Anal. Chem. 2003, 75, 1348-1354
Ap p lic a t io n o f Cyc la m -Ca p p e d
â-Cyc lo d e x t rin -Bo n d e d S ilic a P a rt ic le s a s a Ch ira l
S t a t io n a ry P h a s e in Ca p illa ry
Ele c t ro c h ro m a t o g ra p h y fo r En a n t io m e ric
S e p a ra t io n s
Yinha n Gong a nd Hia n Ke e Le e *
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Republic of Singapore 117543
Two novel types of substituted cyclam-capped â-cyclodex-
trin (â-CD)-bonded silica particles have been prepared
and used as chiral stationary phases in capillary electro-
chromatography (CEC). The two stationary phases have
a chiral selector with three recognition sites: â-CD,
cyclam, and the latter’s sidearm. They exhibit excellent
enantioselectivities in CEC for a wide range of compounds
produced better enantioseparations than did either selector alone
as a result of cooperative functioning of the â-CD and the crown
ether.1
0-12
However, many crown ethers, cyclams, and derivatized
CDs with high UV/ vis absorption characteristics or poor solubility
in water are not suitable to be used as CE additives for direct
detection. Alternatively, they can be bonded onto silica support
to be used as CSPs in LC to separate chiral compounds. Although
as a result of the cooperative functioning of the anchored
crown ether-capped â-CD has been used to model the receptor
â-CD and cyclam. After inclusion of the metal ion (Ni2
+
)
13-15
sites of enzymes for a long time,
its use as a stationary phase
selector for chromatography has seldom been studied.16 We have
previously reported that the crown ether-capped â-CD-bonded
silica particles showed excellent enantioselectivities when used
from the running buffer into the substituted cyclams and
their sidearm ligands, the bonded stationary phases
become positively charged and can provide extra electro-
static interactions with ionizable solutes and enhance the
dipolar interactions with some polar neutral solutes. This
enhances the host-guest interaction with some solutes
and improves chiral recognition and enantioselectivity.
These new types of stationary phases exhibit great poten-
tial for fast chiral separations in CEC.
3
as CSPs in LC. Since cyclams have similar structures and proper-
ties to crown ethers, it was of interest to us to prepare cyclam-
capped â-CD-bonded silica particles for study of their enantiose-
lectivities when used as new CSPs in LC. To the best of our
knowledge, we were among the first to report a convenient method
involving successive multiple-step liquid-solid-phase reactions on
the silica surface to synthesize cyclam-capped â-CD-bonded silica
particles.4
Development and application of new chiral stationary phases
(
CSPs) with high selectivities to separate chiral molecules is one
Capillary electrochromatography (CEC) is a modern LC
technique combining the high efficiency of CE with the high
selectivity usually obtained in high-performance liquid chroma-
tography (HPLC).17 As in HPLC, the stationary phase packed-
capillary columns are used for the separation of solutes of interest.
The mobile phase in CEC is transported through a capillary
column by means of electroosmotic flow (EOF) instead of
pressure, as in HPLC. Neutral solutes are separated by partitioning
between the mobile and the stationary phases. Charged solutes
have an additional electrophoretic mobility in the applied electric
field in CEC, and the separation is achieved by the combined
of the most active areas of liquid chromatography (LC).1 Chiral
separations are important in various fields,5 such as natural
product research, stereospecific synthesis, chiral drugs in the
pharmaceutical industry, and chiral compounds in environmental
studies. Many chiral separations have been accomplished using
â-cyclodextrin-type stationary phases as CSPs in LC.5,8,9 Recently,
it was shown that the combination of a crown ether and â-CD as
a buffer additive in capillary electrophoresis (CE) sometimes
-4
-7
*
Corresponding author. Tel: (65)-6874-2995. Fax: (65)-6779-1691, E-mail:
chmleehk@nus.edu.sg.
(
1) Dermaux, A.; Lynen, F.; Sandra, P. J. High Resolut. Chromatogr. 1 9 9 8 , 21,
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1348 Analytical Chemistry, Vol. 75, No. 6, March 15, 2003
10.1021/ac0204909 CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/08/2003