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Chinese Chemical Letters 23 (2012) 615–618

Preparation of quercetin imprinted core–shell organosilicate

microspheres using surface imprinting technique

Peng Yang a,b, Wen Dan Hou c, Hong Deng Qiu b, Xia Liu b, Sheng Xiang Jiang b,*a Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute

of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, Chinab Graduate University of the Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, China

c School of Basic Medical Sciences, Lanzhou University, Lanzhou 730000, China

Received 26 October 2011

Available online 29 March 2012

Abstract

In this work, the quercetin imprinted core–shell microspheres were prepared using silica surface imprinting technique. A simple

sol–gel procedure was used for the synthesis of the imprinted materials with 3-aminopropyltriethoxysilane as functional monomer

and tetraethyl orthosilicate as crosslinker. The SEM images indicated that the MIPs shell was successfully grafted onto the silica

surface. The characteristics of the molecularly imprinted polymers such as capacity, selectivity and absorption dynamic were

investigated by rebinding experiments. The results showed that the prepared MIPs had good imprinting effect and adsorption

amount of quercetin.

# 2012 Sheng Xiang Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Keywords: Molecular imprinting technology; Sol–gel; Surface imprinted polymers

Molecularly imprinted polymers (MIPs) are synthetic materials with artificially generated recognition sites able to

specifically rebind a target molecule in preference to other closely related compounds [1]. During the past decades

these materials have attracted much attention because of their potential applications in many fields, such as

chromatography [2], sensors [3], drug delivery, and catalysts [4].

Quercetin is probably the most extensively studied flavonoid owing to its proposed beneficial effects in a wide range

of diseases such as cardiovascular and inflammatory disorders and cancer therapy [5]. Several studies have been

reported for the determination and separation of quercetin by MIPs [6–8]. In those studies, MIPs were derived from

organic polymers synthesized from vinyl or acrylic monomers by bulk polymerization. Those polymer networks

showed high selectivity for quercetin, however, such traditional organic polymer-based MIPs have some

disadvantages, for example many recognition sites are embedded in the bulk materials which make it difficult to

remove the original templates inside and adsorb the temples outside. Moreover, organic polymer-based MIPs are

deficiency in mechanical stability for many applications and will be swelling in organic solvents.

In this paper, a simple method was proposed to synthesis silica supported core–shell MIP microspheres. After that,

the characteristics of those microspheres were investigated.

* Corresponding author.

E-mail address: sxjiang@lzb.ac.cn (S.X. Jiang).

1001-8417/$ – see front matter # 2012 Sheng Xiang Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

doi:10.1016/j.cclet.2012.02.002

P. Yang et al. / Chinese Chemical Letters 23 (2012) 615–618616

1. Experimental

Quercetin didydrate (99%) was obtained from Acros (NJ, USA). 3-Aminopropyltriethoxysilane (APTS) was from

the Chemical Industrial Corporation of Gaizhou (China). Tetraethyl orthosilicate (TEOS) was from Tianjin No. 1

Chemical Reagent Factory (China). Acetic acid and methanol were from Tianjin Chemical Reagent Factory (China);

ammonia was from Baiyin Liangyou Chemical Reagent Factory (China). Silica gel of 5 mm spherical porous particles

was made in our laboratory. Deionized water, methanol used in chromatography test were filtered through a 0.45 mm

membrane and degassed by an ultrasonic bath before use. All the reagents above are of analytical grade.

Quercetin imprinted microspheres were prepared according to the previous report [9] with a little modification.

First, 5 g of silica gel was activated in 200 mL of 10% hydrochloric acid by refluxing under stirring for 12 h. The

product was washed with deionized water to neutral and dried under vacuum at 110 8C for 12 h. Then, 68 mg of

quercetin was dissolved in the mixture of 30 mL of methanol, 0.3 mL of APTS and 5.7 mL of TEOS under stirring.

After the solution was stirred for 30 min, 1.0 g of activated silica gel and 1 mL of 3 mol/L HAc were added, the sol–gel

process was occurred. The mixture was stirred for 15 h at room temperature. After the sol–gel process, the product was

washed with methanol, methanol/ammonia (19:1, V/V) and deionized water to remove the template and reactants. The

resulting particles were dried under vacuum at 60 8C for 12 h and the MIPs were obtained.

