One‐Electron Oxidation and Sensitivity of Uric Acid in On‐Line Electrochemistry and in Electrospray Ionization Mass Spectrometry

The sensitivity of detection of uric acid (H₂U) in positive ion mode electrospray ionization mass spectrometry (ESI MS) was enhanced by uric acid oxidation during electrospray ionization. With a carrier solution of pH 6.3>pK_a1=5.4 of H₂U, protonated unoxidized uric acid [H₂U+H]⁺ (m/z 169) was detected together with the protonated uric acid dimer [2H₂U+H]⁺ (m/z 337). The dimer likely forms by 1e^? oxidation of urate (HU^?) followed by rapid radical dimerization. A covalent structure of the dimer was verified by H/D exchange experiments. Efficiency of 2e^?, 2H⁺ oxidation of uric acid is low during ESI in pH 6.3 carrier solution and improves when a low on‐line electrochemical cell voltage is floated on the high voltage of the ES in on‐line electrochemistry ESI MS (EC/ESI MS). The intensity of the uric acid dimer decreases with an increase in the low applied voltage. In a carrier solution with 0.1 M KOH, pH 12.7>pK_a2=9.8 of H₂U, allantoin (Allnt) (MW 158.04), the final 2e^?, 2H⁺ oxidation product of uric acid, was detected as a potassium complex [K(Allnt)+K]⁺ (m/z 235) and the [2H₂U+H]⁺ dimer was not detected. In direct ESI MS analysis of 1000‐fold diluted urine [NaHU+H]⁺ (pK_sp NaHU=4.6) was detected in 40/60 (vol%) water/methanol, 1 mM NH₄Ac, pH ca. 6.3 carrier solution. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity in ESI and EC/ESI MS measurements of uric acid.     

Simultaneous Determination Baicalin and Forsythin in Shuanghuanglian Oral Liquid by HPLC/DAD and LC‐ESI‐MS

Rapid, simple and reliable HPLC/DAD and LC‐ESI‐MS methods for the simultaneous determination of baicalin and forsythin in the traditional Chinese medicinal preparation Shuanghuanglian oral liquid were described and validated. The separation condition for HPLC/DAD was optimized using a BDS hypersil C18 column (Thermo, 2.1 × 150 mm, particle size 5 μm) by gradient elution using methanol‐0.2 % ammonium acetate as the mobile phase. The suitable detection wavelength was set at 277 nm for the quantitative analysis of baicalin and forsythin in this method. Some operational parameters of the ESI interface were optimized, negative m/z 445[M?H]^? for baicalin and negative m/z 593[M+CH₃COO]^? for forsythin, positive m/z 447[M+H]⁺ for baicalin and positive m/z 552[M+NH 4]⁺ for forsythin, respectively. These HPLC/DAD and LC‐ESI‐MS methods were validated in terms of recovery, linearity, accuracy and precision (intra‐ and inter‐day validation). These methods can be used as a complementary method for the commercial quality control of Shuanghuanglian oral liquid and its pharmaceutical preparations.     

Differentiation of Boc‐protected α,δ‐/δ,α‐ and β,δ‐/δ,β‐hybrid peptide positional isomers by electrospray ionization tandem mass spectrometry

Two new series of Boc‐N‐α,δ‐/δ,α‐ and β,δ‐/δ,β‐hybrid peptides containing repeats of L ‐Ala‐δ⁵‐Caa/δ⁵‐Caa‐L ‐Ala and β³‐Caa‐δ⁵‐Caa/δ⁵‐Caa‐β³‐Caa (L ‐Ala = L ‐alanine, Caa = C‐linked carbo amino acid derived from D ‐xylose) have been differentiated by both positive and negative ion electrospray ionization (ESI) ion trap tandem mass spectrometry (MS/MS). MSⁿ spectra of protonated isomeric peptides produce characteristic fragmentation involving the peptide backbone, the Boc‐group, and the side chain. The dipeptide positional isomers are differentiated by the collision‐induced dissociation (CID) of the protonated peptides. The loss of 2‐methylprop‐1‐ene is more pronounced for Boc‐NH‐L ‐Ala‐δ‐Caa‐OCH₃ (1), whereas it is totally absent for its positional isomer Boc‐NH‐δ‐Caa‐L ‐Ala‐OCH₃ (7), instead it shows significant loss of t‐butanol. On the other hand, second isomeric pair shows significant loss of t‐butanol and loss of acetone for Boc‐NH‐δ‐Caa‐β‐Caa‐OCH₃ (18), whereas these are insignificant for its positional isomer Boc‐NH‐β‐Caa‐δ‐Caa‐OCH₃ (13). The tetra‐ and hexapeptide positional isomers also show significant differences in MS² and MS³ CID spectra. It is observed that ‘b’ ions are abundant when oxazolone structures are formed through five‐membered cyclic transition state and cyclization process for larger ‘b’ ions led to its insignificant abundance. However, b₁⁺ ion is formed in case of δ,α‐dipeptide that may have a six‐membered substituted piperidone ion structure. Furthermore, ESI negative ion MS/MS has also been found to be useful for differentiating these isomeric peptide acids. Thus, the results of MS/MS of pairs of di‐, tetra‐, and hexapeptide positional isomers provide peptide sequencing information and distinguish the positional isomers. Copyright © 2010 John Wiley & Sons, Ltd.     

