Reconsidering the activation entropy for anomerization of glucose and mannose in water studied by NMR spectroscopy

Article abstract of DOI:10.1016/j.molstruc.2015.03.038

The anomerization of monosaccharides is a very important process to understand how their stereoisomers are stabilized in aqueous solutions. For glucose and mannose, it has been known that α- and β-anomers of hexopyranose exist as the major components. In order to examine the anomerization pathway for glucose and mannose in aqueous solutions, it is indispensable to determine the thermodynamic parameters such as the activation energy, the activation Gibbs free energy (ΔG^?), enthalpy (ΔH^?), and entropy (ΔS^?). Although several research groups reported these quantities in aqueous solution, they have still been controversial especially for ΔS^?. In this paper, we employ ¹H NMR spectroscopy for monitoring the population of both α- and β-anomers of glucose and mannose. The contribution of ΔS^? to ΔG^? for glucose in water is estimated to be ca. 30%, while that for mannose is 8.0%. The large difference in ΔS^? suggests that the anomerization pathway is not the same for glucose and mannose.

Full text of DOI:10.1016/j.molstruc.2015.03.038

Journal of Molecular Structure 1093 (2015) 195–200
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Reconsidering the activation entropy for anomerization of glucose and
mannose in water studied by NMR spectroscopy
a
a
b,
⇑
Ami Kosaka , Misako Aida , Yukiteru Katsumoto
a
Graduate School of Science, Hiroshima University, Kagami-yama 1-3-1, Higashi-hiroshima 739-8526, Japan
Faculty of Science, Fukuoka University, Nanakuma 8-19-1, Jonan-ku 814-0810, Japan
b
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
We reexamine the thermodynamic parameters of the anomerization for glucose and mannose.
NMR spectroscopy enable us to estimate the population of the both epimers in D O.
to G for glucose in water is clearly different for glucose and mannose.
It is suggested that the anomerization pathway is not the same for glucose and mannose.
2
à
à
The contribution of
DS
a r t i c l e i n f o
a b s t r a c t
Article history:
The anomerization of monosaccharides is a very important process to understand how their
Received 9 December 2014
Received in revised form 20 March 2015
Accepted 23 March 2015
stereoisomers are stabilized in aqueous solutions. For glucose and mannose, it has been known that
- and b-anomers of hexopyranose exist as the major components. In order to examine the anomerization
pathway for glucose and mannose in aqueous solutions, it is indispensable to determine the thermody-
a
Available online 31 March 2015
à
à
namic parameters such as the activation energy, the activation Gibbs free energy (
D
G ), enthalpy (
DH ),
à
and entropy (
have still been controversial especially for
monitoring the population of both - and b-anomers of glucose and mannose. The contribution of
G for glucose in water is estimated to be ca. 30%, while that for mannose is 8.0%. The large difference
DS ). Although several research groups reported these quantities in aqueous solution, they
Keywords:
Glucose
Mannose
Anomerization
NMR
Activation entropy
à
1
D
S . In this paper, we employ H NMR spectroscopy for
à
a
DS
à
to
in
D
D
à
S
suggests that the anomerization pathway is not the same for glucose and mannose.
Ó 2015 Elsevier B.V. All rights reserved.
Introduction
Both the anomers can be found in biological systems. Glycogen
and starch, which are made of -glucose, are used for the energy
resources of animals and plants. On the other hand, b- -glucose is
the monomer unit of cellulose that is a building block of plant cells
and fiber. Human beings cannot digest cellulose, thus it is added to
a-D
Saccharides and their derivatives are key compounds for life
science. Saccharides play an important role not only in nucleic
acids as the skeletal backbone, but also in tissues and organs as
the osmolytes and cryoprotective agents [1]. In food sciences,
polysaccharides are often used for controlling gelation processes.
