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Retinoids are important endogenous compounds responsible for regulating multiple biological events. Currently, the qualitative and quantitative information about retinoid concentrations in human ti...

The reaction allows the formation of xanthenones and chromans with three contiguous stereocenters with high to excellent enantioselectivity and moderate to mostly excellent diastereoselectivity.

Phytoplasmas were detected in Sophora japonica cv. golden and Robinia pseudoacacia with diseased branches of witches'-broom collected in Haidian district, Beijing, China. Phytoplasma cells were observed in phloem sieve elements of symptomatic S. japonica cv. golden by transmission electron microscopy. The presence of phytoplasmas was further confirmed by sequence determination of partial gene sequences of 16S rDNA, rp (ribosomal protein) and secY. Phylogenetic trees and virtual restriction fragment length polymorphism (RFLP) analyses indicated that the phytoplasmas causing S. japonica cv. golden witches'-broom (SJGWB) and R. pseudoacacia witches'-broom (RPWB) belong to the 16SrV (elm yellows) group, and they are most closely related to subgroup 16SrV-B, rpV-C and secYV-C jujube witches'-broom (JWB) phytoplasma. Comparative analyses indicated that the phytoplasma of RPWB was closer to the JWB and that R. pseudoacacia might serve as an alternative host plant of JWB phytoplasma.

An unusual macrocyclic biflavone, selacyclicbiflavone A ( 1 ), have been isolated from Selaginella uncinata . The structure was elucidated on the basis of rigorous spectroscopic analysis including 1D and 2D NMR experiments as well as HRESIMS techniques. The absolute stereochemistry of compound 1 was further confirmed by comparing experimental data with calculated electronic circular dichroism (ECD) spectra. This is the first report of the macrocyclic biflavone with an unprecedented methylene bridge. A possible biosynthetic pathway was also postulated.

Nonadiabatic quantum dynamical calculations have been carried out on the two coupled potential energy surfaces (12A' and 22A') (Mota et al., J Theor Comput Chem 2009, 8, 849) for the title reaction. Initial state-resolved reaction probabilities and cross sections for ground and excited states for collision energies of 0.0051.0 eV are determined, respectively. Nonadiabatic transition is enhanced about four times by isotopic substitution of N + NH by N + ND reaction. It turns out that the nonadiabatic effects exert no significant contribution in the N + ND ? N2 + D reaction. (c) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Approx. 4% of patients experiencing chronic infection of human HCV (hepatitis C virus) ultimately develop HCC (hepatocellular carcinoma). The NS5A (non-structural protein 5A) encoded by HCV has been reported to have an oncogenic role during HCV infection, but the precise mechanism remains largely unclear. The aim of this study is to investigate the signal transduction pathways that mediate the role of NS5A in hepatocarcinogenesis. HepG2 cells were transfected with a plasmid expressing HCV NS5A protein. Subsequently, cell proliferation was analysed by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay and cell counting, apoptosis was analysed by Hoechst 33342 staining, and the gene expression profile was identified by microarray and subsequently validated by RT-PCR (reverse transcription-PCR). The protein levels of survivin, p53, NOS2A (nitric oxide synthase 2A), cyclin D1 and NF-κB (nuclear factor κB) were monitored by Western blotting. Our results showed that transfection of HCV NS5A expression plasmid significantly down-regulated the expression of nine genes and up-regulated the expression of ten genes among the 104 genes detectable by the microarray associated with signalling transduction. The increased expression of survivin mRNA and protein, down-regulated p53 protein levels and increased NOS2A, cyclin D1 and NF-κB protein levels were further identified. Our results suggested that HCV NS5A protein can enhance survivin transcription by increasing p53 degradation and stimulating NOS2A expression as well as NF-κB relocation to the nucleus. The functions of survivin in anti-apoptosis and regulation of cell division might mediate the role of NS5A in HCV-induced HCC.

This communication describes a new study of microstructures of double network (DN) gels, which were prepared in two steps: firstly, an across-linked polymer (the first network) was prepared, and then the other compound (the second network) was synthesized in the first network. A novel micro/nanostructure has been found in the DN gels. Meanwhile, solid composites with micro/nanostructures have been obtained as well.

Hf1−xSixO2 gate dielectrics grown by UV-photo-induced chemical vapor deposition (UV-CVD) using Hf(OBut)2(mmp)2 and tetraethoxysilane as precursors have been deposited on Si substrate. Composition dependence of the interfacial microstructure of the Hf1−xSixO2/Si gate stacks has been investigated via Fourier transform infrared spectroscopy (FTIR) systematically. It has been indicated that the physical properties of the Hf1−xSixO2 films can be effectively optimized by adjusting the silicon contents incorporated in the films. In order to evaluate its potential implementation as an alternative dielectric in future devices, detailed electrical characterization of Au/Hf1−xSixO2/Si capacitor has been performed as functions of the silicon contents and the UV-annealing time. Copyright © 2010 John Wiley & Sons, Ltd.

