Enhanced enantioselectivity of molecularly imprinted polymers formulated with novel cross-linking monomers

Article abstract of DOI:10.1021/ma025710z

To enhance the performance of molecularly imprinted polymers (MIPs), three new cross-linking monomers were designed, synthesized, and evaluated as matrix elements for molecularly imprinted polymers. Hybrid cross-linking monomers incorporating methacrylamide/methacrylate (NOBE), vinyl ketone/methacrylamide (NAG), and vinyl ketone/methacrylate (MVK) polymerizable groups, were synthesized and used to prepare MIPs and compared to a traditional MIP formulated with EGDMA. The resulting macroporous MIPs were evaluated by HPLC for their ability to separate the enantiomers of a chiral template. The MIP formulated with the cross-linking monomer NAG showed the highest enantioselectivity and complete baseline resolution for a racemic mixture of the template. Enhancement in selectivity in this MIP may be attributed to the presence of the amide group which can promote hydrogen bonding via favorable 1,3 donor-acceptor interactions with the template, the morphology of the polymeric material obtained due to differences in reactivity between the polymerizable groups and improved resolution in cavity formation as a consequence of shorter cross-linker size.

Full text of DOI:10.1021/ma025710z

Macromolecules 2003, 36, 5105-5113
5105
Enhanced Enantioselectivity of Molecularly Imprinted Polymers
Formulated with Novel Cross-Linking Monomers
Ma r th a Sibr ia n -Va zqu ez a n d Da vid A. Sp iva k *
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803
Received October 4, 2002; Revised Manuscript Received April 15, 2003
ABSTRACT: To enhance the performance of molecularly imprinted polymers (MIPs), three new cross-
linking monomers were designed, synthesized, and evaluated as matrix elements for molecularly imprinted
polymers. Hybrid cross-linking monomers incorporating methacrylamide/methacrylate (NOBE), vinyl
ketone/methacrylamide (NAG), and vinyl ketone/methacrylate (MVK) polymerizable groups, were
synthesized and used to prepare MIPs and compared to a traditional MIP formulated with EGDMA. The
resulting macroporous MIPs were evaluated by HPLC for their ability to separate the enantiomers of a
chiral template. The MIP formulated with the cross-linking monomer NAG showed the highest
enantioselectivity and complete baseline resolution for a racemic mixture of the template. Enhancement
in selectivity in this MIP may be attributed to the presence of the amide group which can promote hydrogen
bonding via favorable 1,3 donor-acceptor interactions with the template, the morphology of the polymeric
material obtained due to differences in reactivity between the polymerizable groups and improved
resolution in cavity formation as a consequence of shorter cross-linker size.
In tr od u ction
Research toward improving molecularly imprinted
polymer (MIP) materials has focused primarily on the
choice of template or functional monomer of the pre-
polymer complex. One aspect of MIPs that has been
overlooked is that approximately 80-90% of the MIP’s
matrix is composed of the cross-linking monomer, with
the remaining 10-20% comprised of functional mono-
mers. The large percentage of cross-linking monomer
materials in imprinted polymers presents the possibility
of a commensurate improvement in polymer properties.
Thus, we have redirected our focus on the design and
synthesis of cross-linking monomers for molecular im-
printing. Improving the binding site behavior in MIPs
by improving the scaffold materials finds analogy with
enzymatic systems, where active-site interactions are
influenced by the rest of the protein structure.1 The
design, synthesis, and evaluation of new classes of cross-
linked polymers that can optimize the performance of
molecularly imprinted polymers are presented in this
report.
F igu r e 1. Cross-linking monomers commonly used for mo-
lecular imprinting.
The first cross-linking monomer to be employed for
molecular imprinting in organic polymers was divinyl-
benzene (DVB, 1),2 which is still a useful cross-linker
today. An early comparison of ethylene glycol dimeth-
acrylate (EGDMA, 2) and butanediol dimethacrylate
(BDMA, 4) to DVB quickly determined the best cross-
linking matrix to be EGDMA.3 EGDMA has been the
cross-linker of choice ever since. A relatively new cross-
linker that has shown some improvement over EGDMA
is the trifunctional monomer 2,2-bis(hydroxymethyl)
butanol trimethacrylate (TRIM, 5), which is commer-
cially available.4 This was also found to be true of the
similar cross-linker pentaerythritol triacrylate (PETRA)
but not of the tetrafunctional cross-linker pentaeryth-
ritol tetraacrylate (PETEA).5 A number of bis(acryl-
amide) and bis(methacrylamide) cross-linkers have been
synthesized and shown to be successful as imprinting
matrices.6,7
F igu r e 2. Hybridization of monomer 2 and 3 to form a new
cross-linking monomer.
Since imprinted polymer formulations have predomi-
nantly used EGDMA (2), the majority of functional
monomers have been developed with polymerizable
groups compatible with the reactivity of the meth-
acrylate moiety of EGDMA. Therefore, it was of interest
to develop new cross-linking monomers that maintained
compatibility with previously developed functional mono-
mers. In designing a new cross-linking monomer,
EGDMA was taken as the lead compound. Various
compatible dimethacrylamide compounds have been
previously investigated with encouraging results for
MIP development. However, the new dimethacryla-
mides reported, including the EGDMA analogue ethyl-
enediamine dimethacrylamide shown in Figures 1 and
2 (3), were found to be primarily soluble in polar organic
solvents such as DMF and methanol. In general, the
* Corresponding author. Telephone: (225) 578 2868. Fax: (225)
578 3458. E-mail: David_Spivak@chem.lsu.edu.
10.1021/ma025710z CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/20/2003

5106 Sibrian-Vazquez and Spivak
Macromolecules, Vol. 36, No. 14, 2003
Sch em e 1a
use of polar solvents interferes with the formation of
noncovalent prepolymer complexes in the molecular
imprinting process.8 Therefore, in an effort to obtain a
cross-linker with the positive traits of both lead com-
pounds 2 and 3, the first design investigated was a
product of “molecular breeding” the dimethacrylate
species with the dimethacrylamide species to give
compound 6 (NOBE) shown in Figure 2. Once synthe-
sized (discussed in the next section), the hybrid mono-
mer 6 was indeed found to be soluble in nonpolar
organic solvents such as chloroform and methylene
chloride.
a
Reaction conditions: (a) H2CdC(CH3)COCl/Et3N/CH2Cl2,
40 °C/23 h.
was 20% after 40 h at room temperature; optimization
of this procedure gave a 59% yield by using 2.5 equiv of
methacryloyl chloride and triethylamine to ethanola-
mine at 40 °C/23 h.
A second design principle to be applied in this
investigation stemmed from an idea put forth by a
report by Wulff and co-workers, who noticed the smaller
EGDMA gave MIPs with better enantioselectivity than
MIPs made with the larger BDMA (4).3 It is often
overlooked that the templates and the monomers im-
printing these templates are roughly on the same order
of magnitude in size. Thus, spatial resolution of tem-
plate by the cavities formed in the matrix is limited to
the cross-linker dimensions. Therefore, it can be rea-
soned that smaller cross-linking monomers would im-
prove the ability of the matrix to more snugly wrap
around a template during polymerization. If EGDMA
is taken as the lead compound, shortening the distance
between the two polymerizable methacrylate groups can
be accomplished by either eliminating the oxygen atom
or the carbon atom of the glycol unit. Since elimination
of one of the glycol carbon atoms in EGDMA would
involve unlikely formation of a central acetal spacer, the
design of choice was narrowed to either elimination of
one of the oxygen atoms or elimination of one oxygen
and one carbon atom of the glycol backbone of the
monomer. The latter, compound 7 (MVK), was chosen
due to its shorter length. An alternative to compound
7, yet still employing the same distance parameters, is
compound 8 (NAG), where the methacrylate moiety of
compound 7 is replaced by a methacrylamide group. The
amide group contributes changes in interactive func-
tionality as well as conformational rotor flexibility,
which influence the binding results discussed later. The
contribution of the newly introduced vinyl ketone po-
lymerizable moiety can be investigated using cross-
linker 9 (EDVK), which maintains the same distance
parameters. All of these cross-linking compounds were
targeted for investigation toward improvement of MIP
matrices.
