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排序方式: 共有59条查询结果,搜索用时 15 毫秒
1.
Shaul M. Aharoni Willis B. Hammond John S. Szobota Divakar Masilamani 《Journal of polymer science. Part A, Polymer chemistry》1984,22(10):2579-2599
Polyamides and related model compounds were prepared from carboxy acids and primary amines by reacting them with triphenylphosphite in an appropriate solvent at 100°C. The reactions proceeded in the absence of organic base but were accelerated by the addition of bases such as pyridine. Nevertheless, even the powerful combination of 13C and 31P NMR failed to indicate the presence of pyridinium phosphite in the reaction mixture. In the reaction of a primary amine and carboxyl groups a detectable amount of the diphenoxy aminophosphine intermediate was observed. The end products are the amides, phenol, and diphenyl phosphite. When primary amine was not present a slow formation of a phenyl ester of the carboxylic acid was evident. All the intermediate species and the end products were formed with or without added pyridine. A mixed anhydride of carboxylic acid and phosphite was never seen. The results in this article are fundamentally the same as those in the companion article (I) for which the data were obtained at 280°C in the absence of solvent and base. However, because the reaction went quickly to completion at 280°C, the diphenoxy aminophosphine intermediate was not observed. A mechanism for the amidation in which the diphenoxy aminophosphine is an initial reaction intermediate is proposed. This species reacts with the carboxylic acid through an intramolecular substitution to give an amide. This mechanism may be valid for the high-temperature reactions as well. Several minor unclear points are indicated. 相似文献
2.
Marta Snchez Isabel Urea-Vacas Elena Gonzlez-Burgos Pradeep Kumar Divakar Maria Pilar Gmez-Serranillos 《Molecules (Basel, Switzerland)》2022,27(15)
The genus Cetraria s. str. (Parmeliaceae family, Cetrarioid clade) consists of 15 species of mostly erect brown or greenish yellow fruticose or subfoliose thallus. These Cetraria species have a cosmopolitan distribution, being primarily located in the Northern Hemisphere, in North America and in the Eurasia area. Phytochemical analysis has demonstrated the presence of dibenzofuran derivatives (usnic acid), depsidones (fumarprotocetraric and protocetraric acids) and fatty acids (lichesterinic and protolichesterinic acids). The species of Cetraria, and more particularly Cetraria islandica, has been widely employed in folk medicine for the treatment of digestive and respiratory diseases as decoctions, tinctures, aqueous extract, and infusions. Moreover, Cetraria islandica has had an important nutritional and cosmetic value. These traditional uses have been validated in in vitro and in vivo pharmacological studies. Additionally, new therapeutic activities are being investigated, such as antioxidant, immunomodulatory, cytotoxic, genotoxic and antigenotoxic. Among all Cetraria species, the most investigated by far has been Cetraria islandica, followed by Cetraria pinastri and Cetraria aculeata. The aim of the current review is to update all the knowledge about the genus Cetraria covering aspects that include taxonomy and phylogeny, morphology and distribution, ecological and environmental interest, phytochemistry, traditional uses and pharmacological properties. 相似文献
3.
A self-supporting ZSM-5 monolith with a hierarchical porosity was prepared using polyurethane foam (PUF) as a structural template and a hydrothermal synthesis procedure. The synthesized monolith was characterized and investigated towards the adsorption and catalytic oxidation of trichloroethylene (TCE). Adsorption of TCE was studied gravimetrically and oxidation of TCE was studied using a vapor-phase down-flow reactor. Monolithic ZSM-5 displayed good sorption properties and completely oxidized TCE. Conversion levels of 50% and 90% were achieved at reduced temperatures (by ~50 ℃) when compared with the conversion temperatures obtained from the powder counterparts. Besides the activity of the monolith towards TCE adsorption and oxidation, it was stable and enhanced diffusion, thereby reducing pressure drops to a great extent owing to its hierarchical porous nature. 相似文献
4.
Divakar Vishwanath Swamy S. Girimanchanaika Dukanya Dukanya Shobith Rangappa Ji-Rui Yang Vijay Pandey Peter E. Lobie Basappa Basappa 《Molecules (Basel, Switzerland)》2022,27(3)
Novel PARP inhibitors with selective mode-of-action have been approved for clinical use. Herein, oxadiazole based ligands that are predicted to target PARP-1 have been synthesized and screened for the loss of cell viability in mammary carcinoma cells, wherein seven compounds were observed to possess significant IC50 values in the range of 1.4 to 25 µM. Furthermore, compound 5u, inhibited the viability of MCF-7 cells with an IC50 value of 1.4µM, when compared to Olaparib (IC50 = 3.2 µM). Compound 5s also decreased cell viability in MCF-7 and MDA-MB-231 cells with IC50 values of 15.3 and 19.2 µM, respectively. Treatment of MCF-7 cells with compounds 5u and 5s produced PARP cleavage, H2AX phosphorylation and CASPASE-3 activation comparable to that observed with Olaparib. Compounds 5u and 5s also decreased foci-formation and 3D Matrigel growth of MCF-7 cells equivalent to or greater than that observed with Olaparib. Finally, in silico analysis demonstrated binding of compound 5s towardsthe catalytic site of PARP-1, indicating that these novel oxadiazoles synthesized herein may serve as exemplars for the development of new therapeutics in cancer. 相似文献
5.
