Synthesis and transformation of N-oxides of some imidazo[4,5-b]pyrazine derivatives

The Böckelheide reaction was accomplished with a number of imidazo[4,5-b]pyrazine N-oxides, and the N-oxidation of the resulting acetoxy(hydroxy)methyl derivatives of imidazo[4,5-b]pyrazine and 6-bromo-1-methylimidazo[4,5-b]pyrazine was studied. The hydrolytic cleavage of 6-bromo-1-methylimidazo[4,5-b]pyrazine and its 4-N-oxide was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 690–693, May, 1975.     

Pyrazines and their N-oxides

Two isomeric mono-N-oxides of 2-aminopyrazine and the 1,4-di-N-oxide have been synthesized. A marked fall in the capacity of these compounds for nucleophilic exchange reactions and for rearrangements in acid and alkaline media has been found, which distinguishes them from the corresponding N-oxides of 2-aminoquinoxaline.For part I, see [5].     

PMR spectra of 2-substituted pyrazines and the corresponding pyrazine N-oxides and N,N′-dioxides

The PMR spectra of pyrazine, its 2-substituted derivatives, and the corresponding N-oxides and N,N-dioxides were investigated. The character of the change in the chemical shifts in the N-oxides and N,N-dioxides of unsubstituted pyrazine indicates the electron-donor effect of the NO group. An additive effect of the NO groups on the chemical shifts of the ring protons is observed in pyrazine N,N-dioxide. An appreciable interaction of the substituent with the N₍₁₎O group and a weak interaction with the N₍₄₎O group occur in N-oxides and N,N-dioxides of 2-substituted pyrazines. A significant increase in the ortho and meta spin-spin coupling constants of the ring protons is noted when the nitrogen atoms are oxidized. The sign of the spin-spin coupling constant (J₃₅) through the NO group was determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 266–273, February, 1972.     

Magnetic field controlled floating-zone single crystal growth of intermetallic compounds

Radio-frequency (RF) floating zone single crystal growth is an important technique for the preparation of single bulk crystals. The advantage of the floating-zone method is the crucible-free growth of single crystals of reactive materials with high melting points. The strong heat diffusion on the surface, as well as the melt convection in the molten zone due to induction heating, often leads to an undesired solid-liquid interface geometry with a concave (towards the solid phase) outer rim. These concave parts aggravate the single crystal growth over the full cross-section. A two-phase stirrer was developed at IFW Dresden in order to avoid the problems connected with these concave parts. It acts as a magnetic field pump and changes the typical double vortex structure to a single roll structure, thus pushing hot melt into the regions where the concave parts may arise. The current in the secondary coil is induced by the primary coil, and the capacitor and the resistance of the secondary circuit are adjusted to get a stable 90 degree phase-shift between the coil currents. Single crystal growth of industrial relevant RuAl and TiAl intermetallic compounds was performed based on the material parameters and using the adjusted two-phase stirrer. Very recently, the magnetic system was applied to the crystal growth of biocompatible TiNb alloys and antiferromagnetic Heusler MnSi compounds.     

Langmuir-Blodgett films of hydrophobins HFBI and HFBII

Hydrophobins are small fungal proteins, which have remarkable surface-chemical properties. They self-assemble at hydrophobic/hydrophilic interfaces and work as adhesive agents and coatings. Sixteen layer Langmuir-Blodgett films of hydrophobins HFBI and HFBII from the fungus Trichoderma reesei were prepared and studied using grazing-incidence X-ray diffraction and reflectivity techniques. Both kind of films contain hexagonally ordered crystallites on the substrate with unit cell parameters of a = b = 54 Å (HFBI) and a = b = 55 Å (HFBII). The structure is similar to the structure of monolayer Langmuir-Blodgett films.     

High‐energy‐resolution diced spherical quartz analyzers for resonant inelastic X‐ray scattering

A novel diced spherical quartz analyzer for use in resonant inelastic X‐ray scattering (RIXS) is introduced, achieving an unprecedented energy resolution of 10.53 meV at the Ir L₃ absorption edge (11.215 keV). In this work the fabrication process and the characterization of the analyzer are presented, and an example of a RIXS spectrum of magnetic excitations in a Sr₃Ir₂O₇ sample is shown.     

Study of the nucleophilic substitution reactions of 2,4,10-trichloropyrimido[5,4-b]quinoline

A number of pyrimido[5,4-b]quinoline derivatives were synthesized. It is shown that in the reaction of 2,4,10-trichloropyrimido[5,4-b]quinoline (II) with strong nucleophilic reagents (OCH₃ and SH) both of the halogens of the pyrimidine ring are replaced, while with amines substitution of the halogens of the pyrimidine ring proceeds successively; under more severe conditions, all three halogen atoms of II are replaced by amine residues.