Synchrotron Nuclear Spectroscopy of Nitrogenase and Hydrogenase - Nature's Nanoparticle Catalysts

by Stephen P. Cramer, UC Davis and Lawrence Berkeley National Laboratory

Wednesday 20 Oct 2010, 13:00 → 14:00 Europe/Berlin

Bldg. 25b, room 109

Nitrogenase is the enzyme responsible for the ‘fixation’ of nearly inert atmospheric dinitrogen to ammonia. It is ultimately responsible for half of the world’s protein, while the other half depends on industrial fertilizer produced with hydrogen derived from fossil fuels. Another type of enzyme, hydrogenase, catalyzes the interconversion of dihydrogen with protons and electrons. These enzymes use unusual forms of Fe-S clusters or Fe carbonyls, and their catalytic mechanisms are not understood. A powerful and relatively new way to study Fe in biological systems is Nuclear Resonance Vibrational Spectroscopy (NRVS). In this synchrotron radiation technique, a sample is excited with a ~1 meV bandwidth beam near a Mössbauer resonance, and the delayed fluorescence is recorded as a function of excitation energy. When applied to Fe samples, NRVS is only sensitive to vibrations involving motion of ⁵⁷Fe. We will present results on model compounds, small Fe-S proteins, and nitrogenase, and hydrogenase, and the needs and prospects for future improvements will be discussed. If time permits, results using other nuclear spectroscopies (nuclear forward scattering – NFS and synchrotron perturbed angular correlation – SRPAC) will also be presented.