Molecular dynamics simulations of $^1$H NMR relaxation in Gd$^{3+}$--aqua

Abstract

Atomistic molecular dynamics simulations are used to investigate 1 H NMR T1 relaxation of water from paramagnetic Gd 3+ ions in solution at 25 • C. Simulations of the T1 relaxivity dispersion function r1 computed from the Gd 3+ -1 H dipole-dipole autocorrelation function agree within ≃ 5% of measurements above f0 5 MHz, without any adjustable parameters in the interpretation of the simulations. The agreement between simulated and measured r1 above f05 MHz (i.e. B0 0.1 T) shows potential for predicting r1 in chelated Gd 3+ contrast-agents used for clinical MRI, without any adjustable parameters or models. Below f0 5 MHz the simulation overestimates r1 compared to measurements, which is used to estimate the zero-field electron-spin relaxation time. The most strongly bound water molecule to the Gd 3+ complex evinces an autocorrelation function consistent with the mono-exponential decay used in the Solomon-Bloembergen-Morgan (SBM) inner-sphere model.