BI Yanhong et al. / Chinese Journal of Catalysis, 2012, 33: 1161–1165
reduced the activity of the enzyme with unsatisfactory results.
Recently, Zhao [18] reported that the kosmotropic anions
and chaotropic cations of the ILs were capable of stabilizing
the structure of proteins, while chaotropic anions and kosmo-
tropic cations destabilize them. According to the literature, the
relative orders of the kosmotropicity and chaotropicity of ions
100
80
60
40
20
ꢀ
ꢀ
in stabilizing the enzyme are Clꢀ > Brꢀ > Iꢀ > BF4 > PF6 and
C2MIm+ > C3MIm+ > C4MIm+ > C6MIm+ > C8MIm+
>
C10MIm+, respectively. Obviously, the results confirmed by our
study showed that the enzyme activity was not consistent with
this sequence of ions. We suspected that when water was in-
volved in the enzymatic reaction, the interactions between the
ions of the IL and the substrate or product may be also re-
sponsible for the above-mentioned phenomena in addition to
the viscosity of the IL and the change in the native microen-
vironment of the enzyme.
1
2
3
4
5
6
Batch
Fig. 2. Reusability of black plum seed meal. Reaction conditions: 0.5
mmol D-glucose, 4.0 mmol tyrosol, 7.0 U black plum seed meal, 0.02 ml
C6MImǜBF4, 0.4 ml phosphate buffer (pH 5.9, 100 mmol/L), 1.58 ml
dioxane, 50 °C, 200 r/min.
parable with or lower in IL-containing systems than that ob-
ꢀ
3 Conclusions
served in a control reaction system. For the BF4 -based ILs,
however, the initial reaction rate and maximum yield ascended
with increasing alkyl chain length from C2 to C6, showing a
similar trend to those obtained with CnMIm·PF6 and CnMIm·I
(n = 2–6). Among all the ILs tested, the best results were ob-
served in a C6MIm·BF4-containing system with a yield of
24.5%. One explanation is that the longer hydrophobic alkyl
chain in the cation has a lower tendency to “absorb” the es-
sential water from the enzyme, thus maintaining its activity
[16]. However, the initial reaction rate and yield dropped with
further elongation of the alkyl chain of the ILs, such as
C8MIm·PF6 and C10MIm·I. The increment viscosity of the ILs
caused by the longer alkyl chain may lead to a decrease of
substrate and product mass transfer rate, resulting in a lower
yield [21]. Interestingly, in contrast, the addition of C4MImǜCl
and C4MImǜBr, two ILs that have hydrogen bonding potential,
It can be concluded that the synthesis of salidroside using
ȕ-glycosidase from black plum seeds can be successfully
conducted in several IL-containing systems. Among the ILs
examined, 1-alkylimidazolium ILs with linear C6 were shown
to be the most suitable for the reaction especially when the
enzymatic reaction was performed in a C6MIm·BF4-containing
system. Additionally, the results confirmed by our study indi-
cate that there was no direct correlation between the catalytic
activity of the enzyme and the sequence of the kosmotropic and
chaotropic characteristics of the ions. Further investigation into
the correlation of the ions based on ILs with low- or
high-density water in enzymatic reactions will be reported in
due course.
References
Table 3 Effect of the ILs on the enzymatic synthesis of salidroside
1
2
3
Hu X L, Lin S X, Yu D H, Qiu S F, Zhang X Q, Mei R H. Cell
Biol Toxicol, 2010, 26: 499
Ionic liquid
—
V0/(mmol/(L·h))
Time (h)
72
Yield (%)
18.8
18.9
22.6
24.5
17.2
21.2
24.3
19.0
4.9
3.2
2.9
2.9
3.3
2.3
2.9
3.0
2.7
0.2
0.2
0.7
0.9
1.0
2.9
2.3
Qian E W, Ge D T, Kong S K. J Ethnopharmacol, 2011, 133:
308
C2MIm·BF4
C4MIm·BF4
C6MIm·BF4
C2MIm·PF6
C4MIm·PF6
C6MIm·PF6
C8MIm·PF6
C4MIm·Cl
C4MIm·Br
C2MIm·I
72
68
Akita H, Kurashima K, Nakamura T, Kato K. Tetrahedron:
Asymmetry, 1999, 10: 2429
64
72
4
5
6
Wu S X, Zu Y G, Wu M. J Biotechnol, 2003, 106: 33
Wang M L, Guo C X. Chin J Catal, 2011, 32: 1051
Akita H, Kawahara E, Kishida M, Kato K. J Mol Catal B, 2006,
40: 8
72
72
72
56
7
8
Yang R L, Li N, Zong M H. J Mol Catal B, 2012, 74: 24
Lu W Y, Lin G Q, Yu H L, Tong A M, Xu J H. J Mol Catal B,
2007, 44: 72
56
9.5
56
11.6
13.0
16.2
21.9
17.4
C3MIm·I
56
9
Tong A M, Lu W Y, Xu J H, Lin G Q. Bioorg Med Chem Lett,
2004, 14: 2095
C4MIm·I
72
C6MIm·I
72
10 Yu H L, Xu J H, Lu W Y, Lin G Q. J Biotechnol, 2008, 133: 469
C10MIm·I
72
11 Tong A M, Xu J H, Lu W Y, Lin G Q. J Mol Catal B, 2005, 32:
Reaction conditions: 0.5 mmol D-glucose, 4.0 mmol tyrosol, 7.0 U black
plum seed meal, 0.02 ml ILs, 0.4 ml phosphate buffer (pH 5.9, 100
mmol/L), 1.58 ml dioxane, 50 °C, 200 r/min.
83
12 Lau R M, Van Rantwijk F, Seddon K R, Sheldon R A. Org Lett,
2000, 2: 4189