Preparation and preliminary application of 5-HMF@SiO₂ micro-particles

Abstract

A new approach for the surficial-modification of silica with 5-HMF as a functional molecule was first designed. The infrared spectrum, X-ray photoelectron spectroscopy and elemental analysis showed that the modified-SiO₂ particles were successfully established. Full dispersion of SiO₂ and the introduction of gallic acid were confirmed to be favorable for the 5-HMF content. The retention behavior of bovine serum albumin on the modified-SiO₂ particle suggested that the novel particles could serve as a promising stationary phase on the identification of the particular proteins.

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1. Introduction

5-Hydroxymethylfurfural (5-HMF) is a furan-based compound derived from the dehydration of fructose or glucose, present in coffee, baking products and intravenous fluids.¹ 5-HMF can be utilized as an intermediate for valuable chemicals and fuels instead of fossil sources such as 2,5-dihydroxymethylfuran, 2,5-bis (hydroxymethyl) tetrahydrofuran, 2,5-diymethylfuran and 2,5-furandicarboxylic acid.² Consequently, many studies have focused on the conversion of 5-HMF by fructose or glucose. Metal catalysts, ionic liquids and two-phase system have achieved significant progress on high selectivity and efficient conversion.³ 5-HMF has also been revealed to possess various pharmacological activities, for instance, anti-oxidant and anti-proliferative activity, modifying intracellular sickle haemoglobin, inhibiting sickling of red blood cells, protection of acute hypobaric hypoxia and enhance cognitive function.⁴ 5-HMF can be detected in processed Fructus Corni, a Chinese medicine used to invigorate the liver and kidney; it was also presented in processed steamed ‘Rehmanniae Radix’ for several diseases such as anemia and diabetes.⁵ Although some research found the human colon cancer cell line CaCo-2, the human epithelial kidney cell line HEK 293, and the mouse lymphoma cell line L5178Y showed DNA damage in the presence of 5-HMF, the contradictory results maybe caused by 5-sulfooxymethylfurfural, which is a more harmful metabolite of 5-HMF.⁶ Therefore, more study of 5-HMF is needed.

Inorganic/organic hybrid particles based on the surface modification of inorganic fillers have attracted increasing attention because of their combination of inorganic materials and organic molecules, and have been applied in numerous aspects of catalysis, materials, pharmaceuticals, electrochemical sensors and chromatography.⁷ As an important part of inorganic particles, silica has attracted considerable interest for its significant properties such as excellent mechanical properties, high specific surface area, facile synthesis and commercial availability.⁸ In addition, the presence of silanol groups on the surface of silica gel is in favor of chemical modification.⁹ Silane coupling agents have been used on a large scale for the surface modification of silica gel for their unique structural function. Silicon ether groups can react with silica gel under moderate conditions, and the terminal groups (including vinyl, epoxy, methacryl, amino, mercapto, and chlorine) can react with many types of organic compounds. In that way, inorganic silica has some organic functions. At present, great efforts have been placed toward fabrication to expand the properties and applications of silica-based composites by assembling small organic molecules on the surface,¹⁰ many of them demonstrated excellent separation as stationary phases in liquid chromatography.¹¹

Although many types of hybrid particles have served in various areas, there has been little study on protein recognition. Herein, we describe an appropriate strategy for the fabrication of 5-HMF@SiO₂ microspheres, and attempt to expand its applications to protein recognition. As illustrated in Scheme 1, 5-HMF@SiO₂ micro-particles were prepared through five simple and convenient reactions. Gallic acid was introduced to enhance the density of 5-HMF using its three phenolic hydroxyl groups reacting with 5-HMF bromide. N-(2-Aminoethyl)-N′-[3-(dimethoxymethylsilyl)propyl]-1,2-ethanediamine (HD-702), a silane coupling agent, was used as a linker for SiO₂ and the gallic acid derivative contained 5-HMF, which also served to decrease the impact of SiO₂ to 5-HMF by its ten-atom long-chain. First, compounds 1 and 2 were synthesized by concise esterification and bromination. Intermediate 3 was obtained by the etherification of compound 1 with 2. The aminolysis of intermediate 3 with N-(2-aminoethyl)-N′-[3-(dimethoxymethylsilyl)propyl]-1,2-ethanediamine gained the critical organosilylated ligand 4. The target 5-HMF@SiO₂ micro-particle was finally prepared by hydrolysis with 7 μm silica gel. The target particle was determined by infrared spectroscopy (IR), elemental analysis (EA), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption and desorption analysis. The synthesized particle was used as a novel stationary phase in liquid chromatography for preliminary protein recognition of bovine serum albumin.

