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

Jacob A. Berenbeim, Natalie G.K. Wong, Martin C.R. Cockett, Giel Berden, Jos Oomens, Anouk M. Rijs, Caroline E.H. Dessent

Research output: Contribution to JournalArticleAcademicpeer-review


A key decay pathway by which organic sunscreen molecules dissipate harmful UV energy involves excited-state hydrogen atom transfer between proximal enol and keto functional groups. Structural modifications of this molecular architecture have the potential to block ultrafast decay processes, and hence promote direct excited-state molecular dissociation, profoundly affecting the efficiency of an organic sunscreen. Herein, we investigate the binding of alkali metal cations to a prototype organic sunscreen molecule, oxybenzone, using IR characterization. Mass-selective IR action spectroscopy was conducted at the free electron laser for infrared experiments, FELIX (600-1800 cm-1), on complexes of Na+, K+ and Rb+ bound to oxybenzone. The IR spectra reveal that K+ and Rb+ adopt binding positions away from the key OH intermolecular hydrogen bond, while the smaller Na+ cation binds directly between the keto and enol oxygens, thus breaking the intramolecular hydrogen bond. UV laser photodissociation spectroscopy was also performed on the series of complexes, with the Na+ complex displaying a distinctive electronic spectrum compared to those of K+ and Rb+, in line with the IR spectroscopy results. TD-DFT calculations reveal that the origin of the changes in the electronic spectra can be linked to rupture of the intramolecular bond in the sodium cationized complex. The implications of our results for the performance of sunscreens in mixtures and environments with high concentrations of metal cations are discussed.

Original languageEnglish
Pages (from-to)19522-19531
Number of pages10
JournalPhysical chemistry chemical physics : PCCP
Issue number35
Publication statusPublished - 16 Sept 2020
Externally publishedYes


This work was funded through the Leverhulme Trust Research Project Grant RPG-2017-147. We thank the University of York and the Department of Chemistry for provision of funds for the OPO laser system, and the University of York High Performance Computing service, Viking, and the Research Computing team, for the provision of computational resources. We gratefully acknowledge the Nederlandse Organisatie voor Wetenschappe-lijk Onderzoek (NWO) for the support of the FELIX Laboratory. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.

FundersFunder number
Horizon 2020 Framework Programme730872
Leverhulme TrustRPG-2017-147


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