Single-molecule junctions, in which a single molecule bridges a gap between metal electrodes, have attracted significant attention due to their potential applications in ultra-small electronic devices and their unique structure. Single-molecule junctions are one-dimensional nanomaterials having two metal–molecule interfaces. Thus, unconventional properties and functionalities that would not be observed in other phases (e.g., isolated molecules and bulk crystals) are expected to appear in these nanomaterials. Despite interest in these expected unconventional properties, several issues have been noted with the investigation and practical application of the unique properties of single-molecule junctions.
To explore new functionality, we have investigated single-molecule junctions using a combined approach comprising fabrication, characterization, and measurement. First, we have explored a new generation of the metal–molecule interfaces formed by direct π-bonding. The interfaces made by the direct π-bonding have increased electronic conductance at the single-molecule junction, reaching the theoretical limit, 1 G0 (2e2/h), which is the conductance of typical metal monoatomic contacts. Secondly, we have developed new characterization techniques combined with a variety of spectroscopic methods to observe a single molecule confined between metal electrodes. This has allowed us to reveal structural and electronic details of single-molecule junctions, such as the number of molecules, molecular species, interface-structure, electronic structure, and dynamics. Based on the development of the metal–molecule interface structures and the combined spectroscopic characterization techniques, we have searched for new single-molecule junction functionality. By controlling the metal–molecule interface structures, single molecular switching functionality with multiple conductance states and a programmable single-molecule junction with various electronic functionalities have been realized. Our newly developed interface structure, characterization technique, and the functionality of the single-molecule junction opens the door for future research in the field of single-molecule junctions.
Intracellular signal transduction systems consisting of sophisticated molecular networks are essential to provide almost all cellular functions. Any abnormal activation of enzymes included in this network can be directly linked to various disease states. Therefore, cellular function can be altered if we can modulate this signal transduction process. In this context, artificial signal converters, which respond to particular abnormal signaling to activate transgene transcription, are introduced. Such molecular systems use polymer materials grafted with cationic peptides, which are a specific substrate of target protein kinase or protease. This concept which is called D-RECS, DDS in response to cellular signals, could have potential for design of disease cell specific therapeutic or diagnostic (imaging) systems using pathological signaling as a target. Molecular design and structural factors affecting signal response in such systems are discussed.
Frontier orbital theory is demonstrated by investigating the appropriately divided parts of transition states, useful for understanding an essential aspect of transition-metal- and lanthanide-mediated reactions. Atomic orbitals are in phase with each other in the outer space of the antibonding orbitals of the bonds between transition-metal and main-group atoms.
We investigated stable radical distribution and particle tracks in sucrose irradiated by C-ion irradiation with continuous wave (CW) electron paramagnetic resonance (EPR) and 9 GHz EPR imaging. Both EPR results were compared with X-ray irradiation at a similar dose. Radical distribution in sucrose crystals induced by C-ion and X-ray irradiation were completely different. The 2D EPR imaging results suggested that radical species were mostly located inside the sucrose crystal. Fewer radicals were found on the surface region of the sucrose crystal. The high radical intensities in relation to the C-ion energy deposition are clearly observed at Bragg peak region. No trace of the stable radicals was found after the peak region. The stable radicals of sucrose were distributed as a result of recombination of radicals induced by particle interaction. For the first time, the present EPR images showed the stable radical distribution and particle tracks in the crystal in association with particle-sucrose interaction.
We developed a simple method for producing arrays of stretchable DNAs, called DNA garden, for single-molecule fluorescence measurements. The method is based on microcontact printing of biotinylated bovine serum albumin (biotin-BSA) on a coverslip coated by 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer and on the subsequent tethering of neutravidin and biotinylated DNA. Without the need for a microfabricated substrate used for DNA tethering, it facilitates single-molecule investigations of DNA and DNA-binding proteins based on fluorescence microscopic imaging. The salient advantage of DNA garden is continuous observation of DNA in the repeated cycles of extension and relaxation by flow control, enabling the characterization of processes occurring in and on the relaxed DNA. The DNA garden was applied to the detection of cleavage sites of restriction enzymes and for the observation of the sliding dynamics of a tumor suppressor, p53, along extended DNA at the single-molecule level. Furthermore, experiments based on the repetitive extension and relaxation of DNA demonstrated that p53 causes looping of DNA, probably by connecting multiple regions of the relaxed DNA. The DNA garden is expected to be a powerful tool for the single-molecule imaging assay of DNA and DNA-binding proteins.
Amygdalus pedunculata is expected to be a good candidate plant for desert reclamation (“greening”) since it has notable tolerance to cold and drought and can grow in a wide range of area with different soil types and moisture contents. In this study, hierarchical porous activated carbon (AC) with high surface area and large mesoporous volume was developed from Amygdalus pedunculata shell (APS) for an electric double-layer capacitor (EDLC) application. The AC activated at 900 °C by K2CO3 possessed a highly developed hierarchical porosity network of a coexistence of micropores and mesopores. The AC with the specific surface area of 2030 m2 g−1 and mesopore percentage of 82% showed superior capacitive performance in 20 wt % H2SO4 electrolyte using a bipolar cell by means of cyclic voltammetry (CV) and galvanostatic charge–discharge (GC) measurements. A maximum capacity of 210 F g−1 was achieved at current density of 0.05 A g−1 from the AC prepared from APS and K2CO3 with the mixed weight ratio of 2:3 under the activation conditions of 900 °C and 60 min. The present APS-derived AC is a promising electrode material from green raw materials for EDLCs.
