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1.
The near-infrared (NIR) absorption of toluene-sulfonate-diacetylene crystals (PTS) has been investigated during thermal polymerization. It is shown by comparative NIR and IR spectroscopy of deuterated and of protonated PTS at various temperatures, that these absorptions are vibronic in nature. They can be assigned unambiguously to distinct parts of the molecule. No low-lying electronic state has been found. 相似文献
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M. Morgan H. M. D. R. Herath P. J. Cabot P. N. Shaw A. K. Hewavitharana 《Analytical and bioanalytical chemistry》2012,404(10):3111-3121
Dynorphin A 1–17 (DYN A) is an endogenous neuropeptide that is of interest due to its diverse roles in analgesia, inflammation and addiction. Upon release, DYN A is subject to metabolism by a range of enzymes and its biotransformation is dependent on the site and environment into which it is released. In this study, we investigated the biotransformation of DYN A in rat inflamed tissue at pH?7.4 and 5.5, in rat serum and in trypsin solution. DYN A-porcine was incubated at 37?°C in each matrix over a range of incubation periods. The resultant fragments were separated using a C4 column and detected by mass spectrometry using total ion current mode. Incubation of DYN A in trypsin solution and in rat serum resulted in 6 and 14 fragments, respectively. Incubation in inflamed rat paw tissue occasioned 21 fragments at pH?7.4 and 31 fragments at pH?5.5. Secondary breakdown of some larger primary fragments was also observed in this study. 相似文献
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Ondeykal JG Herath KB Jayasuriya H Polishook JD Bills GF Dombrowski AW Mojena M Koch G DiSalvo J DeMartino J Guan Z Nanakorn W Morenberg CM Balick MJ Stevenson DW Slattery M Borris RP Singh SB 《Molecular diversity》2005,9(1-3):123-129
The chemokines (CXCL9, CXCL10 and CXCL11) and associated CXCR3 receptor are expressed during the inflammatory process from multiple sclerosis, atherosclerosis or organ transplantation resulting in the recruitment of lymphocytes leading to tissue damage. It is hypothesized that blocking of the ligand/CXCR3 receptor interaction has potential to provide opportunity for development of agents that would block tissue rejection. In this paper, four classes of natural product inhibitors (IC50 ranging 0.1–41 M) have been described that block the CXCR3 receptor interaction of IP-10 ligand. These include a cyclic thiopeptide (duramycin), polyketide glycosides (roselipins), steroidal glycosides (hypoglausin A and dioscin) and a novel alkyl pyridinium alkaloid that were isolated by bioassay-guided fractionation of the organic extracts derived from actinomycete, fungal, plant and marine sources and discovered using 125 I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC50 of 0.1 M. Roselipins 2A, 2B and 1A showed IC50 values of 14.6, 23.5, and 41 M, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC50 values of 2.1, 0.47 and 3 M, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC50 of 0.67 M. 相似文献
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Microbial metabolism of the cancer chemopreventive agent, curcumin [(1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione] (1) with Pichia anomala (ATCC 20170) yielded four major metabolites, 5-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)heptan-3-one (2), 5-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl)heptan-3-one (3), 1,7-bis(4-hydroxy-3-methoxyphenyl)heptan-3,5-diol (4), 5-hydroxy-1,7-bis(4-hydroxyphenyl)heptane-3-one (5) and two minor products, 1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)heptane-3,5-diol (6) and 1,7-bis(4-hydroxyphenyl)heptane-3,5-diol (7). The structures of compounds 2-5 were established on the basis of spectroscopic data. Compounds 6 and 7 were assigned tentative structures. 相似文献
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Apsara K. Herath Manoj R. Bhandari Delphine Gout Muhammed Yousufuddin Carl J. Lovely 《Tetrahedron letters》2017,58(41):3913-3918
The utility of the thio acid-azide coupling reaction to afford amides is explored in imidazole-containing substrates for application in the total synthesis of examples of oroidin alkaloids. Good yields of the expected amides are obtained in both monomeric and dimeric substrates. Bis azides react preferentially at the 2-azido position but hydrosulfenylation and reduction interfere. 2-Thiophenyl and 2-oxo groups were evaluated as 2-amino surrogates, the thioether delivered the expected amide, whereas 2-imidazolone gave a mixture of the expected amide and the hydrosulfenylation product. 相似文献
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Hewavitharana AK Herath HM Shaw PN Cabot PJ Kebarle P 《Rapid communications in mass spectrometry : RCM》2010,24(24):3510-3514
