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首页> 外文学位 >The role of water in the formation and structure of oligomer/alpha-cyclodextrin inclusion complexes.
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The role of water in the formation and structure of oligomer/alpha-cyclodextrin inclusion complexes.

机译：水在低聚物/α-环糊精包合物的形成和结构中的作用。

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摘要

alpha-Cyclodextrin (alpha-CD), a cyclic oligosaccharide, can form inclusion complexes (ICs) with polymer molecules in the columnar crystal in which alpha-CD molecules stack to form a molecular tube. As-received alpha-CD in the cage crystal structure can form an IC with neat poly(ethylene glycol) (PEG). The transformation of alpha-CD from cage to columnar structure as a result of IC formation is tracked with wide-angle X-ray diffraction as a function of temperature, atmospheric water vapor content and guest molecular weight and hydrophobicity. A first-order kinetic model is used to describe the kinetics of the complexation. The time required to complex PEG(200) (MW = 200 g/mol) at low water activities is greater than 300 hours whereas a few hours are necessary at high water activities. Additionally, the complexation kinetics of the linear alkane, hexatriacontane (HTC), mixed with solid alpha-CD are slower than PEG(600) (MW = 600 g/mol), which has a similar molecular weight and all-trans end-to-end length as HTC.; Complementary water vapor sorption and wide-angle X-ray diffractomery (WAXD) were performed on oligomer/alpha-CD ICs to determine their structures and stabilities. To discern the effect of guest molecule hydrophobicity on water adsorption isotherms, PEG(600) and HTC guests were used. Sorption isotherms for PEG(600)/alpha-CD IC are similar to those obtained for pure alpha-CD and PEG(600), suggesting the presence of dethreaded PEG(600) in the sample. WAXD collected before and after water vapor sorption of PEG(600)/alpha-CD IC indicated a partial conversion from columnar to cage crystal structure, the thermodynamically preferred structure for pure alpha-CD, due to dethreading of PEG600. This behavior does not occur for HTC/alpha-CD IC. Sorption isotherms collected at 20, 30, 40 and 50°C allowed the calculation of the isosteric heats of adsorption and the integral entropies of adsorbed water which are characterized by minima that indicate the monolayer concentration of water in the ICs. Solid-state 13C NMR suggests a dramatic increase in HTC and alpha-CD molecular motion upon complexation.
机译：α-环糊精（α-CD）是一种环状寡糖，可以与柱状晶体中的聚合物分子形成包合物（ICs），在该晶体中α-CD分子堆叠形成分子管。笼状晶体结构中所接收的α-CD可以与纯聚乙二醇（PEG）形成IC。 IC形成的结果是，α-CD从笼状结构转变为柱状结构，并通过广角X射线衍射来跟踪温度，大气中水蒸气含量以及客体分子量和疏水性的变化。一阶动力学模型用于描述络合动力学。在低水活度下络合PEG（200）（MW = 200 g / mol）所需的时间大于300小时，而在高水活度下需要几个小时。此外，与固体α-CD混合的直链烷烃六三金刚烷（HTC）的络合动力学比PEG（600）（MW = 600 g / mol）慢，后者具有相似的分子量和全反式端基。 -结束长度为HTC。对低聚物/α-CDIC进行互补的水蒸气吸附和广角X射线衍射（WAXD），以确定其结构和稳定性。为了区分客体分子疏水性对水吸附等温线的影响，使用了PEG（600）和HTC客体。 PEG（600）/α-CDIC的吸附等温线类似于纯α-CD和PEG（600）的吸附等温线，表明样品中存在脱螺纹PEG（600）。在PEG（600）/α-CDIC的水蒸气吸附之前和之后收集的WAXD表明，由于PEG600脱线，部分从柱状晶体结构转变为笼状晶体结构，这是纯α-CD的热力学优选结构。对于HTC / alpha-CD IC，不会发生此行为。在20、30、40和50°C下收集的吸附等温线可以计算出吸附的等热量和被吸附水的积分熵，这些特征的最小值表示IC中水的单层浓度。固态13 C NMR表明，络合后HTC和α-CD分子运动显着增加。

著录项

  • 作者

    Hunt, Marcus A.;

  • 作者单位

    North Carolina State University.;

  • 授予单位 North Carolina State University.;
  • 学科 Chemistry Polymer.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 166 p.
  • 总页数 166
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 高分子化学（高聚物）;
  • 关键词

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