Molecular Recognition in Terms of a Dimensionless Index. 2. Thermodynamic Patterns of Intermolecular Interactions of PEG and Its Alcohol Substrates

The systems containing poly(ethylene glycol) (PEG) receptor and its alcohol substrate (n-C_nH_2n+1OH, n = 1−5 and i-C₃H₇OH) were used to examine molecular exo-recognition between their constituent components in terms of the dimensionless index. On the basis of the hypothesis that all the local orientation-based fits of the common part of two alcohols on the same a receptor are subjected to the same a pattern of intermolecular interactions, two sorts of patterns of intermolecular orientation-based fitting between the PEG receptor and its alcohol substrate are believed to be responsible for the thermodynamic behavior accompanied by alcohol−PEG interactions on the two different kinds of PEG receptors. The interaction entropies estimated from these patterns are found to be in reasonable accordance with their experimental observations. The patterns of orientation-based fitting between PEG and alcohol are ascribed to the average patterns of PEG−alcohol exo-recognition on the thermodynamics time scale.