Study of interrelation between processes in the thunderstorm atmosphere and energetic cosmic rays with the Groza Tien Shan developmental installation

A Groza installation for studying a lightning discharge mechanism in thunderclouds and clarifying its interrelation with cosmic rays has been designed in the Tien Shan high-altitude cosmic-ray station. The basic results obtained with the Groza installation consisting of detectors serving different purposes and synchronously initiated by a trigger pulse are presented.     

Malonyl peroxides in organic synthesis (microreview)

Chemistry of Heterocyclic Compounds - A summary of the most recent applications of malonyl peroxides as reagents in organic synthesis is discussed. The microreview covers the latest selected...     

Atomistic fibrillar architectures of polar prion-inspired heptapeptides

This article provides the computational prediction of the atomistic architectures resulting from self-assembly of the polar heptapeptide sequences NYNYNYN, SYSYSYS and GYGYGYG. Using a combination of molecular dynamics and a newly developed tool for non-covalent interaction analysis, we uncover the properties of a new class of bionanomaterials, including hydrogen-bonded polar zippers, and the relationship between peptide composition, fibril geometry and weak interaction networks. Our results, corroborated by experimental observations, provide the basis for the rational design of prion-inspired nanomaterials.

This article provides the computational prediction of the atomistic architectures resulting from self-assembly of the polar heptapeptide sequences NYNYNYN, SYSYSYS and GYGYGYG.     

Water-catalyzed isomerization of the glycine radical cation. From hydrogen-atom transfer to proton-transport catalysis

The isomerization reactions of the glycine radical cation, from [NH₂CH₂COOH]⁺, I, to [NH₃CHCOOH]⁺, II, or [NH₂CHC(OH)₂]⁺, III, in the presence of a water molecule have been studied theoretically. The water molecule reduces dramatically the energy barriers of the III and IIII tautomerizations owing to a change in the nature of the process. However, the role of the water molecule depends on the kind of isomerization, the catalytic effect being more important for the IIII reaction. As a consequence, the preferred mechanism for the interconversion of glycine radical cation I to the stablest isomer, III, is the direct one-step mechanism instead of the two step (III and IIIII) process found for isolated [NH₂CH₂COOH]⁺. When using ammonia as a solvent molecule, a spontaneous proton-transfer process from [NH₂CH₂COOH]⁺ to NH₃ is observed and so no tautomerization reactions take place. This behavior is the same as that observed in aqueous solution, as has been confirmed by continuum model calculations.Contribution to the Jacopo Tomasi Honorary Issue     

Triplet (pi,pi) reactivity of the guanine-cytosine DNA base pair: benign deactivation versus double tautomerization via intermolecular hydrogen transfer

Ab initio computations (CASSCF/6-31G* supported by CAS-PT2 single-point calculations) are used to study the reactivity of the triplet excited state of the guanine-cytosine DNA base pair. When the triplet excitation is centered on cytosine there is a competition between benign deactivation to the ground state and a hydrogen transfer route that can trigger double tautomerization. The calculated barriers favor the benign deactivation, but this route goes through a singlet/triplet intersystem crossing with small spin-orbit coupling. Therefore, the potentially mutagenic, double tautomerization route cannot be ruled out completely, and the two paths are probably an alternative to the well-known cytidine photodimerization reaction.     

Richter-type magnetic after-effect in manganese ferrite

A study was made of magnetic after-effect of the Richter type in samples of non-stoichiometric manganese ferrites differing by their excess of manganese and having a different content of oxygen.     

A new method for measuring the susceptibility of paramagnetic and diamagnetic substances

The paper deals with a number of methods for measuring the susceptibility of paramagnetic and diamagnetic substances mentioning their disadvantages. The principle of a new method for measuring susceptibility is given and the instrument described. The good operation of the instrument is demonstrated on several examples of measurement.     

Experimental confirmation of the predicted shallow donor hydrogen state in zinc oxide

We confirm the recent prediction that interstitial protium may act as a shallow donor in zinc oxide, by direct spectroscopic observation of its muonium counterpart. On implantation into ZnO, positive muons--chemically analogous to protons in this context--form paramagnetic centers below about 40 K. The muon-electron contact hyperfine interaction, as well as the temperature and activation energy for ionization, imply a shallow level. Similar results for the cadmium chalcogenides suggest that such shallow donor states are generic to the II-VI compounds. The donor level depths should serve as a guide for the electrical activity of interstitial hydrogen.     

A solar system model with dissipation

A problem of motion for an arbitrary number of planets is discussed with consideration of the forces of gravitational interaction according to the law of universal gravitation. The planets are assumed to be homogeneous viscoelastic spheres. In the process of motion, the planets are deformed and the dissipation of energy takes place due to internal viscous forces. On the basis of the motion separation method, an approximate system of equations is obtained to describe the motion of planet centers of mass and the variation of planet angular momenta with respect to the centers of mass. The equations of motion contain small conservative corrections to the law of universal gravitation and small dissipative forces whose influence causes a decrease of the total mechanical energy. The motion under consideration admits the following first integral: the law of angular momentum conservation for the system with respect to the centers of mass. When the system executes the steady motion corresponding to its rotation with a constant angular velocity as a rigid body, the dissipative forces do not perform work, since the deformed planets have no time-dependent deformations.     

99mTc-Labelled Compounds Prepared with Ti(III) as Reducing Agent

In preparation of ^99mTc-labelled compounds it is possible to use TiCl₃ instead, of SnCl₂; in most cases, however, this substitution changes the biodistribution parameters. The preparations have then a slower blood clearence, being cumulated in bones in larger amounts; bone diagnostics (HEDSPA and pyrophosphate) are opposite cases. This fact makes itself felt in ^99mTc-Ti-gluconate which, in its turn, loses the character of kidney agent cumulating, in a marked way, in bones. From diagnostic point of view, the ^99mTc-Ti-labelled compounds possess, in most cases, worse parameters as compared with those prepared by means of tin dichloride. Preparation of technetium-labelled compounds requires inert nitrogen atmosphere. Time stability of these preparations within 24 hours is good a whole.