MALDI Mass Spectrometry Imaging of Neuronal Cell Cultures

Mass spectrometry imaging (MSI) provides the ability to detect and identify a broad range of analytes and their spatial distributions from a variety of sample types, including tissue sections. Here we describe an approach for probing neuropeptides from sparse cell cultures using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MSI—at single cell spatial resolution—in both MS and tandem MS modes. Cultures of Aplysia californica neurons are grown on an array of glass beads embedded in a stretchable layer of Parafilm M. As the membrane is stretched, the beads/neurons are separated physically and the separated beads/neurons analyzed via MALDI TOF MS. Compared with direct MS imaging of samples, the stretching procedure enhances analyte extraction and incorporation into the MALDI matrix, with negligible analyte spread between separated beads. MALDI tandem MSI using the stretched imaging approach yields localization maps of both parent and fragment ions from Aplysia pedal peptide, thereby confirming peptide identification. This methodology represents a flexible platform for MSI investigation of a variety of cell cultures, including functioning neuronal networks.     

Absolute rate constants of decay of aryl-substituted carbonyl oxides

The decay kinetics of a series of carbonyl oxides (CbO)—4-methylbenzophenone oxide, 2,5-dimethylbenzophenone oxide, 4-chlorobenzophenone oxide, 2-bromobenzophenone oxide, and acetophenone oxide—were studied by the pulse photolysis technique in acetonitrile, benzene,n-decane, andn-pentane. The absorption spectra were studied, and the absorption coefficients and absolute rate constants of CbO decay were determined. The absorption maxima observed in the spectra of carbonyl oxides range within 405±25 nm. The decay rate constant was found to depend on both the CbO structure and the medium. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 677–681, April, 1999.     

Evaluation of standard and advanced preprocessing methods for the univariate analysis of blood serum 1H-NMR spectra

Proton nuclear magnetic resonance (¹H-NMR)-based metabolomics enables the high-resolution and high-throughput assessment of a broad spectrum of metabolites in biofluids. Despite the straightforward character of the experimental methodology, the analysis of spectral profiles is rather complex, particularly due to the requirement of numerous data preprocessing steps. Here, we evaluate how several of the most common preprocessing procedures affect the subsequent univariate analyses of blood serum spectra, with a particular focus on how the standard methods perform compared to more advanced examples. Carr–Purcell–Meiboom–Gill 1D ¹H spectra were obtained for 240 serum samples from healthy subjects of the Asklepios study. We studied the impact of different preprocessing steps—integral (standard method) and probabilistic quotient normalization; no, equidistant (standard), and adaptive-intelligent binning; mean (standard) and maximum bin intensity data summation—on the resonance intensities of three different types of metabolites: triglycerides, glucose, and creatinine. The effects were evaluated by correlating the differently preprocessed NMR data with the independently measured metabolite concentrations. The analyses revealed that the standard methods performed inferiorly and that a combination of probabilistic quotient normalization after adaptive-intelligent binning and maximum intensity variable definition yielded the best overall results (triglycerides, R = 0.98; glucose, R = 0.76; creatinine, R = 0.70). Therefore, at least in the case of serum metabolomics, these or equivalent methods should be preferred above the standard preprocessing methods, particularly for univariate analyses. Additional optimization of the normalization procedure might further improve the analyses.     

基体归一定量技术在激光烧蚀-等离子体质谱法锆石原位多元素分析中的应用

探讨了内标法和基体归一法校准的基本原理。基体归一校准法的基本步骤为:先用简单外标法测得样品中尽可能全的主、次、痕量元素含量,氧化物加和后进行100%归一,得到灵敏度校正系数,对所有元素的测定结果进行修正。修正结果的可靠性在很大程度上取决于测定元素是否"完全"。由于锆石的基体元素组成简单且易于测定,很适合用基体归一法校准。在激光剥蚀-电感耦合等离子体质谱法(LA-ICP-MS)微区原位分析中,应用基体归一校准法的最大优点是:可以避免预先用其它微区分析技术对未知样品中的内标元素进行定量。该技术可适用于具有环带结构、难以找到均匀分布的内标元素的地质样品的元素空间分布测定。在高分辨ICP-MS(Element2)和NewWave-UV-213激光系统上,应用基体归一定量技术同时分析了锆石中主、次、痕量共54种元素。对未知锆石样品的分析,基体归一法与内标法结果的一致性令人满意。分析德国蛇纹岩标准玻璃ATHO-G中相对误差<25%的有52个元素,<10%的有36个元素;大多数元素的相对标准偏差<10%。     

