59Co solid-state NMR as a new probe for elucidating metal binding in polynucleotides

Although magnesium fulfills several essential biochemical roles, direct studies on this ion are complicated by its unfavorable spectroscopic characteristics. This contribution explores the possibility of monitoring magnesium-nucleic acid binding via a combination of Co(NH3)6]3+ as surrogate for Mg(H2O)6]2+, and of high-resolution solid-state 59Co NMR as a spectroscopic probe. Such strategy quenches fast cationic exchanges between bound and free states, while exploiting the superior NMR properties of the 59Co spin. Experiments on relatively small amounts of tRNA can then discern resonances corresponding to different metal binding environments. These characterizations were assisted by studies on model compounds and by multinuclear 31P-59Co recoupling experiments.