Anionic surfactant templated chiral nanospheres and their enantioselective adsorption

Article abstract of DOI:10.1039/c3nj00219e

Monodispersed chiral mesoporous spheres of nanometer size with high specific area and good thermal stability were synthesized using the chiral anionic surfactant (N-palmitoyl-l-phenylalanine) as a template according to the co-structure directing agent (CSDA) method. The resulting mesoporous nanospheres were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle X-ray powder diffraction (XRD) and nitrogen sorption experiments. The particle distribution was 190-210 nm with pore diameters of 3-4 nm. The enantioselective ability of this chiral mesoporous silica, after extraction of the chiral surfactant, was investigated by the selective adsorption of enantiomers and racemic solutions of alanine. The chiral selective adsorbability of this material type was shown by the asymmetric preferential adsorption of alanine as observed using circular dichroism (CD) spectroscopy and was further verified in a racemic mixture of valine. It was found that the adsorption of l-alanine was higher than that of d-alanine on as-prepared chiral mesoporous materials with a chiral selectivity factor of 3.15, which generates new possibilities for enantiomeric separation and other enantioselective applications.

Full text of DOI:10.1039/c3nj00219e

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Table of contents entry
Monodipersed chiral mesoporous silica spheres with chiral pores which can be used in
chiral adsorptive separation have been synthesized by self-assembly with an anionic
surfactant as the template.

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Anion surfactant templated chiral nanospheres and their
enantioselective adsorption
Bin Di *a b, Lifei Cheng a, Qiuling Jiang a, Mengxiang Su a, Weiqiang Hao c
Abstract
5
10
15
20
Monodispersed chiral mesoporous spheres of nanometer size and with high specific
area and good thermal stability were synthesized using the chiral anion surfactant
(NꢀpalmitoylꢀLꢀphenylalanine) as a template according to the coꢀstructure directing
agent (CSDA) method. The resulting mesoporous nano spheres were characterized by
scanning electron microscopy (SEM), transmission electron microscopy (TEM), small
angle Xꢀray powder diffraction (XRD) and nitrogen sorption experiments. The
particle distribution was 190 nmꢀ210 nm with pore diameters of 3 nmꢀ4 nm. The
enantioselective ability of this chiral mesoporous silica, after extraction of the chiral
surfactant, was investigated by the selective adsorption of enantiomers and racemic
solutions of alanine. The chiral selective adsorbability of this material type was shown
by the asymmetric preferential adsorption of alanine as observed by circular
dichroism (CD) spectroscopy and was further verified in a racemic mixture of valine.
It was found that the adsorption of Lꢀalanine was higher than that of Dꢀalanine on
asꢀprepared chiral mesoporous materials with a chiral selectivity factor of 3.15, which
generates new possibilities for enantiomeric separation and other enantioselective
applications.

