Trapped In Critical Condition

Molecular motion can be controlled with shaped light fields. LMU researchers use this concept to develop uracil strategies for the RNA base, which simplify spectroscopic access to RNA photoshaden.

LMU researchers around Regina de Vivie-Riedle , Professor of Theoretical Chemistry at the LMU, have developed a model that allows the photochemical reaction to be specifically analyzed for ribonucleic acid (RNA) in the case of UV radiation. UV radiation leads to chemical reactions in DNA and RNA, which can lead to damage in genetic information. In order to elucidate the molecular mechanisms involved in the formation of such photosyntheses, the dynamics of isolated RNA nuclein bases are investigated in numerous studies with short laser pulses. A protective mechanism of nature makes the work more difficult: the molecules excited by light release the energy very quickly. "This minimizes the risk of photoshooting, but at the same time the state can be characterized poorly spectroscopically"

A team around Regina de Vivie-Riedle, together with Spiridoula Matsika from the Temple University in Pennsylvania (former Humboldt scholarship holder at the LMU), shows how this ultra-fast process can be controlled with the help of specially shaped light fields. One of these light fields holds the molecule much longer in the excited state than usual, as if a pause key were pressed. "The lifetime of the critical excited state can be prolonged from about 190 femtoseconds with short pulse excitation with unformed light to 50 picoseconds and more with shaped light," says de Vivie-Riedle. The researchers are currently reporting on the Journal of the American Chemical Society .

They are based on previous experiments with femtosecond pulses, which show that after UV excitation, uracil relaxes rapidly again into the basic state. The LMU chemists have optimized the laser pulses in simulations to different targets and can either accelerate or significantly slow the relaxation process of Uracil. In particular by catching in the critical state, the path is opened for subsequent spectroscopic investigations of the reactions leading to photoschaden. The authors assume that the results can also be transferred to other nuclein bases. "We are confident that our simulations will contribute to a more targeted investigation of the chemical processes leading to photoshooting," says de Vivie-Riedle.