Home About us Contact
|
Home About us Contact | ||
|
|
||
Positional Isomers (positional + isomer)
Selected AbstractsDiamino-C,N-diarylpyridine Positional Isomers as Inhibitors of Lysophosphatidic Acid Acyltransferase-,.CHEMINFORM, Issue 4 2006Feng Hong Abstract For Abstract see ChemInform Abstract in Full Text. [source] Assessment of Relative Stabilities of Positional Isomers of Polyhedral Heteronuclear Clusters via a Simplified Method of Bond Energy Calculations Based on Tight-Binding Approach and Adjacent Matrix Method: Applications to Binary Icosahedral Clusters.CHEMINFORM, Issue 5 2003Boon K. Teo No abstract is available for this article. [source] Structure elucidation of thermal degradation products of amlodipineMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2007A. Siva Lakshmi Devi Abstract Thermal degradation of amlodipine base causes intramolecular reactions affording three cyclic products, referred to as AMLDEG-I, AMLDEG-II, and AMLDEG-III, respectively. AMLDEG-I is a cyclized product formed by intramolecular elimination of ammonia from amlodipine. AMLDEG-II is a positional isomer of AMLDEG-I. AMLDEG-III is also intramolecular cyclisation product. The three degradation products were isolated by column chromatography and characterized by FT-IR and 1H and 13C NMR spectroscopy data. The AMLDEG-III was crystallized and its structure was solved by single crystal X-ray diffraction (SXRD). Copyright © 2007 John Wiley & Sons, Ltd. [source] S -(4-Nitrophenyl) 4-nitrobenzenethiosulfonateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Iván Brito The title compound, C12H8N2O6S2, (I), is a positional isomer of S -(2-nitrophenyl) 2-nitrobenzenethiosulfonate [Glidewell, Low & Wardell (2000). Acta Cryst. B56, 893,905], (II). The most obvious difference between the two isomers is the rotation of the nitro groups with respect to the planes of the adjacent aryl rings. In (I), the nitro groups are only slightly rotated out of the plane of the adjacent aryl ring [2.4,(6) and 6.7,(7)°], while in (II) the nitro groups are rotated by between 37 and 52°, in every case associated with S,S,C,C torsion angles close to 90°. Other important differences between the isomers are the C,S,S(O2),C torsion angle [78.39,(2)° for (I) and 69.8,(3)° for (II) (mean)] and the dihedral angles between the aromatic rings [12.3,(3)° for (I) and 28.6,(3)° for (II) (mean)]. There are two types of C,H...O hydrogen bond in the structure [C...O = 3.262,(7),Å and C,H...O = 144°; C...O = 3.447,(7),Å and C,H...O = 166°] and these link the molecules into a two-dimensional framework. The hydrogen-bond-acceptor properties differ between the two isomers. [source] Separation of cytokinin isomers with a partial filling-micellar electrokinetic chromatography-mass spectrometry approachELECTROPHORESIS, Issue 10 2008Liya Ge Abstract A new method based on partial filling-MEKC (PF-MEKC) directly coupled to ESI-MS was developed for the simultaneous separation and determination of 13 structurally similar cytokinins, including various geometric and positional isomers of cytokinins. On the basis of the resolution of the neighboring isomer peaks, different parameters (i.e., pH and concentration of buffer, surfactant concentrations, length of the injected micellar plug, organic modifier, and applied separation voltage) were optimized to achieve a satisfactory PF-MEKC separation. Under optimum conditions, the separation of 13 cytokinin standards was accomplished within 25,min. MS/MS with multiple reaction monitoring detection was carried out to obtain sufficient selectivity. PF-MEKC-MS/MS allowed for the direct identification and confirmation of the cytokinins present in banana (Musa spp.) pulp sample after extraction and purification. Finally, trans- zeatin riboside (ZR) and trans- zeatin (Z) were unambiguously identified in banana pulp. It is anticipated that the current PF-MEKC-MS method can be applied to analyze cytokinins in a wide range of biological samples. [source] Compositional effects on electrophoretic and chromatographic figures of merit in electrokinetic chromatography with cetyltrimethylammonium bromide/sodium octyl sulfate vesicles