Photochemistry of bicyclo[2.2.2]oct-7-ene-2,5-diones and the corresponding 5-hydroxyimino and 5-methylene derivatives

Synthesis and photochemistry of several title compounds 1-3 containing multiple chromophoric systems are described. The Diels-Alder reactions of 2,6,6-trimethylcyclohexa-2,4-dienone (5) with acetylenes 6a-d provided the adducts 7a-d, which upon hydrolysis furnished the desired bicyclo[2.2.2]octenediones 1a-d. Oximes 2a-d were prepared from diones 1a-d by treatment with hydroxylamine hydrochloride in pyridine. 5-Methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d were obtained via chemoselective Wittig reaction of the corresponding diones 1a-d. Bicyclo[2.2.2]octenediones 1a-c underwent chemoselective oxa-di-pi-methane rearrangement under sensitized conditions and suffered formal ketene extrusion upon direct irradiation. Direct irradiation of 1d afforded 11d via formal ketene extrusion but under sensitization it remained unchanged. Oximes 2a-d suffered ketene extrusion upon direct irradiation and E/Z isomerization under sensitized conditions. On the other hand, 5-methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d generally underwent 1,3-acyl shift. The plausible courses of all these photochemical processes are discussed.     

Reversible anion exchanges between the layered organic-inorganic hybridized architectures: syntheses and structures of manganese(II) and copper(II) complexes containing novel tripodal ligands

Six noninterpenetrating organic-inorganic hybridized coordination complexes, [Mn(3)(2)(H(2)O)(2)](ClO(4))(2).2 H(2)O (5), [Mn(3)(2)(H(2)O)(2)](NO(3))(2) (6), [Mn(3)(2)(N(3))(2)].2 H(2)O (7), [Cu(3)(2)(H(2)O)(2)](ClO(4))(2) (8), [Mn(4)(2)(H(2)O)(SO(4))].CH(3)OH.5 H(2)O (9) and [Mn(4)(2)](ClO(4))(2) (10) were obtained through self-assembly of novel tripodal ligands, 1,3,5-tris(1-imidazolyl)benzene (3) and 1,3-bis(1-imidazolyl)-5-(imidazol-1-ylmethyl)benzene (4) with the corresponding metal salts, respectively. Their structures were determined by X-ray crystallography. The results of structural analysis of complexes 5, 6, 7, and 8 with rigid ligand 3 indicate that their structures are mainly dependant on the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and metal ions. While in complexes 9 and 10, which contain the flexible ligand 4, the counteranion plays an important role in the formation of the frameworks. Entirely different structures of complexes 5 and 10 indicate that the organic ligands greatly affect the structures of assemblies. Furthermore, in complexes 5 and 6, the counteranions located between the cationic layers can be exchanged by other anions. Reversible anion exchanges between complexes 5 and 6 without destruction of the frameworks demonstrate that 5 and 6 can act as cationic layered materials for anion exchange, as determined by IR spectroscopy, elemental analyses, and X-ray powder diffraction.     

Synthesis and Crystal Structure of Dinuclear Copper Cluster Compound ［Cu（dtp）PPh_3］_2

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Laser flash photolysis of fullerols of C60 and of C70 in aqueous solutions

Fullerols of C₆₀ and of C₇₀ [C₆₀(OH)_n, C₇₀(OH)_m], water-soluble fullerene derivatives, unlike some other fullerene derivatives (such as C₆₀ (C₄H₆O), C₆₀ (C₃H₇N) and C₆₀ [C(COOEt)₂]_x), do not result in excited triplet state but in ionization via monophotonic process in aqueous solutions with 248 nm laser. The quantum yields of formation of hydrated electron (Φ_e ⁻) are determined to be 0.08 and 0.11 for fullerols of C₆₀ and of C₇₀ respectively at room temperature (ca. 15°C) with KI solution used as reference. By laser flash photolysis and oxidation of sulfate radical anion SO₄ ⁻, the fullerol radical cation or neutral radical of C₆₀ is confirmed to be existent and the transient absorption spectra of fullerol radical cation of C₇₀ are observed for the first time. Project supported by the National Natural Science Foundation of China     

Quantitative Non-Covalent Functionalization of Carbon Nanotubes

We report a convenient method for quantitative non-covalent functionalization of single-walled carbon nanotubes (SWNT) with phthalocyanine (Pc) compounds, in which a surface coverage of 49% was achieved. The effect of several process parameters on the functionalization process was elucidated. Firstly, as-produced SWNT gave the largest extent of functionalization compared with purified SWNT and as-produced multi-walled carbon nanotubes (MWNT). Secondly, the extent of functionalization was sensitive to the specific molecular structures of the Pc compounds. Finally, in terms of solvent selection, dimethylformamide (DMF) was found to give the largest extent of functionalization, which is then followed by chloroform (CHCl₃) and 1,2-dichlorobenzene (ODCB). The method reported in this paper provides new insights on the interactions between Pc molecules and carbon nanotubes and paves the way for rational control of the degree of functionalization, which is an important step from the perspective of carbon nanotube applications. Electronic supplementary material Supplementary material for this article is avilable at and is accessible for authorised users.     