Syn th esis of 2-Meth yl-N-(3-m eth yl-2-oxobu t-3-
en yl)a cr yla m id e (NAG). Several attempts for the
synthesis of 2-methyl-N-(3-methyl-2-oxobut-3-enyl)acry-
lamide (8) were made using the acyl chloride derived
from N-Boc-glycine. The nucleophilic addition of isopro-
penylmagnesium bromide and isopropenyl manganese
iodide to the acyl chloride derived from N-Boc-glycine
was unsuccessful. An alternative approach for the
synthesis of the monomer 8 entailed the nucleophilic
addition of isopropenylmagnesium bromide to N-Boc-
glycine N-methoxy-N-methyl amide. The reaction be-
tween N-methoxy-N-methyl amides and nucleophiles
such as Grignard reagents or alkyllithiums followed by
acidic hydrolysis has been used successfully in the
synthesis of ketones. In his studies, Weinreb11 showed
that a variety of N-methoxy-N-methyl amides undergo
nucleophilic addition to provide a variety of ketones in
good yields. These reactions are highly selective, and
the formation of alcohols by overaddition of the nucleo-
phile is rarely observed, which is one of the main
drawbacks in the reaction of acyl halides and esters with
Grignard reagents. Another advantage of this reaction
is that no racemization products have been found in the
synthesis of ketones derived from N-protected amino
acids.12
Reaction of the N-Boc-glycine N-methoxy-N-methyl
amide with isopropenylmagnesium bromide to give tert-
butyl 3-methyl-2-oxobut-3-enylcarbamate initially gave
a low yield (32%), accompanied by a large number of
side products. The procedure was modified, by lowering
the reaction temperature from 0 to -15 °C, adding the
nucleophile quickly, and reducing the reaction time, to
avoid isomerization of the isopropenylmagnesium bro-
mide and other side reactions which culminated in an
83% yield.
It was anticipated that deprotection of the amino
group of tert-butyl 3-methyl-2-oxobut-3-enylcarbamate
by acid hydrolysis using HCl/Et2O13 would give the
corresponding hydrochloride, which would be easily
isolated from the reaction mixture; however, the analy-
sis by 1H NMR and IR showed that the compound
obtained from the hydrolysis of N-Boc-methacryloyl
glycine did not correspond to the 3-methyl-2-oxobut-3-
en-1-aminium chloride. Instead, the product of an
intramolecular Michael addition was obtained via the
protonated enone after loss of the tert-butoxycarbonyl
unit.14 Considering these results, a new strategy using
N-methoxy-N-methyl amides as a protecting group for
the carboxylic acid was used in the synthesis of this
monomer.
Resu lts a n d Discu ssion
Syn th esis of Cr oss-Lin ker s. Syn th esis of 2-(Meth -
a cr yloyla m in o)eth yl 2-Meth yl Acr yla te (NOBE).
Synthesis of 2-(methacryloylamino)ethyl 2-methyl acry-
late (6) has been reported by Chan9 who prepared this
monomer by acylation of ethanolamine in a two-step
route with an overall yield of 46%. Our approach for
the synthesis of 6 took as reference the one-pot proce-
dure reported by Anderson and Mosbach for the syn-
thesis of N,O-bisacryloyl-L-phenylalaninol,10 using equi-
molar amounts of ethanolamine to methacryloyl chloride
and triethylamine (Scheme 1). The yield for this reaction
N1-methoxy-N1-methylglycinamide chloride (12) was
synthesized by acidic hydrolysis of N-tert-Boc-Glycine
N-methoxy-N-methyl amide (11) using HCl/Et2O in 94%
yield. 2-Methyl-N-(3-methyl-2-oxobut-3-enyl)acrylamide

Macromolecules, Vol. 36, No. 14, 2003
Molecular Imprinted Polymers 5107
Sch em e 2a
Sch em e 4a
a
Reaction conditions: (a) HCl.HN(OCH3)(CH3)/Et3N/CH2Cl2/
N2, rt/16 h; (b) C3H5MgBr, THF/N2, -78 °C/30 min, 0 °C/30
min.
Sch em e 5a
a
a
Reaction conditions: (a) H2CdC(CH3)CO2H/DCC/DMAP/
Reaction conditions: (a) HCl/Et2O, N2, 0 °C/6 h; rt/18 h;
CHCl3, rt/4 d.
(b) H2CdC(CH3)COCl/DMAP/Et3N/CH2Cl2, rt/48 h; (c)
C3H5MgBr, THF/N2, -15 °C/10 min, rt/25 min.
the amide in THF; (yields 30-40%). Esterification of the
hydroxyl group to give compound 17 can be done using
either protocols involving the use of DCC/DMAP17 or
the acyl chloride/Et3N,10 with comparative yields in the
range of 67-89%. Nucleophilic addition of isopropenyl-
magnesium bromide to the Weinreb amide 17 in order
to produce the vinyl ketone (7) gave a low yield (18%),
under the best conditions.
Sch em e 3a
Syn th esis of 2,7-Dim eth yl-octa -1,7-d ien e-3,6-d i-
on e (EDVK). Synthesis of 2,7-dimethyl-octa-1,7-diene-
3,6-dione (9) was based in the work published by Sibi18
and co-workers, who successfully prepared asymmetric
1,2-diketones using N-methoxy-N-methyl diamides de-
rived from oxalyl chloride. As shown in Scheme 4, the
N,N′-dimethoxy-N,N′-dimethyl-succinamide (19) derived
from succinoyl dichloride (18) was prepared according
to the procedure reported by Uchiyama.19 Nucleophilic
addition of 2 equiv of isopropenylmagnesium bromide
to 19 gave the 1,4-diketone (9) with yields in the range
of 23-27%.
Syn th esis of 2-(Acetyla m in o)eth yl 2-Meth a cr yl-
a te (21). As shown in Scheme 5, compound 21 was
synthesized by acylation of 20 with MAA using DCC as
the coupling reagent in a 35% yield.
F or m a tion of Im p r in ted P olym er s. To evaluate
the performance of the new cross-linking monomers,
dansyl-L-phenylalanine (22) was chosen as the template.
Dansyl-L-phenylalanine was chosen because it has a
single chiral center allowing for evaluation of chiral
recognition as a diagnostic of polymer performance.
Three functional groups, a sulfonamide, a tertiary
amine, and a carboxylic acid provide three points for
electrostatic and hydrogen-bonding interactions for the
complex prior to polymerization.
a
Reaction conditions: (a) NMM/i-BuCO2Cl/HCl.HN(OCH3)-
(CH3)/CH2Cl2/N2, -15 °C/1 h, rt/12 h; (b) LiOH/THF/MeOH, 0
°C/20 min; (c) H2CdC(CH3)CO2H/DCC/DMAP/CH2Cl2, rt/7 d;
(d) C3H5MgBr, THF/N2, -78 °C/30 min, 0 °C/30 min.