Detection and imaging of chrome yellow (lead chromate) in latent prints,solid residues,and minerals by laser‐desorption/ionization mass spectrometry (LDI‐MS)

In the past, chrome yellow (lead chromate, PbCrO₄), a bright orange‐red substance, has been widely used as an inorganic pigment in the production of paints, coatings, and plastics. Herein, we demonstrate that laser desorption/ionization mass spectrometry (LDI‐MS) is a powerful tool for the detection of lead chromate in solid residues. In fact, lead chromate in trace amounts is easily detectable by LDI‐MS even from residues left as latent prints. For example, a latent print obtained by stamping the exposed laterally cut surface of a pencil over 50 years old on an acetonitrile‐moistened paper, was successfully imaged for both lead and chromate using a Synapt G2 HDMS mass spectrometer. After rastering the print with a 355 nm laser beam and recording positive‐ and negative‐ion mass spectra over the range m/z 50–1200, we generated false‐color ‘heat maps’ (single‐ion images) for ²⁰⁸Pb^+• (m/z 207.98) and Cr₂O₆^−• (m/z 199.85). The heat maps matched closely with the faint visual image of the pencil imprint. Moreover, our results confirmed that lead chromate was used in the pigment coatings of old pencils. Evidently, LDI‐MS imaging is an efficient procedure to survey for the presence of lead and chromate in minerals and other materials. Copyright © 2017 John Wiley & Sons, Ltd.     

High irradiance laser ionization mass spectrometry for direct speciation of iron oxides

A novel method has been developed that allows the direct speciation analysis of iron oxides based on a modified laser ionization orthogonal time-of-flight mass spectrometer. Time resolved mass spectra were acquired for the investigation of elemental ions and oxide ions generated by a laser ionization source. Speciation methodologies, including the identification of characteristic ions and the use of ion abundance ratios were evaluated for the differentiation of the oxides. The influence of operating parameters on the distribution of cluster ions was investigated, and their mechanism of formation discussed.     

Experimental designs dedicated to the evaluation of a membrane extraction method: membrane-assisted solvent extraction for compounds having different polarities by means of gas chromatography–mass detection

Membrane-assisted solvent extraction was applied for the determination of different classes of compounds in water, having K _o/w (octanol–water partition coefficient) values between 10¹ (aniline) and 10⁸ (methyl stearate), by means of experimental designs. Four solvents were investigated—propan-2-ol, ethyl acetate, diisopropyl ether and cyclohexane—as well as extraction time, temperature, salt impact, pH and methanol addition. The best choice was diisopropyl ether, 50 °C, 30 min and an addition of 3 g of sodium chloride at pH 2 for polar compounds. The relative standard deviation (n = 3) was found in the range from 5 to 17%. Recoveries ranged between 34 and 100%. Membrane-assisted solvent extraction was successfully applied to a fast screening method dedicated to an unknown wastewater sample.     

