of carbo amino acid present at the N-terminus.     

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.     

Differentiation of the diastereomeric synthetic precursors of isofebrifugine and febrifugine by electrospray ionization tandem mass spectrometry

Febrifugine is an alkaloid with potent antimalarial activity isolated from Dichroa febrifuga and Hydrangea umbellate, and it exists naturally with its diastereomeric component, isofebrifugine. Here we report the differentiation of diastereomeric synthetic precursors of isofebrifugine (1, cis) and febrifugine (2, trans) and a structurally similar model diastereomeric pair without a halogen substituent (3 and 4) by electrospray ionization (ESI) tandem mass spectrometry. Compounds 1-4 contain a tert-butoxycarbonyl (BOC) substituent, and the collision-induced dissociation (CID) spectra of the [M+H](+), [M+Na](+) and [M+Li](+) ions of 1-4 include the expected product ions corresponding to the loss of C(4)H(8) (isobutene) and of C(5)H(8)O(2) (BOC-H). Loss of C(5)H(8)O(2) is dominant in cis isomers (1 and 3) and/or loss of C(4)H(8) ions is dominant in trans isomers (2 and 4). The decomposition of [M+H](+) ions shows stereoselectivity in the formation of the [M+H-(BOC-H)-C(3)H(5)OBr](+) and [M+H-(BOC-H)-C(6)H(5)CH(2)OH](+) ions. The [M+Cat](+) ions (where Cat = Na or Li) additionally show loss of NaBr and HBr from [M+Cat-(BOC-H)](+), and these product ions are constantly more abundant in cis isomers than in trans isomers. The stereoselectivity for the product ion corresponding to the loss of [(BOC-H)+C(3)H(5)OBr] from [M+H](+) ions differs from that from [M+Cat](+) ions.     

Electrospray tandem mass spectrometry of underivatised acetylated xylo-oligosaccharides

Acetylated neutral (Xyl(n)Ac(m)) and acidic xylo-oligosaccharides (Xyl(n)Ac(m)MeGlcA, and Xyl(n)Ac(m)MeGlcAHex) obtained by partial acid hydrolysis of Eucalyptus globulus wood glucuronoxylans and fractionated by preparative ligand exchange/size-exclusion chromatography were identified by electrospray ionisation mass spectrometry (ESI-MS). Low molecular weight acetylated xylo-oligosaccharides were studied by ESI-tandem mass spectrometry (MS/MS). All the acetylated xylo-oligosaccharides showed an abundant ion due to the neutral loss of 60 Da (CH(3)CO(2)H) in the MS/MS spectra. The presence of diacetylated xylo-oligosaccharides was confirmed by the ions formed by loss of two molecules of acetic acid. Furthermore, characteristic [Xyl(res)Ac(2)+Na](+) and [XylAc(2)+Na](+) ions, and ions due to loss of XylAc(2), indicate that both acetyl groups are located in the same Xyl residue. On the other hand, losses of Xyl(res)Ac and XylAc are also observed as well as [Xyl(res)Ac+Na](+) and [XylAc+Na](+) , indicating the location of both acetyl groups in different Xyl residues, in some cases even in adjacent xyloses. The MS/MS spectra of triacetylated xylo-oligosaccharides were complex due to the presence of different isobaric xylo-oligosaccharides containing the acetyl groups at different locations in the xylo-oligosaccharide backbone. In the MS/MS spectra of acidic xylo-oligosaccharides, the ion at m/z 387, [Xyl(res)AcMeGlcA+Na](+), indicates that the acetyl groups are preferentially linked to Xyl substituted with MeGlcA. However, acidic xylo-oligosaccharides with the acetyl and 4-O-methylglucuronic acid groups in different Xyl residues were also identified. In neutral and in acidic xylo-oligosaccharides several possible locations of the acetyl groups were identified, namely at terminal positions. In summary, ESI-MS/MS is shown to be a powerful tool for the characterisation of acetylated patterns in complex mixtures of oligosaccharides.     

Characterization of alkylacyl,alk-1-enylacyl and lyso subclasses of glycerophosphocholine by tandem quadrupole mass spectrometry with electrospray ionization

Positive ion tandem quadrupole mass spectrometric methods for structural characterization of the subclasses of sn-glycero-3-phosphocholine (PC), including alkylacyl- and alk-1-enylacylphosphocholine and lysophosphatidylcholine (LPC), are described. Following collisionally activated dissociation, the [M + Li](+) ions generated by electrospray ionization yield abundant informative fragment ions that permit structural determination, and distinction of regioisomers among lysophosphatidylcholine can be easily achieved. In contrast, structurally informative ions arising from [M + H](+) or [M + Na](+) ions are less prominent. The most abundant ion observed in the product-ion spectra of the [M + Li](+) ions of plasmenyl- and plasmanyl-PC and of LPC arises from loss of N(CH(3))(3) ([M + Li - 59](+)). This feature permits their distinction from a product-ion spectrum arising from a diacylphosphatidylcholine, in which the [M + Li - 183](+) ion reflecting loss of phosphocholine is the most prominent. Examples for identification of various subclasses of PC in biological extracts by tandem mass spectrometry applying various constant neutral loss scannings are also shown.     

