Chiral Separations Using Proteins and Peptides as Chiral Selectors - Chiral Separations by Capillary Electrophoresis - page 154

A fourth way for the ACEC technique is to chemically immobilize a protein
onto the surface of fused-silica capillaries. BSA was bound to the capillary wall
[57]. The method includes etching the capillary wall with sodium hydroxide, epoxy-
diol coating with 3-glycidoxypropyltrimethoxysilane followed by hydrolysis with
hydrochloric acid, and activation with tresyl chloride and BSA coupling. Avidin
was bound to an aminopropyl-silylated fused-silica surface using glutaraldehyde by
a Schiff base formation reaction [58].
A i fth way for the ACEC technique is to encapsulate a protein using a sol-gel
method. Two proteins, BSA and OMCHI, were encapsulated in tetramethoxysilane-
based hydrogel and their enantioselectivity was evaluated for the separation of tryp-
tophan, benzoin, eperisone, and chlorpheniramine enantiomers [59]. Furthermore,
a sol-gel/organic hybrid composite material using gelatin or chitosan with tetra-
methoxysilane was prepared for the BSA-encapsulated monolithic column for
ACEC [60]. The monolithic column prepared from chitosan with tetramethoxysilane
showed a higher enantioselectivity for tryptophan enantiomers and the composite
materials exhibited a higher stability compared to the silica sol-gel column.
Another approach is the use of protein-dextran polymer networks for ACE appli-
cation. BSA was covalently linked to a high-molecular-mass dextran (M r 2,000,000)
using cyanogen bromide, and applied to the enantioseparation of leucovorin enantio-
mers [61]. Since the capillary was coated with linear polyacrylamide, an EOF would
be small. Thus, the polymer would not l ow out of the capillary during the course
of several hours of the run. It was found that the amount of protein in the polymer
network could be varied by dilution with nonderivatized dextran. This can be useful
for optimizing the enantioseparation of a solute that adsorbs strongly to the ligand.
The BSA-dextran polymer network can be removed and replaced by means of a
syringe or by applying a fresh polymer mixture to the capillary.

6.4.2.2 Peptide Selectors
Basic peptides such as Lys-Tyr and Lys-Ser-Tyr were adsorbed onto the capillary wall
and used for separations of tyrosine, phenylalanine, and fenoprofen enantiomers [21].
The polyelectrolyte multilayer coating was constructed in situ with alternating
rinses of positively and negatively charged polymers. Poly(diallyldimethylammonium-
chloride) and poly(l-lysine) hydrobromide [poly(l-lysine)] were used as the cationic
polymers, and the polymeric surfactants poly(sodium undecanoyl-l-leucylalaninate)
[poly(l-SULA)] and poly(sodium undecanoyl-l-alanylleucinate) [poly(l-SUAL)] were
used as the anionic polymers [62]. The enantioseparations of the

β -blockers, labetalol

and sotalol, and the binaphthyl derivatives, 1,1 ′ -bi-2-naphthyl-2,2 ′ -dihydrogen

phosphate, 1,1 -diamine were attained with

high run-to-run and capillary-to-capillary reproducibilities using a polyelectrolyte
multilayer coating by poly(l-lysine) and poly(l-SULA).

′ -bi-2-naphthol and 1,1-binaphthyl-2,2 ′

6.5 NEW DEVELOPMENTS
The separation of (

)- trans -benzo[ a ]pyrene tetrols (BPTs) can be accom-
plished by the l ow-through partial-i lling ACE (FTPFACE) using a cross-reactive
monoclonal antibody (mAb) against a polycyclic aromatic hydrocarbon [24]. In the

± )- cis - and ( ±