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New Analytical Methods
Construction and Application of a Database for a Five Dimensional Identification of Natural Compounds in Garcinia species by means of UPLC-ESI-TWIMS-TOF-MS–Introducing Gas Phase Polyphenol Conformer Drift Time Distribution Intensity Ratios Timo D. Stark, Josef Ranner, Benedikt Stiglbauer, Patrick Weiss, Sofie Stark, Onesmo B. Balemba, and Thomas Hofmann J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b06157 • Publication Date (Web): 21 Dec 2018 Downloaded from http://pubs.acs.org on January 2, 2019
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Journal of Agricultural and Food Chemistry
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Construction and Application of a Database for a Five
2
Dimensional Identification of Natural Compounds in
3
Garcinia species by means of UPLC-ESI-TWIMS-TOF-
4
MS–Introducing Gas Phase Polyphenol Conformer Drift
5
Time Distribution Intensity Ratios
6 7
Timo D. Stark,§* Josef Ranner,§ Benedikt Stiglbauer,§ Patrick Weiss,§
8
Sofie Stark,§ Onesmo B. Balemba,$ and Thomas Hofmann§
9 10
§Lehrstuhl
11
Universität München, Lise-Meitner-Str. 34, 85354 Freising, Germany
12
$Department
für Lebensmittelchemie und Molekulare Sensorik, Technische
of Biological Sciences, University of Idaho, Moscow, ID, USA
13 14 15 16 17 18 19
*
To whom correspondence should be addressed
20
PHONE
+49-8161-71-2911
21
FAX
+49-8161-71-2949
22
E-MAIL
[email protected] 23
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ABSTRACT
26
34 reference compounds from G. buchananii were analyzed by means of
27
UPLC-ESI-IMS-TOF-MS to build a database consisting of retention time,
28
accurate m/z of precursors and fragment ions as well as rotationally averaged
29
collision cross-sectional area (CCS).
30
compounds analyzed in bark extract in different concentrations and solvent
31
systems showed excellent intra- as well as interday precision (RSD ≤0.9%).
32
The established database was applied on different organs of G. buchananii as
33
well as G. kola, G. mangostana and G. cambogia enabling a fast and reliable
34
identification of these natural bioactives. For several compounds more than
35
one drift time species could be highlighted which we propose to be hydrogen
36
bond stabilized rotational isomers transferred from solution to gas phase. We
37
used all CCS values of one compound, and we propose to add also the
38
intensity ratio of the conformers as a new and additional characteristic
39
compound
40
applications to reduce dereplication and false positives and strengthen the
41
identification.
parameter
in
The CCS value of six selected
compound
identification/screening/database
42 43 44
KEYWORDS:
Ion
mobility,
CCS,
CCS
intensity
45
polyphenols, GB-2 7''-O-β-D-glucopyranosyl-6''-malonic acid, UNIFI database,
46
drift time
47
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ratios,
conformers,
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INTRODUCTION
50
Ion mobility spectrometry (IMS) is a rapid and sensitive technique to separate
51
complex mixtures of (bio)molecules prior to mass spectrometry (MS). Strong
52
benefits arise between these two complementary methods as the information
53
about gas phase ions were significantly increased. IM is able to separate ions
54
from small molecules (< 500 Da) up to megadalton protein complexes based
55
on their differential mobility through a buffer gas, thus, resolve ions that may
56
be indistinguishable by MS alone, or to determine structural information like
57
rotationally averaged collision cross-sectional area (CCS). Moreover, IM-MS
58
offers the chance to obtain insights into the conformational dynamics of a
59
system, sharing unique means of characterizing flexibility and folding
60
changes.1,2
61
Quite a few publications deal with the power of IM-MS in positive ion mode for
62
structural characterization and the study of conformational dynamics of
63
proteins, the relationship between protein crystal structures and their CCS in
64
the gas phase. As nonnative protein conformations are rarely isolated in
65
solution, they are often stable in the gas phase in varying charge states.
66
Differences in the structures of nonnative conformations in the gas phase are
67
often large enough to allow different charge states and shapes enabling
68
separation because of differences in their mobilities through a gas.2-4
69
Recently, IM-MS has been recognized for having significant research/applied
70
industrial potential and comprises multi-/cross-disciplinary areas of science,
71
the applications and impact from decades of research are only now beginning
72
to be utilized for small molecule species.5 CCS was used as additional
73
identification point in pesticide analysis,6,7 IM-MS to investigate different
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conformers of 25-hydroxyvitamin D3,8 positional isomers of drug metabolites
75
and glucuronide positional isomers,9,10 isomeric carotenoids,11 regioisomers of
76
methylenedianiline,12 and protonation isomers.13,14 Interestingly, most of the
77
described applications also used the positive ion mode for small molecules.
78
Only few publications deal with the negative ion mode, e.g. the structural
79
characterization of the deprotonated leucine-enkephaline peptide anion or
80
glucuronide positional isomers of naringenin as well as β-estradiol.10,15
81
The genus Garcinia, familiy Guttiferae, exists in about 400 species in which
82
extracts and pure isolates causes different forms of bioactivity such as anti-
83
inflammatory,16 antimicrobial,17 anticancer,18 and antioxidant properties.19-21
84
Stem and root bark extracts of G. buchananii are traditionally used in Africa to
85
treat various conditions associated with HIV/AIDS such as herpes zoster,
86
cryptococcal meningitis, tuberculosis and chronic diarrhea, diabetes and
87
cardiovascular diseases as well as illnesses including diarrhea and pain.22-25
88
In recent years, G. buchananii has attracted interest as its stem bark extract
89
exhibit anti-diarrheal and antinociceptive as well as antioxidant effects.26-30
90
Activity-guided fractionation of stem and root bark as well as
91
phytochemical analysis of leaf extract of G. buchananii lead to the discovery
92
of
93
polyisoprenylated benzophenones,32,33 xanthones,32,33 the seco-xanthone 1,5-
94
dimethoxyajacareubin,32 the
95
glycosides,30,35 (3α8'') and (3α6'')-linked biflavonoids, mainly biflavanones
96
and -glycosides.30,32-38 We discovered that (2R,3S,2''R,3''R)-manniflavanone
97
(17, numbering refers to Table 1) is the major compound of G. buchananii
98
bark extract and also prominent in root and leaf extract and exhibits very
numerous
compounds
including
benzoyl
depsidone
4
glucuronosyl
glycerols,31
garcinisidone-G,32 flavanone-C-
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potent in vitro antioxidant activities.30,32,35 Biological tests revealed that 17
100
protects proliferating skeletal muscle cells against oxidative stress, stimulates
101
myotube formation and causes a relaxation of gut smooth muscle by
102
modulating calcium mobilization including the influx by means of L-type
103
calcium channels.39,40
104
To date, neither chemical nor bioactivity investigations have been performed
105
on extracts from branch bark, fruit rind, fruit flesh and seed of G. buchananii.
