Two new ent-kaurane diteroenoids from Isodon excisoides

Two new ent-kaurane diterpenoids taihangexcisoidesin A and B(1 and 2),were isolated from the EtOAc extract of the leaves of Isodon excisoides.Their structures were determined on the basis of spectroscopic methods.     

Synthesis and fluorescence properties of cerium-KMgF_3 through a solvothermal process

Phosphor of KMgF_3:Ce~(3+)is synthesized through solvothermal method at 180℃and characterized by means of X-ray powder diffraction(XRD)and environment scanning electron microscopy(ESEM).X-ray photoelectron spectroscopy(XPS)is applied to the study of the energy band structure of KMgF_3:Ce~(3+)and confirms the oxygen content of the product is very low.The fluorescence spectra of the rare-earth ion-doped KMgF_3 is investigated by the fluorescence spectrophotometer.In the emission spectra,there is a broadban...     

Highly efficient removal of allyloxycarbonyl(Alloc)function provides a practical orthogonal protective strategy for carbohydrates

Highly efficient removal of allyloxycarbonyl(Alloc)group was achieved in the presence of CH3COONH4,Pd[P(C6H5)3]4,and NaBH4 in MeOH-THF,within 5 min in almost quantitative yields(90%,isolated yield)without affecting acetyl,benzoyl,isopropylidene,benzylidene,allyl,benzyl,benzyl carbonate,or azido groups.     

Interaction of zinc oxide clusters with molecules related to the sulfur vulcanization of polyolefins ("rubber")

The vulcanization of rubber by sulfur is a large‐scale industrial process that is only poorly understood, especially the role of zinc oxide, which is added as an activator. We used the highly symmetrical cluster Zn₄O₄ (T_d) as a model species to study the thermodynamics of the initial interaction of various vulcanization‐related molecules with ZnO by DFT methods, mostly at the B3LYP/6‐31+G* level. The interaction energy of Lewis bases with Zn₄O₄ increases in the following order: CO62H₄3H₆2S₂<1,4‐C₅H₈2O2S3N?CH₃COO^?. The corresponding binding energies range from ?57 to ?262 kJ mol^?1. However, Brønsted acids react with the Zn₄O₄ cluster with proton transfer from the ligand molecule to one of the oxygen atoms of Zn₄O₄, and these reactions are all strongly exothermic [binding energies [kJ mol^?1] in parentheses: H₂O (?183), MeOH (?171), H₂S (?245), MeSH (?230), C₃H₆ (?121), and CH₃COOH (?255)]. The important vulcanization accelerator mercaptobenzothiazole (C₇H₅NS₂, MBT) containing several donor sites reacts with the Zn₄O₄ cluster with proton transfer from the NH group to one of the oxygen atoms of ZnO, and in addition the exocyclic thiono sulfur atom and the nitrogen atom coordinate to one and the same zinc atom, resulting in a binding energy of ?247 kJ mol^?1. A second isomer of [(MBT)Zn₄O₄] with a strong O? H???N hydrogen bond rather than a Zn? N bond is only slightly less stable (binding energy ?243 kJ mol^?1). The NH form of free MBT is 36 kJ mol^?1 more stable than the tautomeric SH form, while the sulfurized MBT derivative benzothiazolyl hydrodisulfide C₇H₅NS₃ (BtSSH) is most stable with the connectivity >CSSH.     

Effects of emulsifier charge and concentration on pancreatic lipolysis. 1. In the absence of bile salts

An in vitro study is performed with sunflower oil-in-water emulsions to clarify the effects of type of used emulsifier, its concentration, and reaction time on the degree of oil lipolysis, α. Anionic, nonionic, and cationic surfactants are studied as emulsifiers. For all systems, three regions are observed when surfactant concentration is scaled with the critical micelle concentration, C(S)/cmc: (1) At C(S) < cmc, α ≈ 0.5 after 30 min and increases up to 0.9 after 4 h. (2) At C(S) ≈ 3 × cmc, α ≈ 0.15 after 30 min and increases steeply up to 0.9 after 2 h for the cationic and nonionic surfactants, whereas it remains around 0.2 for the anionic surfactants. (3) At C(S) above certain threshold value, α = 0 for all studied surfactants, for reaction time up to 8 h. Additional experiments show that the lipase hydrolyzes molecularly soluble substrate (tributirin) at C(S) > cmc, which is a proof that these surfactants do not denature or block the enzyme active center. Thus, we conclude that the mechanism of enzyme inhibition by these surfactants is the formation of a dense adsorption layer on an oil drop surface, which displaces the lipase from direct contact with the triglycerides.     

