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1H NMR Relaxation Study of a Magnetic Ionic Liquid as a Potential Contrast Agent

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journal contribution
posted on 03.09.2015, 00:00 by Carla I. Daniel, Fabián Vaca Chávez, Carla A. M. Portugal, João G. Crespo, Pedro J. Sebastião
A proton nuclear magnetic relaxation dispersion 1H NMRD study of the molecular dynamics in mixtures of magnetic ionic liquid [P66614]­[FeCl4] with [P66614]­[Cl] ionic liquid and mixtures of [P66614]­[FeCl4] with dimethyl sulfoxide (DMSO) is presented. The proton spin–lattice relaxation rate, R1, was measured in the frequency range of 8 kHz–300 MHz. The viscosity of the binary mixtures was measured as a function of an applied magnetic field, B, in the range of 0–2 T. In the case of DMSO/[P66614]­[FeCl4] the viscosity was found to be independent from the magnetic field, while in the case of the [P66614]­[Cl]/[P66614]­[FeCl4] system viscosity decreased with the increase of the magnetic field strength. The spin–lattice relaxation results were analyzed for all systems taking into account the relaxation mechanisms associated with the molecular motions with correlation times in a range between 10–11 and 10–7s, usually observed by NMRD, and the paramagnetic relaxation contributions associated with the presence of the magnetic ions in the systems. In the case of the DMSO/[P66614]­[FeCl4] system the R1 dispersion shows the relaxation enhancement due to the presence of the magnetic ions, similar to that reported for contrast agents. For the [P66614]­[Cl]/[P66614]­[FeCl4] system, the R1 dispersion presents a much larger paramagnetic relaxation contribution, in comparison with that observed for the DMSO/[P66614]­[FeCl4] mixtures but different from that reported for other magnetic ionic liquid system. In the [P66614]­[Cl]/[P66614]­[FeCl4] system the relaxation enhancement associated with the paramagnetic ions is clearly not proportional to the concentration of magnetic ions, in contrast with what is observed for the DMSO/[P66614]­[FeCl4] system.