Mapping the intrinsic absorption properties and photodegradation pathways of the protonated and deprotonated forms of the sunscreen oxybenzone

Wong, Natalie G. K.; Berenbeim, Jacob A.; Hawkridge, Mathew; Matthews, Edward; Dessent, Caroline E. H.

doi:10.1039/c8cp06794e

Cited by 32 publications

(72 citation statements)

References 59 publications

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“…This allows us to monitor how the absorbance of the anion varies with wavelength, while simultaneously measuring the production of any photoproducts . Our laser‐based approach is in the spirit of a number of recent studies where advanced spectroscopic techniques have been applied to sunscreen molecules under highly‐controlled conditions …”

Section: Introductionmentioning

confidence: 99%

“…Gas‐phase photochemical studies provide a complementary approach to mapping photodegradation where photoproducts can be directly identified, and experimental results can be straightforwardly compared to theoretical calculations. However, gas‐phase laser spectroscopy of the ionic forms of sunscreen molecules are currently sparse, with only oxybenzone having been studied very recently in its protonated and deprotonated forms . Notably, deprotonated oxybenzone was observed to photofragment with production of methyl radicals in the UVB.…”

Section: Introductionmentioning

confidence: 99%

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Direct Observation of Photochemical Free Radical Production from the Sunscreen 2‐Phenylbenzimidazole‐5‐Sulfonic Acid via Laser‐Interfaced Mass Spectrometry

2019

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The common sunscreen molecule 2-phenylbenzimidazole-5sulfonic acid (PBSA) is studied in its gas-phase deprotonated form ([PBSA-H] À ) for the first time as an important step in achieving a better understanding of its behavior as a photosensitizer. UV laser-interfaced mass spectrometry is employed, revealing that [PBSA-H] À photofragments into three ionic products (m/z 208, 193, and 80) with distinctive wavelengthdependent production profiles. Both the m/z 208 and 80 channels produce associated neutral free radical species.showing that its hot ground-state dissociates only into m/z 193 (statistical fragment). Therefore, the m/z 208 and 80 fragments which are produced strongly through the UVA/UVB are characterized as non-statistical photofragments associated with non-ergodic excited-state decay. Our observation of nonstatistical photofragments reveal that [PBSA-H] À is not behaving as a model sunscreen molecule. Further, our results indicate that the T 1 state, associated with photosensitization, decays with direct free radical production.[a] N.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Direct Observation of Photochemical Free Radical Production from the Sunscreen 2‐Phenylbenzimidazole‐5‐Sulfonic Acid via Laser‐Interfaced Mass Spectrometry

2019

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“…Gas-phase UV photodissociation experiments were conducted in an AmaZon SL dual funnel electrospray ionization quadrupole ion trap (ESI-QIT) mass spectrometer (Bruker Daltonics Inc., Billerica, MA, USA), which was modified to allow LIMS. 41,43,57 Avobenzone (AB) was purchased from Sigma-Aldrich (St. Louis, MO, USA) and HPLC-grade EtOH was purchased from Fisher Scientific, Inc. (Pittsburgh, PA, USA), both used as received. Solutions of AB (1 × 10 −4 mol dm −3 ) in EtOH were electrosprayed using typical instrumental parameters (nebulizing gas pressure of 10.0 psi; injection rate of 0.33 mL/h; drying gas flow rate of 8.0 L/min), and run in positive ion mode at a capillary temperature of 100°C.…”

Section: Methodsmentioning

confidence: 99%

“…We use laser-interfaced mass spectrometry (LIMS) to select ions that are then subjected to wavelength-dependent laser photodissociation, allowing us to measure the gas-phase absorption spectrum. 41,42 LIMS has recently been shown to be a useful tool for studying isomeric systems. 43−47 Applying LIMS to AB•H + allows us to selectively investigate the photochemistry of both enol and keto tautomers, and to probe the extent to which tautomerization occurs, away from any influences of the bulk-phase environment.…”

