Highly Selective Isomerization of Glucose into Fructose Catalyzed by a Mimic Glucose Isomerase

Article abstract of DOI:10.1002/cctc.201900143

An amphoteric phenolic compound with carboxyl and amino functional groups was synthesized and used as mimic glucose isomerase to catalyze the isomerization of glucose into fructose. The mimic enzyme displayed excellent catalytic activity for isomerization

Full text of DOI:10.1002/cctc.201900143

Accepted Article
Title: High selective isomerization of glucose into fructose catalyzed by
a mimic glucose isomerase
Authors: Ni Zhang, Xiang-Guang Meng, Yan-Yan Wu, Hong-Jin Song,
Fei Wang, Hong Huang, and Jing Lv
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10.1002/cctc.201900143
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High selective isomerization of glucose into fructose catalyzed by
a mimic glucose isomerase
Ni Zhang,[a] Xiang-Guang Meng,*[a] Yan-Yan Wu,[a] Hong-Jin Song,[a] Hong Huang,[a] Fei Wang,[a] and
Jing Lv[a]
Abstract: An amphoteric phenolic compound with carboxyl and
amino functional groups was synthesized and used as mimic
glucose isomerase to catalyze the isomerization of glucose into
fructose. The mimic enzyme displayed excellent catalytic activity for
isomerization of glucose to fructose under mild conditions. The yield
of fructose and selectivity of fructose could reach 33.0% and 93.5%
after reacting 4 h, respectively, at pH 8.5 and 80 °C. The catalysis
reaction rate constant kcat and Michaelis constants KmG, KmF were
calculated. The activation energy of glucose to fructose was
evaluated as 65.9 kJ mol-1. The possible catalysis reaction
mechanism was proposed. The acid-base groups on the catalyst
play an important role in proton extraction and transfer, as well as in
the rotation of local carbon chain, which leads to the highly selective
isomerization of glucose into fructose under mild conditions.
As a result, yield of 17-31% and selectivity of 43-62% were
obtained with 10 mol% catalyst at 100 °C.[10] For separation and
easy recovery of catalyst, many natural and man-made solid
materials such as hydrotalcites,[11,12] immobilized amines,[13]
zeolites in alkaline-exchange form,[14] mesoporous ordered
molecular sieves of the M41S family,[15] zirconium carbonate,[16]
and anion-exchanged resins[17] have been reported as efficient
solid base catalysts. Michailof et al. used MgO as
heterogeneous catalyst for isomerization of glucose into fructose,
leading to 44% conversion of glucose and 75.8% selectivity of
fructose were obtained in H2O solvent. The addition of organic
solvents DMSO, DMA and sulfolane significantly reduced the
selectivity of fructose.[18,19] Many Lewis acids catalysts were also
employed for the isomerization reaction, such as CrCl3, AlCl3
and SnCl4.[20] The successful applications of materials containing
Ti, Sn β-zeolites and mesoporous silica were reported.[21-23] It is
desirable to use solid heterogeneous catalysts in industrial
large-scale processes due to the advantage of the easy
recycling and reuse.[18] Recently, Saravanamurugan and
Tsapatsis proposed an alternative route to achieve high yield
fructose through combining glucose isomerization, fructose
ketalization and fructosidehydrolysis.[24,25] Although considerable
efforts have been devoted to the isomerization of glucose to
fructose in the past years, the selectivity in fructose was usually
less than 75%, which is particularly unsatisfactory.[20]
Introduction
The utilization of renewable lignocellulosic biomass in the world
is extremely important to solve the problems of resource
shortage, for example fossil fuels depletion and the pollution of
environment,[1-3] and glucose is the main product of degradation
of biomass. Compared with glucose, fructose is easier to convert
into important platform compounds such as hydroxylmethylfurfu-
ral (HMF), levulinic acid, and other versatile platform chemicals
and liquid fuels.[4,5] Therefore, conversion of glucose into
fructose was regarded as a key intermediate step in biomass
valorization.[6] In past years, considerable efforts have been
devoted to improving yields and selectivity of fructose by
investigating various homogeneous and heterogeneous catalytic
systems. Early investigations for the isomerization of glucose
involved the utility of soluble alkalis, such as sodium hydroxide
and calcium hydroxide at high pH values and room
temperature.[7-9] Under these conditions, the reaction suffered
from a low rate of isomerization and numerous byproducts. To
improve the selectivity of fructose, an alternative method was to
replace inorganic bases with organic bases, for example
triethylamine. Recently Tessonnier et al. reported several
organic amines catalyzed isomerization of glucose to fructose.
