Isolation by crystallization of translational isomers of a bistable donor-acceptor [2]catenane.

The template-directed synthesis of a bistable donor-acceptor [2]catenane wherein both translational isomers--one in which a tetrathiafulvalene unit in a mechanically interlocked crown ether occupies the cavity of a cyclobis(paraquat-p-phenylene) ring and the other in which a 1,5-dioxynaphthalene unit in the crown ether resides inside the cavity of the tetracationic cyclophane--exist in equilibrium in solution, has led to the isolation and separation by hand picking of single crystals colored red and green, respectively. These two crystalline co-conformations have been characterized separately at both the molecular and supramolecular levels, and also by dynamic NMR spectroscopy in solution where there is compelling evidence that the mechanically interlocked molecules are present as a complex mixture of translational, configurational, and conformational isomers wherein the isomerization is best described as being a highly dynamic and adaptable phenomenon.

Application of compressive sensing in SFAI measurement for faster sound speed assessment.

Quick quality assessment of fluid (liquid and gas) is a key requirement for many industries. Acoustic parameters like sound speed in fluid or sound attenuation in fluid can serve as a crucial marker for assessing fluid quality as any deviation of those parameters points to adulteration or degradation of the fluid. Swept Frequency Acoustic Interferometry (SFAI) is a well-known noninvasive technique for taking measurements of fluid's acoustic parameters (e.g. sound speed in fluid, sound attenuation in fluid, etc.) from outside the container walls. In this work, we focused on assessing sound speed in liquid through SFAI while applying compressive sensing technique to make very fast scans which are otherwise not possible through standard SFAI measurements. We report the possibility of 25 times faster scanning speed to measure sound speed in fluid when compared to standard SFAI based frequency scans. In addition, the proposed technique significantly reduces the volume of data that needs to be processed twenty-four hours a day basis.

Radically enhanced molecular switches.

The mechanism governing the redox-stimulated switching behavior of a tristable [2]rotaxane consisting of a cyclobis(paraquat-p-phenylene) (CBPQT(4+)) ring encircling a dumbbell, containing tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units which are separated from each other along a polyether chain carrying 2,6-diisopropylphenyl stoppers by a 4,4'-bipyridinium (BIPY(2+)) unit, is described. The BIPY(2+) unit acts to increase the lifetime of the metastable state coconformation (MSCC) significantly by restricting the shuttling motion of the CBPQT(4+) ring to such an extent that the MSCC can be isolated in the solid state and is stable for weeks on end. As controls, the redox-induced mechanism of switching of two bistable [2]rotaxanes and one bistable [2]catenane composed of CBPQT(4+) rings encircling dumbbells or macrocyclic polyethers, respectively, that contain a BIPY(2+) unit with either a TTF or DNP unit, is investigated. Variable scan-rate cyclic voltammetry and digital simulations of the tristable and bistable [2]rotaxanes and [2]catenane reveal a mechanism which involves a bisradical state coconformation (BRCC) in which only one of the BIPY(•+) units in the CBPQT(2(•+)) ring is oxidized to the BIPY(2+) dication. This observation of the BRCC was further confirmed by theoretical calculations as well as by X-ray crystallography of the [2]catenane in its bisradical tetracationic redox state. It is evident that the incorporation of a kinetic barrier between the donor recognition units in the tristable [2]rotaxane can prolong the lifetime and stability of the MSCC, an observation which augurs well for the development of nonvolatile molecular flash memory devices.

Surface Potential Simulation and Electrode Design for in-Ear EEG Measurement.

The need for everyday-real-time EEG sensing has resulted in the development of minimalistic and discreet wearable EEG measuring devices. A front runner in this race is in-ear worn device. However, the position of the ear as well as its restricted accessibility poses certain challenges in the design of such devices - from the type of materials used to the placement of electrodes. These choices are important as they will determine the quality of the EEG signal available and in turn the accuracy of the application. We therefore create a simulation model of the human ear, allowing us to understand the impact of these choices on our design of an In-Ear EEG wearable. We first study the signal acquisition characteristics of a proposed gold-plated electrode against two other state-of-the-art electrode materials for in-ear EEG data collection. We further validate this electrode choice by fabricating a personalized silicone-based earpiece and collecting in-situ EEG data. This work explores the properties of using gold plated electrodes in capturing in-ear EEG signals enabling unobtrusive collection of the brain physiology data in real world setting.

Syntheses and dynamics of donor-acceptor [2]catenanes in water.

A subset of mechanically interlocked molecules, namely, donor-acceptor [2]catenanes, have been produced in aqueous solutions in good yields from readily available precursors. The catenations are templated by strong hydrophobic and [π···π] stacking interactions, which serve to assemble the corresponding supramolecular precursors, prior to postassembly covalent modification. Dynamic (1)H NMR spectroscopic investigations performed on one of these [2]catenanes reveal that the pirouetting motion of the butadiyne-triethylene glycol chain occurs with a dramatically lower activation enthalpy, yet with a much higher negative activation entropy in water, compared to organic solvents. The preparations of mechanically interlocked molecules in water constitute the basis for the future development of complex functional molecular machinery in aqueous environments.

Electrostatic barriers in rotaxanes and pseudorotaxanes.

