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101.
Won Sick Woo Sam Sik Kang Otto Seligmann V. Mohan Chari Hildebert Wagner 《Tetrahedron letters》1980,21(44):4255-4258
From the seeds of Phytolacca americana two new lignans, Americanin B and D, have been isolated and their structures elucidated mainly by spectroscopic methods 相似文献
102.
K. Wagner 《Angewandte Chemie (International ed. in English)》1970,9(1):50-54
Addition compounds of formic acid with tertiary organic bases in ratios higher than that required for salt formation (3:1 and 2:1 adducts) contain formic acid in a highly activated form. In particular, the 3:1 adducts of formic acid with trimethylamine and triethylamine are liquid reducing agents that are convenient to handle and are suitable for use in many selective reductions. These addition compounds have a surprisingly strong reducing action on sulfur dioxide, which is rapidly converted, even at low concentrations, into crystalline rhombic sulfur. Sulfones and polysulfones can be prepared in good yields by three-component reactions from activated formic acid, sulfur dioxide, and polarized vinyl compounds. 相似文献
103.
A micro determination for free uronic acids based on Tollens' reaction is proposed. Sources of error in earlier methods are avoided by the use of phosphoric acid, a reagent solution in glacial acetic acid, and extraction of the dye with toluene. Free glucuronic acid can be determined in presence of glucuronosides of the phenol-ether type up to molar ratios of ca. 1 : 5. Reliable results can also be obtained in the presence of other carbohydrates. 相似文献
104.
Nanowires of an iodine containing Pb-Sb-sulfosalt have been synthesized by chemical vapor transport. Their structure was studied using high-resolution transmission electron microscopy and X-ray powder diffraction. The lattice parameters show values equal to a=4.9801(4) nm, b=0.41132(8) nm (with two-fold superstructure), c=2.1989(1) nm and β=99.918(6)°. These parameters and the results of a multislice simulation are in good agreement with the mineral pillaite, Cu0.10Pb9.16Sb9.84S22.94Cl1.06O0.5 (space group C2/m, a=4.949(1) nm, b=0.41259(8) nm, c=2.1828(4) nm, and β=99.62(3)°). Microprobe and EDX analyses yielded a chemical composition of Cu0.507(5)Pb8.73(9)Sb8.15(8)I1.6S20.0(2) which is close to natural pillaite but contains no oxygen and iodine instead of chlorine. The structure of the investigated material is based on chains of M-S polyhedra (M=Pb or Sb) typical for the architecture of sulfosalts implying iodine atoms in trigonal prismatic coordination with Pb atoms from the M-S polyhedra of neighboring chains. The [010] superstructure of the specimen was found to be unstable under electron beam irradiation with a rapid decrease of the b lattice parameter from 0.8 to 0.4 nm within 5 min. 相似文献
105.
This work presents a study of the thermal
degradation of ultra-high molecular mass polyethylene (UHMWPE) stabilized
with natural (α-tocopherol and carvacrol) and synthetic antioxidants.
Thermogravimetric analysis in dynamic mode was used to determine the apparent
activation energies of different samples. The stabilization of UHMWPE with
low concentrations (around 0.3%) of α-tocopherol is enough to obtain
an efficient thermal performance of the polymer. Carvacrol is also a good
stabilizer for UHMWPE, but at higher concentration than in the case of α-tocopherol.
The comparison of apparent activation energy between samples with natural
and synthetic antioxidants in similar concentration shows that α-tocopherol
is a better stabilizer in terms of their thermal performance. 相似文献
106.
