A novel approach with controlled nucleation and growth for green

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A novel approach with controlled nucleation and growth for green synthesis of size-controlled cyclodextrin-based metal -organic frameworks based on short-chain starch nanoparticles Chao Qiu, Jinpeng Wang, Huang Zhang, Yang Qin, Xueming Xu, and Zhengyu Jin J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b03144 • Publication Date (Web): 28 Aug 2018 Downloaded from http://pubs.acs.org on August 30, 2018

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Journal of Agricultural and Food Chemistry

Graphical Abstract

Add seeds

γ-CD

Resveratrol (Res) Nucleation

Res in water Res in ethanol Res loaded MOFs in water Res loaded MOFs in ethanol

1.0

Controlled growth

0.9

A0/A

0.8

Short amylose seeds

0.7 0.6 0.5 0.4 0.3

0

2

4

6

8

Time (h)

10

12

14

16

Stabilization of Res loaded MOFs

γ-CD-MOFs

Scheme 1. Schematic representation of the size-controlled synthesis of γ-CD-MOFs through facile and green seed-mediated method.

ACS Paragon Plus Environment


1

A novel approach with controlled nucleation and growth for green

2

synthesis of size-controlled cyclodextrin-based metal−organic

3

frameworks based on short-chain starch nanoparticles

4

Chao Qiua,b,c, Jinpeng Wanga,b,c, Huang Zhanga,d, Yang Qina,b, Xueming Xua,b,c,

5

Zhengyu Jina,b,c,*

6 7

a. State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi,

8

Jiangsu 214122, China

9

b. School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu

10

214122, China

11

c. Synergetic Innovation Center of Food Safety and Nutrition, Jiangnan University,

12

Wuxi 214122, China

13

d. School of Food Engineering, Henan University of Animal Husbandry and Economy,

14

Zhengzhou, Henan, 450046, China

15

* Corresponding author:

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[email protected] (Z. Jin)).

Zhengyu

Jin (Tel:/Fax: 86-51085913299; Email:


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ABSTRACT: In this study, the nano and micro-sized cyclodextrin-based

18

metal–organic

19

short-chain starch nanoparticles as seeds through seed-mediated method. The

20

morphology, size, crystal structure, thermal and N2 adsorption properties of

21

CD-MOFs prepared at different time intervals were investigated. The scanning

22

electron microscopy results showed that the size variation from nanometer to

23

millimeter could be controlled by crystal growth time. The CD-MOFs based on

24

short-chain starch nanoparticle had higher crystallinity and N2 uptake, thus indicating

25

that the method of seed-mediated was more facile and efficient than the previous

26

approach. Resveratrol (Res) is a natural polyphenol compound that has anticancer and

27

antimicrobial activities against several pathogens. However, this compound suffers

28

from poor stability. Trans-Res rapidly isomerizes when exposed under ultraviolet or

29

visible light. The results showed that the stability of Res was substantially enhanced

30

by its encapsulation in CD-MOF crystals.

31

KEYWORDS: γ-cyclodextrin, resveratrol, seed-mediated method, cytotoxicity,

32

stability

frameworks

(CD-MOFs)

were

successfully


conducted

using


33

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INTRODUCTION

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Metal–organic frameworks (MOFs) as porous crystalline solid materials have

35

attracted increasing interest because of their diverse potential applications, including

36

gas adsorption,1-3 separation,4 molecular recognition,5,6 and drug delivery carrier.7-10

37

MOFs were composed of metal ions and multitopic organic ligands bridged by

38

coordination bonds. Compared with conventional material, MOFs have distinct

39

advantages, such as a large surface area, tunable size and ultra-high porosity.11

40

However, MOFs based on non-food grade organic linkers and transition metals

41

considered to be toxic are not acceptable for food and biomedical applications.7,12

42

Cyclodextrins (CDs) are a kind of natural cyclic oligosaccharides, which were

43

produced from enzymatic degradation of starch or starch derivates.13 Compared with

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natural α-CD and β-CD, γ-CD has larger hydrophobic cavities, higher water solubility,

45

and more favorable bioavailability. Therefore, there is a growing demand for γ-CD in

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the food, cosmetic, and biomedical industries. Recently, environment-friendly

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γ-CD-based MOFs synthesized through the coordination of γ-CD and K or Na ions

48

have been reported.14-16 In the originally reported synthesis, CD-MOFs ranging in size

