Two new xanthones isolated from the stem bark of Garcinia lancilimba

Two new xanthones, 1,5,6-trihydroxy-6',6'-dimethyl-2H-pyrano(2',3':3,4)-2-(3-methylbut-2-enyl)xanthone (1) and 1,6,7-trihydroxy-6',6'-dimethyl-2H-pyrano(2',3':3,2)-4-(3-methylbut-2-enyl)xanthone (2), have been isolated from the stem bark of Garcinia lancilimba (Guttiferae), together with six known xanthones. Their structures were identified on the basis of extensive spectral evidence including detailed 2D NMR and HR-MS data. Two new compounds showed moderate inhibitory effect on human breast cancer MDA-MB-435S cell line.     

Comparison of predicted native structures of Met-enkephalin based on various accessible-surface-area solvent models

We examine the variation and similarity of the native structures predicted from various accessible-surface-area solvent models for peptide Met-enkephalin. Both ECEPP/2 and ECEPP/3 force fields have been used in conjunction with ten different sets of accessible-surface-area parameterization. The native structures were determined by an implementation of the basin hopping Monte Carlo technique. The results suggest that the implicit solvent models examined in this study should be employed in computer simulations with extreme caution. In addition, the effect of fixing or not fixing the peptide angles omega has been examined. We conclude that fixing omega generally gives rise to a poor prediction.     

Production and Characteristics of the Whole-Cell Lipase from Organic Solvent Tolerant <Emphasis Type="BoldItalic">Burkholderia</Emphasis> sp. ZYB002

The thermostable and organic solvent tolerant whole-cell lipase (WCL) was produced by Burkholderia sp. ZYB002 with broad spectrum organic solvent tolerance. The production medium of the WCL was primarily optimized, which resulted in the maximum activity of 22.8 U/mL and the 5.1-fold increase of the WCL yield. The optimized culture medium was as follows (% w/v or v/v): soybean meal 2, soybean oil 0.5, manganese sulfate 0.1, K₂HPO₄ 0.1, olive oil 0.5, initial pH 6.0, inoculum density 2, liquid volume 35 mL in 250-mL Erlenmeyer flask, and incubation time 24 h. The biochemical characterization of the WCL from Burkholderia sp. ZYB002 was determined, and the results showed that the optimal pH and temperature for lipolytic activity of the WCL was 8.0 and 65°C, respectively. The WCL was stable at temperature up to 70°C for 1 h and retained 79.2% of its original activity. The WCL was highly stable in the pH range from 3.0 to 8.5 for 6 h. Ca²⁺, K⁺, Na⁺, NO₃⁻, etc. ions stimulated its lipolytic activity, whereas Zn²⁺ ion caused inhibition effect. The WCL was also relatively stable in n-butanol at a final concentration of 50% (v/v) for 24 h. However, the WCL was strongly inhibited in Triton X-100 at a final concentration of 10% (v/v). The WCL with thermal resistance and organic solvent tolerance showed its great potential in various green industrial chemical processes.     

Nanosheet-enhanced enantioselectivity in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols

The use of suitable chiral ligands is an efficient means of producing highly enantioselective transition-metal catalysts. Herein, we report a facile, economic, and effective strategy for the design of chiral ligands that demonstrate enhanced enantioselectivity and catalytic efficacy. Our simple strategy employs naturally occurring or synthetic inorganic nanosheets as huge and rigid planar substituents for, but not limited to, naturally available α-amino-acid ligands; these ligands were successfully used in the vanadium-catalyzed asymmetric epoxidation of allylic alcohols. The crucial role of the inorganic nanosheets as planar substituents in improving the enantioselectivity of the reaction was clearly revealed by relating the observed enantiomeric excess with the distribution of the catalytic centers and the accessibility of the substrate molecules to the catalytic sites. DFT calculations indicated that the LDH layer improved the enantioselectivity by influencing the formation and stability of the catalytic transition states, both in terms of steric resistance and H-bonding interactions.     

The use of ultrasound to enhance the degradation of the Basic Green by cast iron

The effect of pH, amount of cast iron and initial concentration on the removal ratio of Basic Green by cast iron combined with ultrasound was investigated. It was shown that the reduction of Basic Green was enhanced by ultrasound. In all combined systems, the decolorization efficiency is more than 95%, but removal ratio of CODcr decreased with the increasing pH or initial dye concentration and increased with the increase of the amount of cast iron.     

