8 research outputs found
Structural Dynamics of Overcrowded Alkene-Based Molecular Motors during Thermal Isomerization
Synthetic
light-driven rotary molecular motors show complicated structural dynamics
during the rotation process. A combination of DFT calculations and
various spectroscopic techniques is employed to study the effect of
the bridging group in the lower half of the molecule on the conformational
dynamics. It was found that the extent to which the bridging group
can accommodate the increased folding in the transition state is the
main factor in rationalizing the differences in barrier height and,
as a consequence, the rotary speed. These findings will be essential
in designing future rotary molecular motors
Tuning the Rotation Rate of Light-Driven Molecular Motors
Overcrowded
alkenes are among the most promising artificial molecular
motors because of their ability to undergo repetitive light-driven
unidirectional rotary motion around the central Cī»C bond. The
exceptional features of these molecules render them highly useful
for a number of applications in nanotechnology. Many of these applications,
however, would benefit from higher rotation rates. To this end, a
new molecular motor was designed, and the isomerization processes
were studied in detail. The new motor comprises a fluorene lower half
and a five-membered-ring upper half; the upper-half ring is fused
to a <i>p</i>-xylyl moiety and bears a <i>tert</i>-butyl group at the stereogenic center. The kinetics of the thermal
isomerization was studied by low-temperature UVāvis spectroscopy
as well as by transient absorption spectroscopy at room temperature.
These studies revealed that the <i>tert</i>-butyl and <i>p</i>-xylyl groups in the five-membered-ring upper half may
be introduced simultaneously in the molecular design to achieve an
acceleration of the rotation rate of the molecular motor that is larger
than the acceleration obtained by using either one of the two groups
individually. Furthermore, the new molecular motor retains unidirectional
rotation while showing remarkably high photostationary states
Multi-State Regulation of the Dihydrogen Phosphate Binding Affinity to a Light- and Heat-Responsive Bis-Urea Receptor
A responsive
bis-urea receptor can be switched between three isomers
using light and heat as evidenced by <sup>1</sup>H NMR and UVāvis
spectroscopy. Anion binding experiments (<sup>1</sup>H NMR titrations,
ESI-MS) reveal a high selectivity for dihydrogen phosphate. Importantly,
a large difference in binding affinity to the interchangeable isomers
is observed, which is further rationalized by DFT calculations. As
a consequence, the amount of bound substrate can be controlled via
photo- and thermal isomerization in a three-step process
Molecular Stirrers in Action
A series
of first-generation light-driven molecular motors with
rigid substituents of varying length was synthesized to act as āmolecular
stirrersā. Their rotary motion was studied by <sup>1</sup>H
NMR and UVāvis absorption spectroscopy in a variety of solvents
with different polarity and viscosity. Quantitative analyses of kinetic
and thermodynamic parameters show that the rotary speed is affected
by the rigidity of the substituents and the length of the rigid substituents
and that the differences in speed are governed by entropy effects.
Most pronounced is the effect of solvent viscosity on the rotary motion
when long, rigid substituents are present. The Ī± values obtained
by the <i>free volume</i> model, supported by DFT calculations,
demonstrate that during the rotary process of the motor, as the rigid
substituent becomes longer, an increased rearranging volume is needed,
which leads to enhanced solvent displacement and retardation of the
motor
Asymmetric Synthesis of First Generation Molecular Motors
A general
enantioselective route to functionalized first generation
molecular motors is described. An enantioselective protonation of
the silyl enol ethers of indanones by a AuĀ(I)ĀBINAP complex sets the
stage for a highly diastereoselective McMurry coupling as a second
enhancement step for enantiomeric excess. In this way various functionalized
overcrowded alkenes could be synthesized in good yields (up to 78%)
and good to excellent enantiomeric excess (85% eeā>98% ee)
values
Control of Surface Wettability Using Tripodal Light-Activated Molecular Motors
Monolayers of fluorinated light-driven
molecular motors were synthesized
and immobilized on gold films in an altitudinal orientation <i>via</i> tripodal stators. In this design the functionalized
molecular motors are not interfering and preserve their rotary function
on gold. The wettability of the self-assembled monolayers can be modulated
by UV irradiation
Photoswitching of DNA Hybridization Using a Molecular Motor
Reversible control
over the functionality of biological systems
via external triggers may be used in future medicine to reduce the
need for invasive procedures. Additionally, externally regulated biomacromolecules
are now considered as particularly attractive tools in nanoscience
and the design of smart materials, due to their highly programmable
nature and complex functionality. Incorporation of photoswitches into
biomolecules, such as peptides, antibiotics, and nucleic acids, has
generated exciting results in the past few years. Molecular motors
offer the potential for new and more precise methods of photoregulation,
due to their multistate switching cycle, unidirectionality of rotation,
and helicity inversion during the rotational steps. Aided by computational
studies, we designed and synthesized a photoswitchable DNA hairpin,
in which a molecular motor serves as the bridgehead unit. After it
was determined that motor function was not affected by the rigid arms
of the linker, solid-phase synthesis was employed to incorporate the
motor into an 8-base-pair self-complementary DNA strand. With the
photoswitchable bridgehead in place, hairpin formation was unimpaired,
while the motor part of this advanced biohybrid system retains excellent
photochemical properties. Rotation of the motor generates large changes
in structure, and as a consequence the duplex stability of the oligonucleotide
could be regulated by UV light irradiation. Additionally, Molecular
Dynamics computations were employed to rationalize the observed behavior
of the motorāDNA hybrid. The results presented herein establish
molecular motors as powerful multistate switches for application in
biological environments
Photoswitching of DNA Hybridization Using a Molecular Motor
Reversible control
over the functionality of biological systems
via external triggers may be used in future medicine to reduce the
need for invasive procedures. Additionally, externally regulated biomacromolecules
are now considered as particularly attractive tools in nanoscience
and the design of smart materials, due to their highly programmable
nature and complex functionality. Incorporation of photoswitches into
biomolecules, such as peptides, antibiotics, and nucleic acids, has
generated exciting results in the past few years. Molecular motors
offer the potential for new and more precise methods of photoregulation,
due to their multistate switching cycle, unidirectionality of rotation,
and helicity inversion during the rotational steps. Aided by computational
studies, we designed and synthesized a photoswitchable DNA hairpin,
in which a molecular motor serves as the bridgehead unit. After it
was determined that motor function was not affected by the rigid arms
of the linker, solid-phase synthesis was employed to incorporate the
motor into an 8-base-pair self-complementary DNA strand. With the
photoswitchable bridgehead in place, hairpin formation was unimpaired,
while the motor part of this advanced biohybrid system retains excellent
photochemical properties. Rotation of the motor generates large changes
in structure, and as a consequence the duplex stability of the oligonucleotide
could be regulated by UV light irradiation. Additionally, Molecular
Dynamics computations were employed to rationalize the observed behavior
of the motorāDNA hybrid. The results presented herein establish
molecular motors as powerful multistate switches for application in
biological environments