Taxane diterpenoids from seeds of Taxus mairei

A new 2(3-->20) abeotaxane, taxumairone A (1), and a new cis-p-coumaroyl myo-inositol have been isolated from the seeds of Taxus mairei in addition to taxin B (2), taxinine A, taxuspine X, decinnamoyltaxinine E, 5alpha-cinnamoyloxy-9alpha,10beta,13alpha- triacetoxy-taxa-4(20)11-diene and 5alpha-cinnamoyloxy-2alpha,9alpha,10beta,+ ++13alpha-tetraacetoxy-taxa-4(20)11-diene. The structure of 1 was determined by 2D-NMR spectral analysis and chemical correlation with taxin B (2). Compound 1 exhibited potent cytotoxicity against human colon carcinoma cells with an ED50 of 0.1 microg/ml.     

Regulating electrodeposition behavior through enhanced mass transfer for stable lithium metal anodes

Electrode process kinetics is a key part that determines the morphology of metal electrodeposition.However,the liquid-phase mass transfer process and its effect on lithium(Li)metal electrodeposition are still poorly understood.Herein,the effect of mass transfer on the electrodeposition behavior of Li metal is explored.Experiments and COMSOL Multiphysics simulations reveal that the enhanced mass transfer,which is induced by ultrasonic wave,can homogenize the ion flow on the surface of electrode to obtain uniform Li nucleation.Meanwhile,the rapid mass transfer of Li⁺provides sufficient cations around the germinated Li to avoid preferential growth of Li in a specific direction.Based on the simultaneous regulation of nucleation and growth behavior,a smooth and compact Li deposits can be achieved,which exhibit a small polarization voltage during repeated Li plating/striping and a considerably enhanced cyclability.This work enriches the fundamental understanding of Li electrodeposition without dendrite structure and affords fresh guidance to develop dendrite-free metal anodes for metal-based batteries.     

Poly(ionic liquid)s: a new material with enhanced and fast CO2 absorption

Novel sorbent and membrane materials for CO2 separation, poly(ionic liquid)s made from ionic liquid monomers, poly[p-vinylbenzyltrimethyl ammonium tetrafluoroborate](P[VBTMA][BF4]) and poly[2-(methacryloyloxy)ethyltrimethylamnonium tetrafluoroborate](P[MATMA][BF4]) have absorption capacities 7.6 and 6.0 times of those of room-temperature ionic liquids, e.g.[bmim][BF4], respectively, with reversible and fast sorption and desorption.     

Alterations in mitochondrial and apoptosis-regulating gene expression in photodynamic therapy-resistant variants of HT29 colon carcinoma cells

Photodynamic therapy (PDT) is a novel cancer therapy inducing irreversible photodamage to tumor tissue via photosensitizer-mediated oxidative cytotoxicity. The cellular and molecular responses associated with PDT are only partially understood. We have reported previously the generation of several photosensitizer-specific PDT-resistant cell variants of HT29 human colon adenocarcinoma cells by selecting cells from sequential PDT treatment using different photosensitizers. In this report, we describe the use of messenger RNA (mRNA) differential display to identify genes that were differentially expressed in the parental HT29 cells compared with their resistant variants. In comparison with parental HT29 cells, mRNA expression was increased in the PDT-resistant cell variants for BNIP3, estrogen receptor-binding fragment-associated gene 9, Myh-1c, cytoplasmic dynein light chain 1, small membrane protein I and differential dependent protein. In contrast, expression in the PDT-resistant variants was downregulated for NNX3, human HepG2 3' region Mbol complementary DNA, glutamate dehydrogenase, hepatoma-derived growth factor and the mitochondrial genes coding for 16S ribosomal RNA (rRNA) and nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 4. The reduction for mitochondrial 16S rRNA in the PDT-resistant variants was confirmed by Northern blotting, and the elevated expression of the proapoptotic BNIP3 in the PDT-resistant variants was confirmed by Northern and Western blotting analysis. We also examined the expression of some additional apoptosis-regulating genes using Western blotting. We show an increased expression of Bcl-2 and heat shock protein 27 and a downregulation of Bax in the PDT-resistant variants. In addition, the mutant p53 levels in the parental HT29 cells were reduced substantially in the PDT-resistant variants. We suggest that the altered expression in several mitochondrial and apoptosis-regulating genes contributes to PDT resistance.     

