Molecular motion of alcohols Adsorbed in ACF hydrophobic nanoslits as studied by solid-state NMR
Molecular motion of alcohols Adsorbed in ACF hydrophobic nanoslits as studied by solid-state NMR
复制标题
通过固态核磁共振研究吸附在 ACF 疏水纳米缝中的醇的分子运动
DOI：
10.1007/s10450-015-9669-5
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发表时间：
2015
期刊：
影响因子：
3.3
通讯作者：
Taro Eguchi
中科院分区：
文献类型：
--
作者：
Hiroaki Omichi;Takahiro Ueda;Taro Eguchi
The molecular motion and local structure of methanol-d1(CH3OD) and ethanol-d1(C2H5OD) in activated carbon fiber (ACF) with a slit width of 0.7 and 1.1 nm have been investigated by solid-state1H and2H NMR.2H NMR spectra for alcohols confined in ACF gave a so-called Pake doublet below 140 K, which were characterized by the2H quadrupole coupling constant (QCC) of 185 kHz and the asymmetric parameter of the electric-field-gradient tensor (η) of 0.1. The QCC value of the deuteron was indicative of the hydrogen bond formation with the O···O distance of ca. 0.27 nm, suggesting the solid-like feature of alcohols in ACFs. The quadrupole broadening vanished on heating and the single isotropic resonance line was observed. Alcohol molecules were undergoing a rapid motion like as in the bulk liquid, indicating a transition from solid to liquid in ACFs. Temperature-dependent1H NMR spectra were used for evaluating theEavalue for reorientation in solid-like alcohols, whereas the2H NMR spectra were used for obtaining the translation accompanying reorientation in liquid-like alcohols. Alcohols with a bilayered structure in ACF with a slit width of 1.1 nm gave similarEavalues, whereas C2H5OD in ACF with a slit width of 0.7 nm, in which a monolayered structure is expected, exhibited a cross-over of two activation processes at 172 K. The variation inEawas probably caused by the structural relaxation concerning with the hydrogen bonding formation and/or excitation of the large amplitude local motion. The competition of the directionality of hydrogen bonds and a freedom of molecular orientation plays an important role to characterize the intermolecular structure as well as the physicochemical properties in amphipathic molecules in confinement.