(13) was synthesized employing the methodology used
in the synthesis of 6. Since the starting material in this
case corresponds to a hydrochloride, a preliminary
neutralization of the HCl with Et3N was necessary. The
best reaction conditions were those in which the Et3N
was in a high excess; however, the yield was relatively
low (44%). Under the same conditions, adding a 10%
mol of DMAP as catalyst, the yield for this reaction was
improved from 44 to 66%. 2-methyl-N-(3-methyl-2-
oxobut-3-enyl)acrylamide (8) was synthesized by nu-
cleophilic addition of isopropenylmagnesium bromide to
13 to give a 54% yield. The low yield is attributed to
the formation of side products due to polymerization,
isomerization of the isopropenylmagnesium bromide,
and nucleophilic attack on the amide functionality.
Scheme 2 shows the overall synthesis for monomer 8.
Syn th esis of 2-Meth yla cr ylic Acid 3-Meth yl-2-
oxo-bu t-3-en yl Ester (MVK). As shown in Scheme 3,
the first intermediate 15 was synthesized from (acetyl-
oxy)acetic acid (14) using a protocol involving the initial
formation of a mixed anhydride with isobutyl chloro-
formate followed by nucleophilic attack of the amine to
produce the amide.15 Basic hydrolysis16 of the ester
group using an equimolar amount of LiOH produced the
2-hydroxy-N-methoxy-N-methylacetamide (16). Better
yields (63-65%) were obtained when LiOH solid was
added directly to a solution of the amide in THF/MeOH,
rather than adding 1 N LiOH/MeOH to a solution of
Molecularly imprinted polymers were synthesized
using the L- enantiomer of dansyl phenylalanine com-
plexed with the functional monomer methacrylic acid
(MAA) in acetonitrile. Recovery of the template after
Soxhlet extraction with methanol was in the range of

5108 Sibrian-Vazquez and Spivak
Ta ble 1. Ch r om a togr a p h ic Resu lts for
Da n syl-L-P h en yla la n in e a n d Da n syl-D-p h en yla la n in e on
Im p r in ted P olym er s Usin g th e New Cr oss-lin k in g
Mon om er sa
Macromolecules, Vol. 36, No. 14, 2003
Ta ble 2. Ch r om a togr a p h ic Resu lts for Boc-L-tyr osin e a n d
Cbz-L-tr yp top h a n on Im p r in ted P olym er s Usin g th e
Hybr id Cr oss-Lin k in g Mon om er s NOBE a n d NAGa
Boc-L-tyrosine
Cbz-L-tryptophan
k′L k′D
cross-linking
monomer
template
entry
k′L
k′D
R
R
cross-linking extracted,
t
RL(av),
min
t
RD(av),
min
entry
monomer
%
k′L
k′D
R
1
2
3
EGDMA, 2
NOBE, 6
NAG, 8
0.41 0.23 1.78
2.24 1.22 1.84
0.78 0.33 2.36
3.72 1.39 2.68
1
2
3
4
5
6
7
EGDMA, 2
NOBE, 6
NAG, 8
90
98
80
56
85
77
79
3.87
9.20
15.6
4.10
4.18
9.17
7.65
3.58
5.66
6.95
4.01
4.08
8.58
6.51
0.24 0.14 1.7
2.09 0.90 2.3
4.2 1.32 3.2
0.29 0.26 1.1
0.29 0.27 1.1
1.22 1.08 1.1
0.88 0.60 1.5
8.03 2.56 3.14 18.08 3.54 5.11
a
HPLC conditions: particle size, 20-25 µm; column size, 100
× 2.1 mm; mobile phase, acetonitrile/acetic acid 99/1; analytes, 1
mM Boc-L-tyrosine, 1 mM Boc-D-tyrosine, 0.2 mM Cbz-L-tryp-
tophan, 0.2 mM Cbz-D-tryptophan, and acetone (used to determine
void volume); flow rate, 0.1 mL/min; wavelength detection, 270
nm for Boc-tyrosine and 260 nm for Cbz-tryptophan; injected
volume, 5 µL.
MVK, 7
EDVK, 9
EGDMA + 21b
EGDMA + 21c
a
HPLC conditions: particle size, 20-25 µm; column size, 75 ×
2.1 mm; mobile phase, acetonitrile/acetic acid 99/1; analytes, 0.1
m M dansyl-L-phenylalanine, 0.1 mM dansyl-D-phenylalanine, and
acetone (used to determine void volume); flow rate, 0.1 mL/min;
in Figure 3 is obtained from the D-enantiomer in the
first peak, and the L-enantiomer in the second, broader
peak; a behavior often seen for MIPs. In comparison,
the imprinted polymer using EGDMA (entry 1) as the
cross-linking monomer did not give any chromato-
graphic resolution of the dansyl-phenylalanine enan-
tiomers and resulted in complete overlapping of the two
peaks. This example shows that even though there is a
significant R value from enantiomers injected sepa-
rately, the very low retention times give rise to poor
resolution of peaks in Figure 3 because the width of each
peak at half-height is very large compared to retention
time. Although there was some improvement in the
binding affinity and specificity, as reflected in the
capacity factors k′ for imprinted polymers in entries 4
and 5 with respect to the traditional EGDMA (entry 1),
these polymers also did not show chromatographic
resolution of the enantiomers.
b
wavelength detection, 330 nm; injected volume, 5 µL. MIP
formulated with 50% of 21. c MIP formulated with 25% of 21.
The improvement of molecular recognition by the
imprinted polymer using the cross-linking monomer
NOBE (entry 2) vs the traditional EGDMA imprinted
polymer must be attributed to the presence of the amide
group. The generality of improved binding properties
for various types of templates is verified by Table 2,
which shows the results of imprinting Boc-L-tyrosine
and Cbz-L-tryptophan.
F igu r e 3. Elution profile of a racemic mixture of dansyl-
phenylalanine [(1) D-enantiomer, (2) L-enantiomer] injected on
columns (75 × 2.1 mm) packed with (a) MIP-EGDMA, (b)
MIP-NOBE, and (c) MIP-NAG: particle size 20-25 µm;
mobile phase acetonitrile/acetic acid 99/1; flow rate 0.1 mL/
min; injected volume 5 µL; wavelength detection 330 nm.
The trends in Table 2 follow the same trends seen in
Table 1; specifically, polymers made with NAG show the
best selectivity, the highest binding affinity, and the
only imprinted polymers to give baseline separation in
chromatography. One possible reason for the improve-
ment in enantioselectivity is participation of the amide
group of NOBE in hydrogen-bonding interactions with
the template. If this is the case, cross-linkers incorpo-
rating amide groups can be considered functional groups
as well. Although amides generally form weak interac-
tions with other functional groups, the capacity factors
for NOBE show that considerable binding does in fact
take place. This binding is due to the amide group, and
it is not seen for the isosteric EGDMA. Another possible
reason for the improvement in enantioselectivity by
NOBE may be due to increased rigidity of the entire
matrix, imparted by the amide bond in the cross-linker.
Since amide bonds are more conformationally rigid than
ester bonds, the introduction of the amide bond into the
backbone of the cross-linking monomer may maintain
binding site fidelity, in addition to possible conforma-
tional control within the matrix unavailable using the
traditional EGDMA.
56-98%, depending on the cross-linker used (Table 1).
The selectivity of the polymers was determined by
HPLC under isocratic conditions at room temperature.
Capacity factors (k′) were obtained in order to determine
separation factors (R) of the L- and D-enantiomers of
dansyl phenylalanine (R ) k′L/k′D). Table 1 shows the
capacity and separation factors for the imprinted poly-
mers using the new cross-linking monomers (entries
2-5) vs an imprinted polymer using the traditional
polymer formulation with EGDMA as the cross-linking
monomer (entry 1).
