Electrochemistry: connector of sciences

Journal of Solid State Electrochemistry -     

Glass column connector for a gas chromatograph

A cheap glass—metal connector is described for use with glass columns, to avoid the problems of O-rings or special ferrules. The device is valuable in gas chromatography of amino acid derivatives.     

Intermetallic communication through a 1,3,5-triethynylbenzene connector

The electrochemical behavior of two series of homo- and heterometallic 1,3,5-triethynylbenzene-based transition metal complexes containing [(η²-dppf)(η⁵-C₅H₅)Ru], [(PPh₃)₂(η⁵-C₅H₅)Os], [(^tBu₂bpy)(CO)₃Re], and [(bpy)(CO)₃ClRe] (dppf = 1,1′-bis(diphenylphosphino)ferrocene; ^tBu₂bpy = 4,4′-di-tert-butyl-2,2′-bipyridyl; bpy = 2,2′-bipyridyl-5-yl) building blocks have been studied, showing that there is electronic interaction between the appropriate metal atoms. The electronic absorption spectra reveal high energy bands corresponding to intraligand π → π∗ transitions (bpy, alkynyl) and low energy absorptions which are attributed to MLCT transitions; replacement of ruthenium by osmium results in a blue-shift of the MLCT bands. The associated radical cations of three complexes were in situ generated by chemical oxidation and characterized by continuous wave electron paramagnetic resonance (EPR) investigations in X-band performed at low temperatures.     

Two-dimensional DNA origami assemblies using a four-way connector

Two-dimensional self-assembly of DNA origami structures was carried out using a connector that has connection sites at all four edges. By utilizing this four-way connector, five and eight origami monomers were assembled to form a cruciate and a hollow square structure, respectively.     

A molecular half-wave rectifier

This paper describes the performance of junctions based on self-assembled monolayers (SAMs) as the functional element of a half-wave rectifier (a simple circuit that converts, or rectifies, an alternating current (AC) signal to a direct current (DC) signal). Junctions with SAMs of 11-(ferrocenyl)-1-undecanethiol or 11-(biferrocenyl)-1-undecanethiol on ultraflat, template-stripped Ag (Ag(TS)) bottom electrodes, and contacted by top electrodes of eutectic indium-gallium (EGaIn), rectified AC signals, while similar junctions based on SAMs of 1-undecanethiol-SAMs lacking the ferrocenyl terminal group-did not. SAMs in these AC circuits (operating at 50 Hz) remain stable over a larger window of applied bias than in DC circuits. AC measurements, therefore, can investigate charge transport in SAM-based junctions at magnitudes of bias inaccessible to DC measurements. For junctions with SAMs of alkanethiols, combining the results from AC and DC measurements identifies two regimes of bias with different mechanisms of charge transport: (i) low bias (|V| < 1.3 V), at which direct tunneling dominates, and (ii) high bias (|V| > 1.3 V), at which Fowler-Nordheim (FN) tunneling dominates. For junctions with SAMs terminated by Fc moieties, the transition to FN tunneling occurs at |V| ≈ 2.0 V. Furthermore, at sufficient forward bias (V > 0.5 V), hopping makes a significant contribution to charge transport and occurs in series with direct tunneling (V ? 2.0 V) until FN tunneling activates (V ? 2.0 V). Thus, for Fc-terminated SAMs at forward bias, three regimes are apparent: (i) direct tunneling (V = 0-0.5 V), (ii) hopping plus direct tunneling (V ≈ 0.5-2.0 V), and (iii) FN tunneling (V ? 2.0 V). Since hopping does not occur at reverse bias, only two regimes are present over the measured range of reverse bias. This difference in the mechanisms of charge transport at forward and reverse bias for junctions with Fc moieties resulted in large rectification ratios (R > 100) and enabled half-wave rectification.     

A molecular bowl sumanene

Nonplanar polyaromatic carbon molecules including fullerenes and carbon nanotubes have been attracting great interest due to their potential as materials, catalysts, etc. In this context, bowl-shaped polyaromatic hydrocarbons (π bowls) are considered to be key materials in the science of nonplanar π-conjugated carbon systems. Among π bowls, we focused on a molecular bowl "sumanene (C(21)H(12))" featuring a C(3v) symmetric structural motif present in fullerenes or carbon nanotube molecules. In this article, we present the research on sumanenes to date, including their synthesis, structural characterization, derivatization, complexation, and their potential uses as electrical materials. The characteristic structural feature of a sumanene depends on three sp(3) hybridized carbon atoms at the benzylic positions. Facile functionalization via selective formation of benzylic anions gives stereoselective substituted compounds, the π-extended derivatives, and the deeper π bowls. Furthermore, the dynamically flexible aspect based on bowl-to-bowl inversion is also described. The crystal with a columnar bowl-in-bowl stacking exhibits a high electron transport ability with anisotropy. Complexation with a cyclopentadienyl iron cation results in the first selective formation of the concave-bound complex as a π-bowl complex.     

