title: Computational contribution to the electrophoretic enantiomer separation mechanism and migration order using modified β-cyclodextrins.
abstract: Capillary electrophoresis (CE) is an extremely effective technique in many kinds of separations, including separation of enantiomers. Some additional techniques may be necessary to determine the enantiomer migration order (EMO) and also the mechanism involved in chiral recognition. This paper reports the development and optimization of a CE method for enantioseparation of racemic mixture of both R- and S-stereoisomers of tramadol (TRM) with a computational contribution for the EMO determination and the responsible mechanisms for chiral distinction. Parameters such as composition and concentration of background electrolyte (BGE) and type and concentration of cyclodextrins (CD) were evaluated. For calculations, a sequential methodology was used, resorting to semiempirical Parametric Model 3 (PM3) followed by calculations accomplished using density functional theory. The best results were obtained with sulfated-β-CD (s-β-CD) and carboxymethyl-β-cyclodextrin (cm-β-CD) as chiral selector. Calculations show that the inclusion of TRM is not a probable process due to the shape of the TRM molecule and the size CDs cavities. Therefore, the chiral recognition process occurs by the formation of association complexes between modified β-CD and groups of TRM molecules. The structural analysis of the fragments of complexes at a pH of 10 and a thermodynamic analysis of the complexes' formation process allows determining the EMO. Comparing results obtained experimentally and computationally, it seems that the developed method is adequate for separation of TRM enantiomers and the computational methodology is also adequate to get a sense of the system at a molecular level.
authors.affiliation: Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, São João del-Rei, Minas Gerais, Brazil.
authors.forename: Matheus
authors.initials: M
authors.lastname: Cecilio Fonseca
authors.affiliation: Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, São João del-Rei, Minas Gerais, Brazil.
authors.forename: Ricky Cássio
authors.initials: RC
authors.lastname: Santos da Silva
authors.affiliation: Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, São João del-Rei, Minas Gerais, Brazil.
authors.forename: Clebio Soares
authors.initials: CS
authors.lastname: Nascimento
authors.affiliation: Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, São João del-Rei, Minas Gerais, Brazil.
authors.forename: Keyller
authors.identifier: 0000-0003-1067-1919
authors.initials: K
authors.lastname: Bastos Borges
mesh_terms: D002951:Citrates / Q000737:chemistry; D019075:Electrophoresis, Capillary / Q000295:instrumentation / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D013237:Stereoisomerism; D013816:Thermodynamics; D014147:Tramadol / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D002951:Citrates; D047392:beta-Cyclodextrins; D014147:Tramadol
keywords: Capillary electrophoresis; Chiral recognition mechanism; Density functional theory; Enantiomer migration order; Modified β-cyclodextrin; Tramadol