Surface-activated and matrix-assisted laser desorption/ionization mass spectrometry of organotellurium compounds

Various types of ionization of organotellurium compounds in mass-spectrometric study are considered, with diphenyl telluroxide as example. The mass spectra of diphenyl telluroxide are presented. The possibility of applying surface-activated and matrix-assisted laser desorption/ionization mass spectrometry to organotellurium compounds is examined.     

A Compact Second-Harmonic Generator for Tasks of Precision Spectroscopy Within the Range of 240–600 nm

We develop a universal design of a second-harmonic generator enabling a high-efficiency conversion of the CW laser radiation to a range of 240–600 nm. The distinctive features of the generator are its compact size and high stability achieved using an all-in-one (monolithic) hermetic body frame, which enables applications of this device in a broad range of precision spectroscopy and laser cooling. We design three systems for radiation conversion to ranges of 280, 410, and 560 nm and present their characteristics. The systems are used for laser cooling of magnesium ions (280 nm) and thulium atoms (410 nm). Due to the conversion efficiency and stability, the second-harmonic generators developed surpass most commercially available systems of Western manufacturers.     

Metallic beta-phase silicon nanowires: Structure and electronic properties

Electronic band structure and energetic stability of two types of 〈110〉 and 〈001〉 oriented silicon nanowires in β-Sn phase with the surface terminated by hydrogen atoms were studied using density functional theory. It was found that β-Sn nanowires are metastable with zero band gap against to nanowires in diamond phase. The relative energy of the studied wires tends to the energy of the bulk silicon crystal in β-Sn phase.     

Cover Feature: Mechanism of Oxidative Activation of Fluorinated Aromatic Compounds by N-Bridged Diiron-Phthalocyanine: What Determines the Reactivity? (Chem. Eur. J. 63/2019)

The biodegradation of compounds with C−F bonds is challenging due to the fact that these bonds are stronger than the C−H bond in methane. In this work, results on the unprecedented reactivity of a biomimetic model complex that contains an N-bridged diiron-phthalocyanine are presented; this model complex is shown to react with perfluorinated arenes under addition of H₂O₂ effectively. To get mechanistic insight into this unusual reactivity, detailed density functional theory calculations on the mechanism of C₆F₆ activation by an iron(IV)-oxo active species of the N-bridged diiron phthalocyanine system were performed. Our studies show that the reaction proceeds through a rate-determining electrophilic C−O addition reaction followed by a 1,2-fluoride shift to give the ketone product, which can further rearrange to the phenol. A thermochemical analysis shows that the weakest C−F bond is the aliphatic C−F bond in the ketone intermediate. The oxidative defluorination of perfluoroaromatics is demonstrated to proceed through a completely different mechanism compared to that of aromatic C−H hydroxylation by iron(IV)-oxo intermediates such as cytochrome P450 Compound I.     

AM1 studies of photoelectron spectra

Five ionization potentials for thesp,ac andsp, sp conformers of (acetylthiomethyl)trifluorosilane MeC(O)SCH₂SiE₃ and six ionization potentials for the same conformers of (benzoylthiomethyl)trifluorosilane PhC(O)CH₂SiF₃ were calculated by the semiempirical AM1 method. The resulting values are in good agreement with the data of photoelectron spectroscopy only for thesp.ac conformers. The structure of the preferred conformer of (acetylthiomethyl)trifluorosilane was confirmed by measurement of its dipole moment in the gas phase. The influence of the long-range inductive effect (field effect) on the energy of nonbonding electrons of the carbonyl oxygen atom in the series of acetic acid derivatives was observed. For Part 9, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 236–241, February, 1998.     

Saturated nitrogen-containing heterocycles. 12. Stereochemical properties of hydroxyalkylpyrrolidines using 13C NMR spectroscopy

The ¹³C NMR spectra of fifteen compounds in a series of alkyl- and arylsubstituted cis-isomers of hydroxyalkylpyrrolidines have been recorded, and they have been fully interpreted on the basis of configurational and conformational assignments.For Communication 11, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1201–1204, September, 1988.     

Structure and reactivity of 2-methyl-9-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-one

It has been shown that the alkylation of 2-methyl-9-hydroxy-4H-pyrido[1,2-a]pyrimidin-4-one takes place at the oxygen atom, but electrophilic substitution takes place mainly at position 8 of the molecule (the ortho position relative to the hydroxy group).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1660–1666, December, 1992.     

Synthesis and 13C NMR spectra of 5-alkyl-1,4-diaza- and 5-alkyl-1-aza-4-oxabicyclo [3.3.0]octan-8-ones

A group of previously unreported 5-alkyl-1,4-diaza- and 5-alkyl-1-aza-4-oxabicyclo[3.3.0]octan-8-ones have been synthesized from the ethyl esters of -ketocarboxylic acids and ethylenediamine or ethanolamine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1405–1408, October, 1987.     

On multiple orthogonal polynomials for three Meixner measures

Multiple orthogonal polynomials for three discrete Meixner measures with identical exponential decay at infinity are studied. These polynomials are the denominators of the type II Hermite–Padé approximants to some hypergeometric functions. The limit distribution of zeros of such polynomials scaled in a certain way is described in terms of equilibrium logarithmic potentials and in terms of algebraic curves.