Surface plasmon resonance to determine apparent stability constants for the binding of cyclodextrins to small immobilized guests

Surface plasmon resonance (SPR) has been used to determine apparent stability constants for the non-covalent interactions of cyclodextrin (CD) hosts with small organic guests. This technique allows detection of the molecular interactions by monitoring changes in refractive index at gold surfaces on which the guests are immobilized. The magnitude of an SPR response is proportional to the mass change at a surface, and thus the technique has most commonly been used in the past to study large molecules such as proteins and DNA. Now SPR has been employed to study the interactions of αCD, βCD, γCD, per-2,6-dimethyl-βCD and Molecusol™ (hydroxypropyl-βCD) with immobilized N-(1-adamantylmethyl)-, N-octyl-, N-benzyl-, N-(4-metliylbenzyl)-, N-(4-tert-butylbenzyl)- and N-(1-pyrenylmethyl)-amides. Methods are outlined for obtaining high-quality, reproducible binding data. The magnitudes (10 ²-10⁴ M^-1) and trends in the apparent stability constants so observed are generally consistent with values reported for analogous solution-phase studies. The results show that SPR is suitable to study host-guest interactions of small molecules such as cyclodextrins.