Volume 72, Nº 13 (2017)
- Ano: 2017
- Artigos: 12
- URL: https://journals.rcsi.science/1061-9348/issue/view/11411
Articles
Identification of Regions in Apomyoglobin that Form Intermolecular Interactions in Amyloid Aggregates Using High-Performance Mass Spectrometry
Resumo
The formation of amyloid aggregates in human organs and tissues causes the development of incurable diseases. However, experimental studies of the mechanism of amyloid formation by proteins and the structural characteristics of amyloids are complicated because of the heterogeneity and high molecular weight of the aggregates. We used limited proteolysis and mass spectrometry for the identification of regions in the apomyoglobin polypeptide chain, which give rise to intermolecular interactions in amyloid structures. Tandem mass spectroscopy enabled the identification of regions in the myoglobin polypeptide chain, which form the core of amyloid structures. It was shown that the main structural elements for the formation of the core of amyloid fibrils in myoglobin were regions from 60 through 90 and from 97 through 124 amino acid residues. These regions coincide well with those theoretically predicted. This approach yielded important data on the structure of protein molecules in aggregates and on conformational rearrangements of apomyoglobin upon amyloid formation.
A “Low-Molecular” Approach to the Identification of Microorganisms by MALDI Mass Spectrometry
Resumo
A new approach to the identification of microorganisms is presented. It includes the transformation of their MALDI mass spectra aimed at reducing mass scale by one order of magnitude and the use of standard software for building mass spectral libraries of low-molecular compounds and library searches. A library of 728 transformed (“rescaled”) mass spectra of 182 strains for some Streptococcus species was built. With this library, the rate of true microorganism identification was estimated by cross-comparison between library mass spectra (internal validation of the approach). The true identification rate was 84% for three Streptococcus species, which corresponds to the average trueness of species identification by MALDI as found in the literature. The proposed approach to identification can be considered as a method of choice for solving identification problems under consideration.
Mass Spectrometric Detection of Charged Silver Nanoclusters with Hydrogen Inclusions Formed by the Reduction of AgNO3 in Ethylene Glycol
Resumo
In the problem of the production silver nanoparticles, mass spectrometry allows one to identify nanoclusters as nuclei or intermediates in the synthesis of nanoparticles and to understand the mechanisms of their formation. Using low-temperature secondary emission mass spectrometry, we determined the cluster composition of a system formed in the microwave treatment of a solution of AgNO3 in ethylene glycol (M). Along with silver ion–ethylene glycol associates Мm ⋅ Ag+ (m = 1–5) and small silver clusters AgMn+ (n = 1–9), unusual silver clusters with one hydrogen atom [AgnH]+ (n = 2, 4) were observed. Possible pathways for the formation of silver nanoparticles taking into account hydrogen-containing cluster intermediates are discussed.
Tryptamine: a Reactive Matrix for MALDI Mass Spectrometry
Resumo
A possibility of using tryptamine as a reactive matrix for the analysis of non-polar carbonyl compounds by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has been shown. Presence of a terminal primary amine group in the tryptamine molecule predetermines the formation of Schiff bases from aliphatic and alicyclic carbonyl compounds. No additional matrix compounds are necessary to register MALDI mass spectra, because the excess of the derivatization agent plays the role of a matrix. MALDI mass spectra demonstrate high efficiency of desorption/ionization of the derivatives. To discover reactive matrices, a set of aromatic primary amines (mainly substituted anilines) has been tested, but they have not demonstrated matrix properties.
Disentangling of Information About the Structure of Biomolecules Based on the Decomposition and Separation of Two-Dimentional Charge Distributions of Ions
Resumo
Electrospray ionization mass spectra of biomolecules typically consist of a series of multiply charged ions because of the transfer of protons or other charge carriers between ions of biomolecules and the surrounding liquid or gas. The distribution of intensities of ions retained charge carriers contains information about the spatial structure of biomolecules. A new method is developed for the separation and decomposition of multidimensional charge distributions of ions bearing other charge carriers, such as alkali metal ions, along with protons. The proposed method ensures the estimation of the probability of charge carrier retention by separate functional groups for the selected conformations of biomolecules. The paper describes the application of this method to the analysis of a two-dimensional charge distribution of horse heart cytochrome C, resulting in the revelation of at least two its structural forms under the studied conditions.
Determination of Methylphosphonic Acid in Human Blood Plasma by High-Performance Liquid Chromatography–Tandem Mass Spectrometry
Resumo
Using high-performance liquid chromatography combined with tandem mass spectrometric detection, an approach has been developed for the determination of the most stable nerve agent biomarker, methylphosphonic acid, in human blood plasma. The proposed method is based on the derivatization of methylphosphonic acid with p-bromophenacyl bromide. The optimization of conditions for human plasma sample preparation, mass spectrometric detection conditions, and gradient elution program has been performed. The proposed approach has demonstrated satisfactory reproducibility and selectivity of the determination; the limit of detection for methylphosphonic acid in human plasma was 3 ng mL–1.
Gas-Phase Fragmentation Studies of Biotinylated, Hexaethylene Glycol–Spacered Oligosaccharides—Molecular Probes—Using Electrospray Mass Spectrometry on a Hybrid High-Resolution Mass Spectrometer
Resumo
The electrospray ionization high-resolution mass spectra of biotinylated hexaethylene glycol–spacered molecular probes bearing biologically relevant carbohydrate moieties in positive and negative modes were recorded and interpreted. Collisionally induced decay mass spectra (positive mode) revealed different patterns depending on the charge of the parent ion, attached cations (or ions), the composition, and the sequence of carbohydrate fragments. The most intense peaks (two series) originated from the sequential cleavage of glycoside bonds resulting in charge location on the reducing end (Y series observed for all of the test compounds) or nonreducing end (B series). Hexaethylene glycol chain fragmentation giving rise to the cleavage of the C–O bond remote from the biotin moiety was observed. Other fragment ions lighter than the above by a difference of (C2H4O)n were absent or much smaller. Similar fragmentation was found for all of the nonsulfated biotinylated glycosides with the hexaethylene glycol spacer thus demonstrating that this type of fragmentation was characteristic of such molecular probes. Similar cleavages along with biotin moiety decay via the elimination of H2S and H2CS were observed for negative ions in the collisionally induced decay mass spectra of sulfated and neutral molecular probes.
