When trying to define rigorously whether an arrangement of atoms is sufficiently stable to be considered a molecule, IUPAC suggests that it "must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state".  This definition does not depend on the nature of the interaction between the atoms, but only on the strength of the interaction. In fact, it includes weakly bound species that would not traditionally be considered molecules, such as the helium dimer , He 2 , which has one vibrational bound state  and is so loosely bound that it is only likely to be observed at very low temperatures.
Oxidative stress is caused by the increased production of reactive oxygen (ROS) and nitrogen (RNS) species, including superoxide , hydroxyl (OH • ), peroxyl (ROO • ), alkoxyl (RO • ) and peroxynitrite (ONOO • ), as well as nonradical species, such as singlet oxygen ( 1 O 2 ), ozone (O 3 ), and hydrogen peroxide (H 2 O 2 ) [ 16 ]. These chemical species are generated by a wide variety of processes, including mitochondrial respiration, ischemia/reperfusion, inflammation, and the metabolism of exogenous compounds [ 17 ]. The excessive generation of ROS might oxidise cellular biomolecules, including carbohydrates, proteins, lipids, and DNA. The oxidation of these molecules can facilitate carcinogenesis-related processes, such as cellular transformation, proliferation, apoptosis resistance, angiogenesis, and metastasis via genetic alterations, including DNA damage, mutation, epigenetic changes, and genetic instability [ 18 ].