Rapid separation and identification of furocoumarins in Angelica dahurica by high‐performance liquid chromatography with diode‐array detection,time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High‐performance liquid chromatography with diode‐array detection (HPLC/DAD), time‐of‐flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QITMS) were used for separation, identification and structural analysis of furocoumarins in Angelica dahurica. Two furocoumarins (imperatorin and isoimperatorin) in Angelica dahurica extract were identified unambiguously by comparing their relative retention times, characteristic ultraviolet information and accurate mass measurement. A formula database of known furocoumarins in Angelica dahurica was established, against which the other 21 furocoumarins were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to distinguish the isomers, multi‐stage mass spectrometry (MSⁿ, ion trap mass spectrometry) was used. General fragmentation behavior of the furocoumarins in the ion trap mass spectrometer was studied by the two furocoumarin standards, and their fragmentation rules in MSⁿ spectra were summarized. These deduced fragmentation rules of furocoumarins were successfully implemented in distinguishing the three groups of isomers in Angelica dahurica by HPLC/QITMS. By using the three different analytical techniques, 23 furocoumarins in Angelica dahurica were tentatively identified within 30 min. Finally, HPLC/TOFMS fingerprints of Angelica dahurica were established by which it can be concluded that a rapid and effective method based on the three analytical techniques for identification of chemical components was established. This can provide help for further quality control of Angelica dahurica and pharmacology mechanism study of furocoumarins in Angelica dahurica. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis of lignans in Schisandra chinensis and rat plasma by high‐performance liquid chromatography diode‐array detection,time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High‐performance liquid chromatography/diode‐array detection (HPLC/DAD), time‐of‐flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QIT‐MS) were used for separation, identification and structural analysis of lignans in Schisandra chinensis and rat plasma after oral administration of the herbal extract. Six lignans in Schisandra chinensis extract were identified unambiguously by comparing the retention time, their characteristic ultraviolet (UV) absorption and accurate mass measurement. A formula database of known lignans in Schisandra chinensis was established, against which the other 15 lignans were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to distinguish the isomers, multi‐stage mass spectrometry (ion trap mass spectrometry, MSⁿ) was also used. The fragmentation behavior of the lignans in the ion trap mass spectrometer was studied by the six lignan standards, and their fragmentation rules in MSⁿ spectra were summarized. These deduced fragmentation rules of lignans were successfully implemented in distinguishing the three groups of isomers in Schisandra chinensis by HPLC/QIT‐MS. By using the three different analytical techniques, 21 lignans in Schisandra chinensis were identified within 30 min. After oral administration of the extract, 11 lignans in rat plasma were detected and identified by comparing their retention time, characteristic UV absorption and accurate mass measurement of peaks in HPLC/TOFMS chromatograms of the herbal extract. Finally, HPLC/TOFMS fingerprints of Schisandra chinensis in vitro and rat plasma in vivo were established. It is concluded that a rapid and effective method based on three analytical techniques for identification of chemical components was established, which is useful for rapid identification of multiple components in Schisandra chinensis in vitro and in vivo. In addition, it can provide help for further pharmacology and action mechanism study of lignans in Schisandra chinensis. Copyright © 2009 John Wiley & Sons, Ltd.     