Scheme 1 Synthetic strategy for 5-HMF@SiO₂.

2. Experimental sections

2.1. Materials

All reagents and solvents were purified and dried using standard techniques. The melting points were determined on an X-4 apparatus without correction. The infrared (IR) spectra were obtained on a Shimadzu FT-IR 440 spectrometer in the 4000–500 cm⁻¹ range. The mass spectra were performed on a Shimadzu GC-MSQP 2010 instrument (Shimadzu, Japan). ¹H NMR and spectra were obtained on a Bruker AVANCF 400 MHz instrument with TMS as the internal standard. The chemical shift multiplicities were reported as follows: s, singlet; d, doublet; t, triplet; m, multiplet. XPS was carried out on a Kratos AXIS ULtrabld energy dispersive X-ray spectrometer (Manchester, England). Elements analysis was measured on vario MACRO cube Elementar (Hanau, Germany). High-resolution mass spectra were obtained on a Shimadzu HPLC-IT-TOF-MS (Shimadzu, Japan).

2.2. The preparation of the samples

2.2.1. Preparation of gallicin (1).

To a solution of gallic acid (3.00 g, 17.6 mmol) in methanol was added concentrated hydrochloric acid (6 mL). The solvent was evaporated after reflux for 4 h and the residue was placed in a vacuum overnight to afford the pure product (2.61 g, 80.0% yield). White solid; mp: 200–201 °C; ESI-MS (m/z): 183.0413 [M]⁺. ¹H NMR (400 MHz, CD₃OD): δ 7.04 (s, 2H, –ArH̲), 3.82 (s, 3H, –OCH̲₃).

2.2.2. Preparation of 5-(bromomethyl) furan-2-carbaldehyde (2).

Trimethylbromosilane was added to a solution of 5-hydroxymethylfurfural (1.26 g, 10.0 mmol). The resulting solution was stirred at r.t. for another 4 h. The reaction was terminated using a saturated NaHCO₃ solution. The organic phase was washed with water (1 × 100 mL) and brine solution (2 × 50 mL), dried over anhydrous Na₂SO₄, and evaporated to obtained 5-(bromomethyl) furan-2-carbaldehyde (1.46 g, 77.2% yield). Brown solid; EI-MS (m/z): 187.9 [M]⁺. ¹H NMR (400 MHz, CDCl₃): δ 9.62 (s, 1H, –CH̲O), 7.20 (d, J = 3.6 Hz, 1H, –CH=CH̲CCHO), 6.60 (d, J = 3.6 Hz, 1H, –CH̲=CHCCHO), 4.50 (s, 2H, –CH̲₂Br).

2.2.3. Preparation of compound (3).

To a solution of gallicin (0.41 g, 2.2 mmol) in DMF was added anhydrous K₂CO₃ (1.52 g, 11.0 mmol). After stirring for 0.5 h, KI (1.28 g, 7.7 mmol) and compound 2 (1.46 g, 7.7 mmol) were added to the solution. The mixture was filtered after heating at 80 °C for 15 h. The solution was diluted with water and extracted by ethyl acetate. The organic phase was washed with brine solution (2 × 50 mL), dried over anhydrous Na₂SO₄, and evaporated. The residue was purified by column chromatography (petroleum ether : ethyl acetate = 2 : 3). Orange solid; ESI-MS (m/z): 507.0955 [M]⁺. ¹H NMR (400 MHz, CDCl₃) δ 9.67 (s, 2H, –CHO), 9.59 (s, 1H, –CHO), 7.43 (s, 2H, –ArH), 7.27 (d, J = 3.6 Hz, 2H, –CH=CH̲CCHO), 7.18 (d, J = 3.5 Hz, 1H, –CH=CH̲CCHO), 6.69 (d, J = 3.6 Hz, 2H, –CH̲=CHCCHO), 6.58 (d, J = 3.5 Hz, 1H, –CH̲=CHCCHO), 5.18 (s, 4H, –CH̲₂Br), 5.17 (s, 2H, –CH̲₂Br), 3.94 (s, 3H, –OCH̲₃).