49

of 40–500 µm were prepared at room temperature for a week.17 Subsequently, in order

50

to

51

cetyltrimethylammonium bromide (CTAB) as an emulsifier has been reported.18

52

However, addition of CTAB increased risk of sample contamination.8 The size of

53

MOF materials is critical for their various properties and applications. Therefore,

54

much effort has been made using microwave or ultrasound, mechanical, and

prepare

small

CD-MOFs,

a

modified

method


by

the

addition

of

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sonochemical methods to shorten the incubation time and to create smaller MOF

56

crystals.19,20 However, these methods are difficult in manufacture for cost-effective

57

and scale-up production. In the previous study, we successfully synthesized small

58

CD-MOFs with an average size of 1.8-3.9 µm though seed-mediated method.21

59

Although smaller CD-MOFs are obtained, the effective control of particle size is still

60

a difficult challenge. Based on the classical crystallization mechanism, the preciseness

61

of size control could be ensured by the controlled nucleation and growth.22 Therefore,

62

in this study, we hypothesis that the size variation from nanometers to millimeters

63

could be controlled by crystal-growth time. Furthermore, in order to obtain more

64

perfect crystalline CD-MOFs, we optimized the preparation methods of CD-MOFs

65

using seed-mediated growth combined with anti-solvent method. The addition of

66

anti-solvent induces supersaturation, and the longitudinal variations of interfacial

67

tension provide a driving force for the rapid formation of CD-MOF crystals. The

68

convenient nucleation control method developed in this study has not been reported.

69

Resveratrol (Res) is a natural nonflavonoid polyphenol compound found in plants,

70

food, and beverages.23 It has attracted great interest because of its many beneficial

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biological effects, such as lipid metabolism modulation,23 low-density lipoprotein

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protection from oxidative and free radical damage,24 and anticancer and antimicrobial

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activities.25,26 However, this compound suffers from poor stability. Res exists in two

74

isomeric forms, namely, cis and trans, and only trans-Res is biologically active.

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Trans-Res has limited stability under the influence of light, temperature and certain

76

pH levels, which can cause isomerization or degradation.27 In recent years, Res has



77

been encapsulated by employing various matrices, such as liposomes,28 proteins,29 and

78

CDs.30 However, there are as yet no reports on the encapsulation of Res in CD-MOFs

79

and the stability of Res in such a system. Thus, this study aimed to conduct the rapid

80

synthesis of size-controlled CD-MOFs based on SNPs and to demonstrate the

81

enhancement of the stability and controlled release of Res encapsulated in the

82

CD-MOFs.

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MATERIALS AND METHODS

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Materials. γ-CD and Res were obtained from Sigma Co., Ltd (Shanghai, China).

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Waxy maize starch, absolute ethanol, and methanol were purchased from Sinopharm

86

Chemical Reagent Co. Ltd. (Shanghai, China).

87

Synthesis of γ-CD-MOFs based on SNP seeds. The SNPs seeds were prepared

88

following the method of Sun et al.31 The γ-CD-MOFs were prepared by mixing γ-CD

89

(0.25 mmol) with KOH (2 mmol) in 10 mL pure water with the pre-addition of 5 mL

90

MeOH. Then 10 mg of SNP seeds were dispersed in above solution. The mixed

91

solution was filtered with a organic filter membrane (0.45 µm), followed by vapor

92

diffusion at 50 °C for 1–6 h. Afterwards, 15 mL of MeOH was added drop-wise (0.25

93

mL/min) into the solution to trigger the precipitation. The treatment conditions were

94

selected based on pre-experiment results, different amounts of MeOH (15-60 mL)

95

were selected as anti-solvent, so that the small and uniform particles would be

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obtained. Finally, the MOF crystals were collected and washed three times with

97

absolute MeOH, and dried at 45 °C overnight.

