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281.
Herein we document the first total synthesis of mangiferaelactone and thus establish its absolute configuration. The central nonenolide ring was constructed using ring closing metathesis and Yamaguchi esterification. The key alcohol fragment was synthesized by the Bernet–Vasella fragmentation of C-ribofuranoside. 相似文献
282.
Rajeswara Rao Nakka Venkatappa Rao Thumu Ramana Reddy SVS Sanjeeva Rao Buddhiraju 《辐射效应与固体损伤》2013,168(5):439-450
We have investigated the effects of gamma irradiation on chemical structure, thermal and morphological properties of biodegradable semi-crystalline poly (glycolic acid) (PGA). PGA samples were subjected to irradiation treatment using a 60Co gamma source with a delivered dose of 30, 60 and 90?kGy, respectively. Gamma irradiation induces cleavage of PGA main chains forming ~O?H2 and ?H2COO~ radicals in both amorphous and crystalline regions. The free radicals formed in the amorphous region abstract atmospheric oxygen and convert them to peroxy radicals. The peroxy radical causes chain scission at the crystal interface through hydrogen abstraction from methylene groups forming the ~?HCOO~ (I) radical. Consequently, the observed electron spin resonance (ESR) doublet of irradiated PGA is assigned to (I). The disappearance of the ESR signal above 190°C indicates that free radicals are formed in the amorphous region and decay below the melting temperature of PGA. Fourier transform infrared and optical absorption studies confirm that the groups are not influenced by gamma irradiation. Differential scanning calorimetry (DSC) studies showed that the melting temperature of PGA decreased from 212°C to 202°C upon irradiation. Degree of crystallinity increased initially and then decreased with an increase in radiation as per DSC and X-ray diffraction studies. Irradiation produced changes in the physical properties of PGA as well as affecting the morphology of the material. 相似文献
283.
Biju Basumatary Dr. R. V. Ramana Reddy Rahul Prof. Dr. Jeyaraman Sankar 《Angewandte Chemie (International ed. in English)》2018,57(18):5052-5056
An expanded porphyrinoid has been obtained by a simple ring expansion from a contracted porphyrinoid, namely corrole. Spectroscopic, structural, and computational investigations reveal peculiar π‐conjugation and geometry. The effect of extended π‐conjugation is evident from perturbed redox behavior and photophysical properties. Owing to the strong diatropic ring current of the corrole and cross‐conjugation, the molecule exhibits a non‐aromatic nature for the expanded π‐circuit, as evident from NMR studies. 相似文献
284.
Tandem One Pot and Efficient Method for the Palladium‐Reagent‐Catalyzed Cross‐Coupling of Quinazoline Thiols
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P. Satya Karuna R. V. V. Ramana Murthy M. R. P. Reddy Naresh Kumar Katari Kummari Srinivas 《Journal of heterocyclic chemistry》2016,53(3):784-788
A facile synthesis of 1,4‐dihydroquinazolines from 2‐aminobenzyl amine and carbon disulfide via dithiocarbamate performed at room temperature is reported. Corresponding S‐alkyl quinazoline derivatives were obtained from 1,4‐dihydroquinazolines in one‐pot reactions under the palladium reagents after addition of alkyl halides. The versatility of this synthetic protocol has been demonstrated with various halo benzenes. The products thus obtained have been characterized by MP, IR, 1H‐NMR, and mass spectroscopy. 相似文献
285.
Multiutility sophorolipids as nanoparticle capping agents: synthesis of stable and water dispersible Co nanoparticles 总被引:1,自引:0,他引:1
Kasture M Singh S Patel P Joy PA Prabhune AA Ramana CV Prasad BL 《Langmuir : the ACS journal of surfaces and colloids》2007,23(23):11409-11412
Sophorolipids are a class of glycolipids that can be obtained from fatty acids by simply treating them with yeast cells (Candida bombicola, ATCC 22214) and glucose. In this letter, we demonstrate the application of sophorolipids obtained from oleic acid as a capping agent for Co nanoparticles. Upon capping the nanoparticle surface, the sugar moiety of these sophorolipids is exposed to the solvent environment, making the nanoparticles stable and water-redispersible. 相似文献
286.
A concise approach for the total synthesis of aculeatin D and 6-epi-aculeatin D employing differentially protected anti, anti-1,3,5-triol alkyne prepared from alpha-D-glucoheptonic-gamma-lactone derivative is documented. Phenol protecting group manipulation for selective O-debenzylation during the hydrogenation of the diyne intermediate and one-pot phenolic oxidation with concomitant spiroketalization highlight the accomplished total synthesis. 相似文献
287.
Ramana V. Ankem 《Tetrahedron letters》2008,49(46):6547-6549
The third-order rate constants for the pH-dependent formation of the carbinolamides generated from the reaction of formaldehyde and benzamide, 4-chloro, 4-nitro, 4-methyl and 4-methoxybenzamide, are reported. The acid-catalyzed reaction was found to occur via rate-limiting proton transfer, whereas the hydroxide-dependent reaction occurred via a specific-base process. Coupling the rate constants for carbinolamide formation reported herein with the previously established rates for carbinolamide breakdown yielded equilibrium constants for the carbinolamides studied in water. 相似文献
288.
Ultra-fine (<1 microm) microfilters are required to effectively trap microbial cells. We designed microfilters featuring a rain drop bypass architecture, which significantly reduces the likelihood of clogging at the cost of limited cell loss. The new rain drop bypass architecture configuration has a substantially lower pressure drop and allows a better efficiency in trapping protozoan cells (Cryptosporidium parvum and Giardia lamblia) in comparison to our previous generation of a microfilter device. A modified version displaying sub-micron filter gaps was adapted to trap and detect bacterial cells (Escherichia coli), through a method of cells labeling, which aims to amplify the fluorescence signal emission and therefore the sensitivity of detection. 相似文献
289.
Nitration o f the aromatic amines with urea nitrate in sulphuric acid gave exclusively the p-isomer and when the p-position is blocked, the nitration occurred to give a m-nitroaniline derivative in excellent yields. However, nitration was not effected at o-position. Mechanistic aspect of this reaction is also discussed. 相似文献
290.
We give simple proofs of the essential properties of the Beurling–Selberg function and its odd part by viewing them as solutions to difference equations. 相似文献