Aspects of structural order in 209Bi-containing particles for potential MRI contrast agents based on quadrupole enhanced relaxation

ABSTRACTQuadrupole relaxation enhancement (QRE) has been suggested as the key mechanism for a novel class of field-selective, potentially responsive magnetic resonance imaging contrast agents. In previous publications, QRE has been confirmed for solid compounds containing 209Bi as the quadrupolar nucleus (QN). For QRE to be effective in aqueous dispersions, several conditions must be met, i.e. high transition probability of the QN at the 1H Larmor frequency, water exchange with the bulk and comparatively slow motion of the Bi-carrying particles. In this paper, the potential influence of structural order within the compounds (‘crystallinity’) on QRE was studied by nuclear quadrupole resonance (NQR) spectroscopy in one crystalline and two amorphous preparations of Triphenylbismuth (BiPh3). The amorphous preparations comprised (1) a shock-frozen melt and (2) a granulate of polystyrene which contained homogeneously distributed BiPh3 after common dissolution in THF and subsequent evaporation of the solvent. In...