scholarly journals Beyond switches: Rotaxane- and catenane-based synthetic molecular motors

2008 ◽  
Vol 80 (1) ◽  
pp. 17-29 ◽  
Author(s):  
Euan R. Kay ◽  
David A. Leigh
Keyword(s):  
Molecular Motors ◽  
Physical Science ◽  
Statistical Physics ◽  
Biological Process ◽  
Molecular Level ◽  
Molecular Machines ◽  
Interlocked Molecules ◽  
Recent Developments ◽  
New Generation ◽  
First Time

Nature uses molecular motors and machines in virtually every significant biological process, but learning how to design and assemble simpler artificial structures that function through controlled molecular-level motion is a major challenge for contemporary physical science. The established engineering principles of the macroscopic world can offer little more than inspiration to the molecular engineer who creates devices for an environment where everything is constantly moving and being buffeted by other atoms and molecules. Rather, experimental designs for working molecular machines must follow principles derived from chemical kinetics, thermodynamics, and nonequilibrium statistical physics. The remarkable characteristics of interlocked molecules make them particularly useful for investigating the control of motion at the molecular level. Yet, the vast majority of synthetic molecular machines studied to date are simple two-state switches. Here we outline recent developments from our laboratory that demonstrate more complex molecular machine functions. This new generation of synthetic molecular machines can move continuously and progressively away from equilibrium, and they may be considered true prototypical molecular motors. The examples discussed exemplify two, fundamentally different, "Brownian ratchet" mechanisms previously developed in theoretical statistical physics and realized experimentally in molecular-level devices for the first time in these systems.

scholarly journals Molecular, Supramolecular, and Macromolecular Motors and Artificial Muscles

MRS Bulletin ◽  
2009 ◽  
Vol 34 (9) ◽  
pp. 671-681 ◽  
Author(s):  
Dongbo Li ◽  
Walter F. Paxton ◽  
Ray H. Baughman ◽  
Tony Jun Huang ◽  
J. Fraser Stoddart ◽  
...  
Keyword(s):  
Chemical Synthesis ◽  
Molecular Motors ◽  
Molecular Level ◽  
Biological Systems ◽  
Molecular Machines ◽  
Mechanical Action ◽  
Artificial Muscles ◽  
Molecular Scale ◽  
Recent Developments ◽  
External Stimuli

AbstractRecent developments in chemical synthesis, nanoscale assembly, and molecular-scale measurements enable the extension of the concept of macroscopic machines to the molecular and supramolecular levels. Molecular machines are capable of performing mechanical movements in response to external stimuli. They offer the potential to couple electrical or other forms of energy to mechanical action at the nano- and molecular scales. Working hierarchically and in concert, they can form actuators referred to as artificial muscles, in analogy to biological systems. We describe the principles behind driven motion and assembly at the molecular scale and recent advances in the field of molecular-level electromechanical machines, molecular motors, and artificial muscles. We discuss the challenges and successes in making these assemblies work cooperatively to function at larger scales.

Recent developments in low-voltage SEM of polymers

1993 ◽  
Vol 51 ◽  
pp. 866-867
Author(s):  
S.J. Krause ◽  
W.W. Adams
Keyword(s):  
Low Voltage ◽  
Chromatic Aberration ◽  
Thermal Electron ◽  
Analytical Technique ◽  
Recent Developments ◽  
Beam Currents ◽  
New Generation ◽  
First Time ◽  
Voltage Scanning ◽  
Beam Damage