A self-complementary molecular cleft

Reaction of silver(I) salts with a new octadentate ligand generates a novel self-complementary molecular cleft which forms dimers in the solid state, stabilised by pi-stacking interactions and intermolecular C-H...M interactions.     

A hybrid molecular machine

A versatile example of a molecular machine is described. The stationary part is an iron protoporphyrin complex, bearing two movable side chains with terminal donor groups. Changing the pH or the electrochemical potential, as well as the injection of CO, alters the affinity of the donor groups toward the metal ion, thus promoting intra-molecular motion of the pendant arms. The possibility of controlling the molecular motion through inputs of different nature, changeable at will, makes this system the first example of a hybrid molecular machine.     

On-chip connector valve for immunoaffinity chromatography in a microfluidic chip

A miniature valve that operates between a chip port and a tube fitting was developed. The valve functions by means of a rotor, 3 mm in diameter and 1.5 mm in height, made of Teflon, with a 0.2-mm diameter hole at its center that is co-axial with the tube fitting. It also has a radial groove, 0.85 mm long, 0.2 mm wide, and 0.2 mm deep, at the bottom surface, starting at its center. The chip port and the tube fitting have an offset of 0.75 mm, and, thus, the rotation of the rotor can make an on and off connection between the chip port and the groove, which is connected to the tubing. The valve had a pressure resistance of at least 1.0 MPa. The on-chip valve can be placed in position by adding only a single part, a valve rotor, and no changes in the fabrication of the glass microchip are required. Since the valve functions as a part of a connector, we refer to it as an on-chip connector valve. Immunoaffinity chromatography of a fluorescence-labeled recombinant antibody fragment was carried out in a glass microchip using the valves.     

Ortho-selectivity in aluminophosphate molecular sieves: A molecular simulation study

Monte Carlo adsorption simulations of xylenes have been performed in aluminophosphate molecular sieve structures. A new force field fitted for o-xylene in AlPO₄-5 was used. It is shown that force fields have good transferability among the aluminophosphate sieves series and the new force field adequately describes the experimentally observed adsorption isotherms for xylene/AlPO₄-5. A previous investigation of adsorption isotherms and structural analysis has been extended to AlPO₄-8 and VPI-5 sieves. In AlPO₄-8, like in AlPO₄-5, the variations in the channels diameters and the corresponding interaction energy of the molecule-crystal lattice drive all molecular positioning. In VPI-5, the modulation between wide and narrow regions becomes negligible due to the larger pore diameter, so no ortho-selectivity was observed. The simulations confirm the ortho-selectivity mechanism proposed to aluminophosphates.     

A neutral zwitterionic molecular solid

We report on the acid ethylenedithiotetrathiafulvaleneamidoglycine (EDT-TTF-CO-NH-CH(2)-CO(2)H; 1; EDT-TTF=ethylenedithiotetrathiafulvalene) and the 1:1 adduct [(EDT-TTF)(·+)-CO-NH-CH(2)-(CO(2))(-)][(EDT-TTF)-CO-NH-CH(2)-(CO(2)H)]·CH(3)OH (2), a new type of hydrogen-bonded, 1:1 acid/zwitterion hybrid embrace of redox peptidics into a two-dimensional architecture, an example of a system deliberately fashioned so that oxidation of π-conjugated cores toward the radical-cation form would interfere with the activity of the appended ionizable residues in the presence of a templating base during crystal growth. First-principles calculations demonstrate that, notwithstanding preconceived ideas, a metallic state is more stable than the hole-localized alternatives for a neat 1:1 neutral acid/zwitterion hybrid. The inhomogeneous Coulomb field associated with proton-shared, interstacks O-H···O hydrogen bonds between the ionizable residues distributed on both sides of the two-dimensional π-conjugated framework leads, however, to a weak hole localization responsible for the activated but high conductivity of 1 S cm(-1). This situation is reminiscent of the role of the environment on electron transfer in tetraheme cytochrome c, in which the protonation state of a heme propionate becomes paramount, or ion-gated transport phenomena in biology. These observations open rather intriguing opportunities for the construction of electronic systems at the interface of chemistry and biology.     

