Resonant electron capture by 5-Br-2'-deoxyuridine.

The results of the study of resonant electron capture by molecules of 5-Br-2'-deoxyuridine (BrdUrd) over the range of electron energies from near zero to 14 eV are described. In the thermal energy range, long-lived molecular negative ions, unstable with respect to autoneutralization and dehalogenation, have been registered. Examination of the kinetics of these decay processes led us to the conclusion that the most probable structure for molecular negative ions is that with an extended C-Br bond, which was predicted earlier using quantum-chemical calculations. Estimates have shown that the BrdUrd molecule owns a significant electronic affinity of 0.93-1.38 eV. The most intense fragmentation channel leads to the abundant formation of Br- ions. The dissociative electron attachment cross section for Br- ions formation was estimated to amount to no less than 1.65 × 10-15 cm2, indirectly implying a fairly intense formation of complementary highly reactive deoxyuridine-5-yl particles. These particles are known to be responsible for the radiosensitizing properties of BrdUrd.

Resonant electron capture by aspartame and aspartic acid molecules.

RATIONALE: The processes for dissociative electron capture are the key mechanisms for decomposition of biomolecules, proteins in particular, under interaction with low-energy electrons. Molecules of aspartic acid and aspartame, i.e. modified dipeptides, were studied herein to define the impact of the side functional groups on peptide chain decomposition in resonant electron-molecular reactions. METHODS: The processes of formation and decomposition of negative ions of both aspartame and aspartic acid were studied by mass spectrometry of negative ions under resonant electron capture. The obtained mass spectra were interpreted under thermochemical analysis by quantum chemical calculations. RESULTS: Main channels of negative molecular ions fragmentation were found and characteristic fragment ions were identified. CONCLUSIONS: The СООН fragment of the side chain in aspartic acid is shown to play a key role like the carboxyl group in amino acids and aliphatic oligopeptides. Copyright © 2016 John Wiley & Sons, Ltd.

Electron ionization and dissociation of aliphatic amino acids.

We present experimental and theoretical study of electron ionization and dissociative ionization to the gas phase amino acids valine, leucine, and isoleucine. A crossed electron/molecular beams technique equipped with quadrupole mass analyzer has been applied to measure mass spectra and ion efficiency curves for formation of particular ions. From experimental data the ionization energies of the molecules and the appearance energies of the fragment ions were determined. Ab initio calculations (Density Functional Theory and G3MP2 methods) were performed in order to calculate the fragmentation paths and interpret the experimental data. The experimental ionization energies of parent molecules [P](+) 8.91 ± 0.05, 8.85 ± 0.05, and 8.79 ± 0.05 eV and G3MP2 ionization energies (adiabatic) of 8.89, 8.88, and 8.81 eV were determined for valine, leucine, and isoleucine, respectively, as well as the experimental and theoretical threshold energies for dissociative ionization channels. The comparison of experimental data with calculations resulted in identification of the ions as well as the neutral fragments formed in the dissociative reactions. Around 15 mass/charge ratio fragments were identified from the mass spectra by comparison of experimental appearance energies with calculated reaction enthalpies for particular dissociative reactions.

Study of fragmentation pathways of metastable negative ions in aliphatic dipeptides using the statistical theory.

RATIONALE: Dipeptide molecules are good model systems for investigation of resonant reactions of low-energy electrons with proteins. The present work is devoted to the study of the processes of formation and fragmentation of negative ions in aliphatic dipeptides glycyl-glycine and glycyl-alanine. The metastable decays of negative ions were detected in these objects, and have been investigated with the aim of clarification of the mechanisms of fragmentation. METHODS: The effective yield curves for negative ions as functions of electron energy were obtained using a magnetic sector mass spectrometer rebuilt for generation and detection of negative ions. For analysis of the observed metastable decays statistical and thermochemical approaches have been used. RESULTS: The ions structures, the enthalpies of formation of neutral and charged particles, and the rate constants of dissociative reactions have been found. CONCLUSIONS: Comparison of the experimental results with theoretical data leads to the conclusion that metastable ion decay proceeds with minimal structural changes avoiding complicated rearrangements and isomerization processes.

Dissociative electron attachment to glycyl-glycine, glycyl-alanine and alanyl-alanine.

