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991.
T. A. Khan W. D. Lauppe H. A. Selič H. Lawin G. Sadler M. Shaanan K. Sistemich 《Zeitschrift für Physik A Hadrons and Nuclei》1975,275(3):289-296
A windowless Si(Li) electron detector has been used in conjunction with the gas filled fission product separator JOSEF to study totally converted transitions in Zr and Mo isotopes. The existence of twoβ-decay modes in96Y,98Y and100Nb is confirmed. The half-lives of theβ-decaying levels feeding O 2 + states in96Zr and98Zr are 6.0 ± 0.4 sec and 0.60±0.05 sec respectively. A search for other first excited O 2 + states shows that no such states are apparent in100Zr and104Mo. 相似文献
992.
Asymmetric catalytic epoxidation of alkenes such as styrenes, chromenes and indene using transition metal complexes both inhomogeneous and heterogeneous phase has been discussed in this review. The various strategies to make the catalysts recyclable by introducing in-built phase transfer ability, converting these to dimeric form, exchanging into clays and supporting on polymeric or inorganic supports are discussed at length. 相似文献
993.
M. Niyaz Khan 《国际化学动力学杂志》2002,34(2):95-103
The kinetics of the aqueous cleavage of N‐ethoxycarbonylphthalimide (NCPH) in CH3NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH ENMBC A B , where ENMBC, A , and B represent ethyl N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)benzoyl]carbamate, N‐hydroxyl group cyclized product of ENMBC, and o ‐(N‐methyl‐N‐hydroxycarbamoyl)benzoic acid, respectively. The rate constant k1 obs at a constant pH, obeys the relationship k1 obs = kw + knapp [Am]T + kb[Am]T2, where [Am]T is the total concentration of CH3NHOH buffer and kw is first‐order rate constant for pH‐independent hydrolysis of NCPH. Buffer‐dependent rate constant kb shows the presence of both general base and general acid catalysis. Both the rate constants k2 obs and k3 obs are independent of [Am]T (within the [Am]T range of present study) at a constant pH and increase linearly with the increase in aOH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95–103, 2002 相似文献
994.
Commercial glucooligosaccharide mixtures (Polycose) and polysaccharide hydrolysates (acid and enzymatic) were fractionated by hydrophilic interaction chromatography and observed by pulsed amperometric detection. Seven peaks were observed when 625 ng of glucose oligomers in Polycose were fractionated. The between-run precision of retention times (n = 10, 100 μg, 15 peaks) ranged from a relative standard deviation (R.S.D.) of 0.09 to 0.40%; between-run precision of peak areas (n = 10) for the same separations had values that ranged from 2.66 to 14.4%. Injection-to-injection time was 48 min. When polysaccharide hydrolysates were fractionated using a gradient program capable of resolving all of the oligosaccharide species, dextran-derived -(1→6)- glucooligosaccharides were retained to a greater degree than amylose-derived -(1→4)-glucooligosaccharides, which were retained to a greater degree than β-(2→1)-fructooligosaccharides derived from inulin. Excluding the peaks that eluted before glucose or fructose, 25 to 35 peaks were observed after fractionation of the hydrolysates. Differences in elution profiles were observed between acid and enzymatic hydrolysis products of the same polysaccharide as well as between hydrolysis products of different polysaccharides. In conjunction with high-performance size-exclusion chromatography, the method demonstrated the effect of preheating starch before hydrolysis with isoamylase. 相似文献
995.
Symmetrical 1,3-disubstituted ureas and cyclic ureas have been synthesized from corresponding isocyanates and diisocyanates by a new versatile, simple and quick method in the presence of tertiary amines at room temperature. The method under investigation has several advantages over the existing techniques, as it is simple to carry out; does not require complicated equipment; work-up is simple, as it does not use expensive chemicals. Moreover, the yields are almost quantitative. It has a potential for commercial applications in pharmaceutical chemistry. 相似文献
996.