2.2.4. Preparation of compound (4).

HATU (0.68 g, 1.8 mmol) was added to a mixture of compound 3 (0.51 g, 1.0 mmol) and HD 702 (0.25 g, 1.0 mmol) in THF; the solution was stirred at r.t. for 6 h. The solvent was evaporated and washed with dried methanol and DMSO to obtain the product. ¹H NMR (400 MHz, DMSO-d₆): δ 8.33 (s, 1H), 6.88 (s, 2H), 6.66 (s, 1H), 3.51 (s, 3H), 2.51 (s, 10H), 1.36 (s, 2H), 0.86 (s, 1H).

2.2.5. Purification of silica gel. Silica gel (7.50 g, 7 μm) was dispersed in 2 M HCl (150 mL) and heated under reflux for 3 h. The mixture was cooled, poured in tri-distilled water and the supernatant was abandoned. The procedure was repeated until a neutral solution obtained. Silica gel was filtered and dried under 105 °C.

2.2.6. Preparation of 5-HMF@SiO₂.

2.2.6.1 General procedure A for 5-HMF@SiO₂-1. To a solution of compound 4 (0.5 g) in ethanol (50 ml) was added silica gel (2.0 g, 7 μm). The mixture was heated at 70 °C for 8 h; filtered; successively washed with dimethyl sulfoxide, tri-distilled water and methanol; and dried at 60 °C.
2.2.6.2 General procedure B for 5-HMF@SiO₂-2. To a solution of compound 4 (0.5 g) in toluene (500 ml) was added silica gel (2.0 g, 7 μm), the mixture was heated under reflux for 8 h; filtered; successively washed with dimethyl sulfoxide, tri-distilled water and methanol; and dried at 60 °C.

2.3. Column packing

5-HMF@SiO₂-2 micro-particle was homogenised with tri-distilled water and packed into stainless steel columns (50 mm × 4.6 mm) as the stationary phase. For comparison, the SiO₂ were also pumped into the columns with the same dimensions.

2.4. Procedure of chromatography

A 2.5 × 10⁻⁴ TFA was used as the mobile phase in the chromatography experiments to investigate the retention behaviour of BSA. Chromatography was performed at a detection wavelength of 284 nm with a flow rate of 0.2 mL min⁻¹ and 1.0 mL min⁻¹.

3. Results and discussion

3.1. Preparation of 5-HMF@SiO₂

The synthetic route is shown in Scheme 1. Gallic acid was catalyzed by hydrochloric acid under reflux in methanol to afford gallicin (1). The bromination of 5-hydroxymethylfurfural by trimethylbromosilane obtained compound 2. The high resolution mass spectrum (Fig. S5–S7†) revealed mono-substituted (m/z 291.0516), bi-substituted (m/z 399.0741) and tri-substituted (m/z 507.0955) products of gallicin. A great excess compound 2 was beneficial to form the tri-substituted product of gallicin, finally, improving the concentration of 5-hydroxymethylfurfural in 5-HMF@SiO₂. 5-HMF@SiO₂ was obtained by two different conditions, ethanol exactly dissolved 4 and a great excess volume of toluene served as the solvents. The reactions were performed at 70 °C and reflux temperature of toluene. 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2 were obtained separately using the abovementioned two methods. To remove the unreacted components, surface-modified SiO₂ particles were washed successively with dimethylsulfoxide, tri-distilled water and methanol.

3.2. Characterization of 5-HMF@SiO₂

A comparison of the IR spectra between original and surface-modified SiO₂ shown in Fig. 1 confirmed the relationship and distinction between SiO₂ and 5-HMF@SiO₂. In the spectrum of the original SiO₂ particles, the characteristic absorption peak at 3447 cm⁻¹ in the spectrum was assigned to the –OH group. The vibration band of 1101 cm⁻¹ belonged to the Si–O asymmetric stretching band. Moreover, the vibration peaks at 467 and 797 cm⁻¹ were attributed to the Si–O bond rocking and bending, respectively. The characteristic peaks of 5-HMF@SiO₂ at 2929 and 2856 cm⁻¹ were assigned to the C–H asymmetric and symmetric stretching vibration of –CH₂. The stretching vibration of C=O in 5-HMF appeared at about 1650 cm⁻¹. These new peaks revealed the successful grafting of SiO₂ particles.¹²

Fig. 1 IR spectra of SiO₂, 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2.

