Copolymerized polymeric surfactants: Characterization and application in micellar electrokinetic chromatography

Abstract

An achiral monomeric surfactant (sodium 10-undecenyl sulfate, SUS) and a chiral surfactant (sodium 10-undecenoyl L-leucinate, SUL) were synthesized and polymerized individually to form poly-SUS and poly-SUL. These surfactants were then copolymerized at various molar ratios to produce a variety of copolymerized surfactants (CoPSs), possessing both achiral (sulfate) and chiral (leucinate) head groups. The CoPSs, poly-SUS, poly-SUL, and sodium dodecyl sulfate were characterized using several analytical techniques. The aggregation numbers of the polymeric surfactants and the partial specific volumes were determined by the use of fluorescence quenching and density measurements, respectively. These polymeric surfactants were investigated as novel pseudostationary phases in micellar electrokinetic chromatography (MEKC) for the separation of chiral and achiral solutes. Solute hydrophobicity was found to have major influence on the MEKC retention of alkyl phenyl ketones. In contrast, hydrogen-bonding ability of benzodiazepines is the major factor that governs their retention, but hydrophobicity has an insignificant effect on MEKC retention of benzodiazepines.

Thermodynamic studies of the interaction of molecular micelles and copolymerized molecular micelles with benzodiazepines and alkyl phenyl ketones using MEKC

“…The details of the modified synthetic procedure are reported in a study by Wang and Warner [10]. The synthesis of CoMMs has been previously published [18].…”

“…This trend becomes more noticeable with alkyl phenyl ketones. It should be mentioned that an increase in mole fraction of sulfate head group in the CoPMMs improves the hydrophobicity of the molecular micelle [18]. For benzodiazepines the contribution of DH7 to DG7 is greater than that of DS7.…”

“…Due to the hydrophobicity of the benzodiazepines (their log P values range from 2.31 to 3.86) and the pseudostationary phases, hydrophobic interaction plays a significant role in retention of these solutes. In addition, as a result of the hydrogen bond donating and/or hydrogen bond accepting functional groups on the benzodiazepine molecules, hydrogen bonding is believed to play a more significant role than the hydrophobic interaction [18]. Thus, the chemistry on and around the micellar surface can be altered by temperature.…”

“…The electropherograms of benzodiazepines at 407C are shown in Fig. 1 and the corresponding electropherograms for 207C are presented in our earlier publication [18]. For example, at 407C, the migration order of diazepam (peak 5) and oxazepam (peak 6) was reversed using poly-SUL (Fig.…”

“…These changes, in turn, will manipulate the chemistry around the micellar head groups and thus influence analyte partitioning between the pseudostationary phase and the BGE. It should be mentioned that temperature has no significant effect on the methylene selectivity, which is correlated with the hydrophobicity [18].…”