Positional targets for lingual consonants defined using electromagnetic articulography

The study examined the positional targets for lingual consonants defined using a point-parameterized approach with Wave (NDI, Waterloo, ON, Canada). The overall goal was to determine which consonants had unique tongue positions with respect to other consonants. Nineteen talkers repeated vowel-consonant-vowel (VCV) syllables that included consonants /t, d, s, z, , k, g/ in symmetrical vowel contexts /i, u, a/, embedded in a carrier phrase. Target regions for each consonant, characterized in terms of x,y,z tongue positions at the point of maximum tongue elevation, were extracted. Distances and overlaps were computed between all consonant pairs and compared to the distances and overlaps of their contextual targets. Cognates and postalveolar homorganics were found to share the location of their target regions. On average, alveolar stops showed distinctively different target regions than alveolar fricatives, which in turn showed different target region locations than the postalveolar consonants. Across talker variability in target locations was partially explained by differences in habitual speaking rate and hard palate characteristics.     

Hygroscopic growth of aerosol scattering coefficient:A comparative analysis between urban and suburban sites at winter in Beijing

A humidity controlled inlet system was developed to measure the hygroscopic growth of aerosol scattering coefficient in conjunction with nephelometry at an urban site of Chinese Academy of Meteorological Sciences (CAMS) in Beijing and a rural site at Shangdianzi Regional Background Air Pollution Monitoring Station (SDZ) outside Beijing during winter, from December 2005 to January 2006. Measurements were carried out at a wavelength of 525 nm with an Ecotech M9003 nephelometer. The hygroscopic growth function (or factor) of the aerosol scattering coefficientf(RH) increased continuously with increasing relative humidity (RH) and showed no obvious "step-like" deliquescent behavior at both sites during the experiment. The average growth factorf(RH) at the SDZ site could reach 1.5 when RH increased from less than 40% to 92%, and to 2.1 at the CAMS site when RH increased from less than 40% to 93%. The average hygroscopic growth factor at a relative humidity of 80%, f(RH=80±1%), was found to be about 1.26±0.15 at CAMS and 1.24±0.11 at SDZ. Further analysis indicated that under relatively polluted conditions, the average hygroscopic growth factor was higher at the CAMS site than that at the SDZ site. However, under relatively clean air conditions, the difference between the two sites was small, showing a hygroscopic growth behavior similar to those of burning biomass or blowing dust. These results reflected the different characteristics of aerosol types at the two sites.     

HYDROGENATION OF NITROBENZENE TO FORM ANILINE IN LIQUID PHASE AT ATMOSPHERIC PRESSURE

Aromatic amine compounds and their derivatives are important intermediates of fine chemicals like dye and medicine.The former hydrogenation catalyst has many problems,such as environment pollution caused by old technology,strict reaction condtion,complicated equipment,bad property of catalyst and so on.Holy ^[1] firstly reported the hydrogenation of nitrobenzene on modified polystyrene Pd catalyst.But how to improve the activity,selectivity and stability of the polymer suppoorter catalyst needs to studyfurther.We prepared a series of polymer supported catalysts by the methods of adsorption and mechanical mixting ,selected a high active catalyst Pd-Ah-1 by observing the hydrogenation of nitrobenzene.     

Charge‐Transfer Complexes Between the Sulfur Molecules SO2, S2O,S3, SONH,and SOCl2 and the Amine Donors NH3 and NMe3 — A theoretical Study

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