1 research outputs found
Synthesis, Structure, and Local Molecular Dynamics for Crystalline Rotors Based on Hecogenin/Botogenin Steroidal Frameworks
The synthesis and solid-state characterization
of a series of cyclic/acyclic
molecular rotors derived from naturally occurring steroidal 12-oxosapogenins
are described. The bridged molecular rotors with rigid steroidal frameworks
were obtained by employing ring-closing metathesis (RCM) as a key
step. The X-ray diffraction technique was employed for determination
and refinement of the crystal and molecular structure of selected
models giving good quality single crystals. In the case of the bridged
hecogenin molecular rotor <b>11</b><i><b>E</b></i> for which poor quality crystals were obtained, an NMR crystallography
approach was used for fine refinement of the structure. Solid state
NMR spectroscopic techniques were applied for the study of local molecular
dynamics of the featured acyclic/cyclic molecular rotors. Analysis
of <sup>13</sup>C principal components of chemical shift tensors and
chemical shift anisotropy (CSA) as well as heteronuclear <sup>1</sup>H–<sup>13</sup>C dipolar couplings (DC) unambiguously proved
that aromatic rings located in the space within the rigid steroidal
framework both for cyclic and acyclic rotors are under kHz exchange
regime. Experimental results were confirmed by theoretical calculations
of rotation barrier on the density functional theory level. Small
distinctions in the values of CSA and DC for the rotors under investigation
are explained on the basis of differences in their molecular structures