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Spectroscopic Studies on the Oxidation of Catechin in Aqueous Solution
박기민,Chul-Ho Park,Ik-Jun Yang,Jeong-Im Yang,Ji-Eun Yeom,박형련 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.9
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.
Physicochemical Properties of Protoporphyrin IX by Metal Ions in Acetonitrile-Water Mixture Solution
박기민,Jeong-Im Yang,Ho-Suk Lee,이지범,박철호,박형련 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.6
The UV-vis absorption spectrum of protoporphyrin IX shows a very sharp and strong absorption maximum peak at 398nm in acetonitrile-water mixture solution (1:1 v/v). When divalent metal ions such as Cu2+, Zn2+, and Ca2+ ion were added to protoporphyrin IX, metal protoporphyrin IX complexes were thereby produced. Cu-protoporphyrin IX complexes have the largest formation constant (Kf) among them. The fluorescence intensity of protoporphyrin IX was diminished by the presence of Cu2+, Zn2+, Ca2+, Mn2+, and Ni2+ ions as quenchers. However, Mg2+, Mn2+, and Ni2+ ions are hardly combined with protoporphyrin IX. Mg2+ ion does not take part in the fluorescence quenching process of protoporphyrin IX in acetonitrile-water mixture solution. According to the Stern-Volmer plots, fluorescence quenching by Cu2+, Zn2+,and Ca2+ ions involves static quenching, which is due to complex formation. On the contrary, dynamic quenching has a large influence on the overall quenching process, when Mn2+ and Ni2+ ions were added to protoporphyrin IX in acetonitrile-water mixture solution.