106
Therefore, this study had four aims: (i) to build a database under UNIFI
107
informatics platform from Waters Corporation consisting of retention time,
108
accurate m/z of the corresponding precursors, accurate m/z of the most
109
prominent fragment ions and CCS with 34 isolated pure reference compounds
110
from G. buchananii, (ii) to demonstrate the “proof of concept” using various so
111
far not investigated organs of G. buchananii, (iii) to demonstrate the potential
112
for future applications by applying the database to other Garcinia species (G.
113
mangostana, G. kola and G. cambogia), and (iv) to characterize deprotonated
114
polyphenol anions in the gas phase yielding in more than one CCS value of a
115
compound and, therefore, in a new characteristic compound parameter, the
116
drift time distribution intensity ratio.
117 118
MATERIALS AND METHODS
119
Chemicals. H2O for chromatographic separations was purified with a
120
Milli-Q Gradient A10 system (Millipore, Schwalbach, Germany), and solvents
121
used were of HPLC-MS-grade (Merck, Darmstadt, Germany). Deuterated
122
solvents were obtained from Euriso-Top (Saarbrücken, Germany).
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Plant Material. Leaves, stem and root bark from G. buchananii trees in
124
their natural habitats in Masheshe, Karagwe, Tanzania. In addition, root bark,
125
stem bark, branch bark, leaves and fruit from G. buchananii were collected
126
from trees in their natural habitats in Kamagambo, Karagwe, Tanzania. Fruits
127
were peeled to obtain fruit rind, flesh and seeds. All samples were dried and
128
grounded to powder. A voucher specimen of the powders were deposited at
129
the University of Idaho Stillinger herbarium (voucher # 159918). Ethanolic G.
130
kola seed extract (origin South Africa) was obtained from PepsiCo (New York,
131
USA) and G. mangostana fruit and fruit juice (Hanoju Bio Mangosteen Saft
132
Premium 100%) were purchased in a local supermarket (Freising, Germany).
133
The Hanoju Bio Mangosteen juice was freeze-dried (90 ml) to yield 10.7 g
134
powder. The fruit was opened and separated into juice, fruit bark, flesh,
135
seeds, fruit shaft and sepal and freeze-dried, respectively. G. cambogia whole
136
fruit capsules (500 mg per capsule) as food supplement were purchased via
137
Amazon.
138
Extraction and Isolation. Extraction of G. buchananii seed powder and
139
MPLC separation was performed as described for root, leaf and bark
140
powder.30-33 14 fractions (M1-M14) were collected, concentrated under
141
reduced pressure and freeze-dried. 12 was isolated from fraction M5 and 13
142
from M6. Chromatography of MPLC fraction 5 was performed using a RP
143
column (10 250 mm, phenylhexyl, 5 μm; Phenomenex, Aschaffenburg,
144
Germany) as the stationary phase. The effluent (4.2 ml/min) was monitored at
145
270 nm and an isocratic gradient consisting of a mixture (53/47, v/v) of
146
aqueous HCO2H (0.1% in H2O) and MeOH was applied. Collected fractions
147
were concentrated under reduced pressure and freeze-dried twice, affording 6
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(2R,3S,2''R,3''R)-GB-2 7''-O-β-D-glucopyranosyl-6''''-malonic acid (12, Figure
149
1): colorless powder; UV (MeOH) λmax = 335, 288, 227, 206 nm; CD (MeOH,
150
0.66 mmol/L): λmax (ΔƐ) = 351 (+1.4), 309 (-3.2), 283 (+11.6), 236 (-5.8), 232 (-
151
4.9), 217 (-11.6), 203 (-0.2); HRESIMS m/z 821.1568 [M-H]- (calcd for
152
C39H33O20, 821.1565); 1H NMR (DMSO-d6, 27 °C, 500 MHz) data, see Table
153
1; 13C NMR (DMSO-d6, 27 °C, 125 MHz) data, see Table 2.
154
13 was obtained from M6 by semipreparative HPLC (4.2 ml/min, 270 nm)
155
using a ThermoHypersil ODS (10 250 mm, 5 μm; Kleinostheim, Germany)
156
column as the stationary phase and a mixture (62/38, v/v) of aqueous HCO2H
157
(0.1% in H2O) and MeOH, and the MeOH content was linearly increased to
158
41% within 20 min. Collected fractions were concentrated under reduced
159
pressure and freeze-dried twice, affording (2R,3S,2''R,3''R)-GB-1 7''-O-β-D-
160
glucopyranoside (13, Figure 1): colorless powder; UV (MeOH) λmax = 338,
161
289, 226 nm; CD (MeOH, 0.49 mmol/L): λmax (ΔƐ) = 369 (+2.0), 315 (-4.3),
162
287 (+9.1), 249 (-4.2), 243 (-4.0), 230 (-10.7), 226 (-10.3), 222 (+11.9), 204
163
(+0.1), 202 (-0.7); HRESIMS m/z 719.1625 [M-H]- (calcd for C26H31O16,
164
719.1612);
165
Information (SI) Table S1;
166
Table S2 (SI).
