Unidirectional Rotation Research Articles

A hemithioindigo molecular motor for metal surface attachment.

Functionalization of surfaces with responsive molecular entities is currently an important research field allowing the organization of molecular functions in space in a defined way and thus accessing emergent properties not observed in solution. Herein we report on the synthesis of a hemithioindigo molecular motor bearing thioether feet for surface attachment on its thioindigo fragment. We also give a full theoretical description of its ground state energy profile together with an experimental evaluation of the visible light driven unidirectional rotation in solution. Comparison with the corresponding unsubstituted original motor shows that after feet-attachment the hemithioindigo molecular motor is fully operative with a similar maximum attainable speed and degree of unidirectionality.

Spontaneous rotation of ratchet wheel with soft boundary in active particle bath

Self-propelling motionisubiquitous in the biological world, ranging from the molecular-level transportation of motor proteins along the microtubules, to the swimming of bacteria on a micrometer scale. An intriguing topic is to design microdevices or micromotors that can rectify the random motion and convert the energy into mechanical work. Here we design a soft microdevice, which may possess the advantages such as damage resistance, durability and adaptability, by utilizing two-dimensional Langevin dynamics simulation. We use a flexible chain to mimic the soft boundary of microdevice. We investigate the dynamical behaviors of microdevice when it is immersed in a thin film of active particle suspension. We find that the microdevicecan rotateunidirectionally and hence output the work. To uncover the physical mechanism of unidirectional rotation, we calculate the pressure distribution along the soft boundary. The spontaneous symmetry breaking of flexible boundary is the origin of the unidirectional rotation, which can lead to the inhomogeneous pressure distribution and hence torque on ratchet. It is because the persistent motion drives the particles to accumulate near the boundary and induce the soft boundary to deform. Further, we focus on the effect of active force and particle density on the angular velocity. With the increase of active force, the average angular velocity increases monotonically due to the increase of torque. With the increase of the number density of active particles, the average angular velocity increases. This is because the aggregation of a large number of particles is beneficial to the increase of ratchet torque. Additionally, we pay attention to the effect of rotational diffusion rate, <i>D</i><sub>r</sub>, of active particles and the number of ratchet wheels. We find the average angular velocity decreases with the increase of rotation diffusion <i>D</i><sub>r</sub> because ofthe ability of particles to weakly accumulate at high <i>D</i><sub>r</sub>s. The average angular velocity also decreases with the increase of the number of ratchet wheels. This is because a large number of ratchet wheels weaken the asymmetry of pressure distribution and hence reduce the torque on wheel. Our work provides a new insight into the design of soft microdevices for studying the non-equilibrium system.

Polarization-based tachometer for measuring spinning rotors.

We report on the polarization analysis of shortpulse ultraviolet radiation produced by third-harmonic generation in a gas of coherently spinning molecules. A pulse of twisted linear polarization imprints a unidirectional rotational motion to the molecules leading to an orientation of their rotational angular momenta. A second pulse, time-delayed with respect to the first one, circularly polarized in the plane of rotation of the molecules, acts as a driving field for third-harmonic generation. The angular momentum and energy conservation applied to this process foresees the generation of two Doppler-shifted circularly-polarized harmonics of opposite handedness. Our analysis reveals that spinning molecules enable the generation of a well polarized third-harmonic radiation exhibiting a high degree of ellipticity. Tracking the orientation of the latter allows a time-capture of the molecular axis direction from which the average angular velocity of the rotating molecules is inferred. This method provides a user-friendly polarization-based tachometer for measurement of the rotational speed of spinning nonlinear rotors.

Unidirectional rotation of circles driven by chiral active particles**Project supported by the National Natural Science Foundation of China (Grant Nos. 21674096 and 21873082).

The dynamics of two-dimensional rigid circles filled with chiral active particles are investigated by employing the overdamped Langevin dynamics simulations. Unidirectional rotation of rigid circles is observed, and the rotational angular velocity () relies mainly on the length (l), the number (, and tilt angle (γ) of boards, and the angular velocity (ω) and area fraction (ρ) of chiral active particles. There are optimum values for these parameters at which the average angular velocity of circle reaches its maximum. The center-of-mass mean square displacement for circles drops by about two orders of magnitude for large angular velocity ω of chiral active particles with oscillations in the short-time regime. Our work demonstrates that nanofabricated objects with suitable designs immersed in a bath of chiral active particles can extract and rectify energy in a unidirectional motion.