One of the most common, but important monosaccharide is glu-
cose, which predominantly forms hexopyranose rings in aqueous
solutions. Hexopyranose has two possible stereochemical isomers
due to the position of OH group on the C1 carbon (see Fig. 1 for
the chemical structures of glucose and mannose). These two iso-
mers are called anomers. The stereostructure of the anomers is
characterized by the orientation of the C1–O1 bond that can be
D
many kinds of diet foods as bulk. Living things properly use
a- or
b- -glucose in accordance with the situation. Therefore, the
D
anomerization of glucose in water had attracted keen interests of
biochemists and life scientists.
It has been considered that in gas phase the a-anomer of glu-
cose becomes stable as a result of the so-called ‘‘anomeric effect’’,
which is often denoted when organic chemists explain the stability
of stereoisomers after the substitution of the functional groups on
the hexopyranose ring. In fact, a quantum chemical calculation
axial (
a
) or equatorial (b) to the puckered six-membered ring [2].
revealed that the formation of
able in vacuo [3]. On the other hand, it was experimentally
reported that b- -glucose becomes more stable in aqueous media
4]. The increase in the stability of the b-anomer in water is
considered as an important result of hydration effects on the
a-D-glucose is energetically favor-
D
[
⇑
Corresponding author.
E-mail address: katsumoto@fukuoka-u.ac.jp (Y. Katsumoto).
http://dx.doi.org/10.1016/j.molstruc.2015.03.038
022-2860/Ó 2015 Elsevier B.V. All rights reserved.
0

1
96
A. Kosaka et al. / Journal of Molecular Structure 1093 (2015) 195–200
Fig. 1. The chemical structures of glucose and mannose.
anomerization. Karabulut and Leszczynski suggested by the use of
quantum chemical calculation that the interaction between
the water and the lone pairs of the anomeric oxygen atom in
aldose [10,13,15]. The other is the pathway through the carbocation
+
3
intermediate [16]. In this scenario, a H O ion in solution transfers a
proton to the OH group attached to C1, and then the protonated OH
+
b-
D-glucose is stronger than that for
a
-anomer because of the steric
(OH
carbocation.
In this study, we reexamine the reaction rate and the activation
2
) is eliminated from the hexopyranose ring so that C1 forms
hindrance [3].
The anomerization of glucose in water occurs within a couple of
hours [5–10]. This suggests that the activation energy of the
anomerization (E ) for glucose in water is relatively low so that
a
the reaction can be investigated by the use of a conventional
spectroscopic method such as infrared spectroscopy and NMR.
However, there are only a limited number of reports available for
energy of the anomerization for two monosaccharides, glucose and
mannose, by using NMR spectroscopy. The NMR spectroscopy is
used for monitoring the population and conformation of anomers.
The systematic studies on two different monosaccharides may give
us a new insight into the anomerization process in water.
E
7
(
a
of glucose. Nagata et al. have determined that E
2 kJ mol
a
of glucose is
by using the mutarotase–glucose oxidase method
mutarotase-GOD method) [11,12]. It is of note that they estimated
the value of by monitoring only the concentration of
b- -glucose. Lee et al. have measured the thermodynamic constants
ꢁ1
Experimental section
E
a
The
from Sigma Aldrich and TCI and used without further purification.
O (Cambridge Isotope Laboratories Inc., 99.9%) was used as
received. The concentration of monosaccharides in D O was
wt%. All NMR spectra were measured on JEOL ECA 500 MHz at
a-glucose, b-glucose, and D-(+)-mannose were purchased
D
of anomerization of glucose and mannose by the use of optical rota-
tion (OR) spectroscopy and gas liquid chromatography (GLC) [14].
D
2
2
The population ratio of
a- and b-D-glucose in water at equilibrium
1
has been found to be 36:64, and the activation enthalpy for the
à
ꢁ1
a temperature from 10 to 40 °C.
anomerization,
DH , is 67.3 kJ mol . For the GLC study on the
anomerization, trimethylsilylation of the isomers is required before
the measurement. Although the OR and GLC techniques can provide
Results and discussion
à
the activation entropy of the anomerization (DS ), the value has still
1
been controversial, because these techniques are not sensitive to the
absolute concentration of each anomer.