Gilardi R Mesot J Drew A Divakar U Lee SL Forgan EM Zaharko O Conder K Aswal VK Dewhurst CD Cubitt R Momono N Oda M 《Physical review letters》2002,88(21):217003
We report here the first direct observations of a well ordered vortex lattice in the bulk of a La(2-x)Sr(x)CuO(4+delta) single crystal (slightly overdoped, x = 0.17). Our small angle neutron scattering investigation of the mixed phase reveals a crossover from triangular to square coordination with increasing magnetic field. The existence of an intrinsic square vortex lattice has never been observed in high-temperature superconductors and is indicative of the coupling of the vortex lattice to a source of anisotropy, such as those provided by a d-wave order parameter or the presence of stripes. 相似文献
6.
We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented. 相似文献
7.
Z-scan studies on porphyrin derivative 总被引:2,自引:0,他引:2
K. Kandasamy K. Divakar Rao Rekha Deshpande P.N. Puntambekar Bhanu P. Singh Shankar J. Shetty T.S. Srivastava 《Applied physics. B, Lasers and optics》1997,64(4):479-484
Received: 10 January 1996 / Revised version: 15 June 1996 相似文献
8.
The polymerization of diallyl phthalate has been studied in two solvents, benzene (GRadical = 0.7) and chloroform (GR = 11.2), γ-radiation being used to investigate the effect of the solvent on the rates of polymerization and also chain transfer to the solvent. Kinetic analysis shows that in benzene solution the initiating species come almost exclusively from the monomer, but in chloroform they arise only from the solvent. The latter was further confirmed from the chlorine analysis of the polymer wherein chloroform appears to have telomerized with diallyl phthalate. In neither of the solvents was high molecular weight polymer obtained. The kp/kt1/2 for the polymerization of DAP was found to be 3.3 × 10?4 and 1.17 × 10?3 in benzene and chloroform solutions, respectively. The chain-transfer constant CS was 11.25 × 10?3 and 9.75 × 10?3 for benzene and chloroform, respectively. 相似文献
9.
Nanocrystalline cuboidal ceria has been synthesized by low-temperature hydrothermal reaction of cerium nitrate hexahydrate with hexamethylene tetramine. The particles have been doped with La and Gd by adding aqueous solution of the nitrate salts of the metals to the reaction mixture. The pure and doped particles are cubic in crystal structure and 10-25 nm in size. The pure and La-doped ceria are cuboidal in morphology, whereas the Gd-doped particles are irregular in shape. High-resolution TEM imaging and image simulation indicates that atomic level steps are present on the particle surfaces. The particles are faceted parallel to the {1 1 1} and {1 0 0} crystallographic planes and a continuous switching takes place between the two possible surface facets. It appears that the surface energies of the {1 1 1} and {1 0 0} facets are quite similar in magnitude and the interplay of surface energy determines the particle shape. Chemically sensitive imaging and spectroscopy shows that the dopants are homogeneously distributed within the particles and that the oxidation state of Ce is a mixture of +3 and +4. No preferential segregation either of the dopant or the oxidation state was observed. However, since the facet switching does depend on the chemistry of the dopant, there must be an affect on the atomic scale. 相似文献
10.
R. Divakar D. Sundararaman V.S. Raghunathan 《Progress in Crystal Growth and Characterization of Materials》1997,34(1-4):263-269
AlCuFe quasicrystal has been considered a novel icosahedral quasicrystal in as much as it can be produced in both thermodynamically stable and metastable state. It is also recognised to be a face centred structure. The system has been studied extensively in the recent past and several contentious results have been obtained. For example, evidences have been presented for both reversible and irreversible transformation of the quasicrystalline phase to the crystalline phases. Similarly, distinct transition metal sites have been proposed based on the Mossbauer studies. A subsequent study of this in fact shows an absence of such distinct sites. It has been shown that in this system, vacancy type of defects of very large concentrations exist. Many of these factors bring into question, the various structural models that have been postulated to explain the icosahedral structure obtained in the system. A critical examination of these various aspects of the AlCuFe quasicrystal is presented. 相似文献