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Introduction
Chirality is highly prevalent in nature, and the design and synthesis of chiral
compounds [1], supramolecular assemblies and functional materials have been
important subjects in scientific research. Chiral mesoporous silica materials have
shown great potential in chiral adsorption, separation and chiral catalysis with their
highly ordered helical structures, high specific surface area and large pore volume and,
as a result, have become important research topics. In 1999, Mark J proposed that
chiral organic functional groups could be doped in the wall and skeleton of silica
materials to improve their chiral molecular recognition ability [2]. As a result, in
recent years, the synthesis of chiral materials containing chiral groups in their
frameworks with chiral silane precursors prepared through coꢀcondensation has
become a major topic in chiral materials. However, it was not until 2006 that a chiral
hybrid mesoporous silica with chiral framework bridging groups was synthesized [3].
This delay was mainly because the synthesis and purification of optically active chiral
silicon sources is difficult. It is difficult to guarantee the synthetic efficiency, and
there is poor reproducibility associated with the syntheses. It was then found that
mesoporous silica with a chiral pore structure could be obtained using chiral or achiral
surfactants as a template [4ꢀ11], and compared to the chiral silicon source, the chiral
and achiral surfactant is simpler to obtain and is relatively inexpensive. This is
particularly true when using an anionic surfactant, as this type of surfactant is always
biodegradable and obtained from sustainable resources and is thus environmentally
friendly and nontoxic [12]. However, there are still some problems associated with
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this type of material. Synthetic procedures for the surfactant are often elaborate and
difficult to duplicate, and polynary surfactants can be required to obtain helical
structured silica, sometimes even requiring other small chiral molecules to induce
chirality and to increase the ee value of the mesoporous silica [13].
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Currently, the major area of research is the development of new materials, and a
variety of chiral mesoporous silica (CMS) have been synthesized with different
anionic chiral surfactants. These materials have been synthesized by adjusting the
reaction temperature, reaction time, stirring speed and other reaction parameters to
produce many types of irregular morphologies, such as helical ribbons [14], helical
tubes [15], and hollow spheres [16]. Although many types of novel materials have
been obtained successfully, very few of them have been applied to practical
applications involving chiral selectivity, and some materials have not shown good
chiral separation performance with helical structures [17].
In this work, monodispersed mesoporous silica spheres with chiral pores were
synthesized using the chiral surfactant C16ꢀLꢀPhe as a single template and
tetraethylorthosilicate (TEOS) as
a
silane precursor along with the
coꢀstructureꢀdirecting agent NꢀtrimethoxysilylpropylꢀN,N,Nꢀtrimethyl ammonium
chloride (TMAPS). Various parameters affecting the morphological and porous
properties of the nanospheres, including the alkali concentration, molar composition
of the reaction system and the reaction temperature, are discussed in detail in the
following sections. Furthermore, the adsorption of chiral compounds with asꢀprepared
CMS was investigated, along with their application in chiral adsorption based on

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systemic synthetic research. The results show that the chirality from the template was
successfully induced on the mesoporous materials.
Experimental
Chemicals
LꢀPhenylalanine was purchased from Sinopharm Chemical Reagent Co., Ltd,
tetraethylorthosilicate (TEOS) was purchased from TCI, Inc. (Japan),
NꢀtrimethoxysilylpropylꢀN,N,Nꢀtrimethyl ammonium chloride (TMAPS, 50% in
methanol) was purchased from Gelest Inc. (Morrisville, USA), and hexadecanoyl
chloride was purchased from Aladdin, Inc. (Shanghai, China). DLꢀValine, Lꢀalanine,
Dꢀalanine and DLꢀalanine were all purchased from Sinopharm Chemical Reagent Co.,
Ltd. Deionized water was purified through a PL5242 Purelab Classic UV (PALL Co.
Ltd., Washington, USA) before use. All other reagents, including acetone, ethyl
acetate, petroleum ether and absolute ethyl alcohol, were of analytical quality and
used as received.
Synthesis of N-palmitoyl-L-phenylalanine(C16-L-Phe)
The chiral surfactant used in this work was an anion surfactant that was obtained by
the reaction of amino acids and hexadecanoyl chloride in a mixed solution of water
and acetone [18]. In our study, the derivative of LꢀPhe was chosen as the single
template due to its large steric hindrance and high enantiopurity, i.e., enantiomeric
excess (ee) [19]. NꢀPalmitoylꢀLꢀphenylalanine (C16ꢀLꢀPhe) was synthesized from
LꢀPhe as shown in Figure 1. LꢀPhe (0.012 mmol) and NaOH (0.024 mmol) were
dissolved and mixed in solution with 20 ml acetone and 30 ml deionized water. The