Isomer differentiation via collision‐induced dissociation: The case of protonated α‐, β2‐ and β3‐phenylalanines and their derivatives

A combination of electrospray ionisation (ESI), multistage and high‐resolution mass spectrometry experiments is used to examine the gas‐phase fragmentation reactions of the three isomeric phenylalanine derivatives, α‐phenylalanine, β²‐phenylalanine and β³‐phenylalanine. Under collision‐induced dissociation (CID) conditions, each of the protonated phenylalanine isomers fragmented differently, allowing for differentiation. For example, protonated β³‐phenylalanine fragments almost exclusively via the loss of NH₃, only β²‐phenylalanine via the loss of H₂O, while α‐ and β²‐phenylalanine fragment mainly via the combined losses of H₂O + CO. Density functional theory (DFT) calculations were performed to examine the competition between NH₃ loss and the combined losses of H₂O and CO for each of the protonated phenylalanine isomers. Three potential NH₃ loss pathways were studied: (i) an aryl‐assisted neighbouring group; (ii) 1,2 hydride migration; and (iii) neighbouring group participation by the carboxyl group. Finally, we have shown that isomer differentiation is also possible when CID is performed on the protonated methyl ester and methyl amide derivatives of α‐, β²‐ and β³‐phenylalanines. Copyright © 2010 John Wiley & Sons, Ltd.     

Antioxidant Pathways and One‐Electron Oxidation of Dopamine and Cysteine in Electrospray and On‐Line Electrochemistry Electrospray Ionization Mass Spectrometry

Dopamine [DA]⁺ (m/z 154), DA dimer [2DA‐H]⁺ (m/z 307) and DA quinone [DAQ]⁺ (m/z 152) are detected in positive ion mode electrospray ionization mass spectrometry (ESI MS) of dopamine in 50/1/49 (vol%) water/acetic acid/methanol. H/D exchange experiments support a covalent structure of DA dimer. Thus, ESI of DA may involve 1e^?, 1H⁺ oxidation processes followed by rapid radical dimerization. The DA quinone signal is low in ESI MS, which indicates a low efficiency of the 2e^?, 2H⁺ oxidation reaction. On‐line electrochemistry ESI MS (EC/ESI MS) with low electrochemical cell voltage floated on high ES voltage increases electrospray current and improves sensitivity for DA. The DA quinone signal increases and DA dimer signal decreases. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity of ESI and EC/ESI MS measurements. A DA quinone‐cysteine adduct [DAQ+Cys]⁺ was detected in solutions of DA with cysteine (Cys). ESI MS and EC/ESI MS indicate formation of the DA quinone‐cysteine adduct by 1e^? pathway. Oxidation pathways in ESI MS are relevant to biological reactivity of DA and Cys.     

HPLC‐DAD and HPLC‐ESI‐MS separation,determination and identification of the spin‐labeled diastereoisomers of podophyllotoxin

Spin‐labeled nitroxide derivatives of podophyllotoxin had better antitumor activity and less toxicity than that of the parent compounds. However, the 2‐H configurations of these spin‐labeled derivatives cannot be determined by nuclear magnetic resonance (NMR) methods. In the present paper, a 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, identification of four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 position. In the HPLC‐ESI/MS spectra, each pair of diastereoisomers of the spin‐labeled derivatives in the mixture was directly confirmed and identified by [M+H]⁺ ions and ion ratios of relative abundance of [M‐ROH+H]⁺ (ion 397) to [M+H]⁺. When the [M‐ROH+H]⁺ ions (at m/z 397) were selected as the precursor ions to perform the MS/MS product ion scan. The product ions at m/z 313, 282, and 229 were the common diagnostic ions. The ion ratios of relative abundance of the [M‐ROH+H]⁺ (ion 397) to [M+H]⁺, [A+H]⁺ (ion 313) to [M‐ROH+H]⁺, [A+H‐OCH₃]⁺ (ion 282) to [M‐ROH+H]⁺ and [M‐ROH‐ArH+H]⁺ (ion 229) to [M‐ROH+H]⁺ of each pair of diastereoisomers of the derivatives specifically exhibited a stereochemical effect. Thus, by using identical chromatographic conditions, the combination of DAD and MS/MS data permitted the separation and identification of the four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 in the mixture.     