Over the past decade low voltage scanning electron microscopy (LVSEM) of polymers has evolved from an interesting curiosity to a powerful analytical technique. This development has been driven by improved instrumentation and in particular, reliable field emission gun (FEG) SEMs. The usefulness of LVSEM has also grown because of an improved theoretical and experimental understanding of sample-beam interactions and by advances in sample preparation and operating techniques. This paper will review progress in polymer LVSEM and present recent results and developments in the field.In the early 1980s a new generation of SEMs produced beam currents that were sufficient to allow imaging at low voltages from 5keV to 0.5 keV. Thus, for the first time, it became possible to routinely image uncoated polymers at voltages below their negative charging threshold, the "second crossover", E2 (Fig. 1). LVSEM also improved contrast and reduced beam damage in sputter metal coated polymers. Unfortunately, resolution was limited to a few tenths of a micron due to the low brightness and chromatic aberration of thermal electron emission sources.

scholarly journals Stochastically pumped adaptation and directional motion of molecular machines

2018 ◽  
Vol 115 (38) ◽  
pp. 9405-9413 ◽  
Author(s):  
R. Dean Astumian
Keyword(s):  
Single Molecule ◽  
Molecular Motors ◽  
High Efficiency ◽  
Probability Distributions ◽  
Molecular Machines ◽  
High Energy ◽  
Stochastic Thermodynamics ◽  
Recent Developments ◽  
Directional Motion ◽  
External Fluctuations

Recent developments in synthetic molecular motors and pumps have sprung from a remarkable confluence of experiment and theory. Synthetic accomplishments have facilitated the ability to design and create molecules, many of them featuring mechanically bonded components, to carry out specific functions in their environment—walking along a polymeric track, unidirectional circling of one ring about another, synthesizing stereoisomers according to an external protocol, or pumping rings onto a long rod-like molecule to form and maintain high-energy, complex, nonequilibrium structures from simpler antecedents. Progress in the theory of nanoscale stochastic thermodynamics, specifically the generalization and extension of the principle of microscopic reversibility to the single-molecule regime, has enhanced the understanding of the design requirements for achieving strong unidirectional motion and high efficiency of these synthetic molecular machines for harnessing energy from external fluctuations to carry out mechanical and/or chemical functions in their environment. A key insight is that the interaction between the fluctuations and the transition state energies plays a central role in determining the steady-state concentrations. Kinetic asymmetry, a requirement for stochastic adaptation, occurs when there is an imbalance in the effect of the fluctuations on the forward and reverse rate constants. Because of strong viscosity, the motions of the machine can be viewed as mechanical equilibrium processes where mechanical resonances are simply impossible but where the probability distributions for the state occupancies and trajectories are very different from those that would be expected at thermodynamic equilibrium.

scholarly journals Green light powered molecular state motor enabling eight-shaped unidirectional rotation

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Aaron Gerwien ◽  
Peter Mayer ◽  
Henry Dube
Keyword(s):  
Molecular Motors ◽  
Molecular Level ◽  
Molecular Motor ◽  
Green Light ◽  
Molecular Machines ◽  
Molecular State ◽  
Molecular Devices ◽  
External Energy ◽  
Fixed Sequence ◽  
Crossing Point

Abstract Molecular motors convert external energy into directional motions at the nano-scales. To date unidirectional circular rotations and linear motions have been realized but more complex directional trajectories remain unexplored on the molecular level. In this work we present a molecular motor powered by green light allowing to produce an eight-shaped geometry change during its unidirectional rotation around the central molecular axis. Motor motion proceeds in four different steps, which alternate between light powered double bond isomerizations and thermal hula-twist isomerizations. The result is a fixed sequence of populating four different isomers in a fully unidirectional trajectory possessing one crossing point. This motor system opens up unexplored avenues for the construction and mechanisms of molecular machines and will therefore not only significantly expand the toolbox of responsive molecular devices but also enable very different applications in the field of miniaturized technology than currently possible.