The ability to control the kinetic barriers governing the relative motions of the components in mechanically interlocked molecules is important for future applications of these compounds in molecular electronic devices. In this Full Paper, we demonstrate that bipyridinium (BIPY(2+)) dications fulfill the role as effective electrostatic barriers for controlling the shuttling and threading behavior for rotaxanes and pseudorotaxanes in aqueous environments. A degenerate [2]rotaxane, composed of two 1,5-dioxynaphthalene (DNP) units flanking a central BIPY(2+) unit in the dumbbell component and encircled by the cyclobis(paraquat-p-phenylene) (CBPQT(4+)) tetracationic cyclophane, has been synthesized employing a threading-followed-by-stoppering approach. Variable-temperature (1)H NMR spectroscopy reveals that the barrier to shuttling of the CBPQT(4+) ring over the central BIPY(2+) unit is in excess of 17 kcal mol(-1) at 343 K. Further information about the nature of the BIPY(2+) unit as an electrostatic barrier was gleaned from related supramolecular systems, utilizing two threads composed of either two DNP units flanking a central BIPY(2+) moiety or a central DNP unit flanked by a BIPY(2+) moiety. The threading and dethreading processes of the CBPQT(4+) ring with these compounds, which were investigated by spectrophotometric techniques, reveal that the BIPY(2+) unit is responsible for affecting both the thermodynamics and kinetics of pseudorotaxane formation by means of an intramolecular self-folding (through donor-acceptor interactions with the DNP unit), in addition to Coulombic repulsion. In particular, the free energy barrier to threading (ΔG(f)(++)) of the CBPQT(4+) for the case of the thread composed of a DNP flanked by two BIPY(2+) units was found to be as high as 21.7 kcal mol(-1) at room temperature. These results demonstrate that we can effectively employ the BIPY(2+) unit to serve as electrostatic barriers in water in order to gain control over the motions of the CBPQT(4+) ring in both mechanically interlocked and supramolecular systems.

Donor-acceptor oligorotaxanes made to order.

Five donor-acceptor oligorotaxanes made up of dumbbells composed of tetraethylene glycol chains, interspersed with three and five 1,5-dioxynaphthalene units, and terminated by 2,6-diisopropylphenoxy stoppers, have been prepared by the threading of discrete numbers of cyclobis(paraquat-p-phenylene) rings, followed by a kinetically controlled stoppering protocol that relies on click chemistry. The well-known copper(I)-catalyzed alkyne-azide cycloaddition between azide functions placed at the ends of the polyether chains and alkyne-bearing stopper precursors was employed during the final kinetically controlled template-directed synthesis of the five oligorotaxanes, which were characterized subsequently by (1)H NMR spectroscopy at low temperature (233 K) in deuterated acetonitrile. The secondary structures, as well as the conformations, of the five oligorotaxanes were unraveled by spectroscopic comparison with the dumbbell and ring components. By focusing attention on the changes in chemical shifts of some key probe protons, obtained from a wide range of low-temperature spectra, a picture emerges of a high degree of folding within the thread protons of the dumbbells of four of the five oligorotaxanes-the fifth oligorotaxane represents a control compound in effect-brought about by a combination of C-H···O and π-π stacking interactions between the π-electron-deficient bipyridinium units in the rings and the π-electron-rich 1,5-dioxynaphthalene units and polyether chains in the dumbbells. The secondary structures of a foldamer-like nature have received further support from a solid-state superstructure of a related [3]pseudorotaxane and density functional calculations performed thereon.

Rapid thermally assisted donor-acceptor catenation.

Charged donor-acceptor [2]catenanes containing cyclobis(paraquat-p-phenylene) as the ring component can be synthesised in yields of up to 88% in under one hour by heating two precursors in the presence of macrocyclic polyether templates in N,N-dimethylformamide at 80 °C.

A tristable [2]pseudo[2]rotaxane.

A strategy towards increasing the lifetime of the metastable state of a [2]rotaxane incorporating tetrathiafulvalene, 1,5-dioxynaphthalene and bipyridinium (BIPY(2+)) is presented. Incorporation of BIPY(2+) served multiple roles as an electrostatic barrier to relaxation, a supramolecular recognition site for bis-1,5-dioxynaphthalene[38]crown-10 macrocycle, and upon reduction a recognition site for the mechanically bonded cyclobis(paraquat-p-phenylene) ring.

A general synthesis of macrocyclic pi-electron-acceptor systems.

Cyclocondensations of aromatic diamines with 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridinium salts afford doubly or quadruply charged, macrocyclic, N,N'-diarylbipyridinium cations. These are tolerant of a wide range of acids, bases, and nucleophiles, although they appear to undergo reversible, one-electron reduction by tertiary amines. Single-crystal X-ray analysis demonstrates the presence of a macrocycle conformation in which the 4,4'-bipyridinium and 4,4'-biphenylenedisulfonyl residues are suitably spaced and aligned for complexation with pi-donor arenes, and NMR studies in solution indeed confirm binding to 1,5-bis[hydroxy(ethoxy)ethoxy]naphthalene.

Homopolymer micelles in heterogeneous solvent mixtures.

Amphiphilic homopolymers containing a hydrophilic and a hydrophobic functionality in each monomer unit have been shown to form polar or apolar containers depending on the solvent environment. When presented with a mixture of solvents, these polymeric containers are capable of releasing certain guest molecules. The fundamental mechanism behind these properties is investigated, and the utility of these assemblies in separations has been demonstrated with an example.

Dendrimers with both polar and apolar nanocontainer characteristics.

Amphiphilic dendrimers with a custom-designed biaryl repeat unit have been synthesized. These dendrimers afford hydrophobic nanocontainers in polar solvents and hydrophilic nanocontainers in apolar solvents. These container properties were investigated using dye incorporation studies. The aggregation states of these dendrimers are also reported using DLS studies.

Invertible amphiphilic homopolymers.

Stimuli-responsive polymers and assemblies are viable candidates for the so-called "smart" materials. In this communication, we report a new class of amphiphilic homopolymers that forms micelle-like structures in polar solvents and inverted micelle-like structures in apolar solvents. We demonstrate that these superstructures are the result of the changes in the molecular-level conformations in the monomer.