98

Characterization. The atomic force microscopy (AFM) morphology of SNPs


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seeds was observed following the method reported by Wang et al.32 The scanning

100

electron microscopy (SEM) morphology of γ-CD-MOFs obtained at different times

101

was observed using the method of Qiu et al.21 The particle size of γ-CD-MOF crystals

102

were obtained by Image J 1.45 software, accurately by choosing at least 100 MOF

103

particles from different SEM micrographs. The X-ray diffraction patterns of

104

γ-CD-MOF crystals were analyzed using a Bruker X-ray diffractometer (D2 PHASER,

105

Bruker AXS Inc., Germany) following the method reported by Chen, Tian, Sun, Cai,

106

Ma & Jin.33 The cytotoxicity of the CD-MOF crystals was determined using

107

undifferentiated Caco-2 cells as described previously.34

108

Res loading and Stabilization. The inclusion experiments were performed

109

according to the method of Moussa et al.,35 with some modifications. Briefly, 20 mg

110

γ-CD-MOF crystals obtained after 6 h were ultrasonic dispersed in 5 ml of absolute

111

ethanol. Res (4 mg) dissolved in absolute ethanol was added to obtain a final 14 µM

112

concentration in dark places. Then, the crystals were centrifuged and washed thrice

113

with absolute ethanol, and the same amount of water or absolute ethanol was added.

114

The interactions and steady state between the γ-CD-MOFs and Res were determined

115

by using an ultraviolet-visible (UV-vis) spectrophotometer (Shimadzu-2600, Kyoto,

116

Japan) at different time intervals (0–14 h).

117

In vitro release. The in vitro release of Res from Res-loaded γ-CD-MOFs was

118

determined by the dialysis method, as described by Qiu et al.36 In brief, 10 mg of

119

Res-loaded γ-CD-MOFs were redispersed in 10 mL of release media and were placed

120

into the dialysis bag (molecular cut off, 10 kDa), surrounded by 150 mL different



121

media (pH 1.2 HCl solution, pH 7.4 and 6.8 phosphate buffer) to simulate the

122

different physiological pH conditions at 37 °C with a constant gentle stirring. At

123

pre-determined time points (0-24 h), the amount of Res released in the three different

124

medium was determined by UV-vis spectroscopy (at 304 nm). The cumulative release

125

was quantified as follows: Cumulative release (%) =

126

The amount of Res released × 100 Total amount of Res

127

Statistical analysis. All the experimental data were presented as mean values ±

128

standard deviations in triplicate. Statistical significance analysis was performed by

129

Tukey's test using SPSS 17.0 software (SPSS Inc., Chicago, USA). Differences were

130

considered at a significance level of 95% (P﹤0.05).

131

RESULTS AND DICUSSION

132

Morphology and particle size of SNP seeds and γ-CD-MOF. The atomic force

133

microscopy (AFM) images and the particle size distributions of SNP seeds are shown

134

in Figure 1. The SNP seeds displayed spherical shapes, and the mean diameter was

135

approximately 80 nm based on the AFM images (Figure 1). The small SNPs with a

136

uniform size could be used as seeds for the synthesis of γ-CD-MOF. The SEM

137

morphological images and particle size distributions of the γ-CD-MOFs obtained at

138

different times (1–6 h) with and without SNP seeds are presented in Figure 2 and

139

Figure 3, respectively. In the absence of SNP seeds, the shapes of the synthesized

140

γ-CD-MOF were recorded as a uniform cubic by SEM with an average size of 3–5 µm,

141

which was consistent with previous reported with a 3–5 µm particle size

142

distribution.10 A slight increase in particle diameter was observed with the increase in


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time, thus indicating that the crystal growth was relatively slow in the absence of SNP

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seeds. However, no significant change in shape was observed in the determination

145

time (1–6 h). Interestingly, for the seed-mediated synthesis of γ-CD-MOFs, the size

146

variation from nanometer to millimeter could be controlled by crystal growth time.

147

Furthermore, the shapes of γ-CD-MOF obtained after 6 h changed from cubic to

148

cuboid (Figure 2F). To our knowledge, the morphologies of γ-CD-MOFs are almost

149

always cubic in shape, as no similar report has been made up to now. The particle size

150

of γ-CD-MOFs based on SNP seeds was in the range of 140–260 nm when the crystal

151

growth time was 1 h (Figure 3D). However, the particle size of γ-CD-MOFs obtained

152

after 3 and 6 h increased significantly in the range of 400–600 nm (Figure 3E) and

153

1–3 µm (Figure 3F), respectively. The formation of small γ-CD-MOFs based on SNP

154

seeds should experience following stages: the self-assembly forms nucleus; the crystal

155

nucleus growth and coagulation, and the aggregation of γ-CD-MOF crystals.

156

Therefore, the size variation from nanometer to millimeter could be controlled by

157

crystal growth time.

