Quantitative mass spectrometry for bacterial protein toxins--a sensitive, specific, high-throughput tool for detection and diagnosis

Matrix-assisted laser-desorption time-of-flight (MALDI-TOF) mass spectrometry (MS) is a valuable high-throughput tool for peptide analysis. Liquid chromatography electrospray ionization (LC-ESI) tandem-MS provides sensitive and specific quantification of small molecules and peptides. The high analytic power of MS coupled with high-specificity substrates is ideally suited for detection and quantification of bacterial enzymatic activities. As specific examples of the MS applications in disease diagnosis and select agent detection, we describe recent advances in the analyses of two high profile protein toxin groups, the Bacillus anthracis toxins and the Clostridium botulinum neurotoxins. The two binary toxins produced by B. anthracis consist of protective antigen (PA) which combines with lethal factor (LF) and edema factor (EF), forming lethal toxin and edema toxin respectively. LF is a zinc-dependent endoprotease which hydrolyzes specific proteins involved in inflammation and immunity. EF is an adenylyl cyclase which converts ATP to cyclic-AMP. Toxin-specific enzyme activity for a strategically designed substrate, amplifies reaction products which are detected by MALDI-TOF-MS and LC-ESI-MS/MS. Pre-concentration/purification with toxin specific monoclonal antibodies provides additional specificity. These combined technologies have achieved high specificity, ultrasensitive detection and quantification of the anthrax toxins. We also describe potential applications to diseases of high public health impact, including Clostridium difficile glucosylating toxins and the Bordetella pertussis adenylyl cyclase.     

KMgF3:Ni2+晶体的占位、局部结构、吸收光谱和顺磁g因子的统一解释

利用完全对角化方法和强场耦合方案,采用半自洽场(semi-SCF)自由Ni2+的d轨道模型和Ni2+-6X-(x=F,Cl,Br,I)络合物的μ-κ-α模型研究,建立了含有过渡族金属离子的晶体的局域结构与吸收光谱和顺磁g因子之间的定量关系,对KMgF3:Ni2+晶体的占位、局域结构、吸收光谱和顺磁g因子作出了统一解释,预测了KMgF3:Ni2+晶体的光谱精细结构.所得理论计算结果与实验值符合得很好.     

Surface analysis of polymers and catalysts

Summary The use of solid-state mass spectrometry for studying polymers is evaluated. Structural differences between polymers can be obtained by laser mass spectrometry by observing fingerprint-like spectra in the range m/z<250. Secondary-ion mass spectra (SIMS) revealed fragments that show the spacing of the repeat unit of the polymer up to m/ z 3,500. Oligomer distributions of low molecular weight polymers can be estimated by laser mass spectrometry. The order of monomer addition can be estimated by measuring three-carbon fragment ions in polyvinylidene fluoride. The value of SIMS for studying surface reactions is reviewed. Detection of surface impurities on polymer surfaces is possible using the laser microprobe LAMMA-1000. The specific example discussed involves detecting dye molecules on polystyrenes.The use of X-ray photoelectron spectroscopy (ESCA) for the study of supported catalysts is evaluated. Variations of the surface structure and reactivity of the deposited phase, brought about by changing the active phase loading, some preparation variables or by modifying the carrier, were monitored by ESCA. The results were compared to those obtained from classical methods such as transmission electron microscopy, chemisorption and gravimetric measurements; they correlated with catalytic behavior.

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Oberflächenanalyse von Polymeren und Katalysatoren

Zusammenfassung Der Einsatz der Festkörper-Massenspektrometrie zur Untersuchung von Polymeren wird bewertet. Strukturunterschiede bei Polymeren können durch Laser-Massenspektrometrie erhalten werden, indem fingerprintähnliche Spektren im Bereich m/z < 250 beobachtet werden. Sekundärionen-Massenspektren (SIMS) offenbaren Fragmente, welche die Länge der Basiszellen bei Polymeren bis zu m/z-Werten von 3500 anzeigen. Oligomerverteilungen von Polymeren mit kleinerem Molekulargewicht können durch Laser-Massenspektrometrie beurteilt werden. Der Grad einer Monomerenaddition kann durch Messung von C₃-Fragment-Ionen in Polyvinylidenfluorid erkannt werden. Ein Überblick über die Bedeutung von SIMS für die Untersuchung von Oberflächenreaktionen wird gegeben. Der Nachweis von Verunreinigungen auf Polymer-Oberflächen gelingt durch den Einsatz der Laser-Mikrosonde LAMMA-1000. Das angeführte Beispiel enthält auch den Nachweis von Farbstoffmolekülen auf Polystyrolen.Die Anwendung der Röntgen-Photoelektronenspektroskopie (ESCA) zur Untersuchung von Trägerkatalysatoren wird ebenfalls bewertet. Änderungen der Oberflächenstruktur und der Reaktivität der aufgebrachten Phase, die durch Änderungen der Phasenbeschichtung oder gewisser Präparationsparameter oder durch Trägermodifizierung verursacht wurden, sind mit Hilfe von ESCA kontrolliert worden. Die Ergebnisse wurden mit denen verglichen, die mit Hilfe klassischer Methoden gewonnen wurden, wie Transmissionselektronenmikroskopie, Chemiesorption und gravimetrische Bestimmungen; sie korrelieren mit dem katalytischen Verhalten.

