Fuel-driven self-assembly of actin filaments and microtubules is a key component of cellular organization. Continuous energy supply maintains these transient biomolecular assemblies far from thermodynamic equilibrium, unlike typical synthetic systems that spontaneously assemble at thermodynamic equilibrium. Here, we report the transient self-assembly of synthetic molecules into active materials, driven by the consumption of a chemical fuel. In these materials, reaction rates and fuel levels, instead of equilibrium composition, determine properties such as lifetime, stiffness, and self-regeneration capability. Fibers exhibit strongly nonlinear behavior including stochastic collapse and simultaneous growth and shrinkage, reminiscent of microtubule dynamics.
Nanomachines of the future will require molecular-scale motors that can perform work and collectively induce controlled motion of much larger objects. We have designed a synthetic, light-driven molecular motor that is embedded in a liquid-crystal film and can rotate objects placed on the film that exceed the size of the motor molecule by a factor of 10,000. The changes in shape of the motor during the rotary steps cause a remarkable rotational reorganization of the liquid-crystal film and its surface relief, which ultimately causes the rotation of submillimetre-sized particles on the film.
The use of dissipative self-assembly driven by chemical reaction networks for the creation of unique structures is gaining in popularity. In dissipative self-assembly, precursors are converted into self-assembling building blocks by the conversion of a source of energy, typically a photon or a fuel molecule. The self-assembling building block is intrinsically unstable and spontaneously reverts to its original precursor, thus giving the building block a limited lifetime. As a result, its presence is kinetically controlled, which gives the associated supramolecular material unique properties. For instance, formation and properties of these materials can be controlled over space and time by the kinetics of the coupled reaction network, they are autonomously self-healing and they are highly adaptive to small changes in their environment. By means of an example of a biological dissipative self-assembled material, the unique concepts at the basis of these supramolecular materials will be discussed. We then review recent efforts towards man-made dissipative assembly of structures and how their unique material properties have been characterized. In order to help further the field, we close with loosely defined design rules that are at the basis of the discussed examples.
The characteristics of molecular electronic devices are critically determined by metal-organic interfaces, which influence the arrangement of the orbital levels that participate in charge transport.Studies on self-assembled monolayers (SAMs) show (molecule-dependent) level shifts as well as transport-gap renormalization, suggesting that polarization effects in the metal substrate play a key role in the level alignment with respect to the metal's Fermi energy. Here, we provide direct evidence for an electrode-induced gap renormalization in single-molecule junctions. We study charge transport in single porphyrin-type molecules using electrically gateable break junctions.In this set-up, the position of the occupied and unoccupied levels can be followed in situ and with simultaneous mechanical control. When increasing the electrode separation, we observe a substantial increase in the transport gap with level shifts as high as several hundreds of meV for displacements of a fewÅngstroms. Analysis of this large and tunable gap renormalization with image-charge calculations based on atomic charges obtained from density functional theory confirms and clarifies the dominant role of image-charge effects in single-molecule junctions.
Fueling the future: A fibrillar network (red fibers, see figure) is formed from an activated building block (red), which is obtained from a synthetic gelator (blue) in a dissipative self‐assembly process that is fueled by an alkylating agent. When the available energy is depleted, the system reverts to its thermodynamic equilibrium, that is, an isotropic solution.
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