Analysis of rodent brains with X‐ray fluorescence (XRF) microscopy combined with immunohistochemistry allowed us to demonstrate that local Cu concentrations are thousands of times higher in the glia of the subventricular zone (SVZ) than in other cells. Using XRF microscopy with subcellular resolution and intracellular X‐ray absorption spectroscopy we determined the copper (I) oxidation state and the sulfur ligand environment. Cu K‐edge X‐ray absorption near edge spectroscopy is consistent with Cu being bound as a multimetallic Cu‐S cluster similar to one present in Cu‐metallothionein. Analysis of age‐related changes show that Cu content in astrocytes of the SVZ increases fourfold from 3 weeks to 9 months, while Cu concentration in other brain areas remain essentially constant. This increase in Cu correlates with a decrease in adult neurogenesis assessed using the Ki67 marker (both, however, can be age‐related effects). We demonstrate that the Cu distribution and age‐related concentration changes in the brain are highly cell specific.

Water oxidation is the key half reaction in artificial photosynthesis. An absence of detailed mechanistic insight impedes design of new catalysts that are more reactive and more robust. A proposed paradigm leading to enhanced reactivity is the existence of oxyl radical intermediates capable of rapid water activation, but there is a dearth of experimental validation. Here, we show the radicaloid nature of an intermediate reactive toward formation of the O-O bond by assessing the spin density on the oxyl group by Electron Paramagnetic Resonance (EPR). In the study, an¹⁷O-labeled form of a highly oxidized, short-lived intermediate in the catalytic cycle of the water oxidation catalystcis,cis-[(2,2-bipyridine)₂(H₂O)Ru^IIIORu^III(OH₂)(bpy)₂]⁴⁺was investigated. It contains Ru centers in oxidation states [4,5], has at least one Ru^V= O unit, and shows |A_xx| = 60G¹⁷O hyperfine splittings (hfs) consistent with the high spin density of a radicaloid. Destabilization of π-bonding in thed³Ru^V= O fragment is responsible for the high spin density on the oxygen and its high reactivity.