ESR spectroscopic characterization of spin labeled procaine in homogeneous solutions and membrane mimetic systems

► Solvent effect on ESR spectra of the spin-labeled procaine, sl-PRC, is discussed. ► Amphiphile/water partition coefficients of the protonated drug are estimated. ► The partition is determined by both electrostatic and hydrophobic interactions. ► In vesicles the sl-PRC molecule extends toward the center of the aggregate. ► In micelles the spin label is located relatively close to the interface.