The electronic structure of a biochromophore (i.e. light absorber) is strongly perturbed by its surrounding environment, e.g. water or amino acid residues within protein pockets or crevices. To reveal the intrinsic electronic properties, it is therefore necessary to study isolated molecules in vacuo. Many biochromophores are ionic in their natural environment, which renders experiments complicated as it is not possible to produce enough absorbing species for traditional light transmission spectroscopy. In Aarhus we have developed state-of-the-art apparatus to record gas-phase absorption spectra of macromolecular ions. The technique is based on the combination of an electrospray ion source, a multipole ion trap for pre-storage, an electrostatic ion storage ring, and pulsed tuneable lasers and relies on measurements of the delayed dissociation of photoexcited ions (action spectroscopy). In this talk I will present some recent results for porphyrin and metalloporphyrin ions. Porphyrin containing proteins are ubiquitous in nature and are responsible for key biological processes, such as photosynthesis, oxygen transport and storage, and sensing. One important target system is heme which is a porphyrin with an iron atom located in the centre bound to four ring nitrogens. It colours blood red and is located in hydrophobic pockets of heme proteins with minimal access to water. We gradually build up the microenvironment of the heme to elucidate the impact of single molecules on the heme electronic structure. Such information is important in bioanalytical spectroscopy and for monitoring conformational changes and dynamics. Our latest results which show how nitric oxide (NO) perturbs the absorption bands will be presented. Interactions with NO are particularly interesting as heme-NO proteins play a key role in many physiological functions, for example blood clotting and vasodilation upon the bite of blood-sucking insects. Finally, our spectra provide a natural testing ground for future quantum chemical theories and methods.

 References

[1]  M.K. Lykkegaard, A. Ehlerding, P. Hvelplund, U. Kadhane, M.-B.S. Kirketerp, S. Brøndsted Nielsen, S. Panja, J.A. Wyer, and H. Zettergren, J. Am. Chem. Soc., 130, 11856 (2008)

[2]  M.K. Lykkegaard, H. Zettergren, M.-B. S. Kirketerp, A. Ehlerding, J.A. Wyer, U. Kadhane, and S. Brøndsted Nielsen, J. Phys. Chem. A, 113, 1440 (2009) 

[3]  J.A. Wyer and S. Brøndsted Nielsen, J. Chem. Phys., 133, 084306 (2010)

[4]  K. Støchkel, J.A. Wyer, M.-B.S. Kirketerp and S. Brøndsted Nielsen, J. Am. Soc. Mass Spectrom., 21, 1884-1888 (2010)

[5]  J.A. Wyer, C.S. Jensen, and S. Brøndsted Nielsen, Int. J. Mass Spectrom., 308, 126-132 (2011)

[6]  J.A. Wyer, and S. Brøndsted Nielsen, Angew. Chem. Int. Ed., 51, 10256-10260 (2012)

Coffee/tea and cake will be served from 15:05