Solvent effects on sunscreen active ingredients using Raman spectroscopy

We present Raman spectra of five sunscreen active ingredients in 10 solvents. Shifts in the UV absorption maxima and the CO Raman mode wavenumber are observed for some of the sunscreens as a function of solvent. Correlations between the observed wavenumber shifts and solvent properties indicate that hydrogen bonding is a key interaction between sunscreen active ingredients and solvent. Interestingly, the relative Raman intensities are also sensitive to the hydrogen-bonding and polarizability properties of the solvent, reflecting differential stabilization of the sunscreen's resonance structures. These results suggest an ‘expanded polarizability’ view of the solvent's effect on the solute. The observed wavenumber and relative intensity changes were also utilized to identify the active agents present in commercial sunscreen preparations from their in situ Raman spectra. Copyright © 2003 John Wiley & Sons, Ltd.

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