as the pseudostationary phase.ELECTROPHORESIS, Issue 5 2008Part 1: Effect of the phase ratio Abstract The effect of the phase ratio on the electrophoretic and chromatographic properties of unilamellar vesicles comprised of cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) was investigated in EKC. The surfactant concentration of the vesicles was 0.9, 1.2, 1.5, and 1.8% w/v, with a mole ratio of 1:3.66 (CTAB/SOS). Results were compared to those obtained using SDS micelles at concentrations of 1.0% (w/v, 35,mM) and 1.5% (52,mM). The CTAB/SOS vesicles (0.9,1.8% w/v) provided a significantly larger elution range (5.7,,,tves/t0,,,8.7) and greater hydrophobic (methylene) selectivity (2.8,,,,CH2,,,3.1) than SDS micelles (3.1,,,tmc/t0,,,3.3; ,CH2,=,2.2). Whereas the larger elution range can be attributed to the 25% reduction in EOF due to the interaction of unaggregated CTAB cations and the negatively charged capillary wall, the higher methylene selectivity is likely due to the lower concentration of water expected in the CTAB/SOS vesicle bilayer compared to the Palisades layer of SDS micelles. For a given phase ratio, CTAB/SOS vesicles are somewhat less retentive than SDS micelles, although retention factors comparable to those observed in 1.0,1.5% SDS can be obtained with 1.5,1.8% CTAB/SOS. A linear relationship was observed between phase ratio and retention factor, confirming the validity of the phase ratio model for these vesicles. Unique polar group selectivities and positional isomer shape selectivities were obtained with CTAB/SOS vesicles, with both types of selectivities being nearly independent of the phase ratio. For four sets of positional isomers, the elution order was always para < ortho < meta. Finally, the thermodynamics of solute retention was qualitatively similar to that reported for other surfactant aggregates (micelles and microemulsions); the enthalpic contribution to retention was consistently favorable for all compounds, whereas the entropic contribution was favorable only to hydrophobic solutes. [source] Micro-reactor for transesterification of plant seed oilsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 5 2009Phattaraporn Kaewkool Abstract The fatty acid compositions of vegetable or other plant seed oils are generally determined by gas chromatography (GC). Methyl esters (the most volatile derivatives) are the preferred derivatives for GC analysis. Esters of higher alcohols are good for the separation of volatile and positional isomers. All the esters of the C1,C8 alcohols of vegetable oils were silmilarly prepared by passing the reaction mixture containing the desired alcohol, oil and tetrahydrofuran through the micro-reactor (a 3-mL dispossible syringe packed with 0.5,g of NaOH powder). The reaction products were acidified with acetic acid and the mixture was analyzed by high-performance size exclusion chromatography and GC. Transesterification was quantitative for primary alcohols, but an appreciable amount of free fatty acids was formed for secondary alcohols. Coriander seed oil was quantitatively esterified with 2-ethyl 1-hexanol with the micro-reactor in less than 1,min. Oleic and petroselinic acid 2-ethyl 1-hexyl esters are baseline separated on an Rtx-2330 capillary column (30,m×0.25,mm, 0.25,µm film thickness). [source] The influence of cytosine methylation on the chemoselectivity of benzo[a]pyrene diol epoxide-oligonucleotide adducts determined using nanoLC/MS/MSJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2009James Glick Abstract Benzo[a]pyrene is a major carcinogen implicated in human lung cancer. Almost 60% of human lung cancers have a mutation in the p53 tumor suppressor gene at several specific codons. An on-line nanoLC/MS/MS method using a monolithic nanocolumn was applied to investigate the chemoselectivity of the carcinogenic diol epoxide metabolite, ( ± )-(7R,8S,9S,10R)-benzo[a]pyrene 7,8-diol 9,10-epoxide [( ± )- anti -benzo[a]pyrene diol epoxide (BPDE)], which was reacted in vitro with a synthesized 14-mer double stranded oligonucleotide (5,-ACCCG5CG7TCCG11CG13C-3,/5,-GCGCGGGCGCGGGT-3,) derived from the p53 gene. This sequence