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Photochemical processes in biological chromophores and clusters.Goal of the research
The goal of our projects is to understand photochemical processes in biological systems, such as DNA or proteins. Unfortunately, the large size and structural complexity of such biological molecules hampers the direct experimental and theoretical characterization. We therefore use a bottom-up approach and first investigate the inherent properties of the isolated chromophores by experiment and theory. Next, we explore how the photochemical processes are influenced by a local environment by studying molecular clusters of increasing size. Like assembling a puzzle, the systematic study of all relevant interactions can lead to the description of complex biological systems through knowledge of all relevant local properties. While it would be overly optimistic to hope for a complete understanding of photochemical processes in biology, this approach clearly offers fundamental insight into the chemical and physical properties of increasingly large systems. Spectroscopy of molecular clustersThe investigation of small molecular clusters containing one or several biological chromophores allows the controlled introduction of directed molecular interactions, e.g. hydrogen bonding or base stacking in DNA bases. Our experimental tools include femtosecond time-resolved electron and mass spectroscopy. Time resolved spectroscopy pump-probe spectroscopy allows the observation of excited state processes in real time. Electron spectroscopy allows the direct assignment of electronic structure. The combination of pump-probe and electron spectroscopy thus allows to follow the evolution of electronically excited states along a (photochemical) reaction coordinate Mass spectroscoy diagnoses the composition of the investigated cluster species. Together with the fs pump probe technique this offers a direct correlation of cluster composition and excited state processes. We also have the a unique ability to perform and interpret time-resolved electron-ion coincidence experiments, where electronic structure can be assigned to observed cluster masses. Spectroscopy of protonated molecular ionsThe evaporation of neutral molecules is only practical for small chromophores and clusters. For bigger molecules, the generation of a molecular beam with only one or few molecular / cluster species is difficult. Mass selection before the pump-probe experiment is therefore desirable to remove unwanted species from the beam. The electrospray ionization source facilitates the evaporation of large protonated molecules and the resulting charged particles are easily mass selected before the optical experiment. The investigation of larger, covalently bound molecular ions The investigation of cationic species formed in an electrospray source allows the investigation of larger molecules where chemical subunits interact with the chromophore of interest.Our experimental tools include femtosecond laser in the application laboratories of the MBI, Wiley McLaren mass spectrometers and Electron-ion coincidence spectrometers. A liquid-jet photoelectron spectrometer is currently under construction. |