Highly luminescent glycocluster: silole-core carbosilane dendrimer having peripheral globotriaose

A novel glycocluster periphery functionalized by globotriaose (Galα1-4Galβ1-4Glcβ1-) possessing a silole moiety as a luminophor was synthesized. The photoluminescence spectrum of the glycocluster in pure water showed extremely strong emission at 475 nm. Analogous intense emission of the silole dendrimer was also observed in a lower water fraction of water/acetone mixture. The water fraction of the silole dendrimer solution strongly affected the emission intensity; however, these luminescences were constantly detected at around 475 nm.     

Radiation damage analysis of 7,7,8,8,-tetracyanoquinodimethane (TCNQ) and 2,3,5,6,-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4TCNQ) by electron diffraction and electron energy loss spectroscopy

The electron irradiation sensitivity is compared between TCNQ and F(4)TCNQ. The characteristic doses, D(1/e), determined by the attenuation of the diffraction intensities are 0.08-0.11Ccm(-2) for TCNQ, and 0.04-0.06Ccm(-2) for F(4)TCNQ, respectively. It is found that F(4)TCNQ is more sensitive to radiation damage than TCNQ in spite of the substitution of hydrogen with fluorine. From electron energy-loss spectroscopy (EELS), it is found that the damaging process for the two materials begins in a similar way, as seen from mass loss and spectrum changes observed for doses which exceed the characteristic dose. Although sensitive to the sample orientation, the carbon K-edge fine structures of TCNQ are almost preserved below the critical dose. Theoretical calculation predicts that the scission of hydrogen contributes to the spectrum shape very little compared to nitrogen scission. Beyond the characteristic dose, fluorine loss from F(4)TCNQ occurs faster than nitrogen loss but little loss of carbon is observed. In a similar way, nitrogen loss from TCNQ occurs beyond the characteristic dose, while carbon appears constant. From detailed analysis of the carbon and nitrogen K-edge fine structures of TCNQ and F(4)TCNQ, it is found that the pi* peak of nitrogen in TCNQ decreases below the characteristic dose, while pi* loss of nitrogen in F(4)TCNQ, and pi* loss and sigma* increase of carbon in both materials are observed beyond the characteristic dose. The changes in the fine structures are believed to be due to the chemical alteration such as cross-linking, in which the pi-bonding system of nitrogen or carbon turns into sigma-bonding. The difference in characteristic dose between TCNQ and F(4)TCNQ is explained by considering "effective molecular occupancy", where F(4)TCNQ has a larger intermolecular empty space than TCNQ.     

Hofstadter butterfly and integer quantum hall effect in three dimensions

For a three-dimensional (3D) lattice in magnetic fields we have shown that the hopping along the third direction, which normally smears out the Landau quantization gaps, can rather give rise to a Hofstadter's butterfly specific to 3D when a criterion is fulfilled by anisotropic (quasi-one-dimensional) systems. In 3D the angle of the magnetic field plays the role of the field intensity in 2D, so that the butterfly can occur in much smaller fields. We have also calculated the Hall conductivity in terms of the topological invariant in the Kohmoto-Halperin-Wu formula, and each of sigma(xy),sigma(zx) is found to be quantized.     

Kinetics and mechanism of oxygen atom transfer from methyl phenyl sulfoxide to triarylphosphines catalyzed by an oxorhenium(V) dimer

An oxorhenium(V) dimer, [PMeReO(mtp)](2), D, where mtpH(2) is 2-(mercaptomethyl)thiophenol, catalyzes oxygen atom transfer reaction from methyl phenyl sulfoxide to triarylphosphines. Kinetic studies in benzene-d(6) at 23 degrees C indicate that the reaction takes place through the formation of an adduct between D and sulfoxide. The equilibrium constants, K(DL), for adduct formation were determined by spectrophotometric titration, and the values of K(DL) for MeS(O)C(6)H(4)-4-R were obtained as 14.1(2), 5.7(1), and 2.1(1) for R = Me, H, and Br, respectively. Following sulfoxide binding, oxygen atom transfer occurs with either internal or external nucleophilic assistance. Because [MeReO(mtp)](2) is a much more reactive catalyst than its monomerized form, MeReO(mtp)PPh(3), loss of the active catalyst during the time course of the reaction must be taken into account as a part of the kinetic analysis. As it happens, sulfoxide catalyzes monomerization. Monomerization by triarylphosphines was also studied in the presence of sulfoxide, and a mechanism for that reaction was also proposed. Both the phosphine-assisted monomerization and the phosphine-assisted pathway for oxygen atom transfer involve transition states with ternary components, D, sulfoxide, and phosphine, which we suggest are structural isomers of one another.     

Determination of absolute structure of macroviracins by chemical synthesis

The relative and absolute configurations of macroviracins have been established by the stereocontrolled synthesis of methyl ester 2a of the C(22) carboxylic acid, a constitutive fatty acid of macroviracin A (1), and their comparison to a sample 2 derived from the natural product 1. [structure: see text]     

Synthetic studies on maitotoxin. 3. Stereoselective synthesis of the BCDE-ring system

The stereoselective synthesis of the BCDE-ring system of maitotoxin has been accomplished through a two-directional strategy for the construction of polycyclic ether. The key reactions involve SmI 2-induced double cyclization of a beta-alkoxyacrylate and a double dihydroxylation for construction of the B- and E-rings.     

Synthetic studies on maitotoxin. 1. Stereoselective synthesis of the C'D'E'F'-ring system having a side chain

The stereoselective synthesis of the maitotoxin C'D'E'F'-ring system having a side chain has been accomplished through a convergent strategy. The key reactions include Horner-Wadsworth-Emmons coupling of the C'D'E'-ring and the side chain and subsequent construction of the F'-ring by silane reduction of dihydropyran.     

First total synthesis of vialinin A, a novel and extremely potent inhibitor of TNF-alpha production

Vialinin A, a powerful inhibitor (IC50 90 pM) of TNF-alpha production, was synthesized from sesamol in 11 steps with 28% overall yield. The key reactions include a double Suzuki coupling of electron-rich aryl triflate with phenylboronic acid and an oxidative deprotection of bis-MOM ether. In addition, the related synthetic studies also suggest the necessity for structural revision of ganbajunin C, a positional isomer of vialinin A.