167
Ultra
1H
NMR (DMSO-d6, 27 °C, 500 MHz) data, see Supporting
Performance
13C
NMR (DMSO-d6, 27 °C, 125 MHz) data, see
Liquid
Chromatography
–
Electrospray
168
Ionisation-Ion Mobility-Time-of-Flight Mass Spectrometry (UPLC-ESI-IM-
169
TOF MS).
170
Plant material (G. buchananii and mangostana, 5 mg each) were suspended
171
in a mixture of acetonitrile and water (1:1, v/v, 1 ml), vortexed for 1 min,
172
ultrasonicated (10 min) and centrifuged (5000 rpm, 5 min). The obtained
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extracts were membrane filtered and diluted to a final volume of 1 ml. Fruit
174
and fruit juice extracts were prepared in a tenfold higher concentration.
175
Ethanolic G. kola seed extract was prepared in a concentration of 2 mg/ml
176
(acetonitrile/water 1:1, v/v). G. cambogia whole fruit capsule extracts were
177
prepared as described above (1 and 10 mg/ml) and, additionally, a solid
178
phase extraction (Chromabond C18ec, 1g, 60 Å, 45 µm, Macherey-Nagel,
179
Düren, Germany) with whole fruit capsule (1.2 g) was performed. The SPE
180
column was activated, loaded with the sample, washed with 1% acetonitrile
181
and flushed with MeOH (70 ml), the MeOH fraction collected, evaporated and
182
dissolved in MeOH (4 ml).
183
Aliquots (8 µl) of the extracts were analyzed by means of UPLC-ESI-TWIMS-
184
TOF MS on a Waters Vion HDMS mass spectrometer (Waters, Manchester)
185
coupled to an Acquity i-class UPLC system (Waters, Milford) equipped with a
186
2 x 150 mm, 1.7 µm, BEH C18 column (Waters) consisting of a binary solvent
187
manager, sample manager and column oven. Operated with a flow rate of 0.4
188
ml/min at 45 °C, the following gradient was used for chromatography: starting
189
with a mixture (10/90, v/v) of aqueous HCO2H (0.1% in H2O) and MeCN
190
(0.1% HCO2H), the MeCN content was increased to 40% within 8 min, to 80%
191
within 1 min, to 90% within 2 min, to 100% within 1 min, kept constant for 1
192
min, decreased to 10% within 1 min and finally kept constant for 1 min at 10%.
193
Scan time for the HDMSe method was set to 1.0 sec. Analyses were
194
performed in ESI sensitivity mode using the following ion source parameters:
195
capillary voltage 2.3 kV in negative mode and 3.0 kV in positive mode, source
196
temperature 120 °C, desolvation temperature 550 °C, cone gas flow 50 l/h
197
and desolvation gas 900 l/h. Data processing was performed by using UNIFI
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1.8 (Waters). All data were lock mass corrected on the pentapeptide leucine
199
enkephaline (Tyr-Gly-Gly-Phe-Leu, m/z 554.2615, [M-H]-) in a solution (50
200
pg/µl) of ACN/0.1% HCO2H (1/1, v/v). Scan time for the lock mass was set to
201
2.0 s with an interval of 0.5 min. Calibration of the Vion in the range from m/z
202
50 to 1200 was performed using a solution of the MajorMixTM (Waters). The
203
UPLC and Vion systems were operated with UNIFITM software (Waters).
204
Collision energy ramp for HDMSe was set from 20 to 30 eV. Further details of
205
the Vion IMS qTof instrument and processing and detection parameters for
206
application of the database are listed in the SI (Table S3).
207 208
RESULTS AND DISCUSSION
209
By means of UPLC-UV-ESI-TOF-MS we detected two biflavanone
210
glycosides as major constituents next to manniflavanone in G. buchananii
211
seed extract, therefore, compounds 12 and 13 were isolated and
212
characterized.
213
Compound 12 (Figure 1) was isolated as a colorless powder and
214
showed a pseudomolecular ion peak m/z 821.1568 [M-H]- (calcd. 821.1565) in
215
the HR-ESI-MS (Figure S1, SI), corresponding to the molecular formula of
216
C39H34O20. The UV spectrum was very similar to reported biflavanones30,32-38
217
and the loss of 44 as well 162 Da in the high-collision energy mass spectrum
218
(MSe) was representative for a decarboxylation and hexose unit which yielded
219
the elemental composition of GB-2 or buchananiflavanone. However, further
220
characteristic mass fragments of m/z 447, 429, 419, 403, 269, and 125
221
indicated a GB-2 aglycone (Figure S2, SI).38
222
The 1H NMR spectrum of compound 12 (Figure S4, SI) in DMSO-d6 at
223
27 °C showed sharp signals and the typical signal doubling as known from
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literature for biflavananones,30,32,33,35,38 indicating rotational conformers in a
225
ca. 3:1 ratio. The sets of aliphatic C-ring protons H-3 and H-2 as well as H-3''
226
and H-2'' coupling with each other were observed substantiating the GB-2
227
biflavananone aglycone structure. The coupling constants of J=12 Hz of these
228
protons verified their diaxial (trans) orientation. The COSY,
229
as well as 1H-13C HMBC NMR spectra (Figures S5-S8, SI) indicated the
230
presence of two carboxyl (δC 167.2, 168.1) and two carbonyl carbons (δC
231
195.5, 196.8, 197.9), 19 methine carbons, two methylene, and 14 further
232
carbons and were quite similar to that of (2R,3S,2''R,3''R)-GB-2 7''-O-β-D-
233
glucopyranoside.38 One methylene and two carboxyl groups could be
234
additionally detected which highlighted a malonic acid residue. The complete
235
assignments of 1H and
236
Tables 1 and 2. The fingerprint correlation in the 1H-13C HMBC spectrum
237
(Figure S8, SI) of both conformers between the proton H-3 and neighboring
238
carbon atom C-8'', C-8a'', and C-7'' demonstrated the intramolecular (38'')-
239
linkage of the two flavanone constituent units. The β-D-glucopyranosyl moiety
240
in both conformers was located at C-7'' as evidenced by the HMBC correlation
241
of the anomeric proton with C-7''. The couplings of the diastereotopic protons
242
H-6'''' to the carboxyl C-1''''' disclosed the linkage of the malonic acid unit to C-
243
6'''' of the β-D-glucopyranosyl moiety. The absolute configuration of 12 was
244
defined by comparison of its experimental and the published ECD curves of
245
(2R,3S,2''R,3''R)-manniflavanone 7‘‘-O-β-D-glucp and (2R,3S,2''R,3''R)-GB-2
246
7‘‘-O-β-D-glucp.38 The results showed that the ECD curve of 12 (Figure S9,
247
SI) was consistent with the ECD spectrum of the corresponding glycosides as
248
well as aglycones.30,35,38 On the basis of these data, compound 12 was
13C
13C, 1H-13C
HSQC
NMR of the two conformers at 27 °C are given in
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assigned as (2R,3S,2''R,3''R)-GB-2 7''-O-β-D-glucopyranosyl-6''''-malonic acid,
250
a
251
biflavanone glucopyranosyl malonic acid derivative.