A Guide to Monte Carlo Simulations in Statistical Physics

2021 ◽  
Author(s):  
David Landau ◽  
Kurt Binder
Keyword(s):  
Machine Learning ◽  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Graduate Students ◽  
Physical Science ◽  
Statistical Physics ◽  
Condensed Matter ◽  
Physical Systems ◽  
Recent Developments ◽  
New Material

Dealing with all aspects of Monte Carlo simulation of complex physical systems encountered in condensed matter physics and statistical mechanics, this book provides an introduction to computer simulations in physics. The 5th edition contains extensive new material describing numerous powerful algorithms and methods that represent recent developments in the field. New topics such as active matter and machine learning are also introduced. Throughout, there are many applications, examples, recipes, case studies, and exercises to help the reader fully comprehend the material. This book is ideal for graduate students and researchers, both in academia and industry, who want to learn techniques that have become a third tool of physical science, complementing experiment and analytical theory.

scholarly journals Green Light Powered Molecular State Motor Enabling Eight-Shaped Unidirectional Rotation

2019 ◽  
Author(s):  
Aaron Gerwien ◽  
Peter Mayer ◽  
Henry Dube
Keyword(s):  
Molecular Motors ◽  
Molecular Level ◽  
Molecular Motor ◽  
Green Light ◽  
Molecular Machines ◽  
Molecular State ◽  
Molecular Devices ◽  
External Energy ◽  
Fixed Sequence ◽  
Crossing Point

Molecular motors convert external energy into directional motions at the nanoscale. To date unidirectional circular rotations and linear motions have been realized but more complex directional trajectories remain unexplored on the molecular level. In this work we present a molecular motor powered by green light allowing to produce an eight-shaped geometry change during its unidirectional rotation around the central molecular axis. Motor motion proceeds in four different steps, which alternate between light powered double bond isomerizations and thermal hula-twist isomerizations. The result is a fixed sequence of populating four different isomers in a fully unidirectional trajectory possessing one crossing point. This motor system opens up new avenues for the construction and mechanisms of molecular machines and will therefore not only expand the toolbox of responsive molecular devices but enable unprecedented applications in the field of miniaturized technology in the future.<br>

scholarly journals Green Light Powered Molecular State Motor Enabling Eight-Shaped Unidirectional Rotation

2019 ◽  
Author(s):  
Aaron Gerwien ◽  
Peter Mayer ◽  
Henry Dube
Keyword(s):  
Molecular Motors ◽  
Molecular Level ◽  
Molecular Motor ◽  
Green Light ◽  
Molecular Machines ◽  
Molecular State ◽  
Molecular Devices ◽  
External Energy ◽  
Fixed Sequence ◽  
Crossing Point

Molecular motors convert external energy into directional motions at the nanoscale. To date unidirectional circular rotations and linear motions have been realized but more complex directional trajectories remain unexplored on the molecular level. In this work we present a molecular motor powered by green light allowing to produce an eight-shaped geometry change during its unidirectional rotation around the central molecular axis. Motor motion proceeds in four different steps, which alternate between light powered double bond isomerizations and thermal hula-twist isomerizations. The result is a fixed sequence of populating four different isomers in a fully unidirectional trajectory possessing one crossing point. This motor system opens up new avenues for the construction and mechanisms of molecular machines and will therefore not only expand the toolbox of responsive molecular devices but enable unprecedented applications in the field of miniaturized technology in the future.<br>

Shot-noise simulations of HREM images of polymer crystals

1989 ◽  
Vol 47 ◽  
pp. 342-343
Author(s):  
Philippe Pradère ◽  
Edwin L. Thomas
Keyword(s):  
Low Dose ◽  
Molecular Level ◽  
High Resolution Electron Microscopy ◽  
Crystal Defects ◽  
Inorganic Materials ◽  
Photographic Emulsion ◽  
Polymer Crystals ◽  
Resolution Electron ◽  
Recent Developments ◽  
Lattice Images

