Surface scattering via bulk continuum states in the 3D topological insulator Bi2Se3

We have performed scanning tunneling microscopy and differential tunneling conductance (dI/dV) mapping for the surface of the three-dimensional topological insulator Bi(2)Se(3). The fast Fourier transformation applied to the dI/dV image shows an electron interference pattern near Dirac node despite the general belief that the backscattering is well suppressed in the bulk energy gap region. The comparison of the present experimental result with theoretical surface and bulk band structures shows that the electron interference occurs through the scattering between the surface states near the Dirac node and the bulk continuum states.     

Polycyclic N‐Heterocyclic Compounds. Part 82: Synthesis and Evaluation of Anti‐Platelet Aggregation Activity of 2,4‐Disubstituted 5,6‐Dihydro[1]benzothiepino[5,4‐d]pyrimidine and Related Compounds

We have synthesized a large number of tricyclic 2‐substituted 4‐alkylamino‐5,6‐dihydro[1]benzothiepino[5,4‐d]pyrimidines as part of our research to develop new effective anti‐platelet drugs. A variety of alkyl and aryl groups were used as substituents at the 2‐position. Evaluation of the effects of the newly synthesized compounds on collagen‐induced platelet aggregation revealed several promising anti‐platelet candidates with potencies superior to aspirin.     

Polycyclic N‐Heterocyclic Compounds. Part 81: Synthesis and Evaluation of Pentacyclic 1,2,4,5‐Tetrahydro[1]benzothieno[2′,3′:6,7]thiepino[4,5‐e]imidazo[1,2‐c]pyrimidine and Related Compounds as Potential Antiplatelet Aggregators

Dehydrative ring closure reactions were carried out on fused 4‐(2‐hydroxyethylamino) (or 2‐hydroxyethoxy or 2‐hydroxyethylthio)pyrimidines ( 2a , 2b , 2c ) to give fused 2,3‐dihydroimidazo[1,2‐c] (or 2,3‐dihydrooxazolo[3,2‐c] or 2,3‐dihydrothiazolo[3,2‐c])pyrimidines. This reaction produced the pentacyclic 1,2,4,5‐tetrahydro[1]benzothieno[2′,3′:6,7]thiepino[4,5‐e]imidazo[1,2‐c]pyrimidine ( 3a ) and 1,2,4,5‐tetrahydro[1]benzothieno[2′,3′:6,7]thiepino[4,5‐e]thiazolo[3,2‐c]pyrimidinium chloride ( 3c ) from the 2‐hydroxyethylamino‐derivative and 2‐hydroxyethylthio‐derivative, respectively. In contrast, 2‐hydroxyethoxy‐derivative ( 2b ) gave the rearrangement product, 3‐(2‐chloroethyl)‐5,6‐dihydro[1]benzothieno[3′,2′:2,3]thiepino[4,5‐d]pyrimidin‐4(3H)‐one ( 4 ). Effects of the synthesized compounds on collagen‐induced platelet aggregation were also evaluated.     

Polycyclic N‐Heterocyclic Compounds. Part 80: Synthesis and Evaluation of Effects on In Vitro Pentosidine Formation of 5,6‐Dihydro[1]benzothieno[3′,2′:2,3]thiepino[4,5‐d]pyrimidine and Related Compounds

Reaction of 3‐(3‐cyanopropylthio)[1]benzothiophene‐2‐carbonitrile with tert‐BuONa gave 5‐amino‐1,2‐dihydro[1]benzothieno[3,2‐d]thieno[2,3‐b]pyridine and 5‐amino‐2,3‐dihydro[1]benzothieno[3,2‐b]thiepin‐4‐carbonitrile. The latter compound served as a convenient scaffold for the synthesis of the new heterocycles, [1]benzothieno[3′,2′:2,3]thiepino[4,5‐d]pyrimidines. All of our new tetracyclic products were evaluated for in vitro inhibitory activity on the formation of pentosidine, which is one of representative advanced glycation end products.     