Table 1 shows that imprinted polymers formulated
with cross-linking monomers in entries 1-3 showed a
high selectivity for the original template. The imprinted
polymer using NAG as the cross-linking monomer (entry
3) gave the highest separation factor, exhibiting a 2-fold
improvement vs the traditional formulation with EGD-
MA (entry 1). This improvement in molecular recogni-
tion of the template is emphasized by Figure 3, dem-
onstrating the ability of the imprinted polymer in entry
3 to resolve a mixture of the two enantiomers of dansyl
phenylalanine. Complete baseline resolution as shown
The NAG further shows improvement in selectivity
over NOBE. Comparing these cross-linkers, both have
a single amide bond capable of hydrogen-bonding in-

Macromolecules, Vol. 36, No. 14, 2003
Molecular Imprinted Polymers 5109
Ta ble 3. Su r fa ce Ar ea a n d P or e An a lysis on th e
Im p r in ted P olym er s
teractions with the template that can provide greater
rigidity to the backbone of the polymer. Table 1 shows
that the amide bond is responsible for the similar
increase in binding affinities of NAG and NOBE vs
EGDMA. Since this increase is of the same order of
magnitude for NAG and NOBE, the increased selectivity
of NAG is not due merely to the presence of the amide
bond. There are two differences between these cross-
linkers: (1) the spacer between the cross-linking points
is reduced from six atoms to four, and (2) the methacry-
late group of NOBE is substituted by a methacrolein
group in the cross-linking monomer NAG. Simply
comparing the monomer NAG to NOBE does not supply
enough information to discern whether the size or
change in polymerizable group is responsible for the
enhancement in selectivity. Therefore, two new cross-
linking monomers, MVK and EDVK, were investigated.
surface area pore vol,b pore diam,c
entry
polymer
(BET),a m2/g
mL/g
Å
1
2
3
4
5
6
7
EGDMA, 2
NOBE, 6
NAG, 8
165
51
154
92
136
91
106
0.486
0.510
0.488
0.191
0.480
0.728
0.416
118
402
127
83
141
319
156
MVK, 7
EDVK, 9
EGDMA + 21d
EGDMA + 21e
a
Determined using the BET model on a seven-point linear plot.
b BJ H cumulative adsorption pore volume. c BJ H adsorption aver-
d
age pore diameter. MIP formulated with 50% of 21. e MIP
formulated with 25% of 21.
Ta ble 4. Un r ea cted Dou ble Bon d s Deter m in ed by
Solid -Sta te 13C CP -MAS NMR
cross-linking
monomer
unreacted double
bonds, %
Both MVK and EDVK monomers have the same
length dimensions as NAG; however, the amide nitrogen
in NAG is replaced with an oxygen for MVK and a
carbon for EDVK. If size of the cross-linker was the key
to enhanced selectivity, then polymers imprinted using
these monomers should also exhibit improved separa-
tion factor values. Table 1 shows this is not the case,
instead these monomers produced MIPs that were less
selective than polymers imprinted using the cross-
linkers NAG, NOBE, or EGDMA. Furthermore, if
enhanced selectivity of NAG vs NOBE was due to the
substitution of a methacrolein polymerizable group in
place of the methacrylate polymerizable group, it would
be reasonable to suggest the polymers imprinted using
MVK and EDVK cross-linkers should show enhanced
selectivity vs polymers imprinted using traditional
EGDMA. However, the separation factors in Table 1
show that this is not the case, and incorporation of the
methacrolein polymerizable group is not by itself re-
sponsible for increased selectivity seen by MIPs made
with NAG cross-linker.
entry
1
2
3
4
5
EGDMA, 2
NOBE, 6
NAG, 8
MVK, 7
EDVK, 9
17
23
24
15
19
between aggregates.20 Porosity is controlled by the
interaction of the forming polymer matrix and the
solvent (referred to as “porogen”) as phase separation
occurs. Data from BET analysis of the new materials
by nitrogen adsorption-desorption porosimetry are
shown in Table 3. The nitrogen adsorption-desorption
isotherms indicate that all polymers have average pore
diameters in the macroporous range, essentially in the
same order of magnitude as the polymer made using
the traditional MIP formulation with EGDMA. With the
exception of MVK, the polymers also exhibited pore
volumes essentially of the same order of magnitude. The
polymer made with MVK had a low pore volume which
is responsible also for low surface area. With the
exception of polymers made with NOBE, MVK, and the
MIP formulated with 50% of 21, the surface areas for
the other polymers were within the same order of
magnitude. While low porosity is the origin of low
surface area for the MVK polymer, the low surface area
for the NOBE polymer is due to the larger pore size. As
with earlier porosity studies on MIPs,8 there is no direct
correlation of surface area or porosity with MIP perfor-
mance; however, the data presented here show that
macroporous polymers made with the new cross-linkers
are similar in this respect to the well-characterized
EGDMA polymers.
13C CP -MAS NMR An a lysis. Quantitative estima-
tion of the unreacted double bonds by 13C CP-MAS NMR
(Table 4) was obtained from the integrated intensity of
the carbonyl resonance assigned to the unsaturated
carbonyl, relative to the total integrated intensity of the
saturated carbonyl:21 167 and 175 ppm for methacrylate,
167 and 177 ppm for methacrylamide, and 190 and 210
ppm for vinyl ketone. The average number of unreacted
double bonds was 20% with all polymers falling close
to that value. The NOBE and NAG cross-linkers showed
the highest number of free double bonds, which most
likely corresponds to slow reactivity by the methacryl-
amide moiety. There are no correlations between re-
sidual double bonds and polymer performance in the
literature. This is mainly due to the fact that there is
one other published result on the solid-state NMR
analysis of photopolymerized MAA/EGDMA imprinted
On the basis of these data, enhancement in selectivity
for the imprinted polymer using NAG may be the result
of cooperative interactions between functional groups in
the monomer. This may result in a polymer with greater
stability, capable of maintaining the fidelity of the
original imprinted binding site. Another possibility is
the close proximity of donor and acceptor functionality
that can provide cooperative hydrogen-bonding interac-
tions. NAG has a shorter distance between the nitrogen
of the amide group and the carbonyl group of the
methacrolein group, providing donor-acceptor interac-
tions in a favorable 1,3 disposition that would promote
chelating interactions. On the other hand, NOBE pro-
vides donor-acceptor in a less favorable 1,5 disposition,
forcing the amide and carbonyl groups to act indepen-
dently. Even if chelation is not at the root of binding
improvement, the smaller spacer group between the
donor and acceptor functionalities on NAG may provide
more positive interactions per square angstrom of
polymer in the vicinity of the template vs NOBE or other
longer cross-linkers. The higher density of polymer
functionality in the vicinity of the template may provide
a general basis for improved molecular recognition for
the new MIPs.
An a lysis of P or osity a n d Su r fa ce Ar ea . Most
MIPs are part of a class of polymers known as
macroporous polymers. The morphology of these mate-
rials is known and actually consists of aggregates of
material with macro-, meso-, and micropores formed

5110 Sibrian-Vazquez and Spivak
Macromolecules, Vol. 36, No. 14, 2003
polymers, which reported residual double bond content
on the order of 9%.8 To test whether it is the residual
unreacted methacrylamide functionality that is respon-
sible for the increased molecular recognition (specificity
and binding affinity) of the template molecules, com-
pound 21 was synthesized, and substituted for NOBE
to provide the desired pendant amide functionality.