new
compound,
an
ent-naringenin-(C3C8'')-dihydroquercetin-linked
252
Compound 13 (Figure 1) was isolated as a colorless powder and
253
showed a pseudomolecular ion peak m/z 719.1613 [M-H]- (calcd. 719.1612) in
254
the HR-ESI-MS (Fig. S10, SI), corresponding to the molecular formula of
255
C26H32O16. 1 and 2 D NMR of the major conformer, CD and UV spectroscopy
256
as well as mass spectrometry (Figures S11-S17, SI) were in line to
257
(2R,3S,2''R,3''R)-GB
258
glucopyranoside which was earlier described in unripe fruits of Clusia
259
paralicula.41
1
as
well
as
(2R,3S,2''R,3''R)-GB-1
7''-O-β-D-
260
34 isolated and fully characterized reference compounds from G.
261
buchananii were analyzed by means of UPLC-ESI-TOF-MS on a VION IMS-
262
QTOF mass spectrometer in the negative ion mode to build a database under
263
UNIFI informatics platform consisting of retention time, accurate m/z of the
264
corresponding precursors, accurate m/z of the most prominent fragment ions
265
and CCS (Table 3). It is interesting to mention that by means of IM and the
266
resulting drift time the different compound classes could be clearly separated:
267
the three xanthones showed the lowest CCS with 143-174 Å2, followed by the
268
two benzoyl glucuronosyl glycerols as well as six flavanone-C/O-glycosides or
269
flavonol-C-glycoside with CCS of 179-185 Å2 or 199-206 Å2, respectively. The
270
11 biflavonoids were evaluated with 219-225 Å2, the four polyisoprenylated
271
benzophenones with 249-250 Å2 and the four biflavanone–glycosides with
272
256-263 Å2. Only four compounds do not belong to one of the six compound
273
classes, the seco-xanthone 1,5-dimethoxyajacareubin (27) with a CCS of
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190.3 Å2, the depsidone garcinisidone-G (30) (183.2 Å2), the flavanone-
275
chromone biflavonoid preussianone (15) (194.1 Å2) and the diglycoside
276
apigenin-8-C-β-D-glcp-2''-O-L-rhap (9) (227.3 Å2) (Figure 2).
277
To check the stability of the CCS in a matrix sample, the intra- as well
278
as interday precision of the CCS of six selected compounds in a G.
279
buchananii bark extract was analyzed over a concentration range of three
280
magnitudes (Table 4). Additionally, the influence on the CCS area of different
281
solvents and formic acid ratio used for the chromatography, and therefore of
282
the ionization process, was investigated. In summary, the standard deviation
283
(SD) ranged between 0.1 and 0.9% and the average over 129 data points is
284
0.5%, which represents excellent precision of the CCS area. Consequently,
285
the CCS value is a compound specific parameter like m/z or fragments and
286
independent from the chromatographic conditions which could also be
287
combined with direct MS infusions. This is a very big advantage compared to
288
the retention time of a compound which changes with other column chemistry,
289
length, column age, flow rate, temperature as well as solvents and buffers.
290
In a next step, the established database was applied on different
291
organs of G. buchananii, including stem, branch, fruit and root bark, as well as
292
leaves, seeds and fruit flesh and the peak targeting is based on four fulfilled
293
criteria (Table 3): retention time (±0.12 min), accurate m/z of the
294
corresponding precursors (± 10 ppm), accurate m/z of the most prominent
295
fragment ions (± 10 mDa) and CCS (± 1.2 %). To the best of our knowledge,
296
branch and fruit bark as well as seeds and fruit flesh have never been
297
investigated so far. 22 compounds were detected in stem bark, mainly
298
biflavanoid
glycosides
and
their
corresponding
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flavonoid
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glycosides, polyisoprenylated benzophenones as well as the xanthone
300
jacareubin (29) (Table S4, SI). In root and branch bark the same number and
301
a very similar composition could be verified like in stem bark, with just minor
302
differences in 15 as well as ulmoside A (5), helicioside A (7) and isoprenyl
303
tetra hydroxyxanthone (28) (Table S5-S6, SI). In leaves, 25 compounds could
304
be identified, similar components to the barks mentioned so far, but no
305
xanthones instead 30 as well as the two benzoyl glucuronosyl glycerols (3, 6)
306
(Table S7, SI). The analysis of the seeds showed 16 identified compounds
307
and to be a rich source of isogarcinol (34) and mainly biflavanoid glycosides
308
and their corresponding aglycones as well as flavonoid glycosides (Table S8,
309
SI). It is interesting to mention that among others the edible part of G.