contained codons 157 and 158, which are considered mutational ,hot spots' and have also been reported as chemical ,hot spots' for the formation of BPDE-DNA adducts. In evaluating the effect of cytosine methylation on BPDE-DNA adduct binding, it was found that codon 156, containing the nucleobase G5 instead of the mutational hot spot codons 157 (G7) and 158 (G11), was the preferential chemoselective binding site for BPDE. In all permethylated cases studied, the relative ratio for adduction was found to be G5, G11 > G13 > G7. Permethylation of CpG dinucleotide sites on either the nontranscribed or complementary strand did not change the order of sequence preference but did enhance the relative adduction level of the G11 CpG site (codon 158) approximately two-fold versus the unmethylated oligomer. Permethylation of all CpG dinucleotide sites on the duplex changed the order of relative adduction to G5, G7 > G11 > G13. The three- to four-fold increase in adduction at the mutational hot spot codon 157 (G7) relative to the unmethylated or single-stranded permethylated cases suggests a possible relationship between the state of methylation and adduct formation for a particular mutation site in the p53 gene. Using this method, only 125 ng (30 pmol) of adducted oligonucleotide was analyzed with minimal sample cleanup and high chromatographic resolution of positional isomers in a single chromatographic run. Copyright © 2009 John Wiley & Sons, Ltd. [source] Discrimination and identification of the six aromatic positional isomers of trimethoxyamphetamine (TMA) by gas chromatography-mass spectrometry (GC-MS)JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2008Kei Zaitsu Abstract A reliable and accurate GC-MS method was developed that allows both mass spectrometric and chromatographic discrimination of the six aromatic positional isomers of trimethoxyamphetamine (TMA). Regardless of the trifluoroacetyl (TFA) derivatization, chromatographic separation of all the investigated isomers was achieved by using DB-5ms capillary columns (30 m × 0.32 mm i.d.), with run times less than 15 min. However, the mass spectra of the nonderivatized TMAs, except 2,4,6-trimethoxyamphetmine (TMA-6), showed insufficient difference for unambiguous discrimination. On the other hand, the mass spectra of the TFA derivatives of the six isomers exhibited fragments with significant intensity differences, which allowed the unequivocal identification of all the aromatic positional isomers investigated in the present study. This GC-MS technique in combination with TFA derivatization, therefore, is a powerful method to discriminate these isomers, especially useful to distinguish the currently controlled 3,4,5-trimethoxyamphetmine (TMA-1) and 2,4,5-trimethoxyamphetmine (TMA-2) from other uncontrolled TMAs. Copyright © 2007 John Wiley & Sons, Ltd. [source] Attachment of neutrals during tandem mass spectrometry of sulfonic acid dyes andintermediates in an ion trapJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2002Adrian Weisz Abstract Several positional isomers of 2-(2-quinolinyl)-1H -indene-1,3(2H)-dione mono- and disulfonic acids prepared as reference materials for development of analytical methods involved in FDA certification of D&C Yellow No. 10 (Quinoline Yellow) were found consistently to show [MH + 14]+ ions when their electrospray- or atmospheric pressure chemical ionization-prepared MH+ ions were subjected to collisional activation. The source of these ions was found to be the methanol used as solvent in these procedures which combined with their [MH , H2O]+ ions under chemical ionization conditions. The reaction was found to be sensitive to their isomeric and chemical structures and other examples of this process are reviewed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Enthalpies of formation and isomerization of cis - and trans -decalin, and their oxa-analogs by G3(MP2)//B3LYP calculationsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2009Esko Taskinen Abstract G3(MP2)//B3LYP calculations have been carried out on trans - and cis -decalin, and their mono-, di-, tri-, and tetraoxa-analogs. The main purpose of the