CdTe and CdTe/CdS quantum dots (QDs) were synthesized via hydrothermal method in one-step processes just by controlling reaction time. A gradual thermal decomposition of thiol ligand N-acetyl-l-cysteine results in formation of a CdS shell on a CdTe core. The experimental results of X-ray diffraction and energy dispersive X-ray spectroscopy indicated that growth of the CdS shell started in a longer reaction time than 30 minutes and that the thickness of the CdS shell increased with increasing the reaction time. The CdTe/CdS QD exhibited a longer photoluminescence-decay time than the CdTe core QD due to the type-II band alignment, and the decay time in the CdTe/CdS QDs increased with an increase in the reaction time. The increase in the decay time in the CdTe/CdS QDs was qualitatively reproduced by a decrease in an overlap integral of electron and hole wave functions caused by an increase of the CdS shell thickness.
Palladium complexes with pincer ligands containing one pyridine and two N-heterocyclic carbene units with acetyl-protected d-glucopyranosyl groups in C-C-N and C-N-C arrangements were synthesized. The complexes form diastereomers due to the twisted pincer ligands and chiral d-glucopyranosyl units. The diastereomers of the C-C-N complex are in equilibrium in solution, whereas only one of the diastereomers of the C-N-C complex forms kinetically. Deprotection of the acetyl groups in the ligands afforded water-soluble complexes with one of the hydroxide groups in the d-glucopyranosyl groups coordinated to the metal ion. In CD3OD, the deprotected complex with the C-N-C ligand gradually decomposed, whereas that with the C-C-N ligand was stable at room temperature. The complexes catalyzed Suzuki–Miyaura cross-coupling reactions in water with turnover numbers of 75,000 for the C-C-N and 8,900 for C-N-C complexes. The C-C-N complex was not deactivated by the addition of metallic Hg meaning that the active species is the complex itself or its derivatives having the pincer ligand. On the other hand, the C-N-C complex exhibited no catalytic activity for the coupling reaction in the presence of metallic Hg, meaning that the active species are heterogeneous catalysts, such as Pd nanoparticles.
In the present work, electrochemical synthesis of novel pyrimido[4,5-b]indoles was directly carried out via the electrochemical oxidation of catechols in the presence of 2,4-diamino-6-hydroxypyrimidine in an aqueous media. The results suggested that electrogenerated o-benzoquinone moieties participated in the Michael-type addition reaction with 2,4-diamino-6-hydroxypyrimidine via the ECEC mechanism. These new compounds were synthesized in high yields and purity in an aqueous solution without toxic reagents or catalyst and with high atom economy in ambient conditions.
A highly efficient one-pot preparation of manganese/graphite oxide (MnOX/GO) composite from graphite and KMnO4 is described. Hummers preparation method of GO requires a stoichiometric amount of KMnO4, as a result, the method produces a large amount of reduced Mn species. The Mn residue generally is a waste, therefore, we envisioned converting it to value-added materials. A MnOX/GO composite was prepared in one-pot by treating the unpurified GO with aqueous KOH. The composite was characterized by XRD, XAFS, SEM and TEM. Among various applications of the MnOX/GO composite, we applied it as a recyclable catalyst for bromination of saturated hydrocarbons, one of the most basic but important chemical transformations. The MnOX/GO composite is expected to be an efficient catalyst because of the high surface area and high accessibility of substrates derived from the 2-dimensional sheet structure. When the reaction of a saturated hydrocarbon and Br2 in the presence of catalytic MnOX/GO was performed under fluorescent light irradiation, a brominated product was formed in high yield in a short reaction time. GO could strongly bind with Mn to prevent elution to the liquid phase, enabling the high recyclability.
Ethyl 2-cyano-3-alkoxypent-2-enoates were synthesized in moderate yields via the coupling reaction between α,β-unsaturated acetals and cyanoacetate, catalyzed by [RuHCl(CO)(PPh3)3]. The E- and Z-isomers were separated and determined by X-ray crystallography for the first time. Structural distortion associated with steric hindrance around the tetrasubstituted alkene moiety was revealed: e.g., the C(carbonyl)–C(α)–C(β) angle expands to about 125°. Density functional theory calculation was performed, and the restricted B3LYP hybrid functional with the 6-31G(d,p) basis set was found to successfully elucidate the solid-state structure and conformation, as well as spectroscopic properties. A plausible formation mechanism was proposed, in which the Ru complex catalyzed the C=C bond migration of the α,β-unsaturated acetal to give the corresponding ketene acetal and assisted the subsequent condensation reaction with cyanoacetate to some extent.