Enantiomeric Separations of Chiral Sulfonic and Phosphoric Acids with Barium-Doped Cyclofructan Selectors via an Ion Interaction Mechanism

详细信息    查看全文

• 作者：Jonathan P. Smuts ; Xin-Qi Hao ; Zhaobin Han ; Curran Parpia ; Michael J. Krische ; Daniel W. Armstrong
• 刊名：Analytical Chemistry
• 出版年：2014
• 出版时间：January 21, 2014
• 年：2014
• 卷：86
• 期：2
• 页码：1282-1290
• 全文大小：386K
• ISSN：1520-6882

文摘

New cyclofructan-6 (CF6)-based chiral stationary phases (CSPs) bind barium cations. As a result, the barium-complexed CSPs exhibit enantioselectivity toward 16 chiral phosphoric and sulfonic acids in the polar organic mode (e.g., methanol or ethanol mobile phase containing a barium salt additive). Retention is predominantly governed by a strong ionic interaction between the analyte and the complexed barium cation as well as hydrogen bonding with the cyclofructan macrocycle. The log k versus log [X], where [X] = the concentration of the barium counteranion, plots for LARIHC鈥揅F6-P were linear with negative slopes demonstrating typical anion exchange behavior. The nature of the barium counteranion also was investigated (acetate, methanesulfonate, trifluoroacetate, and perchlorate), and the apparent elution strength was found to be acetate > methanesulfonate > trifluoroacetate > perchlorate. A theory based upon a double layer model was proposed wherein kosmotropic anions are selectively adsorbed to the cyclofructan macrocycle and attenuate the effect of the barium cation. van鈥檛 Hoff studies for two analytes were conducted on the LARIHC鈥揅F6-P for three of the barium salts (acetate, trifluoroacetate, and perchlorate), and the thermodynamic parameters governing retention and enantioselectivity are discussed. Interestingly, for the entropically driven separations, enantiomeric selectivity can increase at higher temperatures, even with decreasing retention.