Both solution- and solid-state NMR provide unparalleled insight into the structures of biomolecular and biomimetic systems, allowing for detailed investigation of function, mechanism, and molecular behavior. For a biomimetic synthetic guest-host cavitand system, we find that embedding in the cavitand alters the relaxation rates of guest protons relative to guest free in solution, with more pronounced effects for guest protons more deeply embedded in the cavitand. In addition to altering relaxation rates, the cavitand catalyzes the exchange of protons on bound guest molecules for deuterons and provides a path for teasing out the mechanism of this process, suggesting heavy involvement from the benzimidazole groups in the walls of the cavitand. Finally, preliminary data collected on the larger pyridoxal-5'-phosphate (PLP)-dependent enzymatic system ornithine decarboxylase hint at an initial proposal for the protonation states in the enzyme active site, which largely help to direct the reaction outcome in PLP systems, and provide a starting point for the elucidation of the larger enzyme structure. These results highlight the many different ways that NMR can be used to answer questions at the molecular level and enhance the richness of our understanding of these complicated systems.
Bethany G. Caulkins (Sun,) studied this question.