紫外光谱法研究环糊精对2,4-滴丙酸甲酯对映体的包合作用

    采用紫外光谱法研究β-环糊精(β-CD)、羧甲基-β-环糊精(CM-β-CD)和部分甲基化-β-环糊精(PM-β-CD)对 2,4-滴丙酸甲酯包合作用的对映体差异.在298.15～318.15 K的温度范围内,3种环糊精均能与2,4-滴丙酸甲酯形成 1∶1 型的包合物,其包合常数值大小依次为 KPM-β-CDKCM-β-CD>Kβ-CD,且随着温度的升高而降低.经计算,热力学参数ΔG、ΔH 和ΔS 均为负值,说明包合反应是放热反应且能自发进行,焓变是形成包合物的主要驱动力.对于同一环糊精主体而言,R-2,4-滴丙酸甲酯比 S-2,4-滴丙酸甲酯易于被包合,且 KR /KS 的顺序与包合常数 K 值的次序一致.     

Improvement of the desorption of the pesticide 2,4‐D via complexation with HP‐β‐cyclodextrin

Inclusion complex formation of 2,4‐dichlorophenoxyacetic acid (2,4‐D) with hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) has been proposed as a way of modifying the behaviour of the pesticide in the soil environment. The present study assesses the effect of complex formation on 2,4‐D physicochemical properties (aqueous solubility, crystallinity and dissolution rate) and its behaviour on soils. The solid complexes were prepared using different methods (spray drying, kneading and heating in a sealed container). To confirm the complex formation in the solid state differential scanning calorimetry, hot stage microscopy and x‐ray diffraction techniques were employed. Complex formation in solution was studied by phase solubility. The presence of HP‐β‐CD increased the 2,4‐D solubility nine times approximately. The apparent stability constant was determined as 98.6 M ⁻¹. The dissolution rates of the 2,4‐D/HP‐β‐CD complexes were examined and compared with that of the pure pesticide. The results indicated that the complex may have great utility as a rapid way of dissolving the pesticide. Batch experiments were performed to study the adsorption–desorption of 2,4‐D on soils and the influence of the HP‐β‐CD over these processes. The results showed that HP‐β‐CD could increase the desorption of 2,4‐D previously adsorbed on soils. © 2000 Society of Chemical Industry