Microrotor of a chain-grafted colloidal disk immersed in the active bath: The impact of particle concentration, grafting density, and chain rigidity.

In an earlier work, we discussed the possibility to realize a microrotor by immersing a chain-grafted colloidal disk in a thin film of active-particle suspension. Under certain conditions, the colloidal disk rotates unidirectionally driven by the bath active particles. Here we systematically study the role of active-particle concentration, grafting density, and chain rigidity in the phenomenon of the spontaneous symmetry breaking of the chain configurations and the unidirectional rotation of the disk. We find that high chain rigidity can help stabilize both the collective asymmetric chain configurations and the rotation of the disk, while it has a weak impact on the rotational speed/efficiency. Increasing the number of grafted chains can also stabilize the rotation but has a negative impact on the rotational speed/efficiency. Active particles power the rotation of the colloidal disk, yet their contribution saturates beyond a certain concentration. Our work provides new insights into the active systems with chain-structured objects and the design of soft/deformable micromachines.

Intramolecular Torque Study of a Molecular Rotation Stimulated by Electron Injection and Extraction.

Rotation-inducing torque based on interatomic forces is a true indicator of internal molecular rotations. We use the induced intramolecular torque to study the underlying rotational mechanism stimulated by an electron injection or extraction for the rotor molecule 9-(2,4,7-trimethyl-2,3-dihydro-1 H-inden-1-ylidene)-9 H-fluorene, which consists of a "rotator" fragment and a "stator" fragment. The results show that the charged molecule in a quartet spin state can rotate internally, while that in the doublet state cannot. The torque on the rotator in the quartet state always maintains unidirectional rotation. In addition, the attachment/extraction of an electron leads to the reduction of the rotational energy barrier by about 18 kcal/mol, facilitating a more favorable molecular rotation than in the neutral singlet state. Our finding provides a molecular-level understanding of various transformation pathways for experimental designs and further demonstrates the effectiveness of the torque approach.

Fulgides as Light-Driven Molecular Rotary Motors: Computational Design of a Prototype Compound.

A new family of light-driven molecular rotary motors utilizing the fulgide motif is proposed and its prototype molecule is studied by quantum chemical calculations and nonadiabatic molecular dynamics simulations. The new motor performs pure unidirectional axial rotation of the rotor blade with high quantum efficiency (ϕ ∼ 0.55-0.68) and ultrafast dynamics (⟨ t⟩ S1 ∼ 200-300 fs) of its successive photoisomerization steps. The photocyclization reaction typical of fulgide compounds is blocked by the design of the new motor and never occurred in the molecular dynamics simulations. The new motors can be synthesized from easily available precursors. In view of its remarkable photoisomerization ability, the new motor represents a prospective class of compounds for the use in nanosized molecular devices.

Overdamped non-contact rectifiers

We study the dynamics of overdamped systems in a symmetric periodic potential against an external load. Using numerical and analytical methods, we show that a symmetric driving signal cannot rectify these systems while an asymmetric one can rectify them, causing its unidirectional rotation. We consider the case where the driving signal is multiharmonic. We find that the mean velocity of the system increases to get the highest value, by appropriate tuning of parameters.

