Study on Urocanic Acid in the Human Skin Surface (II):Geometrical Isomers and Sunscreen Effect

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The photoprotective aspect of urocanic acid as a natural sunscreen agent in the human skin surface was studied. At first, a new method for the fractional determination of trace amount of geometrical isomers of urocanic acid was developed by high performance liquid chromatography. The limit of detection was 2.4ng for cis urocanic acid and 2.0ng for trans urocanic acid, respectively. Then, influence of age, sex, sampling position of human materials and seasons upon the total amount of urocanic acid and the ratio of geometrical isomers (cis and trans isomer) in the human skin surface were determined in detail using this analytical method. Moreover, the photoisomerization of urocanic acid in water was observed and the protection factors of sodium trans urocanic acid and photoisomerized sodium urocanic acid were experimentally compared. The obtained results showed that both isomers acted as sunscreen agents and suggested that photoprotective effect arose from not only isomerization energy but also photo absorption.
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