310
buchananii fruit contains the most components, namely 26. All compound
311
classes
312
benzophenones and the recently in leaves identified 1-O-4-hydroxybenzoyl-
313
3-O-α-D-glucuronosylglycerine (3). The fruit rind extract revealed 25
314
compounds with similar composition to the fruit in which garcicowin C (32),
315
garcinol (33) and 15 could not be observed, but found 27 and quercetin-6-C-
316
β-D-glcp (1).
are
represented,
highlighting
several
polyisoprenylated
317
In summary, the extracts of different organs of G. buchananii tree
318
principally showed a similar chemical composition pattern, as some
319
compounds are ubiquitous, like e.g. GB-1, GB-2, manniflavanone, -O-
320
glycoside, buchananiflavanone, isogarcinol but there were also clear
321
differences. For example: 3, 9, 10, 23 and 25 are markers for leaves,31,33 fruit
322
and fruit rind. Unique organ markers are euxanthone (26) for fruit, 6 and 30 for
323
leaves, 12 for seeds, 27 for fruit bark and 28 for branch bark. For the proof of
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324
principle, the database constructed with compounds isolated from seeds,
325
leaves, stem and root bark was applied on the corresponding extracts and on
326
additional organs not investigated so far, namely, branch bark, fruit rind and
327
fruit extract and yielded fast and very reliable results based on four fulfilled
328
criteria.
329
To strengthen the benefits of the constructed database, we applied it to
330
other Garcinia species, namely, G. kola (seeds), G. mangostana (juice, pulp,
331
seeds, sepal, fruit shaft, exo- and mesocarp) and G. cambogia (whole fruit
332
capsules). 14 compounds could be identified in an ethanolic extract of G. kola
333
seeds (Table S11, SI), whereas 7, (2R,3S,2‘‘S)-buchananiflavanon (11), 9, 26,
334
32-34 could be detected for the first time. The application of the database on
335
different organs of G. mangostana revealed six different compounds, thereof
336
five (3, 4, 6, 10 and 29) were identified for the first time in this species (Table
337
S12, SI). In contrast, the analysis of the whole fruit capsules of G. cambogia,
338
also additionally enriched via SPE, did not show any hit. This is surprising as
339
at least 33 along with other polyisoprenylated benzophenones as well as
340
xanthones have already been described in G. cambogia fruits.42
341
Positive ESI in combination with TWIM-MS could resolve or indicate
342
protomers of small molecules or different confomers or proteins,2,13,14 in
343
contrast, in the negative ESI mode such investigations are rarely found, like
344
deprotomers of ortho, meta, and para hydroxybenzoic acid and a
345
deprotonated porphyrin derivative.43,44
346
By means of NMR spectroscopy we observed rotational conformers in
347
solution for compounds 8 and 11-25,30,32,33,35,38 and, therefore, had a closer
348
look on the TWIM-MS data of these compounds. Exemplified for 17 (Figure
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3A), two different drift time species could be detected, which showing identical
350
retention time, accurate mass and fragments, but a CCS of 224.1 and 309.1
351
Å2 (Table 3) and an intensity ratio of 95.3/4.7%. To clarify if the detected drift
352
time species could be attributed to either deprotomers, rotational isomers or in
353
general to gas phase conformers, the nine fold methylated analogue of 17
354
was analyzed, only highlighting one drift time species and proposing that the
355
hydrogen bond stabilized rotational isomers 17a and 17b were transferred
356
from solution to gas phase (Figure 3B).
357
positive ion mode revealed very similar CCS values and, especially, a drift
358
time intensity distribution of 94.7/5.3%, which further strengthen our
359
suggestion. We have exemplary checked the intra- and interdaily stability of
360
the intensity of the drift time distribution of the manniflavanone (17)
361
conformers under our conditions as well as different solvents listed in Table 5.
362
Intraday a ratio of 95.2/4.8%±0.1% RSD, interday of 96.0/4.0%±0.2%RSD
363
and with different solvents and acid concentration of 96.4/3.6%±0.5% RSD
364
was determined. The mean over all (21) analyses is 96.0/4.0±0.6%RSD which
365
seems to be quite robust. Other compounds showed comparable data. The
366
data for the diverse drift time intensity distributions is summarized in Table 6.
367
With the exception of 8 and 12, basically, the denser drift time species is
368
dominating, at least 72% for 2, normally >80-90%. It is very interesting to
369
mention, that vice versa for the corresponding glycosides 8 and 12 the higher
370
CCS is dominating. This observation was further strengthened by the
371
glycosides 11 (data not shown) and 13 which showed the same shift (Figure
372
4). We propose to use all CCS values of one compound, and also the intensity
373
ratio of the conformers as a new characteristic compound parameter next to
15
UPLC-ESI-TWIMS of 17 in the
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m/z, fragments, Rt and CCS in compound identification/screening/database
375
applications to reduce false positives and strengthen the identification. By
376
plotting the mass vs. the CCS values of the major rotational conformers (in
377
case of two or more drift time species) of all compounds the strong linear
378
correlation between molecular weight and CCS can be depicted which is in
379
line with literature (Figure 2).5,7 By trend, increasing molecular weight reflects
380
in increasing CCS whereas to keep in mind that this plot was performed with
381
the major conformer. In TWIMS, bigger ions roll over the wave, whereas
382
smaller ions “surfing” on the traveling wave exciting the gas-filled mobility cell
383
earlier. By comparing manniflavanone (17) with its 7’’-O-glucoside (8), and
384
therefore 162 Da heavier, the CCS of the major conformers (224.3 261.7
385
Å2) seems to follow the general trend with increasing molecular weight
386
(Figure 5). But if we directly compare the drift time distributions of the first and
387
the second conformers the CCS values are decreasing (309.0 261.7 and
388
224.3 212.6 Å2) with increasing m/z, respectively, or more precisely, by
389
glycosylation (Figure 5). The same results could be determined for 21 and 18
390
as well as their corresponding glycosides 11 and 13 and even more for 12, the
391
glucopyranosyl malonic acid derivative of GB-2 (Table 5). Further studies on
392
the CCS values of the isomers of manniflavanone 14, 17 and 19 revealed that
393
the major drift time species of these three compounds are sharing the same
394
CCS value of 224 Å2 although the discrimination is possible via the minor
395
conformer (no minor conformer for 14, 326.2 for 19 and 309.0 Å2 for 17) and
396
therefore enables the identification of the isomers in plant extracts by means
397
of direct infusion experiments without column chromatography (Table 3 and
398
5). Another example for the influence of the stereochemistry on the CCS
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value is the comparison of (2R,3R)-taxifolin-6-C-β-D-glucopyranoside (2) and
400
its diastereomer ulmoside A (5), differing in the configuration of the agycone.
