Enantiomer separation of propranolol and tryptophan using bovine serum albumin functionalized silica nanoparticles as adsorbents

Article abstract of DOI:10.1039/c5ra17535f

The immobilization of popular chiral selectors on the surface of nanomaterials to prepare new chiral adsorbents for preparative chiral separation is a research hotspot in separation science nowadays. In this study, bovine serum albumin (BSA) modified silica nanoparticles were prepared by using polydopamine (PDA) as a versatile multifunctional secondary reaction platform. The preparation method was facile, cost-effective and environmentally friendly. The new chiral adsorbents were then investigated for the separation of representative chiral drug enantiomers. For propranolol and tryptophan, the multi-step adsorption enhanced the chiral performance to a great degree. On increasing the starting percent enantiomeric excess (%, e.e.) of the enantiomeric mixtures, the %, e.e. value of the resulting solution increased to almost 100% under the same operating conditions. For simplicity and rapidness, the results of adsorption were measured by capillary electrophoresis (CE) using carboxymethyl-β-cyclodextrin (CM-β-CD) or α-cyclodextrin (α-CD) as additives into the background electrolyte solution. The experimental results also showed that the thus-prepared nanomaterials could be readily recycled at least three times, demonstrating their great stability and possibility in practical use.

Full text of DOI:10.1039/c5ra17535f

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Enantiomer separation of propranolol and
tryptophan using bovine serum albumin
Cite this: RSC Adv., 2015, 5, 93850
functionalized silica nanoparticles as adsorbents†
a
Wei Li,a Guo-Sheng Dingbc and An-Na Tang
*
The immobilization of popular chiral selectors on the surface of nanomaterials to prepare new chiral
adsorbents for preparative chiral separation is a research hotspot in separation science nowadays. In this
study, bovine serum albumin (BSA) modified silica nanoparticles were prepared by using polydopamine
(PDA) as a versatile multifunctional secondary reaction platform. The preparation method was facile,
cost-effective and environmentally friendly. The new chiral adsorbents were then investigated for the
separation of representative chiral drug enantiomers. For propranolol and tryptophan, the multi-step
adsorption enhanced the chiral performance to a great degree. On increasing the starting percent
enantiomeric excess (%, e.e.) of the enantiomeric mixtures, the %, e.e. value of the resulting solution
increased to almost 100% under the same operating conditions. For simplicity and rapidness, the results
of adsorption were measured by capillary electrophoresis (CE) using carboxymethyl-b-cyclodextrin (CM-
b-CD) or a-cyclodextrin (a-CD) as additives into the background electrolyte solution. The experimental
results also showed that the thus-prepared nanomaterials could be readily recycled at least three times,
demonstrating their great stability and possibility in practical use.
Received 29th August 2015
Accepted 26th October 2015
DOI: 10.1039/c5ra17535f
www.rsc.org/advances
when used as the adsorbent materials.9 In comparison with
other NPs, such as polymer-based and metal NPs, silica-based
1. Introduction
NPs (SiNPs) own many advantages such as regular shapes,
uniform sizes, good biocompatibility, no swelling in aqueous
and organic solvents, and easy post-modication with different
functional groups, etc.10
Chirality is a widespread phenomenon in nature and organ-
isms.1 The separation of chiral components to pure enantio-
mers is of great importance to pharmaceutical, food,
toxicological and clinical analysis. In general, a single pure
isomer is the active component of one drug and the other
isomer may be inactive, or even have dramatic, negative side
effects.2 Many methods including HPLC,3 CE,4 membrane-
based separation,5 preferential crystallization6 and asymmetric
synthesis7 have been applied to separate, identify, and quantify
chiral compounds. However, these methods are generally costly
and time-consuming, especially when used for preparative
purpose.