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mixed solution was kept stirring at 0 ºC~5 ºC. Hexadecanoyl chloride (0.0132 mmol)
was then added dropwise, and the pH of the solution was maintained at or above 12
by adding high concentrations of a sodium hydroxide solution. The dropwise addition
was finished within half an hour, and stirring was continued for another 10 h to ensure
complete reaction. Concentrated hydrochloric acid was then added to guarantee that
the solution pH was reduced to approximately 1. The final product was purified by
extraction in ethyl acetate and washing with ionized water, followed by drying at 50
ºC under vacuum .
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Synthesis of materials
In a typical synthesis, C16ꢀLꢀPhe (0.404 g, 1 mmol) and 1 M NaOH (1.26 ml) were
dissolved in deionized water (30.8 ml) with stirring. When a transparent and clear
solution was obtained, a mixture of TMAPS (0.14 g, 0.54 mmol) and TEOS (1.23 g,
5.9 mmol) was added for 36 h at 30 ºC. The products were recovered by
centrifugation and washed with deionized water and ethanol, followed by drying at 50
ºC. In the end, the template was removed by calcination at 650 ºC for 6 h. The molar
100
composition
ratio
of
the
gel
obtained
was
as
follows:
C16ꢀLꢀPhe/TMAPS/NaOH/TEOS/H2O 1:0.54ꢀ1.08:1.03–1.56:5.9:1781. The samples
were denoted as CMSꢀn (n=1ꢀ6). The detailed molar compositions for the synthesis of
CMSꢀn are listed in Table 1.
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Characterization
Infrared spectra were recorded on a JASCOꢀ4100 Fourier Transform Infrared (FT/IR)
spectrometer (JASCO, Tokyo, Japan). Scanning electron microscopy (SEM) images

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were obtained using a Hitachi Sꢀ3400N II (Hitachi Ltd., Tokyo, Japan) operating at an
accelerating voltage of 20 kV. The samples were deposited onto a sample holder with
an adhesive carbon foil and sputtered with gold prior to imaging. Transmission
electron microscopy (TEM) was performed using a JEOL JEMꢀ200CX (JEOL Ltd.,
Tokyo, Japan) at an accelerating voltage of 120 kV. Xꢀray powder diffraction (XRD)
patterns were recorded on a Thermo ARL X’TRA Xꢀray diffractometer (Thermo
Fisher Scientific, Waltham, USA) using CuKα radiation (λ= 1.54 Å). The nitrogen
sorption experiments were performed at 77 K on an ASAP 2020 analyzer
(Micromeritics Corporate, Norcross, USA). The samples were out gassed at 373 K
and dehydrated under vacuum conditions for 5 h prior to measurement. The
Brunauer–Emmett–Teller (BET) surface areas were calculated from the adsorption
data over a relative pressure range from 0.0 to 1.0. The pore size distributions were
calculated from the adsorption and desorption branches using the
BarrteꢀJoyerꢀHalenda (BJH) model.
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Chiral adsorption measurements were performed with a JASCO Jꢀ810 circular
dichroism spectra system (JASCO, Tokyo, Japan) using a cylindrical quartz cell (0.5
ml) at room temperature. Most of the racemic amino acids were used as received to
prepare solutions in distilled water or methanol. Each adsorption was repeated in
triplicate.
Results and discussion
A typical FTꢀIR spectrum of the CMSꢀ3 material is presented in Figure 2a. Figure 2b
shows the difference between materials before calcination and after calcination, and

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the bands at 3400 cm−1, 1100 cm−1 are ascribed to the vibrational peaks of the SiꢀOꢀSi
in the framework. The presence of peaks at 2923 cm−1 and 2852 cm−1 in Figure 2b are
evidence of C16ꢀLꢀPhe, and from the two FTꢀIR spectra, it can be observed that the
surfactant was removed successfully by calcination.
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A TEM image of CMSꢀ3 (Figure 3a) clearly shows the existence of a wormꢀlike
pore structure throughout the nanoparticles. This result is consistent with that obtained
from XRD, which shows a weak diffraction peak (Figure 3b). The nitrogen sorption
isotherm of CMSꢀ3 (Figure 3c) is of type IV with a hysteresis loop, suggesting that
the material has a mesoporous structure. The pore diameters are in the range of 3–4
nm. The pore volume is calculated to be 0.75 cm3g−1 (Figure 3d). The other physical
parameters are listed in Table 2. The BET specific surface area was calculated to be
600 m2/g and demonstrates that the synthesized material has a high specific surface
area. A SEM image of typical spheres of CMSꢀ3 (Figure 3e) shows the partical size is
about 200nm.
Compared with conventional mesoporous silica, the formation of CMS is
extremely sensitive to the synthetic conditions, such as the reaction basicity. During
the synthesis of CMS, the mesoporous organosilicas were synthesized with different
molar percentages of NaOH/C16ꢀLꢀPhe. When the molar percentage was 1.03 or 1.15,
the reaction solution became turbid in less than 10 min upon addition of the silicane
precursors. When the molar percentage was increased to 1.26, the turbid solution
occurred 20 min after the silicane precursors were added. When the percentage was
further moderately increased, it took more time for a turbid solution to appear.

