Preparation and Catalytic Properties of Transition Metal Doped ZSM-5 Zeolites

Metal silicates of ZSM-5 type structure were prepared by doping silicate gels with chromium, manganese, cobalt, nickel, and copper ions, respectively, followed by reacting hydrothermally. The resultant materials were characterized by the metal content, x-ray powder diffraction, ion exchange capacity, surface area, thermal stability, and temperature programmed desorption of ammonia for acidity measurement. In addition, the catalytic properties of these metal silicates were examined using ethanol conversion as a probe reaction. The effect of transition metal content on the catalysis for dehydration, dehydrogenation, oligomerization, cracking, and cyclization to the aromatics was established and compared with that of HZSM-5 catalyst.     

Iron catalysed assembly of an asymmetric mixed-ligand triple helicate

The 2-pyridinecarbaldehyde isonicotinoyl hydrazone (HPCIH) family of ligands are typically tridentate N,N,O chelators that exhibit very high in vitro activity in mobilizing intracellular Fe and are promising candidates for the treatment of Fe overload diseases. Complexation of ferrous perchlorate with HPCIH in MeCN solution gives the expected six-coordinate complex Fe(II)(PCIH)(2). However, complexation of Fe(II) with 2-pyridinecarbaldehyde picolinoyl hydrazone (HPCPH, an isomer of HPCIH) under the same conditions leads to spontaneous assembly of an unprecedented asymmetric, mixed-ligand dinuclear triple helical complex Fe(II)(2)(PCPH)(2)(PPH), where PPH(2-) is the dianion of bis(picolinoyl)hydrazine. The X-ray crystal structure of this complex shows that each ligand binds simultaneously to both metal centres in a bidentate fashion. The dinuclear complex exhibits two well separated and totally reversible Fe(III/II) redox couples as shown by cyclic voltammetry in MeCN solution.     

15N-NMR Spectra of Azoles with Two Heteroatoms

The ¹⁵N-NMR spectra of azoles, with natural isotope abundance, have been measured under different experimental conditions, and chemical shifts are reported for imidazoles, pyrazoles, oxazoles, isoxazoles, thiazoles, and isothiazoles. General trends of substituent effects in this heterocyclic series are discussed based on the data of 67 substituted azoles, dihydro- and tetrahydroazoles. ¹⁵N, ¹H spin-coupling constants have been determined from spectra obtained by [¹H] → ¹⁵N polarizationtransfer experiments, i.e. an application of INEPT and DEPT pulse sequences. Two-bond and three-bond coupling constants are fully assigned and are discussed in terms of the specific pathways in azoles. The potential of structural applications of the new data is illustrated for isomeric nitro-imidazoles and highly-substituted pyrazoles, and in the case of ring-chain tautomerism of 2-substituted tetrahydrooxazoles.     

Chiral shift reagent for amino acids based on resonance-assisted hydrogen bonding

[structure: see text] A chiral aldehyde that forms resonance-assisted hydrogen bonded imines with amino acids has been developed. This hydrogen bond not only increases the equilibrium constant for imine formation but also provides a highly downfield-shifted NMR singlet for evaluating enantiomeric excess and absolute stereochemistry of amino acids.     

Esterification‐nitration of Ortho‐hydroxyphenyl Carboxylic Acids and Benzoic Acids with Cerium(IV) Ammonium Nitrate (CAN)

A convenient and useful esterification was realized, and this reaction proceeded without a dehydrating reagent or water removal equipment. A series of ortho‐hydroxyphenyl carboxylic acids and benzoic acids were transformed to their corresponding methyl esters under CAN/CH₃OH reaction conditions. Whereas in an aprotic solvent, acetonitrile, sp³‐C tethered ortho‐hydroxyphenyl carboxylic acids undergo simultaneous o,p‐dinitration and intramolecular esterification reactions in good yields. Also, 2‐((1 E)‐2‐nitrovinyl)‐4‐nitro‐phenol ( 3e ) showed selective cytotoxicities toward MCF‐7, HEP G2, and HEP 3B cell lines with IC₅₀ values of 23.50, 7.33, and 7.59 ug/mL, respectively.     

K2Mo4O13 phases prepared by hydrothermal synthesis

Hydrothermal synthesis in the K-Mo oxide system was investigated as a function of the pH of the reaction medium. Four compounds were formed, including two K₂Mo₄O₁₃ phases. One is a new low-temperature polymorph, which crystallizes in the orthorhombic, space group Pbca, with Z=8 and unit cell dimensions a=7.544(1) Å, b=15.394(2) Å, c=18.568(3) Å. The other is the known triclinic K₂Mo₄O₁₃, whose structure was re-determined from single crystal data; its cell parameters were determined as a=7.976(2) Å, b=8.345(2) Å, c=10.017(2) Å, α=107.104(3)°, β=102.885(3)°, γ=109.760(3)°, which are the standard settings of the crystal lattice. The orthorhombic phase converts endothermically into triclinic phase at ca. 730 K with a heat of transition of 8.31 kJ/mol.     

