Luminescence spectroscopy of isolated macromolecular ions in vacuo

Note: The colloquium will take place thorough zoom via the link: https://zoom.us/j/4459928099

Meeting ID: 445 992 8099

There are many occurrences of fluorescence and bioluminescence in nature, e.g., the Green Fluorescent Protein (GFP) or the luciferase enzyme that is responsible for light emission from fireflies. The photoactive molecules within these two proteins are both negatively charged (anions) and are surprisingly non-fluorescent when isolated in vacuo. Which interactions with the protein microenvironment are needed to turn on the fluorescence? This question is not only interesting from a fundamental point of view but also in biotechnology. Indeed, much work is devoted to develop bright fluorescent proteins or dyes in the red region of the visible spectrum where tissue transmission is high. My group tackles the question from a bottom-up approach as we study isolated molecular ions in vacuo and their intrinsic photophysics. In addition to protein biochromophores, we are interested in ionic dyes that are used in Förster Resonance Energy Transfer (FRET) experiments. Our work is based on home-built instruments, one important one being LUNA (LUminescence iNstrument in Aarhus) that allows us to measure fluorescence from larger ions produced by electrospray ionization. We have used this setup to study rhodamine monomer cations as well as homodimers (two identical dyes) and heterodimers (two different dyes) where the two dye cations are separated by flexible methylene linkers or more rigid linear linkers. In the case of heterodimers we see clear evidence of FRET in gas-phase systems, i.e., energy transfer from the initially photoexcited donor dye to the acceptor dye. I will present the results and discuss how the presence of one dye significantly affects the other. One of our future goals is to turn on light emission from protein biochromophores, either by cooling to low temperatures or by the attachment of polar molecules. This may be accomplished with a new setup (LUNA2) where the luminescence cell (trap) is cooled to liquid nitrogen temperature.