Nanoparticles (NPs) are referred to the particles that the size
between 1 and 100 nm, which have gained signicant interest
and been applied in various areas such as physics, chemistry,
material science, biology, etc. in recent years.8 NPs hold great
promise for their small size, large surface area and pore volume
A large number of chiral selectors are currently available,
among which cyclodextrins (CDs), proteins, chiral crown ethers,
chiral surfactants, ligand-exchange complexes and linear poly-
saccharides are most popular.11–20 Nowadays, the hyphenation
of classical chiral selectors with NPs to prepare new nano-
materials for chiral separation is intriguing, and has attracted
much attention.21 Ghosh and coworkers, for example, synthe-
sized magnetic silica nanoparticles, which were graed with
carboxymethyl-b-cyclodextrin (CM-b-CD) via carbodiimide acti-
vation. The adsorption behavior of certain chiral aromatic
amino acid enantiomers on this material was then detailedly
investigated.22 Similarly, Wu et al. fabricated and characterized
teicoplanin-conjugated mesoporous silica magnetic nano-
particles (TE-MSMNPs) as novel chiral magnetic nano-selectors.
It was experimentally shown that they were effective in the
direct chiral separation of ve racemic compounds in phos-
phate buffer.23 Although these materials are successful to some
extents for chiral separation, multistep reactions and higher
temperature were usually necessary in their preparation
processes, which would inevitably result in rising costs and
lowered batch to batch reproducibility. As a widely used chiral
selector, BSA is known to be able to bind some drugs
aResearch Center for Analytical Sciences, College of Chemistry, Collaborative
Innovation Center of Chemical Science and Engineering, Nankai University, 94
Weijin Road, Tianjin 300071, P. R. China. E-mail: tanganna@nankai.edu.cn
bTianjin Key Laboratory for Modern Drug Delivery & High-Efficiency, School of
Pharmaceutical Science and Technology, Tianjin University, 92 Weijin Road, Tianjin
300072, P. R. China
cAnalysis center, Tianjin University, 92 Weijin Road, Tianjin 300072, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra17535f
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enantioselectively, due to its specic three-dimensional struc- Dopamine hydrochloride (DA) (99%) was obtained from Tianjin
ture.24–26 Recently, Fu et al.27 reported the immobilization of BSA Heowns Biochem LLC (Tianjin, China). Bovine serum albumin
on the magnetic Fe3O4 nanoparticles through electrostatic (BSA, MW 68 000) was purchased from Solarbio Life Science
ꢀ
adsorption interaction. Although they had proved to be useful (Beijing, China) and stored at 4 C. Carboxymethyl-b-cyclodex-
for the separation of chiral drug enantiomers, the new materials trin (CM-b-CD, >98%, molecular weight z 1551, degree of
are susceptive to recycle use due to the instable electrostatic substitution
z 7.05) was purchased from Zhiyuan Bio-
interactions between BSA and NPs. So, the design and facile Technology Co., Ltd. (Binzhou, China). a-Cyclodextrin (a-CD)
preparation of NPs-based chiral materials with good stability is was purchased from Aladdin Industrial Corporation (Shanghai,
still a highly desirable concern.
China). L-Tryptophan (L-Trp, >98%), D-tryptophan (D-Trp, >98%)
Since its emergence in 2007, polydopamine (PDA) has were purchased from TCI (Shanghai) Development Co., Ltd.
attracted much attention because it can be used as a versatile (Shanghai, China). Propranolol tablets were purchased from
coating material on the surface of nearly all kinds of materials Tianjin Lisheng Pharmaceutical Co., Ltd. (Tianjin, China). The
(inorganic or organic).28 PDA can also be used to create a variety purity is 10 mg per tablet. Stock solution of propranolol was
of ad-layers (additional layer) for secondary reactions through extracted from tablets with methanol. The concentration of
Michael addition or Schiff base reactions.29–31 For example, Cao stock solution was 5.8 mg mLꢁ1. Stock solutions were stored in
ꢀ
and coworkers prepared efficient oil/water separation mesh the dark at 4 C.
