NMR relaxation rate constants are powerful probes of the functional dynamics of biological macromolecules, such as proteins and nucleic acids. However, variations in choice of models used to analyze relaxation data obscure variations due to critical biological or chemical effects. Bootstrap aggregation, a recently developed statistical method, circumvents the model selection problem and enables more consistent and insightful interpretation of NMR relaxation data.

The efficiency of MRI contrast agents can increase by exploiting magnetization transfer effects occurring in slow-rotating nanoparticles containing a paramagnetic metal ion and a large number of exchangeable surface protons, which can increase the water proton relaxation rate. Occurrence of magnetization transfer should also be considered to determine accurate metal–proton distances from the experimental proton relaxation rates for protons farther than 15 Å from the paramagnetic metal.

We studied spin dynamics in nuclear spin systems at low magnetic fields, where strong coupling among nuclear spins of the same kind, here ¹³C, is expected. Such conditions are known to be favorable for coherent polarization transfer. However, to our surprise, interactions with other nuclei, i.e., protons, lead to a breakdown of the strong coupling conditions. By using a two-field nuclear magnetic resonance approach, we can manipulate low field-spin dynamics and reintroduce strong coupling.