Nonaqueous synthesis of metal oxide nanoparticles:Review and indium oxide as case study for the dependence of particle morphology on precursors and solvents

Nonaqueous solution routes to metal oxide nanoparticles are a valuable alternative to the well-known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review, we give an overview of the various nonaqueous routes to metal oxides, their surface functionalization and their assembly into well-defined nanostructures. However, we will strongly focus on surfactant-free processes developed in our group. Within the various reaction systems such as metal halides—benzyl alcohol, metal alkoxides—benzyl alcohol, metal alkoxides—ketones, metal acetylacetonates—benzyl alcohol and metal acetylacetonates—benzylamine we will discuss representative examples in order to show the versatility of this approach. The careful characterization of the organic species in the final reaction mixtures provides information about possible condensation mechanisms. Depending on the system several reaction pathways have been postulated: (i) elimination of organic ethers as result of condensation between two metal alkoxide precursors; (ii) C–C bond formation between the alkoxy ligand of the metal alkoxide precursor and the solvent benzyl alcohol under formation of a metal hydroxyl species, which can undergo further condensation; (iii) ketimine and aldol-like condensation steps, which in the metal acetylacetonate systems are preceded by a solvolysis of the precursor, involving C–C bond cleavage. In the second part of the paper we will focus on the synthesis of indium oxide nanoparticles using different precursors and solvents. Indium oxide represents an instructive example how the oxide precursors and the solvents influence the particle morphology. These findings make it possible to tailor particle size and shape of a particular metal oxide by the appropriate choice of the reaction system.     

Thermodynamic possibilities and constraints of pure hydrogen production by a chromium,nickel, and manganese-based chemical looping process at lower temperatures

The reduction of chromium, nickel, and manganese oxides by hydrogen, CO, CH₄, and model syngas (mixtures of CO + H₂ or H₂ + CO + CO₂) and oxidation by water vapor has been studied from the thermodynamic and chemical equilibrium point of view. Attention was concentrated not only on the convenient conditions for reduction of the relevant oxides to metals or lower oxides at temperatures in the range 400–1000 K, but also on the possible formation of soot, carbides, and carbonates as precursors for the carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of very stable Cr₂O₃ to metallic Cr by hydrogen or CO at temperatures of 400–1000 K is thermodynamically excluded. Reduction of nickel oxide (NiO) and manganese oxide (Mn₃O₄) by hydrogen or CO at such temperatures is feasible. The oxidation of MnO and Ni by steam and simultaneous production of hydrogen at temperatures between 400 and 1000 K is a difficult step from the thermodynamics viewpoint. Assuming the Ni—NiO system, the formation of nickel aluminum spinel could be used to increase the equilibrium hydrogen yield, thus, enabling the hydrogen production via looping redox process. The equilibrium hydrogen yield under the conditions of steam oxidation of the Ni—NiO system is, however, substantially lower than that for the Fe—Fe₃O₄ system. The system comprising nickel ferrite seems to be unsuitable for cyclic redox processes. Under strongly reducing conditions, at high CO concentrations/partial pressures, formation of nickel carbide (Ni₃C) is thermodynamically favored. Pressurized conditions during the reduction step with CO/CO₂ containing gases enhance the formation of soot and carbon-containing compounds such as carbides and/or carbonates.     

Layered molybdenum oxide thin films electrodeposited from sodium citrate electrolyte solution

Molybdenum oxide thin films were prepared electrochemically onto the selenium predeposited tin oxide-coated glass substrates using 0.22 M sodium citrate (C₆H₅Na₃O₇) solution (pH 8.3) and sodium molybdate as a precursor. Cyclic voltammetry was used to determine the deposition potential effects on molybdenum compound speciation, while quantitative thin film composition was obtained from X-ray photoelectron spectroscopy depth profiles. Thin molybdenum film growth and composition was potential dependant. Predominant molybdenum species was Mo(IV) at all deposition potentials and deposition times. Optical properties of the molybdenum oxide thin films were determined using UV–VIS spectroscopy. The absorption edge varied between 560 and 650 nm, whereas optical band gap values—between 1.79 and 2.19 eV—well within the limits for solar light-induced chemical reactions.     

