Bardeen Research Group

Department of Chemistry | University of California @ Riverside | 501 Big Springs Road | 127-131 CS-1

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Bardeen Research Group
University of California, Riverside * Department of Chemistry
501 Big Springs Rd * Riverside, CA 92521, USA
Phone: +1.951.827.2723 * Fax: +1.951.827.4713 * Email: christob@ucr.edu

 

UV-Filters & Photoprotection

Improving Photoprotection
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Although it is possible to design organic materials that transform photon energy into useful work, it is often the case that photons do more harm than good.  This is especially the case for humans, where the effects of  solar UV radiation on the skin range from the cosmetic (photoaging) to deleterious (skin cancers).   Understanding the chemical processes that occur in the skin is complicated by the fact that the skin is opaque, making traditional spectroscopic methods difficult to apply.  We have two parallel efforts dedicated to ameliorating the effects of UV radiation on human skin.
sunscreens gif

 

 

 

 

The chemical structures of the four most common UV-filters used in over-the-counter sunscreens in the U.S.  Avobenzone is a UVA filter absorbing radiation between 320 nm and 400 nm.  Oxybenzone (B3), octocrylene (OC), and octylmethoxycinnamate (OMC) are UVB filters that absorb radiation between 280 nm and 320 nm. Avobenzone in particular is photolabile, which dramatically affects its efficacy.

 

 

 

 

 

 

 

 

 

 

 

ROSSkin

The number of UV-induced (20 mJ cm-2) reactive oxygen species (ROS) generated in nucleated epidermis is dependent upon the lenght of time UV-filters octocrylene (OC), octylmethoxycinnamate (OMC) or benzophenone-3 (B3) remain on the skin surface.

Two-photon fluorescence images acquired immediately following application of each formulation (2 mg cm-2) to the surface show that the number of ROS produced is dramatically reduced relative ot the skin (-) UV-filter control. After each UV-filter reamins on the skin surface for t=20 min, the number of ROS generated increases, although it remains below the number generated in the control.

By t=60 minutes, the filters generate ROS above the control. The data show that when all three of the UV-filters penetrate into the nucleated layers, the level of ROS increases above that produced naturally by epidermal chromophores under UV illumination
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1.  Photophysics of Sunscreen Molecules. 

The energy level structure and relaxation rates of many molecules used in commercial sunscreens are unknown.  

We are currently studying the basic photophysics of these molecules both in solution and in sunscreen formulations, which are basically highly concentrated emulsions.  Issues like photostability and the existence of long-lived reactive states will be examined.

 

2.  In Vivo Assessment of UV Photodamage. 

We have developed two-photon fluorescence imaging protocols to monitor light-induced reactive oxygen species (ROS) at different depths within the skin.

These fluorescence assays allow us, for example, to evaluate the ability of sunscreens to prevent ROS and photodamage in the skin. 

Publications (for a complete Publication list, see Publications link)

  1. "Photochemical degradation of the UV filter octyl methoxycinnamate in solution and in aggregates," K. M. Hanson, S. Narayanan, V. M. Nichols, and C. J. Bardeen, Photochem. Photobiol. Sci., 14, 1607-1616 (2015).
  2. "Antioxidants in sunscreensfor improved ROS photoprotection," Hanson, K. M.; Beasley, D. G.; Meyer, T. A.; Bardeen, C. J. Cosm. Toil., 126, 712-716 (2011).Cover Article
  3. "Singlet quenching proves faster is better for photostability," Bonda, C.; Pavlovic, A.; Hanson, K. M.; Bardeen, C. J. Cosm. Toil., 125, 40-48 (2010) Best paper award, Society of Cosmetic Chemists, 2010.


1.  Photophysics of Sunscreen Molecules. 

The energy level structure and relaxation rates of many molecules used in commercial sunscreens are unknown.  

We are currently studying the basic photophysics of these molecules both in solution and in sunscreen formulations, which are basically highly concentrated emulsions.  Issues like photostability and the existence of long-lived reactive states will be examined.