Molecular mechanistic insights into coupling of ion transport to ATP synthesis

A wealth of molecular mechanistic insights has been provided into the coupling of ion transport to ATP synthesis based on a two-ion theory of biological energy coupling. A kinetic scheme that considers the mode of functioning of a single F1FO-ATP synthase molecule with H+-A− cotransport and unidirectional rotation of the c-rotor in the membrane-bound FO-portion of the enzyme has been developed. Mathematical analysis leads to a detailed enzyme kinetic model applicable to a population of molecules which is compared with experimental data on the pH dependence of ATP synthesis. The model agrees well with the experimental data, and a single equation with a single set of standard enzymological kinetic parameters has been shown to explain the experimental data over the entire range of conditions for the chloroplast ATP synthase. The analysis gives novel insights into kinetic and mechanistic characteristics of ATP synthesis in FO. These include an order imposed on ion binding and unbinding events in FO, the essential role of the anion in direct activation of the ATP synthase (in addition to its role as a permeant ion), and the integration in a novel way of the functions of cooperativity and cotransport of dicarboxylic acid anions and protons during physiological ATP synthesis. Further, Wyman's pioneering classical work on the thermodynamics of linked functions has been shown to offer a new approach to distinguish between various models of energy coupling in ATP synthesis. All these results have been found to be inconsistent with Mitchell's chemiosmotic theory and are shown to be in agreement with Nath's torsional mechanism of energy transduction and ATP synthesis.

Transmission of Unidirectional Molecular Motor Rotation to a Remote Biaryl Axis.

Molecular motors undergo repetitive directional motions upon external energy input. A profound challenge is the defined transfer of directional motor motions to remote entities at the molecular scale. Herein, we present a molecular setup that allows for the transfer of the directional rotation of a light-powered motor unit onto a remote biaryl axis via an ethylene glycol chain link. Based on a combination of X-ray crystallographic analysis, ECD, and NMR experiments as well as a comprehensive theoretical assessment, we provide evidence for the coupled stepwise directional motions of both molecular units. With the presented setup, facile integration of molecular motor units into larger functional frameworks and complex molecular machines can be explored consciously in the future.

Efficient electromagnetic energy harvester for railroad transportation

An electromagnetic energy harvester is designed to produce electricity from rail track deflections induced by passing trains. Whereas typical existing vibration energy harvester technologies are built for low power applications of milliwatts range, the proposed harvester will be designed for higher power applications for major track-side equipment such as warning signals, wireless communications, track switches, track health monitoring systems, etc., which typically require a power supply ranging between several watts (continuous) to thousand watts (with intermittent duty cycle). Facing the challenge of large pulse vibrations on the track when trains pass by, a mechanical motion rectifier (MMR) with single shaft design is introduced to streamline the motion and force transmissions, by transforming bidirectional pulse vibrations into the unidirectional rotation at relatively steady speed. Bench tests indicate that 10–100 W of energy harvesting capability from train induced vibration and up to 74% efficiency. Simulations also indicate that the MMR mechanism can significantly increase the power output over the traditional harvesters while substantially reducing the average force amplitude under the same displacement input.

The influence of roller motion on profile and hardness of T2 worm

The rolling process of T2 worm is studied by numerical simulation and experiment in this paper. The rolling forming of the worm part is realized by using the two rollers forming method with parallel axes and the radial feed at the same time as rotation. Firstly, the influence of the unidirectional rotation and reciprocating rotation of the roller on the hardness of the teeth, the strain distribution and the streamline distribution of the worm are analyzed. The results show that in numerical simulation, the tooth shape of reciprocating rolling workpiece is symmetrical according to the central axis of the tooth, and the workpiece has no axis displacement. The hardness distribution of both sides of the tooth of the reciprocating rolling workpiece is more uniform than that of the unidirectional rolling workpiece, and the streamline distribution is more uniform and symmetrical. The strain variation in the numerical simulation is consistent with the experimental variation of hardness and streamlines. It shows that the reciprocating rolling has substantial help to the strength and hardness of the lifting worm. Then, the analysis of the teeth of the simulated and experimental parts show that the maximum difference of the gear parameters between the analogy and the experimental parts is 1.46%, and the accuracy of the numerical simulation is higher.

Cargos Rotate at Microtubule Intersections during Intracellular Trafficking

Intracellular cargos are transported by molecular motors along actin and microtubules, but how their dynamics depends on the complex structure of the cytoskeletal network remains unclear. In this study, we investigated this longstanding question by measuring simultaneously the rotational and translational dynamics of cargos at microtubule intersections in living cells. We engineered two-faced particles that are fluorescent on one hemisphere and opaque on the other and used their optical anisotropy to report the rotation of cargos. We show that cargos undergo brief episodes of unidirectional and rapid rotation while pausing at microtubule intersections. Probability and amplitude of the cargo rotation depend on the geometry of the intersecting filaments. The cargo rotation is not random motion due to detachment from microtubules, as revealed by statistical analyses of the translational and rotational dynamics. Instead, it is an active rotation driven by motor proteins. Although cargos are known to pause at microtubule intersections, this study reveals a different dimension of dynamics at this seemingly static state and, more importantly, provides direct evidence showing the correlation between cargo rotation and the geometry of underlying microtubule intersections.

