Revisiting paramagnetic relaxation enhancements in slowly rotating systems: how long is the long range?

Abstract. Cross-relaxation terms in paramagnetic systems that reorient rigidly with slow tumbling times can increase the effective longitudinal relaxation rates of protons more than 1 order magnitude. This is evaluated by simulating time evolution nuclear magnetization using a complete rate-matrix approach. The calculations show Solomon dependence on metal–proton distance (as r−6) be incorrect for farther 15 Å from metal and thus cause sizable errors R1-derived restraints used, instance, protein structure determination. Furthermore, chemical exchange these bulk water enhance rate solvent far expected equation. Therefore, it may contribute significantly to proton measured at magnetic resonance imaging (MRI) fields presence slow-rotating nanoparticles containing ions large number exchangeable surface protons.