The processes of negative ions formation of dipeptides glycyl-glycine, glycyl-alanine and alanyl-alanine in the conditions of resonant electron capture have been studied with a help of negative ions mass spectrometry. Using a thermochemical approach, the main channels of fragment negative ions formation were found and the structure of the ions were established. The isobaric ions have been identified by the experiments with high mass resolution. The cross sections of fragment ions formation were measured. The metastable fragmentation of [M-H](-) and [M-COOH](-) ions in the energy range 4.5-7.5 eV have been found.

Genotypological method of analysis of individual responsiveness of an organism in experiment.

The principle of a genotypological method of analysis of individual responsiveness of an organism in experiment is formulated on the basis of data in the literature and the results of the author's own investigations. The main objective of a genotypological method is the determination of the constitutional typological features of responsiveness and their markers on the basis of similar or different norms of reaction and paratypical factors. It is proposed that individual responsiveness in a population be determined by way of disclosing in individuals the corresponding markers previously established in linear and non-linear animals in experiment, while observing a number of necessary conditions. These markers, capable of playing the role of indicators of a "constitutional typological reaction norm" and also of an individual reaction norm with respect to a concrete agent, are called genotypological markers.

Influence of products of the vital activity of helminths on the corticosterone content in the adrenals and blood.

The content of corticosterone in the adrenals and blood plasma, as well as the weight of the adrenals and their histology, were investigated in 77 inbred rats (38 animals of the August line and 39 animals of the Wistar line). It was shown that after products of ascarid metabolism were administered to the experimental rats, the corticosterone content in the adrenals and blood plasma changed substantially. Despite the equal doses of the agent administered, statistically significant differences between lines were detected in the corticosterone indices in the blood plasma of the experimental rats, and they were also present in the control (healthy) animals. In the latter, no differences between lines were established in the corticosterone content in the adrenals, although in the experimental rats these differences arose at many periods of observation. It is concluded that the level of corticosterone content of the blood in the initial normal state, as well as the degree of its deviations from the initial norm, are determined (with equal conditions with respect to paratypic factors) by the genetic constitution (genotype) of the organism.

[Genotypical characteristics of the immunological Vi-antibody maturation depending on the effect of Vi-antigen deposit in the body]. / Genotipicheskie osobennosti immunologicheskogo sozrevaniia Vi-antitel v zavisimosti ot effekta deponirovaniia Vi-antigena v organizme.

The authors carried out a comparative analysis of the changes in the antibody synthesis and their immunological maturation in the immunization with various doses of the Vi-antigen of linear rats differing by the capacity to deposit this antigen. August rats with a high capacity to deposit the Vi-antigen (in comparison with Wistar rats in which this capacity was less) were characterized by an increased level of highly avid antibodies. The interlinear differences were found in the character of the changes in the antibody synthesis depending on the immunizing dose of the antigen. Genotypical peculiarities of the immunological maturation of the antibodies were demonstrated. The authors suppose that the described phenomenon was genetically determined and referred to the factors determining the individual immunological reactivity. In the choice of the optimal immunizing doses of the antigens the authors recommend complex determination of the antibody level and the degree of their avidity.

[Peculiarities of immunological response to the administration of Vi-antigen in patients suffering from typhoid fever and in experimental animals]. / Osobennosti immunologicheskogo otveta na vvedenie Vi-antigena u bol'nykh briushnym tifom i éksperimental'nykh zhivotnykh

Vi-antigen parenterally administered into the organism could be revealed on erythrocytes with the aid of inhibition of erythrocyte sedimentation reaction with immune Vi-serum. Patients with typhoid fever displayed positive results in 53.8% of cases. There were differences in the incidence of detection of the Vi-antigen in August and Wistar rats conditioned by theigenotype and due to the different capacity of their erythrocytes to sorb this antigen. Peculiarities of immunological response to the Vi-antigen administration depended on its sorption by erythrocytes in the organism and were the same in patients with typhoid fever and in the linear animals. A decreased capacity of erythrocyte to sorb Vi-antigen induced its more rapid elimination from the organism and caused a weak production of specific antibodies; this should be taken into consideration in immunotherapy of typhoid fever.