Two 3D supramolecular polymers constructed from an amino acid and a high-nuclear Ln6Cu24 cluster node

The first successful attempt to construct 3D supramolecular frameworks with high-nuclear 3d-4f heterometallic clusters as a node is reported. The self-assembly of Ln3+, Cu2+ and amino acid in solution leads to the formation of two polymers, 35-nuclear complex [Sm6Cu29] 1 with a primitive cubic net-like structure and 36-nuclear complex [Nd6Cu30] 2 with a face-centred cubic network type structure. Glycine and L-proline, respectively, were used as ligands. It should be noted that 2 has a chiral framework. X-ray structure analyses show that 1 crystallizes in the triclinic P1 space group (a=19.6451(8), b=20.4682(8), c=20.7046(8) A, alpha=89.453(1), beta=66.290(1), gamma=68.572(1) degrees, V=7003.0(5) A3 and Z=1) and 2 belongs to the cubic P2(1)3 space group (a=b=c=32.4341(3) A, V=34 119.7(5) A3 and Z=4). Both complexes utilize Ln6Cu24 octahedral clusters as nodes and trans-Cu(amino acid)2 groups as bridges. Electrical conductivity measurements reveal that both polymers behave as semiconductors.     

Oxidation of Stereo‐regular Poly(styrene‐co‐4‐methylstyrene) by Cobalt(II) Acetate Tetrahydrate/Sodium Bromide Catalyst

Chemical modification on the stereo‐regular poly(styrene‐co‐4‐methylstyrene) (sPS‐PMS) was attempted in this study. Metallocene copolymerization of styrene (St) and 4‐methylstyrene (MSt) was performed by using η⁵‐pentamethylcyclopentadienyl‐titanium(IV)tributoxide (Cp*Ti(OBu)₃)/methylaluminoxane (MAO)/tri‐iso‐butylaluminum (TIBA) catalyst in the bulk state. Cobalt(II) catalyst was then applied to oxidize the benzylic methyl group on the MSt units of the resulting sPS‐PMS copolymer. Both aldehyde and carboxylic acid in the oxidized products were resolved by the FTIR and ¹H NMR. The oxidized sPS‐PMSs exhibit a low and a high‐temperature T_g and T_m corresponding to the transitions in the amorphous and the crystalline regions. Hydrogen‐bond and polar interactions between the aldehyde and carboxylic acids tend to interrupt the regular chain packing of the oxidized sPS‐PMS, resulting in the lowering of T_m with oxidation level. The oxidized sPS‐PMS showed better adhesion to glass fiber than pure sPS‐PMS copolymer as evaluated from the respective SEM fractured micrographs.     

Synthesis and biological activity of novel epothilone aziridines

[reaction: see text]. A series of 12alpha,13alpha-aziridinyl epothilone derivatives were synthesized in an efficient manner from epothilone A. The final semisynthetic route involves a formal double-inversion of stereochemistry at both the C12 and C13 positions. All aziridine analogues were tested for effects on tubulin binding polymerization and cytotoxicity. The results indicate that the aziridine moiety is a viable isosteric replacement for the epoxide in the case of epothilones.     

High-yield solvothermal formation of magnetic CoPt alloy nanowires

One-dimensional (1D) magnetic nanomaterials have attracted much attention recently because of their applications in magnetic recording and spintronics. Nevertheless, it remains a challenge to prepare free-standing magnetic nanowires in high yield. This Communication reports the successful high-yield synthesis of an interesting 1D ferromagnetic CoPt alloy by direct decomposition of platinum acetylacetonate and cobalt carbonyl compound in ethylenediamine solvent through a solvothermal reaction. The CoPt alloy nanowires obtained have a tunable diameter of 10-50 nm and a length along the longitudinal axis of up to several microns, depending on crystallization temperature and reaction time. A unique formation mechanism involving coarsening and ripening under solvothermal conditions was discovered. This research opens new opportunities in synthesizing nanomaterials through low-temperature solvothermal processes.     

Photoisomerization and photodissociation of aniline and 4-methylpyridine

Photoisomerization and photodissociation of aniline and 4-methylpyridine at 193 nm were studied separately using multimass ion imaging techniques. Photofragment translational energy distributions and dissociation rates were measured. Our results demonstrate that more than 23% of the ground electronic state aniline and 10% of 4-methylpyridine produced from the excitation by 193 nm photons after internal conversion isomerize to seven-membered ring isomers, followed by the H atom migration in the seven-membered ring, and then rearomatize to both methylpyridine and aniline prior to dissociation. The significance of this isomerization is that the carbon, nitrogen, and hydrogen atoms belonging to the alkyl or amino groups are involved in the exchange with those atoms in the aromatic ring during the isomerization.     