401
Interestingly, both stereoisomers showed two drift time species, probably
402
gaseous conformers, whereas the CCS of the major conformer of 2 and of the
403
minor conformer of 5 is bigger and the values differed in 4 Å2, each. Also the
404
intensity ratios of the two drift time species differed clearly. Moreover, 2
405
highlighted the possibility of a third drift time species (Figure 6). Again, the
406
identification of 2 or 5 in plant extracts would be possible by means of direct
407
infusion experiments without column chromatography and TWIMS with the
408
different CCS values and intensity ratios of the drift time species (Table 3 and
409
5).
410
Although literature and our own studies showed a high correlation between
411
m/z and CCS trusting on m/z alone to predict CCS is not adequate as many
412
ions have the same m/z but different 3D structure as demonstrated for the
413
stereoisomers (2 and 5), and, especially glycosylation increases the molecular
414
weight by 162 Da but yielded in a more compact structure and smaller CCS
415
(8, 11-13). We demonstrated that the CCS value is a robust and precise
416
compound parameter and to use all CCS values of one compound, and
417
beyond that propose the intensity ratio of the conformers as a new
418
characteristic compound parameter next to m/z, fragments, Rt and CCS. The
419
constructed database could be used as a fast, robust and reliable
420
dereplication tool and the determined CCS values could be used in public,
421
growing databases.
422 423 424
ACKNOWLEDGEMENT
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425 426
We thank PepsiCo (New York, USA) for providing the G. kola seed extract.
427
ASSOCIATED CONTENT
428 429 430
Supporting Information
431
UPLC-UV-ESI-TOF MS, MSe, CD, 1- and 2D NMR spectra of compound 12
432
and 13, and Tables summarizing all COSY, HSQC and HMBC couplings of
433
13, detailed instrument parameters of the Vion IMS qTOF and processing
434
options of the database as well as compound identification in the different
435
plant organs of G. buchananii and G. mangostana and G. kola seed extract
436
using the in house database. This information is available free of charge via
437
the Internet at http: //pubs.acs.org.
438
Notes
439
The authors declare no competing financial interest.
440 441
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Table 1. 1H NMR data of the major and minor conformers of 12 at 27 ℃ (DMSO-d6, 500 MHz) δH in ppm (multiplicity, J in Hz) H no. Flavanone-unit (I) H no. Flavanone-unit (II) aA bB aA bB I-2 5.48 (d, 12.1) 5.71 (d, 12.1) II-2‘‘ 4.88 (d, 11.2) 4.91 (d, 11.9) I-3 5.09 (d, 12.1) 4.48 (d, 12.1) II-3‘‘ 4.25 (d, 11.2) 3.99 (d, 11.9) I-6 5.89 (d, 2.1) 5.84 (d, 1.6) II-6‘‘ 6.22 (s) 6.40 (s) I-8 5.77 (d, 2.1) 5.82 (d, 1.7) II-2‘‘‘ 6.81 (d, 2.0) 6.85 (d, 1.5) e I-2‘ 7.23 (d, 8.2) 7.09 (d, 8.3) II-5‘‘‘ 6.65 (d, 8.2) e I-3‘ 6.61 (d, 8.2) 6.74 (d, 8.3) II-6‘‘‘ 6.68 (dd, 2.0, 8.3) I-5‘ 6.61 (d, 8.2) 6.74 (d, 8.3) I-6‘ 7.23 (d, 8.2) 7.09 (d, 8.3) I-5-OH 12.08 (s) 11.97 (s) δH in ppm (multiplicity, J in Hz) H no. Glucopyranoside-unit H no. Malonic acid-unit aA bB aA bB d 1‘‘‘‘ 4.73 (d, 7.0) 5.02 (d, 7.8) 2‘‘‘‘‘ 3.34 (s) 3.35 2‘‘‘‘ 3.33c 3.12c 3‘‘‘‘ 3.33c 3.28c c 4‘‘‘‘ 3.17 3.13c 5‘‘‘‘ 3.67 (m) 3.67d e 6‘‘‘‘α 4.06 (dd, 7.4, 11.9) e 6‘‘‘‘β 4.37 (d, 10.9) Sets A and B are respectively in an intensity ratio of (~1:0.3) in 12. Additional OH signals as brs for 4', 3''' and 4''' at 11.71, 8.96, 5.75 and 4.70 ppm. aA represents major conformer of 12 at 27 ℃, bB represents minor conformer of 12 at 27 ℃, coverlapped with H O peak, assigned with COSY and HSQC 2 experiments. doverlapped with major signal, assigned with HSQC experiments. e not assignable, probably overlapped with signals of major conformer.