A site-renormalized molecular fluid theory

The orientation-dependent pair distribution function for molecular fluids on site-site potentials is expanded in a topological analog of the diagrammatically proper site-site theory of liquids [D. Chandler et al., Mol. Phys. 46, 1335 (1982)]. The resulting functions are then used to diagrammatically renormalize the molecular fluid theory. A result is that the diagrammatically proper interaction site model theory is shown to be a linearized, minimal angular basis set approximation to this site-renormalized molecular theory. This framework is used to propose a new, exact, and proper closure to the diagrammatically proper interaction site model theory. The resulting equation system contains a bridge function expansion in the proper site-site theory. In addition, the construction of the theory is such that the molecular pair distribution function, in full dimensionality, is intrinsic to the theory. Furthermore, the theory is equivalent to the molecular Ornstein-Zernike treatment of site-site molecules in the basis set expansion of Blum and Torruella [J. Chem. Phys. 56, 303 (1971)]. A significant formal result of the theory is the demonstration that certain classes of diagrams which would otherwise be considered improper in the interaction site model formalism are included in the angular expansion of molecular interactions. Numerical results for several apolar homonuclear models and an apolar heteronuclear model are shown to quantitatively improve upon those of reference interaction site model and our recent proper variant with respect to simulation. Significant numerical results are that the various thermodynamic quantities obey the exact symmetries and sum rules within numerical error for the different sites in the heteronuclear case, even for the low order approximation used in this work, and the theory is independent of the so-called auxiliary site problem common to previous site-site theories.     

改进的分子连接性方法

通过用Mulliken键级来加权分子连接性指数中的点价,使分子轨道理论与分子连接性指数有机地结合起来,将分子连接性指数改进成为一种量子拓扑指数。对比发现,分子连接性指数的点价与Mulliken键级具有相近的物理意义,而Mulliken键级更具有独特的优越性。利用改进的分子连接性指数对几种具有代表性的烃类与其体积、疏水常数以及热力学性质进行了关联,得到了满意的结果。     

A parallel molecular dynamics strategy

This article presents a strategy to perform molecular dynamics simulations using parallel processing techniques on a parallel-distributed loosely coupled system consisting of IBM host computers (4341 and 4381) with attached scientific processors (FPS-164). This substantially enhances our ability to perform fast and more realistic large scale many-body trajectory simulations. A powerful extention of the computational range of molecular dynamics the parallel approach offers the opportunity to substantially reduce the simulation time to allow a longer simulation period to study more realistic models and larger systems. It is flexible and uses, for the most part, standard products and straightforward implementation with a broad range of applicability. The implementation of a simulation of water molecules with the inclusion of two- and three-body interactions is discussed. Some considerations in the design and implementation of parallel programs on a loosely coupled system are also presented.     

A Bayesian molecular interaction library

We describe a library of molecular fragments designed to model and predict non-bonded interactions between atoms. We apply the Bayesian approach, whereby prior knowledge and uncertainty of the mathematical model are incorporated into the estimated model and its parameters. The molecular interaction data are strengthened by narrowing the atom classification to 14 atom types, focusing on independent molecular contacts that lie within a short cutoff distance, and symmetrizing the interaction data for the molecular fragments. Furthermore, the location of atoms in contact with a molecular fragment are modeled by Gaussian mixture densities whose maximum a posteriori estimates are obtained by applying a version of the expectation-maximization algorithm that incorporates hyperparameters for the components of the Gaussian mixtures. A routine is introduced providing the hyperparameters and the initial values of the parameters of the Gaussian mixture densities. A model selection criterion, based on the concept of a `minimum message length' is used to automatically select the optimal complexity of a mixture model and the most suitable orientation of a reference frame for a fragment in a coordinate system. The type of atom interacting with a molecular fragment is predicted by values of the posterior probability function and the accuracy of these predictions is evaluated by comparing the predicted atom type with the actual atom type seen in crystal structures. The fact that an atom will simultaneously interact with several molecular fragments forming a cohesive network of interactions is exploited by introducing two strategies that combine the predictions of atom types given by multiple fragments. The accuracy of these combined predictions is compared with those based on an individual fragment. Exhaustive validation analyses and qualitative examples (e.g., the ligand-binding domain of glutamate receptors) demonstrate that these improvements lead to effective modeling and prediction of molecular interactions.