Several mechanisms of anomerization have been proposed
based on the reaction energy experimentally estimated
2
H NMR spectrum of a- and b- glucose in D O
1
2
Fig. 3 shows the H NMR spectra of a- and b-glucose in D O at
1
25.0 °C. The H NMR spectra of these two anomers are different
1
[
10,13,15,16]. Two feasible pathways for the anomerization of
from each other. The assignments of the H NMR signals for
glucose are illustrated in Fig. 2. One of them occurs in an acid
aqueous solution through the formation of the free aldehyde form,
glucose proposed by Roslund et al. [17] are summarized in
Table 1. The chemical structures of glucose with the definition of
(
(
a)
b)
Fig. 2. Reaction pathways for the anomerization of glucose (a) through aldehyde intermediate and (b) through the carbocation intermediate.

A. Kosaka et al. / Journal of Molecular Structure 1093 (2015) 195–200
197
Fig. 3. 1H NMR chart of (a)
a-glucose and (b) b-glucose in D O.
2
Table 1
Fig. 3, the coupling constants observed for H6b signals in
a
- and
Chemical shift of the 1H signals for
a- and b-glucose.
b-glucose are well-isolated from the others. Although the H5 signals
of b-glucose overlap with H3, the coupling constant can be obtained
with a reasonable precision because the relative intensities of the
Chemical shift/ppm
-glucose
Assignment Literature
16]
a
b-glucose
signals are obviously different. As a result, we determined the vici-
This
study
Splitting Literature
[16]
This
study
Splitting
3
nal coupling constant for b-glucose as
JH5H6b = 5.7 Hz, indicating
[
that the dihedral angle of O5–C5–C6–O6 (/) for b-glucose estimated
by Eq. (1) is one of the following: ca. 6°, 93°, 167°, or 93°. Note that
H1
H2
H3
H4
H5
H6a
H6b
5.214
3.516
3.696
3.393
3.817
3.823
3.745
5.21
3.52
3.70
3.39
3.81
3.84
3.75
d
4.627
3.226
3.469
3.385
3.447
3.879
3.704
4.63
3.23
3.46
3.38
3.44
3.89
3.70
d
dd
dd
dd
ddd
dd
dd
dd
dd
dd
ddd
dd
dd
/
= 6° is not realistic according to the torsional potential energy
profile reported in Ref. [18].
3
For
-glucose is similar to that for b-glucose. It implies that the
orientation of the O6–H group to hexopyranose ring between
- and b-glucose is not so different. Thus, the change in the chemical
a-glucose, JH5H6b = 5.4 Hz is obtained, indicating that / of
a
a
shifts of H6a and H6b due to the anomerization is possibly ascribed
to the difference in the hydration state of O6–H group between
atoms are given in the left panel of Fig. 1. As shown in Table 1, the
chemical shifts of the protons obtained here are in good agreement
with the reported ones. By comparing the proton signals for a- and
a- and b-glucose.
b-glucose, a large difference in the chemical shift on H1, H2, H3,
and H5 are found. These shifts should arise from the change in
the magnetic shielding of each proton by the anomerization. On
the contrary, the chemical shifts of H4 for both anomers are simi-
lar. This is expected because H4 is attached to the farthest carbon
from C1, at which the anomerization occurs. It is worthy of note
that the shifts in H6a and H6b arising from the anomerization
are larger than that in H4, even though H6a and H6b are far from
C1. This indicates that the hydrogen bonding of the hydroxyl
1
2
H NMR spectrum of a- and b- mannose in D O
1
2
Fig. 4 shows the H NMR spectra of a- and b-mannose in D O at
1
25.0 °C. The complete assignments of the H signals for mannose
are listed in Table 2 [19]. By comparing the chemical shifts
between the two anomers of mannose, it is found that the differ-
ences for H1, H3, H4, and H5 are significant. On the contrary, the
chemical shifts of H2 for both anomers are similar. As described
in the previous section, these shifts should arise from the change
in the magnetic shielding of each proton by the anomerization.
