Constrictive binding energy

Figure 6.48 Constrictive binding energy - the activation energy for guest enty to the cavity.

Hemicarceplexes are stabilized by intrinsic and constrictive binding energy. The latter, a physical barrier, is the activation free energy required for a guest to enter the inner cavity and typically amounts to 25-30kcalmol In carceplexes, this barrier is so high that guest escape is impossible without host destraction. Isolated from the bulk phase, the... 

An interesting way to analyze contribntions that make up constrictive binding is to measure the steric kinetic isotope effects (SKIEs) by comparing decomplexation rates of hemicarceplexes with isotopically labeled guests. The physical origin of a steric isotope effect is the smaller zero-point energy (ZPE) of the C-D bond as compared to that... 

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