Vol 72, No 13 (2017)

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.

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 М_m ⋅ Ag⁺ (m = 1–5) and small silver clusters AgM_n⁺ (n = 1–9), unusual silver clusters with one hydrogen atom [Ag_nH]⁺ (n = 2, 4) were observed. Possible pathways for the formation of silver nanoparticles taking into account hydrogen-containing cluster intermediates are discussed.

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.

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.

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.

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.