However, the shifts in H2 and H4 of mannose are different from
those for glucose. Interestingly, the H2 signal of mannose does
not show a large shift with anomerization, even though the H2 is
attached to the carbon next to C1.
If the magnetic shielding of the H2 proton is influenced not only
by the through-bond effect but also by the through-space one, it is
possible that the apparent insensitivity of the chemical shift is
concerned with the fact that the H2 proton is axial to the hex-
opyranose ring. In this case, the chemical shift of H2 may be sensi-
tive to the orientation of the hydroxyl group on C1. Indeed, the
chemical shift of H2 for glucose is significantly different from that
for mannose, implying the orientation of the H2 proton to the hex-
opyranose ring is crucial to determine the chemical shift. The shift
in H4 by the anomerization is possibly explained by the 1,3-diaxial
(
O6–H) group is affected by the anomerization and/or the orienta-
tion of the O6–H group in - and b-glucose is different.
a
The glucose has several conformers concerned with the rotation
of the C5–C6 and C6–O6 bonds. The rotamers due to the C6–O6
rotation may not be identified on the spectrum, because the
rotation of the C6–O6 bond is generally faster than the proton
relaxation time. On the other hand, it is possible to evaluate the
C5–C6 rotamers by the use of Karplus equation if those conformers
are stable enough. The vicinal coupling constant between H5 and
3
H6b protons ( JH5H6b) is correlated with the dihedral angle of
O5–C5–C6–O6 (/) by the following Karplus-type equation [18].
JH5H6b ¼ 5:06 þ 0:45 cos / ꢁ 0:90 cos 2/ þ 0:80 sin / þ 4:65 sin 2/
ð1Þ
The splitting of H5 and H6b signals are ddd and dd, respectively,
which are caused by the vicinal and geminal couplings. As seen in

1
98
A. Kosaka et al. / Journal of Molecular Structure 1093 (2015) 195–200
Fig. 4. 1H NMR chart of (a)
a-mannose and (b) b-mannose in D O.
2
which is also consistent with the value of 1.84–2.01 kJ mol 1 deter-
ꢁ
Table 2
Chemical shift of the 1H signals for
a- and b-mannose.
mined by GLC and OR [14]. Quantum chemical calculations have
suggested that in the gas phase the a-anomer of both glucose and
Chemical shift/ppm
-mannose
Assignment Literature
18]
mannose is more stable than the b-anomer, in which the O–H
groups forms the intramolecular hydrogen-bond [20]. In water,
the OH groups of glucose and mannose may change their orienta-
tions because of the hydration, implying that the stability of b-glu-
cose is owing to the hydration. The hydration effects on the stability
a
b-mannose
This
study
Splitting Literature
[18]
This
study
Splitting
[
H1
H2
H3
H4
H5
H6a
H6b
5.05
3.79
3.72
3.52
3.70
3.74
3.63
5.05
3.80
3.71
3.52
3.68
3.74
3.62
d
4.77
3.85
3.53
3.44
3.25
3.74
3.60
4.77
3.82
3.53
3.45
3.26
3.78
3.60
d
dd
dd
dd
ddd
dd
dd
dd
dd
dd
ddd
dd
dd
of the anomers may be different for glucose and mannose.
1
The H NMR spectra of
a
- and b-glucose show the time-
dependent changes caused by anomerization. To monitor the
population of both monomers, we chose the H1 proton of -glucose
a
and H2 of b-glucose, because they are well isolated from the other
proton signals as shown in Fig. 3. Note that the H1 proton signal of
b-glucose is not used, because the peak is located at the lower
interaction between H2 and H4. That is, the orientational change in
the C2–H2 may affect the chemical shift of H4.
slope of the proton signal of the residual H
the time-dependent change in the mole fraction of the
ꢁg(t) during the anomerization starting from the -anomer. The
value of x ꢁg(t) monotonically decreases as a function of time.
