STUDENT ABSTRACTS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 270

STUDENT ABSTRACTS
The photochemistry of a common UV-B sunscreen absorber
BICE S. MARTINCIGH
School of Pure and Applied Chemistry, University of Natal, Durban, South Africa
The photochemistry of 2 -ethylhexyl- para -methoxy-cinnamate (2-EHMC) is of
fundamental interest as this is currently the most commonly used ultraviolet-B absorber
in sunscreen and cosmetic formulations. The commercial product is available as trans -
EHMC and is known to isomerise to the cis -form in sunlight, and thereby lose some of
its absorbing efficiency. This phenomenon was confirmed by a spectrophotometric
study. The isomers were separated and quantified by using high performance liquid
chromatography (HPLC). This showed the attainment of a photostationary state between
the trans - and cis -isomer. Irradiation of a concentrated solution of trans -EHMC with
wavelengths greater than 300 nm also caused the absorber to dimerise 1 with itself via a
[2 + 2] cycloaddition reaction thereby further decreasing its absorbing power. Six
isomers of the dimer were separated and isolated by a gradient mode of elution in
HPLC. Fourier transform infrared and proton nuclear magnetic resonance spectroscopy
were used to characterise the isolated dimers. It has also been speculated that 2-EHMC
can photobind to constituents of DNA in a manner similar to its self-dimerisation
reaction. Any such sunscreen-DNA photoadduct could be potentially mutagenic and
carcinogenic. The formation of such adducts has been investigated and the identity of
that formed on irradiation of thymidine-5'-monophosphate in the presence of 2-EHMC
was confirmed by capillary zone electrophoresis-mass spectrometry analysis.
Reference
1. Broadbent JK, Martincigh BS, Raynor MW, Salter LF, Moulder R, Sjöberg P, Markides KE (1996)
Capillary supercritical fluid chromatography combined with atmospheric pressure chemical ionisation mass
spectrometry for the investigation of photoproduct formation in the sunscreen absorber 2-ethylhexyl-para-
methoxycinnamate, Journal of Chromatography A 732: 101-110.