Study on the structure-activity of dihydromyricetin and its new production: Myricetin by using ESR and spectroscopic techniques

Article abstract of DOI:10.1007/s10973-013-3538-9

Myricetin (MY) was firstly synthesized from dihydromyricetin (DMY), and its antioxidant activity was analyzed. FTIR, NMR, and TG measurements confirmed that the DMY turned to MY. Scanning electron microscope observation showed that the 2,3-single bond offered great flexibility on the stage of crystallization to form imperfect crystalline regions; hence, DMY tends to form larger columnar crystals than MY. It has been found that the antioxidative efficiency of DMY was superior to MY, based on the measurement of radical scavenging activity by DPPH and the oxidation induction time of PP-antioxidant samples. The 2,3-double bond in MY structure, known as one of the characteristic determinants, was not an important requirement for antioxidant capacity or even negative correlation observed. Such a deduction was further supported by UV-Vis absorption spectra change when the pH was raised to pH 9. It was concluded that the ortho-trihydroxyl group in the B ring provides an antioxidant defense, and the 2,3-single band of C ring provides the structural stability.

Full text of DOI:10.1007/s10973-013-3538-9

J Therm Anal Calorim (2014) 116:241–248
DOI 10.1007/s10973-013-3538-9
Study on the structure–activity of dihydromyricetin and its new
production
Myricetin by using ESR and spectroscopic techniques
•
Mingliang Xin Yujie Ma Weihong Lin
•
•
•
Kai Xu Mingcai Chen
Received: 21 July 2013 / Accepted: 8 November 2013 / Published online: 8 December 2013
´
´
Ó Akademiai Kiado, Budapest, Hungary 2013
Abstract Myricetin (MY) was firstly synthesized from
dihydromyricetin (DMY), and its antioxidant activity was
analyzed. FTIR, NMR, and TG measurements confirmed
that the DMY turned to MY. Scanning electron microscope
observation showed that the 2,3-single bond offered great
flexibility on the stage of crystallization to form imperfect
crystalline regions; hence, DMY tends to form larger
columnar crystals than MY. It has been found that the
antioxidative efficiency of DMY was superior to MY,
based on the measurement of radical scavenging activity by
DPPH and the oxidation induction time of PP-antioxidant
samples. The 2,3-double bond in MY structure, known as
one of the characteristic determinants, was not an impor-
tant requirement for antioxidant capacity or even negative
correlation observed. Such a deduction was further sup-
ported by UV–Vis absorption spectra change when the pH
was raised to pH 9. It was concluded that the ortho-tri-
hydroxyl group in the B ring provides an antioxidant
defense, and the 2,3-single band of C ring provides the
structural stability.
Introduction
Flavonoids are formed in plants from the aromatic amino
acids phenylalanine and tyrosine and malonate. Flavonoids
generally occur in plants as glycosylated derivatives, and
they contribute to the brilliant shades of blue, scarlet, and
orange, in leaves, flowers, and fruits. The basic flavonoid
structure is the flavan nucleus, which consists of 15 carbon
atoms arranged in three rings (C6–C3–C6), which are labeled
A, B, and C (Fig. 1). The various classes of flavonoids differ
in the level of oxidation and pattern of substitution of the C
ring, while individual compounds within a class differ in the
pattern of substitution of the A and B rings. Flavonoids
include flavones, flavanones, isoflavones, flavonols, flava-
nonols, flavan-3-ols, and anthocyanidins.
Dihydromyricetin (DMY), the main bioactive compo-
nent in the stems and leaves of Ampelopsis grossedentata,
is one kind of flavonoids which has many pharmacologic
functions of the organism, such as relieving cough,
removing sputum, inhibiting hypertension, protecting liver,
absorbing ultraviolet radiation [1], antioxidation [2], and
antibacterial properties [3–5].
Keywords Dihydromyricetin ꢀ Myricetin ꢀ
Antioxidant ꢀ Radical scavenging activity
Myricetin (MY) is widely distributed in the human daily
diet such as fruits, beverages, tea, and vegetables [6].
Plants rich in MY also show potential neuroprotective
effects [7]. Furthermore, it was reported that the intake of
flavonols including MY has a favorable effect on the
cognitive performance [8, 9].