Glucose isomerase which catalyzes aldoses to ketoses, was
found in various biological microorganisms, such as Streptomy-
cessp., S. rubiginosus, A. missouriensis, Thermus neapolitana,
etc. The enzymatic isomerization of glucose into fructose has
attracted much attention beacuse of the highly selectivity and
yield of fructose.[26] An sweetener high-fructose corn syrup is
produced via bioconversion approach using immobilized glucose
isomerase at 58 to 60°C, the process gives 43% yield of
fructose.[27] Phosphoglucose isomerase (PGI; EC 5.3.1.9), one
glucose isomerase, catalyses the interconversion of glucose 6-
phosphate (G6P) and fructose 6-phosphate (F6P). The crystal
structure of PGI from the mouse phosphoglucose isomerase at
1.6 Å has been determined, which core fold of protomer and the
interprotomer spatial arrangement of the dimer are similar to
those of already reported crystal structures of other PGIs.[28,29]
The active site involved in isomerization comprises highly
conserved residues, including glutamic acid, histidine, lysine and
arginine residues. In the enzyme catalyzed isomerization of
glucose into fructose, several steps are involved as follows: (i)
[a]
N. Zhang, Y.-Y. Wu, H.-J. Song, F. Wang, H. Huang, J. Lv, Prof. X.-
G. Meng
Key Laboratory of Green Chemistry and Technology
College of Chemistry
ring opening of glucose; (ii) formation of
a cis-enediol
Sichuan University
Chengdu 610064 (P.R. China)
Email: mengxgchem@163.com
intermediate by abstracting proton on C2 of glucose; (iii) transfer
of proton; (iv) ring closure of chain fructose. The residues
histidine and lysine were thought to be related to the ring
opening and closing of monosaccharides, and residues glutamic
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10.1002/cctc.201900143
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acid and arginine to proton abstraction and transfer,
respectively.[28,30] Despite the high activity and selectivity of
natural enzymes, the use of natural enzymes is too expensive
due to the difficulties in isolation and purification and the
sensitivity to environmental conditions.[31]
compounds, which indicated good synergistic effect among the
functional groups. The yield of fructose reached 33.0% in BBTA
catalyzed system for a reaction time of 4 h at pH 8.5 and 80 °C,
which is even higher than 2,2'-((2-hydroxy-3,5-dimethylbenzyl)-
azanediyl)diacetic acid, but less than twice. This indicated that
phenol group played an important role in the catalytic process. It
is noted that for the BBTA catalyzed system, the selectivity of
fructose reached 93.5%.
Here we constructed a novel compound to mimic the PGI. The
carboxyl, phenolic and positive groups in the active site of PGI
were introduced as illustrated in Figure 1. The synthesized
catalyst 2,2',2'',2'''-(((2-hydroxy-5-methyl-1,3-phenylene)bis(met-
hylene))-bis(azanetriyl))tetraacetic acid (BBTA) was employed to
catalyze the isomerization of glucose to fructose. The catalyst
displayed great catalytic activity for the isomerization reaction,
as well as high selectivity in fructose in aqueous solution at
relative low temperature (70-90 ºC).
Table 1. Conversion of glucose and selectivity of fructose in various systems[a]
Conversion of
glucose / %
3.7
Yield of
fructose / %
3.3
Selectivity of
fructose / %
89.2
Catalyst
Bulk solution
CH3COOH
7.6
7.2
94.7
8.2
7.8
95.1
4.5
9.0
4.3
8.2
95.6
91.1
Figure 1. The chemical structure of BBTA.
