Structural dynamics of(bio-) macromolecules probed by optical spectroscopy

In this thesis, spectroscopic analyses on one biological and one non-biological macromolecular system are presented. In both cases, optical experiments shed light onto the (binding resp. conformational) dynamics of the systems’ structure. The first system under examination was the enzyme CO dehydrogenase (CODH) from the bacterium Oligotropha carboxydovorans. Fluores-cence correlation spectroscopy was used as a relatively un-complex assay for the confirmation of a binding between enzymes and larger substrates – here, the specificity of the binding of CODH and the cyto-plasmic membrane was examined by replacing the binding partners. Instrumentation for further investigations on CODH, especially using time-resolved fluorescence spectroscopy had already been developed, but no agreement with the cooperation partner on the continuation of this line of research could be found. Hence, this instrumentation was further used for the characterisation of a different (non-biological) compound. This second system was a dimer of two flexibly linked perylene bisi-mide dyes: di- (perylene bisimide acrylate) – (PerAcr)2. It served as a model system for higher oligomers resp. polymers containing perylene bisimide, which are candidates for the application in organic solar cells. A combination of spectroscopic techniques was used for the character-ization, with time-resolutions down to picoseconds (time-resolved fluorescence spectroscopy resp. anisotropy) and in part with single-molecule sensitivity (fluorescence correlation spectroscopy). By using global analysis methods a description of the measured data with mini-mised sets of free parameters was pursued, yielding robust hypothesis testing. Additionally, comparisons with molecular dynamics simula-tions and modelling were conducted. Among other results, it was thus possible to show that the examined dimers change conformation on μs timescales between two aggregated and one isolated state; and that the isolated conformation shows a fast transfer of excitation energy be-tween the two dyes. The findings were reported in three publications, which are the core of this thesis (chapter 4). In particular the last two publications show a possible way for using poly- (perylene bisimide) in organic solar cells: Instead of relying on the aggregation of the dyes, it should be decidedly avoided and non-coherent energy transfer should be exploited as an efficient transport mechanism