EPR study of low molecular weight organogels by means of a nitroxide spin probe

It is shown that continuous wave electron paramagnetic resonance (EPR) spectroscopy combined with pulsed mode EPR exhibits improvement in studying the structural and dynamic characteristics of gels. This approach applied on bis(leucine) oxalyl diamide ethanol gels revealed that secondary structural units of self-organized gelator molecules promote the interactions with paramagnetic nitroxyl groups exhibiting hydrogen acceptor properties. Ethanol entrapped in the gel network was still prone to glass → crystalline transformation. In the ethanol crystalline state, nitroxide spin lattice relaxation time revealed increased spin-phonon interactions as the gelator concentration was increased, while a complex behaviour was observed in ethanol glass.