2
O. Fig. 5(A) shows
a-glucose
In order to investigate the C5–C6 rotamers of a- and b-mannose,
x
a
a
the coupling constant between H5 and H6b for mannose has to be
determined. The peaks of H5 and H6b split into ddd and dd, respec-
tively. The coupling constant between H5 and H6b for both the
anomers is obtained from the 1H NMR spectra shown in Fig. 4.
The value of JH5H6b is 5.9 Hz, indicating that the O5–C5–C6–O6
dihedral angle is one of the following: ca. 8°, 95°, 165°, or 96°.
a
Fig. 5(B) represents the time-dependent change in the mole frac-
tion of the b-glucose xbꢁg(t) during the anomerization starting from
the b-anomer, and a monotonic decrement is also found. The
a
decrement of x ꢁg(t) and xbꢁg(t) becomes steep when the tempera-
ture increases as shown in Fig. 5, indicating that the reaction rate
gets high. The reaction rate constant, k, can be evaluated by the
least square fitting with using the following single exponential
equation,
Again, the calculation result [18] implies that / = 8° is unrealistic.
3
Note that the quantity of
JH5H6a is 1.9 Hz in consistency with the
3
3
J
H5H6b quantity. For b-mannose,
Although these values are not so far from those observed for
-mannose, it is suggested that the O5–C5–C6–O6 dihedral angle
of -mannose is slightly larger than that of b-mannose.
JH5H6b of 6.3 Hz is obtained.
xðtÞ ¼ ðx
where x
0
ꢁ xeqÞ expðꢁktÞ þ xeq
ð3Þ
a
a
0
is the initial mol fraction of anomer and xeq is the mole
fraction at equilibrium. In the anomerization process of mannose,
we used the integral intensity of the H1 proton of -mannose and
that of H5 of b-mannose to monitor the population change. The
time-dependent change in the mole fraction of the -mannose
ꢁm(t) is recorded at a different temperature as shown in Fig. 6.
Thermodynamic parameters of the anomerization for glucose and
mannose
a
a
The difference in the standard Gibbs energy of the anomeriza-
x
a
tion from
a- to b-anomer
D
r
G
a
?b can be calculated from the equi-
All the time profiles can also be fitted by Eq. (3) and the quantities
of k are determined.
librium constant K = [b]/[
a] by using the following equation.
In order to estimate thermodynamic properties, we employ the
Arrhenius and Eyring plots. Since the reaction rate is possibly
affected by surrounding aqueous media, we must consider that
the parameters determined here may contain the influence from
the hydration of compounds. At the same time, however, we can
also expect that the hydration state of compounds does not signifi-
cantly change because of the temperature range. First, the activa-
½
bꢂ=½ ꢂ ¼ expðꢁ !b=kTÞ
a
D
r
G
a
ð2Þ
where k is the Boltzmann constant, T is the absolute temperature,
[
a
] is the mol fraction of the -anomer at the equilibrium, and [b]
is that for the b-anomer. As a result,
obtained for glucose, suggesting that the b-glucose is more stable
in the aqueous solution. The ?b quantity obtained here is in
good agreement with that previously reported by the use of GLC
a
ꢁ
1
D
r
G
a
?b = ꢁ1.3 kJ mol
is
r a
D G
a
tion energy of anomerization (E ) for glucose and mannose is
estimated by the Arrhenius Plots. As shown in Fig. 7(A), a linear
1
and OR [14]. On the other hand,
D
r
G
a
?b of 1.8 kJ mol for mannose
indicates that the -anomer is more stable in aqueous solution,
a
relationship between ln(k) and 1/T fits quite well for both

A. Kosaka et al. / Journal of Molecular Structure 1093 (2015) 195–200
199
1
2
5 ºC
0 ºC
15 ºC
20 ºC
25 ºC
30 ºC
35 ºC
40 ºC
0
.9
0
0
0
0
0
0
0
.9
.8
.7
.6
.5
.4
.3
25 ºC
3
3
0 ºC
5 ºC
40 ºC
0.8
0
0
.7
.6
(
A)
(B)
0.5
0
0.5
time / 104 s
1.0
1.5
0
0.5
1.0
1.5
time / 104 s
Fig. 5. (A) Time dependent changes in the mole fraction of
b- to -anomer.