The non-imprinted polymers (NIPs) were also prepared and treated in an identical manner according to the above

procedure except for the absence of quercetin during sol–gel process.

2. Results and discussion

The sol–gel method has been proved its exceptional potential by providing a possibility of synthesizing numbers of

new materials with high homogeneity and purity and extraordinary physical and chemical properties [10].

In this work, quercetin imprinted network was prepared using a simple sol–gel method on the surface of silica.

APTS and TEOS were used as functional monomer and crosslinker. First, the complex was formed between quercetin

and APTS mainly by hydrogen bonds, then co-hydrolyzed and co-condensed with activated silica gel in the presence

of acetic acid and water as catalyst. The film contain quercetin was formed on the surface of silica gel through –Si–O–

Si– bind. After removing the template, the imprinted film with tailor-made cavities was remained (Fig. 1).

The morphology of the MIPs was assessed by the scanning electron microscopy (SEM). As shown in Fig. 2, the

silica microspheres are regular spheres and have porous surface before sol–gel process, while the prepared MIPs are

irregular spheres and also the surface is smoother than that of silica microspheres. It can be concluded that the MIPs

shell have been successfully grafted onto the surface of the silica microspheres.

Fig. 1. Preparation of quercetin imprinted polymer using sol–gel process.

P. Yang et al. / Chinese Chemical Letters 23 (2012) 615–618 617

Fig. 2. SEM images of the silica microsphere (left) and MIPs coated silica (right).

Fig. 3. Absorption dynamic curve of the MIPs and NIPs.

Fig. 4. Binding isotherms for quercetin by MIPs and NIPs.

P. Yang et al. / Chinese Chemical Letters 23 (2012) 615–618618

Table 1

The results of selective adsorption test of quercetin and gemistein by MIPs.

Ci (mg/mL) Cfa (mg/mL) Kdb (mg/g) Kc kd

MIPs NIPs MIPs NIPs MIPs NIPs

Quercetin 0.05 0.020 0.035 37.5 10.7 9.15 3.82 2.4

Gemistein 0.05 0.043 0.045 4.1 2.8

a Ci and Cf represent the initial and final concentrations in adsorption test.b Kd refers to the distribution coefficient. Kd = [(Ci � Cf)/Cf] [volume of solution (mL)/mass of MIPs (g)].c K refers to the selectivity coefficient of MIPs. K = Kd(quercetin)/Kd(gemistein).d k refers to relative selectivity coefficient. k = K(MIPs)/K(NIPs).

The capacity and absorption kinetics of MIPs and NIPs were determined by rebinding experiments and calculated

according to the following formula:

Q ¼ ðCi � C f ÞVm

where Q is the amount of quercetin adsorbed, Ci is the initial quercetin concentration, Cf is the final quercetin

concentration, V is the total volume of rebinding aliquot and m is the mass of polymer in each aliquot.

Absorption dynamic curves were performed to evaluate the optimum binding time within 2 h (Fig. 3). The binding

isotherms were evaluated for concentration of quercetin range from 0 to 1.25 mg/mL. As shown in Fig. 4, the

imprinting factor increased with the increase in quercetin concentration. The capacity of MIPs was 6.45 mg/g that was

much higher than previous report which is 0.92 mg/g [6].

To determinate the selectivity of the MIPs, the selective adsorption test of quercetin and gemistein, which is also a

flavonoid and have a similar structure by MIPs was performed using rebinding experiments. The results in Table 1

showed that the selectivity coefficient of MIPs are much higher that of NIPs. The relative selectivity coefficient value

was 2.4, which indicated that the synthesis MIPs have high selectivity for quercetin.

3. Conclusions

A simple procedure was proposed to synthesize the quercetin imprinted core–shell organosilicate microspheres

using surface imprinting technology in this study. The material prepared here was demonstrated as being highly

selective towards quercetin. Sol–gel procedure is a convenient and rapid route for the synthesis of MIPs.

Acknowledgment

We are grateful to the National Science Foundation of China (Nos. 21175143 and 20905073) for the financial

support of this work.

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