Synthesis, Characterization, and Application of Chiral Ionic Liquids and Their Polymers in Micellar Electrokinetic Chromatography

Abstract

Two amino acid derived (leucinol and N-methyl pyrrolidinol) chiral ionic liquids are synthesized and characterized both in monomeric and polymeric forms. Leucinol based chiral cationic surfactant is room a temperature ionic liquid (RTIL), and pyrrolidinol based chiral cationic surfactant melts at 30-35 °C to form ionic liquid (IL). The monomeric and polymeric ILs are thoroughly characterized to determine critical micelle concentration, aggregation number, polarity, optical rotation and partial specific volume. Here in, we present the first enantioseparation using chiral IL as pseudostationary phase in capillary electrophoresis. Chiral separation of two acidic analytes, (±)-alpha-bromophenylacetic acid (±)-(α-BP-AA) and (±)-2-(2-chlorophenoxy)propanoic acid(±)-(2-PPA) can be achieved with both monomers and polymers of undecenoxy carbonyl-L-pryrrolidinol bromide (L-UCPB) and undecenoxy carbonyl-L-leucinol bromide (L-UCLB) at 25 mM surfactant concentration using phosphate buffer at pH 7.50. The chiral recognition seems to be facilitated by the extent of interaction of the acidic analytes with the cationic head group of chiral selectors. Polysodium Nundecenoxy carbonyl-L-leucine sulfate (poly-L-SUCLS) and polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL) were compared at high and low pH for the enantioseparation of (±)-(2-PPA). At pH 7.5, poly-L-SUCLS, poly-L-SUCL and ±-2-PPA are negatively charged resulting in no enantioseparation. However, chiral separation was observed for (±)-(2-PPA) using poly-L-SUCLS at low pH (pH 2.00) at which analyte is neutral. The comparison of chiral separation of anionic and cationic surfactants demonstrates that the electrostatic interaction between the acidic analyte and cationic micelle plays a profound role in enantioseparation.The separation of chiral compounds is currently the center of great interest. 1 This interest can be attributed largely to a heightened awareness that enantiomers of a racemic drug usually display markedly different pharmacological activities. 2,3 The human body metabolizes individual enantiomers by separate pathways to produce different pharmacological effects. Presently, a majority of commercially available drugs are synthetic and chiral. Most of these chiral drugs are obtained as a mixture of two enantiomers during synthesis. 4 In order to avoid the possible undesirable effects of enantiomeric impurity in chiral drug, it is inevitable that only therapeutically active form be marketed. Hence there is a continuous need to develop technologies that have the ability to separate enantiomers. In this study, we report the synthesis, characterization and application of novel IL type surfactants and their polymers for chiral separation of acidic analytes in MEKC. Acidic analytes due to inherent negative charge poorly interact with most commonly employed chiral anionic surfactants at basic pH. As a result, still a large number of acidic analytes could not be resolved by MEKC. The cationic surfactant, undecenoxy carbonyl-L-leucinol bromide (L-UCLB) i...

Ionic Liquids in Separation Techniques

“…The practical utilization of long-chain (C 12 and C 14 ) alkylimidazolium ionic liquids as a new type of surfactant in MEKC was used to separate neutral analytes-methylresorcinol isomers and benzene derivatives. Newly synthesized chiral ILs as surfactants in MEKC have been described in literature (Rizvi & Shamsi, 2006). Chiral separation of two acidic analytes, (±)--bromophenylacetic acid and (±)-2-(2-chlorophenoxy)propanoic acid (±)-(2-PPA) was achieved with both monomers and polymers of undecenoxycarbonyl-L-pryrrolidinol bromide and undecenoxycarbonyl-L-leucinol bromide at 25 mM surfactant concentration at pH 7.50.…”

Chiral ionic liquids: A compendium of syntheses and applications (2005–2012)

“…26) and (6)-2-(2-chlorophenoxy)propanoic acid. 134 The chiral surfactant ionic liquids are undecenoxycarbonyl-L-leucinol bromide (CIL 250; room-temperature IL) and undecenoxycarbonyl-L-pyrrolidinol bromide (CIL 251; m.p. 30-358C).…”

Applications of Chiral Ionic Liquids

“…In the last years, great attention has been paid to the relevance of ILs as new media for capillary electrophoresis with IL-containing background electrolytes. [72] The application of novel IL-type like surfactants and their polymers for chiral separation of acidic analytes in micellar electrokinetic chromatography was reported first by Rizvi and Shamsi in 2006. [73] Two amino acid-derived CILs 60 and 61 as well as their polymers were synthesized and used as pseudo-stationary phase in capillary electrophoresis ( Figure 10).…”