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Porphyrin-sensitized photo-oxidation of hematoxylin in oxygenated solutions

Authors:

Ajith Herath,

Journal of the National Science Foundation of Sri Lanka, LK
About Ajith

Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya.

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Namal Priyantha,

University of Peradeniya, LK
About Namal

Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya.

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Gamini Rajapakse,

University of Peradeniya, LK
About Gamini

Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya.

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Veranja Karunaratne,

University of Peradeniya, LK
About Veranja

Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya.

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Anura Wickramasinghe

University of Peradeniya, LK
About Anura

Department of Chemistry, Faculty of Science, University of Peradeniya, Peradeniya.

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Abstract

This paper describes the oxidation of hematoxylin (HT) in oxygenated aqueous solutions at pH 4.0, upon irradiation with visible light, in the presence of protoporphyrin dimethylester (PPDME) as a photosensitizer. The redox potential for the lowest excited state of PPDME, estimated from its ground state oxidation potential [0.86 V with respect to normal hydrogen electrode (NHE)] and its low energy absorption edge (2.5 eV), was found to be -1.63 V (with respect to NHE). These values clearly indicate that the excited PPDME molecules could transfer their energy to the ground state oxygen in solution, producing the superoxide radical anion (Ο2˙ֿ) or singlet oxygen. Additional experiments carried out in the presence of sodium azide and/or benzoquinone, confirm that the oxidation of HT mainly proceeds through a superoxide radical based mechanism. Under the conditions described above, HT was found to be completely oxidised upon 24 hours of visible light irradiation.

Keywords: Hematoxylin, irradiation, photo-oxidation, photosensitizer, protoporphyrin dimethylester, superoxide anion, visible light.

doi :10.4038/jnsfsr.v35i4.1312

J.Natn.Sci.Foundation Sri Lanka 2007 35 (4): 239-244

 

 


 

How to Cite: Herath, A., Priyantha, N., Rajapakse, G., Karunaratne, V. and Wickramasinghe, A., 2007. Porphyrin-sensitized photo-oxidation of hematoxylin in oxygenated solutions. Journal of the National Science Foundation of Sri Lanka, 35(4), pp.239–244. DOI: http://doi.org/10.4038/jnsfsr.v35i4.1312
Published on 28 Dec 2007.
Peer Reviewed

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