Results and Discussion
20.5
35.3
22.7
33.0
90.3
93.5
Comparison of various catalytic systems
Glucose is difficult to be conversed to fructose in a neutral
aqueous solution. In previous reports, the non-enzyme catalyzed
isomerizations of glucose to fructose were generally carried out
under acidic or alkaline conditions. In this work, we focused on
the nearly neutral and low temperature conditions for the
isomerization of glucose. In glucose isomerase, carboxyl, amino,
imidazole and phenolic groups were generally found in the
catalytic active domain. To design and construct a mimic
isomerase, some compounds with the groups above were
selected and their catalytic ability for the isomerization of
glucose into fructose was studied and the results were listed in
Table 1. From Table 1 it can been found that only 3.7% of
glucose could be conversed after reacting 4 h at pH 8.5 and 80
ºC in the absence of any catalyst. It was also observed that both
single functional compounds (acetic acid and p-methylphenol)
and bifunctional groups compounds (iminodiacetic acid and
aminotriacetic acid) showed weak catalytic activity of
isomerization of glucose, and the conversion of glucose was
less than 10%. Interestingly, the macromolecule composed of
carboxyl, amino and phenol groups exhibited excellent catalytic
performance for the isomerization reaction. From Table 1 it can
be seen that 2,2'-((2-hydroxy-3,5-dimethylbenzyl)azanediyl)-
diacetic acid exhibited much better catalytic performance
compared with single functional and bifunctional groups
BBTA
[a][glucose]0 = 0.2775mol L-1, [catalyst] = 0.014mol L-1, pH 8.5, 80 °C, 4h.
Influence of solvent
To investigate the influence of solvent, the isomerization
reaction catalyzed by BBTA was carried out in several mixed
solvents. The experimental results were listed in Table 2.
Table 2. Conversion of glucose and yield of fructose in various solvents[a]
Conversion of
Yield of
fructose / %
33.0
Selectivity of
fructose / %
93.5
Solvent
glucose / %
H2O
35.3
3.4
THF-H2O
DMF-H2O
DMSO-H2O
3.1
91.2
6.0
5.0
83.3
6.5
5.2
80.0
[a]The ratio of mixed solvents is 1:1(volume ratio). [glucose]0 = 0.2775mol L-1,
[BBTA] = 0.014mol L-1, pH 8.5, 80 °C, 4h.
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From Table 2 it can be seen that solvents cause a significant
effect on the isomerization reaction. When organic solvent THF,
DMF or DMSO was added to the aqueous solution, the
conversion of glucose and yield of fructose decreased
significantly. It seemed that the larger polarity of the solvent, the
greater conversion of glucose and the yield of fructose. The
order is H2O>>DMSO>DMF>THF, which is related to the proton
transfer ability of solvents. This implied that the isomerization
reaction involved a proton transfer process. In the cases of other
ratios of organic solvent to water, such as 7:3 and 3:7, the
conversion of glucose and yield of fructose were also in line with
the order. It is noted that the addition of organic solvent not only
reduced the reaction rate, but also reduced the selectivity of
fructose. Therefore, aqueous solution is the best medium for this
work’s catalytic system.
It was noted that the BBTA catalyzed system gave a satisfactory
selectivity of fructose (S>93%) in the range of pH 7.0 to 8.5,
which compared with the value 8.0 of optimal pH of nature
Streptomyces enzyme and Bacillus enzyme.[34]
Effect of temperature
The isomerization of glucose into fructose is slow due to the
relatively large reaction active energy under neutral aqueous
solution, so the isomerization reactions were usually carried out
at high temperatures (T>100 ºC) to speed up the reaction
process.[20] However, glucose and fructose are unstable and
easy to decompose and result in the low selectivity (S<70%) at
high temperature. In this work, to avoid a low selectivity of
fructose, the reaction of glucose isomerization was carried out in
the range of temperature 70-90 ºC. Figure 3 illustrates the
influence of temperature on both conversion of glucose and yield
of fructose. It can be seen that high temperature promotes the
reaction rate of conversion of glucose. However we further
observed that the yield of fructose reached a maximum in 3-5 h,
and the higher the temperature, the earlier the maximum
appeared (Figure 3(B)). This implied that two processes
involving generation and decomposition of fructose occurred
simultaneously during the catalytic reaction. Expectedly, the
effect of temperature on reaction rate of the generation and
decomposition of fructose is different. The maximum yield of
fructose was observed at 80 ºC and reaction 4h.
