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Virtual Journal for Biomedical Optics

Virtual Journal for Biomedical Optics

| EXPLORING THE INTERFACE OF LIGHT AND BIOMEDICINE

  • Editor: Gregory W. Faris
  • Vol. 2, Iss. 3 — Mar. 7, 2007

Monitoring 2-Ethylhexyl-4-Methoxycinnamate Photoisomerization on Skin Using Attenuated Total Reflection Fourier Transform Infrared Spectroscopy

P. Pangnakorn, R. Nonthabenjawan, S. Ekgasit, C. Thammacharoen, and S. Pattanaargson Wanichwecharungruang

Applied Spectroscopy, Vol. 61, Issue 2, pp. 193-198 (2007)


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Abstract

Photoisomerization and photodimerization of a widely used UVB filter, 2-ethylhexy-4-methoxycinnamate (EHMC) on a ZnSe surface and baby mouse (Mus musculus Linn.) skin were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR). Differentiation between the E- and the Z-EHMC could be achieved by examining the infrared (IR) peak at 981 cm−1 (b peak), which corresponds to the CH rocking deformation vibration of Ph–CH=CH– detected only in the E configuration. By plotting the ratios of the peak area of the b peak and an internal standard peak (1060–998 cm−1) against mole percentage of Z-isomer in the E-Z mixtures, a linear calibration plot was obtained. Thus, a simple estimation of the mole percentage of each configuration in a sample was obtained. At the same UVB exposure, photostationary equilibrium of the E/Z isomerization on the surface varied with the applied amounts of EHMC. Photoisomerizations on ZnSe and on baby mouse skin were comparable. Less than 10% of E-EHMC changed configuration when the mouse skins applied with 1.0–4.0 mg/cm2 E-EHMC were exposed to sunlight for 60 min (UVB radiant exposure of ∼0.30 J/cm2). This corresponded to less than 5% loss in UV filtering efficiency. However, at a typical EHMC skin coverage (∼0.2 mg/cm2), 0.30 J/cm2 UVB exposure induced ∼50% photoisomerization resulting in 25% loss of UV filtering efficiency. No photodimerization was detected even at the extreme EHMC coverage of 4.0 mg/cm2 after a UVB exposure of 0.90 J/cm2.

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Vol. 2, Iss. 3 Virtual Journal for Biomedical Optics

Citation
P. Pangnakorn, R. Nonthabenjawan, S. Ekgasit, C. Thammacharoen, and S. Pattanaargson Wanichwecharungruang, "Monitoring 2-Ethylhexyl-4-Methoxycinnamate Photoisomerization on Skin Using Attenuated Total Reflection Fourier Transform Infrared Spectroscopy," Appl. Spectrosc. 61, 193-198 (2007)
http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=as-61-2-193

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