A Janus molecule (or Janus-faced molecule) is a molecule which can represent both beneficial and toxic effects. The term Janus-faced molecule is derived from the ancient Roman god, Janus. Janus is depicted as having two faces; one facing the past and one facing the future. This is synonymous to a Janus molecule having two distinct purposes: a beneficial and a toxic purpose.
Examples of a Janus-faced molecule are nitric oxide and cholesterol. In the case of cholesterol, the property that makes cholesterol useful in cell membranes, namely its absolute insolubility in water, also makes it lethal...