Photostability of the deprotonated forms of the UV filters homosalate and octyl salicylate: molecular dissociation <i>versus</i> electron detachment following UV excitation

Wong, Natalie G. K.; Rankine, Conor D.; Anstöter, Cate S.; Dessent, Caroline E. H.

doi:10.1039/d2cp01612e

Cited by 4 publications

(8 citation statements)

References 61 publications

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“…OMC is primarily used as a UVB absorber in sunscreen formulations [10] with λmax = 310 nm, so it is notable that the strong band I absorption feature appears significantly red-shifted for the protonated gas-phase species. A similar red shift was observed for protonated oxybenzone [27], where protonation was found to occur in the aromatic conjugated carbonyl group, as is also expected for OMCH + . A recent extensive study by Bardeen and co-workers on UV excitation of OMC found that aggregation was important in its photochemical behaviour, with OMC aggregation leading to a complex mixture of photoproducts (truxillic and truxinic dimers), including the production of UVA photoproducts, which generated singlet oxygen [22].…”

Section: Gas-phase Absorption Spectrum Of Protonated Omcsupporting

confidence: 78%

Section: Gas-phase Absorption Spectrum Of Protonated Omcsupporting

confidence: 77%

“…Given that aggregation effects are implicated in that work, it is useful to consider using gas-phase measurements to investigate the intrinsic photochemical properties of OMC as a basis for future studies of the aggregates. Our group has employed laser-interfaced mass spectrometry (LIMS) to perform such gas-phase investigations on a range of organic sunscreen molecules and complexes, demonstrating the utility of this approach for characterising photostability and mapping photodegradation pathways [24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

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Photochemical Degradation of the UV Filter Octyl Methoxy Cinnamate Probed via Laser-Interfaced Mass Spectrometry

et al. 2022

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Octyl methoxycinnamate (OMC) is a common UVA and UVB filter molecule that is widely used in commercial sunscreens. Here, we used gas-phase laser photodissociation spectroscopy to characterise the intrinsic photostability and photodegradation products of OMC by studying the system in its protonated form, i.e., [OMC·H]+. The major photofragments observed were m/z 179, 161, and 133, corresponding to fragmentation on either side of the ether oxygen of the ester group (m/z 179 and 161) or the C–C bond adjacent to the ester carbonyl group. Additional measurements were obtained using higher-energy collisional dissociation mass spectrometry (HCD-MS) to identify fragments that resulted from the breakdown of the vibrationally hot electronic ground state. We found that the m/z 179 and 161 ions were the main fragments produced by this route. Notably, the m/z 133 ion was not observed through HCD-MS, revealing that this product ion is only produced through a photochemical route. Our results demonstrate that UV photoexcitation of OMC is able to access a dissociative excited-state surface that uniquely leads to the rupture of the C–C bond adjacent to the key ester carbonyl group.

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Section: Gas-phase Absorption Spectrum Of Protonated Omcsupporting

confidence: 78%

Section: Gas-phase Absorption Spectrum Of Protonated Omcsupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

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Photochemical Degradation of the UV Filter Octyl Methoxy Cinnamate Probed via Laser-Interfaced Mass Spectrometry

et al. 2022

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“…It is not always only spectroscopy and theory that are used to study MAs. In Caroline Dessent's lab, 22 photo dissociation and mass spectrometry were used to study the competition between fragmentation and electron detachment involving MAs consisting of the deprotonated forms of two molecules used in sunscreens. Such an approach was important in determining how long these molecules could protect against UV radiation before being photodegraded.…”

Section: A Conventional (Valence)mentioning

confidence: 99%

Molecular Anions Perspective

Simons

2023

J. Phys. Chem. A

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This Perspective attempts to shed light on developments in the theoretical and experimental study of molecular anions highlighting more recent workers in the field. The species I discuss include (i) valence-bound (singly and multiply charged) anions including atmospheric, catalytic, superhalogen, interfacial, and more; (ii) dipole- and correlation-bound anions including their role as doorways to other states and their appearance “in space”, and (iii) metastable anions focusing on tools needed for their theoretical treatment. I also briefly discuss angular distributions of photodetached electrons and their growing utilization in experiments and theory. A recurring theme is the dependence of electron binding energies (EBEs) on the surrounding environment. Some anions that are nonexistent as isolated species evolve to be stable but with small EBEs when weakly solvated (e.g., as in a cluster or at an air–solvent interface). Others existing in isolation only as metastable species become stable when the underlying molecular framework contains one or more positively charged group (e.g., protonated side chains in a peptide) that generates a stabilizing Coulomb potential. On the other hand, a destabilizing Coulomb potential between/among negative sites in a multiply charged anion decreases the EBEs of each such site and generates a repulsive Coulomb barrier that can affect stability.

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“…[13][14][15][16] It is particularly useful in the context of analysing photoproducts, since these can be straightforwardly identified by mass spectrometry following photoexcitation and decay of a precursor ion. In these experiments, the organic chromophore is introduced to the MS via electrospray ionization and studied either as the protonated or deprotonated form of the molecule, [17][18][19] or in a complex with an attached ion-tag, such as an alkali metal cation. [16] The ionic sunscreen precursor ion is isolated in an ion trap, where it is irradiated with photons across the UV range, and the photoproducts obtained at each photoexcitation energy measured.…”

Section: Introductionmentioning

confidence: 99%

Laser Interfaced Mass Spectrometry of the Sunscreen Molecule Octocrylene Demonstrates that Protonation Does Not Impact Photostability

Anstöter,

Wong,

Selwe

et al. 2023

ChemPhotoChem

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Octocrylene (OCR) is a widely used organic sunscreen molecules, and is a dominant component of many sunscreen formulations. Here, we perform the first measurements on the protonated form of OCR, i.e. [OCR+H]+, to probe whether protonation affects the molecule’s photostability. The novel photochemical technique of UV laser‐interfaced mass spectrometry is employed from 400‐216 nm, revealing that the electronic absorption spectrum of OCR across the S1 and S2 states red shift by 40 nm upon protonation. Our measurements reveal that [OCR+H]+ predominantly undergoes photofragmentation into the m/z 250 and 232 ionic products, associated with loss of its bulky alkyl side chain, and subsequent loss of water, respectively. We compare the photochemical fragmentation results with higher‐energy collisional dissociation results to investigate the nature of the photodynamics that occur following UV absorption. The excited state decay pathways over the S1 and S2 excited states of [OCR+H]+ are associated with statistical fragmentation in line with dominant ultrafast decay. This behaviour mirrors that of neutral OCR, demonstrating that protonation does not affect the ultrafast decay pathways of this sunscreen molecule. We discuss our results in the context of the known breakdown of OCR into benzophenone, identifying a potential photoactivated pathway to benzophenone formation in solution.

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Photostability of the deprotonated forms of the UV filters homosalate and octyl salicylate: molecular dissociation versus electron detachment following UV excitation

Abstract: Laser photodissociation of deprotonated salicylates reveals that electron detachment outcompetes molecular dissociation following photoexcitation due to the locations of the minimum energy crossing points on the excited state surfaces.

Cited by 4 publications

References 61 publications

Photochemical Degradation of the UV Filter Octyl Methoxy Cinnamate Probed via Laser-Interfaced Mass Spectrometry

Photochemical Degradation of the UV Filter Octyl Methoxy Cinnamate Probed via Laser-Interfaced Mass Spectrometry

Molecular Anions Perspective

Laser Interfaced Mass Spectrometry of the Sunscreen Molecule Octocrylene Demonstrates that Protonation Does Not Impact Photostability

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