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 stabilityconstants for the non-covalent interactions of cyclodextrin (CD) hosts with smallorganic guests. This technique allows detection of the molecular interactions bymonitoring changes in refractive index at gold surfaces on which the guests areimmobilized. The magnitude of an SPR response is proportional to the mass changeat a surface, and thus the technique has most commonly been used in the past to studylarge molecules such as proteins and DNA. Now SPR has been employed to study theinteractions of CD, CD, CD, per-2,6-dimethyl-CDand Molecusol^TM (hydroxypropyl-CD) with immobilizedN-(1-adamantylmethyl)-, N-octyl-, N-benzyl-, N-(4-methylbenzyl)-,N-(4-tert-butylbenzyl)- and N-(1-pyrenylmethyl)-amides. Methods areoutlined for obtaining high-quality, reproducible binding data. The magnitudes(10²–10⁴ M^-1) and trends in the apparent stability constants so observedare generally consistent with values reported for analogous solution-phase studies. Theresults show that SPR is suitable to study host–guest interactions of small molecules such as cyclodextrins.