A Platform of Phenol-Based Nitroxide Radicals as an "EPR Toolbox" in Supramolecular and Click Chemistry

Abstract

A large number (63) of well-defined nitroxide radicals, all phenol-based TEMPO and PROXYL esters, were synthesized using different strategies based on well-established Steglich esterifications. All of these radicals can be used as spin probes (SPs) and spin labels (SLs) for electron paramagnetic resonance (EPR) spectroscopy of supramolecular systems. Depending on the nature of the functional group(s) on each SP/SL, the synthesized nitroxide radicals serve as polyphilic molecular "toolbox" for the EPR-spectroscopic detection and characterization of specific types of interactions, e. g. π-π interactions, sulfur-sulfur interactions, hydrogen bonding, electrostatic and dipole-dipole interactions, and van der Waals and hydrophobic interactions, in the presence of the selected supramolecular systems of interest (e. g. proteins, peptides). For each synthesized SP/SL the water solubility was gravimetrically determined for use in aqueous solution at pH 7.

Keywords: EPR spectroscopy; click chemistry; radicals; spin labels; supramolecular chemistry.