The Transfer of Excitation Energy from p-Terphenyl to Riboflavin

Abstract

In 1941, Szent-Gyorgyi (1) published an interesting paper entitled Towards a New Biochemistry. In this publication, he speculated that the transfer of energy in proteins was similar to that described for crystal phosphors, namely, that an electron released by external radiation travels a long distance in the crystal before meeting an impurity. At this point, the energy is released. Later, Szent-Gyorgyi (2) became discouraged over this concept of transfer of energy in biological systems owing to lack of experimental evidence for energy levels in proteins. In recent years, however, the concept of transfer of excitation energy between molecules has developed along two general lines: for liquid scintillation counters and for the absorption and utilization of light energy by the plant. It has been demonstrated that numerous compounds in organic solvents will selectively pick up excitation energy and transfer this energy to a second molecule (3-7). The plant physiologists have described such a transfer in diatoms, algae, and chlorphyll-containing bacteria (7-13). In view of these developments on the transfer of energy, it was decided to use these techniques for a study of the possible role of molecules of biological interest in the transfer of energy in liquid systems. The general concept is to study the fluorescence of two substances independently and in combination. In combination, if energy is transferred, the fluorescence of the first substance will decrease and the fluorescence of the second will increase. No attempt will be made to elucidate the actual mechanisms of the transfer (14, 15). Riboflavin was selected as a representative molecule on account of its widespread occurrence in plant and animal tissues and its function as a coenzyme in several important enzyme systems. Riboflavin has a series of absorption bands at 475, 445, 359, and 268 m, and shows fluorescence at 500 to 600 m,.