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Observing and understanding the ultrafast photochemistry in small molecules: applications to sunscreens

Posted on 28. October, 2016.

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Ultraviolet radiation is the most energetic component of the solar spectrum which reaches the Earth, typically subdivided into the UV‑A region, UV‑B, and the most energetic region, UV‑C. These high energy components can cause major disruptions in the biochemistry of life, often in the form of chemical bond breaking.

Throughout the development of the Earth’s atmosphere, the radiation which bombards the Earth’s surface has changed dramatically. Around three billion years ago when the earliest lifeforms on Earth are known to have existed, the atmosphere likely consisted predominately of carbon dioxide and methane, meaning the solar spectrum reaching the Earth’s surface consisted of much UV‑C radiation. As such, these early organisms were forced to migrate away from the surface, or develop other mechanisms in order to reduce exposure in order to survive. The latter is particularly important for the earliest complex lifeforms, the first phototrophs, which needed to absorb sunlight for photosynthesis, but be protected against too much UV‑C exposure.

In this review, the authors' discuss the importance of biological and artificial photoprotection against overexposure to harmful ultraviolet radiation. Transient electronic and transient vibrational absorption spectroscopies are highlighted as important tools in understanding the energy transfer in small molecules, with a focus on the application to commercial sunscreens with representative examples given. Oxybenzone, a common ingredient in commercial sunscreens and sinapoyl malate, a biological sunscreen in plant leaves are
presented as case studies.
Read the full article in Science Progress, Volume 99, Number 3, September 2016, pp. 282-311.

DOI: 10.3184/003685016X14684992086383

Authors: Lewis A. Baker and Vasilios G. Stavros

Keywords: ultraviolet radiation, ultrafast spectroscopy, transient absorption, photoprotection, sunscreens, photochemistry, femtochemistry, oxybenzone, sinapoyl malate

Image: A representation of the probability of disease incidence, with common ailments associated with UVR overexposure (violet) or underexposure (blue) in humans (and in italics for plants). For both humans and plants there are regulated pathways which attempt to maintain a balance between the burden of disease associated with either extreme of UVR exposure, keeping it close to the optimal position and thus the lowest incidence of disease.