Electron Paramagnetic Resonance Study of the Effect that the Covalent Binding of Cyclodextrin Receptors to Silica-Gel Microparticles Has on the Molecular Dynamics and Complexation of Spin-Labeled Guests

摘要

The molecular dynamics of the spin probes of different structures in complexes with cyclodextrins (CDs) which were covalently attached to silica-gel microparticles has been studied by electron paramagnetic resonance (EPR). Two states of the bound spin probes have been found which differ appreciably in rotational mobility and environment polarity. Our results allow one to conclude that the strongly immobilized state is that of CD spin probe complexes which are adsorbed on the hydrophobic regions of the modified silica-gel surface, whereas the weakly immobilized state corresponds to the desorbed complex, the mobility of which is controlled by the conformational flexibility of the linker. The binding constants K were determined for a hydrophobic probe (spin-labeled indole) and two water-soluble spin probes with silica-gel microparticles containing the covalently bound β-CD and phenyl-βCD. The absolute value of the effect that the micropar- ticle surface has on the K value is quite small, and its sign depends on the probe structure and the mode of its intercalation into the CD complex. The competitive binding of the spin-labeled molecules and analytes with CDs has been demonstrated, which can be utilized for the production of the paramagnetic sensors.