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1 November 2005 Spectroscopic and Photochemical Properties of the Lichen Compound Lobaric Acid
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Abstract

Lichens synthesize and accumulate photoprotective compounds against possible damage induced by UV radiation in the photobiont. A biological model has been recently formulated that allows the use of lichens to evaluate changes at different UV radiation levels. The thermodynamics, photophysical and photochemical properties of lobaric acid were studied in acetonitrile, ethanol and Brij 35(3%) micelles at different pH values. Also the sun protector factor (SPF) was determined by in vitro methods. Lobaric acid was extracted from Stereoculon alpinum Laur. and characterized by means of standard procedures. Solutions were irradiated in oxygen and under nitrogen conditions with a UV medium pressure lamp. Lobaric acid absorbs at 287, 303 nm, and no fluorescence emission was observed. The maximum value of the molar extinction coefficient (5479.6 M−1 cm−1) was obtained in Brij 35 at pH 12. Solubility is pH dependant and is highest in Brij 35 at pH 12 (4.45 × 10−4 M). Photoconsumption quantum yields ranged between 10−4 and 10−5 in aerobic and anaerobic experimental conditions. Lobaric acid SPF was very low (0.5) compared with homosalate (4.0), (reference solar filter). Two pKa values, 5.05 (carboxylic acid group deprotonation) and 9.75 (phenolic OH deprotonation), were determined.

María Eliana Hidalgo, Luis Bascuñan, Wanda Quilhot, Ernesto Fernández, and Cecilia Rubio "Spectroscopic and Photochemical Properties of the Lichen Compound Lobaric Acid," Photochemistry and Photobiology 81(6), 1447-1449, (1 November 2005). https://doi.org/10.1562/2005-05-17-RA-530
Received: 16 May 2005; Accepted: 1 August 2005; Published: 1 November 2005
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