Influence of some salts and lower alcohols on the Pfeiffer effect. A close resemblance of the Pfeiffer systems to ionic surfactant solutions

The influence of some inorganic salts and lower alcohols (methanol to pentanol) was examined on the following Pfeiffer-active systems at 25°; [Zn(phen)₃]SO₄-d-cinchonine hydrochloride and -l-strychnine hydrosulfate, [Zn(bpy)₃]SO₄-d-cinchonine hydrochloride, and [Zn(phen)₃]SO₄-ammonium d-α-bromocamphor-π-sulfonate systems in water (phen = 1,10-phenanthroline and bpy = 2,2′-bipyridine). It was found that, except for the last system, the logarithm of the Pfeiffer rotation α_p changes linearly with the logarithm of total counterion concentration C_j, α_p decreases linearly with added alcohol concentration C_A, and the logarithm of the rate of the decrease in α_p with C_A is a linear function of the number of carbon atoms in added alcohol molecules. These phenomena were interpreted to mean that added anions reduce the electrostatic repulsion between [Zn(phen)₃]²⁺ or [Zn(bpy)₃]²⁺ and d-cinchoninium or l-strychninium cation, thereby enhancing the Pfeiffer effect, and that added alcohol molecules penetrate into the aggregates composed of the above complex and chiral cations, thereby diminishing the Pfeiffer effect. It was proposed that the complex must come into direct contact with the chiral environment compound to exhibit the Pfeiffer effect. A close resemblance of the Pfeiffer systems to ionic surfactant solutions was also noted.