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The correlation between excessive exposure to sunlight – specifically, ultraviolet (UV) radiation – and skin cancer is now well established. With skin cancer cases increasing in recent years, it is of the utmost importance to develop sunscreen formulations which maximise photoprotection. Sunscreens act as front line defence, preventing DNA from absorbing UV radiation and thus preventing DNA damage which could potentialy lead to skin cancer. My thesis work sets out to improve sunscreen efficacy by pursuing a comprehensive understanding of the chemical mechanisms by which sunscreen molecules dissipate the excess energy resulting from absorption of UV radiation – referred to as photodynamics.
Ideally, a sunscreen molecule’s photodynamics should occur without any detriment to itself, the mixture which surrounds it (the sunscreen lotion) or the human skin. In addition, the photodynamics should occur on an ultrafast timescale of femto- to picoseconds. In order to follow these processes, I use ultrafast laser spectroscopy techniques both in vacuum and in solution such as time-resolved ion yield and transient electronic absorption spectroscopy, respectively.
Using these methodos, I have found drastic differences in the photodynamics of different sunscreen molecules. For example, one of the most widely used sunscreen ingredients on the market, 2-ethylhexyl-E-4-methoxycinnamate (EHMC, or Uvinul MC80), dissipates toxic UV energy very quickly, i.e. after a couple of picoseconds after UV radiation absorption, and without any compromise to molecular structure. This behaviour is ideal for a sunscreen molecule, because EHMC not only absorbs the energy that could lead to skin damage and cancer, but it also dissipates this energy without causing harm. However, I have observed a different sunscreen molecule, menthyl anthranilate (MenA, or Meradimate), to have a very different behaviour. MenA does not dissipate excess energy effectively and remains in its excited state for much longer than EHMC. My work shows that MenA is, in fact, a detrimental sunscreen ingredient, despite its use in some sunscreen lotions. More importantly, my research has identified why MenA is a poor sunscreen molecule – by comparing it with EHMC – which is an important step to improving sunscreen efficacy.
The EHMC and MenA results highlight the relevance of the research I am conducting, and serve as an example of the important issues that it can address. For example: what exactly changes a molecule’s photodynamics, so that it behaves as an ideal sunscreen? Can we tweak currently available sunscreens so that their photodynamics translate to optimum photoprotection? Despite sunscreens having been on the market for almost 100 years, there is still no comprehensive answer to these questions. However, my thesis work sets out to demonstrate that research targeted towards a comprehensive understanding of photoprotection may be more efficient than the current trial-and-error methods for sunscreen development. This new approach has the potential to create next generation sunscreens which are tailor made for optimum photoprotection.
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3. N. D. N. Rodrigues, M. Staniforth, V. G. Stavros, Photophysics of sunscreen molecules in the gas phase: a stepwise approach towards understanding and developing next-generation sunscreens, Proc. R. Soc. A., 472, 20160677. (2016)
4. N. D. N. Rodrigues, M. Staniforth, J. D. Young, Y. Peperstraete, N. C. Cole-Filipiak, J. R. Gord, P. S. Walsh, D. M. Hewett, T. S. Zwier and V. G. Stavros, Towards elucidating the photochemistry of the sunscreen filter ethyl ferulate using time-resolved gas-phase spectroscopy, Faraday Discuss., 194, 709-729. (2016)
5. M. D. Horbury, L. A. Baker, N. D. N Rodrigues, W. Quan, and V. G. Stavros, Photoisomerization of ethyl ferulate: A solution phase transient absorption study, Chemical Physics Letters, 673, 62-67 (2017).
6. Y. Peperstraete, M. Staniforth, L. A. Baker, N. D. N. Rodrigues, N. C. Cole-Filipiak, W. Quan, and V. G. Stavros, Bottom-up excited state dynamics of two cinnamate-based sunscreen filter molecules, Physical Chemistry Chemical Physics, 18, 28140-28149 (2016).
7. N. D. N. Rodrigues, N. C. Cole-Filipiak, M. D. Horbury, M. Staniforth, T. N. V. Karsili, Y. Peperstraete and V. G. Stavros, Photophysics of the sunscreen ingredients methyl and menthyl anthranilate: a bottom-up approach to photoprotection, In preparation.
1. M. D. Horbury, L. A. Baker, N. D. N. Rodrigues, V. G. Stavros, Photoisomerization of ethyl ferulate: a solution phase transient absorption study, Chem. Phys. Lett., 2017.
2. N. C. Cole-Filipiak, M. Staniforth, N. D. N. Rodrigues, Y. Peperstraete, V. G. Stavros, Ultrafast dissociation dynamics of 2-ethylpyrrole, J. Phys. Chem. A, 2017.
3. N. D. N. Rodrigues, M. Staniforth and V. G. Stavros, Photophysics of sunscreen molecules in the gas-phase: a stepwise approach to understanding and developing the next generation of sunscreens, Proc. R. Soc. A, 2016, 472(2195), 20160677.
4. Y. Peperstraete, M. Staniforth, L. A. Baker, N. D. N. Rodrigues, N. C. Cole-Filipiak, W. D. Quan and V. G. Stavros, Bottom-up excited-state dynamics of two cinnamate-based sunscreen filter molecules, Phys. Chem. Chem. Phys., 2016, 18(40), 28140-28149.
5. N. D. N. Rodrigues, M. Staniforth, J. D. Young, Y. Peperstraete, N. C. Cole-Filipiak, J. Gord, P. S. Walsh, D. Hewett, T. Zwier and V. Stavros, Towards elucidating the photochemistry of the sunscreen filter ethyl ferulate using time-resolved gas-phase spectroscopy, Faraday Discuss., 2016.
6. J. Tandy, C. Feng, A. Boatwright, G. Sarma, A. M. Sadoon, A. Shirley, N. D. N. Rodrigues, E. M. Cunningham, S. Yang, A. M Ellis, Communication: Infrared spectroscopy of salt-water complexes, J. Chem. Phys., 2016, 144(12), 121103.
7. C. A. Arrell, J. Ojeda, M. Sabbar, W. A. Okell, T. Witting, T. Siegel, Z. Diveki, S. Hutchinson, L. Gallmann, U. Keller, F. van Mourik, R. T. Chapman, C. Cacho, N. Rodrigues, I. C.E. Turcu, J. W.G. Tisch, E. Springate, J. P. Marangos, and M. Cherguil, A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions, Rev. Sci. Inst., 85, 2014, 103117.