Molecular Actuators Research Articles

Nanovalves

AbstractThis article features both molecular and supramolecular chemistry involving: i) stimuli‐induced nanoscale movements within mechanically interlocked molecules; ii) the fabrication of mesoporous silica substrates; and iii) the integration of the mechanically interlocked molecular/supramolecular actuators to act as gatekeepers at the entrances to the silica nanopores into which guest dye molecules can be uploaded and released on demand from the mesoporous silica substrates. The supramolecular actuators are based on two [2]pseudorotaxanes—that is, 1:1 complexes that can be dissociated by external inputs, such as acid/base cycles, electrons, and light. The molecular actuators are based on bistable [2]rotaxanes and can be operated mechanically by using either redox chemistry or electrochemistry. After these pseudorotaxanes and bistable rotaxanes have been attached covalently to the orifices of the silica nanopores, stimuli‐controlled mechanical movements within these mechanically interlocked molecules can be harnessed to close and open the nanopores. Therefore, these mechanically interlocked molecules have been employed as nanovalves for controlled sequestering and release of guest dye molecules into and out of the mesoporous silica substrates. These actuators can be regarded as the prototypes of highly controllable drug‐delivery systems.

Conformational Features of an Actuator Containing Calix[4]arene and Thiophene: A Molecular Dynamics Study

Molecular dynamics simulations have been performed for poly(calix[4]arene bis(bithiophene)) in dichloromethane solution. This material responds to its electronic structure variations with significant conformational changes, producing contraction-expansion movements. Simulations have been performed for the three states of this molecular actuator (reduced, oxidized-nondeprotonated, and oxidized-deprotonated), a specific force-field being developed for each case. Results, which are fully consistent with previous ab initio quantum mechanical calculations on an isolated actuating unit, have revealed important findings about the dynamics of the system. Analyses of the flexibility/rigidity of the molecular chain with the state, the interaction of the polymer with the solvent molecules and the influence of environmental factors (as the viscosity of solvent, the counterions and the thermal agitation) on the dynamics have provided important insights to the actuation mechanism.

Approaches to rotary molecular motors

Abstract Interest has recently intensified in the search for molecular motors and actuators capable of delivering useful work to nanodevices under the control of electrochemical or photochemical power sources. While many of these man-made molecular machines are designed to deliver rectilinear motion, very few are proposed for the controlled delivery of rotary motion on the time scale characteristic of intramolecular rearrangements. The adaptation of commo-bis-dicarbollide metallacarborane structures to the possible design and synthesis of such rotary molecular motors is now under investigation. Progress toward this goal will be reported.

Effects of d.c. potential patterns on the performance of ion‐exchange polymer based molecular actuators

AbstractThe dynamic performance (i.e. displacement, current, velocity, and force) of ion‐exchange polymer based actuators (the Nafion™/platinum electrodes) have been examined by developing instrumentation. The CCD imaging technique was examined to evaluate the displacement under the various d.c. potential patterns. Two different d.c. potential patterns with or without a rest were applied to the electrodes at 0.1 Hz. It was better to take a rest at 0 V for the polarization back and forth between +2 and −2 V to give lower current consumption and longer displacement. The actuator produced the force of ca. 0.95 g at 3.25 V in air. The result also demonstrated that higher overpotential has to be avoided to maintain the maximum force. The generative force is in inverse proportion to the length of the actuators. The dimension of the film strongly governs the force production and its performance. Copyright © 2006 John Wiley & Sons, Ltd.

Self-Assembled Polymer Films for Controlled Agent-Driven Motion

Reliable stimuli-responsive materials make up a vital part of molecular medicine and on-chip diagnostics. Here, we describe such a material which exhibits rapid, large-amplitude, reversible deformations and which is formed in a simple, one-material, one-step, self-assembly process. The material is a polymer network comprised of discrete molecular actuators which anisotropically expand in response to their driving stimuli. Tuning the relative orientation of the actuators with respect to one another creates expansion variations throughout a sample, and this is exploited to induce macroscopic motion. The deformation directions are pre-engineered by the molecular positioning, and extremely fast response times and high sensitivity are observed. We describe water- and pH-controlled motion, and we anticipate that the techniques are extendable to other biologically or industrially relevant agents.

A Tunable Dendritic Molecular Actuator

I present an electroresponsive molecular actuator based upon a diblock copolymer of a positively charged dendrimer and a negatively charged linear chain. Brownian dynamics simulations demonstrate the hybrid polyampholyte's ability to apply a force or assume an equilibrium molecular strain tunable with an applied electric field. The free energy as a function of molecular strain at differing electric field strengths, as obtained via the Jarzynski identity, suggests a phase transition in the hybrid.

