A Cu(II)-mediated C-H oxygenation of sterically hindered tripyridine ligands to form triangular Cu(II)3 complexes

Two sterically hindered tris-pyridyl methane ligands, tris(6-methyl-2-pyridyl)methane (L1) and bis(6-methyl-2-pyridyl)pyridylmethane (L2), are newly synthesized. Under aerobic conditions, Ln (n = 1 or 2) reacts with CuX2 (X = Cl or Br), oxygenated at the methine position to LnOH or LnOMe. The former alcoholate ligand creates trinuclear Cu(II) complexes [Cu3(X)(LnO)3](PF6)2 [(X, n) = (Br, 1) 1, (C1, 1) 2, (Br, 2) 3, or (C1, 2) 4] in which the alkoxide oxygen atoms bridge copper centers. The crystal structures of 1-4 are presented along with their magnetic susceptibility data. The weak antiferromagnetic coupling between the Cu(II) centers in this trinuclear arrangement is due to weak interaction of the magnetic orbitals (dz2) which are oriented along three alternate sides in a hexagon of the Cu3O3 core in 1-4. Under anaerobic conditions, L1 reacts with CuBr2 to form a square pyramidal complex [CuL1Br2] (9) with the ligand facially capping. [Cu(Br)2(L1OMe)] (10) was obtained after the suspension of 9 in MeOH was stirred under air for 48 h. In the presence of cyclohexene, 9 is converted to [Cu(Br)(L1)]m (m = 1 or 2) 5 quantitatively to give trans- 1,2-dibromocyclohexane, indicating that Br2 is generated during the reaction. The FAB MS spectrum of [18O]-1 prepared by the reaction of L1 with CuBr2 under 18O2 shows that the ligand of [18O]-1 is L1(18O-.) L1(18OH), L1OCD3, and bis(6-methyl-2-pyridyl) ketone were obtained from reaction of L1 with CuBr2 in CD3OD under 18O2. These results indicate that the origins of the O atom in L1OH and L1OMe are O2 and MeOH, respectively. On the basis of these results, a mechanism of the oxygenation of L1 in the present system will be proposed.     

(Studies on AI-77s,microbial products with pharmacological activity) structures and the chemical nature of AI-77s

The structures of a novel gastroprotective substance AI-77-B and its analogues AI-77-C, D, F and G, which are produced by Bacillus pumilus, are described. Five of the asymmetric centers of AI-77-B have S absolute stereochemistry confirmed by X-ray in combination with chemical studies.     

Polarization dependence of the optical absorption of single-walled carbon nanotubes

Anisotropic optical absorption properties of single-walled carbon nanotubes (SWNTs) are determined from a vertically aligned SWNT film for 0.5-6 eV. Absorption peaks at 4.5 and 5.25 eV are found to exhibit remarkable polarization dependence and have relevance to optical properties of graphite. A method for determining a nematic order parameter for an aligned SWNT film based on the collinear absorption peak at 4.5 eV is presented, followed by the determination of the optical absorption cross section.     

Evolution of the Hall coefficient and the peculiar electronic structure of the cuprate superconductors

Although the Hall coefficient R(H) is an informative transport property of metals and semiconductors, its meaning in the cuprate superconductors has been ambiguous because of its unusual characteristics. Here we show that a systematic study of R(H) in La2-xSrxCuO4 single crystals over a wide doping range establishes a qualitative understanding of its peculiar evolution, which turns out to reflect a two-component nature of the electronic structure caused by an unusual development of the Fermi surface recently uncovered by photoemission experiments.     

Schulzeines A-C, new alpha-glucosidase inhibitors from the marine sponge Penares schulzei

Three new alpha-glucosidase inhibitors, schulzeines A-C (1-3), were isolated from the marine sponge Penares schulzei. Their structures were elucidated by spectral analysis and chemical degradations to be the isoquinoline alkaloids, encompassing two amino acids, and C(28) fatty acid, the last of which was sulfated. Absolute stereochemistry of schulzeines was determined by application of the modified Mosher analysis to fragments obtained by chemical degradation. Schulzeines A-C inhibit alpha-glucosidase with IC(50) values of 48-170 nM.     

Tumor-infiltrating effector cells of alpha-galactosylceramide-induced antitumor immunity in metastatic liver tumor

BACKGROUND: alpha-Galactosylceramide (alpha-GalCer) can be presented by CD1d molecules of antigen-presenting cells, and is known to induce a potent NKT cell-dependent cytotoxic response against tumor cells. However, the main effector cells in alpha-GalCer-induced antitumor immunity are still controversial. METHODS: In order to elucidate the cell phenotype that plays the most important role in alpha-GalCer-induced antitumor immunity, we purified and analyzed tumor-infiltrating leukocytes (TILs) from liver metastatic nodules of a colon cancer cell line (Colon26), comparing alpha-GalCer- and control vehicle-treated mice. Flow cytometry was performed to analyze cell phenotype in TILs and IFN-gamma ELISA was performed to detect antigen-specific immune response. RESULTS: Flow cytometry analysis showed a significantly higher infiltration of NK cells (DX5+, T cell receptor alphabeta (TCR)-) into tumors in alpha-GalCer-treated mice compared to vehicle-treated mice. The DX5+TCR+ cell population was not significantly different between these two groups, indicating that these cells were not the main effector cells. Interestingly, the CD8+ T cell population was increased in TILs of alpha-GalCer-treated mice, and the activation level of these cells based on CD69 expression was higher than that in vehicle-treated mice. Moreover, the number of tumor-infiltrating dendritic cells (DCs) was increased in alpha-GalCer-treated mice. IFN-gamma ELISA showed stronger antigen-specific response in TILs from alpha-GalCer-treated mice compared to those from vehicle-treated mice, although the difference between these two groups was not significant. CONCLUSIONS: In alpha-GalCer-induced antitumor immunity, NK cells seem to be some of the main effector cells and both CD8+ T cells and DCs, which are related to acquired immunity, might also play important roles in this antitumor immune response. These results suggest that alpha-GalCer has a multifunctional role in modulation of the immune response.     

Ligand-ligand redox interaction through some metal-cluster units

The ligand-ligand redox interaction separated by di-, tri-, and hexanuclear cluster units is discussed in terms of the splitting of the redox waves (DeltaE(L)) and the comproportionation constants (Kcom(L)) of the ligand-based mixed valence state. Although two redox-active monodentate ligands in the mononuclear ruthenium(II) complexes (either cis or trans configurations) do not show appreciable splitting in their reduction waves, interestingly those separated by giant triruthenium and hexarhenium cluster units clearly show splitting. The molecular orbital considerations in the literature suggest that these units possess some pi-type molecular orbitals composed of metal dpi and possibly ligand ppi orbitals. Absence of the redox interactions in oxo-bridged diruthenium(II) and oxo-centered trirhodium(III) complexes where such pi molecular orbitals (including an antibonding one) are fully occupied, indicates the importance of empty pi* orbitals for the ligand redox communication.