Table 1 shows the binding results for polymers where
half of the EGDMA component was substituted with
compound 21 (entry 6), or one-fourth of the EGDMA was
substituted with compound 21 (entry 7). This was
anticipated to give polymers with the same pendant
amide functionality as the polymer in entry 2. The data
in entries 6 and 7 show that good binding and selectivity
(seen for entry 2) do not originate from pendant amide
functionality; instead, it must be concluded that the
amide functionality incorporated in the cross-linked
backbone of the polymer is responsible for the enhanced
binding properties of NOBE polymers (and NAG poly-
mers). Last, it should be pointed out that the MIPs made
with the new cross-linkers are similar with respect to
residual double bond content vs standard EGDMA
polymers.
plays a role in promoting positive interactions with the
template to afford molecular recognition.
Exp er im en ta l Section
Ma ter ia ls. Unless otherwise indicated, chemicals were
purchased from Aldrich and used without further purification.
Solvents were obtained from commercial suppliers and used
as is. THF was dried by refluxing over K, followed by
distillation. CH2Cl2 was dried by refluxing over CaH2, followed
by distillation. Reactions under anhydrous conditions were
performed in dry glassware under N2 atmosphere. Reactions
were monitored by thin-layer chromatography using 0.25 mm
Macherey Nagel silica gel glass plates (60F-254), fractions
being visualized by UV light, by iodine, or by staining with
molybdophosphoric acid with subsequent heating. Column
chromatography was carried out with flash silicagel, 32-63
µm from Science Adsorbents Inc.
1
Mea su r em en ts. H NMR and 13C NMR were measured in
CDCl3 unless otherwise indicated on
a Bruker DPX-250
spectrometer. Chemical shifts (δ) are given in ppm relative to
CDCl3 (7.24 ppm, 1H; 77.00 ppm, 13C) unless otherwise
indicated. 13C CP-MAS NMR analysis was performed in a
Chemagnetics Infinity 400 spectrometer. IR spectra were
obtained as neat samples on a Nicolet AVATAR 320 FT-IR
unless otherwise indicated. High-resolution mass spectra
(HRMS) were obtained on a Finnigan MAT900 double sector
instrument, under fast atom bombardent (FAB, liquid sims)
ionization or electrospray ionization (EI). Imprinted polymer-
ization was performed in a photochemical turntable reactor
(ACE Glass Inc.), which was immersed in a constant-temper-
ature bath. A standard laboratory UV light source (a Canrad-
Hanovia medium pressure 450 W mercury arc lamp) jacketed
in a borosilicate double-walled immersion well was placed at
the center of the turntable. HPLC columns were packed using
a Beckman 1108 Solvent Delivery Module, into stainless steel
columns (length 7.5 cm; i.d. 2.1 mm) to full volume for
chromatographic experiments. HPLC analyses were performed
isocratically at room temperature (21 °C) using a Hitachi
Con clu sion s
Using EGDMA as the lead compound, three new
cross-linking monomers were designed, synthesized, and
evaluated as matrix elements for molecularly imprinted
polymers. Polymers made using the new cross-linking
monomers and imprinted with the template dansyl-L-
phenylalanine were evaluated using enantioselectivity
as the figure of merit for MIP performance. Chromato-
graphic evaluation of the imprinted polymers revealed
that MIPs made with amide-functionalized cross-linkers
(NAG, NOBE) showed increased enantioselectivity for
the template molecule vs MVK, EDVK, and the tradi-
tionally used EGDMA. The same trend was observed
when Boc-L-tyrosine and Cbz-L-tryptophan were used
as the template molecules. The origins of the enhanced
selectivity could arise from both molecular and macro-
molecular contributions. At the molecular level, selec-
tivity of template binding may be enhanced by coopera-
tive 1,3-interactions of the amide and carbonyl group
of NAG, vs the more distant 1,5-interaction of NOBE.
A more general enhancement to molecular recognition
in the MIPs employing the new cross-linkers may be
simply attributed to a higher functional group density
by the polymers in vicinity of the template, which may
provide more positive binding interactions vs EGDMA
cross-linked polymers.
L-7100 pump with
a Hitachi L-7400 detector. Pore size
measurementes were obtained in a Quantachrom AUTOSORB-1
AS-1.
2-(Met h a cr yloyla m in o)et h yl 2-Met h yl Acr yla t e (6).
2-Aminoethanol (10) (0.976 g, 16 mmol) was mixed with 15
mL of CH2Cl2, and then Et3N (3.74 g, 5.15 mL, 37 mmol) was
added in small portions to the initial mixture with stirring.
The reaction mixture was cooled to 0 °C and then (3.867 g,
3.6 mL, 37 mmol) methacryloyl chloride was added dropwise
with vigorous stirring and keeping the temperature at 0 °C.
After complete addition of methacryloyl chloride, the temper-
ature was increased to 40 °C and the reaction mixture was
allowed to react 23 h at this temperature. The reaction mixture
was filtered out and the precipitate (Et3NHCl) discarded. The
filtrate was extracted with 0.5 M NaHCO3 (3 × 15 mL) and
0.5 M sodium citrate (3 × 15 mL). The solvent was evaporated
under vacuum, and the compound was isolated by flash
chromatography with EtOAc/hexanes 50/50, EtOAc 100%. The
product (6) was isolated as a pale yellow oil in a 59% yield. 1H
NMR (CDCl3, 250 MHz): δ/ppm ) 6.80 (1H, bs, NH), 5.99 (1H,
m, RO2C(CH3)CdCHa Hb), 5.71 (1H, t, J ) 0.905 Hz, RHNCOC-
(CH3)CdCHcHd), 5.60 (1H, t, J ) 0.517 Hz, RO2C(CH3)Cd
CHaHb), 5.38 (1H, t, J ) 0.517 Hz, RHNCOC(CH3)CdCHcHd ),
4.29 (2H, t, J ) 5.69 Hz, OCH2), 3.60 (2H, quad, J ) 5.69, Hz,
NHCH2), 1.94 (3H, s, CH3), 1.8 (3H, s, CH3). 13C NMR (CDCl3,
62.5 MHz): δ/ppm ) 169.08 (RNHCOR), 167.82 (RCO2R),
140.11 [RHNCO(CH3)CdCH2], 136.25 [RCO2(CH3)CdCH2],
126.40 [RCO2(CH3)CdCH2], 120.04 [RHNCO(CH3)CdCH2]
63.50 (OCH2), 39.29 (NHCH2), 18.90 [RHNCO(CH3)CdCH2],
18.60 [RCO2(CH3)CdCH2]. IR (cm-1): 1722.55, 1660.17, 1628.55,
1453.10, 1336.68, 1161.81, 1083.65, 937.62. HRMS (EI) (M+):
calcd, 197.1052; found, 197.1063.
From a materials point of view, the shorter length of
NAG may provide a better resolved binding site by
wrapping more snugly around the template molecule.
