CONCERNING THE THERMODYNAMICS OF MOLECULAR RECOGNITION IN AQUEOUS AND ORGANIC MEDIA - EVIDENCE FOR SIGNIFICANT HEAT-CAPACITY EFFECTS

Variable-temperature binding studies are used to evaluate the thermodynamics of molecular recognition of a variety of guests by macrocyclic, cyclophane hosts. In both organic (CDC13) and aqueous media, significant heat capacity effects are evident. Curvature in the van't Hoff plots can be well-modeled by assuming a constant value for ΔCp°, and statistical analysis reveals a meaningful improvement in the correlation when ΔCp° is included. Trends in the values for ΔH°29B and ΔS°298 reveal a predominantly enthalpic origin for the “cation-π” effect, which involves the stabilization of a positive charge by the electron-rich face of an aromatic ring. © 1990, American Chemical Society. All rights reserved.