Furthermore, XPS was performed to investigate the elements, functional groups and the difference between the original and surface-modified SiO₂. Fig. 2 showed that original silica gel particle exhibited Si (Si 2s and Si 2p) and O peaks and a C signal; the last peak was assigned to adventitious contamination. The silicon signals were the result of the silicon oxide layer and the underlying silicon substrate. Moreover, the O 1s peak at about 530 eV was also assigned to silicon oxide. The both processed samples showed C, O, and Si signals, but they also showed a N 1s peak at about 400 eV.

Fig. 2 XPS curves of SiO₂, 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2.

The weak peak of N 1s at 397 eV in 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2 indicated that surface-modified SiO₂ contained N compared to the original SiO₂. The N 1s and C 1s core-level spectrum in Fig. 3a–d further revealed the difference between the three particles. The C 1s spectrum was curve-fitted with four peaks at about 284.6, 285.6, 288.1 and 290.0 eV, which were attributed to C–C/C–H, C–O, O=C, and π–π* species, respectively. The N 1s spectrum was resolved into two peaks, major 398.4 and minor 400.1 eV. These suggested that the surface modification of SiO₂ was successful. In addition, the XPS results in Fig. 3c also showed that the nitrogen content in 5-HMF@SiO₂-2 was apparently higher than that of 5-HMF@SiO₂-1. This meant that the great excess volume and reflux temperature of toluene in procedure B benefited the content of 5-HMF in 5-HMF@SiO₂.

Fig. 3 XPS curves of C 1s and N 1s for SiO₂, 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2 ((a) XPS curve of C 1s; (b) fitted-curve for C 1s spectral region; (c) XPS curve of N 1s; and (d) fitted-curve for N 1s spectral region).

The comparison of elemental composition for SiO₂, 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2 was shown in Table 1. The nitrogen and carbon contents in 5-HMF@SiO₂ were higher than that of SiO₂ after surface-modification. In addition, a comparison between 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2 also suggested that the fully-dispersed SiO₂ of procedure B was conducive to the 5-HMF content in 5-HMF@SiO₂. However, the low-proportion of nitrogen directed to a low amount of linker on the surface of SiO₂, highlighting the need for further study to increase the content of the modified compounds.

Table 1 Elemental composition of SiO₂, 5-HMF@SiO₂-1 and 5-HMF@SiO₂-2

Sample	Element
	N [%]	C [%]	H [%]	C/N	C/H
SiO2	0.13	0.35	0.216	2.7164	1.6355
5-HMF@SiO2-1	0.24	1.15	0.355	5.7916	3.2394
5-HMF@SiO2-2	0.47	3.22	0.696	6.7979	4.6230

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The microscopic pore structure was measured by nitrogen adsorption and desorption analysis. The parameters were shown in Table 2. The BET surface area (S_BET), Langmuir surface area (S_Langmuir) and total pore volume (V_p) of modified silica gel were all lower than those of original silica, indicating that the attachments were packed in the mesopores or adhered to the surface of the silica gels. A comparison between the two grafted particles also showed that procedure B was more suitable for surface-modification than procedure A.

Table 2 Nitrogen adsorption/desorption analysis

Sample	SBET (m^2 g^−1)	SLangmuir (m^2 g^−1)	Vp (mL g^−1)
SiO2	220.00	326.12	0.54
5-HMF@SiO2-1	74.32	108.28	0.43
5-HMF@SiO2-2	34.98	51.03	0.38

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3.3. Retention behaviour

Bovine serum albumin was reported to conjugate with 5-HMF.¹³ In this section, the more sufficiently modified silica-based particles, 5-HMF@SiO₂-2, was operated as a novel stationary phase to investigate its chromatographic property for the retention behaviour of bovine serum albumin. The retention time of bovine serum albumin on chromatographic columns with 5-HMF@SiO₂-2 as the stationary phase was apparently prolonged compared to that of the SiO₂ stationary phase, which were 2.02 min for 5-HMF@SiO₂-2 and 0.29 min for SiO₂ at a rate of 0.2 ml min⁻¹ (Fig. 4a). Their retention times were separately 0.42 min and 0.07 min at a rate of 1.0 ml min⁻¹. The capacity of acid-resisting of the new stationary phase was tested over a wide range of acidity, 1 × 10⁻⁶ to 1 × 10⁻² M of TFA. In addition, the column with the modified stationary phase exhibited good reproducibility after serving for two weeks.

