Concerning the thermodynamics of molecular recognition in aqueous and organic media. Evidence for significant heat capacity effects

Abstract

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 (CDCl_3) 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 ΔC_p^0, and statistical analysis reveals a meaningful improvement in the correlation when ΔC_p^0 is included. Trends in the values for ΔH^0_(298) and ΔS^0_(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.