158

X-ray diffraction (XRD) analysis. The XRD patterns of the γ-CD-MOFs

159

obtained at different times (1–6 h) with and without SNP seeds are presented in Figure

160

4. The characteristic diffraction peaks of γ-CD-MOFs obtained at different times at

161

around 4.0, 5.6, 7.0, 13.2, 16.7°, consistent with the literature.8,18 The results showed

162

the crystallinity of the γ-CD-MOFs increased with the extension of the synthesis time.

163

Similarly, Liu et al.8 reported that the crystallinity of CD-MOFs increased when the

164

duration of the preparation was prolonged for 12 h. Interestingly enough, the



165

γ-CD-MOFs based on SNPs showed few times higher crystallinity as evidenced by

166

the sharp peaks in the XRD patterns. Similarly, Xu et al.,9 reported that the MOFs

167

synthesized by a seed-mediated method had high crystallinity. The reason could be

168

explained as follows. The γ-CD was easily adsorbed onto the surface of SNP seeds

169

due to the interactions of hydrogen bonds between SNPs and CDs. In this way, the

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γ-CDs would be arranged in order more easily, which could accelerate the formation

171

of the nucleus. Another possible reason could be because the the addition of seeds

172

increased the nucleation number and enabled the crystal growth process to bypass the

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most energy-intensive step.9 Therefore, the CD-MOFs based on SNP seeds showed

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higher crystallinity than the previous method.

175

Thermogravimetric analysis. For the γ-CD-MOFs without SNP seeds, the

176

thermal degradation temperature increased slightly with the increase in incubation

177

time, and the main mass loss step of the γ-CD-MOFs obtained at 1, 3, and 6 h

178

occurred in the range of 223.4 °C–332.4 °C, 223.6 °C–333.9 °C, and

179

224.9 °C–336.8 °C, respectively. However, compared with that of CD-MOFs, the

180

thermal degradation temperature of γ-CD-MOFs with SNP seeds decreased (Figure 5),

181

and their main mass loss step occurred in the range of 204.6 °C–325.8 °C,

182

217.4 °C–332.2 °C, and 223.8 °C–343.7 °C, respectively. The reduction of molecular

183

weight could be the main factor that lowered the thermal stability. Similarly, Sun et

184

al.,31 reported that SNPs displayed decreased thermal stability because of the lower

185

molecular weight than that of native starch. When the crystallization time was

186

increased from 1 to 6 h, the thermal stability of CD-MOFs with SNP seeds increased


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significantly, thus indicating that a perfect crystalline structure was formed, consistent

188

with the results on crystallinity.

189

Fourier transformation infrared spectroscopy (FTIR) analysis. The FTIR of

190

SNP seeds, γ-CD and γ-CD-MOFs are presented in Figure 6. The strong absorption

191

peak at 3700–3000 cm−1 was attributed to the O–H stretching vibration of the SNP

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seeds, γ-CD, and γ-CD-MOFs. Compared with native γ-CD, the γ-CD-MOF crystals

193

without SNP seeds had a low wavelength. However, the O–H bands of γ-CD-MOFs

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based on SNP seeds shifted to a shorter wavelength, from 3416 cm-1 (γ-CD) to 3380

195

cm-1 (1 h), 3368 cm-1 (3 h), and 3355 cm-1 (6 h), indicating that the hydrogen bonds

196

between molecular chains were stronger. This result demonstrated SNP seeds had an

197

interaction to the γ-CD-MOFs through the hydrogen bonding between molecular

198

chains. Similarly, Zhang et al.37 reported that the O–H bands shifted to a shorter

199

wavelength, indicating that hydrogen bonds were enhanced.

200

Cytotoxicity. The cell viability of CD-MOFs with and without SNP seeds and

201

CD-MOFs obtained by adding CTAB is shown in Figure 7. The CD-MOFs

202

synthesized exhibited a high viability of cells (> 98%) in a low concentration (< 500

203

µg/mL). Even with a high concentration of CD-MOFs reaching 1000 µg/mL, the

204

viability of cells was maintained above 95%. This result indicated that the CD-MOFs

205

based on SNP seeds were safe and nontoxic. To create small CD-MOF crystals, a

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modified method by the addition of CTAB was reported previously.18 However,

207

CD-MOFs synthesized by the addition of CTAB exhibited low toxicity, and the cell

208

viability decreased significantly (only about 82%) when the concentrations increased



209

from 500 µg/mL to 1000 µg/mL. Therefore, the seed-mediated method provides a

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green and safe way to fabricate CD-MOFs.