However, this appears only to be effective in cooperation
with a more rigid cross-linker to maintain the site
fidelity, compared to MVK which has similar size but
does not have the rigid amide linkage. Surface area and
porosity measurements reveal similar characteristics for
all materials. Solid state NMR measurements of re-
sidual double bonds in the new materials show values
close in magnitude for all the polymers. Thus, the new
materials can all be classified as macroporous, without
drastic differences in the polymer materials vs the
standard MAA/EGDMA polymer formulation. Overall,
these results show that the cross-linking monomer is
not merely an inert component of the MIPs, but also
N1-Meth oxy-N1-Meth ylglycin a m id e Ch lor id e (12). N-
Boc-glycine N-methoxy-N-methyl amide (11) (0.874 g, 4 mmol)
was dissolved in 3 mL of dry CHCl3 and cooled at 0 °C under
N2 atmosphere, and then 10 mL of 2 M HCl in ethyl ether

Macromolecules, Vol. 36, No. 14, 2003
Molecular Imprinted Polymers 5111
was added dropwise. The temperature was kept at 0 °C/6 h
and increased to room temperature and the reaction stirred
for 18 h. HCl and ether were purged under a current of N2
with further removal under vacuum. The white sticky solid
residue was washed with ethyl ether (3 × 20 mL) and dried
under vacuum. Yield: 94%. 1H NMR (DMSO-d6, 250 MHz):
δ/ppm ) 8.5 (3H, bs, NH3+), 3.93 (2H, d, CH2), 3.82 [3H, s,
RN(OCH3)(CH3)], 3.25 [3H, s, RN(OCH3)(CH3)]. 13C NMR
(DMSO-d6, 62.5 MHz): δ/ppm ) 167.60 [RCON(OCH3)(CH3)],
62.32 [RCON(OCH3)(CH3)], 34.69 [NCH2CON(OCH3)(CH3)],
32.74 [RCON(OCH3)(CH3)]. IR (cm-1): 3418.68 (broad), 1671.57,
1494.94, 1183.14, 1130.96, 983.41, 907.01. HRMS(FAB) (M +
H+): calcd, 119.0821; found, 119.0825.
N-Met h a cr yloyl Glycin e-N,N-Met h oxym et h yl Am id e
(13). 12 (0.706 g, 4 mmol) was suspended in 5 mL of CH2Cl2
and neutralized with Et3N until pH 7-8. The mixture was
cooled at 0 °C, and then the rest of the Et3N was added. A
total of 20 mmol (2.024 g, 2.78 mL) were added. To this mixture
was added (0.122 g, 1 mmol) DMAP, followed by dropwise
addittion of methacryloyl chloride (1.0454 g, 10 mmol). After
complete addition of methacryloyl chloride, the mixture was
kept at 0 °C for 30 min and then the temperature increased
to room temperature, and the mixture was allowed to react
for 48 h. The reaction mixture was filtered and the precipitate
(Et3N.HCl) discarded. The filtrate was washed with 0.5 M
NaHCO3 (3 × 15 mL) and 0.5 M sodium citrate (3 × 15 mL)
and dried over MgSO4. The solvent was evaporated under
vacuum to leave a brown oil. 13 was isolated by flash
chromatography with EtOAc giving a pale yellow oil in a 66%
yield. 1H NMR (CDCl3): δ/ppm ) 6.70 (1H, bs, NH), 5.73 (1H,
s, RHNCOC(CH3)CdCHa Hb), 5.30 (1H, s, RHNCOC(CH3)Cd
CHaHb), 4.17 (2H, d, J ) 4.42 Hz, CH2), 3.67 [3H, s, RN-
(OCH3)(CH3)], 3.16 [3H, s, RN(OCH3)(CH3)], 1.93 (3H, s, CH3).
13C NMR (CDCl3, 62.5 MHz): δ/ppm ) 170.08 [RCON(OCH3)-
(CH3)], 168.61 [RHNCOC(CH3)CdCH2], 139.68 [RHNCOC-
(CH3)CdCH2], 120.61 [RHNCOC(CH3)CdCH2], 61.93 [RN-
(OCH3)(CH3)], 41.24 (CH2), 32.70 [RN(OCH3)(CH3)], 18.09
(CH3). IR (cm-1): 3349.22, 1658.85, 1621.44, 1533.06, 1313.81,
991.35, 931.64. HRMS(FAB) (M + H+): calcd, 187.1082; found,
187.1078.
2-Meth yl-N-(3-m eth yl-2-oxobu t-3-en yl)a cr yla m id e (8).
13 (0.558 g, 3 mmol) was dissolved in 10 mL of dry THF and
cooled to -15 °C under N2. Isopropenylmagnesium bromide
(15 mL of a 0.5 M solution/THF, 7.5 mmol) was added dropwise
over a period of 5 min during which a pale yellow precipitate
was formed. The mixture was stirred for other 5 min at -15
°C following complete addition of the Grignard reagent and
then brought to room temperature and stirred for 25 min. After
this period, 7.0 mL of saturated NH4Cl solution was added to
quench the reaction. The THF was removed by evaporation
under vacuum and 30 mL of ethyl ether were added to recover
the organic compounds. Phases were separated, and the
organic layer was washed with H2O (2 × 15 mL) and brine (1
× 20 mL), dried over MgSO4, filtered, and concentrated under
reduced pressure. The residue, a pale yellow oil, was separated
by flash chromatography with EtOAc/hexanes 50/50 giving
54% yield for the title product as a yellow oil. 1H NMR (CDCl3,
250 MHz): δ/ppm ) 6.75 (1H, bs, NH), 6.06 [1H, d, J ) 0.948
Hz, RCOC(CH3)CdCHcHd], 5.89 [1H, t, J ) 1.580 Hz, RCOC-
(CH3)CdCHcHd], 5.78 (1H, d, J ) 0.948 Hz, RHNCOC(CH3)Cd
CHa Hb), 5.37 (1H, t, J ) 1.580 Hz, RHNCOC(CH3)CdCHaHb),
4.49 (2H, d, J ) 4.423 Hz, CH2), 1.97 (3H, t, J ) 0.948 Hz,
CH3), 1.91 (3H, t, J ) 0.948 Hz, CH3). 13C NMR (CDCl3, 62.5
MHz) δ/ppm ) 196.20 [RCOC(CH3)CdCH2], 168.52 [RHNCOC-
(CH3)CdCH2], 142.59 [RCOC(CH3)CdCH2], 139.71 [RHNCOC-
(CH3)CdCH2], 126.59 [RCOC(CH3)CdCH2], 120.76 [RHNCOC-
(CH3)CdCH2], 46.03 (CH2), 18.93 (CH3), 17.71 (CH3). IR
(cm-1): 3347.10, 1692.50, 1660.19, 1621.08, 1531.16, 1453.91,
1058.59, 934.88. HRMS(FAB) (M + H+): calcd, 168.0946;
found, 168.1017.
mixture was stirred at -15 °C/15 min followed by the addition
of N,O-dimethyl hydroxylamine hydrochloride (2.21 g, 22
mmol). The mixture was stirred at -15 °C/1 h, allowed to
warm to room temperature, and stirred for 24 h. The reaction
mixture was poured into water (60 mL), and the aqueous phase
was extracted with CH2Cl2 (2 × 50 mL). The combined organic
extracts were dried over MgSO4. The solvent was removed
under vacuum giving a pale yellow oil. The product was
isolated by flash chromatography using EtOAc/hexanes 60/
40. Yield: 95%. 1H NMR (CDCl3, 250 MHz): δ/ppm ) 4.53
(2H, s, CH2), 3.46 [3H, s, RN(OCH3)(CH3)], 2.90 [3H, s RN-
(OCH3)(CH3)], 1.86 (3H, s, CH3). 13C NMR (CDCl3, 62.5
MHz): δ/ppm ) 170.56 (ROCOCH3), 168.09 [RCON(OCH3)-
(CH3)], 61.62 (CH2), 61.19 [RN(OCH3)(CH3)], 32.32 [RN-
(OCH3)(CH3)], 20.64 (CH3). IR (cm-1): 3567.35, 1746.53,
1685.48, 1425.93, 1233.65, 1066.07, 982.08. HRMS(FAB) (M
+ H+): calcd, 162.0688; found, 162.0774.
