The miniaturization of components used in the construction of working devices is being pursued currently by the large-downward (top-down) fabrication. This approach, however, which obliges solid-state physicists and electronic engineers to manipulate progressively smaller and smaller pieces of matter, has its intrinsic limitations. An alternative approach is a small-upward (bottom-up) one, starting from the smallest compositions of matter that have distinct shapes and unique properties-namely molecules. In the context of this particular challenge, chemists have been extending the concept of a macroscopic machine to the molecular level. A molecular-level machine can be defined as an assembly of a distinct number of molecular components that are designed to perform machinelike movements (output) as a result of an appropriate external stimulation (input). In common with their macroscopic counterparts, a molecular machine is characterized by 1) the kind of energy input supplied to make it work, 2) the nature of the movements of its component parts, 3) the way in which its operation can be monitored and controlled, 4) the ability to make it repeat its operation in a cyclic fashion, 5) the timescale needed to complete a full cycle of movements, and 6) the purpose of its operation. Undoubtedly, the best energy inputs to make molecular machines work are photons or electrons. Indeed, with appropriately chosen photochemically and electrochemically driven reactions, it is possible to design and synthesize molecular machines that do work. Moreover, the dramatic increase in our fundamental understanding of self-assembly and self-organizational processes in chemical synthesis has aided and abetted the construction of artificial molecular machines through the development of new methods of noncovalent synthesis and the emergence of supramolecular assistance to covalent synthesis as a uniquely powerful synthetic tool. The aim of this review is to present a unified view of the field of molecular machines by focusing on past achievements, present limitations, and future perspectives. After analyzing a few important examples of natural molecular machines, the most significant developments in the field of artificial molecular machines are highlighted. The systems reviewed include 1) chemical rotors, 2) photochemically and electrochemically induced molecular (conformational) rearrangements, and 3) chemically, photochemically, and electrochemically controllable (co-conformational) motions in interlocked molecules (catenanes and rotaxanes), as well as in coordination and supramolecular complexes, including pseudorotaxanes. Artificial molecular machines based on biomolecules and interfacing artificial molecular machines with surfaces and solid supports are amongst some of the cutting-edge topics featured in this review. The extension of the concept of a machine to the molecular level is of interest not only for the sake of basic research, but also for the growth of nanoscience and the subsequent development of nanotechnology.

Artificial Molecular Machines.

http://www.diit.unict.it/users/spalazzo/materiale/Nanonetworks_Survey.pdf

Nanonetworks: A new communication paradigm

This review provides a comprehensive evaluation of the state-of-knowledge of radiation effects in crystalline ceramics that may be used for the immobilization of high-level nuclear waste and plutonium. The current understanding of radiation damage processes, defect generation, microstructure development, theoretical methods, and experimental methods are reviewed. Fundamental scientific and technological issues that offer opportunities for research are identified. The most important issue is the need for an understanding of the radiation-induced structural changes at the atomic, microscopic, and macroscopic levels, and the effect of these changes on the release rates of radionuclides during corrosion.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/09D70E1FB1A625EC09BB98883C3A5ED3/S0884291400044411a.pdf/div-class-title-radiation-effects-in-crystalline-ceramics-for-the-immobilization-of-high-level-nuclear-waste-and-plutonium-div.pdf

Radiation effects in crystalline ceramics for the immobilization of high-level nuclear waste and plutonium

In the last two decades, considerable progress has been made in the field of molecular biology, which has enabled a molecular-level understanding of a number of interesting biological events. In particular, the discovery of a family of moving proteins and their assemblies has attracted particular attention not only of biologists but also of chemists and physicists.1-5 In response to certain biological stimuli, these proteins perform directed or programmed motions, similar to many tools and machines used in our daily life. Such biological molecular machines play essential roles in a wide variety of biological events, particularly those related to the activities of cells,1 and realize specific functions through their stimuliresponsive mechanical motions. Cytoplasmic proteins such as myosins, kinesins, and dyneins are called “molecular motors” and are the most extensively studied molecular machines.2-5 These protein-based supramolecular conjugates are known to switch back and forth along linear tracks of actin filaments or microtubules and transport substrates at the expense of adenosine triphosphate (ATP) as fuel. The flagellum is a huge protein conjugate that controls the swimming motion of bacteria.6 The bacterial flagellar motor consists of (1) flagellar filaments that are 15 μm long and 120-250 Å in diameter and a (2) motor domain that rotates the flagellar filaments alternately in clockwise and anticlockwise directions. This unique behavior of rotation allows bacteria to swim desirably. ATP synthase is a different type of a molecular machine, which synthesizes and hydrolyzes ATP through its rotary motion.7-9 ATP synthase is built up of two different machinery components, that is, F1 and F0, where the rotation of the former is driven by the free energy released from the hydrolysis of ATP to adenosine diphosphate (ADP); the latter rotates by a flux of ions passing through a membrane and synthesizes ATP. This huge protein complex has a shaft, which rotates just like real rotary motors. Since the rotary motion of ATP synthase occurs in a stepwise manner in response to the hydrolysis of ATP, it is regarded as a biological stepping motor. In addition to these molecular motors, some other biological machines are known, where the hydrolysis of ATP triggers different types of mechanical motions. Representative examples include the family of chap† The University of Tokyo. ‡ PRESTO. 1377 Chem. Rev. 2005, 105, 1377−1400

