Predicting H NMR relaxation in Gd-aqua using molecular dynamics simulations

Atomistic molecular dynamics simulations are used to predict 1 H NMR T 1 relaxation of water from paramagnetic Gd 3+ ions in solution at 25 °C. Simulations of the T 1 relaxivity dispersion function r 1 computed from the Gd 3+ - 1 H dipole-dipole autocorrelation function agree within 8% of measurements in the range f 0 5 ↔ 500 MHz, without any adjustable parameters in the interpretation of the simulations, and without any relaxation models. The simulation results are discussed in the context of the Solomon-Bloembergen-Morgan inner-sphere relaxation model, and the Hwang-Freed outer-sphere relaxation model. Below f 0 5 MHz, the simulation overestimates r 1 compared to measurements, which is used to estimate the zero-field electron-spin relaxation time. The simulations show potential for predicting r 1 at high frequencies in chelated Gd 3+ contrast-agents used for clinical MRI. MD simulations of 1 H NMR relaxivity r 1 for Gd 3+ -aqua agree within 8% of measurements above f 0 5 MHz, without any adjustable parameters or relaxation models. The technique shows potential for simulating r 1 in chelated Gd 3+ contrast-agents used for clinical MRI.