Crystalline materials that comprise π-electron organic molecules exhibit various interesting physical properties and functionalities, related to electrical conductivity, magnetism, optical properties, etc. Conventionally, such properties and functionalities are determined or controlled by the intermolecular π-electron interactions in the crystal. Recently, however, the switching or control of the electronic structure and physical properties based on hydrogen dynamics was realized in a series of purely organic conductors. In this account article, the structure, properties, and switching phenomenon of this new type of organic conductors developed by utilizing proton- and π-electron-donating/accepting abilities are summarized. In addition, a highly polarized π-electron donor-acceptor type semiconductor molecule obtained in connection with the above conductors is also described.
Single-molecule analysis methods facilitate the investigation of the properties of single-molecule junctions (SMJs), in which single molecules are connected between a pair of nanoelectrodes that use nanogap electrodes having a spacing of less than several nanometers. Various methods have been developed to investigate numerous useful parameters for SMJs; for example, the number of molecules connected between a pair of nanoelectrodes can be determined, the types and structures of single molecules can be revealed, localized temperatures within SMJs can be evaluated, and the Seebeck coefficient and the bond strength between single molecules and electrodes can be ascertained. Single-molecule analysis methods have also been used to analyze biopolymers in solutions, and this has resulted in single-molecule sequencing technologies being developed that can determine sequences of base molecules in DNA and RNA along with sequences of amino acids in peptides. Single-molecule analysis methods are expected to develop into digital analysis techniques that can be used to investigate the physical and chemical properties of molecules at single-molecule resolutions.
A new triple-electrode system was developed for the simultaneous determination of l-lactate and d-glucose by using track-etched microporous membrane electrodes, which enabled efficient electrolysis as electroactive substances passed through the electrode. The proposed biosensor was fabricated by alternate stacking of the electrodes and immobilized enzyme reactors along the flow direction of the sample solution. When the sample solution containing l-lactate and d-glucose flowed into the proposed biosensor, hydrogen peroxide was produced by each enzymatic reaction and detected individually by anodization at each detector-electrode positioned downstream of each enzyme reactor. The interfering substances, such as l-ascorbic acid and uric acid, were electrolyzed completely at the pre-reactor electrode that was positioned upstream of the enzyme reactors. As a result, the simultaneous detection of l-lactate and d-glucose was achieved with no other catalytic material such as peroxidase or an electron mediator in the presence of the interferents at physiological concentrations in human blood.
Novel fluorescent nanocomposites prepared by microwave irradiation and electrostatic adsorption have been formulated for developing latent fingermarks on various object surfaces. As-synthesized carbon dots@montmorillonite (C-dots@PGV) nanocomposites were characterized using UV–visible absorption spectroscopy, fluorescence spectroscopy, infrared spectroscopy, TEM/HRTEM, SEM and XRD. Due to its photoluminescence and stable chemical properties, C-dots@PGV nanocomposites powders with intense fluorescence produce sharp and clear development of latent fingermarks with good contrast and satisfactory ridge details. It is widely used for painted metal, glass, plastic and stainless steel surfaces, and the small, fine fluorescent nanocomposites demonstrate great advantages. Especially for multicolor surfaces, the fluorescent probe can help us to observe and photograph using UV light as excitation light source to eliminate background effects. After developing by facile powder technique, the prints emit strong violet-blue fluorescence under UV light (365 nm), at the same time, this nontoxic powder without any organic solvent and dyes can reduce harm to the operators.
Stepwise-field-swept solid-state nuclear magnetic resonance (NMR) experiments, which potentially make it possible to achieve high digital-resolution NMR spectra, are presented using 79/81Br NMR of strontium bromide hydrate. In contrast to the conventional field-swept NMR in which magnetic fields are continuously varied while FID signals are accumulated, FID signals can be observed with a static magnetic field, and the magnetic fields are stepwise changed after each accumulation. Spectral simulations for the field-swept NMR spectra, calculated by a direct diagonalization method in which the Zeeman and quadrupolar Hamiltonians were numerically diagonalized to obtain transition probabilities, are also described. Improvements necessary to achieve high digital-resolution NMR spectra, including the stability of superconducting magnets and DC power supply sources that control the superconducting magnets in non-persistent mode, are briefly discussed.
Divide-and-conquer-type density-functional tight-binding molecular dynamics simulations of the CO2 absorption process in monoethanolamine (MEA) solution have been performed for systems containing thousands of atoms. The formation of carbamate anions has been widely investigated for neutral systems via ab initio molecular dynamics simulations, yet the present study is aimed at identifying the role of hydroxide ions in acid-base equilibrium. The structural and electronic analyses reveal that the hydroxide ion approaches, via Grotthuss-type shuttling, the zwitterionic intermediates and abstracts a proton from the nitrogen atom of MEA. We also estimated the fraction of reacted CO2 and carbamate formed at different initial CO2 concentrations that confirm a high absorbed CO2 concentration decreases the fraction of MEA(C) formed due to the abundance of MEA(Z) in the solution.