M. Xin ꢀ Y. Ma ꢀ W. Lin ꢀ K. Xu ꢀ M. Chen (&)
Guangzhou Institute of Chemistry, Chinese Academy of
Sciences, Guangzhou 510650, People’s Republic of China
e-mail: mcchen@gic.ac.cn
Although quite a lot of research has been carried out on DMY
and MY, only few reports have been studied in the possibility of
DMY turning into MY and the possible relationship between the
structure and antioxidation, for instance, effects of the number of
hydrogen atom in the C ring on antioxidant activities of flavo-
noids. In addition, the effects of pH and temperature on the
structure–activity of both DMY and MY were also studied.
M. Xin
e-mail: xdmingliang@126.com
M. Xin ꢀ Y. Ma ꢀ W. Lin
University of Chinese Academy of Sciences, Beijing 100049,
People’s Republic of China
123

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M. Xin et al.
OH
3'
Fig. 1 Structure of DMY and
MY
OH
3'
OH
OH
OH
4'
5'
4'
2'
2'
B
B
1
O
1
O
8
8
HO
HO
7
9
7
9
1'
1'
5'
OH
2
2
3
6'
6'
A
A
C
4
C
4
3
6
6
10
10
OH
OH
5
5
OH
O
OH
O
Dihydromyricetin (DMY)
Myricetin (MY)
Experimental
UV-8000 spectrophotometer (Metash, China) at room
temperature with 1-cm silica cells.
Reagents
The DPPH assay for radical scavenging activity was
based on the methodology of Piras et al. [11]. A 100-lL
sample of an ethanol solution of each test compound was
added to 3.9 mL of 47-lM DPPH (free radical in ethanol),
vortexed, and kept in the dark for 30 min. The absorbance
of the reaction mixture was then measured at 516 nm to
determine the scavenging activity of testing compound.
The experiments were then repeated at different concen-
trations to calculate the amount required to scavenge 50 %
of DPPH radicals (IC50).
DMY (purity[98.3 %) was gotten from our previous study
[10]. Phenolic synthetic antioxidant Irganox 1010 was
supplied by Shanghai Shine Chemical Co., Ltd. a,a-
diphenyl-b-picrylhydrazyl radical (DPPH) was purchased
by Aladdin. Isotactic PP N-T30S (MFI 3.0 g 10-1 min-1
at 220 °C) was supplied by Sinopec Maoming Company.
All the other reagents were analytic reagent grade, and
double-distilled water was used during the experiment.
An ethanol solution of each sample (80 lL) was added
to 500 lL of 47-lM DPPH in ethanol. A series of volume
of 1.2-mM DMY or 1.2-mM MY stock solution in ethanol
was pipetted into a glass bottle, and the total volume of the
sample was kept equal volume (80 lL) through adding a
certain volume of ethanol. DPPH solution (500 lL) was
then added. After mixing for 30 min vigorously, the solu-
tion was sucked into a capillary tube, and one end of the
tube was sealed. The capillary tube was then placed into a
tube for ESR analysis.
Synthesis of MY
DMY (0.2 g) and double-distilled water (100 g) were put
into a 250-mL flask and heated to reflux for 12 h at 100 °C
and stirred with a magnetic stirrer. After the appearance of
water-insoluble components, the precipitated material was
filtered and washed with excess hot distilled water and then
dried for 24 h in a vacuum oven at 60 °C.
Measurements were conducted at 25 °C on X-band
Bruker A200-9.5/12 ESR spectrometer (Bruker Biospin,
Switzerland). Instrument settings were as follows: micro-
wave frequency 9.8 GHz; microwave power 12 mW;
center field 3527 G; sweep width 120 G; modulation fre-
quency 100 kHz; modulation amplitude 0.94 G; receiver
gain 1 9 105; sweep time 163 s.
Instrumental
Infrared spectra were recorded by a Fourier transform
infrared spectroscopy Bruker TENSOR 27.
1H and 13C spectra were obtained on a Bruker DRX-400
spectrometer in Fourier transform mode. Chemical shift
values are reported using DMSO-d6.
Oxidative induction time (OIT) was measured by a
Perkin Elmer Diamond differential scanning calorimeter
(DSC) according to the standard method (ISO 11357-6,
2008).