work was to obtain enthalpies of formation for these compounds, and to study the relative stabilities of the cis,trans and positional isomers of the various (poly)oxadecalins. Comparison of the computational enthalpies of formation with the respective experimental ones, known only for the decalins and 1,3,5,7-tetraoxadecalins, shows that in both cases the computational values are more negative than the experimental ones, the deviations being ,5 to ,7,kJ,mol,1 for the decalins and ,12 to ,17,kJ,mol,1 for the 1,3,5,7-tetraoxadecalins. The respective computational enthalpies of cis,trans isomerization, however, are in excellent to satisfactory agreement with the experimental data. The cis,trans enthalpy differences vary from +11.0,kJ,mol,1 for decalin to ,15.4,kJ,mol,1 for 1,4,5,8-tetraoxadecalin. Low relative enthalpy values were also calculated for the cis isomers of 1,8-dioxadecalin (,3.7,kJ,mol,1), 1,3,6-trioxadecalin (,4.6,kJ,mol,1), 1,3,8-trioxadecalin (,9.7,kJ,mol,1), 1,4,5- trioxadecalin (,5.6,kJ,mol,1), 1,3,5,8-tetraoxadecalin (,7.3,kJ,mol,1), and 1,3,6,8-tetraoxadecalin (,14.5,kJ,mol,1). Copyright © 2009 John Wiley & Sons, Ltd. [source] Resolution of triacylglycerol positional isomers by reversed-phase high-performance liquid chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 12 2004Svetlana Momchilova Abstract The ability of reversed-phase high-performance liquid chromatography (RP-HPLC) to separate some positionally isomeric disaturated and monounsaturated triacylglycerols (TAGs) as intact species is demonstrated for the first time. Mobile phases of acetonitrile modified with methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, acetone, or dichloromethane were tested for the separation of POP-PPO, PLP-PPL, PEP-PPE, and PDP-PPD (P , palmitic, O , oleic, L , linoleic, E , eicosapentaenoic, D , docosahexaenoic acid residue) on a single RP-HPLC column. The resolution improved with increasing number of double bonds in the acyl residues. While POP and PPO were only partially resolved, PDP and PPD were fully separated with all tested mobile phases, except those containing methanol. Also separated were the four TAGs having the same equivalent carbon number (ECN = 42), PEP, PPE, PDP, and PPD, on a single RP-HPLC column with mobile phase acetonitrile,2-propanol (70:30, v/v) at 0.8 mL/min. In all cases the isomer with the unsaturated acyl residue in either 1- or 3-position was retained more strongly than the respective 2-isomer. [source] Substituent effects of the N,N -dimethyl- sulfamoyl group on the 1H and 13C NMR spectra of positional isomers of quinolines,MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2008Andrzej Ma, lankiewicz Abstract The complete 1H and 13C NMR spectral assignments of seven positional isomers of N,N -dimethylsulfamoylquinolines 2,8 and quinoline have been made using 1D and 2D NMR techniques, including COSY, HMQC and HMBC experiments. ,,H and ,,C substituent effects induced by the sulfamoyl group were determined. The sulfamoyl substituent affects proton and carbon chemical shifts both in the parent and in the fused (pyridine or benzene) ring. Copyright © 2007 John Wiley & Sons, Ltd. [source] Characterization of protostane triterpenoids in Alisma orientalis by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2010Xin Liu A reliable and sensitive ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) method has been optimized and established for analysis of protostane triterpenoids in a commonly used traditional Chinese herbal medicine Alisma orientalis (Sam.) Juzep. The separation of crude extract of A. orientalis was achieved on a Waters ACQUITY HSS T3 column (100,mm,×,2.1,mm, 1.8,µm) eluting with 0.1% (v/v) formic acid/acetonitrile. A total of 20 protostane triterpenoids including 19 known compounds and a new one were well separated within 7,min. The collision-induced dissociation (CID) tandem mass spectrometric (MS/MS) fragmentation patterns of protostane triterpenoids was firstly reported in this study. The hydrogen rearrangement at the C-23-OH leads to dissociation of the bond between C-23 and C-24 in the protostane triterpenoid skeleton during the