The α‐d anomer of 5‐aza‐7‐deaza‐2′‐deoxyguanosine

In the monohydrate of 2‐amino‐8‐(2‐deoxy‐α‐d ‐erythro‐pento­furan­osyl)‐8H‐imidazo­[1,2‐a]­[1,3,5]­triazin‐4‐one, C₁₀H₁₃N₅O₄·H₂O, denoted (I) or αZ_d, the conformation of the N‐gly­cosyl­ic bond is in the high‐anti range [χ = 87.5 (3)°]. The 2′‐deoxy­ribo­furan­ose moiety adopts a C2′‐endo,C3′‐exo(^2′T_3′) sugar puckering (S‐type sugar) and the conformation at the C4′—C5′ bond is ?sc (trans).     

Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden. V. Die Festkörperreaktion 2. Art im System NiO – β-Ga2O3

The Formation of Spinels from β-Ga₂O₃ and Metal Oxides with the Metal in the Oxidation State +2. V. The Solid State Reaction of the Second Kind in the NiO—β-Ga₂O₃ System The reaction of the second kind between Ni_1–zGa_2z/3O, that is NiO presaturated with β-Ga₂O₃, and pure β-Ga₂O₃, which has a negligible solubility for NiO, was investigated between 1 249 and 1 527°C. In accordance with the phase diagram of the NiO—β-Ga₂O₃ system a spinel with the general formula Ni_1–yGa_2+2y/3O₄ is formed in a sandwich type diffusion couple. The reaction follows a parabolic rate law with an activation energy of 84 880 cal/mole; the mechanism is the Wagner mechanism of counterdiffusion of cations. The reaction rate constants of the second kind, determined from interdiffusion profiles in NiO/β-Ga₂O₃ diffusion couples are in good agreement with experimental values.     

Evidence for electron orbital dependence of ion-beam induced attenuations of transient magnetic fields

From measurements of transient magnetic fields (TF) on⁵⁶Fe(2 ₁ ⁺ ) ions in Gd host there is evidence that beam induced attenuations of TF not only depend on the energy loss of the beam ions in the ferromagnet but also on the electron ns-orbitals of the probe ion contributing to the field. This has been demonstrated for 2s- and 3s-electron states of⁵⁶Fe ions which are preferentially populated by setting the ion velocity to their respective orbital Bohr velocities.     

7‐Fluorotubercidin: a halogenated derivative of a naturally occurring nucleoside antimetabolite

The title compound [systematic name: 4‐amino‐5‐fluoro‐7‐(β‐d ‐ribofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine], C₁₁H₁₃FN₄O₄, exhibits an anti glycosylic bond conformation, with a χ torsion angle of −124.7 (3)°. The furanose moiety shows a twisted C2′‐endo sugar pucker (S‐type), with P = 169.8 (3)° and τ_m = 38.7 (2)°. The orientation of the exocyclic C4′—C5′ bond is +sc (gauche, gauche), with a γ torsion angle of 59.3 (3)°. The nucleobases are stacked head‐to‐head. The extended crystal structure is a three‐dimensional hydrogen‐bond network involving O—H...O, O—H...N and N—H...O hydrogen bonds. The crystal structure of the title nucleoside demonstrates that the C—C bonds nearest the F atom of the pyrrole system are significantly shortened by the electronegative halogen atom.     

Interactions and dispersion stability of aluminum oxide colloidal particles in electroless nickel solutions in the presence of comb polyelectrolytes

The effect of comb polyelectrolytes on the dispersion stability of colloidal alumina particles in DI water and commercial electroless nickel (EN) solutions was investigated. Adsorption of polyelectrolytes and major EN components onto colloidal alumina was assessed by TGA, chemical analysis, and zeta potential measurements. Zeta potential measurements were made during titrations of comb-polyelectrolyte-stabilized dispersions with EN solutions to full ionic strength for the first time. The compilation of titration curves made with varying amounts of comb polyelectrolytes provides high resolution and novel insight into the particle/surfactant/EN systems. Continuous decrease in particle/EN components surface interactions with the increase in comb polyelectrolyte coverage is observed. Laser diffraction measurements reveal steric stabilization of nano- and submicronmeter alumina dispersions in both DI water and EN solutions with >7 wt% and >2 wt% comb polyelectrolyte, respectively.     

Synthesis of a precursor for an alumina ceramic reinforced by zirconium dioxide from inorganic compounds in the presence of urea

Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO₂, tlm, after a thermal treatment (1250°C). The structure of samples in the system Al₂O₃-ZrO₂ is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO₂ sol particles in decomposition of urea. The coating of ZrO₂ sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO₂ sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al₂O₃-ZrO₂ was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorption isotherms.     

Silicon–Nitrogen Bond Formation via Heterodehydrocoupling and Catalytic N-Silylation

Silicon–nitrogen bond formation is an important subfield in main group chemistry, and catalysis is an attractive route for efficient, selective formation of these bonds. Indeed, heterodehydrocoupling and N-silylation offer facile methods for the synthesis of small molecules through the coupling of primary, secondary, and tertiary silanes with N-containing substrates such as amines, carbazoles, indoles, and pyrroles. However, the reactivity of these catalytic systems is far from uniform, and critical issues are often encountered with product selectivity, conversions, substrate scope, catalyst activation, and in some instances, competing side reactions. Herein, a catalogue of catalysts and their reactivity for Si−N heterodehydrocoupling and N-silylation are reported.     

Swapping Interface Contacts in the Homodimeric tRNA‐Guanine Transglycosylase: An Option for Functional Regulation

The enzyme tRNA‐guanine transglycosylase, a target to fight Shigellosis, recognizes tRNA only as a homodimer and performs full nucleobase exchange at the wobble position. Active‐site inhibitors block the enzyme function by competitively replacing tRNA. In solution, the wild‐type homodimer dissociates only marginally, whereas mutated variants show substantial monomerization in solution. Surprisingly, one inhibitor transforms the protein into a twisted state, whereby one monomer unit rotates by approximately 130°. In this altered geometry, the enzyme is no longer capable of binding and processing tRNA. Three sugar‐type inhibitors have been designed and synthesized, which bind to the protein in either the functionally competent or twisted inactive state. They crystallize with the enzyme side‐by‐side under identical conditions from the same crystallization well. Possibly, the twisted inactive form corresponds to a resting state of the enzyme, important for its functional regulation.     

An dem Polarisationsapparate

Ohne Zusammenfassung