Scanning electron microscope (SEM) images were taken
on a Hitachi (Japan) S3400N field emission SEM at 10 kV.
The specimen was coated with a very thin layer of gold
before SEM observations.
The thermal decomposition of the samples was per-
formed by a NETZSCH TG 209 F3 Tarsus thermogravi-
metric analyzer (TG) under nitrogen flow from room
Preparation of PP-antioxidant samples
temperature to 700 °C at a heating rate of 10 °C min-1
.
All PP-antioxidant samples were prepared in the similar
procedures: The addition of antioxidant to PP was carried
out by means of a hot plate at 220 °C. The PP-antioxidant
samples were put into a petri dish to be melted and mixed.
The content of antioxidant was fixed at 0.2 mass% in all
A 1.25 mM solution of the DMY and MY in anhydrous
ethanol was prepared as a stock solution. It was diluted to
0.1 mM of concentration with the ethanol and used as the
sample tested. The absorption spectra were obtained on an
123

Structure–activity of dihydromyricetin and its new production
243
the samples of PP-antioxidant. The compositions of testing
materials were listed in Table 1.
hydrogen of the hydroxyl are observed in Table 2. Also in
Table 2, 13C NMR data for DMY and MY are listed. The
2,3-double bond in the heterocyclic C ring of MY enhances
long range coupling; hence, the chemical shifts of C (2)
and C (3) have significant changes. Indeed, from the
Table 2, the chemical shifts of C (3) and C (40) show a
significant overlap, because they have the similar chemical
surroundings after the 2,3-double bond formation.
Results and discussion
Structural analysis of new production
Figure 2 shows the FTIR spectra of DMY and MY. In the
DMY, the broad strong bands around 3,700–3,100 cm-1
are assigned to the O–H stretching vibration of Ar–OH,
while a similar thing happened on MY. It is noted that the
absorption of the methylene is disappeared from 2,956 and
2,871 cm-1 after DMY turned into MY. In addition, the
main absorption maximum of the carbonyl band is even
shifted from 1,646 to 1,660 cm-1. This suggests that there
might be some effect for the 2,3-double bond of the MY
structure in electron delocalization of carbonyl band.
UV–Vis absorption spectra
The use of UV–Vis absorption measurement in determin-
ing various structural features of flavonoid compounds is
attractive because of its speed, simplicity, and economy of
material [12, 13]. In this study, we used the difference
absorption spectroscopy to obtain spectra. The UV–Vis
absorption spectra of DMY and MY were shown in Fig. 3.
As presented in Fig. 3, it can be seen that DMY has two
absorption peaks from 220 to 450 nm. The absorptions in
the peak of 290 nm of UV–Vis spectra correspond to the A
ring portion (benzoyl system, band II), and the weak
absorption in the peak of 330 nm corresponds to B ring
portion (cinnamoyl system, band I) [14]. However, the
conjugations, via the heterocyclic C ring, between A and B
rings has influence on the UV–Vis absorption of MY [15].
Indeed, from the shift of the band evaluated by UV–Vis
absorption, the 240–270 nm band in MY spectra is asso-
ciated mainly with absorption in the A ring and that a
bathochromic shift of the B ring (in 350–400 nm band of
the MY) compared with DMY is the cause of the
NMR spectra
The NMR spectra of DMY and MY are shown in Table 2.
1
In H NMR, all the resonances of 12 hydrogen atoms of
DMY and 10 hydrogen atoms of MY, and even the
Table 1 PP-antioxidant samples prepared via mechanical com-
pounding method
Sample
number
DMY/mass%
MY/mass%
Irganox 1010/mass%
PP
_
_
_
PP-DMY
PP-MY
PP-1010
0.2
_
_
_
0.2
_
_
Table 2 NMR spectroscopic data of DMY and MY (DMSO-d6)
_
0.2
Position
1H NMR
13C NMR
DMY/ppm
DMY/ppm
MY/ppm
MY/ppm
2
4.89
4.39
83.3
71.7
146.9
135.9
175.8
160.7
98.2
3
4
197.7
163.4
96.0
5
11.88
5.84
12.47
6.17
DMY
6
MY
7
10.81
5.88
10.75
6.36
166.8
95.0
163.9
93.2
8
9
162.6
100.5
127.1
107.0
145.7
133.5
145.7
107.0
156.1
103.0
120.8
107.2
145.7
135.9
145.7
107.2
10
10
20
30
40
50
60
3-OH
6.38
8.90
8.21
8.90
6.38
5.76
7.23
9.17
8.75
9.17
7.23
9.28
3600
3200
1600
1200
800
400
Wavenumber/cm–1
Fig. 2 FTIR spectra of DMY and MY
123

244
M. Xin et al.
Thermal stability of DMY and MY
conjugated system via 2,3-double bond throughout the MY
skeleton.