CID process. This dissociation was the characteristic CID fragmentation pathway of this class of triterpenoids, and was useful for further differentiation of some positional isomers which contain an acetyl unit on the C-23 or C-24 position. The identities of isolated compounds were identified by comparing their retention times and CID fragmentation behaviors with those of reference standards or tentatively assigned by matching the empirical molecular formulae with those reported in the literature. It is concluded that this newly established UPLC/Q-TOF-MS method is a powerful approach for structural elucidation of protostane triterpenoids isolated from A. orientalis. Copyright © 2010 John Wiley & Sons, Ltd. [source] First report of non-coloured flavonoids in Echium plantagineum bee pollen: differentiation of isomers by liquid chromatography/ion trap mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2010Federico Ferreres Apicultural products have been widely used in diet complements as well as in phytotherapy. Bee pollen from Echium plantagineum was analysed by high-performance liquid chromatography/photodiode-array detection coupled to ion trap mass spectrometry (HPLC-PAD-MSn) with an electrospray ionisation interface. The structures have been determined by the study of the ion mass fragmentation, which characterises the interglycosidic linkage in glycosylated flavonoids and differentiates positional isomers. Twelve non-coloured flavonoids were characterised, being kaempferol-3- O -neohesperidoside the major compound, besides others in trace amounts. These include quercetin, kaempferol and isorhamnetin glycosides, with several of them being isomers. Acetylated derivatives are also described. This is the first time that non-coloured flavonoids are reported from this pollen, with MS fragmentation proving to be most useful in the elucidation of isomeric structures. Copyright © 2010 John Wiley & Sons, Ltd. [source] Rapid differentiation of isobaric and positional isomers of structurally related glycosides from Phytolacca bogotensisRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2009Guillermo Montoya Through the action of glycosyltransferases, a plant can biosynthetically assemble small different aglycons or 'templates' to various polysaccharides to produce numerous glycoconjugates differing in the type of the attached aglycon, the anomeric configuration of C-1 of the glycosylating sugar, the type of sugar and the different position of attachments of the sugar unit present in the polysaccharide chain. The position of attachments and the anomeric configuration of the different sugar present in the polysaccharide create the opportunity to generate molecules with either the same or very close molecular weights, which have relative structural similarity , forming isobaric and positional isomers. Although isomeric differentiation was once considered outside of the domain of mass spectrometry, this task can now be resolved using tandem mass spectrometry. In a standardized purified glycoconjugate fraction (SPT01) from Phytolacca bogotensis, we report conventional electrospray ionization mass spectrometry and collision-induced dissociation (CID) MS/MS parameters which favored the formation of characteristic product ions. This allowed us to suggest the type of sugar linkages present in a specific glycoconjugate. Ten new glycoconjugate are described from this plant and another twelve known saponins were structurally characterized using the automatic MSn acquisition mode. The differentiation of two pairs of positional isomers and four isobaric glycosides and the production of a library of 30 glycosides present in P. bogotensis were accomplished. Copyright © 2009 John Wiley & Sons, Ltd. [source] Plasma free fatty acid profiling in a fish oil human intervention study using ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2008Nicole Zehethofer A rapid method was developed for the simultaneous profiling of 29 free fatty acids in plasma using ultra-performance liquid chromatography/electrospray ionization tandem mass spectrometry (UPLC/ESI-MS/MS). Barium acetate was used as the cationization agent in