Determination of molecular hydration in solution via changes in magnetic anisotropy

The hydration behaviour of coordination complexes is important for understanding their roles as bio-imaging agents. Determination of hydration is difficult, and various optical and NMR-based techniques have been used. Here we use EPR spectroscopy to unambiguously demonstrate that a t-butyl-pyridyl-functionalised Er(III) DOTA derivative coordinates water, while its methylphosphinate analogue does not.