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81.
A new natural terpenoid, ixoroid (1), was isolated from the flower of Ixora coccinea, along with the known constituents stigmast-5-en-3-O-beta-D-glucoside (2), 5-O-caffeoylquinic acid (3) and D-mannitol (4). The structure of ixoroid was elucidated on the basis of extensive 1D- and 2D-NMR studies and mass spectrometry as 21,23-epoxy-tirucall-7-en-3beta-ol (1). 相似文献
82.
Nekrasov-Okounkov identity gives a product representation of the sum over partitions of a certain function of partition hook length. In this paper, we give several generalizations of the Nekrasov-Okounkov identity using the cyclic symmetry of the topological vertex. 相似文献
83.
84.
Md Lutfor Rahman Shaheen M. Sarkar Eddy M. Farid Sazmal E. Arshad M. S. Sarjadi N. Wid 《Journal of Macromolecular Science: Physics》2018,57(2):83-99
Poly(acrylonitrile)/cellulose block copolymer (PAN-b-cell) was prepared by using a free radical initiating process and then the nitrile functional groups of the PAN blocks of the copolymers were transformed into amidoxime ligands. The resulting poly(amidoxime) ligands could complex with heavy metal ions; for example, the reflectance spectra of the [Cu -ligand]n+ was found to be at the highest absorbance, about 94%, at pH 6. The pH was the key parameter for metal ions sensing by the ligand. The adsorption capacity for copper was very good, 272 mg g?1, with a fast adsorption rate (t1/2 = 10 min). The adsorption capacities for other heavy metal ions such as Fe3+, Cr3+, Co3+ and Ni2+ were also good, being 242, 219, 201 and 195 mg g?1, respectively, at pH 6. The heavy metal ions removal efficiency from water was 98% at low concentration. The data proved that the heavy metal ions adsorption onto the polymer ligands were well fitted with the Langmuir isotherm model (R2>0.99), which suggests that the cellulose-based adsorbent surface namely the poly(amidoxime) ligand, was homogenous and a monolayer. The reusability was examined by a sorption/desorption process for six cycles and the extraction efficiency was determined. This new adsorbent could be reused for 6 cycles without any significant loss in its original removal function. 相似文献
85.
86.
I. Moritz S.A. Shaheen U. Hardebusch J.S. Schilling M. Weger K. Bender D. Schweitzer H.J. Keller 《Solid State Communications》1983,48(3):281-285
The magnetic susceptibility and electrical conductivity of the quasi-one-dimensional organic metal (Perylene)2(AsF6)0.75(PF6)0.35 × 0.85CH2Cl2 was studied in the temperature range 3–300 K. The measured susceptibility can be separated into its defect χd, core χc and enhanced paramagnetic spin susceptibility χp components. χp is found to decrease upon lowering the temperature or applying pressure, in analogy with results on charge transfer compounds such as TTF-TCNQ. The conductivity ratio also decreases with falling temperature. The present results are discussed within the context of a model which takes into account band-narrowing (electron localization) due to strong electron-phonon coupling. 相似文献
87.
Chuan Lin Shaheen A. Al-Muhtaseb James A. Ritter 《Journal of Sol-Gel Science and Technology》2003,28(1):133-141
Very fine nickel hydroxide and oxide xerogel powders were prepared using a new sol-gel synthesis procedure in which nickel ethoxide was produced through the reaction of nickel chloride, as a precursor, with sodium ethoxide in dehydrated ethanol, followed by the hydrolysis of nickel ethoxide with ammonia and drying the resulting hydrogel under subcritical pressures to form the xerogel. The effects of thermal treatment on the surface area, pore volume, crystallinity and particle structure of the resulting xerogels were investigated and found to have significant effects on all of these properties. Overall, the xerogel remained amorphous as Ni(OH)2 space up to 200°C, with little change in the surface area and pore volume. At 250°C, the Ni(OH)2 began to decompose and form crystalline NiO with the uniformity of the crystals increasing with an increase in temperature. The surface area and pore volume decreased sharply when increasingthe temperature beyond 250°C; this was the temperature where maximums of about 270 m2/g and 0.33 cm3/g were exhibited by this composite amorphous Ni(OH)2 and crystalline NiO xerogel powders. At the higher calcination temperatures, very uniform NiO crystals with average crystallite sizes of 1.7 nm and 14.5 nm were obtained at 400 and 600°C, respectively. 相似文献
88.
Summary 1,2-Diphenyl-2-(benzoylhydrazino)ethanol (DBE) and 1,2-diphenyl-2-(p-nitrobenzoylhydrazino)ethanol (DPNBE) form complexes of general formulae [M(H2L)2]X2 and [M2L2] (where M = Co or Ni, H2L and L are the neutral and dibasic forms of the ligands and X = Cl or NO3). The analytical, spectral, magnetic and physical studies show the complexes to be of two types, namely monomeric cationic species prepared in neutral media and neutral binuclear oxygen-bridged species formed in alkaline solution. The ligands are tridentate, coordinating through carbonyl (or enolic) oxygen, azomethine nitrogen and alcoholic oxygen atoms. 相似文献
89.
Khashayar Karimian Farajolah Mohanazadeh Shaheen Rezai 《Journal of heterocyclic chemistry》1983,20(4):1119-1121
Covalent immobilization of the thiazole nucleus on a chloromethylated polystyrene copolymer results in the formation of a catalytically active thiazolium salt, capable of repeated acyloin and benzoin condensations. The nature of the solvent and the substituents on the thiazolium nucleus has been found to have marked effects of the rate of catalysis. 相似文献
90.
Kalauni SK Choudhary MI Khalid A Manandhar MD Shaheen F Atta-ur-Rahman Gewali MB 《Chemical & pharmaceutical bulletin》2002,50(11):1423-1426
From the leaves of Sarcococca coriacea two new steroidal alkaloids, epoxynepapakistamine-A [(20S)-20-(N-methylamino)-3beta-(tigloylamino)-5alpha-pregna-16alpha,17alpha-epoxy-2beta,4beta-di-O-acetate] (1), and epoxysarcovagenine-D [(20S)-20-(N-methylamino)-3beta-(tigloylamino)-5alpha-pregna-2-en-16alpha,17alpha-epoxy-4-one] (2), and two known compounds funtumafrine C [(20S)-20-(N,N-dimethylamino)-5alpha-pregna-3-one] (3) and N-methylfuntumine (4) were isolated. Their structures were elucidated on the basis of their spectral properties. The compounds 1, 3 and 4 were found to have cholinesterase inhibitory activity when tested for the inhibition of electric eel acetylcholinesterase and horse serum butyrylcholinesterase. They inhibited both enzymes in a concentration dependent fashion. 相似文献