Ресурсный центр «Магнитно-резонансные методы исследования»

A.A. Shmyreva, M. Safdari, I. Furó, S.V. Dvinskikh

“NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning”

J. Chem. Phys., 2016, 144, 224201
DOI:10.1063/1.4953540

Orders of magnitude decrease of ²⁰⁷Pb and ¹⁹⁹Hg NMR longitudinal relaxation times T 1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead( ii) halides, the most dramatic decrease of T 1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200–15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.

M.A. Sandzhieva, A.N. Kazakova, I.A. Boyarskaya, A.Yu. Ivanov, V.G. Nenajdenko, A.V. Vasilyev

“Friedel–Crafts Alkylation of Arenes with 2-Halogeno-2-CF3-styrenes under Superacidic Conditions. Access to Trifluoromethylated Ethanes and Ethenes”

J. Org. Chem., 2016, 81, 5032-5045
DOI:10.1021/acs.joc.6b00419

The formation of the corresponding benzyl cations [ArHC⁺–CH(X)CF₃] takes place under protonation of E-/Z-2-halogeno-2-CF₃ styrenes [ArCH═C(X)CF₃, X = F, Cl, Br] in superacids. The structures of these new electrophiles were studied by means of NMR and theoretical DFT calculations. According to these data, in the case of bromo derivatives, the formed cations, most probably, exist as cyclic bromonium ions; however, in the cases of chloro and fluoro derivatives, open forms are more preferable. Subsequent reaction of these benzyl cations with arenes proceeds as Friedel–Crafts alkylation to afford 1,1-diaryl-2-halo-3,3,3-trifluoropropanes [Ar(Ar′)CH–CH(X)CF₃] in high yields (up to 96%) as a mixture of two diastereomers. The prepared halogenopropanes were easily converted into the corresponding mixtures of E-/Z-trifluoromethylated diarylethenes [Ar(Ar′)C═CCF₃] (in yields up to 96%) by dehydrohalogenation with base (KOH or t-BuOK). The mechanism of elimination (E₂ and Ecb) depends on the nature of the leaving group and reaction conditions.

Получено первое прямое экспериментальное подтверждение существования головного мозга у директора РЦ МРМИ. С привлечением иностранных специалистов (Dr. Jing Guo, Dr. Benjamin Koeppe), а также бывших сотрудников РЦ Светланы Пылаевой и д-р Андрея Гуринова в клинике Charite (Берлин, Германия) были зарегистрированы слабые сигналы магнитного резонанса от головы П.М. Толстого. Сделанная на их основе реконструкция (см. рисунок) свидетельствует в пользу гипотезы о существовании у пациента головного мозга.

A.A. Osipov, V.E. Eremyashev, A.S. Mazur, P.M. Tolstoi, L.M. Osipova

“Coordination State of Aluminum and Boron in Barium Aluminoborate Glass”

Glass Physics and Chemistry, 2016, 42(3), 230–237
DOI:10.1134/S1087659616030111

This paper considers the coordination state of boron and aluminum ions in barium aluminoborate glass with a constant ratio of BaO : B₂O₃ = 0.5 and a variable ratio of Al₂O₃ : BaO = 0–3. The dependence of the concentrations of boron and aluminum atoms with a variable coordination number on the Al₂O₃ content was estimated by IR, ¹¹B and ²⁷Al NMR spectroscopy. The nonlinear nature of the obtained dependences was attributed to variations in the aluminum oxide properties. At a content of less than 30 mol % Al₂O₃ serves primarily as a network former, while an increase in the Al₂O₃ concentration results in its higher modifying role in the studied glass.

2-3 июня РЦ МРМИ принял участие в Startup Village 2016 в Сколково. На одном из мероприятий были представлены возможности Научного парка СПбГУ для выполнения исследований по заявкам сторонних организаций. Видеоряд о Startup Village 2016 можно найти тут.