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However, when the molar percentage reached 1.56, the solution remained clear after
stirring for 12 h, implying that CMSꢀ5 could not be obtained. These results indicate
that the polymerization rate was reduced with higher concentrations of NaOH. The
reaction alkalinity was also important to the morphological control, as shown in
Figure 4 (SEM). Spheres of CMSꢀ1 were gathering together with poor dispersibility
(Figure 4a), CMSꢀ2 appeared as ellipsoids with a large range of particle sizes, from
approximately 195 nmꢀ300 nm (Figure 4b). As the alkalinity continued to increase,
CMSꢀ3 became more spherical, and its particle diameter was within 190 nmꢀ210 nm
(Figure 4c). However, when the alkalinity was further increased, CMSꢀ4 began to
exhibit rough surfaces (Figure 4d).
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160
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170
From the experiments and characterization discussed above, it can be concluded
that the reaction alkalinity played an important role in both the reaction rate and the
morphological control. The BET surface area and pore volume were also influenced
by the concentration of NaOH, as inferred from the results of N2
adsorption–desorption isotherms and the corresponding DFT pore size distributions
examined for the calcinated mesoporous materials, as shown in Table 2. As can be
observed from the table, when the molar percentage of NaOH/C16ꢀLꢀPhe was 1.15 or
1.26, there was little difference in the surface area and the diameter distribution
between the final materials, but when the percentage of NaOH/C16ꢀLꢀPhe was
increased to 1.36, the BET surface area decreased, while the range in diameter
distribution increased.
In summary, the selection of reaction alkalinity was very significant due to its

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ability to affect the morphological control and pore structure adjustments. The final
molar percentage of NaOH/C16ꢀLꢀPhe was chosen to be 1.26.
The material morphology can be affected by the reaction temperature. In this
experiment, three different temperatures, 20 ºC, 30 ºC and 50ºC, were studied. At 20
ºC, a turbid solution emerged once the silicane precursors were added, owing to the
incomplete dissolution of surfactant. When the temperature was stepped up to 30 ºC,
the resulting material showed spherical particles with relatively smooth surfaces and
uniform sizes (Figure 4c). At 50 ºC, some irregularꢀshaped solids were synthesized
(Figure 4e). From these results, it can be concluded that at 50 ºC, the conformation of
the surfactant could have been changed, and according to the Che group [20], during
the synthesis of chiral mesoporous silica, temperature is an important condition, as
increasing the reaction temperature accelerates molecular motion, and the chiral
surfactant micelle can become less rigid. It is known that the packing of the organic
surfactant affects the formation of ordered mesostructures [16]. After the above
considerations, 30 ºC was chosen as the final reaction temperature.
A coꢀstructure directing agent (CSDA) interacts with both the organic and
inorganic components in the reaction system [21]. There was an intensive electrostatic
interaction between the chiral surfactant (C16ꢀLꢀPhe) and TMAPS that directed the
chiral micelle arrangement in the channel. Therefore, several molar ratios of TMAPS/
C16ꢀLꢀPhe were investigated to elucidate its effect on morphology. When the molar
ratio of TMAPS/C16ꢀLꢀPhe was 0.54, spherical nanoparticles of CMSꢀ3 with uniform
size were obtained (Figure 4c). After doubling the molar ratio to 1.08, irregular bulky

