Pfeiffer effect, equilibrium shift mechanism

KIRSCHNER ET AL. Equilibrium Shift Mechanism for the Pfeiffer Effect 305... 

The Pfeiffer effect is a term used to describe changes in the optical activity of solutions containing a chiral compound (the environmental substance ) on the addition of a racemic dissymmetric complex. The effect is generally attributed to a shift in the position of the equilibrium between d and l isomers for the racemic complex. The exact mechanism involved in mediating the chiral interaction is unknown. Perhaps surprisingly, both environmental substance and complex may simultaneously be cations. Studies of the Pfeiffer effect usually involve a moderately labile racemic complex [Cr(ox)3]3 is a popular choice for such studies, summarized in Table 82. Other studies of the optical activity of tris oxalates include work on photoinduced optical activity,898 photoracemization899 and the solid-state racemization of K3[Cr(ox)3]. 900 901... 

The experiments described above have led to the conclusion that the chiral-induced equilibrium shift could be induced in the lanthanide (III) complex by a combination of electrostatic and hydrophobic interactions. Hydrogen bonding effects appear to be less important as suggested by experiments carried out under variable pH, temperature, concentration, solvent type, and solution dielectric constant conditions. By analogy to the associated/dissociated equilibrium shift models of Schipper (1978) in which the source of the equilibrium perturbation is attributed to a free energy of mixing, Brittain (1981) and Wu et al. (1989) attempted to ascertain the complex mechanism responsible for this type of Pfeiffer effect. However, their conclusions were opposite as they concluded that the [Tb(DPA)3] complex interacted with the... 

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