Closer inspection of Figure shows a linear connection between the type of molecule and how the free energy of binding changes with increasing degree of substitution. For the tested molecules, a natural interpretation of this is that the 2-hydroxypropyl side chains extends the less polar cavity of HP-β-CD to better accommodate the apolar guests and shield them from the polar solvent. We propose the following linear model for the free energy of binding, ∆G linear bind , of HP-β-CD as a function of DS