ORIGINAL PAPER A new example of reversal of the order of migration of enantiomers, as a function of cyclodextrin concentration and pH, by cyclodextrin-modified capillary zone electrophoresis: enantioseparation of 6,6′-dibromo-1,1′-binaphthyl-2,2′-diol H. Krajian & N. Mofaddel & D. Villemin & P. L. Desbène Received: 11 March 2009 / Revised: 16 June 2009 / Accepted: 18 June 2009 / Published online: 17 July 2009 # Springer-Verlag 2009 Abstract Enantioseparation of 6,6′-dibromo-1,1′-binaphthyl- 2,2′-diol (DBBD) by cyclodextrin-modified capillary zone electrophoresis (CD-CZE) was studied using the three native α, β, and γ cyclodextrins, the three hydroxypropylated cyclodextrins (2-hydroxypropyl-α, β, and γ), heptakis-2,6- di-O-methyl-β-CD (DM-β-CD), and heptakis-2,3,6-tri-O- methyl-β-cyclodextrin (TM-β-CD). First, the acidity constants of DBBD were determined using capillary electrophoresis, before performing enantioseparation. The influence of the concentrations of the studied cyclodextrins on the enantiosepa- ration was explored and the experimental optimal concen- trations were determined and compared to the theoretical optimal concentrations. Moreover, the apparent complexation constants between each studied cyclodextrin and the two DBBD enantiomers were evaluated using a non-linear curve fitting method and three linear plotting methods (x-reciprocal, y-reciprocal and double reciprocal). For TM-β-CD, the order of migration of the enantiomers of DBBD reversed as a function of TM-β-CD concentration. The influence of the nature of methylated cyclodextrin derivatives (methyl-β-CD (M-β-CD) and DM-β-CD) was then studied. Inversion of the order of migration of the enantiomers of DBBD was observed for DM-β-CD, whereas the S enantiomer of DBBD always migrated first for M-β-CD. Keywords 6,6′-Dibromo-1,1′-binaphthyl-2,2′-diol . CD-CZE . Order of migration of enantiomers . Enantioseparation . Methylated cyclodextrins Introduction Analysis of chiral compounds is of great importance in many fields, including pharmaceutical, biological, and catalytic. New asymmetric synthesis methodologies and powerful preparative separation techniques allow for the retrieval of enantiomers with high enantiomeric excess [1]. Biotechnologies and biocatalysis are rapidly expanding fields that produce and purify chiral intermediates [2]. In these fields, only very small amounts of enantiomeric impurities can be allowed to be present in final products. These impurities can have undesirable side effects and toxicity. Therefore, there are considerable efforts underway to develop analytical methods for chiral separations. During the past several years, capillary electrophoresis (CE) has been demonstrated to be a powerful analytical technique for chiral separations. Enantioseparation can be achieved in CE by using chiral selectors. Numerous selectors have been investigated (native CDs and neutral and charged derivatives, macrocyclic antibiotics, chiral crown ethers, chiral calixarenes, chiral imprinted polymers, proteins, polysaccharides, chiral surfactants, and chiral ion- H. Krajian : N. Mofaddel : P. L. Desbène (*) L.A.S.O.C. – IRCOF et IFRMP, Université de Rouen, 55 rue Saint Germain, 27000 Evreux, France e-mail: paul-louis.desbene@univ-rouen.fr D. Villemin Laboratoire de Chimie Moléculaire – Thioorganique, UMR 6507, ENSICAEN, Université de Caen, bd du Maréchal Juin, 14050 Caen, France Present Address: H. Krajian Department of Chemistry, Atomic Energy Commission of Syria, P. O. Box 6091, Damascus, Syria Anal Bioanal Chem (2009) 394:2193–2201 DOI 10.1007/s00216-009-2925-3