The thermal stability of DMY and MY was evaluated by
TG under nitrogen atmosphere. The results of the TG of
DMY and MY are presented in Fig. 7. From Fig. 7, it is
found that the onset decomposition temperature of DMY is
240 °C, however, the fast decomposition temperature of
MY is around 360 °C. In general, the processing temper-
ature range of polyolefin is 180–230 °C. Thus, it implies
that DMY and MY are stable at the polypropylene-pro-
cessing temperature range, and they would be effective in
stabilizing the polymer against thermal degradation.
For confirming the effect of pH on DMY and MY, the
absorption spectra are recorded in Figs. 4, 5. Different pHs
are achieved by varying the amount of hydrochloric acid
and sodium hydroxide. It is noteworthy that the position
and shape of the bands remain almost unchanged for the
DMY and MY at pH 3. In addition, a bathochromic shift of
the band I and band II occurs upon pH range from 3 to 9.
The conclusion may be drawn that a bathochromic shift of
band II in the presence of sodium hydroxide (pH 9) is
caused by the ionization of the 7-hydroxyl group, and the
shift of band I is mainly due to a partial ionization of the
ortho-trihydroxyl groups. According to the pH 7 curves
(Figs. 4, 5), it was shown that the band of DMY almost has
no movement; instead, the band of MY gets bathochromic
shift. It was obvious that the 2,3-double bond in the C ring
was the most sensitive to alkali.
Scavenging effects of DMY and MY on DPPH radical
It is well recognized that the structural feature of flavonoids
that is important for radical scavenging is the ortho-
3.0
Morphology of DMY and MY
DMY
DMY (pH = 3)
DMY (pH = 7)
2.5
The morphologies of DMY and MY have been investigated
by SEM observations, as shown in Fig. 6. It is observed
that the crystal size and volume of DMY are largely
reduced after being transformed into MY. The DMY tends
to form large columnar crystals because of the formation of
the hydrogen band from molecular interactions of the
abundant hydroxyl groups. The SEM analysis reveals that
2,3-single bond offers great flexibility at the stage of
crystallization to form imperfect crystalline regions, so that
DMY can be stacked to build larger tissue constructs.
Instead, due to the formation of 2,3-double bond in the
MY, its crystal size becomes smaller than DMY, because
of increasing the rigidity of the structure compared with
DMY, reducing the defects of molecular.
DMY (pH = 9)
DMY (pH = 9–3)
2.0
1.5
1.0
0.5
0.0
200 220 240 260 280 300 320 340 360 380 400
Wavelength/nm
Fig. 4 UV–Vis absorption spectra of DMY under different pH
conditions
3.0
MY
MY (pH = 3)
MY (pH = 7)
MY (pH = 9)
2.5
2.5
DMY
MY
2.0
1.5
1.0
0.5
0.0
MY (pH = 9–3)
2.0
1.5
1.0
0.5
0.0
200 250 300 350 400 450 500 550 600 650 700
200
250
300
350
400
450
500
Wavelength/nm
Wavelength/nm
Fig. 5 UV–Vis absorption spectra of MY under different pH
conditions
Fig. 3 UV–Vis absorption spectra of DMY and MY
123

Structure–activity of dihydromyricetin and its new production
245
Fig. 6 SEM images of a-1, a-2
DMY and b-1, b-2 MY
100
The ESR measurements of DPPH in the presence of MY
revealed a similar transition of the signal intensity of DPPH
radical which gradually disappeared (Fig. 9). It suggests
that the MY has the ability to scavenge DPPH radical also.
