Properties of backscattered particles produced by protons of energy above 1 TeV in an iron absorber

Backscattered-particle production is studied by means of a detailed simulation of cascade processes in a dense medium. The energy dependence of the albedo and the spatial and angular distributions of various components of this flux are analyzed.     

New computational method for atoms in an intense electromagnetic field

A new representation is found for the interaction of intense circularly polarized light with an atom. A stationary centrosymmetric part, which depends on the field parameter a ₀=F/ω², is separated out from the atom-field interaction. The time-dependent part of the interaction is represented in the form of a multipole expansion with a ₀ taken into account. The application of this representation for calculating the nonlinear dynamic polarizability of a complicated atom in the random-phase approximation with exchange is studied. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 3, 189–193 (10 August 1998)     

Muonium states in semiconductor crystals: Quantum-chemical calculations

The electronic structure of muonium (Mu) located at the bond-centered sites of the silicon and diamond crystals is calculated by the intermediate neglect of differential overlap method. Calculations of the electronicg- and hyperfine interaction tensors of the impurity atom are performed. The results obtained are compared to the experimental properties of “anomalous” muonium Mu^*. It is shown that the properties of Mu located at the bond-centered sites of the Si and C lattices are in qualitative agreement with the observed properties of Mu^*.     

Chirospecific Syntheses of Conformationally Constrained 7-Azabicycloheptane Amino Acids by Transannular Alkylation

A new method is reported for the chirospecific preparation of optically pure 1-carboxy-7-azabicycloheptane amino acids for the generation of peptidomimetics as conformational probes. The method allows for the multigram preparation of these amino acid analogues through use of a thiolactam sulfide contraction and a transannular alkylation sequence as the key C-C bond-forming steps, starting from L-glutamic acid. The route provides access to two common intermediates, 7-(benzyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptane and (1S,4R)-7-(benzyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptanone tert-butyl ester, for elaboration to symmetrical and chiral amino acid homologues, respectively. Decarboxylation of the C-1 carboxy unit of the latter intermediate also demonstrated the applicability of the method for a short, chirospecific preparation of a (+)-epibatidine intermediate, (1S,4R)-7-(tert-butyloxycarbonyl)-1-carboxy-7-azabicyclo[2.2.1]-3-heptanone.     

Electron-impact and chemical ionization detection of nicotine and cotinine by gas chromatography-mass spectrometry in rat plasma and brain.

Nicotine and its metabolite, cotinine, were measured in rat plasma and brain by gas chromatography-mass spectrometry. Both agents were extracted from plasma and brain, separated on a capillary column, and quantified by single-ion monitoring. The major fragment ions of nicotine and cotinine at m/z 84 and m/z 98, respectively, were monitored by electron-impact ionization detection and the protonated molecular ions at m/z 163 and m/z 177, respectively, were monitored by chemical ionization detection. Both compounds were quantified using deuterium-labeled nicotine and cotinine, respectively, as internal standards.     

Enantiospecific synthesis of annulated nicotine analogues from D-glutamic acid. 7-Azabicyclo[2.2.1]heptano[2.3-c]pyridines

The conformationally restricted nicotinoid (1S,4S)-7-methyl-7-azabicyclo[2.2.1]heptano[2,3-c]pyridine dihydrochloride has been prepared enantiospecifically from D-glutamic acid. The method involved a lithium cis-2,6-dimethylpiperidide-mediated intramolecular anionic cyclization of (2S,5R)-N-(tert-butyloxycarbonyl)-5-[3-(4-N-chloropyridinyl]proline methyl ester in tandem with a standard decarboxylation sequence. Reductive amination afforded the desired N-methylated [2.2.1]bicyclonicotinoid. Cyclization of the corresponding iodopyridinylproline methyl ester, obtained via ultrasound-facilitated chloro-iodo exchange, was also effected.     

Luminescent-probe study of the structure of alcohol — Water solutions

Journal of Structural Chemistry -     

Über die lokale Zetafunktion von Shimuravarietäten. Monodromiefiltration und verschwindende Zyklen in ungleicher Charakteristik

Ohne Zusammenfassung

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On the local zeta function of Shimura varieties. Monodromy filtration and vanishing cycles in unequal characteristic

     

Preparation of functionalized, conformationally constrained DTPA analogues from L- or D-serine and trans-4-hydroxy-L-proline. Hydroxymethyl substituents on the central acetic acid and on the backbone

The enantio- and diastereospecific syntheses of conformationally constrained diethylenetriaminepentaacetic acid (DTPA) analogues that are functionalized with a hydroxymethyl linker substituent on the central acetic acid or on the backbone are described. Key synthetic steps include (i) displacement of the 4-hydroxyl group of N-BOC-trans-4-hydroxy-L-proline benzyl ester, via activation as the triflate, with suitable amines derived from L- or D-serine, (ii) the low-temperature alkylation of diethylenetriamines with the triflate of benzyl glycolate, thereby minimizing competitive lactamization, to give DTPA pentabenzyl esters, and (iii) deprotection to afford the corresponding DTPA analogues under very mild hydrogenolysis conditions.