Binuclear complexes of Co(III) containing extended conjugated bis(catecholate) ligands

Binuclear complexes of cobalt(III) have been prepared with 3,3',4,4'-tetrahydroxy-benzaldazine (H4thB), 3,3',4,4'-tetrahydroxy-5,5'-dimethoxybenzaldazine (H4thM), and 3,3',4,4'-tetrahydroxydimethylbenzaldazine (H4thA) as bis(catecholate) ligands that link metal ions separated by 16 A through a conjugated bridge. In one case, [Co2(bpy)4(thM)]2+, stereodynamic properties observed in solution by 1H NMR are associated with valence tautomerism, with formation of a labile hs-Co(II) species by electron transfer from the catecholate regions of the bridge. Electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples. Chemical oxidation of [Co2(bpy) 4(thB)]2+ with Ag+ is observed to occur as a two-electron process forming [Co2(bpy) 4(thB(SQ,SQ))]4+. Attempted crystallization in the presence of air was observed to result in formation of the [Co(bpy)2(BACat)]+ (H2BACat, 3,4-dihydroxybenzaldehyde) cation by aerobic oxidation. Structural characterization is provided for the H4thM ligand and [Co(bpy)2(BACat)](BF4).     

Total synthesis of the disaccharide of bleomycin, 2-0-(α-D-mannopyranosyl)-L-gulopyranose

2-0-(α-$\text{D}$-Mannopyranosyl)-$\text{L}$-gulopyranose, the sugar portion of bleomycin has been synthesized.     

One‐pot Annulation for Biaryl‐fused Monocarba‐closo‐dodecaborate through Aromatic B−H Bond Disconnection

We have developed a one‐pot annulation reaction of monocarba‐closo‐dodecaborate with cyclic diaryliodonium salts to afford biaryl‐fused derivatives. Aryl functionalities are introduced at both the 1‐carbon and unreactive ortho‐boron vertices of the “σ‐aromatic” carborane cage without the need for pre‐functionalization. DFT calculations revealed that the palladium‐catalyzed C?B bond‐formation step in this process proceeds through a concerted metalation–deprotonation (CMD)‐type pathway for the B?H bond disconnection on the aromatic cage, though such bonds are generally regarded as hydridic.     

根霉胞外羧甲基纤维素酶和β－葡糖苷酶的纯化研究

采用柱层析等步骤纯化了根霉Ｇ７的羧甲基纤维素酶及β－葡糖苷酶，回收率分别为４．５％和１９．６％．二种酶的最适酶反应温度都为５５°Ｃ，并都能在较大ｐＨ范围内保持稳定，其中羧甲基纤维素酶具有很高的耐热性，在１００°Ｃ水浴中保持１ｈ也仍可检测出约２０％的酶活性，最适反应ｐＨ为７．０～７．５；而β－葡糖苷酶的热稳性较差，其最适反应ｐＨ为５．０．该两种酶的分子量分别为２．５×１０４和９．５×１０４，而Ｋｍ值则分别为７．４０ｍｇｍＬ－１和０．２１３ｍｇｍＬ－１．     

Oxygen ion conductivity of yttria-niobia mixed oxide with fluoride related structure

The oxygen ion conductivity of Y₂O₃---Nb₂O₅ with a fluorite-like structure was studied. Substitutional solid solutions of Nb₂ O₅ in Y₂O₃ lattice formed the defect fluorite phase and remarkably enhanced the oxygen ion conductivity. Doping with tetravalent cations, especially Ti⁴⁺ or Ce⁴⁺, in yttria-niobia oxide is effective in enhancing the oxygen ion conductivity. Although the n-type semiconducting property appeared below P_O2 = 10⁻¹⁸ atm at 1243 K, the yttria-niobia mixed oxide doped with Ce⁴⁺, Ti⁴⁺, and Zr⁴⁺ stably exhibited oxygen-ion conduction in the wide range of oxygen partial pressures studied.     