211

N2 adsorption isotherms analysis. The nitrogen adsorption and desorption

212

isotherms were determined by using the Micrometrics ASAP2010 system. Compared

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with the CD-MOFs without seeds obtained at 6 h, the γ-CD-MOFs synthesized based

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on SNP seeds obtained at 3 h and 6 h exhibited a higher N2 uptake (Figure 8).

215

However, the γ-CD-MOFs synthesized in a short time had little N2 adsorption (not

216

shown) because of imperfect crystallization, consistent with the results on crystallinity.

217

The measured pore diameter of γ-CD-MOFs synthesized were in the range of

218

2.12-3.24 nm, which shows a characteristic of typical mesoporous materials. The

219

γ-CD-MOFs with SNP seeds obtained at 6 h showed maximize BET (Langmuir)

220

surface areas of 916.2 (1228.6) m2/g, which could be due to more perfect crystalline

221

structure, indicating the porous material could be used as an delivery carriers for food,

222

medicine and biomedical industry. Similarly, Liu et al.,8 reported that the theoretical

223

BET surface areas of γ-CD-MOFs was 1030 m2/g.

224

Stabilization of Res encapsulated in γ-CD-MOF crystals. The stability of Res

225

in the CD-MOF crystals based on SNP seeds obtained after 6 h in an aqueous medium

226

and ethanol was investigated, and the results are shown in Figure 9. The UV-vis

227

spectra of the dissolved Res-loaded CD-MOFs were recorded for 14 h. The MOF

228

crystals did not absorb in the range of measures, consistent with previous reports.38

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However, Res had strong absorbance with two peaks at about 305 nm and 320 nm,

230

respectively, mainly because of the presence of the trans isomer and biologically


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inactive cis forms of Res. In the ethanol system, the difference between two peaks

232

observed was more obvious than in the aqueous solution, indicating that Res was

233

more stable in absolute ethanol. In the aqueous medium, the peak at 320 nm

234

disappeared after 2 h; this disappearance could be due to the degradation of Res.

235

Similarly, the stabilization of Res with CD was reported by Kumar et al.,38 who found

236

that Res was relatively stable in organic solvents like ethanol than in aqueous

237

solutions. Figure 10 compares the absorbance intensity reduction plots of Res and Res

238

encapsulated in γ-CD-MOF crystals in different solvents. A significant reduction was

239

observed with the increase in time, indicating that Res was quite unstable. In the Res

240

system, almost 60% of the Res degraded rapidly in an aqueous medium after 12 h

241

(Figure 10). However, only 32% of the Res was degraded in absolute ethanol. Note

242

that the γ-CD-MOF crystals slowed the rate of degradation and that only about 40%

243

and 19% of the Res was degraded in aqueous solutions and absolute ethanol,

244

respectively, at the determined time; this result could be due to the protection of

245

γ-CD-MOFs against degradation. Similarly, Moussa et al.,35 reported that the stability

246

of curcumin was enhanced because of the incorporation within the pores of the

247

CD-MOF crystals.

248

The cumulative release of Res loaded CD-MOFs. The cumulative release

249

profile of free Res and Res loaded CD-MOFs are shown in Figure 11. Compared to

250

free Res, the Res loaded CD-MOFs showd a remarkable decreased in the percent of

251

released Res (Figure 11). In the first 2 hours, the Res loaded CD-MOFs released only

252

13% of Res, showing a slow release in acidic pH (1.2). The release amounts of Res



253

increased with incubation time, and approximately 25% of the Res was released from

254

the CD-MOFs after 6 h. In contrast, the free Res showed a burst release in which

255

above 85% of Res was released in the first 6 h. For Res loaded CD-MOFs, the slow

256

release was maintained until 24 h. This slow-release behaviour of Res loaded

257

CD-MOFs could be attributed to the formation of compact structure, which could

258

restrict the Res diffusion capacity for the medium. This result suggested that

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CD-MOFs may serve as effective delivery carriers for controlled Res release systems.

