The Separation and Identification of Higher Molecular Weight Fullerenes

A nonaqueous, reversed-phase separation of the fullerenes is described. The bonded-phase, a polymeric octadecyl one, has previously been shown to have a very large separating power for nonplanar polycyclic aromatic hydrocarbons. This work shows that this shape selectivity also is found with the fullerenes, allowing very short retention times while maintaining separation of the C₆₀ and C₇₀ species. Additionally, a fraction containing larger fullerenes was isolated. UV absorbance spectra of these species were obtained. Preliminary spectra of hydrogen chemical ionization mass spectra were also obtained and showed that the fullerenes adsorb large amounts of molecular hydrogen.     

Investigations of the uptake of dimethylsulfoniopropionate by phytoplankton

No change here: Analysis with doubly labeled [(13)C(2)D(6)]DMSP and LC/MS revealed that dissolved DMSP is taken up and stored intracellularly by diverse phytoplankton species without transformation. This is even true for species that produce no quantifiable amounts of DMSP themselves.     

Simultaneous Multiple MS Binding Assays for the Dopamine,Norepinephrine, and Serotonin Transporters

In this work, we present label‐free, mass‐spectrometry‐based binding assays (MS Binding Assays), targeting the human dopamine, norepinephrine, and serotonin transporters (hDAT, hNET, and hSERT) in simultaneous binding experiments. Using a validated LC–ESI‐MS/MS method for quantification of the selective dopamine transporter inhibitor (R,R)‐4‐(2‐benzhydryloxyethyl)‐1‐(4‐fluorobenzyl)piperidin‐3‐ol ((R,R)‐D‐84), the selective norepinephrine transporter inhibitor (S,S)‐reboxetine, and the selective serotonin reuptake inhibitor (S)‐citalopram, binding affinities at the three monoamine transporters could be characterized simultaneously in a single binding experiment. The performed simultaneous saturation and competition experiments yielded results that are in good accordance with those determined in MS Binding Assays addressing the monoamine transporters individually. The results obtained from this study underscore the potential of MS Binding Assays for simultaneous affinity determination at different targets, which is difficult to accomplish with conventional radioligand binding assays.     

MS-binding assays: kinetic, saturation, and competitive experiments based on quantitation of bound marker as exemplified by the GABA transporter mGAT1

A new kind of binding assay is described in which the amount of a nonlabeled marker bound to the target is quantified by LC-ESI-MS-MS. This new approach was successfully implemented with nonlabeled NO 711 as marker and the GABA transporter subtype mGAT1 as target. The native marker bound to the target was liberated from the receptor protein by methanol denaturation after filtration. A reliable and sensitive LC-ESI-MS-MS method for the quantitation of NO 711 was developed, and data from mass spectrometric detection were analyzed by nonlinear regression. Kinetic MS-binding experiments yielded values for k+1 and k-1, while in saturation MS-binding experiments, Kd and Bmax values were determined. In competitive MS-binding experiments, Ki values were obtained for various test compounds covering a broad range of affinities for mGAT1. All experiments were performed in 96-well plate format with a filter plate for the separation step which improved the efficiency and throughput of the procedure. The method was validated by classical radioligand-binding experiments with the labeled marker [3H2]NO 711 in parallel. The results obtained from MS-binding experiments were found to be in good agreement with the results of the radioligand-binding assays. The new kind of MS-binding assay presented herein is further adapted to the conventional radioligand-binding assay in that the amount of bound marker is securely quantified. This promises easy implementation in accordance with conventional binding assays without the major drawbacks that are inherent in radioligand or fluorescence binding assays. Therefore, MS-binding assays are a true alternative to classical radioligand-binding assays.     

Identification of luciferyl adenylate and luciferyl coenzyme a synthesized by firefly luciferase

The firefly luciferase reaction intermediate luciferyl adenylate was detected by RP-HPLC analysis when the luciferase reaction was performed under a nitrogen atmosphere. Although this compound is always specified as an intermediate in the light-production reaction, this is the first report of its identification by HPLC in a luciferase assay medium. Under a low-oxygen atmosphere, luciferase can catalyze the synthesis of luciferyl coenzyme A from luciferin, ATP, and coenzyme A, but in air dehydroluciferyl coenzyme A was produced. The luciferase-catalyzed synthesis of these coenzyme A derivatives may be a consequence of the postulated recent evolutionary origin of firefly luciferases from an ancestral acyl-coenzyme A synthetase.     

