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

作者：Jakobsen Hans J^*; Lindhardt Anders T; Bildsoe Henrik; Skibsted Jorgen; Gan Zhehong; Hung Ivan; Larsen Flemming H

来源：Journal of Physical Chemistry C, 2017, 121(47): 26507-26518.

DOI：10.1021/acs.jpcc.7b08826

Structural characterizations of three different solidgas reaction products, recently obtained from abraded solid-state silicate free radicals reacting with two isotopically enriched methane gases, (CH4)-C-13 and CD4 (a possible sink for methane on MARS) and with (CO2)-C-13, 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 (E-a), and (CO2)-C-13/(CH3)-C-13 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 (= 2022.6 kJ/mol) for CH3 3-site jump motions. The ZCTs for these two compounds are 120 and 162 mu s, respectively, indicative of the high E-a values for CH3/CD3 groups. Determination of Ea for 4-CD3-phenanthrene by low-temperature 2H MAS NMR experiments supplemented the previously reported liquid-state E-a value (E-a = 21 kJ/mol) for 4-CH3-phenanthrene. Finally, such experiments also revealed the structural difference for the free-radical reaction products with (CH4)-C-13 and CD4, i.e, a change from helical to chain structure.

• 出版日期2017-11-30