Patel, Anand Manojkumar; (2021) Synthesis and anion photoelectron spectroscopy studies of oxyluciferins and oxyinfraluciferins. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Firefly bioluminescence occurs by the enzyme catalysed oxidation of D-luciferin to oxyluciferin in its electronically excited by a luciferase in the presence of ATP, Mg2+ and O2 co-factors. Relaxation to its ground state results in the emission of a photon of light. The wavelength of light emission can be altered by mutating the luciferase and/or synthesising analogues of luciferin. In the Anderson group, a synthetic π-extended analogue of luciferin, infraluciferin, was synthesised and exhibited a significant red shifted emission, but was ~ 100 times dimmer than D-luciferin. An understanding of the excited state dynamics of the light emitter oxyluciferin in vacuo may help to design better bioluminescent systems for analytical applications. Part one describes the results of anion photoelectron spectroscopy measurements employed to determine the electronic structure of oxyluciferin in vacuo. These were interpreted with the aid of quantum chemistry calculations performed by another PhD student. Oxyluciferin can exist in three anionic resonance forms (keto, enol and enolate). To track the dynamics of these different species, the known protected derivatives, which trap the resonance forms, were synthesised from the literature and their photoelectron measurements were recorded between wavelengths 359 – 294 nm. The excited state dynamics of the analogues were unravelled by linking spectral features with the calculated excited state energies. Part two describes the synthesis of three protected π-extended resonance forms of oxyinfraluciferin and preliminary photoelectron measurements of the keto and enolate derivatives recorded at 346 nm. The synthesis features two unique cyclisation strategies to form the keto and acetyl-protected enolate derivatives. The acetyl-protected enolate derivative was successfully deacetylated in situ before running photoelectron measurements. Preliminary analysis of the 346 nm photoelectron spectra of keto and enolate derivatives provides a good starting point for future detailed spectroscopic investigations on understanding how increasing the conjugation affects the electronic structure and dynamics relative to their oxyluciferyl derivatives.

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