/pdf/toward-intelligent-molecular-machines-directed-motions-of-5biq6jkgio.pdf

Toward intelligent molecular machines: directed motions of biological and artificial molecules and assemblies.

A number of models have been developed to describe the various amorphization processes and the effects of temperature on the kinetics of amorphization. These models are reviewed and in some cases further developed. In general, these models contain a number of parameters relating to irradiation-assisted and thermal recovery processes, which make their application to existing data sets challenging. Nonetheless, general aspects of the models yield insights into the rate-limiting processes controlling the kinetics of amorphization within a given temperature regime. Several examples are used to illustrate features of the models and to highlight differences in behavior.

Models and mechanisms of irradiation-induced amorphization in ceramics

The transformation of silicon to the amorphous state by implanted ions was studied both experimentally and theoretically. Experimentally, the amount of transformed silicon and the critical ion dose necessary to amorphize the entire implanted layer were determined by ESR. How the critical dose varies with ion mass (Li, N, Ne, Ar, and Kr), ion energy (20–180 keV), and implant temperature (77–475 K) was determined. Theoretically, several phenomenological models were used to analyze these data. The overlap‐damage model was used to determine the critical dose from the data, the size of the amorphous region around the ion track, and the degree of overlap damage required for amorphization. For all implants, the first ion created only predamage, while the second or third ion into the same region caused the amorphous transformation. The critical‐energy‐density model was in good agreement with the measured critical doses. This model assumed that a region would become amorphous if the energy density deposited into atomic processes by the ions exceeded the critical energy density of 6×1023 eV/cm3. For high‐temperature implantations, out‐diffusion models can explain the temperature dependence of the critical dose. Although the analysis is not completely definitive, the critical‐energy‐density model may also be valid at high temperature if diffusion of the damage energy is taken into account. This out‐diffusion of energy from around the ion track occurs via a thermally activated process. Probably, the energy moves with the out‐diffusion of the vacancies from the ion track.

Crystalline to amorphous transformation in ion-implanted silicon: a composite model

Nature has evolved specialized molecules, motor proteins, to actively transport molecules over long distances. Such molecule-based energy dependent transport processes would be useful in nanotechnology or material sciences, for example to facilitate local assembly or repair processes, or to mediate rapid transport of nonbiological molecules. In an effort to elucidate how to control the movement of biological motors in synthetic environments, we use highly oriented poly(tetrafluoroethylene) films functionalized with the motor protein kinesin and find that they are able to direct the motion of microtubules in straight lines along the films' orientation axes. Potential mechanisms by which guidance occurs are discussed.

http://iopscience.iop.org/article/10.1088/0957-4484/10/3/302/pdf

Molecular shuttles: directed motion of microtubules along nanoscale kinesin tracks

We have used optical second-harmonic generation to study surface molecular order in a liquid-crystal (4′-n-octyl-4-cyano-biphenyl, or 8CB) on shear-deposited polymer films. The films are highly oriented layers of polytetrafluoroethylene (PTFE) or high-density polyethylene (HDPE), with a surface topology of uniaxially aligned nanoscale ridges and grooves, which are used as versatile substrates for oriented growth and alignment of other materials. In nematic 8CB cells made with either polymer, the surface monolayers of 8CB were aligned along the polymer orientation axis, and showed C2ν symmetry. In the isotropic phase, the surface monolayer alignment in these cells was lost. Monolayers of 8CB evaporated onto either polymer showed little or no alignment. These data indicate that the PTFE and HDPE films do not produce the strong epitaxylike alignment seen on some cloth-rubbed polymer surfaces. Instead, alignment appears to be primarily caused by surface ridges through an elastic, bulk-mediated mechanism.

John R. Dennis

Papers

Crystalline to amorphous transformation in ion-implanted silicon: a composite model

Molecular shuttles: directed motion of microtubules along nanoscale kinesin tracks

Liquid-crystal alignment on polytetrafluoroethylene and high-density polyethylene thin films studied by optical second-harmonic generation