Water exchange of a ProHance MRI contrast agent: isomer-dependent free-energy landscapes and mechanisms.

The water-exchange reaction in two diastereoisomers of the clinical magnetic resonance imaging contrast agent [Gd(HP-DO3A)(H(2)O)] (also known as ProHance) has been studied using ab initio simulations. On the basis of the molecular-level details of the mechanism derived from these simulations in aqueous solution, we unravel the underlying difference in the free energies and mechanisms of water exchange in the two diastereoisomers. These findings reveal the crucial role played by hydrogen-bonding dynamics and thus suggest their appropriate control in tailoring improved gadolinium-based constrast agents.