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.     

A hybrid density functional study on the electron and hole trap states in anatase titanium dioxide

We present a theoretical study on electron and hole trap states in the bulk and (001) surface of anatase titanium dioxide using screened hybrid density functional calculations. In both the bulk and surface, calculations suggest that the neutral and ionized oxygen vacancies are possible electron traps. The doubly ionized oxygen vacancy is the most stable in the bulk, and is a candidate for a shallow donor in colorless anatase crystals. The hole trap states are localized at oxygen anions in both the bulk and surface. The self-trapped electron centered at a titanium cation cannot be produced in the bulk, but can be formed at the surface. The electron trap level at the surface oxygen vacancy is consistent with observations by photoelectron spectroscopy. The optical absorptions and luminescence in UV-irradiated anatase nanoparticles are found to come from the surface self-trapped hole and the surface oxygen vacancy.     

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.     

Evolved gas analysis with skimmer interface and ion attachment mass spectrometry for burnout monitoring of organic additives in ceramic processing

A monitoring of the individual pyrolysis of mixed polymer as a binder for ceramic processing was carried out as an application of evolved gas analysis-mass spectrometry (EGA-MS) with a skimmer interface and ion attachment mass spectrometry (IAMS). It could detect characteristic species evolved by the pyrolysis of the organic additives, according to the instrumental advantages as the transmission of the gaseous species with no transformation by the skimmer interface and complete soft ionization for gaseous species by IAMS technique. Further, the pyrolysis behavior of blended polymers as a binder could be monitored individually as EGA curves of characteristic species evolved by the pyrolyses.     

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.     

Barrier height imaging of Si(1 1 1)3 × 1-Ag reconstructed surfaces

We investigated the bias voltage polarity dependence of atomically resolved barrier height (BH) images on Si(1 1 1)3 × 1-Ag surfaces. The BH images were very similar to scanning tunneling microscopy (STM) images in both the empty and filled states. This similarity strongly supports the interpretation that the BH image reflects the vertical decay rate of the surface local density of states (LDOS). Differences in contrast and protrusion shapes between BH and STM images were observed. We attributed these differences to the geometric contribution to the STM image and to the improved spatial resolution of the BH image due to the lock-in technique.     

Characterization of novel cation-ordered compounds with fluorite and α-PbO2 related structures prepared by oxidation of Sn-Nb-O pyrochlore

Two cation-ordered phases were prepared by the oxidation of a pyrochlore phase as a precursor in the Sn-Nb-O system. One was a cation-ordered fluorite related phase, whose unit cell volume was eight times larger than that of the fluorite structure, similar to the κ-CeZrO₄ phase. The other was a cation-ordered α-PbO₂ phase, in which the ordered arrangement of cations was distinctly different from the well-known cation-ordered α-PbO₂ structures such as wolflamite and columbite. The chemical compositions of the phases, including valence states of cations, local structure and electronic structure near the energy band gap were studied. The compositions of the precursor and its oxidized phases were evaluated, respectively, to be Sn^II_1.62(Nb^V_1.86Sn^IV_0.14)O_6.55 and Sn^IV_0.81(Nb^V_0.93Sn^IV_0.07)O_4.085, i.e. Sn^IV_1.62(Nb^V_1.86Sn^IV_0.14)O_8.17, by TG-DTA and ICP analyses, ¹¹⁹Sn Mössbauer spectroscopy and X-ray photoemission spectroscopy. It was ascertained using IR and Raman spectroscopies that the structural framework of the cation-ordered fluorite related phase was close to that of the precursor pyrochlore phase, and the structural framework of the cation-ordered α-PbO₂ phase was distinct from that of the precursor pyrochlore. The Mössbauer parameters obtained showed a strong deviation of oxygen atoms contained in the SnO₈ polyhedron in the cation-ordered fluorite related phase from the cubic arrangement for the ideal fluorite related structure, and a lower site symmetry of Sn^IV in the cation-ordered α-PbO₂ than in rutile SnO₂. An increase in the energy band gap from ∼2.5 eV for the precursor pyrochlore to ∼3.5 eV for the oxidized phases was attributed to the vanishing of Sn 5s² lone-pair states upon oxidation of Sn^II in the precursor to Sn^IV in the oxidized phases.     

Tautomers of extended reduced pyrazinacenes: a density-functional-theory based study

We present a structural and electronic inspection of reduced pyrazinacenes within the DFT framework. Our analysis provides a clear indication that compounds in which reduced pyrazine rings are well separated from each other are rather stable. Conversely, if the reduced pyrazine rings approach each other or cluster together, the compounds become increasingly unstable. The tautomers analyzed are likely to possess properties suitable for application as proton transport materials due to protic isomerism processes. On the basis of our findings, we propose that protic transport should occur through a concerted proton transfer without involving intramolecular aggregation of the dihydropyrazine groups. Furthermore, the electronic structure analysis shows that this class of compounds can be classified as small bandgap semiconducting materials, possessing even metallic character depending on the tautomeric structure, and with potential nanotechnological applications in molecular electronics and fuel cells.