Influence of a water rinse on the structure and properties of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) films

Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) films exhibit a complex structure of interconnected conductive PEDOT domains in an insulating PSS matrix that controls their electrical properties. This structure is modified by a water rinse, which removes PSS with negligible PEDOT loss. Upon PSS removal, film thickness is reduced by 35%, conductivity is increased by 50%, and a prominent dielectric relaxation is eliminated. These results suggest that the removed PSS is not associated with PEDOT and that the conductive domain network is not substantially altered by the removal of a significant fraction of insulator. The removal of PSS may benefit organic light emitting diode fabrication by reducing acid attack on indium tin oxide electrodes and lead to more robust performance in switching circuits by extending the working frequency range.     

The binding energy of two nitrilotriacetate groups sharing a nickel ion

Among the various molecular interactions used to construct supramolecular self-assembling systems, homoliganded metallic NTA-Ni-NTA complexes have received little attention despite their considerable potential applications, such as the connection of different biochemical functions. The stability of this complex is investigated here by using two concordant nanotechniques (surface forces apparatus and vesicle micromanipulation) that allow direct measurements of adhesion energies due to the chelation of nickel ions by nitrilotriacetate (NTA) groups grafted on surfaces. We show that two NTA groups can share a nickel ion, and that the association of a Ni-NTA complex with an NTA group has a molecular binding energy of 1.4 kcal/mol. Binding measurements in bulk by isothermal titration calorimetry experiments give the same value and, furthermore, indicate that the Ni-NTA chelation bond is about five times stronger than the NTA-Ni-NTA one. This first direct proof and quantification of the simultaneous chelation of a nickel ion by two NTA groups sheds new light on association dynamics involving chelation processes and offers perspectives for the development of new supramolecular assemblies and anchoring strategies.     

Functional GPCR microarrays

This paper describes G-protein-coupled receptor (GPCR) microarrays on porous glass substrates and functional assays based on the binding of a europium-labeled GTP analogue. The porous glass slides were made by casting a glass frit on impermeable glass slides and then coating with gamma-aminopropyl silane (GAPS). The emitted fluorescence was captured on an imager with a time-gated intensified CCD detector. Microarrays of the neurotensin receptor 1, the cholinergic receptor muscarinic 2, the opioid receptor mu, and the cannabinoid receptor 1 were fabricated by pin printing. The selective agonism of each of the receptors was observed. The screening of potential antagonists was demonstrated using a cocktail of agonists. The amount of activation observed was sufficient to permit determinations of EC50 and IC50. Such microarrays could potentially streamline drug discovery by helping integrate primary screening with selectivity and safety screening without compromising the essential functional information obtainable from cellular assays.     

Prediction of a linear polymer made of xenon and carbon

Electronic structure calculations predict the existence of a novel type of a chemically bound noble gas compound. The predicted species is an extended linear and periodic polymer, made of the repeat unit -(XeCC)-, where CC is the acetylenic group. The polymer has a strong partly ionic nature, with positive partial charge on the xenon atoms and a negative one on the CC groups. High energy barriers are found for the removal of a Xe atom from the chain, indicating high stability. This is the first polymer with a noble-gas-containing building block.     

Mechanochromism of piroxicam accompanied by intermolecular proton transfer probed by spectroscopic methods and solid-phase changes

Structural and solid-state changes of piroxicam in its crystalline form under mechanical stress were investigated using cryogenic grinding, powder X-ray diffractometry, diffuse-reflectance solid-state ultraviolet-visible spectroscopy, variable-temperature solid-state (13)C nuclear magnetic resonance spectroscopy, and solid-state diffuse-reflectance infrared Fourier transform spectroscopy. Crystalline piroxicam anhydrate exists as colorless single crystals irrespective of the polymorphic form and contains neutral piroxicam molecules. Under mechanical stress, these crystals become yellow amorphous piroxicam, which has a strong propensity to recrystallize to a colorless crystalline phase. The yellow color of amorphous piroxicam is attributed to charged piroxicam molecules. Variable-temperature solid-state (13)C NMR spectroscopy indicates that most of the amorphous piroxicam consists of neutral piroxicam molecules; the charged species comprise only about 8% of the amorphous phase. This ability to quantify the fractions of charged and neutral molecules of piroxicam in the amorphous phase highlights the unique capability of solid-state NMR to quantify mixtures in the absence of standards. Other compounds of piroxicam, which are yellow, are known to contain zwitterionic piroxicam molecules. The present work describes a system in which proton transfer accompanies both solid-state disorder and a change in color induced by mechanical stress, a phenomenon which may be termed mechanochromism of piroxicam.     

Mixed effect of the supporting electrolyte and the zinc anode in the electrochemical homocoupling of 2-bromopyridines catalyzed by nickel complexes in an undivided cell

[reactions: see text] Nickel-catalyzed electroreductive homocoupling of 2-bromomethylpyridines and 2-bromopyridine has been investigated in an undivided cell in the presence of a zinc sacrificial anode. A series of reactions were performed with various types and concentrations of supporting electrolyte. It was observed that a key step in this process is the formation of an arylzinc through a nickel-zinc transmetalation. This intermediate can be transformed back to the reactive arylnickel species to afford the homocoupling as the final product. The back process from the arylzinc intermediate is, however, suppressed in the presence of high concentration (0.2 M) of tetraalkylammonium salts. On the contrary, with NaI, the formation of the dimer is not prevented, whatever the NaI concentration.     

The role of chelating diamine ligands in the goldberg reaction: a kinetic study on the copper-catalyzed amidation of aryl iodides

The mechanistic details of the Cu-catalyzed amidation of aryl iodides are presented. The kinetic data suggest that the diamine ligand prevents multiple ligation of the amide. The formation of an amidocuprate species external to the catalytic cycle helped to rationalize the dependence on diamine concentration and the inverse dependence on amide concentration at low diamine concentrations. The intermediacy of a Cu(I) amidate was established through both its chemical and kinetic competency.     

An extremely stable and orthogonal DNA base pair with a simplified three-carbon backbone

A nucleotide C3HQ with a minimal three-carbon backbone displays unprecedented pairing strength and orthogonality in a homopair C3HQ:C3HQ in the presence of one equivalent of Cu2+. The pairing stability in DNA even exceeds the related base pair having the regular 2'-deoxyribose backbone. This discovery of a synergy between an artificial backbone and base-pairing scheme opens new avenues for the economical design of modified oligonucleotides with tailored properties.     

Air-breathing laminar flow-based microfluidic fuel cell

This communication reports the design and characterization of an air-breathing laminar flow-based microfluidic fuel cell (LFFC). The performance of previous LFFC designs was cathode-limited due to the poor solubility and slow transport of oxygen in aqueous media. Introduction of an air-breathing gas diffusion electrode as the cathode addresses these mass transfer issues. With this design change, the cathode is exposed to a higher oxygen concentration, and more importantly, the rate of oxygen replenishment in the depletion boundary layer on the cathode is greatly enhanced as a result of the 4 orders of magnitude higher diffusion coefficient of oxygen in air as opposed to that in aqueous media. The power densities of the present air-breathing LFFCs are 5 times higher (26 mW/cm2) than those for LFFCs operated using formic acid solutions as the fuel stream and an oxygen-saturated aqueous stream at the cathode ( approximately 5 mW/cm2). With the performance-limiting issues at the cathode mitigated, these air-breathing LFFCs can now be further developed to fully exploit their advantages of direct control over fuel crossover and the ability to individually tailor the chemical composition of the cathode and anode media to enhance electrode performance and fuel utilization, thus increasing the potential of laminar flow-based fuel cells.