Anal. Chem. 1998, 70, 2789-2795
Molecularly Imprinted Polymeric Adsorbents for
Byproduct Removal
Lei Ye,* Olof Ramstro1m, and Klaus Mosbach
Pure and Applied Biochemistry, Chemical Center, Lund University, P.O. Box 124, S-221 00 Lund, Sweden
noncovalently imprinted polymers have been prepared in less polar
organic solvents, hydrophobic interactions have not been exten-
sively utilized, at least not as a main interaction for polymer
preparation. However, these may, in some cases, enhance the
recognition capabilities for the obtained polymers when analyzed
in an aqueous environment. From a practical point of view, the
easy self-assembling in polymer preparation and the fast recogni-
tion kinetics of the obtained polymers have made the noncovalent
strategy attractive for applications in different areas. Nonco-
valently imprinted polymers have been explored as tailor-made
chiral separation phases,5 molecularly imprinted “immuno” as-
says,6,7 recognition units in sensors,8 and solid-phase extraction
materials.9 Spherical, molecularly imprinted polymer beads
exhibited better flow characteristics in chromatography and higher
binding capacities compared to ordinary bulk polymers, which
are ground and sieved to provide irregularly shaped fragments.10,11
The molecularly imprinted polymer beads may extend molecular
imprinting to more practical applications. In addition, we have
demonstrated a novel application of molecularly imprinted poly-
mers (MIPs) as auxiliary reagents in enzymatic reactions, e.g.,
the synthesis of an artificial sweetener precursor, Z-aspartame.12
For the noncovalent preparation of MIPs, the print molecule
forms complexes with one or more molecules of functional
monomers. While a single functional monomer, of either acidic
or basic nature, is used routinely, simultaneously utilizing multiple
functional monomers provides more possibilities in achieving the
optimal complexation between the print molecule and the mono-
mers and, therefore, may enhance the recognition capabilities. It
has been found that the recognition capabilities of MIPs for
derivatized amino acids can be improved by introducing two
chemically distinct functional monomers.13 In the present study,
this approach is extended to a dipeptide derivative, N-(benzyloxy-
carbonyl)aspartylphenylalanine methyl ester (ZAPM). Consider-
ing the versatile isomers of this dipeptide family and the close
similarities among them, the effects of both template structure
In this study, both diastereo- and enantioselective adsor-
bents for a dipeptide derivative were prepared using a
molecular imprinting technique. The diastereo- and
enantioisomers for the dipeptide derivative N-(benzyloxy-
carbonyl)aspartylphenylalanine methyl ester (ZAP M), in
addition to the r- and â-isomers, were chosen as test
compounds for the investigation of the imprinting effect.
The close similarities between the structures of different
isomers make it possible to interpret the roles of template
structure on specific molecular recognition. A highly
specific byproduct scavenger was prepared by simulta-
neously incorporating methacrylic acid and vinylpyridine
as functional monomers. The binding selectivities of
polymeric adsorbents for the r- and â-isomers are shown
to be greatly enhanced by introducing enantiocomple-
mentarities into the polymer matrixes. An anti-â-L,L-
ZAP M polymer was applied in a solid-phase extraction
protocol, for the purification of the product in the chemical
synthesis of N-protected aspartame. Finally, polymer
beads were also imprinted against â-L,L-ZAP M using
suspension polymerization performed in perfluorocarbon
fluid. The imprinted polymer beads displayed the same
binding characteristics as the imprinted bulk polymer and
can be envisaged for the use of product purification in
chromatographic mode.
Analogous to natural recognition units such as enzymes,
antibodies, and receptors, various synthetic mimics of these
bioactive components have been produced by molecular imprint-
ing techniques.1-4 The print molecule can be removed after the
microscopic molding process and the obtained polymeric matrixes
become ready to recognize the corresponding print species. The
diastereo- and enantiospecificities of molecularly imprinted poly-
mers much depend on the complexation between the print
molecule and the functional monomers during polymerization, as
well as between the analyte and the prearranged polymer func-
tionalities in the later binding process. In the noncovalent
strategy, complex formation (self-assembling) is based on the
noncovalent interactions between the print molecule and the
functional monomers. Among the most often employed are
hydrogen bonds and ionic interactions. So far, since most
(5) Kempe, M. Anal. Chem. 1 9 9 6 , 68, 1948-1953.
(6) Vlatakis, G.; Andersson, L. I.; Mu¨ ller, R.; Mosbach, K. Nature 1 9 9 3 , 361,
645-647.
(7) Ramstro¨ m, O.; Ye, L.; Mosbach, K. Chem. Biol. 1 9 9 6 , 3, 471-477.
(8) Kriz, D.; Ramstro¨ m, O.; Svensson, A.; Mosbach, K. Anal. Chem. 1 9 9 5 , 67,
2142-2144.
(9) Muldoon, M. T.; Stanker, L. H. Anal. Chem. 1 9 9 7 , 69, 803-808.
(10) Mayes, A. G.; Mosbach K. Anal. Chem. 1 9 9 6 , 68, 3769-3774.
(11) Ansell R. J.; Mosbach K. J. Chromatogr., A 1 9 9 7 , 787, 55-66.
(12) Ramstro¨ m, O.; Ye, L.; Krook, M.; Mosbach, K. Chromatographia 1 9 9 8 , 47,
465-469.
* To whom correspondence should be addressed: (phone) +46 46 2229560;
(fax) +46 46 2224611; (e-mail) Lei.Ye@tbiokem.lth.se.
(1) Mosbach, K.; Ramstro¨ m, O. Bio/ Technology 1 9 9 6 , 14, 163-170.
(2) Ansell, R. J.; Kriz, D.; Mosbach, K. Curr. Op. Biotechnol. 1 9 9 6 , 7, 89-94.
(3) Shea, K. J. Trends Polym. Sci. 1 9 9 4 , 2, 166-173.
(13) Ramstro¨ m, O.; Andersson, L. I.; Mosbach, K. J. Org. Chem. 1 9 9 3, 58, 7562-
7564.
(4) Wulff, G. Angew. Chem., Int. Ed. Engl. 1 9 9 5 , 34, 1812-1832.
S0003-2700(98)00069-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 05/28/1998
Analytical Chemistry, Vol. 70, No. 14, July 15, 1998 2789