Syntheses and phosphorescent properties of blue emissive iridium complexes with tridentate pyrazolyl ligands

Novel neutral mixed-ligand Ir(N=C=N)(N=C)X complexes (N=C=N = 1,3-bis(3-methylpyrazolyl)benzene (bpzb), 1,5-dimethyl-2,4-bis(3-methylpyrazolyl)benzene (dmbpzb), and 1,5-difluoro-2,4-bis(3-methylpyrazolyl)benzene (dfbpzb); N=C = 2-phenyl pyridine (ppy); and X = Cl or CN) have been synthesized and characterized. An X-ray single-crystal structure of the complex Ir(dmbpzb)(ppy)Cl shows that the nitrogen atom in the ppy ligand occupied the trans position to the carbon atom in the tridentate N=C=N ligand of dmbpzb with the Ir-C bond length of 1.94(1) A, whereas the coordinating carbon atom occupied the trans position of chlorine. Electrochemical data show that the complexes exhibit an oxidation Ir(III/IV) process in the potential range of +0.5 approximately 0.9 V and two irreversible reductions at approximately -2.6 and -3.0 V against Fc (0)/Fc (+), respectively. All of the Ir(III) complexes do not emit phosphorescence at room temperature, although strong phosphorescence is exhibited at 77 K with the 0-0 transition centered at around 450 nm and lifetimes of 3-14 mus. DFT calculations indicate that the HOMOs are mainly localized on iridium 5dpi and chlorine ppi*, whereas the LUMOs are mainly from the ppy ligand pi* orbitals. The phosphorescence originates from a (3)LC state mixed with the (3)MLCT and (3)XLCT ones. Temperature-dependent lifetime measurements of Ir(dfbpzb)(ppy)Cl reveal the existence of a thermal deactivation process with a low activation energy (1720 cm (-1)) and very high frequency factor (2.3 x 10 (13) s (-1)). An unrestricted density functional theory indicates that the dd state, in which both the Ir-N (pyrazolyl) bond lengths increase considerably, exists almost at the same energy as that for the phosphorescent state. A thorough analysis based on the potential energy surfaces for the T 1 and S 0 states allows us to determine the reaction pathway responsible for this thermal deactivation. The calculated activation energies of 1600 approximately 1800 cm (-1) are in excellent agreement with the observed values.     

Cationic rare-earth metal bis(tetrahydridoborato) complexes: direct synthesis, structure and ring-opening polymerisation activity toward cyclic esters

Rare-earth metal tris(borohydrides) [Ln(BH4)3(thf)3] (Ln = Y, La, Nd, Sm) are converted with one equivalent of the Br?nsted acid [NEt3H]+[BPh4]- in thf into the monocationic bis(borohydride) complexes [Ln(BH4)2(thf)5]+[BPh4]-. They efficiently initiate the ring-opening polymerisation of epsilon-caprolactone.     

Possible oxidative polymerization mechanism of 5,6-dihydroxyindole from ab initio calculations

The reactivity of 5,6-dihydroxyindole and its major dimers has been studied with the use of a recently proposed general-purpose reactive indicator (Anderson et al. J. Chem. Theory Comput. 2007, 3, 358-374) from ab initio density-functional theory calculations. Theoretical prediction has reasonably explained previously isolated oligomers up to tetramers. The oxidative polymerization is governed by the electron-transfer-controlled reaction. The electrostatic interaction plays a regioselective role in the reactant complex and/or intermediates. A monomer-dimer coupling is able to form trimers, while a part of it is prevented by the exchange repulsion, i.e., steric hindrance. Therefore, a dimer-dimer coupling is also able to form tetramers.     

Enhanced radical-scavenging activity of naturally-oriented artepillin C derivatives

More than two-fold augmentation in the radical-scavenging activity of artepillin C could be achieved via altering the O-H bond dissociation enthalpy of artepillin C by means of structural modifications.