Dynamic Solid-State NMR Experiments Reveal Structural Changes for a Methyl Silicate Nanostructure on Deuterium Substitution

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DOI

  • Hans J. Jakobsen
  • Anders T. Lindhardt
  • ,
  • Henrik Bildsøe
  • ,
  • Jørgen Skibsted
  • Zhehong Gan, National High Magnetic Field Laboratory
  • ,
  • Ivan Hung, National High Magnetic Field Laboratory
  • ,
  • Flemming H. Larsen, Københavns Universitet

Structural characterizations of three different solid-gas reaction products, recently obtained from abraded solid-state silicate free radicals reacting with two isotopically enriched methane gases, 13CH4 and CD4 (a possible sink for methane on MARS) and with 13CO2, are derived from various dynamic solid-state NMR experiments. These include cross-polarization/depolarization zero-cross times (ZCTs), variable temperature (VT) NMR to study 3-site jump CH3/CD3 activation energies (Ea), and 13CO2/13CH3 molecular species as a spy to determine the approximate diameters for the channel structures for some of these structures. Literature Ea data indicate that l-alanine and 4-CH3-phenanthrene exhibit the highest known Ea values (= 20-22.6 kJ/mol) for CH3 3-site jump motions. The ZCTs for these two compounds are 120 and 162 μs, respectively, indicative of the high Ea values for CH3/CD3 groups. Determination of Ea for 4-CD3-phenanthrene by lowerature 2H MAS NMR experiments supplemented the previously reported liquid-state Ea value (Ea = 21 kJ/mol) for 4-CH3-phenanthrene. Finally, such experiments also revealed the structural difference for the free-radical reaction products with 13CH4 and CD4, i.e, a change from helical to chain structure.

OriginalsprogEngelsk
TidsskriftJournal of Physical Chemistry C
Vol/bind121
Nummer47
Sider (fra-til)26507-26518
Antal sider12
ISSN1932-7447
DOI
StatusUdgivet - 30 nov. 2017

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