The ESI CAD fragmentations of protonated 2,4,6‐tris(benzylamino)‐ and tris(benzyloxy)‐1,3,5‐triazines involve benzyl–benzyl interactions: a DFT study

The electrospray ionization collisionally activated dissociation (CAD) mass spectra of protonated 2,4,6‐tris(benzylamino)‐1,3,5‐triazine (1) and 2,4,6‐tris(benzyloxy)‐1,3,5‐triazine (6) show abundant product ion of m/z 181 (C₁₄H₁₃⁺). The likely structure for C₁₄H₁₃⁺ is α‐[2‐methylphenyl]benzyl cation, indicating that one of the benzyl groups must migrate to another prior to dissociation of the protonated molecule. The collision energy is high for the ‘N’ analog (1) but low for the ‘O’ analog (6) indicating that the fragmentation processes of 1 requires high energy. The other major fragmentations are [M + H‐toluene]⁺ and [M + H‐benzene]⁺ for compounds 1 and 6, respectively. The protonated 2,4,6‐tris(4‐methylbenzylamino)‐1,3,5‐triazine (4) exhibits competitive eliminations of p‐xylene and 3,6‐dimethylenecyclohexa‐1,4‐diene. Moreover, protonated 2,4,6‐tris(1‐phenylethylamino)‐1,3,5‐triazine (5) dissociates via three successive losses of styrene. Density functional theory (DFT) calculations indicate that an ion/neutral complex (INC) between benzyl cation and the rest of the molecule is unstable, but the protonated molecules of 1 and 6 rearrange to an intermediate by the migration of a benzyl group to the ring ‘N’. Subsequent shift of a second benzyl group generates an INC for the protonated molecule of 1 and its product ions can be explained from this intermediate. The shift of a second benzyl group to the ring carbon of the first benzyl group followed by an H‐shift from ring carbon to ‘O’ generates the key intermediate for the formation of the ion of m/z 181 from the protonated molecule of 6. The proposed mechanisms are supported by high resolution mass spectrometry data, deuterium‐labeling and CAD experiments combined with DFT calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

Gas‐phase fragmentation of γ‐lactone derivatives by electrospray ionization tandem mass spectrometry

Fragmentation reactions of β‐hydroxymethyl‐, β‐acetoxymethyl‐ and β‐benzyloxymethyl‐butenolides and the corresponding γ‐butyrolactones were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) using collision‐induced dissociation (CID). This study revealed that loss of H₂O [M + H ?18]⁺ is the main fragmentation process for β‐hydroxymethylbutenolide (1) and β‐hydroxymethyl‐γ‐butyrolactone (2). Loss of ketene ([M + H ?42]⁺) is the major fragmentation process for protonated β‐acetoxymethyl‐γ‐butyrolactone (4), but not for β‐acetoxymethylbutenolide (3). The benzyl cation (m/z 91) is the major ion in the ESI‐MS/MS spectra of β‐benzyloxymethylbutenolide (5) and β‐benzyloxymethyl‐γ‐butyrolactone (6). The different side chain at the β‐position and the double bond presence afforded some product ions that can be important for the structural identification of each compound. The energetic aspects involved in the protonation and gas‐phase fragmentation processes were interpreted on the basis of thermochemical data obtained by computational quantum chemistry. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification of the absorptive constituents and their metabolites in vivo of Puerariae Lobatae Radix decoction orally administered in WZS‐miniature pigs by HPLC‐ESI‐Q‐TOFMS

