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991.
HO. radical is an aggressive reagent to abstract hydrogen from diverse substitutes and lead them to degradation, however, in
reaction of active oxygen species with lignins, complex phenolic polymers, in dispersed lignocellulose such as pulp for environment-benign
delignification, HO. radicals should be eliminated as more as possible to prevent cellulose from unfavorably concomitant degradation. A reaction
system of O3 is constructed under UV laser flash irradiation, and HO. radicals are controlled efficiently by it. A new mechanism is proposed, for the first time, that O. radicals generated from reaction of O3 with UV laser flash irradiation might be the contributor to scavenge HO. radicals. 相似文献
992.
Brunetto R Gutiérrez L Delgado Y Gallignani M Burguera JL Burguera M 《Analytical and bioanalytical chemistry》2003,375(4):534-538
A column-switching high-performance liquid chromatographic method with UV detection for the determination of cocaine (COC) and benzoylecgonine (BZE) in human blood plasma samples is described. The method uses an alkyl-diol-silica ADS-C18 extraction precolumn. A 50- micro L plasma sample was introduced to the ADS precolumn in order to separate the analytes from proteins and endogenous compounds. The fraction containing COC and BZE was back-flushed and transferred to an Alltech mixed-mode C(18)/cation-exchange analytical column for final separation. The validation of the method revealed quantitative recoveries from 95.0 to 99.0% for COC at three different concentrations (0.5, 1.0 and 2.0 micro g mL(-1)), and from 96.0 to 99.0% for BZE at the same concentration levels with coefficients of variation <4.00% (n=5). The detection limit (signal to noise ratio (S/N)>3) was 0.03 micro g mL(-1) for all the compounds with an injection volume of 50 micro L. However, it was possible to enhance the sensitivity further by injecting larger plasma volumes, up to 200 micro L, at the same optimal conditions. The overlap of sample preparation, analysis and reconditioning of the extraction column, increase the overall sample throughput to 5 samples h(-1). The developed method has been applied to human blood plasma samples from subjects suspected of cocaine abuse. 相似文献
993.
de Meijere A Kozhushkov SI Rauch K Schill H Verevkin SP Kümmerlin M Beckhaus HD Rüchardt C Yufit DS 《Journal of the American Chemical Society》2003,125(49):15110-15113
The enthalpies of formation [Delta(g)] of tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),10(14),11-heptaene (2, 1,2-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1-ene) and tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),8,10(14),11-octaene (3, 1,2,9,10-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1,9-diene) have been determined by measuring their heats of combustion in a microcalorimeter and their heats of sublimation by the transpiration method. Values of the strain energies (SE) [SE(2) = 34.7 kcal mol(-)(1), SE(3) = 42.0 kcal mol(-)(1)] have been derived from the gas-phase heats of formation and are compared with those from MM3 and PM3 calculations and with the corresponding value SE(1) = 30.1 kcal mol(-)(1) for the parent tricyclo[8.2.2.2(4,7)]hexadeca-1(13),4(16),5,7(15),10(14),11-hexaene (1, [2.2]paracyclophane). The higher strain energies of 2 and 3 (by 4.6 and 11.9 kcal mol(-)(1)) are in accord with the well-known increased reactivities of their aromatic rings as a consequence of their increased bending. As revealed by an X-ray crystal structure analysis, the bending in the monoene 2 corresponds to that of 1 and 3 at one of two bridging corners. 相似文献
994.
The paper presents a new method for the generation of acetaldehyde in the amounts that allow to calibrate the measuring system. The method is based on thermal decomposition of surface compounds at the range 130-190 °C, in which an acetaldehyde as the decomposition product is released. The synthetic pathway leading to the desired surface compounds is described. Investigations demonstrated that the synthesis of the compounds on the surface of the support material (silica gel) was carried out homogeneously. The technique proposed was used for the generation of gaseous standard mixtures containing acetaldehyde for the calibration of a thermal desorber-gas chromatograph-flame ionization detector system. 相似文献
995.
Douglas C. Miller Martin R. Johnson John J. Becker James A. Ibers 《Journal of heterocyclic chemistry》1993,30(6):1485-1490
The new 22-π, aromatic “pentaplanar” macrocycle, ozaphyrin ( 6 ), has been synthesized by a McMurry coupling of 5,5′-diformyl-4,4′-dipropyl-2,2′-bipyrrole ( 1 ) with 2,5-bis(5-formyl-4-propyl-2-pyrrolyl)furan ( 5 ). This synthetic pathway to ozaphyrin and its characterization by 1H nmr spectroscopy, uv-visible spectroscopy, cyclic voltammetry, and X-ray crystallography are described. The structure consists of layers of planar, staggered macrocycles stacked perpendicular to the α-axis. Ozaphyrin crystallizes with four formula units in the monoclinic space group C52h-P21/n in a cell of dimensions a = 10.481(7) Å, b = 17.353(17) Å, c = 18.726(12) Å, and β = 102.84(5)° (108 K). The structure has been refined on F2 (5171 unique reflections, 411 variables) to Rw(Fo2) = 0.165. The conventional agreement index R(F) is 0.074 for the 3289 reflections have Fo2>2o(Fo2). 相似文献
996.
