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

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, <i>R</i>₁, 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>B</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 <i>R</i>₁ 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 <i>R</i>₁ 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

¹H NMR Relaxometry and Diffusometry Study of Magnetic and Nonmagnetic Ionic Liquid-Based Solutions: Cosolvent and Temperature Effects

In this work, ¹H NMR relaxometry and diffusometry as well as viscometry experiments were carried out as a means to study the molecular dynamics of magnetic and nonmagnetic ionic liquid-based systems. In order to evaluate the effect of a cosolvent on the superparamagnetic properties observed for Aliquat-iron-based magnetic ionic liquids, mixtures comprising different concentrations, 1% and 10% (v/v), of DMSO-<i>d</i>6 were prepared and studied. The results for both magnetic and nonmagnetic systems were consistently analyzed an suggest that, when at low concentrations, DMSO-<i>d</i>6 promotes more structured ionic arrangements, thus enhancing these superparamagnetic properties. Furthermore, the analysis of temperature and water concentration effects allowed to conclude that neither one of these variables significantly affected the superparamagnetic properties of the studied magnetic ionic liquids