Tang H R, Belton P S
Institute of Food Research, Norwich Research Park, Colney, UK.
Solid State Nucl Magn Reson. 1998 Aug;12(1):21-30. doi: 10.1016/s0926-2040(98)00041-1.
The molecular motions of D-alpha-galacturonic acid monohydrate (GA) and its derivative methyl-alpha-D-galacturonic acid methyl ester monohydrate (MGAM) in the solid state have been studied using 1H NMR. Both protonated and deuterium exchanged samples have been used. Spin-lattice relaxation times in the laboratory and rotating frames as well as second moments have been measured over the temperature range 90-370 K. Analysis of results has shown that in GA spin-lattice relaxation is chiefly by hydroxyl groups and water of crystallization. In MGAM, methyl groups dominate spin-lattice relaxation in the laboratory frame at the low temperature. Hydroxyl groups and water of crystallization contribute to the spin-lattice relaxation in the laboratory frame in the high temperature region. In the rotating frame motion of hydroxyl groups and water of crystallization provide the main relaxation pathway. Changes in the static second moment with temperature can be reasonably well predicted using values of correlation time and motionally averaged second moments obtained by fitting the spin-lattice relaxation data. 13C CPMAS spectra for GA and MGAM are also described.
利用1H NMR研究了D-α-半乳糖醛酸一水合物（GA）及其衍生物α-D-半乳糖醛酸甲酯一水合物（MGAM）在固态下的分子运动。使用了质子化和氘交换样品。在90 - 370 K的温度范围内测量了实验室和旋转坐标系中的自旋晶格弛豫时间以及二阶矩。结果分析表明，在GA中，自旋晶格弛豫主要由羟基和结晶水引起。在MGAM中，低温下甲基在实验室坐标系中主导自旋晶格弛豫。高温区域中，羟基和结晶水对实验室坐标系中的自旋晶格弛豫有贡献。在旋转坐标系中，羟基和结晶水的运动提供了主要的弛豫途径。利用通过拟合自旋晶格弛豫数据获得的相关时间值和动态平均二阶矩，可以较好地合理预测静态二阶矩随温度的变化。还描述了GA和MGAM的13C CPMAS光谱。