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Table 2. 13C NMR data of the major and minor conformers of 12 at 27 ℃ (DMSO-d6, 125 MHz) δC in ppm (C-Type) C no. Flavanone-unit (I) C no. Flavanone-unit (II) aA bB aA bB I-2 82.0 (CH) 81.3 (CH) II-2‘‘ 83.1 (CH) 82.8 (CH) I-3 46.7 (CH) 47.6 (CH) II-3‘‘ 72.1 (CH) 72.2 (CH) I-4 196.8 (C) 195.5 (C) II-4’’ 197.9 (C) 197.9 (C) I-4a 101.1 (C)c 101.4 (C) II-4a’’ 101.9 (C) 101.4 (C)c I-5 163.6 (C) 163.7 (C) II-5’’ 161.9 (C) 162.2 (C) I-6 95.9 (CH) 96.0 (CH) II-6’’ 96.2 (CH) 96.2 (CH) I-7 166.3 (C) 166.2 (C) II-7’’ 162.9 (C) 162.3 (C) I-8 94.8 (CH) 94.7 (CH) II-8’’ 102.4 (C) 102.5 (C) I-8a 162.8 (C) 162.7 (C) II-8a‘‘ 158.9 (C) 159.4 (C) I-1‘ 127.1 (C) 127.9 (C) II-1‘‘‘ 128.0 (C) 127.9 (C) d I-2‘ 129.8 (CH) 128.8 (CH) II-2‘‘‘ 115.1 (CH) 115.7 (CH)e I-3‘ 115.0 (CH) 114.8 (CH) II-3‘‘‘ 144.8 (C) 145.0 (C) I-4‘ 157.7 (C) 157.7 (C) II-4‘‘‘ 145.6 (C) 145.1 (C) I-5‘ 115.0 (CH) 114.8 (CH) II-5‘‘‘ 115.2 (CH)d 115.2 (CH)e I-6‘ 129.8 (CH) 128.8 (CH) II-6‘‘ 117.8 (CH) 119.0 (CH) δC in ppm (C-Type) C no. Glucopyranoside-unit C no. Malonic acid-unit aA bB aA bB f 1‘‘‘‘ 99.9 (CH) 99.7 (CH) 1‘‘‘‘‘ 167.2 (C) 2‘‘‘‘ 72.9 (CH) 73.5 (CH) 2‘‘‘‘‘ 41.9 (CH2) 41.6 (CH2) f 3‘‘‘‘ 75.9 (CH) 76.9 (CH) 3‘‘‘‘‘ 168.1 (C) 4‘‘‘‘ 69.9 (CH) 70.2 (CH) 5‘‘‘‘ 73.8 (CH) 74.0 (CH) f 6‘‘‘‘ 64.0 (CH2) *C-type was deduced from HSQC in combination with 1H experiment. aA represents major conformer at 27 ℃, bB represents minor conformer at 27 ℃, c,d,e
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interchangeable, fnot observable, probably overlapped
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Table 3. The database under UNIFI informatics platform consisting of retention time, accurate m/z of the corresponding precursors,
accurate m/z of the most prominent fragment ions and CCS of 34 isolated reference compounds of G. buchananii. compound
Quercetin-6-C-β-D-glcp (2R,3R)-Taxifolin-6-C-β-D-glcp (2R)-1-O-4-hydroxybenzoyl-3O-α-D-glucuronosyl-glycerol (2R,3R)-Aromadendrin-6-C-β-D-glcp Ulmoside A ((2S,3S)-taxifolin-6-C-β-Dglcp) (2S)-1-O-4-hydroxy-3-methoxybenzoyl-3O-α-D-glucuronosyl-glycerol Helicioside A (2R,3S,2''R,3''R)-Manniflavanone-7''-O-βD-glcp Apigenin-8-C-β-D-glcp-2''-O-L-rhap Vitexin (2R,3S,2''R,3''R)-GB-2 7''-O-β-D-glycp (2R,3S,2''R,3''R)-GB-2 7''-O- β-D-glcp-6''''malonic acid (2R,3S,2''R,3''R)-GB-1 7''-O-β-D-glycp (2R,3S,2''S,3''S)-Manniflavanone (2''R,3''R)-Preussianone (2R,3S)-Buchananiflavonol
nr
expected RT (min)
1
1.46
expected neutral mass (Da) 464.0955
2 3
1.47 1.84
466.1111 388.1006
4 5
1.86 1.86
450.1162 466.1111
6
1.95
418.1111
7 8
2.62 3.24
450.1162 752.1589
9 10 11 12
3.48 3.59 3.62 4.07
578.1636 432.1056 736.1639 822.1643
13 14 15
4.38 4.67 5.31
720.1690 590.1060 480.0693
16
5.10
588.0904
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expected fragment (m/z)
adduct
observed CCS (Å2)*
151.0037, 343.0459, 345.0616, 367.0459, 373.0565 167.0350, 345.0616, 375.0722 137.0244, 211.0612, 249.0616, 267.0722 301.0718, 329.0667, 359.0772 167.0350, 301.0718, 329.0667, 331.0823, 359.0772 108.0217,152.0115
-H
206.4
-H -H
198.6 177.8
-H -H
205.7 194.8
-H
185.2
259.0612, 269.0455 151.0037, 437.0878, 445.0565, 463.0671 293.0455, 311.0561, 413.0878 283.0612, 311.0561, 341.0667 403.0823, 429.0616, 447.0722, 447.0722, 429.0616, 777.1672
-H -H
205.5 263.3
-H -H -H -H
227.3 196.4 259.6 256.9
431.0772, 557.1089, 579.0933 435.0722, 445.0565, 463.0671 149.0244, 217.0142, 341.0667, 461.0514, 311.0561, 435.0722, 437.0878, 445.0565, 461.0514, 463.0671
-H -H -H
256.4 224.3 194.1
-H
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(2R,3S,2''R,3''R)-Manniflavanone (2R,3S,2''R,3''R)-Manniflavanone, conformer (2R,3S,2''R,3''R)-GB-2 (2R,3S,2''R,3''R)-Isomanniflavanone (2R,3S,2''S)-Buchananiflavanone (2R,3S,2''R,3''R)-GB-1 (2R,3S,2´´S)-GB-2a (2R,3S)-Morelloflavone (2R,3S,2''S)-GB-1a (2R,3S)-Volkensiflavone Euxanthone 1,5-Dimethyoxyajacureubin 2-Isoprenyl-1,3,5,6-tetrahydroxyxanthone Jacareubin Garcinisidone G Paucinone C Garcicowin C Garcinol Isogarcinol
17a 17b
5.10 5.10
590.1060 590.1060
18 19
5.77 6.19
574.1111 590.1060
20
6.45
574.1111
21
6.51
558.1162
22 23 24 25 26 27 28 29
7.09 7.20 8.02 8.09 9.39 9.59 9.77 9.85