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In summary, we reported the synthesis of size-controlled CD-MOFs based on

261

SNP seeds for the first time, which provided simple, green and cost effective strategy

262

to fabricate CD-MOFs. The size variation from nanometer (140–260 nm) to

263

millimeter (1–3 µm) could be controlled by crystal growth time. Compared with

264

CD-MOFs without SNP seeds, the crystallinity of the γ-CD-MOFs based on SNP

265

seeds was higher as evidenced by the sharp peaks in the XRD patterns. Therefore, the

266

method of seed-mediated is a more facile and efficient alternative to the previous

267

method. Moreover, the cell cytotoxicity results indicated that the CD-MOFs based on

268

SNP seeds were relatively safe. The stability of Res was substantially enhanced

269

because of the incorporation within the pores of the CD-MOF crystals. Furthermore,

270

Res loaded CD-MOFs exhibited a consequently sustained release within 24 h. The

271

size-controlled CD-MOFs based on SNP seeds could be used as delivery carriers for

272

drug or active component controlled-release systems.

273

Conflict of interest

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No conflicts of interest are declared for any of the authors.


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Acknowledgements

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This work was supported by Postgraduate Research & Practice Innovation

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Program of Jiangsu Province (KYCX18_1758), national first-class discipline program

278

of Food Science and Technology (JUFSTR20180203).



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Figure Captions Figure 1 Atomic force microscopy images of the short linear chain SNPs. Figure 2 SEM morphology images of γ-CD-MOF crystals obtained at different times of 1 h (A), 3 h (B), and 6 h (C), and γ-CD-MOF crystals with added SNP seeds obtained at different times of 1 h (D), 3 h (E), and 6 h (F).

Figure 3 Statistics of the particle size distributions of γ-CD-MOF crystals obtained at different times of 1 h (A), 3 h (B), and 6 h (C), and γ-CD-MOF crystals with added SNP seeds obtained at different times of 1 h (D), 3 h (E), and 6 h (F).

Figure 4 XRD of γ-CD-MOF crystals with and without added SNP seeds obtained at different times (1, 3, and 6 h, respectively).

Figure 5 Thermogravimetric analysis curves of γ-CD-MOF crystals with and without added SNP seeds.

Figure 6 Fourier transformation infrared spectroscopy curves of SNP seeds, γ-CD, and γ-CD-MOF crystals with and without added SNP seeds.

Figure 7 In vitro cell viability of Caco-2 cells against γ-CD-MOF crystals. Figure 8 Nitrogen adsorption–desorption isotherm of γ-CD-MOF crystals with and without added SNP seeds.

Figure 9 UV-visible absorption spectra of Res degradation in an aqueous medium (A: Res; B: Res-loaded γ-CD-MOF) and ethanol (C: Resveratrol; D: Res-loaded γ-CD-MOF) at different determined times (0→5: 0, 2, 4, 6, 9, and 14 h, respectively).

Figure 10 Degradation ratio of Res in an aqueous medium and ethanol at different determined times (0, 2, 4, 6, 9, and 14 h, respectively).


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Figure 11 Release profile of Res and Res loaded CD-MOFs.



Add seeds

γ-CD

Page 24 of 35

Resveratrol (Res) Nucleation


1.0

Controlled growth

0.9

A0/A

0.8

Short amylose seeds

0.7 0.6 0.5 0.4 0.3 0

2

4

6

8

10

12

14

16

Time (h)

Stabilization of Res loaded MOFs

γ-CD-MOFs

Scheme 1. Schematic representation of the size-controlled synthesis of γ-CD-MOFs through facile and green seed-mediated method.


Page 25 of 35


Figure 1 Atomic force microscopy images of the short linear chain SNPs.



Page 26 of 35

D

A

5 µm

1 µm

E

B

5 µm

C

1 µm

F

5 µm

3 µm

Figure 2 SEM morphology images of γ-CD-MOF crystals obtained at different times of 1 h (A), 3 h (B), and 6 h (C), and γ-CD-MOF crystals with added SNP seeds obtained at different times of 1 h (D), 3 h (E), and 6 h (F).


Page 27 of 35


50

A Percentage (%)

Percentage (%)

50 40 30 20 10

D

40 30 20 10

0

0 0

1

2

3

4

5

6

7

8

9

10

0

100 200 300 400 500 600 700 800 900 1000

Size (µm)

Size (nm) 50

B

E Percentage (%)

Percentage (%)

50 40 30 20

30 20 10

10

0

0 0

1

2

3

4

5

6

7

8

9

0

10

100 200 300 400 500 600 700 800 900 1000

Size (nm)

Size (µm)

50

50

C

F Percentage (%)

Percentage (%)

40

40 30 20 10

40 30 20 10

0 0

1

2

3

4

5

6

Size (µm)

7

8

9

10

0 0

1

2

3

4

5

6

7

8

9

10

Size (µm)

Figure 3 Statistics of the particle size distributions of γ-CD-MOF crystals obtained at different times of 1 h (A), 3 h (B), and 6 h (C), and γ-CD-MOF crystals with added SNP seeds obtained at different times of 1 h (D), 3 h (E), and 6 h (F).