The Biosynthesis of the Aroma Volatile 2‐Methyltetrahydrothiophen‐3‐one in the Bacterium Chitinophaga Fx7914

2‐Methyltetrahydrothiophen‐3‐one ( 3 ) is a volatile compound that plays an important role especially in food and flavour chemistry because it contributes to the aroma of several foodstuffs including wine. Although 3 can be formed by chemical reactions during food preparation, it is also produced by microorganisms. Recent studies with yeasts showed that methionine ( 1 ) is a potential precursor of 3 , but the mechanism of the transformation is unknown. The biosynthetic pathway leading to 3 in the bacterium Chitinophaga Fx7914 was probed. Extensive feeding experiments with differently labelled precursors by using liquid cultures of Chitinophaga Fx7914 were performed. The volatiles released by the bacterium were collected by using a closed loop stripping apparatus (CLSA) and analysed by GC–MS. The observed incorporation pattern of the precursors into 3 led to the elucidation of the biosynthetic pathway. One part of the compound 2 originates from homocysteine ( 15 ), which is transformed into 3‐mercaptopropanal ( 17 ). The second biosynthetic building block is pyruvate ( 14 ). An acyloin‐forming reaction furnishes the key intermediate 21 , which cyclises intramolecularly to a diol. Dehydration followed by tautomerisation lead to the cyclic ketone 3 , which is produced by the bacterium in racemic form.     

Identification,Quantification, and Determination of the Absolute Configuration of the Bacterial Quorum‐Sensing Signal Autoinducer‐2 by Gas Chromatography–Mass Spectrometry

Sensing the signal : A gas chromatography–mass spectrometry (GC–MS) method for the analysis of the quorum‐sensing autoinducer‐2 is described. It allows, for the first time, the direct analysis and accurate determination of this highly water soluble signaling compound, which exists in complex equilibria. The application on the caries‐causing bacterium Streptococcus mutans is described.

     

高效液相色谱法直接测定烷基苯磺酸钠的平均相对分子质量

直接用高效液相色谱法将烷基苯磺酸钠按碳数分布分离 ,计算其平均相对分子质量 ;用紫外检测器和电喷雾 ( ESI)质谱进行检测的测定结果均与脱磺基气相色谱法的测定结果一致 ,重复性良好 ,且更为快速简便。     

液相色谱-串联质谱法测定化妆品中多种激素

采用液相色谱-串联质谱法测定化妆品中糖皮质激素、雌激素、雄激素、孕激素等激素的含量。不同形态的化妆品样品以甲醇为提取剂进行超声提取,样品提取液离心后得到上清液经HLB固相萃取小柱净化,用Agilent ZORBAXEclipse XDB-C18柱(1.8μm,2.1 mm×50 mm),乙腈-水作为流动相,梯度洗脱,流速0.3 mL/min,柱温25℃,进样量2.0μL,糖皮质激素、雄激素、孕激素采用正离子扫描模式,雌激素采用负离子扫描模式,多反应监测测定。化妆品样品平均加标回收率为72.31%~97.89%,相对标准偏差为2.24%~11.34%,方法检出限为0.002 mg/kg~0.8 mg/kg。     

Rapid Screening,Identification, Separation,and Purification of Four Bioactive Compounds from Swertia mussotii Franch

Gentiopicroside, mangiferin, sweroside, and isoorientin, the bioactive constituents of Swertia mussotii Franch, have various pharmacological effects, and are used in particular for treating liver disorders. However, efficient methods for their separation are not currently available. In this study, these bioactive compounds were detected in S. mussotii extracts using high-performance liquid chromatography coupled with mass spectrometry, and separated using a combination of high-speed counter-current chromatography and Sephadex LH-20 column chromatography. Their structures were determined by using ¹H and ¹³C nuclear magnetic resonance spectroscopies. The results show that this method is effective for the separation and purification of bioactive compounds from S. mussotii.     

Biosynthesis and identification of volatiles released by the myxobacterium Stigmatella aurantiaca

The volatiles released by agar plate cultures of two strains of the myxobacterium Stigmatella aurantiaca (strains Sg a15 and DW4/3-1) were collected in a closed-loop stripping apparatus (CLSA) and analyzed by GC-MS. Large numbers of substances from different compound classes (ketones, esters, lactones, terpenes, and sulfur and nitrogen compounds) were identified; several of them are reported from natural sources for the first time. The volatiles 2-methyltridecan-4-one (17), its isomer 3-methyltridecan-4-one (20), and the higher homologue 2-methyltetradecan-4-one (18) were identified in the extracts of both strains and were synthesized. In addition, strain Sg a15 produced 2,12-dimethyltridecan-4-one (19), 2-methyltridec-2-en-4-one (23), and a series of phenyl ketones, among them 1-phenyldecan-1-one (14) and 9-methyl-1-phenyldecan-1-one (16), whereas strain DW4/3-1 emitted traces of 10-methylundecan-2-one (21). The biosynthesis of 14 and 16 was examined in feeding experiments with deuterated precursors carried out on agar plate cultures. The leucine-derived starter unit isovalerate was shown to be incorporated into 16, as was phenylalanine-derived benzoic acid into both 14 and 16. The results point to formation both of the phenyl ketones and of the structurally related aliphatic ketones through an unusual head-to-head coupling between a starter unit such as benzoyl-CoA and a fatty acyl-CoA, followed by decarboxylation.     

