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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Solid State NMR Studies of the Molecular Motions in the Polycrystalline α-L-Fucopyranose and Methyl α-L-Fucopyranoside
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Solid State NMR Studies of the Molecular Motions in the Polycrystalline α-L-Fucopyranose and Methyl α-L-Fucopyranoside

机译：固态NMR研究多晶α-L-富精糖和甲基α-L-富精糖苷中分子运动

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摘要

Molecular dynamics of polycrystalline α-L-fucopyranose and methyl α-L-fucopyranoside have been investigated using ~(13)C and ~1H spin relaxation times over a range of temperatures (90-400 K). For methyl α-L-fucopyranoside at 300 K, both methoxyl and methyl groups had much shorter ~(13)C T_1 than the carbons in the pyran ring. ~(13)C T_1 relaxation measurements (at 74.56 MHz) as a function of temperature enabled characterization of the 3-fold rotations of the methoxyl (E_a ～ 9 kJ/mol, τ_c ～ 0.7 * 10~(-13)s) and methyl (E_a ～ 9 kJ/mol, τ_c ～ 2 * 10~(-13)s) groups. Proton T_1(100 MHz) measurements of methyl α-L-fucopyranoside showed that the relaxation processes (E_a ～ 11 kJ/mol, τ_c ～ 0.7 * 10~(-13)s), corresponding to rotations of the methoxyl and methyl groups, are not distinguishable and occurred together at about 131 K. For α-L-fucopyranose, proton T_1 showed a relaxation rate maximum at 224 K, attributed to the 3-fold rotation of methyl group (E_a ～ 15 kJ/mol, τ_0 ～ 2.6 * 10~(-13)s). The rotation processes of the methyl groups dominated T_(1ρ) processes for both saccharides and appeared at the low-temperature end (90-150 K) of the temperature range. Contributions of hydroxyl groups to both T_1 and T_(1ρ) processes were obscured by the overwhelming relaxation efficiency of methyl groups. The proton second moment showed a reduction to a lower value at about 150 K due to the rotation of methyl groups.
机译：使用〜（13）C和〜1H自旋弛豫时间在一定温度范围（90-400 K）内研究了多晶α-L-呋喃二糖和甲基α-L-呋喃二糖苷的分子动力学。对于在300 K下的甲基α-L-呋喃果糖苷，甲氧基和甲基的〜（13）C T_1都比吡喃环中的碳短得多。 〜（13）C T_1弛豫测量值（在74.56 MHz处）是温度的函数，可表征甲氧基的3倍旋转（E_a〜9 kJ / mol，τ_c〜0.7 * 10〜（-13）s），并且甲基（E_a〜9 kJ / mol，τ_c〜2 * 10〜（-13）s）。甲基α-L-呋喃果糖苷的质子T_1（100 MHz）测量表明，弛豫过程（E_a〜11 kJ / mol，τ_c〜0.7 * 10〜（-13）s）对应于甲氧基和甲基的旋转，不能区分，大约在131 K时一起发生。对于α-L-富铀，质子T_1在224 K处显示最大弛豫速率，这归因于甲基的3倍旋转（E_a〜15 kJ / mol，τ_0〜2.6 * 10〜（-13）s）。甲基的旋转过程主导着两种糖的T_（1ρ）过程，并出现在温度范围的低温端（90-150 K）。甲基对弛豫效率的抑制作用掩盖了羟基对T_1和T_（1ρ）过程的贡献。由于甲基的旋转，质子的第二矩在约150 K处显示降低至较低的值。

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