In this study, the technique of high‐performance liquid chromatography coupled with electrospray ionization quadrupole time‐of‐flight mass spectrometry (HPLC‐ESI‐Q‐TOFMS) was used to analyze and identify the absorptive constituents and their metabolites in drug‐containing urine of Wuzhishan (WZS)‐miniature pigs administered with Puerariae Lobatae Radix (PLR) decoction. With the accurate mass measurements (<5 ppm) and effective MS² fragment ions, 96 compounds, including eight original constituents and 88 metabolites, were identified from the drug‐containing urine. Among these, 64 metabolites were new ones and their structures can be categorized into five types: isoflavones, puerols, O‐desmethylangolensins, equols and isoflavanones. In particular, puerol‐type constituents in PLR were first proved to be absorptive in vivo. Meanwhile, the metabolic pathways of PLR in vivo were investigated. On the basis of relative content of the identified compounds, 13 major metabolites accounting for approximately 50% of the contents, as well as their corresponding 12 prototype compounds, were determined as the major original absorptive constituents and metabolites of PLR in vivo. The HPLC‐ESI‐Q‐TOFMS technique proved to be powerful for characterizing the chemical constituents from the complicated traditional Chinese medicine matrices in this research. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of phenolic and triterpenoid compounds in licorice and rat plasma by high‐performance liquid chromatography diode‐array detection,time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High‐performance liquid chromatography with diode‐array detection (HPLC/DAD), time‐of‐flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QITMS) were used for separation and identification of several compounds in licorice and rat plasma after oral administration of the herbal extract. Three phenolic compounds and one triterpenoid in licorice extract were unambiguously identified by comparing with the standard compounds. A formula database of known compounds in licorice was established, against which the other 42 compounds were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to differentiate the isomers, tandem mass spectrometry was also used. The deduced fragmentation behaviors in QITMS were used to distinguish seven groups of isomers in licorice. By means of the three detectors, 46 compounds in licorice were identified. After oral administration of the extract, 25 compounds in rat plasma were detected and identified by comparing and contrasting the compounds measured in licorice with those in the plasma samples by HPLC/TOFMS. It is concluded that a rapid and effective method based on three analytical techniques was established, which is useful for identification of multiple compounds in licorice in vitro and in vivo. The result should be very useful for the quality control and curative mechanism study of licorice. Copyright © 2009 John Wiley & Sons, Ltd.     

Differentiation of lisinopril and its RSS diastereomer by liquid chromatography combined with collision‐induced dissociation mass spectrometry

A simple and sensitive liquid chromatography tandem multiple‐stage mass spectrometry (HPLC/MS/MS) method suitable for bulk lisinopril analysis was developed, by which lisinopril and its RSS isomer were separated and differentiated. In the collision‐induced dissociation (CID) mass spectra of the [M + H]⁺ ions, the abundance of the fragment ion of m/z 246 for lisinopril was about two times higher than the ion of m/z 245; however, the former fragment ion was noted to be a little lower than the latter for RSS isomer at all collision energies. In the CID mass spectra of the [M + Li]⁺ ion, the abundance of the rearrangement ion of m/z 315 for the RSS isomer was about three times higher than that for lisinopril. Furthermore, the difference was supported by the results of energy‐resolved mass spectrometry (ERMS) in the test range of collision energies. Similar differences were also observed between the CID mass spectra of lisinopril and RSS isomer methylester, which indicated that the RSS isomer could be rapidly characterized by the CID mass spectra of both the protonated and lithium adduct ion. Elemental compositions of all the ions were confirmed by Fourier Transform ion cyclotron resonance ESI mass spectrometry (FT‐ICR‐ESI/MS). In addition, theoretical computations were carried out to support the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Separation,interconversion, and insecticidal activity of the cis‐ and trans‐isomers of novel hydrazone derivatives

A series of cis‐ and trans‐isomers of hydrazone derivatives were separated and analyzed through HPLC with diode‐array detection and HPLC‐MS/MS using ESI and ion trap MS. Two single crystals (A‐5‐1 and C‐2‐1) of the trans‐isomers were obtained and determined using X‐ray crystallography data, and the cis‐ to trans‐isomerization under different conditions was discussed. Both of the cis‐ and trans‐isomers of A‐4 and A‐5 exhibited good insecticidal activities against Plutella xylostella.     

Analysis of hydroxyl radical‐induced oxidation process of glucagon by reversed‐phase HPLC and ESI‐MS/MS

Structural modification of a polypeptide hormone, glucagon, by a hydroxyl radical in vitro was investigated by reversed‐phase high‐performance liquid chromatography (RP‐HPLC), and the oxidized site of glucagon was detected by electrospray ionization tandem mass spectrometry (ESI‐MS/MS). It was shown that ²⁷methionine (Met) was oxidized to ²⁷Met sulfoxide by hydroxyl radical, and the production rate of ²⁷Met sulfoxide was faster than that by hydrogen peroxide. In addition, production of ²⁷Met sulfoxide enantiomer was confirmed by RP‐HPLC analysis. cAMP production in a HepG2 cell induced by ²⁷Met sulfoxide glucagon was reduced to approximately 75% as compared with that induced by the native form of glucagon. Copyright © 2009 John Wiley & Sons, Ltd.     

