儿茶素与Al～(3+)的作用及饮茶与铝的聚集性研究

【作者】 唐德松；

【导师】 沈生荣；

【作者基本信息】 浙江大学 ， 茶学， 2003， 硕士

【摘要】 自20世纪70年代中期以来，随着分析技术的发展及在临床上发现铝与多种神经失调疾病、骨软化症及小细胞性贫血等有关，引起人们愈益关注铝在生物学方面可能引起的问题。 因茶树含铝量较高，是典型的聚铝植物。茶汤中铝的浓度大都在1—6mgL^-1，茶汤中90％以上的铝是与有机物质结合的，但是具体与什么物质结合还不清楚。铝的物理化学形态，即暴露的媒介以及生物体的器官中的形态，常常是该元素的生物利用度和毒性的决定因素，铝的吸收和生物代谢动力学在很大程度上依靠与不同配体形成的络合物的性质。茶汤中有机成分复杂，其中许多分子都可以与铝络合，从而影响铝的生物学行为。 儿茶素、氟和铝是茶树体内的重要物质，涉及到茶树生理上的物质运输，茶的饮用与保健诸方面。本课题在化学体系中研究了三种儿茶素（（+）-C，（—）-EC，EGCG）对碱的缓冲能力、Al³⁺对儿茶素缓冲能力的影响、在不同的pH值条件下，儿茶素与Al³⁺的络合作用以及F^-对儿茶素与Al³⁺的络合作用的影响。结果表明，儿茶素溶液对碱有较强的缓冲能力，酯型儿茶素更强，EGCG约是EC或者C的两倍，同时碱也使得儿茶素的紫外—可见吸收发生变化；在儿茶素与Al³⁺络合过程中，儿茶素的紫外—可见吸收光谱发生变化，EGCG在274nm处逐渐下降，而322nm处逐渐升高；C和EC发生红移，而特征吸收峰278nm处变化不明显；EGCG与Al³⁺的络合比在pH5.0的溶液中为1∶1，而在pH6.2的缓冲液中当Al³⁺／EGCG小于2时，络合比是1∶1，当Al³⁺／EGCG大于2时，络合物开始聚合，聚合物中Al³⁺与EGCG的比值是2∶1；在pH6.2的缓冲液中，C与Al³⁺的络合与EGCG相似，但EC与Al³⁺的络合比在Al³⁺／EC小于1时为1∶2，大于1时发生聚合，聚合物中Al³⁺与EC之比为1∶1；儿茶素与铝的络合物 硕士学位论文在较高pH值下的这种聚合，可能会减少铝的吸收。氟能够与儿茶素竟争性的与A广络合，在较低的pH值时，氟的竞争性增强。 正辛醇一水分配系数（Kow）是衡量有机化合物疏水性的一个重要参数，是用来描述有机化合物从水环境向有机体转移及其潜在生物蓄积作用的一个模拟型变量，与有机物的生物富集因子相关联。药理学中也常用药物在正辛醇一水体系中的分配系数作为描述药物亲脂性或疏水性的一个物理参数，它可用来研究药物的溶解度和药物结构与活性及毒性的关系。所以尽管茶汤中的铝的存在形态没有完全研究清楚，但也可以通过测定茶汤铝的KO W值，用以推断饮茶与铝在生物体内的吸收和积累情况。 通过测定红茶、绿茶和乌龙茶茶汤中铝的Kow值，并且考察了在胃和小肠叫值条件下MW的变化情况，发现Ko W值在小肠叫条件下升高，推断茶汤中的铝的吸收主要发生在从胃到小肠的过程中。同时研究了三种儿茶素EGCG、EC、C和茶多酚对铝的Kow的影响。结果发现，以上几种物质都可以明显降低铝的KO W，其中＊＊＊G和茶多酚的影响非常明显。说明儿茶素以及茶多酚都具有降低铝在生物体中聚集的效应。 茶多酚类物质特有的多酚羟基结构，具有与许多金属离子络合的特性，所以茶多酚、儿茶素等在解除金属毒性方面的研究也成为研究者关注的热点。根据Lewis软硬酸碱理论，铝是三价金属离子中最硬的Lewis酸，而多酚类却是Lewis碱（电子对供体，亲核体），两者可以很好的结合。儿茶素、茶多酚对铝的这种作用，可能在影响铝的生物学活性方面起着重要作用，相关的研究也证实了儿茶素、茶多酚的这种作用。更多还原

