Electron transport in a pi-stacking molecular chain

We have investigated the electronic structure and transport properties of a pi-stacking molecular chain which is covalently bonded to a H/Si(100) surface, using the first-principles density functional theory approach combined with Green's function method. The highest occupied molecular orbital (HOMO) dispersion is remarkably reduced, but remains noticeable ( approximately 0.1 eV), when a short pi-stacking styrene wire is cut from an infinitely long wire and sandwiched between metal electrodes. We find that the styrene chain's HOMO and lowest unoccupied molecular orbital (LUMO) states are not separated from Si, indicating that it does not work as a wire. By substituting -NO2 or -NH2 for the top -H of styrene, we are able to shift the position of the HOMO and LUMO with respect to the Fermi level. More importantly, we find that the HOMO of styrene-NH2 falls into the band gap of the substrate and is localized in the pi-stacking chain, which is what we need for a wire to be electrically separated from the substrate. The conductance of such an assembly is comparable to that of Au/benzene dithiolate/Au wire based on chemical bonding, and its tunability makes it a promising system for a molecular device.     

Femtosecond laser modification of living neuronal network

An all-wet femtosecond laser microprocessing technique was utilized for patterning and cutting functional network of living neuronal cells on a multi-electrode dish (MED). The neuronal cells cultured on a source substrate were transferred onto an electrode in a MED probe in solution by utilizing a femtosecond laser-induced impulsive force and a pattern of neuronal cells were formed on the MED probe. The cellular activity of the detached neurons was supported that neurites could be regenerated around the electrodes. As another processing method, the neurons stretching between electrodes were selectively cut by the direct femtosecond laser irradiation and the spontaneous electrical activity of the neuronal network was evaluated. While the spontaneous action potentials of neurons were synchronized before the cutting, the synchronization disappeared after the cutting, indicating that the neuronal network is locally disconnected by the laser cutting. The present method is applicable to artificial reconstruction of living neuronal network.     

Experimental and theoretical analyses of azulene synthesis from tropones and active methylene compounds: reaction of 2-methoxytropone and malononitrile

A representative azulene formation from an active troponoid precursor (2-methoxytropone) and an active methylene compound (malononitrile) has been analyzed both experimentally and theoretically. (2)H-Tracer experiments using 2-methoxy[3,5,7-(2)H(3)]tropone (2-d(3)) and malononitrile anion give 2-amino-1,3-dicyano[4,6,8-(2)H(3)]azulene (1-d(3)) in quantitative yield. New and stable (2)H-incorporated reaction intermediates have been isolated, and main intermediates have been detected by careful low-temperature NMR measurements. The detection has been guided by mechanistic considerations and B3LYP/6-31(+)G(d) calculations. The facile and quantitative one-pot formation of azulene 1 has been found to consist of a number of consecutive elementary processes: (a) The troponoid substrate, 2-methoxytropone (2), is subject to a nucleophilic substitution by the attack of malononitrile anion (HC(CN)(2)(-)) to form a Meisenheimer-type complex 3, which is rapidly converted to 2-troponylmalononitrile anion (5). (b) The anion 5 is converted to an isolable intermediate, 2-imino-2H-cyclohepta[b]furan-3-carbonitrile (6), by the first ring closure in the reaction. (c) A nucleophilic addition of the second HC(CN)(2)(-) toward the imine 6 at the C-8a position produces the second Meisenheimer-type adduct 7. (d) The second ring closure leads to 1-carbamoyl-1,3-dicyano-2-imino-2,3-dihydroazulene (11). A base attacks the imine 11, which results in generation of a conjugate base 12 of the final product, azulene 1.     

Transannular cyclization of (4S,5S)-germacrone-4,5-epoxide into guaiane and secoguaiane-type sesquiterpenes

Germacrone (1) and (4S,5S)-germacrone-4,5-epoxide (2) were isolated, along with guaiane and secoguaiane-type sesquiterpenes, from Curcuma aromatica plants. Compound 2 was derived from 1 and cyclized through transannular (T-A) reactions into various guaiane and secoguaiane-type sesquiterpenes in C. aromatica. The cyclization reaction of 2 was initiated by protonation at an epoxide oxygen atom, followed by cleavage of the epoxide ring and the formation of a C-C bond between C-1 and C-5 to give guaiane-type derivatives. Acidic and thermal treatments of 2 produced twelve sesquiterpenes having guaiane and secoguaiane skeletons. The structures of these products were elucidated by spectral methods, including 2D-NMR spectroscopy. Most were identified as sesquiterpenes isolated from C. aromatica as natural products. The T-A cyclization of 2 occurred via two transition states, a cross conformation and a parallel conformation. The mechanism of the T-A cyclization reaction of 2 is discussed.     

