The spectroscopic behavior of catechin (5,7,3',4'-tetrahydroxyflavan-3-ol), has been studied in the presence and the absence of air using UV-vis absorption spectrophotometry and fluorescence spectroscopy. The UV-vis absorption spectrum of catechin shows a very sharp and strong absorption maximum peak at 275 nm in deaerated water. New absorption maximum peaks appeared in aerated water, as well as in basic aqueous solution, caused by the oxidation of catechin. The absorbances in the UV-vis absorption spectrum of catechin decreased when the solution was left in the dark for a long time. The fluorescence emission spectrum of catechin after a long time period differs markedly from that in freshly prepared solution; the fluorescence maxia shifted as time passes after adding catechin to the solutions. When the deaerated basic catechin solutions were left in the dark for a long time, their fluorescence quantum yields were found to be nearly zero. This suggests that the oxidized catechin molecules were seen to have slowly undergone successive chemical reactions in basic buffer solution.

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The polyhydroxybenzene derivatives can act as antioxidants in living organisms and for this reason considerable effort has been devoted to them.1,2 Particularly, the plantderived polyphenols have received great attention due to their various biological activities, i.e., anticarcinogenic, antiatherosclerotic, antimicrobial, and antioxidant properties.1-8 Polyphenolic substances are commonly referring to the subgroup flavanols that belong to the flavonoid family. They can be easily found in green tea, red wine and numerous fruits and vegetables.9-11 In addition many of the phenolic phytochemical compounds can also been related to the presence of flavanol moieties in their structure.One of the such substances is catechin (5,7,3',4'-tetrahydroxyflavan-3-ol) that is the major constituent of green tea and also one of the flavanol compounds. This substance is known to repair vitamin E as well as to be very efficient scavengers for biologically damaging oxy radicals, such as the superoxide radical and singlet oxygen.12,13 However, catechin is oxidized in water easily to form a yellow solution where the color of the solution varies with time.10 This is because the catechol moiety on the B-ring in catechin is oxidized in an aqueous solution.10,14 Recently, we confirmed that the oxidation in a basic solution is much faster than in the neutral catechin solution.14 Besides, the oxidation depended strongly on the pH values of the solution where higher pH values led to faster oxidation rate of catechin. However, flavan-4-ol (2-Phenylchroman-4-ol) is not contained catechol moiety in the molecule.In this paper, we have synthesized flavan-4-ol (2-phenylchroman-4-ol) and the spectroscopic properties of the substance were evaluated to explain its oxidation in the aqueous solution. Experimental Section1-(2-Hydroxyphenyl)ethanon, benzaldehyde were purchased from Sigma Chemical Co. (St. Louis, U.S.A.) and used without further purification. The other chemicals were reagent grade and used as received. Flavan-4-ol (2-phenylchroman-4-ol) was synthesized by starting from 1-(2-hydroxyphenyl)-ethanone with benzaldehyde in ethanol. Flavan-4-ol synthesized was very slightly soluble in water. Therefore, we first prepared the stock solution of flavan-4-ol in methanol. To prepare the aqueous flavan-4-ol, an aliquot of flavan-4-ol stock solution was transferred to a flask and then vaporized by bubbling high purity argon (99.999%) through. The compound was then dissolved in water using double distilled water, which was obtained by passing distilled water through a Barnstead (U.S.A.) Nanopure II deionization system. The pH of the solution was adjusted by adding HClO 4 , NaOH or ammonium chloride buffer solutions which were prepared from air-free distilled water. These buffer solutions did not absorb any UV light with wavelength longer than 240 nm and therefore would not overlap with the characteristic peaks of flavan-4-ol.The UV/vis absorption spectra of the solutions were then taken by a UV/vis spectrophotometer (Uvikon, model 943, Italy) at room t...