The removal of reactive oxygen species by glutathione peroxidase involves reactions where the chalcogens O, S, and Se play a central role. The thermodynamics of the steps in the removal are investigated by electron structure calculations on a series of reactions involving these chalcogens. Analysis of the free energy-and enthalpy changes for the reactions shows a universal linear relationship, called the chalcogenicity, which may be useful in estimating thermodynamic properties in related reactions. (C) 2013 Elsevier B. V. All rights reserved.