Copper (Cu)-amyloid beta (A beta) interactions play a role in the etiology of Alzheimers disease. This work presents a spectroscopic and electrochemical study of two physiologically relevant A beta-Cu-II complexes, as a function of pH and relative Cu-A beta(1-16) concentrations. Our results reveal that these coordination modes display distinct redox behaviors and provide experimental evidence for the existence of an intermediate Cu-I species. A mechanism for the redox cycling of these complexes is proposed, providing further insight into the redox relevance of A beta-Cu interactions.