Gas-Phase Electron Diffraction and Quantum-Chemical Studies of the Molecular Structure of N,N-dimethyldiaziridine

Molecular structure of N,N-dimethyldiaziridine was studied by gas-phase electron diffraction and quantum-chemical methods. It is confirmed that the molecule has a trans conformation, but the structural parameters r(endo-C–N) 1.448(2) Å, r(exo-C–N) 1.468(2) Å, and r(N–N) 1.514(6) Å differ substantially from the results of our previous electron diffraction study.     

Structural and magnetic properties of Zn-substituted cobalt ferrites prepared by co-precipitation method

Zn substituted cobalt ferrite spinels with the general formula Zn(x)Co(1-x)Fe(2)O(4) (with x varying from 0 to 0.5) were synthesized by a co-precipitation method and calcined at 500 °C and 800 °C. It was found that Zn substitution has a big effect in decreasing the Curie temperature (T(c)), from around 440 °C for the undoped sample to ~180 °C with x = 0.5. However, these values were also strongly affected by the pre-calcination temperature of the samples, thus T(C) shifts from ~275 °C for the x = 0.3 sample to ~296 °C after calcination at 500 °C and 800 °C respectively. These effects are due to facilitation of demagnetisation by substitution of the non-magnetic Zn ions and by production of very small nanoparticles. The latter are removed by higher temperature calcinations and so T(C) increases.     

Projection Method for Cauchy Problem for an Operator-Differential Equation

In the current paper, we study a projection method for a Cauchy problem for an operator-differential equation with a leading self-adjoint operator A(t) and a subordinate linear operator K(t) in a Hilbert space. The projection subspaces are linear spans of eigenvectors of an operator similar to A(t). It is assumed that the operators A(t) and K(t) are sufficiently smooth. Error estimates for the approximate solutions and their derivatives are obtained. The application of the developed method for solving the initial boundary value problems is given.     

Stoichiometric Photochemical Carbene Transfer by Bamford–Stevens Reaction

The photolysis of diazoalkanes is a timely strategy to conduct carbene-transfer reactions under mild and metal-free reaction conditions, and has developed as an important alternative to conventional metal-catalyzed carbene-transfer reactions. One of the major limitations lies within the rapidly occurring side reaction of the carbene intermediate with remaining diazoalkane molecules that result in the use of an excess of the reaction partner and thus impacts on the reaction efficiency. Herein, we describe a protocol that takes advantage of the in situ generation of donor–acceptor diazoalkanes by Bamford–Stevens reaction. Following this strategy, the concentration of the diazoalkane reaction partner can be minimized to reduce unwanted side reactions and to now conduct photochemical carbene transfer reactions under stoichiometric reaction conditions. We have explored this approach in the C−H and N−H functionalization and cyclopropanation reaction of N-heterocycles and could demonstrate the applicability of this method in 51 examples.     

Transport and magnetic properties of multiwall carbon nanotubes before and after bromination

Bulk samples of oriented carbon nanotubes were prepared by electric arc evaporation of graphite in a helium environment. The temperature dependence of the conductivity σ(T), as well as the temperature and field dependences of the magnetic susceptibility χ(T, B) and magnetoresistance ρ(B, T), was measured for both the pristine and brominated samples. The pristine samples exhibit an anisotropy in the conductivity σ_∥(T)/σ_⊥>50, which disappears in the brominated samples. The χ(T, B) data were used to estimate the carrier concentration n ₀ in the samples: n _0ini ～3×10¹⁰ cm^?2 for the pristine sample, and n _0Br～10¹¹ cm^\t—2 for the brominated sample. Estimation of the total carrier concentration n=n _e+n _p from the data on ρ(B, T) yields n _ini=4×10¹⁷ cm^?3 (or 1.3×10¹⁰ cm^?2) and n _Br=2×10¹⁸ cm^?3 (or 6.7×10¹⁰ cm^?2). These estimates are in good agreement with one another and indicate an approximately fourfold increase in carrier concentration in samples after bromination.     

Study of the electronic structure and properties of 13C-isotope-based composites

The morphology and electronic structure of ¹³C-isotope-based graphite composites were studied by transmission electron microscopy (TEM), x-ray diffraction, and x-ray fluorescence spectroscopy. High-resolution TEM images showed that composites contain several forms of carbon particles. According to an x-ray diffraction analysis, the size of graphene stacks of graphite particles is 20 and 40 Å. The CK _α x-ray fluorescence spectra of the initial ¹³C isotope powder and composites based on it detected an increase in the density of high-energy occupied states in comparison with the graphite spectrum. Ab initio quantum chemical calculation of the structure of C₁₅₀ graphene showed that the increase in the density of states stems from the electrons of dangling bonds of boundary carbon atoms of particles ～20 Å in size. Electrical properties of ¹³C-isotope-based samples were studied by analyzing the temperature dependence of the conductivity. It was assumed that the change in the logarithmic dependence of the conductivity observed at liquid-helium temperatures to the linear dependence as the temperature increases is caused by carrier transfers between the disordered graphene layers forming a nanocomposite.     