A highly efficient organocatalytic synthesis of lapachol analogues from the Michael addition of naphthoquinone to various α,β-unsaturated ketones catalyzed by primary amines is presented. Good to high yields (up to 93 %) and high to excellent enantioselectivities (up to 98 % ee) were obtained for the target compounds. MS (ESI) provided evidence for the key intermediates in the proposed mechanism.

The mechanism of the title reactions have been studied by using the DFT (B3LYP/ECP/6-311+G*) level of theory. Both ground and excited state potential energy surfaces are discussed. It is found the reaction mechanism is insertion mechanism both along the CS and CO bond activation branches, but the CS bond activation is much more favorable in energy than the CO bond activation. The reaction of Y atom with SCO was shown to occur preferentially on the ground state (doublet) PES throughout the reaction process, and the experimentally observed species, have been explained according to the mechanism revealed in this work. Different from that of Y + SCO system, the reaction between Y+ cation and SCO involves potential energy curve-crossing which dramatically affects reaction mechanism. Due to the intersystem crossing existing in the reaction process of Y+ with SCO, the intermediates SY+(η2CO) and OY+(η2CS) may not form. All our theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Proton transfer (PT) and excited-state PT process are proposed to account for the fluorescent sensing mechanism of a cyanide chemosensor, 8-formyl-7-hydroxycoumarin. The time-dependent density functional theory method has been applied to investigate the ground and the first singlet excited electronic states of this chemosensor as well as its nucleophilic addition product with cyanide, with a view to monitoring their geometries and spectrophotometrical properties. The present theoretical study indicates that phenol proton of the chemosensor transfers to the formyl group along the intramolecular hydrogen bond in the first singlet excited state. Correspondingly, the nucleophilic addition product undergoes a PT process in the ground state, and shows a similar structure in the first singlet excited state. This could explain the observed strong fluorescence upon the addition of the cyanide anion in the relevant fluorescent sensing mechanism.

The structure of a radiation-protective sulfated polysaccharide, SP-APS, isolated from Spirulina platensis, was investigated by methylation analysis, partial acetolysis and 1H-NMR spectroscopy. The repeating-unit of SP-APS as branched structures was elucidated.

Propyl O-(α-L-rhamncpyranosyl)-(1→3)-[2,4-di-O-(2s-methylbutyryl)-α-L-rham-nopyranosyl]-(1→2)-(3-O-acetyl-β-D-glucopyranosyl)-(1→2)-β-D-fucopyranoside (1), the tetrasac-charide moiety of Tricolorin A, was synthesized in total 23 steps with a longest linear sequence of 10 steps, and overall yield of 3.7% from D-Glucose. The isomerization of the dioxolane-type berzyli-dene in the presence of NIS/AgOTf was observed. Tetrasaccharide 1 exhibited no activity against the cultured P388 cell as Tricolorin A did.

Density functional theory calculations have been performed to explore the potential energy surfaces of CO bond activation in CO2 molecule by gas-phase Nb atom and Nb+ cation for better understanding the reaction mechanism of second-row metal with CO2. The minimum-energy reaction path is found to involve the spin inversion in the different reaction steps. This potential energy curve-crossing dramatically affects the reaction energetic. The present results show that the mechanism is insertion-elimination mechanism along the CO bond activation reaction. All theoretical results not only support the existing conclusions inferred from early experiment but also complement the pathway and mechanism for this reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

The first highly enantioselective organocatalytic Michael addition of 4-hydroxycoumarins is reported.

A highly enantioselective Michael reaction of aromatic ketones with nitroolefins was accomplished in the presence of a chiral bifunctional primary amine―thiourea catalyst and 4-nitrobenzoic acid as the co-catalyst; the corresponding adducts were obtained in excellent enantioselectivities (up to 99 % ee) and yields (up to 98 %). The catalytic mechanism of the Michael reaction was confirmed through the ESI-MS detection of proposed reaction intermediates and the 1 H NMR detection of hydrogen bonding between thiourea and the nitroolefins. DFT calculations showed that chiral moieties of the thiourea impacted the yields and enantioselectivities of the adducts remarkably, which corresponds to the observed experimental results.

Generally, amine-catalyzed enantioselective transformations rely on chiral enamine or unsaturated iminium intermediates. Herein, we report a protocol involving dual activation by an aromatic iminium and hydrogen-bonding. An enantioselective aza-Michael–Henry domino reaction of 2-aminobenzaldehydes with nitroolefins has been developed through this protocol using primary amine thiourea catalysts to provide a variety of 3-nitro-1,2-dihydroquinolines in moderate yields and with up to 90 % ee. The mechanism for the catalytic enantioselective reaction was confirmed by ESI mass spectrometric detection of the reaction intermediates. The products formed are substructures found in skeletons of important biological and pharmaceutical molecules.