Electron Spin Resonance Studies of Substituted 1,4-Naphthoquinones

Abstract

As early as 1885, reddish pigments were observed in the viscera and calcareous skeleta of sea urchins. It was not until 1939, however, that a pure, crystalline pigment was isolated and identified. From that time on and until recently, a plethora of supposedly different pigments were reported to have been isolated. Recent work, however, has proven the identity of many pigments which were once thought to be distinct and, as a result, the number of pigments of unquestioned structure was reduced to six.