As the relation of chirality and activities of drugs is researched deeply, people become to re-alize the clinic importance of chirality. The different enantiomers of a drug can have vastly differ-ent pharmacological activities, pharmacokinetic processes and toxicity[1,2]. The most well-docu- mented example is that of the drug substance thalidomide. Bitter lessons and scientific research promote the interest in single-enantiomer drugs, so the potential of the chiral drug market is enormous[3]. … 相似文献
997.
Turrio-Baldassarri L Battistelli CL Iamiceli AL 《Analytical and bioanalytical chemistry》2003,375(4):589-595
Pressurized Fluid Extraction (PFE) was evaluated for the extraction of polycyclic aromatic hydrocarbons (PAHs) and nitro-derivatives from diesel particulate matter. Extraction conditions were set up by performing several tests in which temperature, solvent strength, pressure, and static time were gradually increased. The results obtained on a laboratory test material made of a "lean" (low content of soluble fraction) Diesel particulate matter indicate that very severe conditions were needed in order to obtain better recoveries of the higher molecular weight molecules. Moreover, extraction efficiency seems to be influenced by the amount of soluble matter in the particulate, so that a "lean" particulate appears more difficult to extract. Recoveries of the deuterated standards of certain PAHs (i.e. indeno[1,2,3- cd]pyrene) were incomplete even with the toughest conditions tested. Experiments carried out on a certified material (SRM 1650 from NIST) also indicate that PFE can perform a better extraction of some of the PAHs than the method used for certification, but still incomplete. Comparison of results obtained on the SRM with different extraction techniques suggests that the composition of the extract varies considerably with the extraction technique and conditions. It is relevant to notice that recent Diesel engines produce leaner particulate: for future materials more drastic extraction conditions will be required. 相似文献
998.
In-situ tapping mode atomic force microscopy (TM-AFM), a powerful, high-resolution imaging technique for determining the structure of surfaces and ex-situ secondary ion mass spectroscopy (SIMS), a multielement, high-depth-resolution method, were used to examine the influence of increasing zinc contents in brass in the early stages of corrosion. Four different samples (pure Cu, pure Zn, Cu/Zn=90/10 wt% and Cu/Zn=70/30 wt%) were studied in order to determine their chemical behaviour under various atmospheric conditions. The in-situ TM-AFM investigations were carried out in synthetic air with 60% relative humidity (RH) and 80% RH with 250 ppb SO(2). The samples for the ex-situ SIMS experiments were weathered over a period of 60 h in 80% RH and 250 ppb SO(2). The in-situ TM-AFM investigations have shown that an increasing Zn content in brass increases the corrosion rate. 相似文献
999.
A very simple, highly sensitive and selective chemiluminescence (CL) method was established for the determination of cysteine. This method is based on the fact that the CL reaction of luminol and hydrogen peroxide can be greatly enhanced by cysteine. The CL intensities at maximum light emission were linearly correlated with the concentration of cysteine over the range of 2.0×10–8–6.0×10–6molL–1 with a detection limit of 7.5×10–9molL–1. The relative standard deviation was 1.7% for the determination of 1.0×10–7molL–1 cysteine (n=9). The feasibility of utilizing the proposed method for the determination of total concentration of cysteine in human serum was examined. 相似文献
1000.
Astrid Trost W. Kleib?hmer Karl Cammann 《Fresenius' Journal of Analytical Chemistry》1997,359(3):249-253
A rapid and uncomplicated method for the fractionation of PCBs leading to an isolation of the highly toxic non-ortho substituted
PCBs is described. The liquid chromatographic separation was achieved on a stationary phase consisting of activated carbon
and Celite 545. Using eluents with different polarity, isolation of the non-ortho substituted PCBs in a single fraction was
achieved. The fractions were analysed by GC/MS. The method was tested by the determination of non-ortho substituted PCBs in
technical mixtures (Aroclor 1254 and Aroclor 1242). The results were compared with those obtained by using an HPLC fractionation
on a porous graphitic carbon column. Finally, the micro-column fractionation was used for the determination of non-ortho substituted
PCBs in native soil samples.
Received: 5 March 1997 / Revised: 4 June 1997 / Accepted: 6 June 1997 相似文献