液相色谱及液质联用技术在环境分析中的应用

高效液相色谱（HPLC）是在经典液相色谱法和气相色谱法的基础上发展起来的新型分离分析技术。20世纪80、90年代后,HPLC技术发展迅速,特别是21世纪初,液相色谱与现代质谱的联机技术有了很大的发展,使HPLC的应用前景更为广阔。在全部已知的有机化合物中近80％的有机化合物属于挥发性低,易受热分解或者大分子化合物,适合于高效液相色谱进行分析。本文主要从HPLC分析方法的特点为切入点,介绍液相色谱及液质联用技术在环境分析中的应用。     

The expanding role of mass spectrometry in metabolite profiling and characterization

Mass spectrometry has a strong history in drug-metabolite analysis and has recently emerged as the foremost technology in endogenous metabolite research. The advantages of mass spectrometry include a wide dynamic range, the ability to observe a diverse number of molecular species, and reproducible quantitative analysis. These attributes are important in addressing the issue of metabolite profiling, as the dynamic range easily exceeds nine orders of magnitude in biofluids, and the diversity of species ranges from simple amino acids to lipids to complex carbohydrates. The goals of the application of mass spectrometry range from basic biochemistry to clinical biomarker discovery with challenges in generating a comprehensive profile, data analysis, and structurally characterizing physiologically important metabolites. The precedent for this work has already been set in neonatal screening, as blood samples from millions of neonates are tested routinely by mass spectrometry as a diagnostic tool for inborn errors of metabolism. In this review, we will discuss the background from which contemporary metabolite research emerged, the techniques involved in this exciting area, and the current and future applications of this field.     

ValC, a new type of C7-Cyclitol kinase involved in the biosynthesis of the antifungal agent validamycin A

The gene valC, which encodes an enzyme homologous to the 2-epi-5-epi-valiolone kinase (AcbM) of the acarbose biosynthetic pathway, was identified in the validamycin A biosynthetic gene cluster. Inactivation of valC resulted in mutants that lack the ability to produce validamycin A. Complementation experiments with a replicating plasmid harboring full-length valC restored the production of validamycin A, thus suggesting a critical function of valC in validamycin biosynthesis. In vitro characterization of ValC revealed a new type of C7-cyclitol kinase, which phosphorylates valienone and validone--but not 2-epi-5-epi-valiolone, 5-epi-valiolone, or glucose--to afford their 7-phosphate derivatives. The results provide new insights into the activity of this enzyme and also confirm the existence of two different pathways leading to the same end-product: the valienamine moiety common to acarbose and validamycin A.     

Characterization of bisphenol A–based epoxy resins by HPLC,GPC, GPC–MALLS,VPO, viscometry,and end group analysis: On the identification of 2,3‐dihydroxypropyl‐containing compounds,determination of molar mass distribution,and branching

Reversed‐phase high performance liquid chromatography (HPLC), conventional gel permeation chromatography (GPC), and gel permeation chromatography coupled with a multiangle laser light scattering photometer (GPC–MALLS) were used for the analysis of epoxy resins based on bisphenol A. Compounds containing 2,3‐dihydroxypropyl group were identified in HPLC chromatograms by means of the derivatization of sample by acetone. The presence of branched molecules was proved by GPC–MALLS using a molar mass versus root mean square (RMS) radius plot or molar mass versus elution volume plot. The molar mass distribution determined by HPLC was compared with that obtained by GPC–MALLS. Molar mass averages measured by means of GPC, GPC–MALLS, vapor pressure osmometry (VPO), and end group analysis (EG) were compared and the differences of results obtained by particular methods were discussed. An appropriate GPC calibration was found on the basis of literature data and the comparison of molar mass averages measured by GPC, VPO, and GPC–MALLS. The refractive index increment of epoxy resins was determined. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2432–2438, 1999     

Surface-plasmon-resonance-based chemical proteomics: efficient specific extraction and semiquantitative identification of cyclic nucleotide-binding proteins from cellular lysates by using a combination of surface plasmon resonance, sequential elution and liquid chromatography-tandem mass spectrometry

Chemical proteomics is a powerful methodology for identifying the cellular targets of small molecules, however, it is biased towards abundant proteins. Therefore, quantitative strategies are needed to distinguish between specific and nonspecific interactions. Here, we explore the potential of the combination of surface plasmon resonance (SPR) coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS) as an alternative approach in chemical proteomics. We coupled cGMP molecules to the SPR chip, and monitored the binding and dissociation of proteins from a human lysate by using sequential elution steps and SPR. The eluted proteins were subsequently identified by LC-MS/MS. Our approach enabled the efficient and selective extraction of low-abundant cyclic-nucleotide-binding proteins such as cGMP-dependent protein kinase, and a quantitative assessment of the less- and nonspecific competitive binding proteins. The data show that SPR-based chemical proteomics is a promising alternative for the efficient specific extraction and quantitative identification of small-molecule-binding proteins from complex mixtures.