ACTH(6–9)PGP Peptide Protects SH-SY5Y Cells from H2O2, tert-Butyl Hydroperoxide,and Cyanide Cytotoxicity via Stimulation of Proliferation and Induction of Prosurvival-Related Genes

Stabilized melanocortin analog peptide ACTH(6–9)PGP (HFRWPGP) possesses a wide range of neuroprotective activities. However, its mechanism of action remains poorly understood. In this paper, we present a study of the proproliferative and cytoprotective activity of the adrenocorticotropic hormone fragment 6–9 (HFRW) linked with the peptide prolyine–glycyl–proline on the SH-SY5Y cells in the model of oxidative stress-related toxicity. The peptide dose-dependently protected cells from H₂O₂, tert-butyl hydroperoxide, and KCN and demonstrated proproliferative activity. The mechanism of its action was the modulation of proliferation-related NF-κB genes and stimulation of prosurvival NRF2-gene-related pathway, as well as a decrease in apoptosis.     

Novel Rearrangement of 3‐Acylaminofuro[2,3‐b]pyridines into 3‐(oxazol‐4‐yl)pyridin‐2‐ones

3‐Acylaminofuro[2,3‐b]pyridine derivatives have been synthesized, and their behavior under acidic and basic conditions was studied. A new base‐catalyzed rearrangement of 3‐acylaminofuro[2,3‐b]pyridine derivatives into 3‐(oxazol‐4‐yl)pyridine‐2‐ones has been founded.     

Evidence from Raman spectroscopy that InhA, the mycobacterial enoyl reductase, modulates the conformation of the NADH cofactor to promote catalysis

InhA, the enoyl reductase from Mycobacterium tuberculosis, catalyzes the NADH-dependent reduction of trans-2-enoyl-ACPs. In the present work, Raman spectroscopy has been used to identify catalytically relevant changes in the conformation of the nicotinamide ring that occur when NADH binds to InhA. For 4(S)-NADD, there is an 11 cm-1 decrease in the wavenumber of the C4-D stretching band (nuC-D) and a 50% decrease in the width of this band upon binding to InhA. While a similar reduction in line width is observed for the corresponding band arising from 4(R)-NADD, nuC-D for this isomer increases 34 cm-1 upon binding to InhA. These changes in nuC-D indicate that the nicotinamide ring adopts a bound conformation in which the 4(S)C-D bond is in a pseudoaxial orientation. Mutagenesis of F149, a conserved active site residue close to the cofactor, demonstrates that this enzyme-induced modulation in cofactor structure is directly linked to catalysis. In contrast to the wild-type enzyme, Raman spectra of NADD bound to F149A InhA resemble those of NADD in solution. Consequently, F149A is no longer able to optimally position the cofactor for hydride transfer, which correlates with the 30-fold decrease in kcat and 2-fold increase in D(V/KNADH) caused by this mutation. These studies thus substantiate the proposal that hydride transfer is promoted by pseudoaxial positioning of the NADH pro-4S bond, and indicate that catalysis of substrate reduction by InhA results, in part, from correct orientation of the cofactor in the ground state.     

4,5-Bis(arylethynyl)-1,2,3-triazoles—A New Class of Fluorescent Labels: Synthesis and Applications

Cu-catalyzed 1,3-dipolar cycloaddition of ethyl 2-azidoacetate to iodobuta-1,3-diynes and subsequent Sonogashira cross-coupling were used to synthesize a large series of new triazole-based push–pull chromophores: 4,5-bis(arylethynyl)-1H-1,2,3-triazoles. The study of their optical properties revealed that all molecules have fluorescence properties, the Stokes shift values of which exceed 150 nm. The fluorescent properties of triazoles are easily adjustable depending on the nature of the substituents attached to aryl rings of the arylethynyl moieties at the C4 and C5 atoms of the triazole core. The possibility of 4,5-bis(arylethynyl)-1,2,3-triazoles’ application for labeling was demonstrated using proteins and the HEK293 cell line. The results of an MTT test on two distinct cell lines, HEK293 and HeLa, revealed the low cytotoxicity of 4,5-bis(arylethynyl)triazoles, which makes them promising fluorescent tags for labeling and tracking biomolecules.