לוח שנה משולב

A detailed electronic model of the catalytic water splitting Mn4O5Ca cluster in Photosystem II of oxygenic photosynthesis is presented that has been developed based on structural data from X-ray crystallography(1) and magnetic resonance (EPR and ENDOR) techniques.(2-5) High field ELDOR-detected NMR (EDNMR) is introduced as an alternative method for the detection of electron-nuclear hyperfine (hf) interactions of insensitive nuclei like 17O and 14N for which it is superior to the more standard ENDOR and ESEEM (HYSCORE) techniques. We have applied EDNMR at W-band (94 GHz) to detect the interaction of the water oxidizing cluster (S2 state, Seff = ½) with magnetic nuclei of amino acids and attached water molecules. In samples exchanged with H217O, 17O hyperfine couplings of three different types of water molecules were detected.(5) They could be assigned based on the structural model from X-ray crystallography(1) which has been refined using density functional theory(4) and comparison with model complexes. Additional experiments like Ca/Sr exchang2(3) and the use of inhibitors (NH3) helped in this endeavor. This data further refine the reaction pathway for O-O bond formation supporting an oxo/oxyl coupling mechanism in the catalytically active state (S4) of the cycle.(6)

Medical imaging is a fast growing field which received a boost in the last years due to advances in the new detector materials and read-out electronics. The new detectors combined with the new software greatly improve the photon count statistics allowing reducing the patient dose due to radioactive ex-posure, bringing at the same time the diagnostic capabilities to the new level. Such a rapid progress in the SPECT (Single Photon Emission Computed Tomography) and CT (Computed Tomography) is of particular interest in the framework of this talk. The most advanced among the existing CT systems utilize scintillating materials coupled with photodiodes to create 2D images used as an input to the 3D image reconstruction. Spectroscopic solid state detectors would allow transforming these systems producing “black and white” images based only on energy-integrated I/I0 information into state of the art photon counting systems known as multi-energy or “true colour” CT. The entry requirements on detectors to be used in these applications is stable operation under X-ray fluxes of 107 to 108 counts•s-1•mm-2.

In this talk I shall discuss the advantages and possible future developments of CdZnTe and CdTe room-temperature semiconductor detectors for developing these innovating medical imaging tech-niques. These detectors have been proven to be the main candidates for that purpose, in particular since their large average atomic mass number combined with the high energy resolution provides ex-cellent quantum efficiency superior to other semiconductor materials.