Beta-endorphin was used as a model peptide to study the effect of solvent and electrospray mass spectrometer parameters in the optimisation of an assay method for multiply charged compounds using liquid chromatography/mass spectrometry (LC/MS). Unlike with singly charged compounds, the charge state distribution has a significant impact in the method development of multiply charged compounds such as peptides. Using a 50% acetonitrile/water solvent mixture, we found that the ion spray voltage had no influence on the charge state distribution. However, increasing declustering potential led to deprotonation of the higher charge states of the peptide thus causing a shift to lower charge states. The mechanism leading to the deprotonation was examined. It was concluded that the deprotonation is due to endoergic proton transfer from the peptide to solvent molecules clustered to the peptide that occurs in the declustering region. The extent of deprotonation increases with increasing proton affinity of the molecules of the non-aqueous solvent component used. Thus, if desired, deprotonation can be avoided by selecting a low proton affinity solvent such as methanol. The focusing potential was also found to have a great influence on the charge state distribution observed. The results of this study enabled us to select the optimum ion to be used in single ion/reaction monitoring mode. They also provided the most favourable parameter values to be used in the method to obtain the best sensitivity for the ion of choice. The results demonstrate the importance of considering the charge state distribution in the optimisation of electrospray LC/MS methods for multiply charged compounds. 相似文献
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H. M. D. R. Herath P. N. Shaw P. Cabot A. K. Hewavitharana 《Rapid communications in mass spectrometry : RCM》2010,24(11):1502-1506
The high‐performance liquid chromatography (HPLC) column is capable of enrichment/pre‐concentration of trace impurities in the mobile phase during the column equilibration, prior to sample injection and elution. These impurities elute during gradient elution and result in significant chromatographic peaks. Three types of purified water were tested for their impurity levels, and hence their performances as mobile phase, in HPLC followed by total ion current (TIC) mode of MS. Two types of HPLC‐grade water produced 3–4 significant peaks in solvent blanks while LC/MS‐grade water produced no peaks (although peaks were produced by LC/MS‐grade water also after a few days of standing). None of the three waters produced peaks in HPLC followed by UV‐Vis detection. These peaks, if co‐eluted with analyte, are capable of suppressing or enhancing the analyte signal in a MS detector. As it is not common practice to run solvent blanks in TIC mode, when quantification is commonly carried out using single ion monitoring (SIM) or single or multiple reaction monitoring (SRM or MRM), the effect of co‐eluting impurities on the analyte signal and hence on the accuracy of the results is often unknown to the analyst. Running solvent blanks in TIC mode, regardless of the MS mode used for quantification, is essential in order to detect this problem and to take subsequent precautions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Castro-Perez J Roddy TP Nibbering NM Shah V McLaren DG Previs S Attygalle AB Herath K Chen Z Wang SP Mitnaul L Hubbard BK Vreeken RJ Johns DG Hankemeier T 《Journal of the American Society for Mass Spectrometry》2011,22(9):1552-1567
A high content molecular fragmentation for the analysis of phosphatidylcholines (PC) was achieved utilizing a two-stage [trap (first generation fragmentation) and transfer (second generation fragmentation)] collision-induced dissociation (CID) in combination with travelling-wave ion mobility spectrometry (TWIMS). The novel aspects of this work reside in the fact that a TWIMS arrangement was used to obtain a high level structural information including location of fatty acyl substituents and double bonds for PCs in plasma, and the presence of alkali metal adduct ions such as [M?+?Li]+ was not required to obtain double bond positions. Elemental compositions for fragment ions were confirmed by accurate mass measurements. A very specific first generation fragment ion m/z 577 (M-phosphoryl choline) from the PC [16:0/18:1 (9Z)] was produced, which by further CID generated acylium ions containing either the fatty acyl 16:0 (C15H31CO+, m/z 239) or 18:1 (9Z) (C17H33CO+, m/z 265) substituent. Subsequent water loss from these acylium ions was key in producing hydrocarbon fragment ions mainly from the α-proximal position of the carbonyl group such as the hydrocarbon ion m/z 67 (+H2C-HC?=?CH-CH?=?CH2). Formation of these ions was of important significance for determining double bonds in the fatty acyl chains. In addition to this, and with the aid of 13C labeled lyso-phosphatidylcholine (LPC) 18:1 (9Z) in the ω-position (methyl) TAP fragmentation produced the ion at m/z 57. And was proven to be derived from the α-proximal (carboxylate) or distant ω-position (methyl) in the LPC. 相似文献