Department of Chemistry, University of California, Riverside, 501 Big Springs Road, 92521, Riverside, CA, USA.
Photochem Photobiol Sci. 2020 Mar 1;19(3):390-398. doi: 10.1039/c9pp00483a. Epub 2020 Feb 26.
The photodegradation of avobenzone (AV), the only ultraviolet filter molecule approved by the Food and Drug Administration to absorb UVA radiation, is an important problem in sunscreen formulations. In this paper, the photophysics and photostability of AV in various solvent systems and in aqueous micelles are studied. AV in its keto-enol tautomer functions as an effective UVA protection agent. AV is highly susceptible to photoinduced diketonization in both nonpolar solvents and in aqueous aggregates but is considerably more stable in polar, protic solvents like methanol. By studying its stability in different surfactant solutions, we show that incorporation of AV into sodium dodecylsulfate (SDS) micelles can achieve stability levels comparable to neat methanol. Steady-state spectral shifts, fluorescence anisotropy, and time-resolved fluorescence decay measurements are all consistent with AV experiencing a polar environment after micellar encapsulation. It is proposed that AV is encapsulated in the palisade layer of the SDS micelles, which allows access to water molecules that facilitate the re-formation of the enol form after photon absorption and relaxation. Although the detailed mechanism of AV tautomerization remains unclear, this work suggests that tuning the chemical microenvironment of AV may be a useful strategy for improving sunscreen efficacy.
阿伏苯宗（AV）的光降解是防晒配方中一个重要问题，它是唯一一种被美国食品和药物管理局批准吸收 UVA 辐射的紫外线滤光剂分子。本文研究了 AV 在各种溶剂体系和水胶束中的光物理和光稳定性。AV 以其酮-烯醇互变异构体形式作为有效的 UVA 保护剂。AV 在非极性溶剂和水聚集体中极易发生光诱导二酮化，但在极性质子溶剂（如甲醇）中则相当稳定。通过研究其在不同表面活性剂溶液中的稳定性，我们表明将 AV 掺入十二烷基硫酸钠（SDS）胶束中可以达到与纯甲醇相当的稳定水平。稳态光谱位移、荧光各向异性和时间分辨荧光衰减测量均表明，胶束包封后 AV 经历了极性环境。据推测，AV 被 SDS 胶束的栅栏层包封，这允许水分子进入，有利于光子吸收和弛豫后烯醇形式的重新形成。尽管 AV 互变异构的详细机制尚不清楚，但这项工作表明，调节 AV 的化学微环境可能是提高防晒霜功效的一种有用策略。
