Avobenzone
A chemical found in sunscreens, it absorbs UVA rays to reduce their penetration into the skin, but does not protect against UVB rays. Avobenzone was patented in 1973 and was approved in the EU in 1978. It was approved by the FDA in 1988. Pure avobenzone is a whitish to yellowish crystalline powder with a weak odor, dissolving in isopropanol, dimethyl sulfoxide, decyl oleate, capric acid/caprylic, triglycerides and other oils. It is not soluble in water.
Avobenzone is a dibenzoylmethane derivative. Avobenzone exists in the ground state as a mixture of the enol and keto forms, favoring the chelated enol. This enol form is stabilized by intramolecular hydrogen-bonding within the β-diketone. Its ability to absorb ultraviolet light over a wider range of wavelengths than many other sunscreen agents has led to its use in many commercial preparations marketed as "broad spectrum" sunscreens. Avobenzone has an absorption maximum of 357 nm.
It is subject to keto-enol tautomerism and exists predominantly enol when dissolved. Upon UV radiation, it may convert to keto form, while converting back to enol form after placing in dark.
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