Particularly, the scavenging effects of MY decreased
markedly from MY-10 to MY-80, and its effect at MY-80
was better than those at DMY-80. These results suggest not
only that the ortho-trihydroxyl group in the B ring, but also
that the 2,3-double bond in the C ring has an effect on the
scavenging efficiency.
DMY
MY
90
80
70
60
50
40
30
DPPH Assay
50 100 150 200 250 300 350 400 450 500 550 600 650 700
Temperature/°C
A flavonol is a flavone with a hydroxyl group at the third
position. MY, having galloyl structure in the B ring,
appeared to be a better antioxidant than quercetin with a
catechol moiety, similarly epigallocatechin and delphinidin
possessing the three vicinal OH groups in the aromatic B
ring.
Fig. 7 TG curves of DMY and MY at a heating rate of 10 °C min-1
in nitrogen
trihydroxyl structure in the B ring. MY has the 2,3-double
bond in conjugation with A ring and B ring, but DMY lacks
the advantage of a 2,3-double bond. We tried to evaluate
the scavenging ability of MY and DMY on the DPPH
radical to obtain further understanding of their structure–
activity relationship. The ESR spectra of DPPH containing
various volumes of DMY are shown in Fig. 8. The spec-
trum in the absence of DPPH exhibited a five-lined feature,
which is typical of free DPPH molecules undergoing rapid
isotropic tumbling. [16, 17] With the increasing DMY
volume, the signal intensity of DPPH radical gradually
disappeared. The DMY could scavenge the DPPH radical,
because the DMY has an ortho-trihydroxyl group in the B
ring, and hence its hydrogen atom easily lose to combine
with DPPH radical.
The stable DPPH free radical was used as a probe for
testing the ability of scavenging free radical of antioxidant
DMY and MY. In its radical form, DPPH shows an
absorbance peak at 516 nm, which progressively weakens
as DPPH reacts with antioxidant. Hence, reducing absor-
bance of the DPPH at 516 nm could correlate the scav-
enging activity of the tested antioxidant. The absorbance at
516 nm is tested respectively for the solution of different
concentrations of the tested antioxidant in a fixed amount
of DPPH to estimate the 50 % inactivation concentration
(IC50) (Fig. 10).
After an overnight incubation, the steady state of the
reaction of both MY/DPPH is achieved in the UV–vis
123

246
M. Xin et al.
Fig. 8 ESR spectra of DPPH in
the presence of DMY of various
volumes ranging from 0 to
80 lL
DPPH
DMY–10
DMY–40
DMY–20
DMY–80
DMY–60
3460
3480
3500
3520
3540
3560
3580 3460
3480
3500
3520
3540
3560
3580
Magnetic field/gauss
Magnetic field/gauss
Fig. 9 ESR spectra of DPPH in
the presence of MY of various
volumes ranging from 0 to
80 lL
DPPH
MY–10
MY–20
MY–40
MY–80
3480
MY–60
3480
3460
3500
3520
3540
3560
3580 3460
3500
3520
3540
3560
3580
Magnetic field/gauss
Magnetic field/gauss
spectra (Fig. 11). By means of a five-parameter logistic
equation, the IC50 values were estimated to be 0.049 lM
for MY, revealing a reduction of 3.9 mol of DPPH per MY
mole and 4.4 [18] moles of DPPH per DMY mole.
radical scavenging abilities or antioxidant effects, exami-
nation of the scavenging effects on the DPPH radical
described in this study has been useful for providing basic
information on the scavenging ability of DMY, MY, and
their structure–activity relationships.
In this study, we used the DPPH radical, a stable free
radical, for the evaluation of the radical scavenging effects
of DMY and MY. Although the reactivity with the DPPH
radical may or may not permit a clear-cut definition of its
It is generally accepted that the attribution of unsaturation
in the heterocyclic C ring may additionally impart the delo-
calization of electrons across the molecule for stabilization of
123

Structure–activity of dihydromyricetin and its new production
247
0.35
–10
–5
0
PP
0.30
0.25
0.20
0.15
0.10
0.05
MY
PP–1010
PP–DMY
PP–MY
5
10
15
0
5
10
15
20
25
30
0
5
10
15
20
25
Moles × 10–8
OIT/min
Fig. 12 Determination of OIT (DSC measurement, 190 °C)
Fig. 10 516 nm absorbance value of a DPPH solution after 40 min
exposure to the increasing quantities of MY
Table 3 OIT values obtained by DSC measurement at 190 °C
0.6
0.5
0.4
Sample
PP
PP-DMY
22.1
PP-MY
12.7
PP-1010
25.8
OIT/min
1.8
induction time (OIT) method. OIT is one of the most
commonly used indicators of polymer stability both in
academic and industrial environment, being the preferred
test used by the laboratory to assess the oxidative stability
of polyolefins [19]. OIT is the time interval between the
initiation of oxygen flow and the onset of the oxidative
reaction in the DSC testing. The more resistant the sample
is to oxidative degradation, the longer the OIT value [20].
