Biomimetic Polymers for Chiral Resolution and Antifreeze Applications
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The chiral recognition ability of the obtained silica was examined by the selective adsorption
of enantiomers from racemic solutions of D, L-valine. In these experiments, the chiral silica
showed chiral recognition toward D-valine enantiomers, compatible to the chirality
imprinted on the silica walls. The chiral recognition reached its maximum value after 16
hours and a chiral selectivity factor of 2.34 was calculated. Following our report on chiral
imprinting of silica by chiral DHBCs, Paik et al 114-115 described the synthesis of chiral silica
with chiral DHBCs in a series of papers. In their first paper, the authors described the
synthesis of chiral mesoporous silica (CMS) spheres. The chiral mesoporous silica particles
were prepared with the use of a chiral DHBC template of poly(ethylene oxide) block with a
D\L-glutamic acid, [PEO 113 - b-(GluA) 10 ] block [Figure 4.3]. The chiral template was extracted
from the CMSs, leaving a chiral print on the silica walls. These particles exhibit a 2-3 nm
pore size and a high surface area of 614 m^2 \g [Figure 4.3], and also show enantioselectivity
towards valine enantiomers, corresponding to the chirality imprinted on the silica support
(selectivity factor of 5.22 was calculated). In a sequential paper, Paik et al reported on the
preparation of CMSs templated with DHBC of a poly(ethylene oxide)block with a D\L-
aspartic acid block, [PEO 45 - b-(D/L-AspA 10 )]. These particles were subjected to D, L-valine
and D, L-alanine solutions, and show high affinity toward one enantiomer corresponding to
the chirality imprinted on the silica support. The selectivity factor was found to be
remarkably high, 7.52.
Fig. 4.3. Synthesis of the Block Copolymer of Poly(ethylene oxide)-L-glutamic Acid [PEO 113 -
b-(L-GluA)n],where n =10. HRTEM images: (a) low magnification (b) high magnification of
CMS spheres (Ex-SiO 2 ) synthesized by templating with PEG 113 - b-(L-GluA) 10.
In a further paper, Paik et al.^116 demonstrated the feasibility of templating nanopolymeric
particles by chiral DHBCs. In their report, chiral-mesoporous-polypyrrole (CMPPy)
nanoparticles were synthesized by use of two DHBC templates based on poly(ethylene
oxide) block with a L/D- glutamic acid block, [PEO 113 - b-(L/D GluA) 10 ] and poly(ethylene
oxide)block with a L/D phenylalanine block, [PEO 113 - b-(L-/D-Phe) 10 ]. The synthesis of
mesoporous polypyrrole nanoparticles was previously described by Fan et al.^117 The
synthesis of chiral polypyrrole was carried out through a minor modification of Fan’s
polymerization procedure. In general, pyrrole monomers were added to a chiral DHBC
ab