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Euan R Kay

Publications and source records attributed to Euan R Kay.

6 recordsLinked to original sources
PubMed2007

Synthetic molecular motors and mechanical machines.

The widespread use of controlled molecular-level motion in key natural processes suggests that great rewards could come from bridging the gap between the present generation of synthetic molecular systems, which by and large rely upon electronic and chemical effects to carry out their functions, and the machines of the macroscopic world, which utilize the synchronized movements of smaller parts to perform specific tasks. This is a scientific area of great contemporary interest and extraordinary recent growth, yet the notion of molecular-level machines dates back to a time when the ideas surrounding the statistical nature of matter and the laws of thermodynamics were first being formulated. Here we outline the exciting successes in taming molecular-level movement thus far, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion. We also highlight some of the issues and challenges that still need to be overcome.

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PubMed2006

Beyond switches: ratcheting a particle energetically uphill with a compartmentalized molecular machine.

Here we correlate chemical (covalent), physical (thermodynamic), and statistical (population distribution) descriptions of behavior with the way that two new types of simple molecular machines (the threads of rotaxanes) perform the task of transporting a Brownian substrate (the rotaxane macrocycle) between two distinguishable binding sites. The first machine-substrate ensemble is a [2]rotaxane that operates through a mechanism that intrinsically causes it to change the average position of the macrocycle irreversibly. This contrasts with the behavior of classic stimuli-responsive molecular shuttles that act as reversible molecular switches. The second system is a compartmentalized molecular machine that is able to pump its substrate energetically uphill using the energy provided by a photon by means of an olefin photoisomerization. Resetting this compartmentalized molecular machine does not undo the work it has carried out or the task performed, a significant difference to a simple molecular switch and a characteristic we recognize as "ratcheting" (see Scheme 8). The ratcheting mechanism allows the [2]rotaxane to carry out the transport function envisaged for the historical thought-machines, Smoluchowski's Trapdoor and Maxwell's Pressure Demon, albeit via an unrelated mechanism and using an input of energy. We define and exemplify the terms "ratcheting" and "escapement" in mechanical terms for the molecular level and outline the fundamental phenomenological differences that exist between what constitutes a two-state Brownian switch, a two-state Brownian memory or "flip-flop", and a (two-stroke) Brownian motor. We also suggest that considering the relationship between the parts of a molecular machine and a substrate in terms of "statistical balance" and "linkage" could be useful in the design of more complex systems and in helping to understand the role of individual amino acids and peptide fragments during the directional transport of substrates by biological pumps and motors.

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PubMed2005

Experimental and theoretical study of the adsorption of fumaramide [2]rotaxane on Au(111) and Ag(111) surfaces.

Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface.

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PubMed2004

A reversible synthetic rotary molecular motor.

The circumrotation of a submolecular fragment in either direction in a synthetic molecular structure is described. The movement of a small ring around a larger one occurs through positional displacements arising from biased Brownian motion that are kinetically captured and then directionally released. The sense of rotation is governed solely by the order in which a series of orthogonal chemical transformations is performed. The minimalist nature of the [2]catenane flashing ratchet design permits certain mechanistic comparisons with the Smoluchowski-Feynman ratchet and pawl. Even when no work has to be done against an opposing force and no net energy is used to power the motion, a finite conversion of energy is intrinsically required for the molecular motor to undergo directional rotation. Nondirectional rotation has no such requirement.

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PubMed2003

Electrochemically switchable hydrogen-bonded molecular shuttles.

A series of [2]rotaxanes containing succinamide and naphthalimide hydrogen-bonding stations for a benzylic amide macrocycle is described. Electrochemical reduction and oxidation of the naphthalimide group alters its ability to form hydrogen bonds to the macrocycle to such a degree that redox processes can be used to switch the relative macrocycle-binding affinities of the two stations in a rotaxane by over 8 orders of magnitude. The structure of the neutral [2]rotaxane in solution is established by (1)H NMR spectroscopy and shows that the macrocycle exhibits remarkable positional integrity for the succinamide station in a variety of solvents. Cyclic voltammetry experiments allow the simultaneous stimulation and observation of a redox-induced dynamic process in the rotaxane which is both reversible and cyclable. Model compounds in which various conformational and co-conformational changes are prohibited demonstrate unequivocally that the redox response is the result of shuttling of the macrocycle between the two stations. At room temperature in tetrahydrofuran the electrochemically induced movement of the macrocycle between the two stations takes approximately 50 micros.

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