Guest‐Induced Photophysical Property Switching of Artificial Light‐Harvesting Dendrimers

An artificial light‐harvesting multiporphyrin dendrimer ( 8P_ZnP_FB ) composed of a focal freebase porphyrin ( P_FB ) with eight zinc(II) porphyrin ( P_Zn ) wings exhibited unique photophysical property switching in response to specific guest molecule binding. UV/Vis titration studies indicated stable 1:2 host–guest complex formation between 8P_ZnP_FB and meso‐tetrakis(4‐pyridyl)‐porphyrin ( TPyP ) for which the first and second association constants were estimated to be >10⁸ M ^?1 and 3.0×10⁷ M ^?1, respectively. 8P_ZnP_FB originally shows 94 % energy transfer efficiency from P_Zn to the focal P_FB . By the formation of the host–guest complex ( 8P_ZnP_FB? 2 TPyP ) the emission intensity of 8P_ZnP_FB is significantly decreased, and an ultrafast charge separation state is generated. The energy transfer process from P_Zn wings to the P_FB core in 8P_ZnP_FB is almost entirely switched to an electron transfer process by the formation of 8P_ZnP_FB? 2 TPyP .     

LC/ESI‐MS/MS characterisation of lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain

Lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain showed an interesting anti‐adhesion activity against biofilm formation of human pathogenic bacterial strains. The chemical characterisation of the crude extract of V9T14 strain was first developed through electrospray ionisation mass spectrometry (ESI‐MS) and ESI‐MS/MS direct infusions: two sets of molecular ion species belonging to the fengycin and surfactin families were revealed and their structures defined, interpreting their product ion spectra. The LC/ESI‐MS analysis of the crude extract allowed to separate in different chromatogram ranges the homologues and the isoforms of the two lipopeptide families. The extract was then fractionated by silica gel chromatography in two main fractions, I and II. The purified biosurfactants were analysed through a new, rapid and suitable LC/ESI‐MS/MS method, which allowed characterising the composition and the structures of the produced lipopeptides. LC/ESI‐MS/MS analysis of fraction I showed the presence of C₁₃, C₁₄ and C₁₅ surfactin homologues, whose structures were confirmed by the product ion spectra of the sodiated molecules [M + Na]⁺ at m/z 1030, 1044 and 1058. LC/ESI‐MS/MS analysis of fraction II confirmed the presence of two main fengycin isoforms, with the protonated molecules [M + H]⁺ at m/z 1478 and 1506 corresponding to C₁₇ fengycin A and C₁₇ fengycin B, respectively. Other homologues (C₁₄ to C₁₆) were revealed and confirmed as belonging to fengycin A or B according to the retention times and the product ions generated, although with the same nominal mass. Finally, a relative percentage content of each homologue for both lipopeptides families in the whole extract was proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

Metal(II) Ion Complexes with 5‐(Pyrazin‐2‐yl)‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thione; Synthesis,Structural Characterization,Acid‐base,and Complexing Properties in Solution

The study reports the synthesis of complexes Co(HL)Cl₂ ( 1 ), Ni(HL)Cl₂ ( 2 ), Cu(HL)Cl₂ ( 3 ), and Zn(HL)₃Cl₂ ( 4 ) with the title ligand, 5‐(pyrazin‐2‐yl)‐1,2,4‐triazole‐5‐thione (HL), and their characterization by elemental analyses, ESI‐MS (m/z), FT‐IR and UV/Vis spectroscopy, as well as EPR in the case of the Cu^II complex. The comparative analysis of IR spectra of the metal ion complexes with HL and HL alone indicated that the metal ions in 1 , 2 , and 3 are chelated by two nitrogen atoms, N(4) of pyrazine and N(5) of triazole in the thiol tautomeric form, whereas the Zn^II ion in 4 is coordinated by the non‐protonated N(2) nitrogen atom of triazole in the thione form. pH potentiometry and UV/Vis spectroscopy were used to examine Co^II, Ni^II, and Zn^II complexes in 10/90 (v/v) DMSO/water solution, whereas the Cu^II complex was examined in 40/60 (v/v) DMSO/water solution. Monodeprotonation of the thione triazole in solution enables the formation of the L:M = 1:1 species with Co^II, Ni^II and Zn^II, the 2:1 species with Co^II and Zn^II, and the 3:1 species with Zn^II. A distorted tetrahedral arrangement of the Cu^II complex was suggested on the basis of EPR and Vis/NIR spectra.     