Photochemical generation of triplet—triplet nitrene pairs in aromatic diazide crystals

The molecular and crystal structures of 4-amino-2,6-diazido-3,5-dichloropyridine and 6-amino-2,4-diazido-1,3,5-triazine, as well as the paramagnetic photolysis products of their crystals at 77 K, were studied using X-ray diffraction analysis and ESR spectroscopy. Triplet nitrenes generated during the photolysis of diazidopyridine form triplet—triplet nitrene pairs, whose ESR spectrum corresponds to the quintet spin state. The high-spin state (S = 2) results from the exchange interaction between two triplet molecules with the zero-field splitting parameters |D| = 1.0280 cm⁻¹ and |E| = 0.0038 cm⁻¹ and the γ angle between two C—N nitrene bonds equal to 133°. This angle is close to an angle of 136.2° between the C-N bonds of two adjacent molecules in the crystal structure. No formation of the triplet—triplet nitrene pairs is observed during the photolysis of crystalline diazidotriazine, whose molecules lie in the parallel planes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 513–520, March, 2008.     

Water sorption and glass transition of freeze-dried camu-camu (myrciaria dubia (H.B.K.) Mc Vaugh) pulp

Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried camu-camu pulp in a wide range of moisture content. Samples were equilibrated at 25°C over saturated salt solutions in order to obtain water activities (a_w) between 0.11–0.90. Samples with a_w>0.90 were obtained by direct water addition. At the low and intermediate moisture content range, Gordon–Taylor model was able to predict the plasticizing effect of water. In samples, with a_w>0.90, the glass transition curve exhibited a discontinuity and T^’_g was practically constant (–58.8°C), representing the glass transition temperature of the maximally concentrated phase(T_g ).     

Calcined Ni—Al layered double hydroxide as a catalyst for total oxidation of volatile organic compounds: Effect of precursor crystallinity

The effect of hydrothermal treatment on properties (crystallinity, porous structure, reducibility, acidity, basicity, and catalytic activity and selectivity in toluene and ethanol total oxidation) of Ni—Al layered double hydroxide precursors and related mixed oxides was examined. The hydrothermal treatment increased considerably both the content of crystalline phase and LDH crystallite size. On the other hand, only a slight effect of the precursor hydrothermal treatment on crystallinity of the related Ni—Al mixed oxides obtained by calcination at 450°C was observed. The reducibility of NiO particles appeared to be hindered considerably compared to the reducibility of pure NiO. Catalytic activity of the Ni—Al mixed oxides prepared from the precursors hydrothermally treated for a short time (4 h) was the highest. The highest amount of acetaldehyde formed during the total oxidation of ethanol, i.e. the worst selectivity was found for the calcined Ni—Al LDH without hydrothermal treatment. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Heterophase synthesis of polymeric organosilanes

A new procedure was suggested for preparing polymeric organosilanes and silanosiloxanes without using a dispersion of an alkali metal in an organic solvent. The procedure allows preparation of linear organopolysilanes —(R₂Si) _n —, whereas reactions of methyl-, phenyl-, and n-hexyltrichlorosilanes with Na/NaCl yield silanosiloxane derivatives [(RSi) _x (RSiO _y ].     

The volume of micropores and the Dubinin—Radushkevich equation

The substantiation and the area of applicability of the Dubinin—Radushkevich equation for determination of the micropore volume in microporous systems from experimental data on adsorption isotherms were examined. It was shown that the micropore volumes found using the standard procedure are overestimated. A more accurate method for determining the mircopore volumes based on the pressure of filling of micropores was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 659–664, April, 1998.     

Laser ablation inductively coupled plasma mass spectrometry for direct analysis of the spatial distribution of trace elements in metallurgical-grade silicon

The spatial distribution and concentration of impurities in metallurgical-grade silicon (MG-Si) samples (97–99% w/w Si) were investigated by use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The spatial resolution (120 μm) and low limits of detection (mg kg⁻¹) for quality assurance of such materials were studied in detail. The volume-dependent precision and accuracy of non-matrix-matched calibration for quantification of minor elements, using NIST SRM 610 (silicate standard), indicates that LA-ICP-MS is well suited to rapid process control of such materials. Quantitative results from LA-ICP-MS were compared with previously reported literature data obtained by use of ICP-OES and rf-GD-OES. In particular, the distribution of element impurities and their relationship to their different segregation coefficients in silicon is demonstrated. Dedicated to Professor Klaus G. Heumann     

