儿茶素活性成分分子印迹聚合物的固相萃取研究

以表没食子儿茶素没食子酸酯(Epigallocatechin-gallate,EGCG)为模板分子,α-甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,在光冷引发条件下合成EGCG分子印迹聚合物,利用该聚合物制成分子印迹固相萃取柱,用于固相萃取茶叶提取物茶多酚,对萃取柱中的清洗液、洗脱剂、上载量等进行了选择.结果表明,在萃取柱上载样品之后,先用V(甲醇):V(水)＝1:9溶液进行清洗,再用V(甲醇):V(乙酸)＝9:1混合液进行目标分子的洗脱,可以得到比较纯的目标物质EGCG(色谱峰相对峰面积达92.4%),萃取柱在上载样品并进行清洗、洗脱之后,EGCG的回收率达69.3%.分子印迹柱具有较好的稳定性和耐用性能,使用20次后其选择性识别能力仍未降低,但空白印迹柱却没有这样的选择性识别能力.     

Biochemical and computational insights of adenosine deaminase inhibition by Epigallocatechin gallate

Epigallocatechin gallate, a flavonoid from Camellia sinensis possess various pharmacological activities such as anticancer, antimicrobial and antioxidant etc. Adenosine deaminase, (ADA), is a key enzyme involved in the purine metabolism, the inhibitors of which is being considered as highly promising candidate for the development of anti-proliferative and anti-inflammatory drugs. In this work we studied adenosine deaminase inhibitory activity of epigallocatechin gallate by using biophysical and computational methods. The enzyme inhibition study result indicated that epigallocatechin gallate possess strong inhibitory activity on ADA. ITC study revealed the energetics of binding. Also the binding is confirmed by using fluorescence spectroscopy. The structural details of binding are obtained from molecular docking and MD simulation studies.     

Production mechanism of proepitheaflagallin, a precursor of benzotropolone-type black tea pigment, derived from epigallocatechin via a bicyclo[3.2.1]octane-type intermediate

An unstable intermediate proepitheaflagallin B (2), a precursor of proepitheaflagallin (3), was isolated as an enzymatic oxidation product of (−)-epigallocatechin (1), and the structure of 2 was determined based on spectroscopic data. The structure and its decomposition revealed that the detailed production mechanism of proepitheaflagallin (3) via a bicyclo[3.2.1]octane-type intermediate was related to that of major black tea pigments, theaflavins.     

The chemiluminescence mechanism of 3,4-bis(3-indolyl)-1H-pyrrole-2,5-dione, and the characteristics of chemiluminescence developed in the reaction with CH(3)CNH(2)O(2)NaOH

The chemiluminescence (CL) mechanism of 3,4-bis(3-indolyl)-1H-pyrrole-2,5-dione (IPD) was investigated using liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) of the products formed after the IPD CL reaction. We found that IPD produced strong CL via the decomposition of dioxetane formed after oxidation of the maleimide and indole moieties in the presence of CH₃CN, H₂O₂ and NaOH. The IPD CL was used for evaluating the antioxidant effect on curcumin and epigallocatechin gallate.     

Chromatographic Retention of Epigallocatechin Gallate on Oligo-β-Cyclodextrin Coupled Sepharose Media Investigated Using NMR

The retention of epigallocatechin gallate (EGCG) on oligo-β-cyclodextrin (oligo-β-CD) bonded agarose chromatographic media was investigated. NMR spectroscopy in solution showed that the EGCG immerses into the β-CD cavity. The association constant calculated by NMR titration was used to estimate a retention factor which accurately reflected chromatographic behaviour. This correlation suggests that oligo-β-CD forms inclusion complexes with EGCG via the same mechanism as monomeric β-CD. Revised: 14 March and 25 April 2006     

Efficient Separation and Purification of Epigallocatechin Gallate (EGCG) Based on EGCG-Imprinted Polymer Prepared with Chitosan as Matrix

A molecularly imprinted polymer (MIP), which was suitable for recognizing epigallocatechin gallate (EGCG), was prepared by using EGCG as template molecule and biocompatible chitosan as a functional matrix in aqueous medium. Molecular recognition ability of the EGCG-imprinted polymer (EIP) was evaluated by high performance liquid chromatography (HPLC). The results show that the EIP has a high imprinting factor (1.32) for EGCG and was used to purify EGCG from crude tea polyphenol efficiently. The percentage of EGCG can be improved from 78.6% in crude tea polyphenol (TP) to 90.1% in product and the adsorption quantity per unit can reach 4.02 mg · g^?1. EIP shows potential excellent prospect in the application of separating and purifying EGCG from TP.     