lms by conjugating N-dodecyl mercaptan (NDM) with PDA
lm. The as-prepared PDA–NDM mesh was highly hydrophobic
and superoleophilic, which could be used effectively for a large
2.2 Apparatus
amount of oil/water separation.32 Iqbal et al. synthesized PDA- TEM were carried out on a Philips Tecnai G20 at 200 kV (PHG,
coated magnetic nanoparticles and polymethacrylic acid-co- Amsterdam, Netherlands). The samples were prepared by
ethylene glycol dimethacrylate submicron particles, then dipping micro grid membrane coated copper grids (300-mesh)
investigated their fast binding kinetics with environmentally into the dispersion of NPs in ethanol. Elemental analysis was
hazardous compounds such as bisphenol A.33
performed by elemental analyzer (vario EL CUBE, Germany) and
The objective of this work is to develop a facile and mild way the zeta potential of the functionalized silica NPs were deter-
for the stable immobilization of chiral selectors on the surface mined with Zetasizer Nano ZS equipments (Malvern Instru-
of nanomaterials, and to realize their repeated use for prepar- ments, Worcestershire, UK). All CE experiments were carried
ative chiral separation. In the present stage, BSA was used as out on a TH-3000 HPCE-HPLC amphibious system equipped
a model chiral selector. Through utilizing PDA coating as with a UV detector and CXTH-3000 data handling soware
a versatile multifunctional secondary reaction platform, the (Tianhui Instruments, Baoding, China). A QL-901 vortex (Hai-
new enantioselective materials of BSA functionalized SiNPs men Kylin-Bell Lab Instruments Co., Jiangsu, China) were used
using PDA coating as a versatile multifunctional secondary to disperse NPs in sample solutions. A TG16-WS centrifuge
reaction platform (SiO2@PDA@BSA) NPs were successfully (Hunan Xiangyi Lab Instruments Co., Changsha, China) was
prepared and used to produce optically pure drug enantiomers. used to centrifuge the samples. The optical rotation of samples
For simplicity and rapidness, the results of adsorption were before and aer adsorption process were estimated on an
measured by capillary electrophoresis (CE) using CM-b-CD or autopol II automatic polarimeter (Rudolph Research Analytical,
a-CD as additives into the background electrolyte solution.34,35 USA) with a 10 cm sample tube under a sodium lamp (l ¼ 589
One-step or multi-step operations using the new adsorbents nm). Fused-silica capillaries of 375 mm o.d. and 75 mm i.d., 50
were optimized to obtain high %, e.e. As increasing the mm i.d. (Yongnian Optic Fiber Co, Hebei, China) were used
adsorption times and the starting %, e.e. of enantiomeric throughout the experiment.
mixtures, the nal %, e.e. value of the resulting solution was up
A capillary with the total length of 38 cm and the effective
to nearly 100%, demonstrating the validity of the new materials length of 28 cm was made by scraping off 3–5 mm of the poly-
in preparative enantioseparation.
mer outside the capillary at an appropriate place. Prior to the
rst use, the capillary was successively rinsed by methanol,
DDW, 1 mol Lꢁ1 NaOH, DDW, 1 mol Lꢁ1 HCl, DDW and
phosphate buffer solution (PBS) for 20 min each.
2. Experimental
2.1 Reagents and chemicals
All chemicals were analytical grade unless noted otherwise.
Double-distilled water (DDW) puried by a Nanopure II system
(Barnstead, USA) was used throughout the experiment. Tetrae-
2.3 Synthesis of the functionalized SiNPs
2.3.1 Preparation of SiNPs. SiNPs were prepared by the
thoxysilane (TEOS) (98%) was purchased from Guotai-Huarong modied Stober method.36 Briey, solution consisting of 2.0 mL
New Chemical Materials (Zhangjiagang, China). Ammonia TEOS (ꢂ9 mmol) in 50 mL of ethanol was rstly prepared. To
¨
ꢀ
(25, wt%), methanol ethanol, acetonitrile, thiourea were this solution at 40 C, a mixture of NH4OH (2.0 mL) and DDW
purchased from Tianda Kewei (Tianjin, China). Phosphoric acid (1.4 mL) was added dropwise with vigorous stirring. Aer 18 h of
(85%),
tris(hydroxymethyl)
aminomethane,
potassium reaction, the particles thus formed were centrifuged and
hydroxide, potassium dihydrogen phosphate and hydrochloric washed with ethanol and DDW repeatedly, and then vacuum-
ꢀ
acid were from Tianjin Guangfu Chemicals (Tianjin, China). dried at 70 C for 3 h.