Preparation of trehalase inhibitor validoxylamine A by biocatalyzed hydrolysis of validemycin a with honeybee (Apis cerana fabr.) β-glucosidase

Validoxylamine A is structurally similar to trehalose and acts a potent competivive inhibitor of trehalase. It has recently been receiving increased attention as a potential material for the development of new insecticides or drugs. In this study, β-glucosidase extracted from honeybees (Apis cerana Fabr.) was used as a catalyst to produce validoxylamine A through enzymatic hydrolysis of validamycin A. β-Glucosidase was separated and purified from honeybees, and its characteristics were examined. The results showed that β-glucosidase was stable across a range of temperatures from 30 to 40°C and across a relatively wide range of pH values from 5.0 to 7.5. Investigation of the biocatalyzed hydrolysis process from validamycin A to validoxylamine A with β-glucosidase revealed that both the substrate (validamycin A) and the product (validoxylamine A) inhibited β-glucosidase activity. The inhibition constant of the substrate K value was 5.01 mM, and that of the product K _ip value was 1.32 mM. This product inhibition was competitive.     

A simple route to porous ZnO and ZnCdO nanowires

Porous ZnO nanowires were obtained in an inexpensive and simple way by thermally oxidizing ZnSe nanowires in air. The morphologies of the precursor and resulted nanowires are almost identical. X-ray diffraction and energy-dispersive X-ray spectroscopy reveal that the zinc blende ZnSe nanowires were transformed into wurtzite ZnO nanowires after oxidation. Transmission electron microscope measurements indicate that the ZnO nanowires are polycrystalline and are composed of nanoparticles and nanopores. ZnCdO nanowires, which were seldom reported previously, have also been prepared in this way. Just like the ZnO nanowires, the ZnCdO nanowires also show the porous structure. Photoluminescence studies on both ZnO and ZnCdO nanowires show intense near-band edge emissions at room temperature. The transition from one kind of nanowires to another by simple thermal oxidization described in this paper may be applicable to some other compound semiconductors and may open a practical route to yield nanowires.     

A Mobile Precursor Determines Amyloid-β Peptide Fibril Formation at Interfaces

The aggregation of peptides into amyloid fibrils plays a crucial role in various neurodegenerative diseases. While it has been generally recognized that fibril formation in vivo may be greatly assisted or accelerated by molecular surfaces, such as cell membranes, little is known about the mechanism of surface-mediated fibrillation. Here we study the role of adsorbed Alzheimer's amyloid-β peptide (Aβ42) on surface-mediated fibrillation using polymer coatings of varying hydrophobicity as well a supported lipid bilayer membrane. Using single molecule fluorescent tracking and atomic force microscopy imaging, we show that weakly adsorbed peptides with two-dimensional diffusivity are critical precursors to fibril growth on surfaces. This growth mechanism is inhibited on the highly hydrophilic surface where the surface coverage of adsorbed peptides is negligible or on the highly hydrophobic surface where the diffusion constant of the majority of adsorbed peptides is too low. Physical properties that favor weakly adsorbed peptides with sufficient translational mobility can locally concentrate peptide molecules on the surface and promote inter-peptide interaction via two-dimensional confinement, leading to fibrillation at Aβ peptide concentration many orders of magnitude below the critical concentration for fibrillation in the bulk solution.     

Regular patterns generated by self-organization of ammonium-modified polymer nanospheres

Macroscopic regular stripe-crack patterns have been observed in the course of drying the aqueous suspensions of ammonium-modified polymer nanospheres. These forms emerged because the evaporation of dispersed water and self-assembly of nanospheres originates shrinkage during drying the aqueous suspensions. The drying condition plays an important role as well as the nature of the ammonium-modified polymer nanospheres for the stripe-crack pattern formation. By means of the vertical deposition method, directional stripe-crack patterns have been achieved in the macroscopic scale. Surprisingly, we have still noted an interesting secondary stripe pattern occurred spontaneously on the stripes.     

Controlling conformations and physical properties of meso-tetrakis(phenylethynyl)porphyrins by ring fusion: synthesis, properties and structural characterizations

The boron trifluoride-catalyzed Rothemund condensations of phenylpropargylaldehyde with 4,7-dihydro-4,7-ethano-2H-isoindole or 3,4-diethylpyrrole in dichloromethane at low temperature give 5,10,15,20-tetrakis(phenylethynyl)porphyrins bearing bicyclo[2.2.2]octadiene and octaethyl substituents, respectively. The former undergoes a retro Diels-Alder reaction to afford 5,10,15,20-tetrakis(phenylethynyl)benzoporphyrin quantitatively. The different conformations of the porphyrin periphery were determined by X-ray diffraction and their redox and spectroscopic properties have been investigated.     

Kinetic resolution of racemic secondary alcohols catalyzed by chiral diaminodiphosphine-Ir(I) complexes

Chiral diaminodiphosphine-Ir(I) complexes were found to efficiently catalyze enantioselective oxidation of racemic secondary alcohols in acetone. In the presence of base, oxidative kinetic resolution of the alcohols proceeded smoothly with excellent enantioselectivity (up to 98% ee) under mild conditions. [reaction: see text].