Spektralphotometrische Bestimmung kleiner Hydrazinkonzentrationen im Wasser

Ohne ZusammenfassungWir sind Herrn Prof. Dr.-Ing. H.Hartmann sowie Herrn Dr. rer. nat. habil. H.Spandau für die Anregung zu der vorliegenden Untersuchung zu Dank verbunden.     

How Does a Membrane Protein Achieve a Vectorial Proton Transfer Via Water Molecules?

We present a detailed mechanism for the proton transfer from a protein‐bound protonated water cluster to the bulk water directed by protein side chains in the membrane protein bacteriorhodopsin. We use a combined approach of time‐resolved Fourier transform infrared spectroscopy, molecular dynamics simulations, and X‐ray structure analysis to elucidate the functional role of a hydrogen bond between Ser193 and Glu204. These two residues seal the internal protonated water cluster from the bulk water and the protein surface. During the photocycle of bacteriorhodopsin, a transient protonation of Glu204 leads to a breaking of this hydrogen bond. This breaking opens the gate to the extracellular bulk water, leading to a subsequent proton release from the protonated water cluster. We show in detail how the protein achieves vectorial proton transfer via protonated water clusters in contrast to random proton transfer in liquid water.     

Nuclear orientation of14N after grazing collisions with a silicon surface

The nuclear orientation of¹⁴N is investigated after the scattering of¹⁴N⁺ ions with energies ranging from 7 to 350 keV from an Si(111)-surface under grazing angles of incidence. For projectile energies above 50 keV, we find a constant nuclear orientationP ₁=〈I _z 〉/I∼22%, whereas towards lower energiesP _I shows a pronounced decrease. Our measurements provide important information in the application of surface scattering to obtain nuclear polarized beams.