C_(70)与臭氧反应机理的理论研究

用半经验AM1方法研究了C_(70)与臭氧环加成反应的反应机理。采用Berny梯度 法优化得到反应的过滤度，并进行了振动分析确诊。计算结果表明：臭氧在C_(70) 6－6单、双键上的环加成反应均为复杂反应，由三步组成：第一步是O_3分子与C_ (70)的6-6单、双键发生1,3-偶极环加成反应，生成分子臭氧化物（即中间体I）， 6－6双键加成为放热反应，6－6单键加成为吸热反应，活化势垒分别为84.7和181. 2 kJ·mol~(-1)；第二步是中间体I的加成，C－C键断裂，生成两性离子中间体II 的放热反应，其势垒分别为61.3和13.3 kJ·mol~(-1)；第三步是中间体II脱去一 个Q_2分子生成具有环氧结构的C_(70)O，均为放热反应，活化势垒分别为169.3和 101.2 kJ·mol~(-1)；第三步是中间体I脱去一个O_2分子生成具有环氧结构的C_ (70)O，均为放热反应，活化势垒分别为169.3和101.2 kJ·mol~(-1)，从反应机理 和动力学角度解释了6－6双键加成优于6-6双键加成优于6-6双键加成优于6-6单键 加成的原因。O_3分子与C_(70)6-6双键的加成反应是协同且同步进行的，与6－6单 键的加成反应是协同但不同步的过程。     

High performance separations of nucleic acids using capillary electrophoresis and high-performance liquid chromatography

High resolution separations of nucleic acids have been performed using high performance capillary electrophoresis (HPCE) and high performance liquid chromatography (HPLC). Electropherograms showing HPCE separations of single and double stranded DNA are presented and compared with HPLC separations. Single base resolution of poly(dA) oligonucleotides in the size range of 12 to 60-mers was achieved in 35 min using HPCE. Plate numbers for HPCE are in the hundreds of thousands and reproducibility is about 1–2 % (RSD). In comparison with HPLC separations, the resolution of nucleic acids obtained using HPCE is much better than that using HPLC, while reproducibility of HPCE is comparable with that of HPLC.     

Access to substituted cyclobutenes by tandem [3,3]-sigmatropic rearrangement/[2 + 2] cycloaddition of dipropargylphosphonates under Ag/Co relay catalysis

We present herein an unconventional tandem [3,3]-sigmatropic rearrangement/[2 + 2] cycloaddition of simple dipropargylphosphonates to deliver a range of bicyclic polysubstituted cyclobutenes and cyclobutanes under Ag/Co relay catalysis. An interesting switch from allene–allene to allene–alkyne cycloaddition was observed based on the substitution of the substrates, which further diversified the range of compounds accessible from this practical method. Significantly, preliminary biological screening of these new compounds identified promising candidates as suppressors of cellular proliferation.

In situ generation of allenes through [3,3]-sigmatropic rearrangement of propargylphosphonates. Divergent allene–allene or allene–alkyne cycloaddition by Ag/Co relay catalysis. Products as promising suppressors of cellular proliferation.     

Determination of six indolic compounds, including melatonin, in rat pineal using high-performance liquid chromatography with serial fluorimetric-electrochemical detection.

A reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous determination of 5-hydroxytryptophan, 5-hydroxyindoleacetic acid, N-acetylserotonin, tryptophan, 5-hydroxytryptamine (serotonin) and melatonin in rat pineal using a buffered aqueous eluent containing acetonitrile and methanol as organic modifiers and an ion-pairing agent to assist in controlling the retention of compounds containing an amine group. Serial fluorimetric-electrochemical detection provided additional assurance of compound identity. Analyte preparation simply involved the sonication of pineals in dilute perchloric acid containing an antioxidant and a chelating agent, followed by centrifugation to clarify. The method simplifies the determination of this range of indolic compounds, which normally would require at least two separate runs with different eluents. Detection limits for melatonin were 60 and 135 pg for fluorimetric and electrochemical detection, respectively. (This represented the "worst case" considering the levels and detection limits of all compounds present.) Using flow programming and a flow-rate varying between 1 and 1.5 ml/min, the analysis time was 27.5 min, which made the determination of ten samples in a working day possible.