Monitoring 2-ethylhexyl-4-methoxycinnamate photoisomerization on skin using attenuated total reflection fourier transform infrared spectroscopy.
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/cm(2) E-EHMC were exposed to sunlight for 60 min (UVB radiant exposure of approximately 0.30 J/cm(2)). This corresponded to less than 5% loss in UV filtering efficiency. However, at a typical EHMC skin coverage ( approximately 0.2 mg/cm(2)), 0.30 J/cm(2) UVB exposure induced approximately 50% photoisomerization resulting in 25% loss of UV filtering efficiency. No photodimerization was detected even at the extreme EHMC coverage of 4.0 mg/cm(2) after a UVB exposure of 0.90 J/cm(2).
Pangnakorn
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P
Sensor Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand. psupason@chula.ac.th
Nonthabenjawan
R
R
Ekgasit
S
S
Thammacharoen
C
C
Pattanaargson Wanichwecharungruang
S
S
D000818:Animals; D000831:Animals, Newborn; D002138:Calibration; D002934:Cinnamates / Q000737:chemistry*; D066298:In Vitro Techniques; D007536:Isomerism; D051379:Mice; D010777:Photochemistry; D012015:Reference Standards; D012867:Skin / Q000737:chemistry* / Q000528:radiation effects; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013473:Sunscreening Agents / Q000737:chemistry*; D014466:Ultraviolet Rays
D002934:Cinnamates; D013473:Sunscreening Agents; C118580:octylmethoxycinnamate