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Towards a deeper understanding of the photodynamics of UV filters for sunscreen applications, using ultrafast spectroscopy and complementary analytical techniques
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Holt, Emily L. (2021) Towards a deeper understanding of the photodynamics of UV filters for sunscreen applications, using ultrafast spectroscopy and complementary analytical techniques. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3781081
Abstract
Sunscreen formulations have been developed to provide an artificial barrier against the adverse health implications of overexposure to solar ultraviolet (UV) radiation. The work contained within this thesis employs a combination of time-resolved (ultrafast) and steady-state spectroscopy, alongside other complementary experimental and computational techniques, to identify molecular relaxation pathways in current and candidate UV filters following photoexcitation. The nature of these pathways are, in turn, insightful for assessing a filter’s suitability for sunscreen use. Increasing existing knowledge on sunscreen filters has been made necessary due to efficacy and environmental concerns with the current, approved options.
Chapter 2 details the photoprotection mechanism of homosalate (HMS), a worldwide-approved UVB (290 – 320 nm) filter in the salicylate family of molecules. Experiments and supporting calculations, both in vacuum and in solution, conclude that HMS undergoes ultrafast excited-state intramolecular proton transfer upon photoexcitation of an enol tautomer. Then, once in the keto tautomer, excess energy is largely dissipated non-radiatively and the original (ground-state) enol tautomer is returned, which is favourable from a photophysical viewpoint.
The remainder of the thesis focuses upon UVA (320 – 400 nm) filters. In Chapter 3, the merits of selective molecular design are explored: specifically, a natureinspired sinapate compound was symmetrically functionalised to have equivalent cis and trans isomers. This maintains the beneficial photophysical properties of the UV filters found in plant leaves, whilst simultaneously alleviating adverse effects that can be induced by cis-trans photoisomerisation, as seen in related cinnamates.
Thereafter, Chapter 4 uses the widely used UVA filter avobenzone as a case study to link ultrafast spectroscopy results to industry-standard in vitro sun protection factor values, via the observation of the recovery of ground-state bleach spectral features. Together, Chapters 3 and 4 then advance to mimicking the application of sunscreen formulations to the skin surface. This was attained using a synthetic skin mimic (Chapter 3) and a heated sample interaction region to model skin surface temperature (Chapter 4). Cosmetics grade emollients were used as solvents in both cases, to model a completed sunscreen blend more closely.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics Q Science > QD Chemistry R Medicine > RS Pharmacy and materia medica |
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Library of Congress Subject Headings (LCSH): | Sunscreens (Cosmetics), Ultraviolet radiation, Skin -- Effect of ultraviolet radiation on, Photoisomerization, Protective coatings | ||||
Official Date: | November 2021 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Molecular Analytical Science Centre for Doctoral Training | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Stavros, Vasilios G. | ||||
Format of File: | |||||
Extent: | xxvii, 163 leaves : illustrations (colour), charts | ||||
Language: | eng |
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