Secure key distribution using correlated randomness in lasers driven by common random light

We propose a secure key distribution scheme based on correlated physical randomness in remote optical scramblers driven by common random light. The security of the scheme depends on the practical difficulty of completely observing random optical phenomena. We describe a particular realization using the synchronization of semiconductor lasers injected with common light of randomly varying phase. We experimentally demonstrate the feasibility of the scheme over a distance of 120 km.     

An application of EGA-MS with skimmer interface to pyrolysis behavior of DHTAM, an antibacterial and antifungal material with thermostability

An application of evolved gas analysis-mass spectrometry (EGA-MS) with skimmer interface was carried out to investigate the pyrolysis mechanism of an antibacterial and antifungal material that is expected with thermostability. The skimmer interface between a furnace and a vacuum chamber with a mass spectrometer transmitted the gaseous species, which were trapped by a general capillary interface. As a result, it became clear that the thermostability of antimicrobial activity was limited by the heat resistance of the coordinate bond between nitrogen and silver in the silver chelate.     

New antitumor sesquiterpenoids from Santalum album of Indian origin

Three new campherenane-type (1, 4, 7) and three new santalane-type (9, 11, 12) sesquiterpenoids, and two aromatic glycosides (21, 22) together with 12 known metabolites including α,β-santalols (14, 18), (E)-α,β-santalals (15, 19), α,β-santaldiols (16, 20), α-santalenoic acid (17), and vanillic acid 4-O-neohesperidoside were isolated from Santalum album chips of Indian origin. The structures of the new compounds, including absolute configurations, were elucidated by 1D- and 2D-NMR spectroscopic and chemical methods. The antitumor promoting activity of these isolates along with several neolignans previously isolated from the same source was evaluated for both in vitro Epstein-Barr virus early antigen (EBV-EA) activation and in vivo two-stage carcinogenesis assays. Among them, compound 1 exhibited a potent inhibitory effect on EBV-EA activation, and also strongly suppressed two-stage carcinogenesis on mouse skin.     

Carbon nanotube motors driven by carbon nanotube

We propose a new type of carbon nanotube (CNT) motor composed of a single-wall CNT (SWCNT) and a double-wall CNT (DWCNT), that are in mechanical contact. The rotational motion of our CNT motor is controllable by the translational motion of the SWCNT along the axis of the DWCNT. From molecular dynamics simulations, we show how our CNT motor can be driven in a controlled manner.     

Reduction of Pt usage in fuel cell electrocatalysts with carbon nanotube electrodes

The 12 wt% Pt-deposited carbon nanotube electrode gives 10% higher voltages than 29 wt% Pt-deposited carbon black and reduces the Pt usage by 60% in polymer electrolyte fuel cells with hydrogen and oxygen.     

Real-time propagation time-dependent density functional theory study on the ring-opening transformation of the photoexcited crystalline benzene

Mechanism of the ring-opening transformation in the photoexcited crystalline benzene is investigated on the femtosecond scale by a computational method based on the real-time propagation (RTP) time-dependent density functional theory (TDDFT). The excited-state dynamics of the benzene molecule is also examined not only for the distinction between the intrinsic properties of molecule and the intermolecular interaction but for the first validation using the vibration frequencies for the RTP-TDDFT approach. It is found that the vibration frequencies of the excited and ground states in the molecule are well reproduced. This demonstrates that the present method of time evolution using the Suzuki-Trotter-type split operator technique starting with the Franck-Condon state approximated by the occupation change of the Kohn-Sham orbitals is adequately accurate. For the crystalline benzene, we carried out the RTP-TDDFT simulations for two typical pressures. At both pressures, large swing of the C-H bonds and subsequent twist of the carbon ring occurs, leading to tetrahedral (sp3-like) C-H bonding. The nu4 and nu16 out-of-plane vibration modes of the benzene molecule are found mostly responsible for these motions, which is different from the mechanism proposed for the thermal ring-opening transformation occurring at higher pressure. Comparing the results between different pressures, we conclude that a certain increase of the intermolecular interaction is necessary to make seeds of the ring opening (e.g., radical site formation and breaking of the molecular character) even with the photoexcitation, while the hydrogen migration to fix them requires more free volume, which is consistent with the experimental observation that the transformation substantially proceeds on the decompression.