Chemical constituents from the colombian medicinal plant Niphogeton ternata

Two coumarins and one polyacetylene, 5-0-(3-chloro-2-hydroxy-3-methylbutyl)-8-methoxypsoralen (1), 2',3'-dihydro-jatamansin (2), and 10-chloro-1-heptadecene-4,6-diyne-3,8,9-triol (3), along with 15 known compounds (4-18), were isolated from the methanol extract of Niphogeton ternata. Their structures were elucidated by spectroscopy.     

电感耦合等离子体原子发射光谱法测定钛酸钡纳米粉体中7种杂质元素

钛酸钡纳米粉体样品用盐酸溶解,在所得样品溶液中用电感耦合等离子体原子发射光谱法测定了以氧化物存在于样品中的7种杂质元素(包括镁、锶、钾、钠、铝、硅及铁),对测定的光谱条件进行了试验并优化达到上述各元素的测定上限为0.1%(质量分数).测得方法的检出限(3S/b)为(单位μg·L-1):2.0(铝),1.0(铁),20.0(钾),0.2(镁),4.0(钠),3.0(硅)及0.5(锶).应用此方法分析了两件实样,所得结果的相对标准偏差(n=6)小于等于2.0%,对其中4种杂质元素(镁、钾、钠和锶)同时用HG/T 3587-1999标准中的方法作分析校核,所得结果与此方法结果一致.     

Cupaniol, a New branched polyprenol, from Cupania latifolia

A new branched polyprenol, designated cupaniol, has been isolated from the methanol extract of the leaves of Cupania latifolia (Sapindaceae). The structure was determined to be (2E,6E,12E,16E)-3,7,13,17,21-pentamethyl-10-(1-methylethenyl)-2,6,12,16,20-docosapentaen-1-ol on the basis of spectral analysis and conversion to a known compound.     

The role of fiber-matrix compatibility in vacuum processed natural fiber/epoxy biocomposites

Cellulose - Utilization of raw natural fibers is a research topic of interest for achieving low-cost and ecofriendly composite materials with properties including low density and high specific...     

Thermochronology of the South American platform in the state of São Paulo, Brazil, through apatite fission tracks

The fission-track method (FTM) in apatite was applied to 45 samples collected in the Serra da Mantiqueira (Mantiqueira mountain range), the Serra do Mar (Mar mountain range), regions next to these mountain ranges and the coastal region between Ubatuba and Santos in the State of São Paulo, Brazil, to study the thermochronology of the South American Platform in southeast Brazil and its influence on Santos and Campos basins. The data presented in this work complement the previously presented data on the same region (Tello Saenz et al., 2003. J. S. Am. Earth Sci. 15, 765–774) with 31 new samples analyzed. The weighted mean of the corrected ages from high Mantiqueira (around 1000 m), , coincides with the South Atlantic opening. The fact that its thermal history starts at a relatively low temperature suggests that the age of would be the formation age of Serra da Mantiqueira due to a rapid pulse, in which tracks had no time to be retained at the closure temperature, that is . The Serra do Mar presents a more complicated thermal history, with several reactivations indicated by the changes in the slope of its cooling curve. The thermal histories obtained in the regions next to these mountain ranges are compatible with the results mentioned above. The Santos Basin has unconformities that agree with changes in the slope thermal histories of the studied region.     

Direct chemical method for preparing 2,3-epoxyamides using sodium chlorite

A direct method for preparing 2,3-epoxyamides from tertiary allylamines via a tandem C-H oxidation/double bond epoxidation using sodium chlorite is reported. Apparently, the reaction course consists of two steps: (i) allylic oxidation of the starting allylamine to corresponding unsaturated allylamide with sodium chlorite followed by (ii) epoxidation of the allylamide to the 2,3-epoxyamide mediated by hypochlorite ion, which is formed in situ by reduction of sodium chlorite. The reaction conditions tolerate the presence of free hydroxyl groups and typical functional groups such as TBS, aryl, alkyl, allyl, acetyl, and benzyl groups; however, when an activated aromatic ring (e.g., sesamol) is present in the substrate, the use of a scavenger is necessary.     

Analysis of why boron avoids sp2 hybridization and classical structures in the BnHn+2 series

We performed global minimum searches for the B(n) H(n+2) (n=2-5) series and found that classical structures composed of 2c-2e B-H and B-B bonds become progressively less stable along the series. Relative energies increase from 2.9?kcal?mol(-1) in B(2) H(4) to 62.3?kcal?mol(-1) in B(5) H(7). We believe this occurs because boron atoms in the studied molecules are trying to avoid sp(2) hybridization and trigonal structure at the boron atoms, as in that case one 2p-AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p-AOs and avoiding having one 2p-AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron-hydride clusters as well as for pure boron clusters and boron compounds in general.     

Synthesis and DPPH radical scavenging activity of prenylated phenol derivatives

The synthesis of twenty six prenylated phenols derivatives is reported. These compounds were obtained under mild conditions via Electrophilic Aromatic Substitution (EAS) coupling reactions between phenol derivatives containing electron-donor subtituents and 3-methyl-2-buten-1-ol using BF(3)×OEt(2). Dialkylations were also produced with this method. The formation of a chroman ring by intramolecular cyclization between a sp2 carbon from the prenyl group with the hydroxyl substituent in the ortho position occurred with some phenols. All the synthesized compounds were evaluated as antioxidants according to a DPPH radical scavenging activity assay. IC(50) values of five synthesized compounds indicated they were as good antioxidants as Trolox?.     

Scope of partial least‐squares regression applied to the enantiomeric composition determination of ketoprofen from strongly overlapped chromatographic profiles

Valuable quantitative information could be obtained from strongly overlapped chromatographic profiles of two enantiomers by using proper chemometric methods. Complete separation profiles where the peaks are fully resolved are difficult to achieve in chiral separation methods, and this becomes a particularly severe problem in case that the analyst needs to measure the chiral purity, i.e., when one of the enantiomers is present in the sample in very low concentrations. In this report, we explore the scope of a multivariate chemometric technique based on unfolded partial least‐squares regression, as a mathematical tool to solve this quite frequent difficulty. This technique was applied to obtain quantitative results from partially overlapped chromatographic profiles of R‐ and S‐ketoprofen, with different values of enantioresolution factors (from 0.81 down to less than 0.2 resolution units), and also at several different S:R enantiomeric ratios. Enantiomeric purity below 1% was determined with excellent precision even from almost completely overlapped signals. All these assays were tested on the most demanding condition, i.e., when the minor peak elutes immediately after the main peak. The results were validated using univariate calibration of completely resolved profiles and the method applied to the determination of enantiomeric purity of commercial pharmaceuticals.