Determination of molecular hydration in solution via changes in magnetic anisotropy

Area of Science:

• Coordination chemistry
• Bio-imaging
• Spectroscopy

Background:

• The hydration behavior of coordination complexes is critical for their application in bio-imaging.
• Accurately determining the hydration state of these complexes is challenging.
• Existing methods like optical and NMR spectroscopy have limitations.

Purpose of the Study:

• To unambiguously determine the water coordination of a functionalized Er^III DOTA derivative.
• To compare the hydration behavior of a pyridyl-functionalised Er^III DOTA complex with its methylphosphinate analogue.
• To establish EPR spectroscopy as a reliable method for assessing complex hydration.

Main Methods:

• Electron Paramagnetic Resonance (EPR) spectroscopy was employed.
• A *t*-butyl-pyridyl-functionalised Er^III DOTA derivative and its methylphosphinate analogue were synthesized and studied.

Main Results:

• EPR spectroscopy provided unambiguous evidence of water coordination in the Er^III DOTA derivative.
• The methylphosphinate analogue of the Er^III DOTA derivative was shown to not coordinate water.
• This highlights the significant impact of ligand functionalization on complex hydration.

Conclusions:

• EPR spectroscopy is a powerful tool for definitively assessing water coordination in lanthanide complexes.
• Ligand structure plays a critical role in dictating the hydration behavior of Er^III DOTA derivatives.
• Understanding hydration is key to optimizing Er^III complexes for bio-imaging applications.