Metal-complex assemblies constructed from the flexible hinge-like ligand H2bhnq: structural versatility and dynamic behavior in the solid state

Novel metal-complex assemblies constructed from the flexible hinge-like ligand H(2)bhnq (H(2)bhnq=2,2'-bi(3-hydroxy-1,4-naphthoquinone)) have been synthesized. The X-ray crystal structures of these compounds reveal that four types of architectures are accessible by variation of the metal ions. In copper(II) compounds 1-3, the chelating bhnq(2-) ions bridge copper(II) centers to form one-dimensional zigzag chains. The chains of 1-3 are arranged by hydrogen-bonding interactions and stacking interactions to produce porous structures. Cobalt(II) and zinc(II) compounds 4 and 5 form one-dimensional helical chains. In 4 and 5, the crystal packing induces spontaneous resolution of the helical chains with chiral cavities formed perpendicular to the helices. Nickel(II) compounds 6 and 7 form cyclic tetramers. The fourth architecture, a dimer (compound 8), is obtained by the reaction of zinc(II) and bhnq(2-) in MeOH. In these compounds, changes of the dihedral angles and the metal-coordination mode of the bhnq(2-) ion induce the structural versatility. The assemblies of the zigzag chains of the copper(II) compounds exhibit reversible vapochromic behavior. UV/Vis, powder X-ray diffraction, EPR, and adsorption isotherm measurements indicate that this vapochromic behavior is based on the hinge-like flexibility of the bhnq(2-) ion.     

Detection of the His-heme Fe2+-NO species in the reduction of NO to N2O by ba3-oxidase from thermus thermophilus

Reaction pathways in the enzymatic formation and cleavage of the N-N and N-O bonds, respectively, are difficult to verify without the structure of the intermediates, but we now have such information on the heme a(3)(2+)-NO species formed in the reaction of ba(3)-oxidase with NO from resonance Raman spectroscopy. We have identified the His-heme a(3)(2+)-NO/Cu(B)(1+) species by its characteristic Fe-NO and N-O stretching frequencies at 539 and 1620 cm(-)(1), respectively. The Fe-NO and N-O frequencies in ba(3)-oxidase are 21 and 7 cm(-)(1) lower and higher, respectively, than those observed in Mb-NO. From these results and earlier Raman and FTIR measurements, we demonstrate that the protein environment of the proximal His384 that is part of the Q-proton pathway controls the strength of the Fe-His384 bond upon ligand (CO vs NO) binding. We also show by time-resolved FTIR spectroscopy that Cu(B)(1+) has a much lower affinity for NO than for CO. We suggest that the reduction of NO to N(2)O by ba(3)-oxidase proceeds by the fast binding of the first NO molecule to heme a(3) with high-affinity, and the second NO molecule binds to Cu(B) with low-affinity, producing the temporal co-presence of two NO molecules in the heme-copper center. The low-affinity of Cu(B) for NO binding also explains the NO reductase activity of the ba(3)-oxidase as opposed to other heme-copper oxidases. With the identification of the His-heme a(3)(2+)-NO/Cu(B)(1+) species, the structure of the binuclear heme a(3)-Cu(B)(1+) center in the initial step of the NO reduction mechanism is known.     

Characterization of fibril reinforced membranes for fuel cells

Characteristics of fibril reinforced membranes developed by Asahi Glass Company are reviewed. PTFE-fibrils <1 μm in diameter are dispersed in ion-exchange membranes uniformly. Mechanical properties, such as tensile strength, tear strength, creep property and compressive property were examined and compared with non-reinforced membranes. Fibril reinforced membranes, even by the addition of a small amount of PTFE-fibrils (2.7 wt.%), show excellent mechanical strength, especially in creep and tear strength. Cell performance is nearly equal to the one using a non-reinforced membrane and cell voltage stays about the same during the cell operation at 80 °C for 3000 h.     

Formation process of silver-polypyrrole coaxial nanocables synthesized by redox reaction between AgNO3 and pyrrole in the presence of poly(vinylpyrrolidone)

We have recently demonstrated a one-step process to fabricate silver-polypyrrole (PPy) coaxial nanocables (Chen, A.; Wang, H.; Li, X. Chem. Commun. 2005, 14, 1863). The formation process of silver-PPy coaxial nanocables is discussed in this article. It was found from the results of TEM and SEM images that large numbers of silver atoms were formed when AgNO3 was added to a pyrrole solution. Then silver atoms transform to silver-PPy nanosheets with regular morphology, which will connect together to be more stable. Silver-PPy nanocables will be able to grow at the expense of the silver-PPy nanosheets. Poly(vinylpyrrolidone) (PVP) plays crucial roles in this process: as a capping agent to form silver nanowires, and as a dispersant of pyrrole monomers, which can influence the site at which pyrrole monomer exists. On the basis of experimental analysis, the possible mechanism was proposed. Because of the effect of PVP, silver ions and pyrrole monomers are apt to be adsorbed at the [111] and [100] facets of silver nanosheets, respectively. Obvious polymerization will take place on the boundary of the [111] and [100] facets. The PPy layer stays stable on the [100] facets. Meanwhile, newly formed silver atoms and silver nanosheets will further ripen and grow on the [111] facets. In a word, the morphology of final products and the formation process are determined by the reaction site between AgNO3 and the pyrrole monomer, which is influenced by PVP.     

Synthesis of novel 1,4-, 3,4-, and 4,5-dihydropyrimidines: First successful POCl3 chlorination and regioselective alkoxycarbonylation

Chlorination of 5,6-dihydropyrimidine-4-(3H)-one derivatives (1) with POCl₃ gave 1,4(3,4)-dihydropyrimidines (3), whose alkoxycarbonylation (ClCOOREt₃N or NaH) afforded regioselectively novel compounds (4). A new Pummerer rearrangement of compound (1, X= ---S(O)CH₃) with ₃, gave compound (5h).     

AISM Data 43-3-01 Seismograms of foreshocks of 1982 Urakawa-oki earthquake

AISM Data Library

AISM Data 43-3-01 Seismograms of foreshocks of 1982 Urakawa-oki earthquake     

An analysis of the through-bond interaction using the localized molecular orbitals—IV: Long-range proton hyperfine coupling in exo- and endo-hydrogens in bicyclo[2.1.1]hex-5-yl radical

The INDO calculations were performed on bicyclo[2.1.1]hex-5-yl radical. From these calculations, it was confirmed that the hyperfine coupling constants depend largely on the geometry of the α hydrogen. The localized MO's were obtained from the canonical MO's calculated by using the INDO method. With the use of the localized MO's thus obtained, the variation in the hyperfine coupling constants at the 6exo- and 6endo-protons in this radical was explained in terms of the through-bond and/or the through-space interactions according to the procedure which we proposed previously. That is by the procedure we can selectively pick up a particular interaction between the specified localized MO's. The hyperfine coupling constant in this radical can be expressed by the summation of several interaction terms. The difference in the hyperfine spin coupling constants of the H_6exo and H_6endo in the radical now concerned has been attempted to explain using MO coefficients of the occupied orbitals.     

Cardiac glycosides: 3. synthesis of β-D-digitoxose analogues

Earlier studies have shown that the β-D-digitoxose (2,6-dideoxy-β-D-mannopyranose) directly attached to the cardiac glycoside steroid C3 has the greatest effect on biological activity. This report describes the synthesis of eight digitoxosides (2a-9a), with widely varying cyclic and acyclic C17β-side groups, and the corresponding C3',C4'-acetonides (2b-9b). NMR analysis of conformational strain introduced by the acetonide groups is supported by crystallographic analysis of the sugars' torsion angles.