One-Way Rotating Photonic Crystal Ring Resonator With High Quality Factor

We propose a planar photonic crystal ring resonator consists of a looped single interface between a regular and a magneto-optical photonic crystal structure. The cavity modes are shown to possess the unidirectional rotation characteristics, and the rotating direction is determined by the direction of an externally applied magnetic field normal to the rotation plane. This unique unidirectional feature results in the realization of cavity with extremely high Q factor of 3.2 × 106, more than one order of magnitude higher than the previous report for cavity with the same ring size [Z. Qiang, W. Zhou, and R. A. Soref, “Optical add-drop filters based on photonic crystal ring resonators,” Opt. Exp ress , vol. 15, no. 4, pp. 1823–1831, Feb. 2007]. As an example of its applications, we present a unidirectional channel-drop filter design based on the one-way rotating photonic crystal ring resonator. Our simulation result shows that a 96.7% backward dropping efficiency can be achieved by this filter.

Design and Treadmill Test of a Broadband Energy Harvesting Backpack With a Mechanical Motion Rectifier

The energy harvesting backpack that converts the kinetic energy produced by the vertical oscillatory motion of suspended loads to electricity during normal walking is a promising solution to fulfill the ever-rising need of electrical power for the use of electronic devices in civilians and military. An energy harvesting backpack that is based on mechanical motion rectification (MMR) is developed in this paper. Unlike the conventional rack-pinion mechanism used in the conventional energy harvesting backpacks, the rack-pinion mechanism used in the MMR backpack has two pinions that are mounted on a generator shaft via two one-way bearings in a way that the bidirectional oscillatory motion of the suspended load is converted into unidirectional rotation of the generator. Due to engagement and disengagement between the pinions and the generator shaft, the MMR backpack has broader bandwidths than the conventional energy harvesting backpacks; thus, the electrical power generated is less sensitive to change in walking speed. Two male subjects were recruited to test the MMR backpack and its non-MMR counterpart at three different walking speeds. For both subjects, the MMR backpack for most of the time generated more power than the non-MMR counterpart. When compared with literature, the MMR backpack had nearly sixfold improvement in bandwidth. Finally, the MMR backpack generated nearly 3.3 W of electrical power with a 13.6 kg load and showed nearly two- to tenfold increases in specific power when compared with a conventional energy harvesting backpack.

Supramolecularly directed rotary motion in a photoresponsive receptor

Stimuli-controlled motion at the molecular level has fascinated chemists already for several decades. Taking inspiration from the myriad of dynamic and machine-like functions in nature, a number of strategies have been developed to control motion in purely synthetic systems. Unidirectional rotary motion, such as is observed in ATP synthase and other motor proteins, remains highly challenging to achieve. Current artificial molecular motor systems rely on intrinsic asymmetry or a specific sequence of chemical transformations. Here, we present an alternative design in which the rotation is directed by a chiral guest molecule, which is able to bind non-covalently to a light-responsive receptor. It is demonstrated that the rotary direction is governed by the guest chirality and hence, can be selected and changed at will. This feature offers unique control of directional rotation and will prove highly important in the further development of molecular machinery.