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solids of CMSꢀ6 with rough surfaces were obtained (Figure 4f). This result shows that
the arrangement of C16ꢀLꢀPhe can be interrupted by the excessively strong
interactions between the coꢀstructureꢀdirecting agent (TMAPS) and the chiral
surfactant (C16ꢀLꢀPhe).
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Circular dichromism (CD) spectroscopy was selected as the method to explore
the chiral recognition of the chiral silica on account of its simplicity, convenience and
inexpensiveness. In this work, we performed selective chiral adsorption
measurements of enantiomers and racemic solutions. The chiral adsorption ability can
be evaluated through these measurements.
For adsorption measurements, 40 mg racemic alanine was weighed and dissolved
in deionized water, after which 120 mg CMSn (n=1ꢀ4) was added. After stirring at
room temperature for 24 h, the optical activity was probed, as shown in Figure 5. The
results demonstrate that templated cavities were successfully formed in our chiral
silica. In other words, the chirality of the primary superstructure of the helical micelle
was memorized and immobilized on the surface of each mesopore such that our
material was able to recognize the chirality [20]. We can see in Figure 5 that with
increased alkalinity, the chiral adsorption capacity of our material increased, but once
the molar ratio of NaOH reached 1.36, the adsorption ability of the material decreased
significantly. This result shows that the chiral transfer of the template may be
influenced by the reaction alkalinity. From this image, we can also see that a stronger
adsorptive capacity was available on CMSꢀ3 relative to CMSꢀ2 but with a smaller
specific surface area, implying that the chiral adsorption capacity is not only related to

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the specific surface area of the material but is also concerned with the volume of the
chiral templated cavity.
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The adsorption dynamics curve of the alanine enantiomers is shown in Figure 6.
This curve shows that the amount of adsorbed Lꢀalanine and Dꢀalanine both increase
rapidly after 2 h, and from 4 h to 16 h, the rate of adsorption gradually decreases until
reaching a maximum value at 16 h, after which, the system reaches equilibrium with
equal rates of adsorption and desorption. This result demonstrates the stronger
adsorption capacity for Lꢀalanine relative to Dꢀalanine. An equilibrium adsorption
ratio of 3.15 was calculated based on the equilibrium amount for the L and D
enantiomers. This chiral selectivity value is reasonable and adequate for enantiomeric
separation [22].
It can be assumed from the adsorption kinetics study of the alanine enantiomers
that the Lꢀchiral template was successfully copied in the cavity of our nanomaterials,
and at the same time, the adsorbability of Dꢀalanine was also shown in our experiment.
Some conjectures can be made regarding the recognition of Dꢀalanine. First, hydrogen
bonding exists between the bulky silanols in the materials and the amino acid
molecules. Second, besides the Lꢀchiral cavity, some Dꢀchiral and achiral binding
sites could be imprinted in the spheres, and this pore structure might arise from the
opposite helical arrangement of the Lꢀchiral template or via nonꢀhelical arrangement.
In addition, the formation of nonchiral sites can result from an incomplete silica
monomer chiral template association [23].
The CD spectra of the alanine and valine enantiomers are shown in Figure 7. As

