5 research outputs found
Macrocyclic Molecular Rotors with Bridged Steroidal Frameworks
In this work, we describe the synthesis and solid-state
dynamics
of isomeric molecular rotors <b>7</b><i><b>E</b></i> and <b>7</b><i><b>Z</b></i>, consisting of
two androstane steroidal frameworks linked by the D rings by triple
bonds at their C17 positions to a 1,4-phenylene rotator. They are
also linked by the A rings by an alkenyl diester bridge to restrict
the conformational flexibility of the molecules and reduce the number
of potential crystalline arrays. The analysis of the resulting molecular
structures and packing motifs offered insights of the internal dynamics
that were later elucidated by means of line shape analyses of the
spectral features obtained through variable-temperature solid-state <sup>13</sup>C NMR; such analysis revealed rotations in the solid state
occurring at kilohertz frequency at room temperature
Macrocyclic Molecular Rotors with Bridged Steroidal Frameworks
In this work, we describe the synthesis and solid-state
dynamics
of isomeric molecular rotors <b>7</b><i><b>E</b></i> and <b>7</b><i><b>Z</b></i>, consisting of
two androstane steroidal frameworks linked by the D rings by triple
bonds at their C17 positions to a 1,4-phenylene rotator. They are
also linked by the A rings by an alkenyl diester bridge to restrict
the conformational flexibility of the molecules and reduce the number
of potential crystalline arrays. The analysis of the resulting molecular
structures and packing motifs offered insights of the internal dynamics
that were later elucidated by means of line shape analyses of the
spectral features obtained through variable-temperature solid-state <sup>13</sup>C NMR; such analysis revealed rotations in the solid state
occurring at kilohertz frequency at room temperature
Macrocyclic Molecular Rotors with Bridged Steroidal Frameworks
In this work, we describe the synthesis and solid-state
dynamics
of isomeric molecular rotors <b>7</b><i><b>E</b></i> and <b>7</b><i><b>Z</b></i>, consisting of
two androstane steroidal frameworks linked by the D rings by triple
bonds at their C17 positions to a 1,4-phenylene rotator. They are
also linked by the A rings by an alkenyl diester bridge to restrict
the conformational flexibility of the molecules and reduce the number
of potential crystalline arrays. The analysis of the resulting molecular
structures and packing motifs offered insights of the internal dynamics
that were later elucidated by means of line shape analyses of the
spectral features obtained through variable-temperature solid-state <sup>13</sup>C NMR; such analysis revealed rotations in the solid state
occurring at kilohertz frequency at room temperature
Solid State Characterization of Bridged Steroidal Molecular Rotors: Effect of the Rotator Fluorination on Their Crystallization
We describe the synthesis and crystallization
of two macrocyclic
steroidal compounds labeled (<i>Z</i>)-<b>1F</b><sub>2</sub> and (<i>E</i>)-<b>1F</b><sub>2</sub>, envisioned
to work as molecular rotors with 1,4-diethynyl-2,3-difluorophenylene
rotators. The introduction of the fluorine atoms rendered different
crystal arrays that were fully characterized by X-ray diffraction,
solid state <sup>13</sup>C NMR, and calorimetric experiments. In both
isomers, the central molecular fragments point the <i>o</i>-fluorine atoms toward their cavity, highlighting the preferred orientation
in the solid state. By analyzing the crystal array, it can be seen
that while the fluorinated <i>Z</i> isomer is isomorphic
to its non-fluorinated analogue, the <i>E</i> isomer shows
significant structural variations in an unanticipated crystal array
with two molecules per asymmetric unit (<i>Z</i>′
= 2)
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