a-glucose during the anomerization from a- to b-anomer, and (B) that of b-glucose during the anomerization from
a
a
monosaccharides. As a result, E of glucose is determined to be
ꢁ
1
6
9.3 kJ mol for anomerization from
a
- to b-anomer, and the E
a
1
1
1
2
0 ºC
3 ºC
5 ºC
0 ºC
ꢁ1
ꢁ1
of glucose from b to
of E
nose, E
quantity of E
a
is 70.9 kJ mol . The 1.6 kJ mol difference
ꢁ1
a
is in good agreement with
D
r
G
a
?b of ꢁ1.3 kJ mol . For man-
ꢁ1
a
from
a
- to b-anomer is estimated to be 83.4 kJ mol . The
0
0
0
0
.9
.8
.7
.6
a
from
a- to b-anomer for mannose is larger by ca.
ꢁ
1
1
2 kJ mol than that of glucose. The tendency is in good agree-
ment the result reported previously [14].
The temperature-dependence of k obtained here can also be
analyzed by means of the Eyring plots. By plotting ln(k/T) as a func-
à
tion of 1/T, we evaluate the activation enthalpy (
tion entropy (
D
H ), the activa-
à
à
DS ), and the activation Gibbs energy (DG ). The
obtained values are listed in Table 3. For glucose the value of
à
ꢁ1
D
(
8
H
from a- to b-anomer is estimated to be 65.2 kJ mol
à
ꢁ1
68.3 kJ mol from b to
1.0 kJ mol . The difference in the DH values between glucose
a
), while for mannose
D
H from
a to b is
ꢁ1
à
and mannose suggests that the recombination energies of the
chemical bonds concerned with the anomerization of the two
monosaccharides is different. The recombination may occur
around the O5C1 bond when the reaction passes through the
aldehyde intermediate, whereas if the reaction pathway is related
0
0.5
1.0
time / 104 s
Fig. 6. Time dependent changes in the mole fraction of
anomerization from - to b-anomer.
a
-mannose in the
to the carbocation intermediate the C1O1 bond is recombined.
a
à
Although the
those reported previously [14],
D
G values for both monosaccharides are similar to
à
DS from a to b obtained here
à
shows
a
large deviation from those. The
D
S
of about
-
-
-
7
8
9
(A)
-13
(B)
-
-
14
15
-
-
10
11
-16
0
.0031 0.0032 0.0033 0.0034 0.0035
0.0032
0.0033
0.0034
0.0035
/T / K-
1
1/T / K
-1
1
Fig. 7. (A) Arrhenius plots for anomerization (the filled circle:
a
- to b-glucose, the open circle: b- to
a
-glucose, and the filled triangle:
a- to bb- mannose) and (B) Eyring plots
of anomerization (the filled circle:
a
- to b-glucose, the open circle: b- to a-glucose, and the filled triangle: a- to b-mannose).

2
00
A. Kosaka et al. / Journal of Molecular Structure 1093 (2015) 195–200
Table 3
Thermodynamic parameters for anomerization of glucose and mannose.