     

Measurement of the surface coverage of V/Al2O3 catalysts by infrared spectroscopy, CO2 chemisorption and ion scattering spectroscopy

Quantitative FTIR studies of alumina hydroxyl groups have been used to measure the surface coverage of V/Al₂O₃ catalysts. The IR spectra show a preferential consumption of the most basic hydroxyls (3769 cm^–1) with the initial V uptake. The integrated area of the hydroxyl region was used to calculate the surface coverage of the catalysts. The surface coverage increased to 0.63 as the V loading increased to 6.7 wt%. The surface coverage results obtained from IR were compared to those measured by ion scattering spectroscopy (ISS) and CO₂ chemisorption. The surface coverages measured by ISS were comparable to those obtained by IR. In contrast, CO₂ chemisorption appears to overestimate the surface coverage of the catalysts. The overestimation of the surface coverage by the CO₂ chemisorption method is attributed to the preferential adsorption of the V phase onto the most basic hydroxyls, the same sites which interact with CO₂.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Quantitative surface characterization using X-ray photoelectron spectroscopy

Use of X-ray Photoelectron Spectroscopy (XPS) for quantitative surface analysis is reviewed. Examples chosen are from our research on heterogeneous catalysts. XPS is useful for measuring distributions of oxidation states because of significant chemical shifts for many elements. However, linewidths complicate analysis of mixtures, necessitating the use of data analysis methodology. Use of factor analysis or deconvolution with non-linear least squares curve fitting gives useful protocols. Five important questions are posed, and some examples of solutions are presented: 1) How many components are present? 2) Where are they located? 3) What do they look like? 4) How much of each component is present? 5) How good is the answer?     

Polymer characterization by combining liquid chromatography with MALDI and ESI mass spectrometry

High-performance polymers are complex mixtures of materials of different size and chemical composition and with different end groups and architecture. To determine the molecular heterogeneity of such systems, hyphenation of several techniques is required. The value of coupling mass spectrometry (MS) with separation techniques has already been recognized - such methods have proved to be among the most powerful for molecular characterization of complex polymer systems.The review focuses on matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) MS coupled with liquid chromatography (LC). Such hyphenation has been used for most polymer analysis by mass spectrometry coupled with separation techniques. The advantages and/or limitations of these techniques for polymer characterization are discussed. Future prospects are briefly outlined.     

Investigation of porphyrins and metalloporphyrins by liquid matrix-assisted laser desorption mass spectrometry

Laser desorption mass spectrometry with liquid matrix-assistance has been used to study a series of selected porphyrins and metalloporphyrins. This work presents the results of using a liquid matrix with fibrous material as the substrate for liquid matrix assisted laser desorption of porphyrins and metalloporphyrins. The liquid matrices used for porphyrin studies were o-nitrophenyl octyl ether (NPOE) and 15-crown-5. The use of a liquid matrix with soft laser ionization enhances molecular ion formation. We also have investigated the use of NPOE as a liquid matrix for identifying mixtures of up to six porphyrins in a single shot spectrum without prior separation. The (M + H)⁺ peak of each metalloporphyrin component in the mixture is clearly indicated in the spectra and no obvious interference effects were observed.     

Studies of pesticides by collision-induced dissociation, postsource-decay, matrix-assisted laser desorption/ionization time of flight mass spectrometry

The use of collision-induced dissociation, postsource decay (CID-PSD) matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of small organic molecules is demonstrated. Three pesticides: paraquat, diquat, and difenzoquat were chosen for this study. The matrices 2,5-dihydroxybenzoic acid (DHB), alpha-cyano-4-hydroxycinnamic acid (alpha-CHCA), and sinapinic acid (SA) were selected to investigate the effect of the matrix on the CID-PSD MALDI spectra of these molecules. Alpha-CHCA and DHB were found to be appropriate matrices for the pesticides studied. Spectra for a given pesticide obtained from different matrices were compared with each other, and the differences between them are discussed. A comparison of CID-PSD MALDI with fast-atom bombardment MS/MS spectra is presented; the agreement of pesticide fragmentation patterns between the two methods indicates that CID-PSD MALDI MS is a reliable and efficient technique for structural elucidation of small molecules.     

Application of cross-correlation analysis to EXAFS: Investigation of the cobalt phase on boron modified cobalt/alumina catalysts

Boron modified Co/Al₂O₃ catalysts, previously characterized by ESCA, are examined by EXAFS. A method of data analysis based on cross-correlation of the (E) spectra is used to determine the relative amounts of Co₃O₄ and cobalt surface phase present on the catalysts. The results are compared with those obtained previously by ESCA. The EXAFS analysis agrees well with the ESCA results. No gas-phase reactions were required to elucidate the relative proportion of cobalt species by EXAFS as is necessary for the ESCA analysis.     

Selection of internal standards for quantitative analysis by matrix-assisted laser desorption-ionization (MALDI) time-of-flight mass spectrometry

 The selection of an appropriate internal standard (IS) for quantification by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is critical for the successful application of quantitative MALDI. Selection of the IS depends on the chemical similarity of the analyte and IS and the mass separation of the analyte and IS as a function of instrumental peak resolution. For the quantification of bovine insulin, a series of internal standards including horse heart cytochrome C, bovine insulin chain B, des-pentapeptide human insulin, and des-octapeptide porcine insulin was investigated. Des-pentapeptide human insulin was found to be the most appropriate internal standard (relative standard deviation of the standard curve slope=2.99%, correlation coefficient=0.988 in the range of 0.5–0.4 μmol/L). Two methods for measuring of the MALDI signal intensity were evaluated, direct peak integration following subtraction of a linear background and non-linear least squares curve fitting. The results obtained with these methods were equivalent. Received: 10 November 1995 / Revised: 4 March 1996 / Accepted: 6 March 1996