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observed from the results, the CD bands of alanine and valine are similar. The results
also demonstrate that they share the same adsorption kinetics and that CMSꢀ3 has a
good chiral identification capacity for small molecules of amino acids. However, the
kinetic processes of chiral recognition of CMSꢀ3 are a bit slow as the system reaches
equilibrium, or equal rates of adsorption and desorption, after 16 h. Generally, rapid
chiral resolution kinetics are essential for specific recognition. Further studies are
currently underway to enhance the adsorption rate, which should improve the
performance of our material for its use in chiral separation techniques.
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260
As described above, CMS has been synthesized using chiral
NꢀpalmitoylꢀLꢀphenylalanine as a template under alkaline conditions at a relatively
low temperature based on the CSDA method. The ammonium group of the CSDA
agent, NꢀtrimethoxysilylpropylꢀN,N,Nꢀtrimethylammonium chloride (TMAPS),
electrostatically interacts with the anionic head groups of the chiral amphiphiles, and
at the same time, the alkoxysilane sites of TMAPS are polymerized with TEOS to
form the silica framework.
Supramolecular selfꢀassembly is the autonomous organization of components into
patterns or structures without human intervention [24], and through this process, the
chirality of the templates can be copied to the inorganic materials. Both graphoepitaxy
and weak directional noncovalent interactions are the driving forces for the formation
of the chiral supramolecular aggregates, especially the intermolecular noncovalent
interactions that include electrostatic interactions, hydrogen bonding and hydrophobic
interactions [25]. The final mesostructures of CMS are determined by the surfactant

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lyotropic liquid crystal phases, which can be described by the surfactant packing
parameter, g=v/a0l, where v is the total chain volume of the surfactant chains, a0 is the
effective head group area at the micelle surface, and l is the kinetic surfactant chain
length. g has been shown to be sensitive to the selfꢀassembled unit structure, and the
selfꢀassembled conditions have likewise been shown to be affected by the surfactant
concentration, the pH of the solution and the reaction temperature [26,27].
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From the above theory, we know that the parameter, g, can be influenced by
changes in the reaction process. The supramolecular aggregates were formed after
CSDA was added with structural changes, so the time when the TEOS was added
might be important for the final mesostructure. In our previous work, wormholeꢀlike
mesostructures were shown via SEM and XRD of CMSꢀ3, and the existence of the
less ordered mesopore structure demonstrated that the mesostructural changes
occurred during the period prior to the addition of TEOS. By adjusting the time of
TEOS addition, the mesoporous structure may be controlled, and therefore, the chiral
adsorptive ability of our CMS could be improved. Some CSDA functional groups
would be immobilized on the channel wall of CMS by soft extraction, and in the
future, CMS with helical mesopores, molecularly imprinted chirality and CSDA
functional groups will be synthesized with optimization of the reaction conditions.
Conclusions
Monodipersed chiral mesoporous silica spheres with chiral pores have been
synthesized by selfꢀassembly with an anionic surfactant as the template. We studied
the conditions influencing the spherical morphology and mesoporous structure of our

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material. The results revealed that the reaction alkalinity, temperature and the molar
ratio of TMAPS to the chiral template are all important in the formation of the chiral
nanospheres. We also demonstrated their enantioselective properties in the resolution
of racemic solutions by CD spectroscopy and studied the chiral adsorption capacity of
single enantiomers and racemic solutions. These chiral mesoporous silica spheres can
be used in chiral adsorptive separation.
At present, the application study of a chiral mesoporous material (CMSꢀ3) in
chiral adsorptive separation is still in its initial stages. According to these results,
many ways to improve these materials exist; likewise, the synthetic processing can be
optimized to increase the chiral pore volume such that the chiral recognition ability
can be improved. Similarly, we can accelerate the chiral adsorption kinetics by
broadening the pore size or including some organic functional groups that are able to
add to the framework of our materials and enhance their interactions with chiral
molecules and materials. More applications will be determined as we continue to
derivatize and modify the surfaces with different functional groups.
Acknowledgments
This work was financially supported by the National Natural Science Foundation of
China (81173022). We thank Professor Shunai Che for her invaluable assistance with
chemical reagents and advice.

