Electrophoresis, Vol.26, No.21, 4172-4186, 2005
Polymeric alkenoxy amino acid surfactants: IV. Effects of hydrophobic chain length and degree of polymerization of molecular micelles on chiral separation of beta-blockers
Four alkenoxy leucine-based surfactants with C-8-C-11 chains containing a terminal double bond, and one C-11 chain surfactant with a terminal triple bond are synthesized and characterized in monomeric and polymeric forms. These polymeric pseudophases are then utilized to study the influence of chain length and DP for the enantioseparations of seven beta-blockers in MEKC. Variations in chain length and concentration of polymeric surfactants showed significant effects on the chiral resolution (R-s) and efficiency (N). A relatively large elution range combined with the highest polarity and aggregation number (A) but the lowest retention time, partial specific volume, and optical rotation generated with C-8-polymeric surfactant results in simultaneous enantioseparation of all seven beta-blockers with higher N and R-s. In particular, highly hydrophobic beta-blockers are better resolved with shorter hydrocarbon chain even at higher surfactant concentration, which is unachievable with longer chain surfactant. On the other hand, polymer derived from C-11-triple bond provided smaller A value compared to C-11-double bond surfactant. However, chiral R-s of hydrophobic beta-blockers are still achievable with the C-11-triple bond surfactant with enhanced N and shorter analysis time. In addition, effect of polymerization concentration is evaluated by polymerizing all five surfactants at five times their respective CMCs and 100 mm equivalent monomer concentrations. Polymerization of shorter chain (C-8 and C-9) double-bonded surfactants at five times their respective CMCs results in higher A values with better chiral R-s and N compared to the same two surfactants polymerized at 100 mm.
Keywords:degree of polymerization;hydrophobic chain length;micelle polymers;simultaneous enantioseparation