Khan F 《Macromolecular bioscience》2005,5(1):78-89
Gamma-radiation-induced graft copolymerization of methyl methacrylate onto natural lignocellulose (jute) fiber was carried out by the preirradiation method in an aqueous medium by using octylphenoxy-polyethoxyethanol as an emulsifier. The different factors that influenced the graft copolymer reaction process were investigated. In the case of radiation-dose-dependent grafting, samples irradiated in the presence of air produced up to 73% graft weight compared to 53% obtained in the case of irradiation in a nitrogen environment. By assuming Arrhenius reaction kinetics, the activation energy (E(a)) of the grafting reaction process was evaluated for different reaction temperatures. Moreover, the graft copolymer reaction was controlled by incorporating a homopolymer-inhibiting agent and three different chain-transfer agents in the reaction medium. The mechanical and thermal properties of jute fiber 'as received' and jute-graft-poly(methyl methacrylate) were also investigated. The results showed that the percentage of grafting with jute fiber has a significant effect on the properties. The kinetic parameters were evaluated from TGA thermograms by using Broido's method in the temperature range 240-350 degrees C. Scanning electron micrographs show that the structural changes on the surface of jute fibers were induced by graft copolymerization of methyl methacrylate monomer. Fiber-fiber surface friction was measured in terms of the average maximum load and the kinetic friction. SEM of jute-graft-poly(methyl methacrylate). 相似文献
997.
A simple and rapid spectrophotometric method has been investigated for the determination of furosemide. The method is based upon simple diazotization reaction. The absorbance was measured at 480 nm. The method is optimized for acidity, amount of reagents required and heating time. The range of linearity was 0.4–10 μg mL?1 of furosemide with molar absorptivity of 1.0 × 104 l mol?1 cm?1. Standard deviation, coefficient of variance, limit of detection and limit of quantification were calculated using authentic standard of furosemide and were found to ± 0.0013,12.7%, 0.16 ppm and 0.52 ppm, respectively. The method was applied to various pharmaceutical preparations containing furosemide. The results of the investigated method for furosemide were compared with available official literature method. The results obtained by the proposed method agree well with the standard established method. 相似文献
998.
Heather Davis Walter Skrzypek Arshad Khan 《Journal of polymer science. Part A, Polymer chemistry》1994,32(12):2267-2274
The iodine binding capacity (IBC) of amylopectin (AP, from potatoes) is determined to be around 0.38% (w/w) of the total AP in the solution. The mass of iodine bound comprises about 13.6% of the mass of AP involved with the complex, suggesting that with every four iodine atoms bound there are 23 anhydroglucose residues (AGU). Since our previous study indicates that four iodine atoms within the helix of 11 AGUs form a chromophore unit in the API complex, only 48% of the AGUs (11 out of 23) in the AP molecule are directly involved with the iodine. The heat of reaction for the API complex formation is determined to be around ?47 kJ/mol of I–I units bound and is significantly lower in magnitude than that of the amylose-iodine (AI) complex [Biopolymers, 31 , 57 (1991)]. A possible mechanism has been proposed for the formation of AI and API complexes with fixed compositions. © 1994 John Wiley & Sons, Inc. 相似文献
999.
Illicium verum Hook. f. is used as an herbal tea to treat colic pain in infants. Reports suggest that Star anise herbal tea may be adulterated with Illicium anisatum Linn. A short and rapid method using microscopy and gas chromatography (GC) was developed to detect I. anisatum Linn., an adulterant in the powdered mixture of I. verum. Anatomical differences in the epicarp cells of I. verum and I. anisatum fruits were clearly defined as examined under fluorescent microscopy and scanning electron microscopy. A GC method was developed for quick identification of possible I. anisatum adulteration with I. verum. 相似文献
1000.
A highly oxygenated, novel pentacyclic bis-oxa-bridged compound 8 was synthesized with remarkable efficiency starting from readily available tetrachloro-5,5-dimethoxyclopentadiene and 1,4-cyclohexadiene in three steps. The ruthenium-catalyzed oxidation of 2:1 bis-adduct 1 followed by a one-pot transformation of the resulting bis-alpha-diketone 3 furnished (after esterification) the title compound in an overall yield of 29.1%. The versatility of this simple method was further demonstrated with other norbornyl alpha-diketones to obtain the corresponding strained oxa-bridged derivatives. 相似文献