Effect of pH
Natural glucose isomerases generally exhibit the best catalytic
activity in weak alkaline solution, with the optimal pH of 7 to
9.[32,33] In order to achieve high conversion of glucose, the non-
enzymatic isomerizations of glucose to fructose were usually
carried out under acidic or alkaline conditions. However the
selectivity of fructose was low.[7-9,22]
60
40
20
0
A
40
30
20
10
0
0
2
4
6
7
8
9
10
11
t / h
pH
B
Figure 2. Plots of conversion of glucose (■) and yield of fructose (●) versus
pH at 80 °C for 4h. [glucose]0 = 0.2775mol L-1, [BBTA] = 0.014mol L-1.
30
20
10
0
From Figure 2 it can be seen that in the presence of BBTA, pH
effect was obvious. The conversion of glucose increased with
increasing pH and arrived 53.8% for reaction of 4 h at 80 °C. It
can be further observed that the variation of the fructose yield
was different from glucose conversion. Firstly the yield of
fructose rapidly increased with increasing pH and up to a yield of
33.0% and selectivity of 93.5% at pH 8.5. Subsequently the yield
decreased slowly in the range of pH 8.5 to 9.5. Although this
phenomenon is unusual, it was also observed in isomerization
reaction catalyzed by natural enzyme Thermus oshimai
(ToGI).[32] Then the yield and selectivity of fructose decreased
rapidly with increasing pH.
0
2
4
6
t / h
Figure 3. Conversion of glucose (A) and yield of fructose (B) with time at pH
8.5 at different temperature. (□)70°C, (☆)75°C, (●)80°C, (▲) 85°C, (◇) 90°C.
[glucose]0 = 0.2775mol L-1, [BBTA] = 0.014mol L-1.
Products analysis and reaction kinetics
To explore the products of isomerization reaction, HPLC,
chromatographic analysis and GC-MS were employed. The
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(
)
(
results showed that besides fructose, there were three other
products including mannose, 1,3-dihydroxyacetone and HMF in
the reaction solution. The products 1,3-dihydroxyacetone and
HMF may be derived from the further reaction of fructose，and
the mannose may come from the isomerization of glucose.[35]
The content of mannose, 1,3-dihydroxyacetone and HMF in
reaction solution were listed in Table 3. Based on these
observations, the catalytic reaction kinetic model of glucose
isomerization was suggested in Scheme 1.
where a1=
, a2=
, a3=
), a4= , a5=
(
)
(
)
, a6=
, a7=
.
,
are the Michaelis constants for the first and second reaction,
respectively. ， and ET is the total concentration of
catalyst. S= [F]/(C0-[G]), where C0 is the initial concentration of
glucose. S represents the selectivity of fructose. Under this
work’s conditions, the value of S changed little within 4 h
reaction and approximating
a constant Sa. The products
increase gradually with reaction proceeding and the products
may influence the reaction rate. To avoid this interference, we
used the data of initial reaction time of 3 h to evaluate the values
of kcat, KmG and KmF in this work. KmG, KmF and kcat were obtained
by nonlinear fitting according to kinetic equations (1) and (2).
The calculated results are listed in Table 4. From Figure 4 it can
be found that the theoretical fitting curves are in good agreement
with the experimental data, and both the multiple correlation
coefficients of glucose conversion and that of fructose yield were
all above 0.97. This indicated that the reaction kinetic model
proposed as Scheme 1 was reasonable.
Table 3. Conversion of glucose and distribution of products[a]
Reaction
time / h
Conversion
of glucose
/ %
Yield / %
1,3-
Fructose
HMF
Mannose
dihydroxyacetone
1
2
3
4
14.5
14.1
22.1
28.2
33.0
0.2
0.5
0.7
0.9
0.08
0.1
0.1
0.3
0.9
1.2
23.2
30.0
0.11
0.12
35.4
[a][glucose]0 = 0.2775mol L-1, [BBTA] = 0.014mol L-1, pH 8.5, 80°C .
