Redox-Neutral Syntheses and Electrochemical Studies of 10-Bromo-Substituted Light-Stable Antivitamin B12 Candidates

This publication describes the straightforward and redox-neutral synthesis of 10-bromophenylethynylcobalamin and its facile conversion to 10-bromoaquacobalamin. In this approach, the phenylethynyl ligand acts as convenient light-stable protecting group that is removed in quantitative yield under acidic conditions. The proteolytic cleavage at pH 2.0 was studied under pseudo-first-order conditions and is 1.5 times slower than that of phenylethynylcobalamin with a hydrogen instead of a bromine at C(10). Preliminary electrochemical studies of organometallic ethynyl-Cbls (Cbl=cobalamin) are reported for the first time. A reduction potential of −0.94 V vs. Ag/AgCl was determined for the Co^III/Co^I reduction of 10-bromophenylethynylcobalamin. The positive potential shift of 180 mV compared to phenylethynylcobalamin is in agreement with earlier electrochemical studies of related cyanocobalamins.     

On submillimeter laser lines from optically pumped12CH3OH

Several new submillimeter laser lines have been observed in a CH₃OH submillimeter laser, optically pumped by CO₂—laser radiation in a low power pulsed mode.Assignments have been suggested for a number of the lines. A few lines have wavelengths close to atmospheric water vapor absorption peaks, and can be observed only when the air path from the submillimeter resonator exit mirror to the detector is kept short or flushed with dry nitrogen.     

磷钼杂多酸修饰电极催化还原测定IO_3~-与BrO_3~-的液相色谱电化学研究

本文介绍了1:12磷钼杂多酸(PMo_(12))修饰电极的制备及其对IO_3~-、BrO_3~-的催化还原作用。本文还研究了在涂敷十六烷基三甲基溴化铵的C_(18)键合固定相上IO_3~-与BrO_3~-的分离方法,并采用修饰电极色谱电化学的方法对IO_3~-与BrO_3~-进行定量测定。IO_3~-、BrO_3~-的量分别在8.0×10(-10)～1.0×10~(-7)mol和1.6×10~(-9)～3.0×10~(-7)mol范围内与峰高呈良好的线性关系,检测限分别为4.0×10~(-10)mol与1.0×10~(-9)mol。用本方法测定IO_3~-和BrO_3~-重现性好、线性范围大,是测定IO_3~-与BrO_3~-的一种实用方法。     

具有纳米尺寸的四聚四硫富瓦烯大环冠醚的合成

以二(碘乙基)醚和2,3-二氰乙硫基四硫富瓦烯衍生物作为起始原料, 采用腈乙基保护与脱保护技术, 通过多步反应以较好的收率合成了两个纳米结构的大环四硫富瓦烯冠醚5a～5b. 通过循环伏安法(CV)研究了化合物4b和5b的电化学性质, 并用¹H NMR谱研究了5b与[60]富勒烯之间的相互作用. 结果表明: 5b存在环结构效应, 与[60]富勒烯有一定程度的电荷转移相互作用.     

EXAFS/FT-IR characterization of tetra-iridium carbonyl clusters bound to tris-(hydroxymethyl)phosphine grafted silica surface catalytically active for propene oxidation to acetone

Structure and catalytic activity of Ir₄(CO)₁₂ bound to tris-(hydroxymethyl)phosphine (THP) grafted silica (THP/SiO₂) was investigated by means of EXAFS, FT-IR and kinetic studies. It was found that Ir₄(CO)₁₂ was uniformly attached on THP/SiO₂ by substitution of CO by THP (Ir₄/THP/SiO₂). The tetra-iridium carbonyl cluster framework was remained during the substitution of THP ligands and two THP ligands coordinated to the iridium carbonyl clusters to form Ir₄(CO)₁₀(THP/SiO₂)₂. species. When Ir₄/THP/SiO₂ was evacuated at 373 K, bridge CO was desorbed and Debye-Waller factor of Ir---Ir contribution derived from EXAFS analysis was increased which suggested that the cluster framework was distorted by the evacuation at 373 K. The resulting sample evacuated at 373 K was an active catalyst for hydroformylation of ethene and partial oxidation of propene, while the Ir₄/THP/SiO₂ without evacuation exhibited poor catalytic activities. The propene oxidation reaction proceed on the Ir₄/THP/SiO₂ evacuated at 323–353 K under subatmospheric pressures to give acetone as a product in high selectivity. The ethene hydroformylation proceed on the evacuated Ir₄/THP/SiO₂ at lower temperatures compared with other conventional iridium catalysts. EXAFS characterization and kinetic studies suggested that the catalytic activities were associated with the structural distortion of the iridium cluster framework due to surface attachment by the bidentate phosphine substitution.     

