Comparative characterization of thermal isomerization rates of 6‐phenyl‐1,5‐diazabicyclo[3.1.0]hexane at convection and microwave heating

Rate constants of thermal isomerization of 6‐phenyl‐1,5‐diazabicyclo[3.1.0]hexane into 1‐(benzyl)‐4,5‐dihydro‐1H‐pyrazole at convection and microwave heating in toluene and chlorobenzene (solvents) were determined within the temperature range 90°C to 120°С. These data were used for the calculation of activation parameters of isomerization. It is shown that microwave heating increases the rate constants at the same temperature by a factor of 2 to 2.5 as compared with those using convection heating. The reason is that the effective temperature of microwave heating exceeds that of convection heating by 6°C to 9°С in toluene and by 12°C to 20°С in chlorobenzene as solvent.     

Yang–Mills instantons and dyons on group manifolds

We consider Euclidean SU(N)$\mathrm{SU}(N)$ Yang–Mills theory on the space G×R$G\times \mathbb{R}$, where G is a compact semisimple Lie group, and introduce first-order BPS-type equations which imply the full Yang–Mills equations. For gauge fields invariant under the adjoint G  -action these BPS equations reduce to first-order matrix equations, to which we give instanton solutions. In the case of G=SU(2)≅S³$G=\mathrm{SU}(2)\cong S^3$, our matrix equations are recast as Nahm equations, and a further algebraic reduction to the Toda chain equations is presented and solved for the SU(3) example. Finally, we change the metric on G×R$G\times \mathbb{R}$ to Minkowski and construct finite-energy dyon-type Yang–Mills solutions. The special case of G=SU(2)×SU(2)$G=\mathrm{SU}(2)\times \mathrm{SU}(2)$ may be used in heterotic flux compactifications.     

Towards the Design of Optically Active Thiophene S-Oxides using Quantum Chemistry

The importance of axially chiral biaryls has risen steeply in the recent decades. This structural motif proved to be successful in catalytic asymmetric synthesis and the configuration of the biaryl axis is decisive for the biological activity. A new approach for the atroposelective synthesis of biaryls would be through a cycloaddition between an enantiopure phenyl-substituted thiophene S-oxide and an alkyne. Importantly, the chiral center of the thiophene S-oxide needs to be stable enough to avoid pyramidal inversion during the cycloaddition. Considering that the racemization of thiophene monoxides has been scarcely investigated so far, we perform a thorough quantum chemical study on the inversion barriers of a large number of chiral thiophene S-oxide derivatives. Our main goal is to identify substitution patterns leading to stable atropisomers at room temperature. Appealingly, the role of stereoelectronic effects and the position of the substituents as well as the importance of aromaticity on the pyramidal inversion barrier are elucidated for the first time.     

Cosmological Scenarios with Bounce and Genesis in Horndeski Theory and Beyond

Journal of Experimental and Theoretical Physics - This essay is a brief review of the recent studies of non-singular cosmological scenarios with bounce and Genesis and their stability in a subclass...     

Effects of external global harmonic influence on chimera states

Nonlinear Dynamics - The effects of the global harmonic force on an ensemble of nonlocally coupled chaotic Rössler oscillators is studied. The autonomous ensemble without external force...     

Parametric instability of a magnetic pendulum in the presence of a vibrating conducting plate

Nonlinear Dynamics - A pendulum with an attached permanent magnet swinging in the vicinity of a conductor is a typical experiment for the demonstration of electromagnetic braking and Lenz’...     

Which Stereoinductor Is Better for Asymmetric Functionalization of α-Amino Acids in a Nickel(II) Coordination Environment? Experimental and DFT Considerations

The results of extended comparative investigation of nickel(II) Schiff base complexes (containing various auxiliary chiral moieties) commonly used as a methodological platform for the asymmetric synthesis of tailor-made α-amino acids are provided. The following issues are addressed: 1) redox activity (determining the possibility for electrochemically induced reactions); 2) quantitative estimation of the reactivity of deprotonated complexes towards electrophiles; and 3) quantum-chemical estimation of noncovalent interactions in the metal coordination environment (which shed light on the origin of the stereochemical outcome observed for different stereoinductors). Possible mechanisms that determine the relationship between the stereochemical configuration of a molecule and its electronic structure are discussed. The DFT-calculated HOMO–LUMO energies and localization, as well as relative energies for the (S)- and (R)-alanine derivatives, that determine the stereoinduction efficiency in thermodynamically controlled reactions in nickel(II) coordination are provided. The computational data are supported by experimental results on the monobenzylation of glycine derivatives.     

Complex Formation of Cyclodextrins with Sulfasalazine in Buffer Solutions

Russian Journal of General Chemistry - Complex formation of α-, β-, and γ-cyclodextrins with sulfasalazine in biologically relevant buffer solutions (pH 1.2 and 7.4) was studied....     

Emission of photoexcited charge carriers from InAs/GaAs quantum dots grown by gas-phase epitaxy

A model describing the emission of photoexcited electrons and holes from an array of InAs quantum dots into the GaAs matrix is suggested. The analytical expression obtained for the emission efficiency takes into account the thermal emission of charge carriers into the GaAs matrix and two-dimensional states of the InAs wetting layer, tunneling and thermally activated tunneling escape, and electron transitions between the quantum-confinement levels in the conduction band of InAs. The temperature dependences of the photosensitivity in the regions of the ground-state and first excited-state optical transitions in InAs/GaAs quantum dots grown by gas-phase epitaxy are investigated experimentally. A number of quantum dot parameters are determined by fitting the results of a theoretical calculation to the experimental data. Good agreement between the theoretical and experimental results is obtained in this way.