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tris buffer. The resulting PDA coatings are much more homo-
geneous and more likely to be coated on the surface of SiNPs
2.3.2 Synthesis of PDA coated SiNPs (SiO2@PDA). The
prepared SiNPs (ꢂ0.5 g) were added to a conical ask in the
presence of 36 mL of 10 mM tris–HCl buffer solution (pH 8.5) by
slow stirring at ambient temperature. Then 80.0 mg of DA dis-
solved into 4 mL 90% ethanol was slowly dropped into the
above solution. Aer 3 h of reaction, the particles thus formed
were centrifuged and washed with tris–HCl buffer solution,
DDW and ethanol for several times to remove the physically
attached DA and residual unattached DA, and then vacuum-
instead of forming
a sheet precipitate of PDA self-
polymerization. The reason is that adding organic solvents
may slow down the speed of DA polymerization, so that PDA
could be better coated on the surface of SiNPs.
The pH of buffer solution is an important factor on the
synthetic progress of NPs. The obtained SiO2@PDA@BSA NPs
from different pH (7.00, 7.17 and 7.40) were used for multi-step
adsorption of propranolol (three times), respectively. The
supernatants for each step were saved and used as the feed
solution for the next step. The results are as shown in Fig. 1.
From this gure, we can see that the NPs synthesized in pH 7.17
showed the best results. Optimum synthetic condition of pH
7.17 is so selected for the further work.
3.1.2 Characterization of functionalized SiNPs. TEM
images of three kinds of NPs (SiNPs, SiO2@PDA NPs, SiO2@-
PDA@BSA NPs) are shown in Fig. 2. It can be observed that
these nanoparticles are sphere-like and uniform in shape with
the size of approximately 150 nm, although having different
functional groups on the surfaces.
ꢀ
dried at 70 C for 3 h.
2.3.3 Synthesis of BSA functionalized SiNPs (SiO2@-
PDA@BSA). BSA was graed onto the PDA-coated SiNPs
surfaces via Michael addition or Schiff base reactions.37 Briey,
0.4 g SiO2@PDA nanoparticles and 5 mg mLꢁ1 BSA were added
to a conical ask in the presence of 40 mL of 20 mM phosphate
buffer solution with different pH (7, 7.17 and 7.4) by slow stir-
ꢀ
ring at 35 C for 24 h. The obtained nanoparticles were centri-
fuged and washed with PBS and DDW for several times to
remove the unbound residues, and then freeze-dried for 24 h
ꢀ
and stored at 4 C.
The results of elementary analysis of pure silica NPs and two
functionalized silica NPs are summarized in Table 1. In
comparison with pure silica NPs, the contents of three elements
(C, H, N) in SiO2@PDA NPs and SiO2@PDA@BSA NPs are all
increased, indicating that amino and alkyl groups have been
successfully bonded onto silica NPs during the synthesis
process. There is a little S element in BSA, from the content of S
in SiO2@PDA@BSA NPs, it is easy to see that BSA were
successfully modied on the silica NPs.
