The redox activity of Cu ions bound to the amyloid-β (Aβ) peptide is implicated as a source oxidative stress in context Alzheimer's disease. In order explain efficient cycling between CuII-Aβ (distorted square-pyramidal) and CuI-Aβ (digonal) resting states, existence low-populated “in-between” state, prone bind both oxidation has been postulated. Here, we exploited partial X-ray induced photore...