Dynamic Micellar Electrokinetic Chromatography. Determination of the Enantiomerization Barriers of Oxazepam, Temazepam, and Lorazepam
作者:Gabriele Schoetz、Oliver Trapp、Volker Schurig
DOI:10.1021/ac991439g
日期:2000.7.1
The temperature-dependent enantiomerization barriers of oxazepam, temazepam, and lorazepam have been determined between 0 and 30 °C by dynamic micellar electrokinetic chromatography (DMEKC) in an aqueous 20 mM borate/phosphate buffer system at pH 8 with 60 mM sodium cholate as chiral surfactant. Interconversion profiles featuring plateau formation and peak broadening were observed and simulated by the new program ChromWin based on the theoretical plate as well as on the stochastic model using the experimental data plateau height, hplateau, peak width at half-height, wh, total retention times, tR, and electroosmotic breakthrough time, t0. Peak form analysis yielded rate constants k and kinetic activation parameters, ΔG⧧, ΔH⧧, and ΔS⧧, of the enantiomerization of oxazepam, temazepam, and lorazepam. At 25 °C, the enantiomerization barrier, ΔG⧧, was determined to be ∼90 kJ mol-1 and the half-lives, τ, were determined to be approximately 21 min. The new approach allows the fast and precise determination of enantiomerization barriers in a biogenic environment and it mimics physiological conditions, as no organic modifiers or abiotic chiral stationary phases (CSP) are employed.
奥沙西泮、
替马西泮和
劳拉西泮的温度依赖性对映异构化势垒已在 0 至 30 °C 范围内通过动态胶束电动色谱 (
DMEKC) 在 pH 8、60 mM
胆酸钠作为手性的 20 mM
硼酸盐/
磷酸盐缓冲液体系中测定表面活性剂。基于理论塔板和随机模型,使用实验数据平台高度、hplateau、半高峰宽、wh、总保留时间,通过新程序 ChromWin 观察和模拟以平台形成和峰展宽为特征的互变曲线、tR 和电渗突破时间 t0。峰形分析得出
奥沙西泮、
替马西泮和
劳拉西泮对映体的速率常数 k 和动力学活化参数 ΔG⧧、ΔH⧧ 和 ΔS⧧。在 25 °C 下,对映体化势垒 ΔG⧧ 确定为 ∼90 kJ mol-1,半衰期 τ 确定为大约 21 分钟。新方法可以快速、精确地测定
生物环境中的对映异构化障碍,并且它模拟生理条件,因为不使用有机改性剂或非
生物手性固定相(C
SP)。