在反向電壓下以硫酸化環糊精分離兒茶酚胺對掌化合物(catecholamines)：不尋常溫度效應

Abstract

本篇論文利用毛細管區帶電泳法添加硫酸化環糊精為對掌選擇劑，於反向電壓、低pH值的條件下，研究溫度對於對掌選擇之效應。選用兩種兒茶酚胺類及兩種結構相似物種之對掌異構物觀察溫度效應。其中發現兩種兒茶酚胺類(catecholamines)及octopamine，即使添加低濃度硫酸鹽衍生化環糊精，其對掌選擇性會隨著溫度增加而增加。而norephedrine的對掌選擇性則隨溫度增加而減少。此現象由於對掌異構物之間，溫度對兩對掌異構物遷移速率改變不一致所造成，當添加硫酸鹽衍生化環糊精在適當的濃度下，(+)型對掌異構物遷移速率改變大於(-)型異構物，則造成此異常的溫度效應。而此不尋常的溫度效應可應用於增加對掌選擇性，及縮短遷移時間。

Temperature effects on the enantioselectivity of basic analytes in CZE enantioseparation were studied under reversed-polarity mode using randomly sulfate-substituted beta-cyclodextrins (MI-S-beta-CD) as chiral seletors. Two catecholamines (epinephrine and isoproterenol) and two structurally related compounds (octapamine and norephedrine) were selected as test compounds in an electrophoretic system at low pH. The mobility differences between the (+)-enantiomers and the (-)-enantiomers of the two catecholamines and dopamine at 40 oC are greater than those at 25 oC with MI-S-beta-CD even at a concentration as low as 0.3 % (w/v). Thus the enantioselectivity of these three basic analytes increases with increasing temperature. This is resulted from the inequality of the temperature effect on the mobility of the two enantiomers. On the contrary, ephedrine behaves differently. The (+)-enantiomers of these basic analytes were found to migrate faster than the (-)-enantiomers. Consequently, the unusual temperature effect on the enantioselectivity can be observed when the mobility difference of the (+)-enantiomer between 40 oC and 25 oC is greater than that of the (-)-enantiomer using MI-S-beta-CD at a concentration greater than about 0.7 %, 0.4 % and 0.3 % (w/v) for enantioseparation of isoproterenol, epinephrine and octopamine, respectively. This unusual temperature effect offers the advantages to enhance enantioselectivity, to improve enantioseparation, and to reduce migration times.