High speed liquid chromatography with small bore columns

Using a specially designed column system, we have systematically investigated the effect of mobile phase velocity on column efficiency. The performance of small bore columns operated at different linear velocities of mobile phase was examined for three different types of injection system. Using the value of H^∞/u or n^∞/t${}_{\text{r}}^{\text{º}}$ as a criterion of a high speed separation, we calculated values of n/t${}_{\text{r}}^{\text{º}}$ for different solutes according to the equation \documentclass{article}\pagestyle{empty}\begin{document}$ {{\rm n}\mathord{\left/ {\vphantom {{\rm n} {{\rm t}_{\rm r}^ \circ }}}\right. \kern-\nulldelimiterspace} {{\rm t}_{\rm r}^ \circ }} = {{{\rm n}^\infty } \mathord{\left/ {\vphantom {{{\rm n}^\infty } {{\rm t}_{\rm r}^ \circ }}} \right. \kern-\nulldelimiterspace} {{\rm t}_{\rm r}^ \circ }}\left({\frac{{1 + {\rm k'}}}{{{\rm k' + }\beta }}} \right)^2 $\end{document}; the results obtained are in agreement with the experimentally determined values. These systematic investigations culminated in the separation of seven compounds in less than 10 s; the respective chromatogram is shown.     

Mechanisms of methane activation and transformation on molybdenum oxide based catalysts

We present a comprehensive survey of different C-H activation pathways over various kinds of active sites of terminal oxygens [=O] and bridge oxygens [-O-] by using Mo3O9 model systems. This allows us to provide some insights into fundamental issues concerning C-H activation by metal oxo species involved in many heterogeneous, homogeneous, and enzymatic processes. We show that H abstraction is the most feasible reaction pathway for the activation of a C-H bond on molybdenum oxides; and that [=O] is more active than [-O-]. Our calculations also suggest that (2+2) can be an alternative if M=O bond possesses a high polarity, while (5+2) can provide another effective pathway if two M=O bonds are in close proximity. Implications for the related heterogeneous, homogeneous, and enzymatic processes are discussed.     

Novel oxovanadium phosphate tubule incorporating 2,2-bipyridine ligands: hydrothermal synthesis and crystal structure of [(V(IV)O)(3)(mu(5)-PO(4))(2)(2,2'-bpy)(mu-OH(2))].1/3H(2)O

The novel tubular framework of [(V(IV)O)(3)(mu(4)-PO(4))(2)(2,2'-bpy)(mu-OH(2))].1/3H(2)O, which was synthesized from hydrothermal reaction, possesses some attractive structural features: (i) O=V(IV)O(4)(OH(2)) octahedra and PO(4) tetrahedra linked together by corner-sharing and face-sharing into a cylinder-shaped channel including 6 water molecules per cell unit, and (ii) (VO)(2,2'-bpy) groups regularly arranged around the tube, so that the 2,2-bpy ligands constitute an organic shell around an aqueous polar channel.     

A step-economic and one-pot access to chiral Cα-tetrasubstituted α-amino acid derivatives via a bicyclic imidazole-catalyzed direct enantioselective C-acylation

C^α-Tetrasubstituted α-amino acids are ubiquitous and unique structural units in bioactive natural products and pharmaceutical compounds. The asymmetric synthesis of these molecules has attracted a lot of attention, but a more efficient method is still greatly desired. Here we describe the first sequential four-step acylation reaction for the efficient synthesis of chiral C^α-tetrasubstituted α-amino acid derivatives from simple N-acylated amino acids via an auto-tandem catalysis using a single nucleophilic catalyst. The synthetic efficiency is improved via a direct enantioselective C-acylation; the methodology affords the corresponding C^α-tetrasubstituted α-amino acid derivatives with excellent enantioselectivities (up to 99% ee). This step-economic, one-pot, and auto-tandem strategy provides facile access to important chiral building blocks, such as peptides, serines, and oxazolines, which are often used in medicinal and synthetic chemistry.

The first four-step sequential reaction for the synthesis of C^α-tetrasubstituted chiral α-amino acid derivatives via auto-tandem catalysis has been developed.     

EPON和WDM-PON的分析比较

文章分析了以太网无源光网络(EPON)和波分复用无源光网络(WDM-PON)的多址技术、物理层关键技术和二层协议,特别针对这两种技术点对点仿真(P2PE)的实现给出了详细的分析,比较了这两种技术的性能,最后给出了结论并指出了二者不同的应用方向.