High Resolution Electron Microscopy (HREM) is a very powerful technique for the study of crystal defects at the molecular level. Unfortunately polymer crystals are beam sensitive and are destroyed almost instantly under the typical HREM imaging conditions used for inorganic materials. Recent developments of low dose imaging at low magnification have nevertheless permitted the attainment of lattice images of very radiation sensitive polymers such as poly-4-methylpentene-1 and enabled molecular level studies of crystal defects in somewhat more resistant ones such as polyparaxylylene (PPX) [2].With low dose conditions the images obtained are very noisy. Noise arises from the support film, photographic emulsion granularity and in particular, the statistical distribution of electrons at the typical doses of only few electrons per unit resolution area. Figure 1 shows the shapes of electron distribution, according to the Poisson formula :

Organic Reactivity Control by Means of Neighboring Groups and Organometallics. A Personal Account

1994 ◽  
Vol 59 (1) ◽  
pp. 1-74 ◽  
Author(s):  
Pavel Kočovský
Keyword(s):  
Transition Metals ◽  
Cyclopropane Ring ◽  
Allylic Substitutions ◽  
Recent Developments ◽  
Cardioactive Drug ◽  
Novel Method ◽  
Metal Catalyzed ◽  
Electrophilic Additions ◽  
Near Future ◽  
First Time

This review summarizes the main topics of our research and covers the period of the last 15 years. The prime interest is focused on various ways of controlling the regio- and stereoselectivity of selected organic reactions, in particular electrophilic additions, cleavage of cyclopropane rings, and allylic substitutions by means of neighboring groups and/or transition and non-transition metals. In the first part, the factors governing the course of electrophilic additions are assessed, culminating in the formulation of selection rules for the reactivity of cyclohexene systems, and in a concise synthesis of the natural cardioactive drug, strophanthidin. These studies also contribute to a better understanding of the mechanisms of electrophilic additions. The second part describes recent developments in the stereo- and regiocontrolled cleavage of cyclopropane rings by non-transition metals (Tl and Hg), and the reactivity and transmetalation (with Pd) of the primary products. This methodology has resulted in novel routes to unique polycyclic structures, and will have synthetic applications in the near future. Evidence for the stereospecific "corner" cleavage of the cyclopropane ring has been provided for the first time for Tl and later for Hg. The third part deals with transition metal-catalyzed allylic substitution. Evidence for a new "syn" mechanism for the formation of the intermediate (π-allyl)palladium complex has been provided, which runs counter to the generally accepted "anti" mechanism. A novel method for a Pd-catalyzed allylic oxidation has been developed and employed in the synthesis of natural sesquiterpenes. The increasing importance of transition and non-transition metals for synthetic organic chemistry is demonstrated by their unique reactivity in a number of the papers included in this review.

Recycling and Reuse in the Roman Economy

2020 ◽  
Keyword(s):  
Building Materials ◽  
Computational Modelling ◽  
Late Antique ◽  
Roman Economy ◽  
Wide Range ◽  
The Status ◽  
Recent Developments ◽  
Methodological Approaches ◽  
First Time ◽  
Site Types

The recycling and reuse of materials and objects were extensive in the past, but have rarely been embedded into models of the economy; even more rarely has any attempt been made to assess the scale of these practices. Recent developments, including the use of large datasets, computational modelling, and high-resolution analytical chemistry, are increasingly offering the means to reconstruct recycling and reuse, and even to approach the thorny matter of quantification. Growing scholarly interest in the topic has also led to an increasing recognition of these practices from those employing more traditional methodological approaches, which are sometimes coupled with innovative archaeological theory. Thanks to these efforts, it has been possible for the first time in this volume to draw together archaeological case studies on the recycling and reuse of a wide range of materials, from papyri and textiles, to amphorae, metals and glass, building materials and statuary. Recycling and reuse occur at a range of site types, and often in contexts which cross-cut material categories, or move from one object category to another. The volume focuses principally on the Roman Imperial and late antique world, over a broad geographical span ranging from Britain to North Africa and the East Mediterranean. Last, but not least, the volume is unique in focusing upon these activities as a part of the status quo, and not just as a response to crisis.

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