Predicting ¹H NMR relaxation in Gd³⁺-aqua using molecular dynamics simulations

Area of Science:

• Computational chemistry
• Nuclear Magnetic Resonance (NMR) spectroscopy
• Magnetic Resonance Imaging (MRI)

Background:

• Paramagnetic Gadolinium (Gd³⁺) ions are crucial for MRI contrast agents.
• Understanding water ¹H NMR T₁ relaxation dynamics is essential for optimizing contrast agent performance.
• Predictive models are needed to guide the design of advanced MRI contrast agents.

Purpose of the Study:

• To utilize atomistic molecular dynamics simulations for predicting ¹H NMR T₁ relaxation of water.
• To validate simulation accuracy against experimental measurements of relaxivity dispersion.
• To explore the potential of simulations in designing chelated Gd³⁺ contrast agents for clinical MRI.

Main Methods:

• Atomistic molecular dynamics simulations were performed at 25 °C.
• ¹H NMR T₁ relaxivity dispersion (r₁) was computed from Gd³⁺-¹H dipole-dipole autocorrelation functions.
• Simulation results were compared with experimental data and analyzed within established relaxation models (SBM, Hwang-Freed).

Main Results:

• Simulations achieved good agreement (within 8%) with experimental r₁ measurements across a broad frequency range (5–500 MHz).
• No adjustable parameters or relaxation models were required for simulation interpretation.
• Discrepancies at lower frequencies (<5 MHz) allowed for the estimation of zero-field electron-spin relaxation time.

Conclusions:

• Atomistic molecular dynamics simulations offer a reliable, parameter-free method for predicting NMR T₁ relaxation.
• The simulation approach holds significant promise for the high-frequency prediction of relaxivity in clinical MRI contrast agents.
• This predictive capability can accelerate the development of improved Gd³⁺-based contrast agents.