2-Hyd r oxy-N-m eth oxy-N-m eth yla ceta m id e. (16). Com-
pound 15 (2.576 g, 16 mmol) was dissolved in THF MeOH/
THF 1/5 (90 mL), the solution was cooled to 0 °C, and then
LiOH (0.3832 g, 16 mmol) was added in one portion. The
reaction mixture was stirred for 20 min at 0 °C, and then water
(40 mL) was added. The solvent was removed under vacuum,
leaving the aqueous phase which was extracted with CHCl3
and dried over MgSO4, and the solvent was removed under
vacuum to give a pale yellow oil. The product was isolated by
flash chromatography using EtOAc. Yield: 60% 1H NMR
(CDCl3, 250 MHz): δ/ppm ) 4.13 (2H, s, CH2), 3.52 [3H, s,
RN(OCH3)(CH3)], 3.48 (1H, s, broad, OH), 3.06 [3H, s, RN-
(OCH3)(CH3)]. 13C NMR (CDCl3, 62.5): δ/ppm ) 173.54
[RCON(OCH3)(CH3)], 61.75 (CH2), 60.10 [RN(OCH3)(CH3)],
37.74 [RN(OCH3)(CH3)]. IR (cm-1): 3421.61 (broad), 1660.35,
1442.80, 1182.55, 1071.84, 987.99. HRMS (FAB) (M + H+):
calcd, 120.0582; found, 120.0665.
2-[Meth oxy(m eth yl)a m in o]-2-oxoeth yl 2-Meth yl Acr yl-
a te. (17). Compound 16 (0.87 g, 7 mmol) was dissolved in CH2-
Cl2 (50 mL). To this solution were added MAA (0.663 g, 7.7
mmol) and DMAP (0.094 g, 0.77 mmol) at room temperature.
After 5 min, DCC (1.589 g, 7.7 mmol) was added and the
reaction mixture was stirred 7 days. The DCU was filtered
and the organic phase was extracted with 0.5 M NaHCO3 (2
× 45 mL), 0.5 M sodium citrate (2 × 45 mL), dried over MgSO4
and the solvent evaporated under vacuum to give a yellow-
orange oil. The product was isolated by flash chromatography
using EtOAc/hexanes 60/40. Yield: 89%. 1H NMR (CDCl3, 250
MHz): δ/ppm ) 6.04 (1H, s, RO2C(CH3)CdCHa Hb), 5.46 (1H,
quin, J ) 1.58 Hz, RO2C(CH3)CdCHaHb), 4.81 (2H, s, CH2),
3.66 (3H, s, RN(OCH3)(CH3)], 3.11 [(3H, s, RN(OCH3)(CH3)],
1.90 (3H, s, CH3). 13C NMR (CDCl3, 62.5 MHz): δ/ppm )
168.34 [RCON(OCH3)(CH3)], 167.39 [RO2C(CH3)CdCH2], 135.96
[RO2C(CH3)CdCH2], 126.90 [RO2C(CH3)CdCH2], 61.83 (CH2),
61.65 [RN(OCH3)(CH3)], 32.61 [RN(OCH3)(CH3)], 18.57 (CH3).
IR (cm-1): 1725.77, 1688.27, 1427.41, 1297.88, 1163.32, 986.46.
HRMS (EI) (M + H+): calcd, 188.0845; found, 188.0436.
2-Meth yla cr ylic Acid 3-Meth yl-2-oxo-bu t-3-en yl Ester
(7). Compound 17 (0.748 g, 4.0 mmol) was dissolved in 45 mL
of dry THF and cooled at -78 °C under N2. Afterward, 0.5 M
isopropenylmagnesium bromide (12.0 mL, 6.0 mmol) diluted
with THF (9 mL), was added dropwise over a period of 5 min.
The mixture was stirred for another 30 min at -78 °C after
complete addition of the Grignard reagent; then the mixture
was brought to 0 °C and stirred for 30 min. After this period,
15 mL of saturated NH4Cl solution was added to quench the
reaction. The THF was removed by evaporation under vacuum
and then ethyl ether (30 mL) was added to recover the organic
compounds. Phases were separated, and the organic layer was
washed with H2O (2 × 40 mL) and brine (1 × 40 mL), dried
over MgSO4, filtered, and concentrated under reduced pres-
sure. The residue, a pale yellow oil, was separated by flash
chromatography with EtOAc/hexanes 20/80 giving 18% yield
for the title product, as a pale yellow oil. 1H NMR (CDCl3, 250
MHz): δ/ppm ) 6.14 (1H, t, J ) 0.948 Hz, RCOC(CH3)Cd
CHcHd), 5.885 (1H, t, J ) 0.948 Hz, RCOC(CH3)CdCHcHd ),
5.77 (1H, t, J ) 1.58 Hz, RO2C(CH3)CdCHa Hb), 5.57 (1H, t,
1.58 Hz, RO2C(CH3)CdCHaHb), 5.09 (2H, s, CH2), 1.91 (3H, t,
2-[Meth oxy(m eth yl)a m in o]-2-oxoeth yl Aceta te (15). To
a solution of (acetyloxy)acetic acid (14) (2.40 g, 20 mmol) in
dry CH2Cl2 (90 mL) under N2 was added N-methylmorpholine
(4.49 g, 44 mmol). The mixture was cooled at -15 °C, and
isobutylchloroformate (3.06 g, 22 mmol) was added. The

5112 Sibrian-Vazquez and Spivak
Macromolecules, Vol. 36, No. 14, 2003
J ) 1.738, 0.79 Hz, CH3), 1.86 (3H, t, J ) 1.58, 0.79 Hz, CH3).
13C NMR (CDCl3, 62.5 MHz): δ/ppm ) 193.93 [RCO(CH3)Cd
CH2], 167.20 [RO2C(CH3)CdCH2], 142.62 [RCO(CH3)CdCH2],
135.98 [RO2C(CH3)CdCH2], 127.00 [RCO(CH3)CdCH2], 125.46
[RO2C(CH3)CdCH2], 65.93 (CH2), 18.69 (CH3), 17.83 (CH3).
IR (cm-1): 1728.99, 1696.33, 1637.07, 1430.18, 1294.80, 1167.64,
1093.52, 1034.89, 941.49, 818.01. HRMS (EI) (M + H+): calcd,
169.0786; found, 169.0702.
mer. The solution was purged by bubbling nitrogen gas into
the mixture for 5 min and then capped and sealed with Teflon
tape and Parafilm. The samples were inserted into a photo-
chemical turntable reactor, which was immersed in a constant-
temperature bath. A standard laboratory UV light source
(medium pressure 450 W mercury arc lamp) jacketed in a
borosilicate double-walled immersion well was placed at the
center of the turntable. The polymerization was initiated
photochemically at 20 °C and the temperature maintained by
both the cooling jacket surrounding the lamp and the constant-
temperature bath holding the entire apparatus. The polym-
erization was allowed to proceed for 10 h and then used for
chromatographic experiments.
Ch r om a togr a p h ic Exp er im en ts. Removal of the template
was achieved by Soxhlet extraction with methanol for 48 h.
