EPR imaging techniques are known to be successful tools for mapping living bodies,
especially because of the high transparency of tissues in the microwave range. This
technique assumes the presence of radicals whose in vivo transport is also controlled
by serum albumins. Accordingly, in this study, the interactions between 3-hydroxymethyl-1-oxyl-4-(pyren-1-yl)-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrole
radical and the human serum albumin molecules were investigated. To clarify the adsorption
processes of this radical onto the surface of human serum albumin (HSA), the interaction
of the OMe derivative of the radical was also examined parallel with the studies on
the radical—HSA interactions. Considering the solubility issues and also to modulate
the transport, inclusion complexes of the radical with a cavitand derivative were
also studied. The latter interactions were observed through fluorescence spectroscopy,
fluorescence polarization, and by EPR spectroscopy. As a double-sensor molecule, we
found that the fluorophore nitroxide is a good candidate as it gave further information
about host-guest interactions (fluorescence, fluorescence polarization, and EPR).
We also found that in the presence of a cavitand, a complex with greater stability
was formed between the sensor molecule and the human serum albumin. Based on these
observations, we can conclude that applying this double-sensor (spin, fluorescent)
molecule is useful in cases when different interactions can affect the EPR measurements.
