RETRACTED ARTICLE: The quantum physiology of oxygen; from electrons to the evolution of redox signaling in the human brain.

Rising atmospheric oxygen (O) levels provided a selective pressure for the evolution of O-dependent micro-organisms that began with the autotrophic eukaryotes. Since these primordial times, the respiring mammalian cell has become entirely dependent on the constancy of electron flow with molecular O serving as the terminal electron acceptor in mitochondrial oxidative phosphorylation. Indeed, the ability to "sense" O and maintain homeostasis is considered one of the most important roles of the central nervous system (CNS) and likely represented a major driving force in the evolution of the human brain. Today, modern humans have evolved with an oversized brain committed to a continually active state and as a consequence, paradoxically vulnerable to failure if the O supply is interrupted. However, our pre-occupation with O, the elixir of life, obscures the fact that it is a gas with a Janus Face, capable of sustaining life in physiologically controlled amounts yet paradoxically deadly to the CNS when in excess. A closer look at its quantum structure reveals precisely why; the triplet ground state diatomic O molecule is paramagnetic and exists in air as a free radical, constrained from reacting aggressively with the brain's organic molecules due to its "spin restriction", a thermodynamic quirk of evolutionary fate. By further exploring O's free radical "quantum quirkiness" including emergent quantum physiological phenomena, our understanding of precisely how the human brain senses O deprivation (hypoxia) and the elaborate redox-signaling defense mechanisms that defend O homeostasis has the potential to offer unique insights into the pathophysiology and treatment of human brain disease.