the positive ion mode for sensitive multiple reaction monitoring (MRM) experiments. The cis- and trans -C18:1 and -C18:2 isomers were baseline-separated using two tandem reversed-phase C18 UPLC columns, while identification of two pairs of positional isomers of C18:3 and C20:3 required isomer-specific product ions, as the analytes were not chromatographically resolved. The assay linearity was greater than three orders of magnitude and correlation coefficients were >0.99; the limits of detections were typically less than 0.2,µM. The method was successfully applied to plasma free fatty acid profiling of samples from volunteers who participated in a randomized crossover study involving the administration of either placebo or fish oil capsules. The results clearly indicate the ability to measure the time profiles of the n -3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in plasma for the volunteers given fish oil capsules while the concentrations of the other free fatty acids and the total free fatty acid concentration in plasma remained virtually constant. Copyright © 2008 John Wiley & Sons, Ltd. [source] Coupling of ion-molecule reactions with liquid chromatography on a quadrupole ion trap mass spectrometerRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2008Yuriy Pyatkivskyy We report for the first time a coupling of gas-phase ion-molecule reactions with chromatographic separations on a quadrupole ion trap mass spectrometer. The interface was accomplished by using a pulsed valve for the introduction of a volatile neutral into the ion trap. The pulsed valve controller is synchronized with the mass spectrometer software. The setup requires some minor modifications to the vacuum system of the commercial quadrupole ion trap but most of the modifications are external to the mass spectrometer. Two applications of this interface are described: differentiation between two phosphoglucose positional isomers and detection of a phosphopeptide in a peptide mixture. Both applications are using the reactivity of trimethoxyborate towards a phosphate moiety in the negative ion mode. The detection of phosphopeptides hinges on our findings that non-phosphorylated peptide anions do not react with trimethoxyborate. This LC/MS detection can be easily visualized in terms of selected reaction monitoring. Copyright © 2008 John Wiley & Sons, Ltd. [source] Electrospray tandem mass spectrometry of alkali-cationized BocN-carbo- ,,, - and - ,,, -peptides: differentiation of positional isomers,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2006P. Nagi Reddy Dissociation pathways of a series of alkali-cationized hybrid peptides, viz., Boc- ,,, - and - ,,, -carbopeptides, synthesized from C-linked carbo- ,3 -amino acids [Caa (S)] and , -alanine (L-Ala), have been investigated by electrospray ionization tandem mass spectrometry. The positional isomers (six pairs) of the cationized ,,, - and ,,, -peptides can be differentiated by the collision-induced dissociation (CID) spectra of their [M,+,Cat-Boc,+,H]+ ions which give characteristic series of alkali-cationized C- (x, y, z) and N-terminal (a, b, c) ions. Another noteworthy difference is cationized ,,, -peptides eliminate a molecule of ammonia whereas this pathway is absent for ,,, -peptides. This is useful for identifying the presence of a , -amino acid at the N-terminus. The CID spectra of [M,+,Cat-Boc,+,H]+ ions of these peptide acids show abundant rearrangement [bn,+,17,+,Cat]+ (n,=,1 to n,1) ions which is diagnostic for distinguishing between , - and , -amino acid at the C-terminus. MSn experiments of [bn,+,Li,H]+ ions from these hybrid peptides showed the loss of CO and 72 u giving rise to [an,+,Li,H]+ and cationized nitrile product ions which render support to earlier proposals that b or [bn,+,Cat,H]+ ions have protonated or cationized oxazolinone structures, respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source] Characterization of isoquinoline alkaloids, diterpenoids and steroids in the Chinese herb Jin-Guo-Lan (Tinospora sagittata and Tinospora capillipes) by high-performance liquid chromatography/electrospray ionization with multistage mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2006Yufeng Zhang This study sought to determine the primary components (isoquinoline alkaloids, diterpenoids and steroids) in crude extracts of the Chinese herb Jin-Guo-Lan, prepared from the roots of Tinospora sagittata and T. capillipes, by liquid chromatography/electrospray ionization multistage mass spectrometry coupled with diode-array detection (LC-DAD/ESI-MSn). After separation on a reversed-phase C18 column using gradient elution, positive and negative ESI-MS experiments were performed. In positive ion mode, the three types of compounds showed very different characteristic ions: strong [M]+ or [M+H]+ ions were observed for isoquinoline alkaloids; [M+NH4]+ and/or [M+HCO2]+ for diterpenoids; [M+HnH2O]+ (n=1,3) for steroids. These adduct ions and/or fragments were used to deduce the mass and categories of known and unknown components in crude extracts, and their structures were further confirmed by ESI-MSn in positive ion mode. Moreover, UV absorption peaks obtained from DAD provided useful functional group information to aid the MSn -based identification. As a result, 11 compounds were unambiguously identified by comparing with standard compounds and 13 compounds were tentatively identified or deduced according to their MSn data. Two of these compounds (13-hydroxycolumbamine and 13-hydroxyjatrorrhizine) were found to be new compounds and another one (13-hydroxypalmatine) was detected for the first time as a natural product. In addition, a [M·CH3H2O].+ ion in MS2 of [M]+ after in-source collision-induced dissociation was used to differentiate positional isomers of protoberberine alkaloids, columbamine and jatrorrhizine. Although the roots of T. sagittata and T. capillipes contain almost identical compounds, the content of the compounds in them is dramatically different, suggesting the necessity for further comparison of the bioactivities of the two species. Copyright © 2006 John Wiley & Sons, Ltd. [source] Separation of a BMS drug candidate and acyl glucuronide from seven glucuronide positional isomers in rat plasma via high-performance liquid chromatography with tandem mass spectrometric detectionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2006Y.-J. Xue A high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the determination of a BMS drug candidate and its acyl glucuronide (1- O - , glucuronide) in rat plasma. A 50-µL aliquot of each plasma sample was fortified with acetonitrile containing the internal standard to precipitate proteins and extract the analytes of interest. After mixing and centrifugation, the supernatant from each sample was transferred to a 96-well plate and injected into an LC/MS/MS system. Chromatographic separation was achieved isocratically on a Phenomenex Luna C18, 3,mm,×,150,mm, 3,µm column. The mobile phase contained 0.075% formic acid in 70:30 (v/v) acetonitrile/water. Under the optimized chromatographic conditions, the BMS drug candidate and its acyl glucuronide were separated from its seven glucuronide positional isomers within 10,min. Resolution of the parent from all glucuronides and acyl glucuronide from its positional isomers was critical to avoid their interference with quantitation of parent or acyl glucuronide. Detection was by positive ion electrospray MS/MS on a Sciex API 4000. The standard curve, which ranged from 5 to 5000,ng/mL, was fitted to a 1/x2 weighted quadratic regression model for both the BMS drug candidate and its acyl glucuronide. Whole blood and plasma stability experiments were conducted to establish the sample collection, storage, and processing conditions. The validation results demonstrated that this method was rugged and repeatable. The same methodology has also been used in mouse and human plasma for the determination of the BMS drug candidate and its acyl glucuronide. Copyright © 2006 John Wiley & Sons, Ltd. [source] Simultaneous detection of monohydroxybenzo[a]pyrene positional isomers by reversed-phase liquid chromatography coupled to electrospray ionization mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 7 2002Hideki Sasaki A liquid chromatographic (LC) method