The measurement of the zeta potential of the aqueous
suspension of NPs is an indirect but useful way to conrm the
existence of functional groups on the surface of NPs. Zeta
potential of the aqueous suspensions of NPs can be affected by
a number of factors including pH, ion concentration and
2.4 Direct enantiomer separation of chiral compounds by
SiO2@PDA@BSA
Direct enantiomer separations of propranolol and tryptophan
were carried out by using SiO2@PDA@BSA NPs as the enan-
tioselective adsorbents. For one-step operation, a certain
amount of SiO2@PDA@BSA NPs were mixed with propranolol
(or tryptophan solution) in PBS buffer. The mixture was ultra-
sonicated and vortexed for 5 min each, and then centrifuged
(10 000 rpm) for 10 min, the supernatant solution thus obtained
was analyzed by chiral CE using CM-b-CD (for propranolol) and
a-CD (for tryptophan) as chiral additives. For the multi-step
operation, SiO2@PDA@BSA NPs were used in batches, and
the supernatants for each step were saved and used as the feed
solution for the next step. The nal solution was collected in
a sample tube for subsequent CE analysis. The results of
adsorption could be expressed by enantiomeric excess (%, e.e.),
½Rꢃ ꢁ ½Sꢃ
%; e:e: ¼
ꢄ 100%
½Rꢃ þ ½Sꢃ
where %, e.e. refers to enantiomeric excess, [R], [S] is the
concentration of R-enantiomer and S-enantiomer, respec-
tively.27 Since chiral CE is used for the analysis, peak areas can
be directly used to calculate %, e.e. instead of concentration.
3. Results and discussion
3.1 Synthesis of BSA functionalized nanoparticles
3.1.1 Optimization of synthesis conditions. In this study,
we used a new way to synthesize SiO2@PDA NPs. The conven-
tional method is simple immersion of substrates in a dilute
aqueous solution of DA, and then buffered to a pH typical of
marine environments (2 mg of DA per milliliter of 10 mM tris–
HCl, pH 8.5), resulting in spontaneous deposition of a thin
adherent polymer lm.28 By contrast, in our method the DA was
Fig. 1 The effect of buffer solution pH on synthesis SiO2@PDA@BSA
NPs. (I) pH 7 (II) pH 7.17 (III) pH 7.4. The other synthesis conditions are
mentioned in Section 2.3.2. CE conditions: 30 mmol Lꢁ1 phosphate
background electrolyte (pH 6.0) containing 1.2 mmol Lꢁ1 CM-b-CD,
5% (v : v) acetonitrile. Detection wavelength, 214 nm; 75 mm i.d.;
rstly dissolved into 90% ethanol, then it is slowly dropped into injection, 6 kV ꢄ 3 s for propranolol; separated voltage, +6 kV.
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Fig. 2 TEM images of SiO2 NPs (A and B), SiO2@PDA NPs (C and D) and SiO2@PDA@BSA NPs (E and F).
charges of ions. Fig. S1† shows the curves of the zeta potential
vs. pH. In the pH range of 2.0–8.0, SiO2@PDA@BSA NPs have
more positive zeta potentials than those of pure SiO2 NPs and
SiO2@PDA NPs. The positive surface charge provided by amino
group also results in a shi of the isoelectric point (IEP).
3.2.2 Effect of adsorption time and mode. The effect of
adsorption time on the enantioseparation efficiency for
propranolol was studied from 5 to 25 min. As shown in Fig. S3,†
results indicated that enantioseparation efficiency increased
when the adsorption time increased from 5 to 10 min. However,
when time was longer than 10 min, the enantioseparation effi-
ciency decreased slightly. Aer 25 min adsorption, enantiose-
paration efficiency increased slightly again. It seems that the
analytes bind strongly with the sorbent and the distribution
equilibrium was easy to achieve in 10 min. However, the ana-
lytes could not be pulled down easily from the sorbent by
desorption solvent with the further increase in adsorption time.
Therefore, the adsorption time was selected as 10 min.
