鋁與兒茶素在茶樹生長上所扮演之角色

Abstract

茶樹為典型的鋁累積作物，而多酚類化合物 (兒茶素類) 為其體內主要之生物分子組成。然而，鋁和兒茶素之間的交互作用目前仍然是不清楚。本篇研究之目的為研究鋁對於兒茶素之轉化作用之影響。反應液在OH/Al莫耳比為 2.5 (pH 5.5)和3.0 (pH 7.0)下，配製成不同比例之Al/catechin 莫耳比分別為0, 0.2, 0.4, 0.6, 0.8, 1.0，之後老化7天和30天。沉澱物利用化學全分析、X射線繞射分析、穿透式電子顯微鏡分析 ( TEM )、電子自旋光譜分析 ( ESR )、橫偏極化魔角13C 核磁共振光譜分析 ( CPMAS )和傅立葉轉化紅外線吸收光譜儀分析 ( FT-IR )。沉澱物的量會隨著Al/catechin 莫耳比以及老化時間增加而增加。沉澱物中的Al/catechin 莫耳比會隋著一開始配製之Al/catechin 莫耳比增加而增加，並且非常接近起使溶液之Al/catechin莫耳比。化學分析和光譜分析都顯示出Al會跟catechin 鍵結並且會形成1:1型錯合物。結晶性的catechin與鋁反應之後會變成無定形之物質。沉澱物 13C NMR光譜分析結果顯示出鋁會與catechin發生錯合反應並且改變了catechin之核磁共振化學位移。FT-IR 光譜分析之結果也指出catechin與鋁錯合反應後，幾個官能基之吸收峰會改變。電子自旋光譜結果顯示出有一個均勻對稱的分隔線，此結果指出有自由基之存在，並顯示為semiquinones，此為土壤有機質之腐質酸存在的主要自由基。

Polyphenols (catechins) is a vital biomolecule in tea plants (Camellia sinensis), which is well known as a typical Al accumulator. However, the interaction between Al and catechin remains obscured. The objective of the present study was to investigate the effect of Al on transformation of (+)-catechin. Solutions with OH/Al molar ratios of 2.5 (pH 5.5) and 3.0 (pH 7.0) prepared at Al/catechin molar ratios (R) of 0, 0.2, 0.4, 0.6, 0.8 and 1.0 were aged for 7 and 30 days, respectively. The precipitates were collected and examined by wet chemistry, X-ray diffraction (XRD), transmission electron microscopy (TEM), electron spin resonance (ESR), cross polarization magic angle (CPMAS) 13C nuclear magnetic resonance (13C NMR) analyses and Fourier transformation infrared absorption spectrometry (FT-IR). The weight of the precipitates increased with increasing Al/catechin molar ratios and with prolonged aging. The molar ratios of Al/catechin in the precipitates increased with increasing the initial Al/catechin molar ratios, and were close to the initial solution Al/catechin molar ratios. The chemical analysis and spectroscopic studies indicated that Al was bonded with catechin forming a 1:1 type complex. The reaction of crystalline catechin with Al resulted in the formation of X-ray noncrystalline precipitates. The solid-state CPMAS 13C NMR spectra of the precipitates show the change in chemical shifts of catechin as a result of catechin complexating with Al. The FT-IR spectra of the Al-catechin precipitates also show the loss of absorption bands of several functional groups compared with catechin. The FT-IR data substantiates this reasoning. The ESR spectra of the precipitates show a single symmetrical line devoid of any fine splitting, indicating presence of free radicals of semiquinones which are commonly present in humified materials.