Chemical ionization mass spectra of natural monohydroxy- and monoacyloxy-substituted dihydropyranocoumarins and dihydrofurocoumarins

Summary The chemical ionization mass spectra of ten compounds of the group of natural monohydroxy and monoacyloxy derivatives of dihydropyranocoumarins and dihydrofurocoumarins have been studied. Their difference from the electron impact mass spectra has been shown. The structural-analytical possibilities of the method of chemical ionization for this series of substances has been determined.M. V. Lomonosov Moscow State University. Patrice Lumumba International Friendship University, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 508–512, July–August, 1977.     

Modeling of the Elementary Processes of Metal Azide Decomposition

An analysis of the available experimental data on the slow and explosive decomposition of metal azides demonstrates that the intermediate product of the reaction is N₆. Based on quantum-chemical calculations, the most symmetrical stable N₆ complexes with cyclic, linear, and previously undetected octahedral configurations are established. The energy balance of reactions is calculated. It is demonstrated that the activation energy of forming the cyclic complex is minimum, and the energy of forming the octahedral complex is maximum. Conditions of forming complexes inside the crystal matrix are discussed. An important role of metal in the formation of complexes from azide groups is demonstrated, in particular, the existence of the stable Me₂N₆ cluster is established.     

Design,Synthesis, and Application of an Optimized Monofluorinated Aliphatic Label for Peptide Studies by Solid‐State 19F NMR Spectroscopy

A conformationally restricted monofluorinated α‐amino acid, (3‐fluorobicyclo[1.1.1]pentyl)glycine (F‐Bpg), was designed as a label for the structural analysis of membrane‐bound peptides by solid‐state ¹⁹F NMR spectroscopy. The compound was synthesized and validated as a ¹⁹F label for replacing natural aliphatic α‐amino acids. Calculations suggested that F‐Bpg is similar to Leu/Ile in terms of size and lipophilicity. The ¹⁹F NMR label was incorporated into the membrane‐active antimicrobial peptide PGLa and provided information on the structure of the peptide in a lipid bilayer.     

On Twisted N = 2 5D Super Yang–Mills Theory

On a five-dimensional simply connected Sasaki–Einstein manifold, one can construct Yang–Mills theories coupled to matter with at least two supersymmetries. The partition function of these theories localises on the contact instantons, however, the contact instanton equations are not elliptic. It turns out that these equations can be embedded into the Haydys–Witten equations (which are elliptic) in the same way the 4D anti-self-dual instanton equations are embedded in the Vafa–Witten equations. We show that under some favourable circumstances, the latter equations will reduce to the former by proving some vanishing theorems. It was also known that the Haydys–Witten equations on product manifolds \({M_5 = M_4 \times \mathbb{R}}\) arise in the context of twisting the 5D maximally supersymmetric Yang–Mills theory. In this paper, we present the construction of twisted N = 2 Yang–Mills theory on Sasaki–Einstein manifolds, and more generally on K-contact manifolds. The localisation locus of this new theory thus provides a covariant version of the Haydys–Witten equation.     

The hydrogenation of methyl on metallic surfaces

The stream technique was used to comparatively analyze the characteristics of the deposition of a-C:H films from methyl radicals transferred by a carrier gas CH₄/C₂H _y /H₂ (y = 2, 4, 6) in a quartz tube with cylindrical insets made of Cu, Ni, Fe, W, Si, and stainless steel (SS), initial and coated with thin Pd or Rh films, over the temperature range 300–1000 K. The deposition of methyl was fully suppressed in a tube section heated to 380–800 K with all the insets specified. During further mixture movement outside this section in the tube with a decreasing wall temperature, carbon deposition resumed. The most effective catalyst of the hydrogenation reaction was stainless steel. Radicals and unsaturated hydrocarbons capable of polymerization at 300–400 K were fully removed from the carrier gas flow (CH₄/C₂H _y /H₂) after several hundreds of collisions with the surface of SS heated to 420–470 K. The possibility of creating an SS recombination filter for hydrocarbon radicals (the performance of radical hydrogenation reactions) transferred by a CH₄/C₂H _y /H₂ laminar flow was demonstrated. The deposition of a thin Pd film (∼10 nm) on steel did not increase the effectiveness of the surface with respect to radical recombination reactions. At the same time, Rh films increased the catalytic effectiveness of the surface of SS with respect to the hydrogenation of methyl and unsaturated hydrocarbons (380–420 K). The data obtained were used to select temperature conditions and mutual arrangement for the construction elements of an ITER diverter made of tungsten and stainless steel.     

Lytic transglycosylase MltB of Escherichia coli and its role in recycling of peptidoglycan strands of bacterial cell wall

The cell wall is an indispensable structure for the survival of bacteria and a target for antibiotics. Peptidoglycan is the major constituent of the cell wall, which is comprised of backbone repeats of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). A peptide stem is appended to the NAM unit, which in turn experiences cross-linking with a peptide from another peptidoglycan in the final steps of cell wall assembly. In the normal course of bacterial growth, as much as 60% of the parental cell wall is recycled, a process that is not fully understood. A polymeric cell wall is fragmented by the family of lytic transglycosylases, and certain key fragments are transported to the cytoplasm for recycling. The genes for the six known lytic transglycosylases of Escherichia coli were cloned, and the enzymes were purified in this study. It is shown that MltB is the only lytic transglycosylase to turn over a synthetic peptidoglycan fragment of two NAG-NAM repeats; hence this enzyme is likely to be the lytic transglycosylase responsible for processing of shorter peptidoglycan strands. Lytic transglycosylases have been proposed to go through an oxocarbenium species that would trap the 6-hydroxyl moiety of the glucosamine residue of muramic acid to generate the so-called 1,6-anhydromuramyl moiety. It is documented herein by characterization of the products of turnover that this process takes place to the total exclusion of the entrapment of a water molecule by the reactive intermediary oxocarbenium species. Furthermore, turnover of the E. coli sacculus (whole cell wall) by MltB was characterized. It is documented that each MltB molecule is able to process the cell wall 14000 times in the course of a single doubling time for E. coli.     

An accurate force field model for the strain energy analysis of the covalent organic framework COF-102

By using an accurate molecular mechanics force field, which was parametrized on the basis of first principles calculations, the network topology of the Covalent Organic Framework COF-102 could correctly be predicted without experimental input. The ctn structure is preferred thermodynamically by 11.2 kcal mol(-1) over the bor topology due to a lower steric strain. The origin for this strain is analyzed in detail.