Chiral separation of dansyl amino acids in capillary electrophoresis using mono‐(3‐methyl‐imidazolium)‐β‐cyclodextrin chloride as selector

Abstract

Enantioseparations of fourteen dansyl amino acids were achieved by using a positively-charged single-isomer beta-cyclodextrin, mono-(3-methyl-imidazolium)-beta-cyclodextrin chloride, as a chiral selector. Separation parameters such as buffer pH, selector concentration, separation temperature, and organic modifier were investigated for the enantioseparation in order to achieve the maximum possible resolution. Chiral separation of dansyl amino acids was found to be highly dependent on pH since the degree of protonation of these amino acids can alter the strength of electrostatic interaction and/or inclusion complexation between each enantiomer and chiral selector. In general, the chiral resolution of dansyl amino acids was enhanced at higher pH, which indicates that the carboxylate group on the analytes may interact with the imidazolium group of cationic cyclodextrin. For most analytes, a distinct maximum in enantioresolution was obtained at pH 8.0. Moreover, the chiral separation can be further improved by careful tuning of the separation parameters such as higher selector concentration (e.g. 10 mM), lower temperature, and addition of methanol. Enantioseparation of a standard mixture of these dansyl amino acids was further achieved in a single run within 30 min.

Monosubstituted positively charged cyclodextrins: Synthesis and applications in chiral separation

“…The optimum buffer pH for chiral separation varied for different series of CDs. For Series I CDs, MIMCDCl (5a) was found to present best resolution abilities towards dansyl amino (Dns-amino) acids at pH l8.0 [40], whilst towards the same analytes, the other Series I CDs enjoyed better enantioseparation abilities at pH 6.0 [41]. For Series II CDs, excellent separations were achieved for most hydroxyl and carboxylic acids at pH in the range of 5.0l7.0.…”

“…Interestingly, when we made a comparison on the resolution ability of our synthesized mono-6-amino-b-CD hydrochlorides [35], mono-6-alkylamino-b-CDs [34, 42 -44], and mono-6-alkylimidazolium-b-CDs [33,40,41] towards Dnsamino acids, it was found that Series I CDs with shorter alkyl chain (R = C n H 2n+1 , n = 4) and ALAMCDCl provided the outstanding resolutions to Dns-amino acids. Similar results can also be found in the imidazoyl directly linked 6-deoxy-6-[4-(2-aminoethyl)imidazoyl]-b-CD (CD-mh), which showed more powerful resolution abilities towards Dns-amino acids than amino directly linked 6-deoxy-6-N-histamino-b-CD (CD-hm) [50].…”

Cyclodextrins in capillary electrophoresis enantioseparations – Recent developments and applications

“…Mono-6-(1-butyl-3-imidazolium)-6-deoxyb-CD was also an effective chiral selector for DNS-amino acids at pH 9.6 [47]. Studying the enantioresolution of DNS-amino acids by the methyl derivative mono-6-(1-methyl-3-imidazolium)-6-deoxy-b-CD (MIM-b-CD) it was noted that increasing the pH of the BGE between pH 6.0 and 9.5 resulted in an increase in the resolution, R S , maximizing about pH 8 and decreasing thereafter [49]. Most analytes could be baseline resolved at pH 8 using MIM-b-CD concentrations between 3 and 10 mM.…”

Indirect Enantioseparation of Amino Acids by CE Using Automated In-Capillary Derivatization with ortho-Phthalaldehyde and N-Acetyl-l-Cysteine

“…For an indirect enantioseparation, a selector is usually also necessary to resolve the derivatives. Selectors that are suitable for direct and indirect enantioseparation include cyclodextrins (CD) [12][13][14], crown ethers [15][16][17], macrocyclic antibiotics [18][19][20], chiral surfactants [21,22] and ligand-exchange complexes [23][24][25][26].…”