OXIDATION PATHWAYS OF NATURAL DYE HEMATOXYLIN IN AQUEOUS SOLUTION

0354402 - ÚFCH JH 2011 RIV CZ eng J - Journal Article
Sokolová, Romana - Degano, I. - Hromadová, Magdaléna - Kocábová, Jana - Gál, Miroslav - Valášek, Michal
OXIDATION PATHWAYS OF NATURAL DYE HEMATOXYLIN IN AQUEOUS SOLUTION.
Collection of Czechoslovak Chemical Communications. Roč. 75, č. 11 (2010), s. 1097-1114. ISSN 0010-0765
R&D Projects: GA ČR GA203/09/1607; GA ČR GA203/08/1157; GA MŠMT OC 140
Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z40550506
Keywords : hemotoxylin * oxidation * dye degradation * cyclic voltammetry
Subject RIV: CG - Electrochemistry
Impact factor: 0.853, year: 2010

The oxidation mechanism of hematoxylin was studied in phosphate buffers and 0.1 M KCl by cyclic voltammetry and UV-Vis spectroscopy under deaerated conditions. The redox potential of hematoxylin in buffered solution strongly depends on pH. A two electron oxidation is preceded by deprotonation. The homogeneous rate of deprotonation process of hematoxylin in 0.1 M phosphate buffer is k(d) = (2.5 +/- 0.1) x 10(4) s(-1). The cyclic voltammetry under unbuffered conditions shows the distribution of various dissociation forms of hematoxylin. The dissociation constants pK(1) = 4.7 +/- 0.2 and pK(2) = 9.6 +/- 0.1 were determined using UV-Vis spectroscopy. The final oxidation product was identified by gas chromatography with mass spectrometry detection as hemathein. The distribution of oxidation products differs under buffered and unbuffered conditions. The dye degradation in natural unbuffered environment yields hemathein and hydroxyhematoxylin, which is absent in buffered solution.
Permanent Link: http://hdl.handle.net/11104/0193411