Molecular motions, structure and hydration behaviour of glucose oligomers in aqueous solution
Molecular motions, structure and hydration behaviour of glucose oligomers in aqueous solution
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DOI：
10.1039/c9cp05214c
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发表时间：
2019-12-07
影响因子：
3.3
通讯作者：
Shikata, Toshiyuki
中科院分区：
文献类型：
--
作者：
Arai, Kengo;Shikata, Toshiyuki
采用频率高达50 GHz的极高频介电谱测量技术，研究了葡萄糖低聚物（Gn，n = 2 ~ 7，聚合度）在水溶液中的聚合度和分子运动、构型和水合行为的温度依赖性。得到的介电谱的水溶液中的Gn分解成四个Debye型弛豫模式。最快的弛豫模式j = 1被分配给样品溶液中的自由水分子的旋转过程。第二快的模式j = 2归因于水合水分子与自由水分子的交换过程，第三模式j = 3被认为是每个重复的吡喃葡萄糖苷（Glu）单元上的羟基在分子内氢键作用后的旋转过程。最慢的模式j = 4在弛豫时间取决于n被分配到Gn分子的整体旋转，具有类似于在低温下的单螺旋V型晶体结构的小片段的配置。介电模式j = 4的存在揭示了Glu单元具有携带平行于Gn骨架的分量的电偶极矩，该分量与C1 -> C4方向对齐。通过模式j = 1的弛豫强度，在10 ° C至70 ° C的温度范围内测定了Gns在水溶液中的每Glu单元的水合水分子数（水合数，n（H））。Gn低聚物在检测的温度范围内高度溶于水，具有轻微依赖于n的n（H）值，并且随着温度升高在约30 ℃下表现出明显的脱水行为。n（H）的这些温度依赖性明显弱于模型Glu单元化合物甲基α-d-吡喃葡萄糖苷（G1）的温度依赖性。然后，葡萄糖低聚物的聚合有效地抑制了G1的脱水行为。
The degree of polymerization and temperature dependencies of the molecular motions, configuration and hydration behaviour of glucose oligomers (Gn, n = 2 to 7, degree of polymerization) in aqueous solutions were investigated using extremely high-frequency dielectric spectrum measuring techniques up to 50 GHz. The obtained dielectric spectra for the aqueous Gn solutions were well decomposed into four Debye-type relaxation modes. The fastest relaxation mode j = 1 was assigned to the rotational process of free water molecules in the sample solution. The second fastest mode j = 2 was attributed to the exchange process of hydrated water molecules with free water molecules, and the third mode j = 3 was recognized as the rotational process of hydroxy groups attached to each repeating glucopyranoside (Glu) unit after their lifetimes of intramolecular hydrogen bonding. The slowest mode j = 4 at a relaxation time depending on n was assigned to the overall rotation of the Gn molecules possessing configurations similar to that of small fragments of single helical V-type crystalline structures at low temperatures. The presence of the dielectric mode j = 4 revealed that the Glu units possessed electric dipole moments carrying a component parallel to the Gn backbone aligned with the C1 -> C4 direction. The number of hydrated water molecules per Glu unit (hydration number, n(H)) was determined for Gns in aqueous solutions in the temperature range from 10 degrees C to 70 degrees C via the relaxation strength of mode j = 1. The Gn oligomers were highly soluble in water within the temperature range examined, possessing n(H) values slightly dependent on n and demonstrated clear dehydration behaviour at approximately 30 degrees C with increasing temperature. These temperature dependencies of n(H) were substantially weaker than those of a model Glu unit compound, methyl alpha-d-glucopyranoside (G1). Then, the polymerization of glucose oligomers effectively depresses the dehydration behaviour of G1.