Characterization of Nα-Fmoc-protected ureidopeptides by electrospray ionization tandem mass spectrometry (ESI-MS/MS): differentiation of positional isomers

Four pairs of positional isomers of ureidopeptides, FmocNH‐CH(R₁)‐φ(NH‐CO‐NH)‐CH(R₂)‐OY and FmocNH‐CH(R₂)‐φ(NH‐CO‐NH)‐CH(R₁)‐OY (Fmoc = [(9‐fluorenyl methyl)oxy]carbonyl; R₁ = H, alkyl; R₂ = alkyl, H and Y = CH₃/H), have been characterized and differentiated by both positive and negative ion electrospray ionization (ESI) ion‐trap tandem mass spectrometry (MS/MS). The major fragmentation noticed in MS/MS of all these compounds is due to ? N? CH(R)? N? bond cleavage to form the characteristic N‐ and C‐terminus fragment ions. The protonated ureidopeptide acids derived from glycine at the N‐terminus form protonated (9H‐fluoren‐9‐yl)methyl carbamate ion at m/z 240 which is absent for the corresponding esters. Another interesting fragmentation noticed in ureidopeptides derived from glycine at the N‐terminus is an unusual loss of 61 units from an intermediate fragment ion FmocNH = CH₂⁺ (m/z 252). A mechanism involving an ion‐neutral complex and a direct loss of NH₃ and CO₂ is proposed for this process. Whereas ureidopeptides derived from alanine, leucine and phenylalanine at the N‐terminus eliminate CO₂ followed by corresponding imine to form (9H‐fluoren‐9‐yl)methyl cation (C₁₄H₁₁⁺) from FmocNH = CHR⁺. In addition, characteristic immonium ions are also observed. The deprotonated ureidopeptide acids dissociate differently from the protonated ureidopeptides. The [M ? H]^? ions of ureidopeptide acids undergo a McLafferty‐type rearrangement followed by the loss of CO₂ to form an abundant [M ? H ? Fmoc + H]^? which is absent for protonated ureidopeptides. Thus, the present study provides information on mass spectral characterization of ureidopeptides and distinguishes the positional isomers. Copyright © 2010 John Wiley & Sons, Ltd.     

Gas‐phase fragmentation study of a novel series of synthetic 2‐oxo‐2H‐benzopyrano[2,3‐d]pyrimidine derivatives using electrospray ionization tandem mass spectroscopy measured with a quadrupole orthogonal time‐of‐flight hybrid instrument

The fragmentation patterns of a series of six novel synthesized benzopyranopyrimidine derivatives 1–6, possessing the same 2‐oxo‐2H‐benzopyrano[2,3‐d]pyrimidine backbone structure, were investigated by electrospray ionization mass spectrometry (ESI‐MS) and tandem mass spectrometry (MS/MS) techniques using a quadrupole orthogonal time‐of‐flight (QqToF)‐hybrid instrument. The series of six pure benzopyranopyrimidine compounds contained three constitutional isobaric isomers (compounds 4–6). A simple methodology, based on the use of ESI (positive ion mode) and increasing the declustering potential in the atmospheric pressure/vacuum interface resulting in collision‐induced dissociation (CID), was used to enhance the formation of the product ions. In general, the novel synthetic benzopyranopyrimidine derivatives 1–6 afforded exact accurate masses for the protonated molecules. This led to the confirmation of both molecular masses and chemical structures of the studied compounds. The breakdown routes of the protonated molecules were rationalized by conducting low‐energy CID‐MS/MS analyses. It was shown that the MS/MS fragmentation routes for the protonated molecules 1 and 2 were similar, and that the MS/MS fragmentations of the constitutional isobaric protonated molecules 5 and 6 were identical. It was also shown that the gas‐phase CID fragmentations of 5 and 6 were different from that of their constitutional isomer 4. Finally, the ESI‐MS and CID‐MS/MS analyses of the protonated molecules that were obtained from the monodeuterated benzopyranopyrimidine derivatives 1–6 confirmed the values obtained for the exact masses, the precise structural assignments of all product ions and all the pathways described in the proposed CID fragmentations. Copyright © 2008 John Wiley & Sons, Ltd.