Table 4. KmG, KmF and kcat of glucose isomerization catalyzed by BBTA[a]
T / °C
70
75
80
85
90
KmG/mol L-1
KmF/mol L-1
104kcat/s-1
0.07
0.05
1.05
0.16
0.13
1.38
0.21
0.19
1.98
0.28
0.23
2.73
0.46
0.30
3.71
Scheme 1. The proposed kinetic model of catalysis reaction.
[a][glucose]0 = 0.2775mol L-1, [BBTA] = 0.014mol L-1, pH 8.5.
According to our experimental results, a kinetic reaction pathway
for isomerization of glucose was proposed: in terms of kinetics,
the binding process of glucose and catalyst should not be
ignored because of the larger molecules of glucose and catalyst.
Hence substrate glucose G first reversibly combines with
catalyst E to generate an intermediate compound EG, whose
reversible rate constants are k1 and k-1, respectively. Then EG
reacts into fructose F and releases catalyst E, which is the rate-
limiting step and the rate constant is k2. Consequently, fructose
F combines with catalyst E to form another intermediate EF,
whose reversible rate constants are k3 and k-3, respectively.
Lastly, the intermediate EF generates G and release E, and also
yields by-products P. Based on the theory of reaction kinetics,
the kinetic equations (1) and (2) were deduced, the detailed
derivation process is described in the Supplementary material.
Equation (1) represent the relationship between time t and
glucose concentration [G]. Equation (2) represent the
relationship between time t and fructose concentration [F].
12000
A
10000
8000
6000
4000
2000
0
0.16
0.18
0.20
0.22
0.24
0.26
0.28
[G] / mol L-1
12000
10000
8000
6000
4000
2000
0
B
0.00
0.02
0.04
0.06
0.08
0.10
[
(
)
]
[ ]
[F] / mol L-1
([ ] )
( )
(
)
Figure 4. Plots of reaction time vs. concentration of glucose (A) and fructose
(B). [glucose]0 = 0.2775mol L-1, [BBTA] = 0.014mol L-1, pH 8.5. (■)70°C,
(●)75°C , (▲)80°C, (◆)85°C, (★)90°C. Solid lines in A and B are the
theoretical fitting curves based on equations (1) and (2), respectively.
(
)
[
]
[
]
(
)
( )
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Effect of temperature
and 6.5, respectively, and pKa of the phenol and tertiary amine
were evaluated as 8.9 and 10.7, respectively, in aqueous
solution at 25 ºC. The experimental results show that the groups
on both sides of the benzene ring of catalyst are independent
and do not affect each other. Hence, in aqueous solution of
about pH 8.5, the phenolic group exists in both neutral and
anionic forms, carboxyl in anionic form and tertiary amine in
cationic form. Negative carboxyl and phenoxy anions could play
important roles in abstracting proton. Although carboxyl groups
are considered to be the key to hydrogen extraction in
isomerization catalyzed by natural enzyme, in this work it is
likely that phenoxy group plays a major role in hydrogen
extraction, which can be evidenced by the obvious change of
yield of fructose near pH 8 (Figure 2). Tertiary amine carrying a
proton may play role in proton transfer, as neutral phenoxy
group acts. Furthermore, the electric field can be formed
between the positive and negative groups, which can induce
obviously the substrate atoms and lead to the rotation of carbon
chain, such as C2-C3 and C3-C4, and this promoted the
generation of products fructose (rotation on C3-C4) and
mannose (rotation on C2-C3). The electrical effect can be
supported by a reduction of the glucose conversion by adding
inorganic salts (Table S1). Based on the analyses above and
It can be seen from Table 4 that values of KmG and KmF were all
relatively small, which showed that the glucose and fructose
have obvious association with catalyst in the kinetic reaction
process. Compared with those values of 0.14-1.02 in natural
enzyme catalyzed isomerization systems,[36-38] the range of
values of KmG and KmF calculated in this work is consistent with
that of natural enzyme. Although the reaction rate constants kcat
were 102-106 folds smaller than those catalyzed by natural
glucose isomerase,[36,37] the catalyst BBTA displayed
considerable catalytic activity and excellent selectivity of fructose
under mild reaction conditions.
