Effects of solvent and micellar encapsulation on the photostability of avobenzone

Abstract

Avobenzone, the only UVA-absorbing molecule approved for use in sunscreens by the FDA, degrades to its diketone structure under UV light. We found that this photoisomerization is effectively prevented when avobenzone is sequestered in micelles.

Determining the photostability of avobenzone in sunscreen formulation models using ultrafast spectroscopy

“…The tautomerisation and subsequent decrease in efficacy of irradiated avobenzone has also been demonstrated using several different comparable methods in earlier publications. [7][8][9][10][11][12][13][14] Previous studies have sought to identify ingredients that stabilise the more effective chelated enol form of avobenzone, such as compatible UV filters or antioxidants. [15][16][17] Micellar and lipid microparticle encapsulation of avobenzone have also been shown to have a role in enhancing its photostability.…”

“…[15][16][17] Micellar and lipid microparticle encapsulation of avobenzone have also been shown to have a role in enhancing its photostability. 9,18 Deuteration of the diketo methylene/enol moiety affects the tautomerisation equilibrium, by shifting it towards the ketone form. 19 Many photofragments of avobenzone have also been identified, which in turn may induce cytotoxic and skin sensitization effects.…”

“…31 A previous TEAS study of avobenzone in cyclohexane, methanol and acetonitrile by Dunkelberger et al identified changes to its electronic excited-state lifetime that were dependent on solvent polarity. 23 Solvent-dependent effects have also been observed by chromatography, NMR and UV-visible spectroscopy; [7][8][9][10]32,33 these techniques (amongst others) are often used in conjunction with TEAS to correlate the long-term behaviours (minutes to hours) of molecules such as avobenzone, with their ultrafast photophysical processes. Computational methods such as density functional theory (DFT), including time-dependent DFT (TD-DFT), can also be used to guide the assessment of a molecule's suitability for sunscreen use.…”

Illuminating the Effect of the Local Environment on the Performance of Organic Sunscreens: Insights From Laser Spectroscopy of Isolated Molecules and Complexes

“…A recent study from Bardeen and co-workers is relevant in this context. They found that encapsulation of avobenzone into sodium dodecylsulfate micelles considerably enhances its photostability ( Hanson et al, 2020 ). This was attributed to the micelle creating an enhanced polar microenvironment, which reduces the propensity of avobenzone to diketonize and hence photodegrade.…”

Unravelling the Photoprotective Mechanisms of Nature-Inspired Ultraviolet Filters Using Ultrafast Spectroscopy

“…Since the effects of UV-A radiation on the skin have been reported, the sunscreen industry and regulatory agencies now desire a broadband sunscreen (i.e., sunscreens that span across both UV-B and UV-A). However, there are still only a few Food and Drug Administration (FDA)/European Union (EU)-approved UV-A filters and the most widely used (avobenzone) is not very photostable [ 34 , 35 , 36 , 37 ]. This implies that research is still required for the identification of effective UV-A filters.…”