Concise total syntheses of the bioactive mesotricyclic diterpenoids jatrophatrione and citlalitrione

The highly functionalized [5.9.5] tricyclic framework resident in jatrophatrione (1) and citlalitrione (2) has been synthesized. The route begins with the tandem anionic oxy-Cope rearrangement/methylation/transannular ene cyclization of 21 and subsequent introduction of a conjugated enone double bond. Hydroxyl-directed 1,4-reduction of this functionality in 25 with LiAlH(4)/CuI/hexamethylphosphoramide/tetrahydrofuran sets the stage for the implementation of a Grob fragmentation and expedited generation of 27. Stereocontrolled intramolecular hydrosilylation allows for the subsequent introduction of a cyclic carbonate as in 53. This intermediate undergoes remarkably efficient, fully regiocontrolled Treibs reaction to generate 54, with this maneuver serving as a pivotal step for making 1 available five steps later. Treatment of 1 with m-chloroperbenzoic acid leads to 2, with attack occurring preferentially on a alpha-face of the double bond more remote to the carbonyl.     

Systematic investigation of the hydrothermal syntheses of Pr(III)-PDA (PDA = pyridine-2,6-dicarboxylate anion) metal-organic frameworks

A series of novel two-dimensional (2D) and three-dimensional (3D) praseodymium coordination polymers, namely, {[Pr3(PDA)4(HPDA)(H2O)8] x 8H2O}n (2), {[Pr2(PDA)3(H2O)3] x H2O}n (3), {[Pr(PDA)(H2O)4] x ClO4}n (4), and { [Pr2(PDA)2(H2O)5SO4] x 2H2O}n (5) (PDA = pyridine-2,6-dicarboxylic anion), was designed and synthesized under hydrothermal conditions. Complexes 1-3 (chainlike polymer, {[Pr(PDA)(HPDA)(H2O)2] x 4H2O}n (1) was also obtained independently by us, although it has been reported recently by Ghosh et al.) were fabricated successfully by simply tuning the Pr/PDA ratio and exhibited various and intriguing topological structures from a 1D chain to a 3D network. While the synthetic strategy of 5 was triggered and further performed only after 1 was structurally characterized. The complexes were characterized by X-ray single-crystal determination, spectroscopic, and variable-temperature magnetic susceptibility analyses. In complex 2 an unusual nanosized square motif as a building block constructed by eight Pr ions was further assembled into a highly ordered 2D grid compound. In complex 3 the decanuclear Pr metal-based structure as a repeat unit interpenetrated to form a novel 3D polymer. Complex 4 was a 3D network polymer fabricated through a hexanuclear Pr ring as a building block, and ClO4- anions as guests were trapped in the cavity. In complex 5 six Pr atoms, two SO4(2-) anions, and carboxylic oxygen bridges constructed an intriguing rectangle structure as a repeat unit in the grid to form a 2D coordination polymer in which the unique bi-bidentate coordination mode of SO4(2-) anion was observed.     

Reduction of 4-nitrophenol catalyzed by nitroreductase

The reduction of 4-nitrophenol catalyzed by nitroreductase in the presence of NADH was investigated in this paper.4-Amino- phenol and 4-bydroxylamino-phenol were found in the reductive products.The relationship between reaction time and the reductive ratio were studied.The similar reducing ratios of 4-nitrophenol were obtained under aerobic and anaerobic conditions.The results indicated that an oxygen-insensitive reaction was proceeded in the reduction of 4-nitrophenol and nitroreductase was an oxygen- insensitive enzyme.The reductive products of 4-nitrophenol were determined by HPLC and MS.     

Pt粒大小对PtNaY/HY体系氢溢出效应的影响

负载型金属催化剂的表面溢出效应(Spillover)是指吸附在金属上的物种可沿固体表面转移到担体上去的现象,是金属活性组分与担体相互作用的一个重要方面。近年来随着金属与担体之间强相互作用(SMSI)研究的逐渐深入,人们注意到溢出效应在SMSI中的重要作用。虽然提出溢出效应已有20多年的历史,并且人们采用不同的实验方法对此进行了广泛的研究,但对以分子筛为担体的负载型金属催化剂体系溢出效应的研究仍比较少。影     

Molecular design of free volume as a route to low-kappa dielectric materials

Polymers incorporating the triptycene subunit were prepared for the molecular-level design of low dielectric constant (low-kappa) materials that can be used to manufacture faster integrated circuits. Triptycenes having restricted rotation by multiple point attachment to the polymer backbone are shown to introduce free volume into the films, thereby lowering their dielectric constants. The triptycene containing polymers exhibit a number of desirable properties including low-water absorption and high thermal stability. Systematic studies wherein comparisons are made between two separate classes of triptycene polymers and their non-triptycene containing analogues demonstrate that proper insertion of triptycenes into a polymer backbone can give rise to a reduction in the material's dielectric constant while also improving its mechanical properties. These characteristics are desired by the semiconductor industry for the next generation of microprocessors and memory to provide insulation of the increasingly shrinking features.