3.2 Optimization of direct enantiomer separation of chiral
compounds
3.2.1 Effect of sample solution (pH and concentration of
buffer). The acidity of the sample solution is a critical parameter
affecting adsorption efficiency, since it determines the analytes
ionic state as well as the surface charge of the adsorbent. In the
case of propranolol, we mixed 3 mg mLꢁ1 BSA functionalized
NPs and propranolol solution using different pH. To investigate
the inuence of pH on adsorption, considering the pH-
dependent stereoselectivity and activity of the immobilized
BSA on NPs, pH values ranging from 6 to 8 were examined in
this work and the results are as shown in Fig. 3. From Fig. 3, we
can see that aer adsorption by NPs at pH 7, the enantiomeric
excess of the resulting solutions is 6.70% in R-propranolol,
which is higher than other pHs. This might be due to well-
maintained BSA conformation which is required for chiral
discriminations. Optimum pH of 7 was so selected for the
further work. The concentrations of PBS buffer were investi-
gated in the range of 10–50 mmol Lꢁ1 (Fig. S2†). 30 mmoL Lꢁ1
PBS buffer was chosen as the optimal condition under which
the highest %, e.e. was obtained.
Three different processes for sample agitation during the
adsorption step were evaluated. As shown in Fig. S4,†
Table 1 Elementary analysis of pure silica NPs and two functionalized
silica NPs
C%/RSD% H%/RSD% N%/RSD% S%/RSD%
NPs
(n ¼ 3)
(n ¼ 3)
(n ¼ 3)
(n ¼ 3)
Fig. 3 The effect of sample solution pH on adsorption of propranolol.
Experimental conditions: 0.58 mg mLꢁ1 racemate propranolol, 30
mmol Lꢁ1 phosphate buffer with 3 mg mLꢁ1 SiO2@PDA@BSA NPs,
ultrasonication for 5 min and vortex for 5 min. CE conditions are the
same as in Fig. 1.
SiO2
SiO2@PDA
1.74/0.036 1.49/0.081
2.46/0.180 1.50/0.053
0.61/0.028
0.66/0.017
0.74/0.014
—
—
SiO2@PDA@BSA 3.66/0.021 1.62/0.007
0.18/0.014
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experimental results showed that adsorption efficiency ob- one-step or multi-step operations. In one-step operation, we
tained only by ultrasonication or vortex was lower than that by mixed 0.58 mg mLꢁ1 propranolol solution or 0.1 mg mLꢁ1
a mix of them. Ultrasonication is benecial for the homoge- tryptophan solution using different amount of chiral selectors
neous dispersion of NPs in solution, which enables the analytes at pH 7.0. As shown in Fig. 4A and B, aer adsorption, the
to interact fully with the sorbent. However, too long ultra- enantiomeric excess of the two compounds improved to
sonication will result in the increase in temperature of sample different degrees.
solution, and so the desorption of analytes from sorbents. Only
To improve the enantioseparation efficiency, we performed
vortex was disadvantageous to the dispersion of NPs. Ulti- the stereoselective adsorption process in a mode of multi-step
mately, a procedure of ultrasonication for 5 min and then vortex operation. As shown in Fig. 5A and B, in the multi-step opera-
for 5 min was selected.
tion, the chiral performance of tryptophan is signicantly
3.2.3 Direct enantiomeric separation of chiral compounds enhanced with increasing the number of operations and the
with one-step or multi-step operations. Direct chiral separation enantiomeric excess is up to 14.50% and with ve operational
of propranolol and tryptophan was carried out to investigate the steps. Moreover, the increase in the enantioselectivity with the
chiral recognition abilities of the BSA functionalized NPs with number of operations is also observed for propranolol to give
enantiomeric excess up to 11.71% with ve-step adsorption.