【Abstract】 Since Middle 70’s of last centuries, along with analytical technology development and clinically utiliziation, researchers discovered that many kinds of dimentia, dialysis encephalopathy, osteomalacia and cellule amaemia are linked with aluminum. Much attention was paid to the possible problems induced by aluminum.Because of the tea plant’s accumulating aluminum, it results in the high aluminum concentration in tea infusion, about 1-6mgL-1. Approximately above 90% aluminum in tea infusions combine with organic compounds, but so far with which kind of organic compounds have not been clear yet. The physi-chemical properties of the aluminum, in environmental and physical conditions, are the determinants of its bioavailability and toxicity. Aluminum absorption and its metabolic kinetics depend on the properties of Al-organics complex to a large extent. Organic compositions in tea infusion are complicated, among them many molecules can combine with aluminum ion and affect its bioactivities.Tea polyphenols, fluoride and aluminum are important substances in tea plant, and they are also the focus of tea infusion concerning human health. In this paper, the buffer abilities of three kinds catechins to NaOH and influenced by Al3+, the complex of catechins with Al3+ and the competition of fluoride were studied. The results showed that, catechins have strong buffer ability to base, EGCG is stronger than EC and C. NaOH can also change the UV-visible spectrum of catechin solutions, and during the complex process with Al3+ the UV-visible spectrum also be changed. Absorption of EGCG at 274nm decreased and increased at 322nm; EC and C’s at 278nm changed little. Ratio of A13+ to EGCG is 1:1 at pH5.0 buffer solution; in pH6.2 buffer solution, when A13+ to EGCG ratio 2, ratio of Al to EGCG in the complex is 1:1, while Al3+ to EGCG ratio >2, complex of Al-EGCG started polymerizing, ratio of Al to EGCG in the polymer is 2:1. In pH6.2 buffer solution, complex of C with A13+ is the same as EGCG, a little difference for EC: when the ratio of Al3+ to EC <1, Al3+ to EC in complex is 1:2, the complex polymerized when the ratio of A13+ to EC >1, A13+ to EC in the polymer is 1:1. Polymerization of Al-catechin complexes may reduce aluminum absorption in intestine. F" can compete A13+ with catechins in solution, and its ability become stronger with decreasing of pH value.Distribution coefficient(Kow) of organic substances between n-octanol and aqueous phase is an important parameter to evaluate its aquapholic, it describes the potential oforganic compound to transfer from environment to organism and accumulate in it, so it is linked with bioconcentation factor. In pharmacology, Kow is also employed to predict the lipophilic, bioactivity and toxicity of new medicines.In our experiment, Kow value was also employed to study the aluminum properties in tea infusion(at gastric and intestine pH condition) and the influences of catechins, tea polyphenols and fluoride on Kow in buffer solution. Results showed that, Kow value rose much higher in intestine pH condition than in gastric, indicating aluminum absorption mainly happened in intestine. Tea polyphenols, catechins and fluoride can greatly reduce aluminum Kow value in buffer, especially tea polyphenols, EGCG and fluoride, showing that these compounds can reduce aluminum accumulation in body respectless the side effects of fluoride.Molecular of tea polyphenols(including catechins) has many hydroxyl groups, and can complex with many kinds of metal ion. Chelating and detoxification metal ions are also the focus of many researchers. According to Lewis soft-hard acid-base theory, aluminum is the hardest trivancy Lewis acid, and polyphenols are Lewis base theoretically, they can combine together tightly. For this property, catechins may play an important role in affecting the bioactivity of aluminum in tea infusion. Some related research work has approved the function.更多还原