558.1162 556.1006 542.1213 540.1056 228.0423 356.1260 328.0947 326.0790
30 31 32 33 34
9.90 10.30 11.30 11.64 12.69
358.1053 634.3506 600.3451 602.3607 602.3607
285.0405, 435.0722, 463.0671 435.0722, 437.0878, 463.0671, 479.0620 296.0326, 419.0772, 447.0722 285.0405, 435.0722, 463.0671, 445.0565 285.0405, 311.0197, 421.0929, 447.0722 269.0455, 296.0326, 403.0823, 431.0772 269.0455, 295.0248, 431.0772 401.0667, 403.0823, 429.0616 295.0248, 389.1031, 415.0823 151.0037, 387.0874, 413.0667 210.0322 108.0217, 123.0452, 231.0663, 272.0326 267.0299, 293.0455, 307.0612, 309.0405 137.0244, 176.0843, 298.0847 109.0295, 497.3272 329.2122, 409.1657 465.3374, 481.3323, 555.3480 108.0217, 109.0295, 465.3374
* CCS for major conformer
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-H -H
224.2 309.1
-H -H
222.4 224.5
-H
221.9
-H
224.9
-H -H -H -H -H -H -H -H
220.4 218.5 220.9 219.1 143.2 190.3 169.9 173.6
-H -H -H -H -H
183.2 249.8 249.4 249.2 248.6
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Table 4. CCS determination of the major conformer of six selected compounds in G. buchananii bark extract and solvents used. analysis
compoud intradaya
CCS expected CCS observed 1 2 3 4 5 6 SD [%]
2 198.6 200.5 199.9 199.7 198.5 197.3 196.8 0.8%
21 224.9 226.1 225.3 224.7 223.7 223.1 223.4 0.6%
18 222.4 224.1 223.7 223.3 222.4 222.4 222.6 0.5%
17 224.2 224.9 224.2 224.5 224.0 222.9 223.2 0.4%
20 221.9 222.8 219.5 221.3 221.8 222.2 221.3 0.6%
34 248.7 250.5 250.4 250.2 249.9 248.5 248.8 0.6%
221.9 223.0 221.5 222.6 222.0 222.7 0.9%
220.6 220.4 220.1 221.0 220.4 220.5 0.7%
248.9 247.6 248.2 248.5 248.6 249.9 0.3%
interdayb
CCS observed 1 2 3 4 5 6 SD [%]
198.6 198.8 199.4 199.6 199.1 198.0 0.3%
223.4 223.5 223.7 223.8 223.1 223.8 0.7%
221.9 222.1 222.3 221.3 222.0 222.1 0.3%
concentrationsc
0.1 µl 1.0 µl 10.0 µl SD [%]
CCS observed 1 2 3 4 5 6 7 SD [%] run 1 2
n.d. 198.8 198.7 0.1%
199.0 198.0 197.2 198.4 196.9 196.7 198.4 0.6%
226.1 225.1 223.7 0.5%
224.2 224.5 223.7 223.2 224.0 223.6 224.1 0.5%
223.9 222.6 222.4 0.5%
223.9 223.9 224.2 0.1%
different
solventse
222.6 221.6 220.5 220.0 220.8 220.4 222.1 0.8%
223.7 224.0 223.1 221.9 222.7 222.2 223.3 0.7%
A 0.1% FA 0.1% FA
n.d. 222.1 221.8 0.1%
221.5 222.1 219.8 219.9 220.3 220.3 222.5 0.7% B ACN MeOH
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n.d. 249.7 248.9 0.4%
250.3 248.5 248.6 247.5 250.3 246.4 249.5 0.6%
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3 4 5 6 7
H 2O 1% FA 1% FA H 2O 1% FA
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ACN ACN 1% FA in ACN MeOH 1% FA in MeOH
Standard Deviation, SD [%]; a six injections; b six injections 11 days later; c 0.1, 1 and 10 µl injections; d n.d. not detected; e the following solvents were used.
Table 5. CCS and ratio of CCS of selected compounds. compound ESI neg
CCS peak 1
response peak 1
ratio peak 1 %
CCS peak 2
response peak 2
ratio peak 2 %
21 18 23 4 17 22 20 16 8 19 12 1 5 2
223.7 222.4 218.9 205.1 224.3 221.1 221.8 221.1 212.6 223.6 205.1 204.8 194.3 198.7
2694701 6285892 1459946 1614750 7796276 583662 2495813 905930 122314 2086970 31488 1002479 282444 3499230
94.9 86.1 92.8 97.1 95.3 91.3 95.5 90.2 2.6 98.3 11.1 94.9 80.6 72.3
336.8 330.3 300.3 289.1 309.0 320.7 303.7 319.3 261.7 326.2 258.2 283.0 287.5 283.3
144546 1012608 113727 48675 382972 55604 117994 98850 4633952 35391 251342 54242 68039 1338972
5.1 13.9 7.2 2.9 4.7 8.7 4.5 9.8 97.4 1.7 88.9 5.1 19.4 27.7
ESI pos 17
226.37
5143482
94.7%
310.95
287531
5.3%
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FIGURE LEGENDS Figure 1. Chemical structures of compounds 12 and 13. Figure 2. Correlation between mass of G. buchananii compounds and the TWIMS-derived CCS values. Figure 3. Drift time distributions of (A) 17a and 17b and (B) nonamethly-17. Figure 4. Drift time distributions of (A) 13a and 13b, (B) 12a and 12b and (B) 8a and 8b. Figure 5. Drift time distributions of (A) 17a and 17b and (B) 8a and 8b. Figure 6. Drift time distributions of (A) 2a and 2b and (B) 5a and 5b.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6
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for TOC only
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