Spin–lattice relaxation studies on deep eutectic solvent/Choliniumtetrachloroferrate mixtures: Suitability of DES‐based systems towards magnetic resonance imaging studies

This study has been undertaken with an aim to investigate the suitability of the deep eutectic solvents (DES)‐based systems for magnetic resonance imaging studies. DESs are used to develop the systems, keeping in mind the fact that these are relatively less toxic than ionic liquids, and hence, DES based magnetic compound is expected to be relatively less toxic than magnetic ionic liquids. In this work, spin–lattice (T1) relaxation measurements are carried out in the binary mixtures of deep eutectic solvent with a paramagnetic component choliniumtetrachloroferrate ([Ch][FeCl4]). Two cholinium ion based DESs, namely ethaline and glyceline have been used for this study. For both ethaline/[Ch][FeCl4] and glyceline/[Ch][FeCl4], T1 is observed to vary significantly with very low concentration of [Ch][FeCl4]. Such an observation can arise due to the high degree of paramagnetic coupling between DESs and [Ch][FeCl4]. The results advocate the suitability of both ethaline/[Ch][FeCl4] and glyceline/[Ch][FeCl4] mixture as a potential T1 contrast agent. Interestingly, when the experiments are carried out in aqueous medium, significant lowering of T1 of water proton with very low concentration of ethaline/[Ch][FeCl4] and glyceline/[Ch][FeCl4] is observed. This study demonstrates that the present systems can act as a suitable T1 contrast agent. T1 relaxation plots for ethaline + [Ch][FeCl4] and glyceline + [Ch][FeCl4] show a significant variation in T1 in both ethaline + [Ch][FeCl4] and glyceline + [Ch][FeCl4] even with very low concentration of [Ch][FeCl4]. This indicates their potential as a suitable T1 NMR contrast agent.