Conservation of ultrafast photoprotective mechanisms with increasing molecular complexity in sinapoyl malate derivatives

Abstract

Sinapoyl malate is a natural plant sunscreen molecule which protects leaves from harmful ultraviolet radiation. Here, the ultrafast dynamics of three sinapoyl malate derivatives, sinapoyl L‐dimethyl malate, sinapoyl L‐diethyl malate and sinapoyl L‐di‐t‐butyl malate, have been studied using transient electronic absorption spectroscopy, in a dioxane and methanol solvent environment to investigate how well preserved these dynamics remain with increasing molecular complexity. In all cases it was found that, upon photoexcitation, deactivation occurs via a trans‐cis isomerisation pathway within ∼20–30 ps. This cis‐photoproduct, formed during photodeactivation, is stable and longed‐lived for all molecules in both solvents. The incredible levels of conservation of the isomerisation pathway with increased molecular complexity demonstrate the efficacy of these molecules as ultraviolet photoprotectors, even in strongly perturbing solvents. As such, we suggest these molecules might be well‐suited for augmentations to further improve their photoprotective efficacy or chemical compatibility with other components of sunscreen mixtures, whilst conserving their underlying photodynamic properties.

Unravelling the Photoprotection Properties of Garden Cress Sprout Extract

“…The assignment of EADS 4 to the cis-isomer is supported through a comparison of the transient absorption profile obtained at ∆t = 2 ns, shown as an inset in Figure 3E,F and Figure 4C, to those reported for SM and its derivatives previously [14,30], which show an identical long-lived feature assigned to the cis-isomer.…”

“…This dynamical process results in a fraction of the excited state population reforming the original trans-isomer, while another fraction completes the isomerisation along the allylic C=C double bond to generate the cis-isomer photoproduct. The cis-isomer photoproduct accounts for the absorption of EADS 4 (at ~360 nm) with a time constant τ 4 , which is >2 ns [14,15,17,19,22,23,25,30].…”

Radiationless mechanism of UV deactivation by cuticle phenolics in plants

“…τ 2 and τ 3 can be associated with the trans - cis isomerization process. In particular, τ 2 relates to the vibrational cooling in the excited state and likely correspond to motion along the ππ * state, while τ 3 describes the internal conversion to the ground state along the photoisomerization coordinate 35 . Finally, a fourth time, τ 4 , present in some instances, has been ascribed to long-lived species with lifetimes of nanoseconds; in the case of the solution of p -coumaric acid, this long lifetime is ascribed to the presence of the cis-isomer.…”

Quantum Mechanics/Molecular Mechanics Studies on the Photophysical Mechanism of Methyl Salicylate

“…Ultraviolet (UV) radiation has a comprehensive impact on human health, such as appropriate exposure to UV can generate vitamin D that has a beneficial effect on human health, but excessive UV exposure can cause detrimental effects such as sunburn, photocarcinogenesis, and photoaging. − Sunscreens are believed to be an effective tool in providing photoprotection for our skin against the UV radiation. The chemical filters used in modern commercial sunscreens play a critical role in photoprotection, which can dissipate the absorbed excessive UV radiation energy as heat through some nondestructive pathways to provide an additionally effective photoprotection for the skin. − Thus, in recent years, a large number of experimental and theoretical studies have focused on the excited-state relaxation dynamics of a variety of chemical UV filters including cinnamates, − eumelanins, − benzophenones, − camphor, , octocrylenes, − and salicylates. − …”