Characterisation and application of ultra-high spin clusters as magnetic resonance relaxation agents

Abstract

In Magnetic Resonance Tomography (MRT) image contrast can be improved by adding paramagnetic relaxation agents such as lanthanide ions. Here we report on the use of highly paramagnetic isostructural Fe^III/4f coordination clusters with a [Fe₁₀Ln₁₀] core to enhance relaxation. Measurements were performed over the range of ¹H Larmor frequencies of 10 MHz to 1.4 GHz in order to determine the relevant parameters for longitudinal and transverse relaxivities. Variation of the lanthanide ion allows differentiation of relaxation contributions from electronic states and molecular dynamics. We find that the transverse relaxivities increase with field, whereas the longitudinal relaxivities depend on the nature of the lanthanide. In addition, the Gd^III analogue was selected in particular to test the interaction with tissue observed using MRT. Studies on biofilms used in waste water treatment reveal that the behaviour of the high-spin clusters is different from what is observed for common relaxation agents with respect to the penetration into the biofilms. The Fe₁₀Gd₁₀ cluster adheres to the surface of the biofilm better than the commercial agent Gadovist.