Observation of a near-threshold enhancement in the omega(phi) mass spectrum from the doubly OZI-suppressed decay J/psi-->gamma(omega)phi

An enhancement near threshold is observed in the omega(phi) invariant mass spectrum from the doubly Okubo-Zweig-Iizuka-suppressed decays of J/psi-->gamma(omega)phi, based on a sample of 5.8 x 10(7) J/psi events collected with the BESII detector. A partial wave analysis shows that this enhancement favors JP=0+, and its mass and width are M=1812(+19)(-26)(stat)+/-18(syst) MeV/c2 and Gamma=105+/-20(stat)+/-28(syst) MeV/c2. The product branching fraction is determined to be B(J/psi-->gammaX)B(X-->omega(phi))=[2.61+/-0.27(stat)+/-0.65(syst)]x10(-4).     

The direct electron transfer of myoglobin based on the electron tunneling in proteins

The electron tunneling of the protein-polypeptide interactions was observed in the study of direct electron transfer of the myoglobin (Mb) on the electrode surface. The Mb was selected as a redox active protein and gelatine was selected to couple with Mb to form an electron tunneling. The electrochemical results indicated the presence of the electron tunneling and the direct electron transfer. The circular dichroism spectra suggested that the beta-sheet chain of gelatine could interact with alpha-helical chain to form an electron tunneling to promote the protein direct electrochemistry. The SDS-PAGE results proved that the electron tunneling between Mb and gelatine was noncovalent hydrogen bonds. The immobilized Mb showed a couple of quasi-reversible redox peaks with a formal potential of -0.37V (vs SCE) in 0.1 M pH 7.0 PBS. The modified electrodes displayed a rapid amperometric response to the reduction of oxygen, H2O2, and nitrite.     

Maoecrystal Z, a cytotoxic diterpene from Isodon eriocalyx with a unique skeleton

[structure: see text] A novel diterpene with an unprecedented tetracyclic 6,7:8,15-di-seco-7,20-olide-6,8-cyclo-ent-kaurane skeleton, named maoecrystal Z (1), has been isolated from the leaves of a Chinese medicinal herb, Isodon eriocalyx (Labiatae). Its structure was determined by comprehensive NMR and MS spectroscopic analysis coupled with single-crystal X-ray crystallographic diffraction. Compound 1 exhibited comparable inhibitory effect against human K562 leukemia, MCF7 breast, and A2780 ovarian tumor cells with IC(50) = 2.90, 1.63, and 1.45 microg/mL and with camptothecin and paclitaxel as the positive controls.     

A numerical scheme to diagnose interferences in gas chromatography-mass spectrometry quantitation of coeluting isotopically labeled and unlabeled counterparts with partially overlapping ion profiles

Quantitation of chromatographically coeluting compounds with partially overlapping mass profiles is a challenging task, especially if only a low-resolution mass spectrometer is available. To examine whether theoretical predictions can be utilized to determine the appropriate concentration ranges of the coeluting compounds that satisfy the non-interfering condition, we utilized an algorithm based upon a two-component model to compare the experimentally measured and predicted quantitation errors. Selected unlabeled and 13C-labeled polychlorinated biphenyl (PCB) congeners were investigated as model compounds. Standard solutions containing various concentration ratios of the unlabeled and 13C-labeled PCB congeners were analyzed, and the data were used to compare with theoretical predictions derived from the chlorine isotopic distributions (35Cl and 37Cl). Good agreements between experimental predictions and theoretical predictions were found on the magnitude of interferences for quantitation of 13C-labeled PCB congeners, as well as on the variability of the quantitation errors with the concentration ratio of 13C-labeled and unlabeled PCB counterparts. In addition, the magnitude of interferences considered in the present study was highly dependent upon the number of coexisting ions included for quantitation and their relative abundances in the mass spectrum. All these results suggest that the magnitude of interferences in quantifying a pair of coeluting compounds with partially overlapping mass spectral profiles can be effectively determined and minimized by carefully selecting the concentration ratio of the coeluting compounds and/or the number of quantitation ions. Finally, the selection of the experimental parameters to satisfy the non-interfering condition can be made purely on the basis of theoretical considerations.     

Novel 1,4-homofragmentation via an alpha-lactone

Conversion of an alpha,alpha-dichloroester to the corresponding alpha-keto acid was unexpectedly complicated by a novel 1,4-homofragmentation. Investigation of the kinetics of this reaction revealed a mechanism involving an alpha-lactone intermediate, which can lead to both the desired alpha-keto acid and the 1,4-homofragmentation, with the product distribution being dependent upon reaction conditions. This information allowed development of a process that affords the alpha-keto acid exclusively and should be generally applicable to the preparation of alpha-keto acids from alpha,alpha-dichloroesters or acids.