has been developed for the separation of 11 monohydroxybenzo[a]pyrenes (OH BaPs) positional isomers, and for their detection using electrospray ionization mass spectrometry (ESI-MS). All OH BaPs isomers were separated on an octadecylsilyl (C18)-bonded amorphous organosilica column utilizing gradient elution with acetonitrile,water and triethylamine (TEA) at pH 11.0 and determined by MS, except 2- and 8-OH BaPs which were coeluted. The lower detection limits were in the range from 1.6,µg/L for 12-OH BaP to 12,µg/L for 5-OH BaP without any sample enrichment. The relative standard deviations of area response were in the range from 1.8% (9-OH BaP) to 4.9% (12-OH BaP) except for 9.4% (7-OH BaP). The developed method was successfully applied to incubation mixtures of BaP and CYP1A1/epoxide hydrolase. This method identified 1-, 3- and 9-OH BaPs as the major metabolites, and 2- (and/or 8-) and 12-OH BaPs as the minor metabolites in the incubation mixture. Copyright © 2002 John Wiley & Sons, Ltd. [source] Electronic Structure and Bonding in Neutral and Dianionic Boradiphospholes: R,BC2P2R2 (R=H, tBu, R,=H, Ph)CHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2009Dandamudi Usharani Abstract Classical and non-classical isomers of both neutral and dianionic BC2P2H3 species, which are isolobal to Cp+ and Cp,, are studied at both B3LYP/6-311++G(d,p) and G3B3 levels of theory. The global minimum structure given by B3LYP/6-311++G(d,p) for BC2P2H3 is based on a vinylcyclopropenyl-type structure, whereas BC2P2H32, has a planar aromatic cyclopentadienyl-ion-like structure. However, at the G3B3 level, there are three low-energy isomers for BC2P2H3: 1),tricyclopentane, 2),nido and 3),vinylcyclopropenyl-type structures, all within 1.7,kcal,mol,1 of each other. On the contrary, for the dianionic species the cyclic planar structure is still the minimum. In comparison to the isolobal Cp+ and HnCnP5,n+ isomers, BC2P2H3 shows a competition between ,-delocalised vinylcyclopropenyl- and cluster-type structures (nido and tricyclopentane). Substitution of H on C by tBu, and H on B by Ph, in BC2P2H3 increases the energy difference between the low-lying isomers, giving the lowest energy structure as a tricyclopentane type. Similar substitution in BC2P2H32, merely favours different positional isomers of the cyclic planar geometry, as observed in 1),isoelectronic neutral heterodiphospholes EtBu2C2P2 (E=S, Se, Te), 2),monoanionic heterophospholyl rings EtBu2C2P2 (E=P,, As,, Sb,) and 3),polyphospholyl rings anions tBu5,nCnP5,n (n=0,5). The principal factors that affect the stability of three-, four-, and five-membered ring and acyclic geometrical and positional isomers of neutral and dianionic BC2P2H3 isomers appear to be: 1),relative bond strengths, 2),availability of electrons for the empty 2p boron orbital and 3),steric effects of the tBu groups in the HBC2P2tBu2 systems. [source] Studies on Chromatographic Properties of Perhydroxycucurbit[6]uril as a New Type of Gas Chromatographic Column Packing MaterialCHINESE JOURNAL OF CHEMISTRY, Issue 2 2008Lai-Sheng LI Abstract Perhydroxycucurbit[6]uril {(HO)12CB[6]} has been used successfully as a stationary phase for packed column gas chromatography for the first time. Perhydroxycucurbit[6]uril stationary phase (PSP) exhibited wide operational temperature, outstanding thermostability and good selectivities to various organic compounds, such as alkanes, aromatic hydrocarbons, alcohols, esters, ketones, amines, etc. It was also found that some positional isomers, such as disubstituted benzenes could be well separated on this column. PSP has excel1ent separation abilities to some complicate samples, for example, commercial toilet water. Some mechanism of the new packing for GC-separation was preliminarily discussed. It was observed that the partial inclusion complexation of PSP with analytes could improve separation selectivity and column efficiency, instead of complete inclusion. Moreover, PSP exhibited low baseline shift even at dramatically programmed temperature for complicate samples covering a wide boiling point range so as to fast assay. [source] | |||||||||||||||||||||||||