Enantiomeric separation by GC on chirasil‐dex: Systematic study of cyclodextrin concentration, polarity, immobilization, and column stability

Abstract

Abstract. Polysiloxane-anchored permethylated 6-cyclodextrin (Chirasil-Dex) was used for enantiomeric separation by GC. Four types of Chirasil-Dex, containing up to 36 % permethylated 0-cyclodextrin by weight, were synthesized and compared with 10 % permethylated P-cyclodextrin dissolved in OV-1701. The influence of the cyclodextrin weight percentage on the chiral separation factor CY and on polarity, as expressed by the Kovats indices, was studied. The chiral separation factors a did not increase significantly above a threshold of -30 % permethylated P-cyclodextrin by weight. The plots of a vs.weight percentage depend on the complexation strength of the chiral solutes, as do the Kovats indices; for weakly complexing solutes, changes in the cyclodextrin concentration result in larger changes in a, but in less pronounced changes in the Kovats indices, as compared to strongly complexing solutes. Column performances were investigated for immobilized and nonimmobilized stationary phases. As expected, immobilization properties were found to depend on the content of Si-H groups in the polysiloxane backbone. Immobilized columns exhibited a much better long-term stability of all chromatographic variables investigated.

Enantiomer separation by pressure-supported electrochromatography using capillaries packed with Chirasil-Dex polymer-coated silica

“…Macroporous silica (Nucleosil, 5 mm, 300 pore size) obtained from Grom (Herrenberg, Germany), was coated with Chirasil-Dex (synthesized according to [28,29] and a dimethylpolysiloxane copolymer containing carboxy groups in toluene solution as described previously [27]. Fused-silica capillaries (100 mm ID; Ziemer, Mannheim, Germany) were slurry-packed (packing bed: 20±25 cm) and conditioned at 380 bar employing an HPLC pump (Sykamp, Gilching, Germany) as described by Behnke et al [30].…”

Synthesis, NMR Spectroscopic Characterization and Polysiloxane‐Based Immobilization of the Three Regioisomeric Monooctenylpermethyl‐β‐cyclodextrins and Their Application in Enantioselective GC

“…The composition of this mixture is strongly dependent on the reaction conditions, i.e., the solvent (DMF or DMSO) and the base (sodium hydroxide, sodium hydride), and varies from batch to batch. We found that, under certain column chromatography conditions [27] for the purification of the mono-oct-7-enylated β-cyclodextrin mixture, the almostpure O-2-substituted product 6 can be obtained after permethylation, with the O-6 product being separated together with the higher oct-7-enylated derivatives. Removing higher-order and non-oct-7-enylated derivatives is necessary at this stage to prevent cross polymerization by any multifunctional groups during the bonding process and to guarantee reproducible amounts of the desired product for hydrosilylation.…”

“…With the same HPLC method and having the single O-2, O-3, and O-6 regioisomers (4, 6, and 9) in hand, we were able to make an assignment of the products obtained by the non-regioselective statistical introduction of the oct-7-enyl spacer followed by permethylation (described in detail elsewhere), [27] whereby the peaks were identified by coinjection (cf. Figure 2, b).…”

“…[26] During subsequent modification of the reaction protocols, as well as purification steps, toward obtaining the elongated mono-oct-7-enyl ether of β-cyclodextrin, [27] a competitive O-2-alkenylation can be envisioned for Chirasil-Dex preparations employed in various chromatographic applications.…”

Gas chromatographic enantioseparation of unfunctionalized chiral alkanes: A challenge in separation science (overview, state of the art, and perspectives)

“…The solution was concentrated to give the white crystalline substance of permethylated monokis ( Chirasil-a-Dex. In an atmosphere of dinitrogen, 180 mg (0.06 mmol) of dimethyl-hydridomethyl-polysiloxane 30,31 containing 10% Si-H-groups, and 80 mg (0.046 mmol) of permethylated monokis-2-(oct-7-enyl)-a-cyclodextrin were diluted in 10 ml of dry toluene. To the refluxing reaction mixture were added a few droplets of a highly diluted solution of hexachloroplatinum acid (H 2 PtCl 6 ) in anhydrous tetrahydrofuran.…”