Archiv 2016

Photophysical investigations of the canonical nucleobases that make up DNA and RNA show that in room-temperature solvents, their excited states decay with (sub)picosecond lifetimes (τ = 0.3–2 ps). The apparent generality of ultrafast excited-state deactivation in the canonical nucleobases has led to the hypothesis that nucleobases are molecular survivors of the harsh UV environment on the early Earth before the emergence of life. [mehr]

Quantum-chemical calculations are essential for the assignment and interpretation of spectra of small molecules as well as complex molecular systems. Large molecular systems present a significant challenge not only because of the increasing computational effort that is required for an accurate quantum-chemical description, but also require new approaches for the interpretation of the large amount of data provided by such calculations. On the other hand, small molecular systems with a complicated electronic structure, such as transition metal complexes, pose additional challenges and their theoretical spectroscopy also requires novel quantum-chemical approaches. [mehr]

Hydration has a drastic impact on the structure and function of flexible biomolecules, such as aromatic ethylamino neurotransmitters. [mehr]

Extended molecules can be solvated at various inequivalent sites and it is useful to learn from experiment on a kJ/mol accuracy scale which solvent docking site is energetically more attractive. Theoretical relative energy predictions are rather easy to make and could thus be rigorously benchmarked by such experimental ratings of docking sites. However, experimental comparison of solvent-solute pair binding energies is not trivial, because it requires low temperature for complex stabilization but still sufficiently high mobility for equilibration. For the class of simple aromatic ethers solvated by methanol, the docking competition is very subtle [1] and we were able to tune it by chemical substitution, switching at will between classical OH-O and more diffuse OH-π docking preferences [2]. This new docking balance experiment profits from linear infrared absorption spectroscopy in supersonic jets [3] and allows for a fairly rigorous test of state-of-the-art quantum chemical predictions for relative hydrogen bond energies. The popular M06-2X density functional is shown to fail quite badly. [mehr]