Interpretation and Simulation of Negative Ion Mass Spectra of Some Phosphorus Organoelement Compounds
Resumo
Negative ion mass spectra for a series of organophosphorus compounds were obtained and negative ion fragmentation processes were treated theoretically. Using O-isopropyl and O-pinacolyl methylphosphonofluoridates as examples, electron affinities of molecules and their fragments were estimated using the UB3LYP/6-311+G(d,p) quantum-chemical approach and energetically more favorable and characteristic routes of dissociative electron attachment, including simple bond cleavage and rearrangements, were determined. Based on the obtained experimental and theoretical data, hypothetic fragmentation patterns were proposed and a special algorithm was compiled to predict negative ion mass spectra for some groups of organophosphorus compounds, such as О-alkyl methylphosphonofluoridates, О,О-alkyl phosphonodichloridates, and О,О′-dialkyl phosphonochloridates. The simulated mass spectra showed a good agreement with the experimental ones, confirming reasonable reliability of the proposed algorithm.
Study of Gaseous Sample Ionization by Excited Particles Formed in Glow Discharge Using High-Resolution Orthogonal Acceleration Time-of-Flight Mass Spectrometer
Resumo
The experimental results of a mass spectral analysis of volatile organic compounds in a gaseous sample, obtained using an original design of an ion source based on the Penning ionization of a gas sample by excited metastable inert gas atoms, are presented. Using ANSYS software, a gas-dynamic simulation of reagent gas flow from discharge zone to ionization region was carried out to analyze the effect of gas flow profile on the transport of metastable atoms and ionization efficiency. The n-octane and toluene samples diluted with helium at 100 ppb mole concentrations were used for our experiments. The resulting mass spectra of n-octane and toluene samples containe far more intensive molecular ions in comparison to n-octane and toluene electron ionization mass spectra from the NIST database. The sensitivity of 5 ions per 1 pg and 130 ions per 1 pg was achieved for n-octane and toluene molecular ions using the developed ion source combined with our mass spectrometer. The corresponding detection limits are 2.3 pg s–1 for n-octane molecular ions and 0.08 pg s–1 for toluene molecular ions. The detection limit for the reported ion source was considered theoretically.
Elucidation of the Chemical Structure of a Gas Chromatographic Artifact of Synthetic Cannabinoid N-(1-Carbamoyl-2-Methylpropyl)-1-(Cyclohexylmethyl)-1H-Indazol-3Ccarboxamide by High-Resolution Mass Spectrometry
Resumo
Synthetic cannabinoids are the most popular psychoactive compounds on the illegal market. In the gas chromatographic determination, some synthetic cannabinoids undergo chemical transformations because of their thermal interaction with the chromatographic system. This paper is devoted to the elucidation of the structure of a gas chromatographic artifact formed from synthetic cannabinoid N-(1-carbamoyl-2-methylpropyl)-1-(cyclohexylmethyl)-1H-indazol-3-carboxamide as a result of dehydration of its terminal carbamoyl moiety. The chemical structure of the artifact is determined by high-resolution mass spectrometry.
Possibilities for Energy Pumping in a Radio-Frequency Quadrupole by Shifted Supersonic Gas Jet. Part I: Accelerated and Excited Atom Transmission
Resumo
Generation of an ion beam and its transmission into a mass analyzer is one of central problems in mass spectrometry. The use of a narrowly directed supersonic gas jet has a number of advantages in comparison with other sampling methods. The aim of this work was to confirm the declared earlier properties of the jet formed at the outlet of a cylindrical channel when the free path length of gaseous atoms at the beginning of the channel is comparable with the channel diameter. The paper describes the ability of such a supersonic jet to conserve an additional energy of jet gas atoms. A significant influence of the temperature of the gas flow on the yield of cyclohexane fragment ions was found, cyclohexane being an admixture in the noble gas jet passing through an electron ionization ion source. A possibility of obtaining a flow of metastable electronically excited atoms inside the jet is also shown. The results of the work confirm the availability of the supersonic gas jet for the design of a high efficiency ion source inside the radio-frequency quadrupole at the input of the mass analyzer.
A New Approach to Increasing the Resolution of a Mass Spectrometer with Wedge-Shaped Reflectors
Resumo
The paper describes the investigation of the ion-optical properties of a laser TOF mass spectrometer including two successively positioned wedge-shaped ion mirrors. Some specific properties of the configuration of ion trajectories near their reflection in the second ion reflector are found. The dependence of aberrations on ion energy acquired toothed shape for the resolution of the analyzer higher than 3000–5000. The approximation of the dependence gave a 15th degree polynomial. The calculation of polynomial coefficients showed a great contribution to the duration of ion packets for aberrations of higher order. The discovered features allowed us to suggest a way of the local correction of nearby trajectories in the total ion flux. By correcting the local motion of individual groups of ions, we could reduce temporary aberration to 1–1.6 ns, depending on ion energy. For the time of ion flight ~35 μs, such duration limits the resolution of the analyzer by a value not less than 10000. The real length of ion drift path was about 30 cm. The total overall sizes of the ionoptical system were ~24 × 19 × 5 cm.