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

Abstract

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.

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

“…The experiments reported here result from applying novel laser-interfaced mass spectrometry within an adapted commercial mass spectrometer, a technique that has considerable broader potential for applied photochemical and photophysical studies. [27,59] In particular, the experiments performed here are not limited to photoCORMs but could be readily applied to other photo-activated prodrugs including platinum anticancer complexes and H2S or CS2 releasing therapeutical agents. [60][61][62] Finally, we note that our results also represent the first direct gas-phase measurement of the wavelength-dependent photochemical branching ratios (quantum ion yields) for a transition metal carbonyl complex.…”

“…Our experimental technique involves transferring the photoCORM from solution into the gas-phase via electrospray ionization and then using novel Laser-Interfaced Mass Spectrometry (LIMS) to measure the gaseous absorption spectrum along with all of the ionic photoproducts produced at each scanned wavelength. [26,27] Thus, we obtain a complete picture of the excited states along with the accompanying photodissociation pathways. We complement these measurements with Cryogenic Ion Vibrational Spectroscopy (CIVS), [28] an advanced experimental technique that provides structural characterization of gaseous ions.…”

Sodium cationization can disrupt the intramolecular hydrogen bond that mediates the sunscreen activity of oxybenzone

“…To check for single-photon conditions, the laser power dependence on signal was determined, as described previously. 8,10 Photofragmentation experiments were conducted with an ion accumulation time of 20 ms and a fragmentation time of 100 ms, thereby ensuring that each mass-selected ion packet interacted with one laser pulse, minimizing the likelihood of multiphoton events. When fluorescence is negligible, 26 the UV excited gaseous ion will fragment upon excited-state relaxation, yielding an action absorption spectrum by photodepletion (PD).…”

“…Recent work from our group has demonstrated how pH can impact at the molecular level on the function of an organic sunscreen. [8][9][10] Upon protonation, both oxybenzone and avobenzone were observed to photodissociate directly from the excited state surface, i.e., undergo non-statistical dissociation, which is an undesirable photodegradation process. A similar effect was also observed for oxybenzone and 2-phenylbenzimidazole-5-sulfonic acid upon deprotonation.…”

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

“…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.…”