à
ꢁ1
à
ꢁ1
à
ꢁ1
ꢁ1
D
G /kJ mol
D
H /kJ mol
DS /J K mol
1H NMR
GLC [14]
O.R. [14]
1H NMR
GLC [14]
O.R. [14]
1H NMR
GLC [14]
O.R. [14]
Glucose
to b
b to
a
95.3 ± 2.5
95.5 ± 2.6
92.51
95.31
92.38
95.31
65.2 ± 1.0
68.3 ± 1.1
ꢁ101.1 ± 7.8
ꢁ90.8 ± 8.1
ꢁ56.48
ꢁ71.55
ꢁ82.84
ꢁ82.01
a
Mannose
to b
b to
a
90.3 ± 1.3
91.59
89.70
91.71
89.66
81.0 ± 0.8
ꢁ24.8 ± 3.7
ꢁ68.99
ꢁ65.52
ꢁ59.50
ꢁ57.15
a
ꢁ
à
1
ꢁ1
1
the
00 J K mol for glucose is larger than the reported one, while
References
ꢁ1
ꢁ1
DS of about 25 J K mol for mannose is much smaller.
à
[1] F. Momany, U. Schnupf, Comput. Techor. Chem. 1029 (2014) 57, http://
dx.doi.org/10.1016/j.comptc.2013.12.007.
Both monosaccharides show the similar
D
G at 298 K. However,
is different from each other. The
DS to DG at 298 K for glucose is ca. 30%, while
à
à
the contribution of
contribution of
that for mannose is only 8%. At the moment, we cannot explain
how the difference in the configuration of the O–H group on C2
DS to DG
à
[
[
[
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8 (1969) 157, http://dx.doi.org/10.1002/anie.
à
à
affects
DS of anomerization. Anyway, the DS quantities imply
that the reaction pathway of anomerization is different for glucose
and mannose. In the case that the anomerization process passes
through an aldehyde intermediate [10,13,15], the flexibility of
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[
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the chain structures after the ring opening may contribute the
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à
quantity of
D
S . If a carbocation process takes place in the anomer-
[
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ization [16], the conformational entropy of the ring is not likely dif-
1
à
ferent for glucose and mannose. In this case, the differences in
DS
1
is possibly owing to the hydration structure of the intermediates.
[
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Conclusion
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For glucose and mannose, we reexamined the thermodynamic
parameters of the anomerization by the use of H NMR spectra.
[
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kakoronbunshu.14.836.
[13] A.M. Silva, E.C. da Silva, C.O. da Silva, Carbohydr. Res. 341 (2006) 1029, http://
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[15] X. Qian, J. Phys. Chem.
jp402739q.
1
à
ꢁ1
ꢁ1
The
DS of about 100 J K mol for glucose is much larger than
ꢁ1
ꢁ1
that for mannose, which is evaluated to be about 25 J K mol
.
[
à
These
in the literatures. The contribution of
water is estimated to be ca. 30%, while that for mannose is 8.0%.
DS values are significantly deviated from the values found
à à
B 117 (2013) 11460, http://dx.doi.org/10.1021/
D
S to DG for glucose in
[
[
[
[
[
16] D. Liu, M.R. Nimlos, D.K. Johnson, M.E. Himmel, X. Qian, J. Phys. Chem. A 114
(2010) 12936, http://dx.doi.org/10.1021/jp1078407.
17] M.U. Roslund, P. Tähtinen, M. Niemitzc, R. Sjöholm, Carbohydr. Res. 343 (2008)
à
The large difference in
D
S suggests that the anomerization path-
way is not the same for glucose and mannose.
1
01, http://dx.doi.org/10.1016/j.carres.2007.10.008.
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dx.doi.org/10.1016/S0066-4103(08)60307-5.
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dx.doi.org/10.1016/j.carres.2009.12.001.
Acknowledgement
This work was partially supported by the Grant-in-Aid for
1
Scientific Research(C) (No. 26410137). The measurement of
H
NMR spectra was made using JEOL ECA 500 MHz at the Natural
Science Center for Basic Research and Development (N-BARD),
Hiroshima University.