CD-MOFs Seeds 6 h

Intensity

CD-MOFs Seeds 3 h CD-MOFs Seeds 1 h CD-MOFs 6 h CD-MOFs 3 h CD-MOFs 1 h 0

5

10

15

20

25

30

35

40

? (° ) 2θ2 (º)

Figure 4 XRD of γ-CD-MOF crystals with and without added SNP seeds obtained at different times (1, 3, and 6 h, respectively).


Page 28 of 35

Page 29 of 35


100 CD-MOFs Seeds 1h

80

CD-MOFs Seeds 3h

Weight (%)

CD-MOFs Seeds 6h

60 CD-MOFs 1h CD-MOFs 3h CD-MOFs 6h

40 20 0 0

100

200

300

400

500

600

O

Temperature ( C)

Figure 5 Thermogravimetric analysis curves of γ-CD-MOF crystals with and without added SNP seeds.

28



Relative Intensity (%)

3162

3368 3380 3371 3403 3414

4000

SNP Seeds CD

3416 3355

3500

3000

Page 30 of 35

CD-MOFs Seeds 6h CD-MOFs Seeds 3h CD-MOFs Seeds 1h CD-MOFs 6h CD-MOFs 3h CD-MOFs 1h

2500

2000

cm

1500

1000

500

-1

Figure 6 Fourier transformation infrared spectroscopy curves of SNP seeds, γ-CD, and γ-CD-MOF crystals with and without added SNP seeds.

29


Page 31 of 35


CD-MOFs 1h CD-MOFs Seeds 1h CD-MOFs 6h CD-MOFs Seeds 6h CD-MOFs CTAB 6 h

100

Cell viability (%)

80 60 40 20 0 0

250 125 500 Concentration (µg/mL)

1000

Figure 7 In vitro cell viability of Caco-2 cells against γ-CD-MOF crystals.

30



Quantity Adsorbed (cm3/g STP)

300

Page 32 of 35

CD-MOFs-6 h with SNP seeds

250 CD-MOFs-3 h with SNP seeds

200

150 CD-MOFs-3 h without Seeds

100

50 0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/Po)

Figure 8 Nitrogen adsorption–desorption isotherm of γ-CD-MOF crystals with and without added SNP seeds.

31


Page 33 of 35


B

A 1.0

1.0

0 0.8

0.6

Absorbance

Absorbance

0 0.8 5

0.4 0.2

5

0.4 0.2 0.0

0.0 -0.2 300

1.0

0.6

350

400

450

-0.2 500

300

W avelength (nm )

350

C

1.0

D

450

500

0

0.8 0

0.8

Absorbance

Absorbance

400

Wavelength (nm)

0.6 5 0.4 0.2 0.0

5 0.6 0.4 0.2 0.0

300

350

400

W avelength (nm)

450

500

300

350

400

450

500

W avelength (nm)

Figure 9 UV-visible absorption spectra of Res degradation in an aqueous medium (A: Res; B: Res-loaded γ-CD-MOF) and ethanol (C: Resveratrol; D: Res-loaded γ-CD-MOF) at different determined times (0→5: 0, 2, 4, 6, 9, and 14 h, respectively).

32



Page 34 of 35


1.0 0.9

0.8

A0/A

0.7

0.6 0.5

0.4 0.3 0

2

4

6

8

10

12

14

16

Time (h)

Figure 10 Degradation ratio of Res in an aqueous medium and ethanol at different determined times (0, 2, 4, 6, 9, and 14 h, respectively).

33


Page 35 of 35


Res loaded CD-MOFs Res

Cumulative release (%)

100

80

60

pH 6.8 pH 1.2

40 pH 7.4 20

0 0

4

8

12

16

20

24

28

Time (h)

Figure 11 Release profile of Res and Res loaded CD-MOFs.

34


A novel approach with controlled nucleation and growth for green

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