Section: Introductionmentioning

confidence: 99%

“…Fundamental studies of the effect of pH on sunscreen molecules to date are sparse. 5,41,48,49 Recent measurements from our group have highlighted the impact of protonation and deprotonation on oxybenzone, in terms of the nature and wavelength dependence of its UV photofragmentation pathways. 41 A separate study of deprotonated 2-phenylbenzimidazole-5-sulfonic acid provided direct evidence for the production of free radical photoproducts following UVA excitation.…”

Section: Introductionmentioning

confidence: 99%

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Unravelling the Keto-Enol Tautomer Dependent Photochemistry and Degradation Pathways of the Protonated UVA Filter Avobenzone

Berenbeim¹,

Wong²,

Cockett³

et al. 2020

Preprint

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Avobenzone (AB) is a widely used UVA filter known to undergo irreversible photodegradation. Here, we investigate the detailed pathways by which AB photodegrades by applying UV laser-interfaced mass spectrometry to protonated AB ions. Gas-phase infrared multiple-photon dissociation (IRMPD) spectra obtained with the free electron laser for infrared experiments, FELIX, (600-1800 cm-1) are also presented to confirm the geometric structures. The UV gas-phase absorption spectrum (2.5-5 eV) of protonated AB contains bands that correspond to selective excitation of either the enol or diketo forms, allowing us to probe the resulting, tautomer-dependent photochemistry. Numerous photofragments (i.e. photodegradants) are directly identified for the first time, with m/z 135 and 161 dominating, and m/z 146 and 177 also appearing prominently. Analysis of the production spectra of these photofragments reveals that that strong enol to keto photoisomerism is occurring, and that protonation significantly disrupts the stability of the enol (UVA active) tautomer. Close comparison of fragment ion yields with the TDDFT-calculated absorption spectra give detailed information on the location and identity of the dissociative excited state surfaces, and thus provide new insight into the photodegradation pathways of avobenzone, and photoisomerisation of the wider class of β-diketone containing molecules.<br>

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Direct Measurement of the Visible to UV Photodissociation Processes for the PhotoCORM TryptoCORM

Cercola

Fischer

Sherman

et al. 2020

Chemistry A European J

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PhotoCORMs are light‐triggered compounds that release CO for medical applications. Here, we apply laser spectroscopy in the gas phase to TryptoCORM, a known photoCORM that has been shown to destroy Escherichia coli upon visible‐light activation. Our experiments allow us to map TryptoCORM's photochemistry across a wide wavelength range by using novel laser‐interfaced mass spectrometry (LIMS). LIMS provides the intrinsic absorption spectrum of the photoCORM along with the production spectra of all of its ionic photoproducts for the first time. Importantly, the photoproduct spectra directly reveal the optimum wavelengths for maximizing CO ejection, and the extent to which CO ejection is compromised at redder wavelengths. A series of comparative studies were performed on TryptoCORM‐CH 3 CN which exists in dynamic equilibrium with TryptoCORM in solution. Our measurements allow us to conclude that the presence of the labile CH 3 CN facilitates CO release over a wider wavelength range. This work demonstrates the potential of LIMS as a new methodology for assessing active agent release (e.g. CO, NO, H 2 S) from light‐activated prodrugs.

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Mapping the intrinsic absorption properties and photodegradation pathways of the protonated and deprotonated forms of the sunscreen oxybenzone

Abstract: Laser photodissociation experiments on gas-phase protonated and deprotonated oxybenzone reveal how the absorption properties and photodegradation products are significantly affected by pH.

Cited by 32 publications

References 59 publications

Direct Observation of Photochemical Free Radical Production from the Sunscreen 2‐Phenylbenzimidazole‐5‐Sulfonic Acid via Laser‐Interfaced Mass Spectrometry

Direct Observation of Photochemical Free Radical Production from the Sunscreen 2‐Phenylbenzimidazole‐5‐Sulfonic Acid via Laser‐Interfaced Mass Spectrometry

Unravelling the Keto-Enol Tautomer Dependent Photochemistry and Degradation Pathways of the Protonated UVA Filter Avobenzone

Direct Measurement of the Visible to UV Photodissociation Processes for the PhotoCORM TryptoCORM

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