Parallel Cascade Selection Molecular Dynamics (PaCS-MD) is an enhanced conformational sampling method for generating structural transition pathways between a given reactant and a product. To promote structural transitions from the reactant to the product, PaCS-MD repeats cycles of conformational resampling of (1) reasonable initial structures and (2) short-time MD simulations restarting the structures with renewed velocities. Appropriately setting a number of these initial structures is essential for efficient PaCS-MD.
We propose a novel, optimal algorithm for specifying suitable initial structures, ninitial, to find structural transitions; this is referred to as dn-PaCS-MD. PaCS-MD typically has a fixed ninitial, while in dn-PaCS-MD it is dynamically reset according to a minimum root mean square deviation (RMSD), defined as an RMSD derivative. dn-PaCS-MD, with the dynamic ninitial accelerates structural transitions to the product, compared to the original PaCS-MD with the fixed ninitial, as confirmed in Chignolin protein-folding. This algorithm was also applied to Human-β-defensin 2, whose X-ray and NMR structures differ in the N-terminal region. Finally, we compared forward and backward transition pathways from the former to the latter generated by our method, and estimated a free energy barrier between them, creating new possibilities to visualize the NMR and X-ray structures in solution.
Dimer 2, trimer 3, hexamer 6, octamer 8, and decamer 10 of 4,4′′-diethynyl-4′,5′-dioctyl-o-terphenyl 1 were synthesized by using copper(II) acetate-mediated Eglington coupling reaction of 1 in pyridine or pyridine–methanol. Although dimer 2 and trimer 3 were formed as major products under high dilution conditions, large oligomers such as hexamer 6, octamer 8, and decamer 10 were obtained in moderate total yield under standard Eglington conditions. The MALDI-TOF MS and GPC behavior of large oligomers exhibit the formation of giant macrocycles 3 nm diameter and 2–4 nm long in one-pot procedure.
We compared adsorption strength of protective agents via ligand exchange of silver nanoparticles synthesized by the improved vacuum evaporation on running oil substrate (VEROS) method. This comparison concerns physical adsorption of protective agents on the surface of silver nanoparticles instead of chemisorption. Clean surfaces of silver nanoparticles synthesized by the improved VEROS method were suitable for this investigation. All the experiments in this study were designed so that as far as possible protective agents did not ionize. Thus, oleic acid capped silver nanoparticles were synthesized by the improved VEROS method. Next, octanoic acid, n-octylamine and oleic acid were used as additive protective agents in ligand exchanges. The ligand exchange is also closely related to physical adsorption strength of protective agents on the surface of metal nanoparticles. Oleic acid on the surface of silver nanoparticles was exchanged by octanoic acid and vice versa under the same experimental conditions. On the other hand, oleic acid on the silver surface was not exchanged by n-octylamine. These results were remarkably different from those reported in general chemical synthetic methods but they were well consistent with our previous study on performance of protective agents in the synthesis of silver nanoparticles with the improved VEROS method.
Self-assembled monolayer FET based on a TTF derivative is described (FET = field-effect-transistor, TTF = tetrathiafulvalene). The molecule is anchored on an alumina dielectric layer through covalent bonding of a phosphonic acid linker. A p-type monolayer FET device is achieved and subsequent chemical doping of this monolayer with F4TCNQ dopants results in an ambipolar device. (F4TCNQ = 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane) Several strange behaviors including a gate voltage shift upon doping seem to be consistent with organic monolayer Mott FET. Finally, temperature dependence of the FET performance, which also fit the anticipated Mott FET behavior, is discussed.
We investigated the adsorption and photocatalytic decomposition of methylene blue (MB) by colloidal suspensions of Rh-doped titanate nanosheets ([Ti4−xRhxO9]2−; Ti4NS:Rhx) prepared by exfoliating H2Ti4−xRhxO9 in aqueous tetramethylammonium hydroxide, revealing that doped nanosheets showed a slightly enhanced adsorption capacity compared to their non-doped counterparts. This behavior was ascribed to the elevated ionic charge of doped Ti4NS and the thus increased volume charge density. Accordingly, Ti4NS:Rhx exhibited a higher MB adsorption capacity than previously reported [Ti3−xRhxO7]2−. Moreover, we found that Ti4NS:Rhx catalyzed the photodegradation of MB under UV light irradiation, additionally showing that the activity of this catalyst can be improved by Rh doping, probably due to the large contribution of Rh3+/Rh4+ shuttling to effective MB degradation.
The stepwise synthesis of AuI4CoIII2 complex with d-penicillaminate and 1,2-bis(dicyclohexylphosphino)ethane, 2+, via metalloligand approach, together with single-crystal X-ray analysis of nitrate salt, (NO3)2, is reported. (NO3)2 adopts normal alternate arrangement of cations and anions in crystal, which is different from non-alternate arrangement in corresponding AuI4CoIII2 complex with d-penicillaminate and 1,2-bis(diphenylphosphino)ethane.
H1.07Ti1.73□0.27O4 (HTO) showed largely enhanced photocatalytic activity upon mixing with a small amount of Au-loaded TiO2 (Au@P25) due to electron transfer from the excited HTO to Au@P25 at the particle interfaces. Equal amounts of Au@P25 and HTO/Au@P25 showed similar activities, despite the fact that the latter contained considerably less Au.