Active metal sites play a key role in the biochemistry of oxygen transport by hemocyanins. Observing the changes in the local electronic structure of the copper sites upon oxygenation is thus essential for understanding their biological functionality. Here, direct access to the electronic structure of the active copper sites in hemocyanin is achieved via L-edge X-ray absorption spectroscopy under physiological conditions. We compare the deoxygenated and the oxygenated states of native hemocyanin and find evidence that the oxygenation does not simply switch the copper valence state between Cu I and Cu II, as assumed classically. In the deoxygenated state, water molecules can enter the active site and keep the copper atoms partially oxidized. The role of water in this process has never been revealed before for lack of L-edge spectroscopy on copper in solution. Besides providing a more detailed electronic picture for the oxygenation process, this study opens a new chapter in investigating the function of proteins under in-vivo-like conditions.
For accurate mass measurements and identification of atomic and molecular species precise mass calibration is mandatory. Recent studies with laser desorption/ionization and time-of-flight analysis of cluster ion production by use of fullerene and gold targets demonstrate the generation of atomic clusters for calibration purposes. Atomic ion results from the Penning trap mass spectrometer ISOLTRAP, in which a carbon cluster ion source has recently been installed, are presented as an application in the field of precision mass spectrometry.
We report the observation of magnetic circular dichroism (MCD) in two-photon photoemission (2PPE). The Heusler alloys Ni2MnGa and Co2FeSi were investigated by excitation with femtosecond laser light, showing MCD asymmetries of A=(3.5+/-0.5)x10;{-3} for Ni2MnGa and of A=(2.1+/-1.0)x10;{-3} for Co2FeSi, respectively. A theoretical explanation is provided based on local spin-density calculations for the magnetic dichroic response; the computed 2PPE MCD agrees well with the experiment. The observed 2PPE magnetic contrast represents an interesting alternative for future time-resolved photoemission studies on surface magnetism practicable in the laboratory.
We present a near edge x-ray absorption fine structure study of artificial chemical vapor deposition diamonds with sizes in the micron range and of size distributed nanodiamonds extracted from the Murchison meteorite. The modified peak shape in the case of the nanodiamond sample is explained by the interplay between the size distribution of the nanodiamonds and quantum confinement effects within a quantitative analysis based on the effective mass approximation theory.
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