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305 Notes and References
a Department of Pharmaceutical Analysis, China Pharmaceutical University, Nanjing
210009, China
b Key Laboratory of Drug Quality Control and Pharmacovigilance, China
Pharmaceutical University, Ministry of Education, Nanjing 210009, China
c High-Tech Research Institute of Nanjing University, Changzhou 213164, China
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315
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Figure captions
Figure 1. Synthesis of NꢀpalmitoylꢀLꢀphenylalanine (C16ꢀLꢀPhe)
Figure 2. (a) FTꢀIR spectra of CMSꢀ3
360
365
370
375
(b) FTꢀIR spectra of CMSꢀ3 (a) before calcination, (b) after calcination
Figure 3. (a) Transmission Electron Microscopy (TEM) of CMSꢀ3
(b) Xꢀray powder diffraction (XRD) patterns of CMSꢀ3
(c) Nitrogen adsorption–desorption isotherm of CMSꢀ3
(d) Pore size distribution of CMSꢀ3
(e) Scanning Electron Microscopy (SEM) of typical spheres of CMSꢀ3
Figure 4. SEM images of the extracted CMSn synthesized under different conditions
(a) CMSꢀ1 (b) CMSꢀ2 (c) CMSꢀ3 (d) CMSꢀ4 (e) CMSꢀ50°C
(f) CMSꢀ6
Figure 5. CD spectrum of a DLꢀalanine solution with CMSn (n=1ꢀ4)
(A) Blank, (B) CMSꢀ1, (C) CMSꢀ2, (D) CMSꢀ3, (E) CMSꢀ4
Figure 6. Curve of the adsorption dynamics from a solution of alanine enantiomers
onto CMSꢀ3
Figure 7. CD spectrum of a racemic amino acid solution with chiral silica as a
function of time: (a) DLꢀAlanine, (b) DLꢀValine

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Table 1.
Molar ratios for the synthesis of CMSꢀn (n=1ꢀ6)
Sample
CMSꢀ1
CMSꢀ2
CMSꢀ3
CMSꢀ4
CMSꢀ5
CMSꢀ6
C16ꢀLꢀPhe
NaOH
1.03
1.15
1.26
1.36
1.56
1.26
TMAPS
0.54
TEOS
5.9
H2O
1781
1781
1781
1781
1781
1781
1
1
1
1
1
1
0.54
5.9
0.54
5.9
0.54
5.9
0.54
5.9
1.08
5.9

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Table 2.
Physicochemical parameters of CMSꢀ2, CMSꢀ3 and CMSꢀ4
Sample
SBET
(m2/g)
644
Pore volume
(cm3/g)
0.84
Pore size
(nm)
CMSꢀ2
CMSꢀ3
CMSꢀ4
3ꢀ5
600
0.75
3ꢀ4
492
0.98
3ꢀ5,10ꢀ25

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Synthesis of N-palmitoyl-L-phenylalanine (C16-L-Phe)
68x27mm (300 x 300 DPI)

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(a) FT-IR spectra of CMS-3
(b) FT-IR spectra of CMS-3 (a) before calcination, (b) after calcination
99x120mm (300 x 300 DPI)

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(a) Transmission Electron Microscopy (TEM) of CMS-3
(b) X-ray powder diffraction (XRD) patterns of CMS-3
(c) Nitrogen adsorption–desorption isotherm of CMS-3
(d) Pore size distribution of CMS-3
(e) Scanning Electron Microscopy (SEM) of typical spheres of CMS-3
85x87mm (300 x 300 DPI)

Page 25 of 28
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SEM images of the extracted CMSn synthesized under different conditions
(a) CMS-1 (b) CMS-2 (c) CMS-3 (d) CMS-4 (e) CMS-50°C
(f) CMS-6
94x107mm (300 x 300 DPI)

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CD spectrum of a DL-alanine solution with CMSn (n=1-4)
(A) Blank, (B) CMS-1, (C) CMS-2, (D) CMS-3, (E) CMS-4
58x40mm (300 x 300 DPI)

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Curve of the adsorption dynamics from a solution of alanine enantiomers
onto CMS-3
58x40mm (300 x 300 DPI)

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CD spectrum of a racemic amino acid solution with chiral silica as a
function of time: (a) DL-Alanine, (b) DL-Valine
134x216mm (300 x 300 DPI)