Influence of the Polydispersity of Polymeric Surfactants on the Enantioselectivity of Chiral Compounds in Micellar Electrokinetic Chromatography

Abstract

Poly(sodium undecenoyl-L-leucinate) (poly-L-SUL) was fractionated by the use of different molecular weight cutoff (MWCO) filters to narrow the polydispersity of the macromolecular sizes of the polymeric surfactant. The resulting polymeric surfactant fractions were characterized by the use of three techniques: (1) pulsed field gradient nuclear magnetic resonance (PFG-NMR) was used to determine the hydrodynamic radii, (2) analytical ultracentrifugation (AUC) was used to determine the molecular weights, and (3) steady-state fluorescence was used to determine the polarity of the nonfractionated and fractionated polymeric surfactants. From the data acquired from PFG-NMR, AUC, and fluorescence, it was noted that the hydrodynamic radii and molecular weight of the fractionated poly-L-SUL increased, while the polarity decreased with the increase in the size of the MWCO filter. However, a similarity in physical properties was observed between the nonfractionated and 10-30K fractionated poly-L-SUL except for the hydrodynamic radius and diffusion coefficients. The influence of different macromolecular sizes of poly-L-SUL on the chiral separation of phenylthiohydantion (PTH)-amino acids and coumarinic derivatives, as test analytes, was elucidated by the use of micellar electrokinetic chromatography (MEKC). The size of polymeric surfactants as a prerequisite for chiral separation was demonstrated by comparing the separation properties of fractionated versus nonfractionated polymeric surfactants. Fractionated poly-L-SUL resulted in enhanced resolution and separation efficiency of the test analytes as compared to the case of the nonfractionated poly-L-SUL. This observation indicates that minimizing polydispersity of polymeric surfactants may be important for some chiral separation applications.

Recent progress in the use of ionic polymers as pseudostationary phases for EKC

“…The effects of molecular weight and polydispersity of polySUL on various properties and EKC separation of PTH-amino acids and coumarinic derivatives were studied by first fractionating a synthesis of poly(SUL) into three molecular weight fractions (5-10 k, 10-30 k, and .30 k) using centrifugal dialysis membrane filters [42]. Unfractionated poly(SUL) was polydispersed and was distributed among the various fractions with the majority of the material in the high molecular weight fraction.…”

Recent advances in micellar electrokinetic chromatography

“…1c) are a further variation on MEKC. Since 2003, the literature regarding polymer micelles has focused on their characterization [38][39][40][41][42][43][44] and applicability [4,36,43,[45][46][47][48][49][50][51]. Polymer micelles have notably different characteristics than conventional micelles.…”

Fundamental Studies on Electrokinetic Chromatography with PEGylated Phospholipid Micelles

“…Actually, Tarus et al reported that the polymerization degree of poly(sodium undecanoyl-L-leucinate) strongly affected the efficiency and resolution of racemic amino acid derivatives. 6 Thus, the introduction of mono-dispersed micelles with no or lower CMC is still desired in MEKC.…”