Since the values of kcat at various temperature were obtained,
the activation energy Ea and pre-exponential factor could be
evaluated by the Arrhenius plots of ln kcat vs. 1/T, as illustrated in
Figure 5. The activation energy and pre-exponential factor of
glucose isomerization were calculated as 65.9 kJ mol-1 and
1.09×106, respectively. The enzyme catalyzed reaction
activation energy of glucose isomerization were reported in the
range of 35-75 kJ mol-1,[38-40] while those Ea of nonenzyme
catalyzed isomerization were in the range of 30-121 kJ mol-1.[41]
The low reaction activation energy under mild condition indicates
that this is an efficient catalytic system for the isomerization of
glucose into fructose.
experimental data,
a possible catalysis mechanism was
proposed as illustrated in Scheme 2 and Scheme 3.
-8.0
-8.4
-8.8
-9.2
Scheme 2. Possible reaction pathways.
2.76
2.80
2.84
2.88
2.92
-1
-1
1000T / K
Figure 5. Plot of ln kcat vs. 1/T for glucose isomerization. [BBTA]=0.014mol L- 1
,
pH 8.5.
Possible catalytic mechanism
In enzyme or non-enzyme catalyzed reaction, cis-enediol was
believed as the intermediate in isomerization of glucose into
fructose, and which formation is the rate-limiting step.[26,42] In this
work, the catalyst contains several functional groups which may
play different role in catalysis reaction. The values of pKa of
these functional groups were determined by titration analysis.
The values of pKa of the mono compound 2,2'-((2-hydroxy-3,5-
dimethylbenzyl)azanediyl)diacetic acid were evaluated as 2.4
and 6.4 of the carboxylic acids, 8.7 of the phenol and 10.4 of the
tertiary amine. The pKa of the BBTA on one side of benzene
ring were evaluated, the values of the carboxylic acids were 2.3
Scheme 3. Propose catalytic mechanism for the generation of fructose.
The catalytic mechanism of glucose into fructose may involve
the following processes: ring-opening of glucose, rotation about
C3-C4, loss and gaining of proton (formation of cis-enediol),
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rotation about C3-C4 again and ring-closure of fructose. The
ring- opening of glucose and the ring-closure of fructose may
due to the transfer of proton by the combining action of positive
tertiary amines and negative carboxyl and phenoxy. The
formation of intermediate cis-enediol is attributed to the
extraction of hydrogen from C2 by phenoxy anion and
subsequent proton delivery from tertiary amine or phenol. The
C3-C4 may occur two times before and after the formation of
intermediate cis-enediol, respectively. The rotation makes the
formation of both cis-enediol and chain fructose in a more
favorable state. It is noted that the rotation of C2-C3 would result
in generation of mannose, this has been supported by products
of reaction in this work. It is obvious that catalysts with positive
and negative groups cause the easily rotation of substrate
chains, and this results in the good selectivity of fructose. As far
as we know, this is the first example to achieve fructose with a
selectivity of more than 90% for the isomerization of glucose in
non-enzymatic catalytic system under mild conditions.
Instruments
NMR (AM-400, Bruker, Switzerland), Elemental Analyzer (Euro-
EA-3000, America), UV-5300 spectrophotometer (Yuanxi Comp-
any, China), High performance liquid chromatography (HPLC)
(LC-10T, Shodex, Japan), with a RI detector (RI-201R, Shodex,
Japan) and a sugar-D chromatographic column. HPLC also with
a UV-vis detector and a C18 column.
Synthesis
The catalyst 2,2'-((2-hydroxy-3,5-dimethylbenzyl)azanediyl)-
diacetic acid was synthesized according to previous report.[43]
The white solid product was obtained. 1H NMR (400 MHz,
DMSO-d6): δ 6.81 (s, 0H), 6.59 (s, 0H), 3.75 (s, 1H), 3.38 (s,
1H), 2.10 (s, 1H), 2.07 (s, 1H). 13C NMR (101 MHz, DMSO): δ
172.4, 152.5, 130.7, 127.6, 126.7, 123.7, 120.8, 55.0, 53.3, 19.9,
15.6.