Mass spectral studies of meso-dialkyl, alkyl aryl and cycloalkyl calix(4)pyrroles under positive and negative ion electrospray ionization conditions

A series of meso-dialkyl, alkyl aryl and cycloalkyl calix(4)pyrroles (1-15) are studied under positive and negative ion electrospray ionization (ESI) conditions. The positive ion spectra show abundant [M + H](+) and [M + Na](+) ions and the negative ion spectra show the [M + Cl](-) (the Cl(-) ions from the solvent) and [M - H](-) ions. The collision induced dissociation (CID) spectra of [M + H](+), [M + Na](+), [M + Cl](-) and [M - H](-) ions are studied to understand their dissociation pathway and compared to that reported for M(+) under electron ionization (EI) conditions. The beta-cleavage process that was diagnostic to M(+) is absent in all the CID spectra of the ions studied under ESI. Dissociation of all the studied ions resulted in the fragment ions formed by sequential elimination of pyrrole (A) and/or dialkyl/alkyl aryl/cycloalkyl (B) groups involving hydrogen migration to pyrrole ring at each cleavage of A--B bond, which clearly reveals the arrangement of A and B groups in the calix(4)pyrroles. The source of hydrogen that migrates to pyrrole ring during A--B bond cleavage is investigated by the experiments on deuterated compounds and [M + D](+) ions; and confirmed that the hydrogen attached to pyrrole nitrogen, hydrogen on alpha-carbon of alkyl group and the H(+)/Na(+) ion that added during ESI process to generate [M + H](+)/[M + Na](+) ions involve in the migration. The yields of [M + Na](+) ions are found to be different for the isomeric meso-cycloalkyl compounds (cycloheptyl, and 2-, 3- and 4-methyl cyclohexyl) and for normal and N-confused calix(4)pyrroles. The isomeric methyl and 3-hydroxy/4-hydroxy phenyl calix(4)pyrroles show specific fragmentation pattern during the dissociation of their [M - H](-) ions.     

Analysis of oligomeric peroxides in synthetic triacetone triperoxide samples by tandem mass spectrometry

Oligomeric peroxides formed in the synthesis of triacetone triperoxide (TATP) have been analyzed by mass spectrometry utilizing both electrospray ionization (ESI) and chemical ionization (CI) to form sodiated adducts (by ESI) and ammonium adducts (by CI and ESI). Tandem mass spectrometry and deuterium isotopic labeling experiments have been used to elucidate the collision‐induced dissociation (CID) mechanisms for the adducts. The CID mechanisms differ for the sodium and ammonium adducts and vary with the size of the oligoperoxide. The sodium adducts of the oligoperoxides, H[OOC(CH₃)₂]_nOOH, do not cyclize under CID, whereas the ammonium adducts of the smaller oligoperoides (n < 6) do form the cyclic peroxides under CID. Larger oligoperoxide adducts with both sodium and ammonium undergo dissociation through cleavage of the backbone under CID to form acyl‐ and hydroperoxy‐terminated oligomers of the general form CH₃C(O)[OOC(CH₃)₂]_xOOH, where x is an integer less than the original oligoperoxide degree of oligomerization. The oligoperoxide distribution is shown to vary batch‐to‐batch in the synthesis of TATP and the post‐blast distribution differs slightly from the distribution in the uninitiated material. The oligoperoxides are shown to be decomposed under gentle heating. Copyright © 2009 John Wiley & Sons, Ltd.     

Mass spectrometric studies of benzoxazine resorcarenes

Eleven differently substituted 3,4-dihydro-2H-1,3-benzoxazine resorcarenes were studied by electrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry, using Fourier transform ion cyclotron resonance (FT-ICR) and time-of-flight (TOF) mass spectrometers, respectively. Under ESI conditions it was possible to transfer the intact resorcarenes from solution to the gas phase, yielding [M + H](+) and [M + 2H](+) ions as the main ions observed. Energy increase of the ions induced ready decomposition through successive eliminations of four CH(2)NR groups. Ion-molecule reactions showed that the ionising proton was situated somewhere inside the molecule and could not be reached with neutral reagent gases. In the host-guest complexation experiments, the benzoxazine resorcarenes studied turned out to be poor hosts for alkali metal and ammonium ions. In MALDI experiments, 2,5-dihydroxybenzoic acid proved to be the best matrix for these compounds. However, the intensity of the [M + H](+) ions was low for all compounds, and extensive fragmentation with consecutive elimination of CH(2)NR groups was observed.     

Colorless, non-luminescent; colorless, luminescent; and yellow, luminescent crystals of the cation [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](+). The roles of anions and hydrogen bonding in determining the aggregation of two-coordinate gold(I) cations

Crystallographic and luminescence studies on salts of the two-coordinate carbene cation, [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](+), demonstrate the ability of the cation to exist in three different states of aggregation. In colorless, non-luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]Cl the cation crystallizes as a monomer with the nearest gold(i) center 6.7890(11) A away. Colorless, luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]AsF(6) forms dimers with an AuAu separation of 3.1288(4) A. These dimers form weakly associated extended chains of cations with additional AuAu separations of 3.6625(5) A. [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)]PF(6) is isostructural. Yellow, luminescent [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](3)(AsF(6))(2)Cl.0.5(H(2)O)(2) and [Au{C(NHCH(3))(NHCH(2)CH(2)OH)}(2)](3)(PF(6))(2)Cl.0.5(H(2)O)(2) form trimers that further aggregate into extended chains with rather short AuAu separations of 3.1301(14) A, 3.1569(14) A and 3.1415(14) A. Absorption, emission and excitation spectra are reported for these salts. The excitation and emission results from the interactions between the gold centers and involves transitions between the filled d(z)((2)) band and the empty p(z) bands with the z axis pointing along the chain of cations.