A high-efficiency road energy harvester based on a chessboard sliding plate using semi-metal friction materials for self-powered applications in road traffic

To explore the alternative resources of traditional energy, ambient-energy scavenging technologies have attracted worldwide attention. In particular, the roadways contain a significant potential for environmental energy harvesting (EEH). In this study, we proposed an innovative road energy harvesting system based on a chessboard sliding plate by using semi-metal friction materials (SMFMs) for collecting the mechanical energy induced by running vehicles. The SMFMs have good frictional properties that enable them to absorb energy well. The proposed system consists of four main components as follows: chessboard sliding plate module, transmission module, micro-generator module and energy storage module. Acting as the energy input mechanism, the chessboard sliding plate module harvests the kinetic energy produced by the friction between the wheel and chessboard plate. The transmission module converts the linear reciprocating motion of the chessboard sliding plate to unidirectional rotation of the input shaft of generator. The energy storage module stores the electric energy generated by the generator module in a supercapacitor. The performance of the proposed system is evaluated through dynamic simulations; the simulation results demonstrate that the system possesses rapid response. Efficiency of 62.38% and 57% are obtained in the simulation and experiments, respectively, validating that the proposed road energy harvesting system is feasible and practical for self-powered applications in road traffic electrical equipment, such as traffic lights, street lamps and speed measuring radar.

A vertical-axis unidirectional rotor for wave energy conversion

A vertical-axis rotor design for wave energy conversion is discussed in this work. The rotor has a number of cup blades laid out around its shaft. In ocean waves, water particles perform omnidirectional motion. While exposed in waves and driven by omnidirectional flows, the rotor performs unidirectional rotation about its vertically oriented shaft. This rotor concept was tested in a wave flume under various rotor parameters and wave conditions. Results show that the rotor's unidirectional behavior is profound, yet fluctuation of the unidirectional angular velocity broadly exists. A parametric study further revealed relations between the rotor's mean angular velocity and some other parameters.

On Improvement of the Frequency Bandwidth of Nonlinear Vibration Energy Harvesters Using a Mechanical Motion Rectifier

This paper presents a broadband vibration energy harvester (VEH) which consists of a monostable Duffing oscillator connected to an electromagnetic generator via a mechanical motion rectifier. The mechanical motion rectifier converts the bidirectional vibratory motion of the oscillator induced by ambient environment vibrations into unidirectional rotation of the generator and causes the harvester to periodically switch between a large- and small-inertia system, resulting in nonlinearity in inertia. By means of analytical and numerical methods, this inertia nonlinearity is shown to have two advantages. First, it allows for more stiffness nonlinearity without inducing nonuniqueness of energy branches and enhances bandwidths of energy harvesting. The effect of mitigating nonuniqueness of energy branches occurs to steady-state and transient responses of the harvester and is experimentally verified by a prototype. The experimental results show a nearly 50% increase in the half power bandwidth via mechanical motion rectification (MMR). Second, it enlarges the basin of attraction of the high-energy branch when multiple energy branches are present. A numerical example shows that a more than 50% increase in the basin area can be achieved via MMR.

Mitochondrial inhibitory factor protein 1 attenuates coupling factor 6-induced aging signal.

Coupling factor 6 (CF6) forces a counter-clockwise rotation of plasma membrane F1 Fo complex, resulting in proton import and accelerated aging. Inhibitory factor peptide 1 (IF1) suppresses a unidirectional counter-clockwise rotation of F1 Fo complex without affecting ATP synthesis. We tested the hypothesis that IF1 may attenuate CF6-induced aging signaling in CF6-overexpressing transgenic (TG) cells. In IF1-GFP overexpressing wild type (WT) cells, the diffuse peripheral staining of tubular mitochondria was observed with a dense widely distributed network around the nucleus. In TG cells, however, the only peri-nuclear network of fragmented mitochondria was observed at 24 h, but it was developed to a widely distributed mitochondrial network of tubular mitochondria at 72 h. TG cells displayed aging hallmarks of telomere attrition, epigenetic alterations, defective proteostasis, and genomic instability with a decrease in emerin and lamin and loss of heterochromatin. IF1 induction rescued TG cells from telomere attrition, expression of genomic instability with the increase in emerin and lamin, and that of epigenetic alterations with recovery of heterochromatin. In defective proteostasis, IF1 induction restored a potent peri-nuclear staining of autolysosomes compared with the baseline weak staining. The decrease in Atg7 was restored, whereas the increase in P62 was abolished. We conclude that genetic disruption of proton signals by IF1 induction suppressed CF6-induced expression of aging hallmarks such as telomere attrition, epigenetic alterations, defective proteostasis, and genomic instability. Given the widespread biological actions of CF6, the physiological and pathological actions of IF1 may be complex.