An intermediate temperature solid oxide fuel cell utilizing superior oxide ion conducting electrolyte, doubly doped LaGaO3 perovskite

LaGaO₃-based perovskite oxide doped with Sr and Mg exhibits high ionic conduction over a wide oxygen partial pressure. In this study, the stability of the LaGaO₃ based oxide was investigated. It became clear that LaGaO₃ based oxide is very stable for reduction and oxidation. SOFCs utilizing LaGaO₃-based perovskite type oxide for electrolyte were further studied for the decreased temperature solid oxide fuel cells. The power generation characteristics of cells were strongly affected by the electrode, both anode and cathode. It became clear that Ni and LnCoO₃ (Ln: rare earth) are suitable for anode and cathode, respectively. Rare earth cations in the Ln-site of Co-based perovskite cathode also have a great effect on the power generation characteristics. In particular, high power density could be attained in the temperature range from 973 to 1273 K by using doped SmCoO₃ for the cathode. The electrical conductivity of SmCoO₃ increases with increasing Sr amount doped for the Sm site and attained the maximum at Sm_0.5Sr_0.5CoO₃. The cathodic overpotential and the internal cell resistance exhibit almost opposite dependence on the amount of doped Sr. Consequently, the power density of the cell reaches a maximum when Sm_0.5Sr_0.5CoO₃ is used for cathode. On this cell, the maximum power density is as high as 0.58 W/cm² at 1073 K, although a 0.5 mm thick electrolyte is used. Therefore, this study reveals that the LaGaO₃ based oxide for electrolyte and the SmCoO₃ based oxide for cathode are promising for solid oxide fuel cells at intermediate temperature. Paper presented at the 97th Xiangshan Science Conference on New Solid State Fuel Cells, Xiangshan, Beijing, China, June, 14–17, 1998.     

Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond Cleavage

It has been established that an electron-deficient cyclopentadienyl rhodium(III) (Cp^ERh^III) complex catalyzes the oxidative and decarboxylative [2+1+2+1] cycloaddition of benzoic acids with diynes through C≡C triple bond cleavage, leading to fused naphthalenes. This cyclotrimerization is initiated by directed ortho C−H bond cleavage of a benzoic acid, and the subsequent regioselective alkyne insertion and decarboxylation produce a five-membered rhodacycle. The electron-deficient nature of the Cp^ERh^III complex promotes reductive elimination giving a cyclobutadiene–rhodium(I) complex rather than the second intermolecular alkyne insertion. The oxidative addition of the thus generated cyclobutadiene to rhodium(I) (formal C≡C triple bond cleavage) followed by the second intramolecular alkyne insertion and reductive elimination give the corresponding [2+1+2+1] cycloaddition product. The synthetic utility of the present [2+1+2+1] cycloaddition was demonstrated in the facile synthesis of a donor–acceptor [5]helicene and a hemi-hexabenzocoronene by a combination with the chemoselective Scholl reaction.     

Determination of cadmium in river water by electrothermal atomic absorption spectrometry after internal standardization-assisted rapid coprecipitation with lanthanum phosphate.

Cadmium ranging from 1 - 8 ng could be coprecipitated quantitatively with lanthanum phosphate at pH 5 - 6 from up to 200 mL of river water samples spiked with 5 microg of indium as an internal standard. Cadmium and indium coprecipitated were measured by using electrothermal atomic absorption spectrometry. The cadmium content in the original sample solution could be determined by internal standardization with indium. Since complete collection of the precipitate and strict adjustment of the volume of the final solution after coprecipitation are not required in this method, the precipitate could be collected by using decantation and centrifugation, and then dissolved with 1 mL of about 2.4 mol L(-1) nitric acid. The proposed method is simple and rapid, and enrichment close to 200-times can be attained; the detection limit (3sigma, n = 6) was 0.63 ng L(-1) in 200 mL of the sample solution.