TY - JOUR
T1 - Dynamic solid-state NMR experiments reveal structural changes for a methyl silicate nanostructure on deuterium substitution
AU - Jakobsen, Hans Jørgen
AU - Lindhardt, Anders T
AU - Bildsøe, Henrik
AU - Skibsted, Jørgen
AU - Gan, Zhehong
AU - Hung, Ivan
AU - Larsen, Flemming Hofmann
PY - 2017/11/30
Y1 - 2017/11/30
N2 - 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.
AB - 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.
U2 - 10.1021/acs.jpcc.7b08826
DO - 10.1021/acs.jpcc.7b08826
M3 - Journal article
SN - 1932-7447
VL - 121
SP - 26507
EP - 26518
JO - The Journal of Physical Chemistry Part C
JF - The Journal of Physical Chemistry Part C
IS - 47
ER -