Fig. 4 Retention behaviour of bovine serum albumin on SiO₂ and 5-HMF@SiO₂-2 ((a) 0.2 ml min⁻¹; (b) 1.0 ml min⁻¹).

4. Conclusions

In summary, we succeeded in the design of a novel stationary phase by the surface-modification of silica gel. 5-HMF was immobilized as a functional molecule on the surface of silica gel. Gallic acid was applied to increase the content of 5-HMF in 5-HMF@SiO₂. The particle was synthesized successfully but at an unsatisfactory bond rate. The retention time of bovine serum albumin on 5-HMF@SiO₂ was remarkably prolonged compared to SiO₂. Because 5-HMF exhibits a range of pharmacological activities, the retention behaviour of bovine serum albumin on the novel stationary phase showed that the prepared particles could be used as a promising new-type stationary phase for the separation and recognition of proteins analysed with a capacity of coupling with 5-HMF. Further study in this area is currently underway.

Acknowledgements

This study was supported by the National Natural Science Foundation of China (No. 81230079, 81202494).

References

1. (a) A. Ramírez-Jiménez, B. García-Villanova and E. Guerra-Hernandez, Food Res. Int., 2000, 33, 833; (b) J. A. Rufián-Henares, C. Delgado-Andrade and F. J. Morales, J. Cereal Sci., 2006, 43, 63; (c) R. L. Prior, X. Wu and L. Gu, J. Agric. Food Chem., 2006, 54, 3744; (d) T. Husoy, M. Haugen, M. Murkovic, D. Jobstl, L. H. Stolen, T. Bjellaas, C. Ronningborg, H. Glatt and J. Alexander, Food Chem. Toxicol., 2008, 46, 3697; (e) M. Ciulu, I. Floris, V. M. Nurchi, A. Panzanelli, M. I. Pilo, N. Spano and G. Sanna, J. Agric. Food Chem., 2015, 63, 4190; (f) B. E. Demirhan, B. Demirhan, C. Sönmez, H. Torul, U. Tamer and G. Yentür, J. Dairy Sci., 2015, 98, 818.
2. (a) S. P. Simeonov, J. A. S. Coelho and C. A. M. Afonso, ChemSusChem, 2012, 5, 1388; (b) T. Stahlberg, W. J. Fu, J. M. Woodley and A. Riisager, ChemSusChem, 2011, 4, 451; (c) S. Subbiah, S. P. Simeonov, J. M. Esperança, L. P. N. Rebelo and C. A. Afonso, Green Chem., 2013, 15, 2849; (d) A. D. Sutton, F. D. Waldie, R. Wu, M. Schlaf, A. Louis III and J. C. Gordon, Nat. Chem., 2013, 5, 428; (e) S. Dutta, S. De and B. Saha, ChemPlusChem, 2012, 77, 259.
3. (a) Y. Román-Leshkov, C. J. Barrett, Z. Y. Liu and J. A. Dumesic, Nature, 2007, 447, 982; (b) Y. Román-Leshkov, J. N. Chheda and J. A. Dumesic, Nature, 2006, 312, 1933; (c) H. Zhao, J. E. Holladay, H. Brown and Z. C. Zhang, Science, 2007, 316, 1597; (d) M. R. Grochowski, W. Yang and A. Sen, Chem.–Eur. J., 2012, 18, 12363; (e) C. Loerbroks, J. van Rijn, M.-P. Ruby, Q. Tong, F. Schüth and W. Thiel, Chem.–Eur. J., 2014, 20, 12298; (f) Y. Zhang, E. A. Pidko and E. J. M. Hensen, Chem.–Eur. J., 2011, 17, 5281; (g) Q. Cao, X. Guo, J. Guan, X. Mu and D. Zhang, Appl. Catal., A, 2011, 403, 98; (h) C. V. McNeff, D. T. Nowlan, L. C. McNeff, B. Yan and R. L. Fedie, Appl. Catal., A, 2010, 384, 65; (i) X. Qi, M. Watanabe, T. M. Aida and R. L. Smith Jr, Catal. Commun., 2009, 10, 1771.