Wagner?M.?Teles Flávia?C.?Machado Carlos?A.?Montanari Carlos?A.?L.?FilgueirasEmail author Terence?C.?Jenkins 《Transition Metal Chemistry》2005,30(6):733-737
The mesoionic compound, 1,4,5-triazole-2-thiolate, is a versatile ligand, capable of binding metal centres in different ways. The present study shows how it reacts with the bridging platinum(II) complex μ-dichlorobis[(chlorotriethylphosphineplatinum(II)], [Pt2(PEt3)2Cl4], originating a bimetallic complex. Both the sulphur atom and nitrogen 3 behave as basic sites, coordinating different platinum centres. An interesting isomerization process, shown by 31P{1H} n.m.r. spectroscopy, occurs at the S-bonded platinum moiety, resulting in a fluxional behaviour of the complex. It is also shown to target CT-DNA with moderate binding affinity.To the memory of Dr. Wagner M. Teles (1971–2004). 相似文献
107.
It is possible directly to separate and analyse, quantitatively and qualitatively, the valepotriates from Valeriana crude extracts or from commercial Valeriana preparations by high-performance liquid chromatography. The separations are achieved on 4 or 8 mm I.D. columns packed with silica gel (particle size 10 micron) with n-hexane-ethyl acetate mixtures as eluent. A refractive index detection system is necessary for determining all of the valepotriates. If the concentration differences between didrovaltratum and valtratum are very great, an ultraviolet (UV) detector must be used and the determination must be conducted in two steps. For valtratum drugs UV detection alone will suffice. As internal standards p-dimethylaminobenzaldehyde should be used for extracts and preparations from valtratum races, and benzaldehyde in the presence of didrovaltratum races. This determination is superior to the combined thin-layer chromatographic-hydroxamic acid method used hitherto with respect to time consumption, precision, and sensitivity. 相似文献
108.
Naringenin is a natural widespread flavanone occurring in different foodstuffs that presents several important biological activities. Although its properties are well documented, its mechanisms of action are still controversial. The present article reports a conformational analysis of naringenin, using the semiempirical AM1 and ab initio methods, at the Hartree–Fock level of theory. The 3-21G, 3-21G*, 6-31G, and 6-31G** basis sets were used. The electron correlation effects were included through the Møller–Plesset second-order perturbation theory. The solvation of naringenin has been investigated through the standard SCRF, the supermolecule (SM), and the combined SM/SCRF models. The results have shown that there are two degenerate forms of naringenin, differing mainly by the orientation of a hydroxyl group (C4—OH). The energy barrier for the interconversion between them is ca. 6 kcal.mol–1, suggesting some conjugation between the -system of the aromatic B ring and the hydroxyl group (C4—OH). 相似文献
109.
Wagner HP Pepich BV Frebis CP Hautman DP Munch DJ Jackson PE 《Journal of chromatographic science》2001,39(6):255-259
The development of the U.S. Environmental Protection Agency (EPA) Method 317.0 is initiated to provide a sufficiently sensitive and fundamental technique for the compliance monitoring of trace levels of bromate in drinking water. After a comparative evaluation of Method 317.0 and elimination of a chlorite interference, this method is tested by a collaborative study in order to determine the precision and bias of the method and evaluate its potential role as a future compliance-monitoring method for inorganic disinfection by-products (DBPs) and trace bromate. This technique provides a practical method for future compliance monitoring for all of the inorganic oxyhalide DBPs including trace concentrations of bromate. 相似文献
110.
An unmediated hydrogen peroxide biosensor based on hemoglobin incorporated in a montmorillonite membrane 总被引:1,自引:0,他引:1
Hemoglobin was incorporated in a montmorillonite membrane. Electrochemical and spectroscopic studies revealed that the electron transfer reactivity and peroxidase activity of the protein were both enhanced. Nevertheless, its structure was still maintained native-like in the membrane. An unmediated hydrogen peroxide biosensor was accordingly prepared. The calibration plot of this H202 sensor was linear in the range of 1.0 x 10(-6)-6.0 x 10(-4) mol L(-1). The relative standard deviation was 3.1% for six successive determinations at a concentration of 1.0 x 10(-4) mol L(-1). The detection limit was 6.0 x 10(-7) mol L(-1). Possible interferences in real sample analyses are discussed. 相似文献