Light induced charge transfer processes in bis-oxo and peroxo dicopper complexes for biomimetic hydroxylation

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Tyrosinase is a ubiquitous metalloenzyme which plays the central role in dioxygen activation for the biosynthesis of hormones and pigments. Despite great efforts in the design of bioinorganic model complexes, the crucial oxygen-transferring step towards phenolic substrates as well as the subsequent reactivity of the resulting catecholates to quinones is still not fully understood. During the first funding period, we were able to characterize a high fidelity functional tyrosinase model. Now, we target a detailed spectroscopic analysis of each step of the catalytic cycle complemented by density functional theory. The planned studies combine classical analytical techniques (low-temperature UV/Vis spectroscopy, catalysis-derived methods, X-ray structure analysis) with inelastic light scattering in the visible, ultra-violet, and vacuum ultra-violet spectral range as well as X-ray absorption spectroscopy. Their utilization allows for the characterization of reaction intermediates enabling the detailed elucidation of the reaction progress and thus delivering truly new insights into tyrosinase. Concomitantly, we investigate the substrate scope and enhance the catalyst performance.The second part of the project aims at the synthesis of a photoactivatable oxygen-transferring system which is subject to combined resonance Raman and XAS studies. The design of this system envisions a biomimetic hydroxylation reactivity upon excitation with suited light sources. In the second period of the Research Group we will continue the development of different methods for sample allocation and manipulation. Our aim is to establish several techniques that allow to access a broad range of timescales within pump-probe (fs) and pump-probe-flow (up to s) experiments of guanidine- and bis(pyrazolyl)methane-based model complexes. As delivery systems we will apply the jet and aerosol technology developed in SP1 as well as Peltier-cooled cryo-systems for stop freeze measurements. For the stimulation of electron transfer, we will use resonance and pump-probe Raman measurements. The basic kinetics of the reactions will also be investigated with time-resolved transmission techniques and complemented by time resolved Raman measurements. Our technical capabilities are complemented by steady state and time resolved X-ray absorption fine structure (XAFS) measurements. Alone and in combination, these techniques allow a detailed characterization of the structure and function of guanidine- and bis(pyrazolyl)methane-based model complexes within the biomimetic catalytic cycle.