Mark Hugo Stockett

My research combines optical spectroscopy and mass spectrometry to experimentally study the molecular building blocks of important biological systems. This approach, known as action spectroscopy, provides information not only about the absorption spectra of these molecules, but also what happens to the molecules after a photon is absorbed. Such light-activated processing of molecular ions lies at the heart of many important chemical reactions both in biological phenomena such as the photosynthesis of vitamin D and the perception of magnetic fields by migratory birds. Photo-processing often leaves the molecules in a very different state, setting the stage for further reactions in their environments. Interactions at the interface between biochromophores and macromolecular surfaces not only tune the optical spectra of the chromophores but also affect their photochemistry. For example, a water molecule within a protein pocket can strongly perturb the electronic structure of a chromophore through hydrogen bond interactions, and also serve as a proton donor to the photo-excited chromophore. A detailed understanding of such micro-environmental effects can be built in a bottom-up approach starting with bare chromophore molecules and model systems of incrementally increased complexity incorporating perturbing agents such as protein side-chains or solvent molecules.

Supported by a Starting Grant from the Swedish Research Council, I am currently establishing an independent research program to measure the electronic properties of cold, gas-phase molecular ions using action spectroscopy. I am developing a new instrument for measuring luminescent light emission (i.e. fluorescence and phosphorescence) from laser excited, gas-phase molecular ions produced by electrospray and stored in a radio-frequency ion trap. This is a capability with tremendous potential which is currently possible in only a handful of labs worldwide. This new apparatus, called the Cryogenic StockhOlm Luminescence (CrySOL) instrument, will be unique in its capability to cool molecular ions to internal temperatures below 10 K. This activity aims to unravel the intrinsic photo-physics of molecular ions in the gas phase, and to quantitatively understand their interactions at the protein interface. The latter is achieved by investigating small model systems where individual perturbations, such as binding of a single side-chain or solvent molecule, can be studied in isolation.

I also perform experiments at various facilities around the world where highly specialized action spectroscopy equipment is available. These include the DESIREE infrastructure at Stockholm University, and the laboratories of my collaborators at Aarhus University (DK) and the University of Melbourne (AU). By combining data from complimentary techniques, e.g. photo-induced dissociation and laser-induced fluorescence, deeper insight can be gained into complex photochemical processes.

A final activity I currently lead is the mass spectrometric study of high-energy collisions between atoms and complex molecular ions. These experiments model the direct action of ion beam cancer therapy on biomolecules and also the processing of interstellar molecules by supernova shocks. As the energy transfered in single high energy collisions is much larger than that employed in typical commercial mass spectrometers, a more complete picture of the statistical unimolecular dissociation rates may be obtained and compared to state-of-the art molecular dynamics simulations. These data are also used to help identify non-statistical (\textit{i.e.} excited-state) fragmentation processes in photochemical experiments.