Chemical CD oscillation and chemical resonance phenomena in a competitive self-catalytic reaction system: a single temperature oscillation induces CD oscillations twice.

Chemical CD oscillation and chemical resonance phenomena appear in a competitive chemical reaction system involving amplification. A pseudoenantiomeric mixture of an aminomethylenehelicene (P)-tetramer and an (M)-hexamer in toluene forms three states, namely hetero-double-helix B, heterodouble-helix C, and dissociated random-coil 2A. When the temperature of the solution is oscillated between -5 and 38 degrees C at a rate of 2 K min(-1), Delta epsilon reaches maxima twice during a single temperature oscillation, which is called a chemical CD oscillation phenomenon. The phenomenon arises from the sharp competition between the two self-catalytic 2A + C-to-2C and 2A + B-to-2B reactions. In addition, the chemical CD oscillation appears, when temperature oscillation occurs at a rate of 2 K min(-1), and higher and lower rates provide a single maximum, a process referred to as the chemical resonance phenomenon. The changes in concentration induced by temperature oscillation repeatedly crossed equilibrium.