Single Crystal X‐ray Diffraction Study of CsHSi2O5

Hydrothermally synthesized CsHSi₂O₅ was studied by single‐crystal X‐ray diffraction. The compound is orthorhombic (space group Pnma). Unit cell parameters are a = 4.9758(3), b = 8.8089(6), c = 12.9295(9) Å with four formula units per cell. The structure was solved by direct methods and refined to a residual R₁ = 0.025 for 621 independent observed reflections with I > 2σ(I) and 41 parameters. Residual electron densities were used to locate positions of the H atoms. They are part of silanol groups and show a disorder involving two positions related by a center of symmetry. The resulting O—H···O distance of 2.44 Å is one of the shortest hydrogen bonded O···O distances in inorganic compounds containing silanol groups. The structure belongs to the class of unbranched zweier double chain silicates. The [Si₂O₄(OH)^—] chains run parallel [100]. Cesium cations providing additional linkage between the anionic ribbons reside in voids between the chains and coordinate to nine oxygen ligands.     

Syntheses and structures of CsHo3Te5 and Cs3Tm11Te18 and the electronic structure of CsHo3Te5

Single crystals of CsHo₃Te₅ and Cs₃Tm₁₁Te₁₈ have been grown as byproducts in the synthesis of CsLnZnTe₃ (Ln=Ho or Tm) through the reaction of Ln, Zn, and Te with a CsCl flux at 850 °C. The crystal structures have been determined from single-crystal X-ray diffraction data. CsHo₃Te₅ crystallizes in space group Pnma of the orthorhombic system whereas Cs₃Tm₁₁Te₁₈ crystallizes in the space group C2/m of the monoclinic system. Each of the compounds adopts a three-dimensional structure; each possesses tunnels built from LnTe₆ octahedra that are filled with Cs atoms. The pseudo-rectangular tunnel in CsHo₃Te₅ is large enough in cross-section to accommodate two symmetrically equivalent Cs atoms. In the Cs₃Tm₁₁Te₁₈ structure there are two different sized tunnels: the smaller one is only large enough to host one Cs atom per unit cell whereas the larger one can accommodate two Cs atoms. The electronic structure of CsHo₃Te₅ was calculated. The band gap is estimated to be about 1.2 eV, consistent with the black color of the crystals.     

Ce_2Mo_3O_(12)超微粒子的制备及催化性能

以硝酸铈和钼酸铵为原料 ,采用溶胶 -凝胶法和微波加热技术制备了Ce2 Mo3 O12 超微粒子催化剂 ,使用DTA -TG ,IR ,XRD以及BET比表面测试等表征手段 ,考察了制备条件对复合氧化物超微粒子形成 ,晶相和比表面积的影响 .同时 ,测试了该样品对甲苯选择性氧化制苯甲醛反应的催化性能 .结果表明 :制备Ce2 Mo3 O12 超微粒子的适宜条件为 :初始溶液pH =1.0 ,柠檬酸 / (铈 +钼 )摩尔比等于 0 .4 ,在此条件下制得的干凝胶 ,经微波加热处理后 ,粒子的比表面积为 35 .8m2 /g ,粒径约为 4 0nm .在由甲苯气相选择氧化制苯甲醛的反应中表现出较好的催化活性     

EPR and Raman investigations into anionic redox chemistry of nanoporous 12CaO·7Al2O3 interacting with O2, H2 and N2O

EPR and Raman spectroscopy jointed with temperature-programmed reduction (TPR) and oxidation (TPO) were used to elucidate of the anionic redox processes occurring during the interaction of dioxygen, nitrous oxide and dihydrogen with nanoporous 12CaO·7Al₂O₃. The results showed that hydrogen and oxygen enter the mayenite cages following a dissociative pathway involving hydride, hydroxyl and peroxide intermediates, respectively. Generation and annihilation of the cage O ₂ ⁻ and O⁻ radicals upon oxidative and reductive treatments, confined to the near to the surface region, were found to be reversible. The key intermediates of this process were identified and a detailed mechanism of the surface and cage reactions was proposed.     

X-ray and neutron diffraction studies of the crystal and molecular structure of the predominant monocarboxylic acid obtained by mild acid hydrolysis of cyanocobalamin. Part I. X-ray diffraction studies of airdried crystals

The crystal structure of air-dried crystals of the O-monocarboxylic acid of cyanocobalamin, E2, has been solved by x-ray analysis. The lattice constants area =14-51 A,b = 1709 A,c = 16.35A, β = 103°; space group P2₁. Phase angles were derived from observations on anomalous dispersion effects for 2567 of the measured 2875 pairs of reflections,hkl andhkl, and used in the solution of the structure. The intensities of reflexions were eye estimated from Weissenberg photographs. The molecular arrangement is very different from that of other cyanocobalamins; the corrin rings of neighbouring molecules are atca 90° to one another. It was not possible to recognise the one acid group among the amides with certainty.