Then the polymers were ground using a mortar and pestle,
the particles were sized using U.S.A. Standard Testing Sieves,
and the fraction between 20 and 25 µm was collected. The
particles were slurry packed, using a solvent delivery module,
into stainless steel columns (length, 75 mm; i.d., 2.1 mm) to
full volume for chromatographic experiments. The polymers
were then washed on line for 12 h using acetonitrile/acetic acid,
98/2, at a flow rate of 0.1 mL/min to remove any residual
template. HPLC analyses were performed isocratically at room
temperature (21 °C). The flow rate in all cases was set at 0.1
mL/min using a mobile phase consisting of acetonitrile/acetic
acid, 99/1, a substrate concentration of 0.1 mM dansyl-
phenylalanine in acetonitrile, and a wavelength detection of
330 nm. The void volume was determined using acetone as
an inert substrate. The separation factors (R) were measured
as the ratio of capacity factors k′L/k′D. The capacity factors were
determined by the relation k′ ) (Rv - Dv)/ Dv, where Rv is the
retention volume of the substrate and Dv is the void volume.
P or e An a lysis. A sample of polymer (70-150 mg) was
degassed at 150 °C/24 h under vacuum. The absorption and
desorption isotherms were obtained using a 20 min equilibra-
tion time. Surface areas were determined according to the BET
model; pore volumes and size distributions, according to the
BJ H model.
N,N′-Dim eth oxy-N,N′-d im eth ylsu ccin a m id e (19). Com-
pound 19 was prepared following a protocol literature,19
providing product as dark brown needles in a 62% yield. Mp:
1
73-75 °C. H NMR (CDCl3, 250 MHz): δ/ppm ) 3.67 [3H, s,
RN(OCH3)(CH3)], 3.14 [3H, s, RN(OCH3)(CH3)], 2.72 (2H, s,
CH2). 13C NMR (CDCl3, 62.5 MHz): δ/ppm ) 173.67 [RCON-
(OCH3)(CH3)], 61.46 [RN(OCH3)(CH3)], 32.45 [RN(OCH3)-
(CH3)], 26.69 (CH2). IR (cm-1): 1660.58, 1454.93, 1392.19,
1194.01, 993.29, 933.47. HRMS (FAB) (M + H+): calcd,
205.1110; found, 205.1194.
2,7-Dim eth ylocta -1,7-d ien e-3,6-d ion e (9). A solution of
diamide 19 (2.02 g, 9.94 mmol) in 80 mL of dry THF under N2
was cooled at -70 °C, followed by dropwise addition of 0.5 M
isopropenylmagnesium bromide in THF (59.6 mL, 29.8 mmol)
diluted in dry THF (30 mL) over 5 min. After complete
addition, the reaction mixture was stirred additional 30 min
at -70 °C, and then the temperature was left to rise to 0 °C
and kept there for 2 h. Saturated NH4Cl (20 mL) was added
to quench the reaction. THF was removed under vacuum, and
the aqueous phase was extracted with ethyl ether (3 × 50 mL).
The organic phase was washed with water (2 × 50 mL) and
brine (50 mL) and dried over MgSO4, and the solvent was
evaporated under vacuum, to leave an orange liquid. The
target product, a pale yellow liquid, was isolated by flash
chromatography on silica gel using EtOAc/hexanes 20/80.
1
Yield: 27%. H NMR (CDCl3, 250 MHz): δ/ppm ) 5.93 (1H,
s, RCOC(CH3)CdCHa Hb), 5.66 (1H, t, J ) 1.422, 0.632 Hz,
RCOC(CH3)CdCHaHb), 2.91 (2H, s, CH2), 1.75 (3H, t, J ) 1.58,
0.948 Hz, CH3). 13C NMR (CDCl3, 62.5 MHz): δ/ppm ) 200.56
[RCO(CH3)CdCH2], 144.5 [RCO(CH3)CdCH2], 124.98 [RCO-
(CH3)CdCH2], 31.74 (CH2), 17.87 (CH3). IR (cm-1): 1674.51,
1453.00, 1368.02, 1070.75, 935.67. HRMS (EI) (M+): calcd,
166.0993; found, 166.0990.
13C CP -MAS NMR An a lysis. 13C CP-MAS NMR data were
collected on a Chemagnetics spectrometer at ambient temper-
ature at a frequency of 100.60 MHz. Samples were packed into
5 mm zirconia rotors (Varian, Palo Alto CA) and spun at 5
kHz. A total of 4096 data points were collected over a spectral
window of 50 kHz: 1H 90° pulse of 4.6 µs; acquisition time
81.92 ms; contact time 5 ms; repetition time 4.0 s.
2-(Acetyla m in o)eth yl 2-Meth a cr yla te (21). N-(2-Hydrox-
yetyl)acetamide (10.0 g, 96.97 mmol) was dissolved in CHCl3
(250 mL). To this solution were added MAA (12.522 g, 145.45
mmol) and DMAP (1.777 g, 14.54 mmol) at room temperature.
After 5 min, DCC (30.01 g, 145.55 mmol) was added, and the
reaction mixture was stirred 4 days. The DCU was filtered,
the organic phase was extracted with 0.5 M HCl (2 × 200 mL),
H2O (1 × 200 mL), 0.5 M NaHCO3 (2 × 200 mL), dried over
MgSO4, and the solvent evaporated under vacuum to give a
colorless oil. The product was isolated by flash chromatography
Ack n ow led gm en t. This research was supported in
part by the Research Corporation, through Cottrell
Scholar Award CS0801, and an NSF CAREER Program
award, CHE-0134290 (D.A.S.). We thank Dr. Dale
Treleaven for assistance with 13C CP-MAS NMR mea-
surements.
1
using EtOAc/hexanes 50/50, EtOAc in a 35% yield. H NMR
(CDCl3, 250 MHz): δ/ppm ) 6.65 (1H, s, ROCNHR), 6.02 (1H,
s,ROCNHCH2CH2OCO(CH3)CdCHaHb),5.49(1H,s,ROCNHCH2-
CH2OCO(CH3)CdCHa Hb),4.12 (2H,t,J )5.42 Hz,RNHCH2CH2-
OCOR), 3.45 (2H, quad, J ) 11.15, 5.6 Hz, RNHCH2CH2-
OCOR), 1.88 (3H, s, RCOCH3), 1.84 (3H, s, ROCO(CH3)Cd
CHaHb). 13C NMR (CDCl3, 62.5 MHz): δ/ppm ) 171.07
(RCONHR), 167.64 [RO2C(CH3)CdCH2], 136.25 [RO2C(CH3)-
CdCH2], 126.26 [RO2C(CH3)CdCH2], 63.61 (ROCH2CH2NHR),
38.87 (ROCH2CH2NHR), 23.23 (CH3COR), 18.49 [RO2C(CH3)Cd
CH2]. IR (cm-1): 3288.27, 3083.16, 2958.86, 1713.91, 1658.95,
1555.36, 1165.83, 1041.19, 945.26. HRMS (FAB) M + H+):
calcd, 172.0895; found, 172.0975.
P olym er P r ep a r a tion . The following procedure was used
for imprinted polymers employing the new cross-linking
monomers. In a 13 × 100 mm test tube, (0.062 g, 0.155 mmol)
of dansyl-L-phenylalanine was dissolved in 1.5 mL of aceto-
nitrile. To this solution was added 8 (1.0617 g, 6.35 mmol)
(NAG), MAA (0.109 g, 1.27 mmol), and AIBN (0.020 g, 0.124
mmol). Similar imprinted polymers were prepared using 6
(NOBE), 7 (MVK), and 9 (EDVK) as the cross-linking mono-
mers. For comparison to traditionally formulated imprinted
polymers, another polymer was imprinted using the formula-
tion above, substituting EGDMA as the cross-linking mono-
Su p p or tin g In for m a tion Ava ila ble: Figures showing 1H
NMR and 13C NMR spectra of all synthesized compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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