Electroanalytical Sensing of Green Tea Anticarcinogenic Catechin Compounds: Epigallocatechin Gallate and Epigallocatechin

A novel electroanalytical methodology for the sensing of anticarcinogenic catechin compounds epigallocatechin gallate (EGCG) and epigallocatechin (EGC) is presented. The protocol is based on the electrochemical oxidation of aminophenol in aqueous solutions, where the quinoneimine oxidation product chemically reacts with the EGCG or EGC compounds resulting in consumption of quinoneimine and consequently results in a reduction in the magnitude of the quinoneimine reduction wave, which is found to provide an analytical signal from which to indirectly detect EGCG and/or EGC.     

Rheological and related study of gelation of xyloglucan in the presence of small molecules and other polysaccharides

Interaction between tamarind seed xyloglucan and the other polysaccharides, gellan gum or xanthan investigated by rheology, differential scanning calorimetry, and related methods was discussed. All these three polysaccharides do not form a gel at lower concentrations by itself at the experimental conditions studied but the gelation of xyloglucan occurs in the presence of gellan or xanthan. Gelation of xyloglucan in the presence of a polyphenol, epigallocatechin gallate, is also discussed. Hence the gelation of these mixtures is caused by the synergistic interaction, and the models for the synergistic interaction were discussed. The gelation of polysaccharides by the synergistic interaction is of great value for food and related industries.     

Structures of enzymatic oxidation products of epigallocatechin

To understand the structures of uncharacterized black tea polyphenols, the oxidation products of (−)-epigallocatechin were investigated. Enzymatic oxidation and subsequent heating of the reaction mixture afforded four new oxidation products (6, and 9–11) along with theasinensins C (4) and E (5), dehydrotheasinensin E (12), epitheaflagallin, hydroxytheaflavin, and desgalloyl oolongtheanin. The structures of the new compounds were determined chemically and spectroscopically. Isotheasinensin E (6) is a C-2 epimer of 5, and compounds 9 and 10 are oxidation products of 12. Another new compound, 11, is a yellow pigment and presumed to be a degradation product of proepitheaflagallin. The results disclosed new oxidation mechanisms that occur during black tea production.     

Selective adsorption of epigallocatechin gallate onto highly reusable gallium doped mesoporous TiO2 nanoparticles adsorbent

This work describes a potential selective adsorption of epigallocatechin gallate by Ga-doped TiO₂ nanoparticles (NPs) and showed excellent adsorption (～99%) and desorption capacity even after the 7th run. The work reports about a surfactant mediated template based synthesis of both pristine and Ga-doped TiO₂ mesoporous NPs to study the adsorption behavior EGCG. EGCG is the most abundant and bio-active compound capable of showing free radical scavenging activity, anticancer, antibacterial, and several other physiological functions. Therefore, extraction of EGCG is highly desirable for incorporation in food items that can effectively increase their nutritional and medicinal values. The pore diameter of the synthesized materials was found to be in the range 8.76–10.38 nm and the specific surface area was found to be around 25.80–58.72 m²/g. The particle size decreased from 25 nm to 15 nm in presence of Ga. A mixture of anatase and brookite phase was observed for all the synthesized TiO₂ NPs. The band gap value initially (3.40 eV) decreased in presence of minute amounts of Ga (3.44 eV) but then increased (3.59 eV) with the increase of Ga percentage. The point of zero charge (PZC) value of the materials lies in the range of 6.6–7.2. The adsorption study was carried out at different pH (1, 3, 5, 7 and 9) with variation of shaking time (1 h, 3 h, 5 h and 7 h). The material containing maximum Ga in the Ga-doped set (Set 3 TiO₂ NPs) showed highest adsorption percentage (99.45%) in pH 1 medium after 5 h shaking. The adsorption isotherm and the kinetics follow the Langmuir model and pseudo-second order respectively. Desorption was studied under high energy gamma rays, shaking, sonication and UV irradiation. The highest desorption (～96%) was obtained with sonication for 30 min.