Dynamics of Hydrogen Bonding in Three-Component Nanorotors

The dynamics of hydrogen bonding do not only play an important role in many biochemical processes but also in Nature's multicomponent machines. Here, a three-component nanorotor is presented where both the self-assembly and rotational dynamics are guided by hydrogen bonding. In the rate-limiting step of the rotational exchange, two phenolic O-H-N,N_{(phenanthroline)} hydrogen bonds are cleaved, a process that was followed by variable-temperature ¹ H NMR spectroscopy. Activation data (ΔG^≠ ₂₉₈ =46.7 kJ mol^-1 at 298 K, ΔH^≠ =55.3 kJ mol^-1 , and ΔS^≠ =28.8 J mol^-1  K^-1 ) were determined, furnishing a rotational exchange frequency of k₂₉₈ =40.0 kHz. Fully reversible disassembly/assembly of the nanorotor was achieved by addition of 5.0 equivalents of trifluoroacetic acid (TFA)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) over three cycles.