Copper(0) Nanoparticles in Click Chemistry: Synthesis of 3,5‐Disubstituted Isoxazoles

An efficient procedure for the synthesis of 3,5‐disubstituted isoxazoles via [3 + 2] cycloaddition reaction of in situ generated nitrile oxides with acetylenes employing readily preparable copper(0) nanoparticles is described. A variety of in situ generated nitrile oxide and acetylenic substrates were engaged in the study and found to undergo cyclization in short duration affording respective isoxazoles in excellent yield. Several amino acid‐derived isoxazoles were also prepared in high yield. Consistent activity of the recovered catalyst was found to be almost same up to three cycles.     

New cage-like metallasiloxane containing Fe<Superscript>III</Superscript> ions in different coordination spheres

The first cage-like ferrophenyl siloxane containing Fe^III ions in different coordination spheres (four iron ions have a trigonal-bipyramidal coordination and two iron ions have a distorted octahedral coordination) was synthesized by the exchange reaction of sodium phenylsilanolate with Fe^III chloride. An exotic lantern-like structure is formed with the involvement of two metal oxide fragments Fe—O—Fe. The structure of this compound was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 522–524, March, 2007.     

Phosphated Alumina Catalysts: Surface Properties and Reactivity towards 2-PrOH Decomposition

Summary. The influence of the type of precursor, the phosphate content, as well as the source of phosphate ions on the surface texture, acidity, and catalytic activity of phosphated aluminas has been described. Phosphated alumina catalysts were prepared by impregnating two different precursors with two different sources of phosphate in different loading levels w = 3, 6, and 10% PO₄ ³⁻. The characterisation of the catalyst was performed using X-ray powder diffraction (XRD), thermal analysis (TG), and nitrogen adsorption–desorption methods at 77 K. The surface acidity of the catalysts has been studied by FT-IR spectroscopy of adsorbed pyridine at different temperatures. Moreover, the activity in the catalytic decomposition of isopropanol (2-PrOH) has been investigated at 520 K. Investigation of the surface properties shows that the addition of phosphate ions does not change the crystal phase (γ-phase) and the samples prepared from gel and phosphoric acid have the highest surface area. An FT-IR study of pyridine adsorption shows both Lewis and Br?nsted acid sites on the surface of the samples prepared from gel, while only Lewis acid sites are detected on the samples prepared from crystalline oxide. The catalytic activity by 2-PrOH conversion shows that the conversion of 2-PrOH as well as the selectivity towards propene formation increases from w = 3 to 6% followed by a decline for w = 10%. Moreover, the strongest activity was detected in case of phosphated alumina gel with w = 6% which gives 97.3% propene and 96.1% conversion of 2-PrOH.     

Quantitative determination of element concentrations in industrial oxide materials by laser-induced breakdown spectroscopy

Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) method is employed for quantitative determination of oxide concentrations in multi-component materials. Industrial oxide materials from steel industry are laser ablated in air, and the optical plasma emission is collected by spectrometers and gated detectors. The temperature and electron number density of laser-induced plasma are determined from measured LIBS spectra. Emission lines of aluminium (Al), calcium (Ca), iron (Fe), manganese (Mn), magnesium (Mg), silicon (Si), titanium (Ti), and chromium (Cr) of low self-absorption are selected, and the concentration of oxides CaO, Al₂O₃, MgO, SiO₂, FeO, MnO, TiO₂, and Cr₂O₃ is calculated by CF-LIBS analysis. For all sample materials investigated, we find good match of calculated concentration values (C _CF) with nominal concentration values (C _N). The relative error in oxide concentration, e _r = |C _CF − C _N|/C _N, decreases with increasing concentration and it is e _r ≤ 100% for concentration C _N ≥ 1 wt.%. The CF-LIBS results are stable against fluctuations of experimental parameters. The variation of laser pulse energy over a large range changes the error by less than 10% for major oxides (C _N ≥ 10 wt.%). The results indicate that CF-LIBS method can be employed for fast and stable quantitative compositional analysis of multi-component materials.