Table 2 The repetitious recycle application of b-CD modified Fe3O4
nanoparticles in enantioseparation for the racemic mixture solution of
tryptophan (L- : D- = 1 : 1, 0.01 mol LÀ1
)
Specific rotation data
[a]a
[a]b
[a]c
1st recycle
2nd recycle
3rd recycle
4th recycle
5th recycle
0
0
0
0
0
35.4
34.3
32.6
33.2
31.1
À34.6
À33.2
À25.5
À22.4
À21.8
a
b
The racemic mixture of amino acids isomers. For the residual
solution after enantioseparation with b-CD modified Fe3O4 nano-
particles. For the residual solution after the release of the absorbed
amino acids isomers with AzoTAB.
c
Fig. 2 H1 NMR of (i) AzoTAB, (ii) b-CD modified Fe3O4 nano-
particles and (iii) b-CD modified Fe3O4 nanoparticles interacting with
AzoTAB.
amino acids. The method using b-CD modified Fe3O4 nano-
particles effectively separates the isomers of different amino
acids, especially for the tryptophan. We believe that the
surface architectures of magnetic nanoparticles on introducing
the CD-based host–guest recognition would afford the chemi-
cal and bio-analytical separation of various molecules in
aqueous media.
were removed by a magnetic separation process. The release
process of the absorbed amino acids isomers was monitored by
H1 NMR analysis and the optical activity characterization.
As shown in Fig. 2, the signals for H-3, H-5 and H-6 were all
upfield shifted dramatically by about 0.08, 0.07 and 0.1 ppm,
respectively. Moreover, the signals of the aromatic protons H-a,
H-b and H-c for AzoTAB also showed a dramatic upfield shift
by about 0.18, 0.19 and 0.07 ppm, respectively. These chemical
shifts of different protons indicate that the AzoTAB formed
an inclusion complex with b-CD in this case, and the absorbed
L-tryptophan was released into the solution. The specific rota-
tion of the resulting solution showed À34.6, close to that of
pure L-tryptophan solutions. The concentration of the released
L-tryptophan was comparable to the concentration decrease of
the racemic mixture tryptophan solution after the magnetic
separation process, which gave further evidence of the total
release of the absorbed L-tryptophan into the solution.
This work was supported by the National Basic Research
Program of China under Grant (No. 2011CB301802), the
National Natural Science Foundation of China (No: 50973101,
21074123, 91027024).
Notes and references
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Then above b-CD modified Fe3O4 nanoparticles containing
AzoTAB were re-dispersed in water and irradiated with UV
light for 10 min. The photo-controlled exclusion reaction of
azobenzene derivatives with b-CD was monitored by UV-Vis
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c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 10317–10319 10319