Molecular Actuators—Designing Actuating Materials at the Molecular Level

Nature evolved an elegant actuating system, muscle, which can be controlled by a relatively small molecule, myosin. We briefly introduce herein an artificial approach based on applying molecular actuating building blocks to mimic the function of muscle. A particular focus of this review is the design of a molecular hinge. Designed molecular mechanisms have great potential to produce quick responses and large deformations.

The Relation of Conducting Polymer Actuator Material Properties to Performance

Materials used in many branches of engineering are of low molecular weight and not flexible. As we develop more sophisticated engineering devices one can look to nature for inspiration and advocate the use of high molecular weight flexible materials. Conducting polymer actuators will soon be used in applications where traditional low molecular weight actuator systems are incapable of mimicking the functionality provided by nature's muscle. To incorporate conducting polymer actuators into engineering systems it is of high importance to not only model and predict the behavior of these actuators but also understand the connection of material properties to performance. In this paper, the importance of fundamental actuation mechanisms and the fundamental material properties of conducting polymer muscles such as ionic diffusion rate, electrochemical operating window, strain to charge ratio, ratio of charge carried by positive versus negative ions, and salt draining are discussed and their effect on performance is demonstrated. The relevance of engineered geometry to the performance of conducting polymer muscles is also shown. Our understanding of what limits the performance of existing conducting polymers actuators provides directions for the improvement of the next generation of conducting polymer actuators.

New perspectives for the design of molecular actuators: thermally induced collapse of single macromolecules from cylindrical brushes to spheres.

New perspectives for the design of molecular actuators: thermally induced collapse of single macromolecules from cylindrical brushes to spheres.

Polymer Nanocontainers

Amphiphilic block copolymers and polyelectrolytes are used to prepare stimuli-sensitive nanocontainers that can be regarded as model systems for host–guest encapsulation and controlled release. Interestingly it is possible to incorporate functional membrane proteins into the walls of these artificial polymer containers. This method can be used to control the exchange of substrates and products of encapsulated enzymes with the external solution, to control virus-assisted loading of the containers with DNA, to apply them as confined reaction vessels for biomimetic mineralization, as nanometer-sized batteries or as molecular motor-driven actuators. This is documented by some representative examples.

Communicating with the building blocks of life using organic electronic conductors

The design and synthesis of inherently conducting polymer materials has resulted in the development of highly efficient bio monitoring and modification systems. These organic electrodes have been used to facilitate interactions with amino acids, proteins, enzymes, antibodies, DNA and even whole cells. Hybrid systems containing biological moieties have been used as sensors and molecular actuators (smart membranes). Biomimetics has also proven useful in the design of efficient synthetic sensing and actuating (artificial muscle) systems.

Bovine serum albumin reverses inhibition of RT-PCR by melanin.

Bovine serum albumin reverses inhibition of RT-PCR by melanin.

Molecular and supramolecular systems for sensing and actuation

Highlights some of the latest findings and research avenues in molecular sensors and actuators and also some of the problems encountered in developing such devices. The following topics are discussed: molecular sensors; biological molecular sensors (including immunosensors); artificial senses (including smell, taste, touch); Langmuir-Blodgett films; synthetic sensors (including gas sensors); molecular actuators (including microactuators); nanoactuators; doping of conducting polymers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Molecular electronics: science and technology for the future

The following topics are discussed: the emergence of molecular electronics research; nanometer scale components; assembly techniques; synthetic organic molecules and biomolecules; the role of protein engineering; hierarchy of biological information processing; common infrastructure for molecular electronics, biosensor and molecular actuator technology; interfacing problems; molecular self-assembly and self-repair. >

Molecular system—sensors and actuators in perspective

In this paper a new concept of a molecular system, which consists of a molecular sensor, a molecular processor and a molecular actuator, is presented. The design and synthesis of molecular devices are discussed. The technical process and scientific method of the molecular system assembly are outlined. To illustrate its important applications, monitoring and controlling brain activity as well as probing and modifying DNA sequences are explored, with some interesting findings.

Instability of conducting polymer, poly(3-alkylthiophene) gel with solvent, temperature and doping and effect of alkyl chain length

Volume, shape and color of poly(3-alkylthiophene)s change drastically with solvent composition and temperature, which is interpreted as characteristic behaviour of conducting polymer gels. Volume shrinkage ratio is larger in a chemically prepared sample than in an electrochemically prepared sample and also depends on alkyl chain length. Drastic shrinkage of poly(3-alkylthiophene)s in chloroform is also observed by adding iodine, which are explained by the formation of apparent cross-linking between polymer main chains by doping. These instabilities are reversible and also are considered to be candidates of molecular actuators.