Conclusions
In this work, a novel catalyst with multiple groups was designed
and synthesized and used as a mimic glucose isomerase. The
mimic isomerase system exhibited a great catalytic activity for
the isomerization of glucose into fructose in weakly alkaline
aqueous solutions at relatively low temperature (70-90 °C ). The
high selectivity (S>93%) of fructose was achieved before 4 h
reaction time. The functional groups phenoxy, carboxyl and
tertiary amino showed an obvious synergistic effect on the
isomerization reactions. The kinetic model of catalysis reaction
was suggested, and the catalysis rate constant kcat and
Michaelis constants KmG and KmF were calculated. The activation
energy Ea= 65.9 kJ mol-1 for the isomerization of glucose into
fructose was evaluated. This work will provide a new technology
and method for the isomerization of glucose into fructose under
mild conditions.
The catalyst BBTA was synthesized by modification of previous
published procedures[44,45] as follows: NaOH (10 g) was added to
140 mL aqueous solution containing iminodiacetic acid (0.125
mol) and p-cresol (0.063 mol) under ice water bath. Then
paraformaldehyde (0.063 mol) was added slowly into the mixture
and the solution was stirred for 30 min at room temperature.
Then the solution was heated to 70 ºC and stirred for 4 h. The
solvent was acidized and removed by vacuum distillation. Then
the pure white solid of BBTA was obtained by recrystallization of
crude products in methanol. The structure of BBTA was given in
Figure 1. Elemental analysis: calcd (%) for BBTA (398.1): C
1
51.26, H 5.57, N 7.03; found: C 51.24, H 5.54, N 7.02. H NMR
(400 MHz, D2O): δ 6.97 (d, J = 8.2 Hz, 1H), 6.87 (d, J = 1.2 Hz,
1H), 6.66 (d, J = 8.2 Hz, 1H), 4.71 (s, 8H), 3.70 (s, 2H), 3.16 (s,
4H), 2.12 (s, 3H). 13C NMR (101 MHz, D2O): δ 178.4, 153.9,
1
130.9, 129.6, 129.2, 122.7, 115.7, 57.0, 55.2, 19.4. The H and
Experimental Section
13C NMR spectra of BBTA were illustrated in Figure S1 and
Figure S2.
Materials
Experimental methods
Iminodiacetic acid, paraformaldehyde, p-Cresol, fructose,
glucose, mannose, 1,3-dihydroxyacetone, HMF
， 2,4-
Typically, 0.25 g glucose and 0.028 g catalyst were added into 5
mL aqueous solution, the solution was sealed, heated and kept
at required temperature. Initially, the pH was adjusted by NaOH
and the N2 was introduced into solution for 30 min, then the
solution was sealed. The reactor was cooled by an ice bath after
a certain reaction time. The glucose, fructose and other products
in the reaction solution were analyzed by GC-MS, chromatogra-
phic analysis. And the concentrations were detected by HPLC.
dimethylphenol were purchased from Adamas Company.
Sodium chloride, sodium hydroxide, sodium sulfate potassium
iodide were purchased from Kelong reagent Company. Solvents
Tetrahydrofuran
(THF),
Dimethylac-etamide
(DMA),
Dimethylsulfoxide (DMSO), methanol, hydrochloric acid and
formaldehyde were purchased from Kelong reagent Company.
Acetonitrile was purchased from Adamas Company,
chromatographic pure grade. All above reagents were used
without further purifcation.
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Ni Zhang, Yan-Yan Wu, Hong-Jin Song,
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High selective isomerization of
glucose into fructose catalyzed by a
mimic glucose isomerase
An amphoteric phenolic compound with carboxyl and amino functional groups was synthesized and used as mimic glucose
isomerase to catalyze the isomerization of glucose into fructose. The mimic enzyme displayed excellent catalytic activity for
isomerization of glucose to fructose under mild conditions. The yield of fructose and selectivity of fructose could reach 33.0% and
93.5% after reacting 4 h, respectively, at pH 8.5 and 80 °C.
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