固相萃取光度法测定饮用水中挥发酚的研究

研究了用Waters Sep-Park-C18小柱固相萃取光度法测定饮用水中挥发酚的方法。水样中经水汽蒸馏分离后的挥发酚，用4－氨基安替比林显色，显色产物可用C18固相萃小柱萃取、乙醇洗脱后用分光光度法测定。方法污染小，操作简便，便于批量样品处理，用于饮用水中挥发酚的测定，结果令人满意。     

5C + 1S] annulation: a facile and efficient synthetic route toward functionalized 2,3-dihydrothiopyran-4-ones

[reaction: see text] A facile and efficient synthetic route toward highly substituted 2,3-dihydrothiopyran-4-ones 2 has been developed via a formal [5C + 1S] annulation of readily available alpha-alkenoyl ketene-(S,S)-acetals 1 with sodium sulfide nonahydrated salt (Na2S x 9H2O) and utilized in the synthesis of 2-(4-chlorophenyl)-6-(morpholin-4-yl)-4H-thiopyran-4-one 5l, an inhibitor of DNA-dependent protein kinase (DNA-PK).     

A simple and efficient biphasic method for the preparation of 4-nitrophenyl N-methyl- and N-alkylcarbamates

Treatment of 4-nitrophenyl chloroformate with alkylammonium hydrochloride salts and solid anhydrous Na₂CO₃ in either CH₂Cl₂ or CH₃CN gave 4-nitrophenyl N-methylcarbamate and other N-alkylcarbamate analogues in excellent yields. Of particular interest is the observation that 4-nitrophenyl N-methylcarbamate, a safer alternative to the highly toxic methyl isocyanate, is obtained in quantitative yield (?95% pure as determined by ¹H NMR) after simple filtration and solvent evaporation.     

Structural changes in the monomeric despentapeptide (B30-B26) insulin crystal

Insulin modified by the removal of its 5 B chain C terminal residues is monomeric but remains substantially potent. The crystal structures of the beef and insulin (dpi) with two molecules in the asymmetric unit has been determined by x-ray analysis. The 3-dimensional structure ofdpi proves to be generally similar to that of native molecule in 2Zn insulin. More detailed comparison reveals that the slight differences in the two independent molecules of beefdpi are distributed uniformly throughout the structure in contrast to insulin in 2Zn insulin, where the structural changes are concentrated in specific regions. The loss of symmetry in thedpi crystal appears to be the inability of the A9 serine to pack effectively in the C2 cell. The efficient packing of the sheepdpi molecule whose crystal structure has also been determined and where A9 is glycine supports this conclusion.     

Physical and chemical properties of a durably efficacious ammonium bicarbonate as a fertilizer and its yield-increasing mechanism

A new fertilizer of cocrystal type,known as durably efficacious ammonium bicarbonate (DEAB),has been developed by adding a certain amount of dicyandiamide (DCD) as an ammonia-stabilizing agent to ammonium bearbenate(AB)during the process of its production.As compared with AB,DEAB was found to have a reduction of direct volatilization loss by 53%,a fertilizer availability period prolonged from 35-45 to 90-110 d,and an increase in the rate of nitrogen in fertilizer being utilized by 5.9%-10.2%,and a saving of the amount of fertilizer to be ap-phed by 20%-30% for the same level of yield,or an increase of the crop yield by over 10% for the same level of ni-tregen fertilization;in addition,it was found to show usually a function of promoting the crop to early mature.It can be apptied as basal dressing all in one time to soil and thus also used as a labour-saving and crop yield-increasing fertil-izer for is non-mtertillage,plastics film covering and water-saving agriculture     

Two new megastigmane O-glucopyranosides from the leaves of Broussonetia papyrifera

Two new megastigmane O-glucopyranosides,named (2R,3R,5R,6S,9R)-3-hydroxy-5,6-epoxy-β-ionol-2-O-β-D-glucopyrano- side(1) and (2R,3R,5R,6S,9R)-3-hydroxyl-5,6-epoxy-acety-β-ionol-2-O-β-D-glucopyranoside(2) together with six known mega- stigmanes,were isolated from the leaves of Broussonetia papyrifera (Linn.) Vent.Their structures were established by chemical methods and spectroscopic techniques including 2D NMR.     

Overlapping spectra resolution using non-negative matrix factorization

Non-negative matrix factorization (NMF), with the constraints of non-negativity, has been recently proposed for multi-variate data analysis. Because it allows only additive, not subtractive, combinations of the original data, NMF is capable of producing region or parts-based representation of objects. It has been used for image analysis and text processing. Unlike PCA, the resolutions of NMF are non-negative and can be easily interpreted and understood directly. Due to multiple solutions, the original algorithm of NMF [D.D. Lee, H.S. Seung, Nature 401 (1999) 788] is not suitable for resolving chemical mixed signals. In reality, NMF has never been applied to resolving chemical mixed signals. It must be modified according to the characteristics of the chemical signals, such as smoothness of spectra, unimodality of chromatograms, sparseness of mass spectra, etc. We have used the modified NMF algorithm to narrow the feasible solution region for resolving chemical signals, and found that it could produce reasonable and acceptable results for certain experimental errors, especially for overlapping chromatograms and sparse mass spectra. Simulated two-dimensional (2-D) data and real GUJINGGONG alcohol liquor GC-MS data have been resolved soundly by NMF technique. Butyl caproate and its isomeric compound (butyric acid, hexyl ester) have been identified from the overlapping spectra. The result of NMF is preferable to that of Heuristic evolving latent projections (HELP). It shows that NMF is a promising chemometric resolution method for complex samples.     

Theoretical Study on the Isomerization Mechanism of Enol Ester from 2-Acyl-1, 3-cyclohexanediones

The present paper employed density function theory to investigate two reaction pathways for isomerization of enol ester proposed by Yang(path a) and the present authors(path a), respectively. The base catalytic effects of solvent triethylamine on these two reactions were also evaluated. It is demonstrated that path B is more preferable than path a due to low barrier height for the rate-determining step.     

Stability studies and purification procedure for nitrite solutions in view of the preparation of isotopic reference materials

The lack of reference materials, accurately certified for nitrite, is a problem in view of the importance of this species for environmental and medical reasons. This work outlines a plan for the preparation of nitrite isotopic reference materials (IRMs) in the form of high purity solutions, certified for their nitrite-nitrogen isotopic composition and nitrite concentration. To achieve the desired accuracy (expanded uncertainty U with a coverage factor k=2 of 相似文献