4. (a) D. D. Kitts, X. M. Chen and H. Jing, J. Agric. Food Chem., 2012, 60, 6718; (b) B. Sachse, W. Meinl, Y. Sommer, H. Glatt, A. Seidel and B. H. Monien, Arch. Toxicol., 2014, 1; (c) O. Abdulmalik, M. K. Safo, Q. Chen, J. Yang, C. Brugnara, K. Ohene-Frempong, D. J. Abraham and T. Asakura, Br. J. Haematol., 2005, 128, 552; (d) A. Hannemann, U. M. Cytlak, D. C. Rees, S. Tewari and J. S. Gibson, J. Physiol., 2014, 592, 4039; (e) M. M. Li, L. Y. Wu, T. Zhao, K. W. Wu, L. Xiong, L. L. Zhu and M. Fan, Cell Stress Chaperones, 2011, 16, 529; (f) Y. Lee, Q. Gao, E. Kim, Y. Lee, S. J. Park, H. E. Lee, D. S. Jang and J. H. Ryu, Pharmacol., Biochem. Behav., 2015, 134, 57.
5. (a) L. J. K. Durling, L. Busk and B. E. Hellman, Food Chem. Toxicol., 2009, 47, 880; (b) A. S. Lin, K. Qian, Y. Usami, L. Lin, H. Itokawa, C. Hsu, S. C. Morris-Natschke and K. H. Lee, J. Nat. Med., 2007, 62, 164.
6. (a) L. J. K. Durling, L. Busk and B. E. Hellman, Food Chem. Toxicol., 2009, 47, 880; (b) I. Severin, C. Dumont, A. Jondeau-Cabaton, V. Graillot and M. C. Chagnon, Toxicol. Lett., 2010, 192, 189; (c) C. Janzowski, V. Glaab, E. Samimi, J. Schlatter and G. Eisenbrand, Food Chem. Toxicol., 2000, 38, 801.
7. (a) Y. C. Lee, M. Shlyankevich, H. K. Jeong, J. S. Douglas and Y. J. Surh, Biochem. Biophys. Res. Commun., 1995, 209, 996; (b) B. H. Monien, H. Frank, A. Seidel and H. Glatt, Chem. Res. Toxicol., 2009, 22, 1123; (c) H. Glatt, H. Schneider and Y. Liu, Mutat. Res., Genet. Toxicol. Environ. Mutagen., 2005, 580, 41.
8. (a) F. Carniato, L. Tei, A. Arrais, L. Marchese and M. Botta, Chem.–Eur. J., 2013, 19, 1421; (b) W. Chaikittisilp, A. Sugawara, A. Shimojima and T. Okubo, Chem.–Eur. J., 2010, 16, 6006; (c) A. T. Dickschat, F. Behrends, M. Bühner, J. Ren, M. Wei, H. Eckert and A. Studer, Chem.–Eur. J., 2012, 18, 16689; (d) J. Djamil, S. A. W. Segler, W. Bensch, U. Schürmann, M. Deng, L. Kienle, S. Hansen, T. Beweries, L. von Wüllen, S. Rosenfeldt, S. Förster and H. Reinsch, Chem.–Eur. J., 2015, 21, 8918; (e) N. Mizoshita, Y. Goto, M. P. Kapoor, T. Shimada, T. Tani and S. Inagaki, Chem.–Eur. J., 2009, 15, 219; (f) R. Sauer, P. Froimowicz, K. Schöller, J.-M. Cramer, S. Ritz, V. Mailänder and K. Landfester, Chem.–Eur. J., 2012, 18, 5201; (g) M. Antoniett, M. Breulmann, C. G. Göltner, H. Cölfen, K. K. Wong, D. Walsh and S. Mann, Chem.–Eur. J., 1998, 4, 2493.