In all PP-antioxidant samples, the content of antioxidant
was fixed at 0.2 mass%, and a standard commercial Irga-
nox 1010 was used as a control to compare the relative
antioxidancy of the DMY and MY under similar condi-
tions. According to the DSC curves (Fig. 12), it was shown
that the pure PP almost immediately turns to the stage of
oxidative degradation under the oxygen atmosphere at
190 °C. The OIT of pure PP only has 1.8 min. Table 3
shows the OIT values of the several PP samples. The OIT
value of PP-MY (12.7 min) is seven times more than that
of pure PP (1.8 min). This result indicates that MY had
some effect on thermal oxidative stability of polypropyl-
ene. The OIT value of PP-DMY is 22.1 min, much higher
than those of pure PP, PP-MY and slightly less than PP-
1010. The above results revealed that the DMY was much
more efficient than MY in preventing thermal oxidative
degradation of PP. It was obvious that the 2,3-single band
of the DMY was the most responsible for the exceptional
antioxidative behavior. The OIT value of the PP-MY is
only 12.7 min which is shorter than that of PP-DMY. One
reason for the shorter OIT of PP-MY could be the
decomposition of antioxidant during the melt compounding
a
0.3
b
c
d
f
0.2
0.1
0.0
g
h
i
400
500
600
700
Wavelength/nm
Fig. 11 UV–vis (350–700 nm) absorbance spectra of MY/DPPH
after the achievement of the steady state; MY moles: (a) = 0,
(b) = 0.13 9 10-7
,
(c) = 0.25 9 10-7
,
(d) = 0.5 9 10-7
,
(f) = 0.75 9 10-7, (g) = 1.0 9 10-7, (h) = 1.5 9 10-7 and (i) MY
the aryloxyl radical. Therefore, the structural characteristic of
flavanols and flavanones with the saturated heterocyclic C
ring might result in a lower antioxidant capacity compared to
the flavones and flavonols. However, the 2,3-double bond in
the heterocyclic C ring of MY was not a structurally important
factor for the enhancement of antioxidant capacity in this
study.
The thermal oxidative degradation of PP-antioxidant
The scavenging ability of molecules in solution is mea-
sured, and the structure–activity relationship on the solid is
analyzed on the oxidative degradation. Therefore, DMY
and MY are utilized as antioxidants for polypropylene.
Several PP-antioxidant samples were prepared, and their
antioxidative activities were demonstrated by oxidation
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M. Xin et al.
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In this article, we have demonstrated for the first time that
DMY could change into MY in the boiling water. The
structure of MY has been evaluated using FTIR and NMR.
The difference of DMY and MY behavior in scavenging
effects and antioxidation has been reflected by several
measurements. The antioxidant of DMY and MY scav-
enging a free radical and its structural relationship were
comprehensively studied. It is found that the 2,3-double
bond in MY structure, known as one of the characteristic
determinants, is not an important requirement for antioxi-
dant capacity or even for the negative correlation observed.
In addition, as antioxidant of PP, the OIT values of DMY
and MY were measured. It has been revealed that the DMY
antioxidant retained excellent stability in PP similar to Ir-
ganox 1010. The 2,3-single band of the DMY is the most
responsible for the exceptional antioxidative behavior. On
the base of the result, the ortho-trihydroxyl group in the B
ring provides the antioxidation, and the 2,3-single band of
C ring provides the structural stability.
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Acknowledgements This study was financially supported from
National Natural Science Foundation of China, NSFC, (51073174)
and the Science and Technology Plan of Guangzhou Municipal
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