The electropherograms of above resulting solution is shown in
Fig. S5.†
Fig. 4 Direct enantiomer separation of compounds (A) 0.58 mg mLꢁ1
propranolol (B) 0.1 mg mLꢁ1 tryptophan with one-step operation at pH
7.0 (30 mmol Lꢁ1 phosphate buffer) by different amount of SiO2@-
PDA@BSA NPs, ultrasonication for 5 min and vortex for 5 min. CE
conditions of propranolol are the same as in Fig. 1. CE conditions of Fig. 5 Direct enantiomer separation of chiral compounds (A) 0.58 mg
tryptophan: 20 mmol Lꢁ1 phosphate background electrolyte (pH 2.5) mLꢁ1 propranolol (B) 0.1 mg mLꢁ1 tryptophan with multi-step opera-
containing 40 mmol Lꢁ1 a-CD, 2% (v : v) methanol. Detection wave- tion at pH 7.0 (30 mmol Lꢁ1 phosphate buffer) by 2 mg mLꢁ1 SiO2@-
length, 254 nm; 50 mm i.d.; injection, 15 kV ꢄ 3 s for propranolol; PDA@BSA NPs, ultrasonication for 5 min and vortex for 5 min. CE
separated voltage, +15 kV.
conditions are the same as in Fig. 4.
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4. Conclusions
In this study, SiO2@PDA@BSA NPs were facilely prepared by
using PDA coating as a versatile multifunctional secondary
reaction platform. The use of these BSA modied NPs as
adsorbents for the preparative enantioseparation of drugs was
then presented with satisfactory results. As increasing the
starting percent enantiomeric excess (%, e.e.) of enantiomeric
mixtures, the nal %, e.e. value of the resulting solution was up
to nearly 100% by using a multi-step adsorption strategy,
demonstrating its validity in preparative enantioseparation,
especially for the products from asymmetric synthesis.
Comparing with other nanoparticles-based chiral adsor-
bents,22,23,27 besides simplicity and environment friendness,
another advantage of the preparation process is the stability of
the nal materials, which had exhibited the ability for recycling
use for at least three times.
Fig. 6 CE analysis of the resulting solutions of 0.1 mg mLꢁ1 tryptophan
after three-step operation at pH 7.0 (30 mmol Lꢁ1 phosphate buffer) by
4 mg mLꢁ1 SiO2@PDA@BSA NPs or SiO2@PDA NPs, ultrasonication for
5 min and vortex for 5 min. CE conditions are the same as in Fig. 4.
Further work will be focused on the use of the strategy to
prepare other chiral selectors-modied nanomaterials and use
them as adsorbents for the preparative separation of chiral
drugs of interest. To further simplify the adsorption process,
superparamagnetic character will be incorporated in the prep-
aration process simultaneously.
Then, to establish enantioseparation using BSA functional-
ized NPs, we utilized multi-step adsorption to achieve enantio-
meric enrichment of D-tryptophan starting from high initial %,
e.e. (75.55%) as shown in Fig. 6. We used 4 mg mLꢁ1 NPs mixed
with ꢂ0.1 mg mLꢁ1 tryptophan solution (L-tryptophan 0.015 mg
mLꢁ1 and D-tryptophan 0.09 mg mLꢁ1), aer adsorption, %, e.e.
of the resulting solution is up to almost 100%. That is to say, the
sample was puried.
The chiral recognition abilities of the BSA functionalized
NPs were further conrmed by polarimetry. The resulting
solutions in Fig. 6 were also carried out by an automatic digital
polarimeter. As shown in Table 2, these results were in agree-
ment with those obtained by the measurement of CE.
Conflict of interest
The authors have declared no conict of interest.
Acknowledgements
Financial support from National Natural Science Foundation of
China (21275081) and National Basic Research Program of
China (2011CB707703) is gratefully acknowledged.
References
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¨
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NPs to test their reusability. Collection of the analytes aer
centrifugation and then washing 15 min with PBS (pH 7.0, 30
mM) by ultrasonication, the NPs could be recycled. As shown in
Fig. S6,† the chiral recognition abilities of these BSA function-
alized NPs remained almost constant and with little loss of
activity aer they were reused at least three times.
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Chiral separation of DL-tryptophan using porous
membranes containing multilayered bovine serum
Original solution
+0.216
+0.216
+0.286
+0.000
SiO2@PDA adsorption
SiO2@PDA@BSA adsorption
SiO2@PDA@BSA adsorption
(blank solution)
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