9. (a) M. Abdollahi, M. Rouhani, M. Hemmati and P. Salarizadeh, Polym. Int., 2013, 62, 713; (b) F. Niepceron, B. Lafitte, H. Galiano, J. Bigarré, E. Nicol and J. F. Tassin, J. Membr. Sci., 2009, 338, 100; (c) B. Radhakrishnan, R. Ranjan and W. J. Brittain, Soft Matter, 2006, 2, 386; (d) J. A. Libera, J. W. Elam and M. J. Pellin, Thin Solid Films, 2008, 516, 6158; (e) O. Prucker, J. Rühe, Macromolecules 1998, 31, 592; (f) C. J. Brinker, R. K. Brow, D. R. Tallant and R. J. Kirkpatrick, J. Non-Cryst. Solids, 1990, 120, 26.
10. (a) J. G. Croissant, X. Cattoën, M. Wong Chi Man, J. O. Durand and N. M. Khashab, Nanoscale, 2015, 7, 20318; (b) P. M. A. Machado, L. M. Lube, M. D. E. Tiradentes, C. Fernandes, C. A. Gomes, A. M. Stumbo, R. A. S. San Gil, L. C. Visentin, D. R. Sanchez, V. L. A. Frescura, J. S. A. Silva and A. Horn, Appl. Catal., A, 2015, 507, 119; (c) M. Opanasenko, P. Štěpnička and J. Čejka, RSC Adv, 2014, 4, 65137; (d) V. Sacchetto, C. Bisio, D. F. Olivas Olivera, G. Paul, G. Gatti, I. Braschi, G. Berlier, M. Cossi and L. Marchese, J. Phys. Chem. C, 2015, 119, 24875; (e) F. Vibert, S. R. A. Marque, E. Bloch, S. Queyroy, M. P. Bertrand, S. Gastaldi and E. Besson, Chem. Sci., 2014, 5, 4716; (f) X. L. Zhang, H. Yamada, T. Saito, T. Kai, K. Murakami, M. Nakashima, J. Ohshita, K. Akamatsu and S. I. Nakao, J. Membr. Sci., 2016, 499, 28.
11. (a) T. Liang, Q. Fu, A. Shen, H. Wang, Y. Jin, H. Xin, Y. Ke, Z. Guo and X. Liang, J. Chromatogr. A, 2015, 1388, 110; (b) X. Liu, J. Feng, X. Sun, Y. Li and G. Duan, Anal. Chim. Acta, 2015, 884, 61; (c) R. Meinusch, K. Hormann, R. Hakim, U. Tallarek and B. M. Smarsly, RSC Adv., 2015, 5, 20283; (d) K. Ohyama, S. Takasago, N. Kishikawa and N. Kuroda, J. Sep. Sci., 2015, 38, 720; (e) E. Tamashima, T. Hayama, H. Yoshida, O. Imakyure, M. Yamaguchi and H. Nohta, J. Pharm. Biomed. Anal., 2015, 115, 201; (f) H. Wang and S. V. Olesik, J. Chromatogr. A, 2015, 1379, 56; (g) Q. Wang, Z. Y. Luo, M. Ye, Y. Z. Wang, L. Xu, Z. G. Shi and L. Xu, J. Chromatogr. A, 2015, 1383, 58; (h) Q. Wang, M. Ye, L. Xu and Z. G. Shi, Anal. Chim. Acta, 2015, 888, 182; (i) W. Yin, L. Cheng, H. Chai, R. Guo, R. Liu, C. Chu, J. A. Palasota and X. Cai, Anal. Bioanal. Chem., 2015, 407, 6217; (j) Y. Zhang, B. Gao, F. An, Z. Xu and T. Zhang, J. Chromatogr. A, 2014, 1359, 26.
12. Y. Yu, M. Z. Rong and M. Q. Zhang, Polymer, 2010, 51, 492.
13. G. Fang, Y. Lv, W. Sheng, B. Liu, X. Wang and S. Wang, Anal. Bioanal. Chem., 2011, 401, 3367.

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Footnotes

† Electronic supplementary information (ESI) available: GC-MS, ESI-HRMS and ¹H NMR spectra for organic compounds. See DOI: 10.1039/c6ra04792k

‡ The two authors contributed equally to this work.

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