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321.
Anna Maria Raspolli Galletti Guido Pampaloni Aldo D'Alessio Yogesh Patil Filippo Renili Simone Giaiacopi 《Macromolecular rapid communications》2009,30(20):1762-1768
Ring‐opening metathesis polymerization (ROMP) of norbornene catalyzed by niobium(V) N,N‐dialkylcarbamates Nb(O2CNR2)5, R = Et ( 1 ), Me ( 2 ) was studied in the presence of methylaluminoxane (MAO) as a cocatalyst. These novel catalytic systems resulted very active in chlorobenzene: 1 in the presence of methylaluminoxane catalyzes the ROMP of norbornene with the highest activity (29 000 kg of polymer/mol of catalyst × hour) never reported up to now for niobium catalysts. The high productivity appears particularly attractive considering that these precursors are rather cheap and easy to synthesize and to handle. Polynorbornenes were characterized by FT‐IR and NMR spectroscopies and by DSC calorimetry. A new FT‐IR method for the swift determination of the cis/trans content of the polymer is presented.
322.
M. S. Raghu C. B. Pradeep Kumar K. Yogesh Kumar M. K. Prashanth B. K. Jayanna 《Journal of heterocyclic chemistry》2019,56(7):2046-2051
A novel class of 3‐(4‐chlorophenyl)‐2‐(substituted)quinazolin‐4(3H)‐one derivatives were synthesized, and the structure of synthesized compounds was characterized by IR, 1H NMR, and mass spectroscopy. The newly synthesized compounds ( 4a–g and 6a–g ) were tested for their in vitro cyclooxygenase (COX) inhibition activity. The compounds have inhibitory profile against both COX‐1 and COX‐2, and some of the compounds are found to be selective against COX‐2. The compound 6g showed distinct inhibitory activity on COXs. The synthesized compounds were evaluated for their potential anti‐inflammatory activity as inhibitors of the proinflammatory cytokines IL‐6. Compounds 4d – g showed the highest level of inhibition among all the tested compounds. Thus, our data suggested that these compounds may represent a new class of potent anti‐inflammatory agents. 相似文献
323.
For a long time, the total synthesis of proteins was considered as a “mission impossible” because of the tedious and complex synthetic steps and demanding purification processes. However, with the development of modern synthetic methodologies, many protein syntheses have now been reported. More importantly, through chemical synthesis, desired modifications can be installed to target proteins precisely, which is a major advantage over traditional bio‐synthesis approaches. This review summarizes the techniques developed for protein assembly, including native chemical ligation, Se‐mediated ligation, and a range of other ligation methods. A few synthetic examples, whereby synthetic proteins with desired modifications have been utilized for related biological research, are also included. We believe that chemical synthesis can provide alternative pathways to solve problems that have hitherto proved insurmountable by traditional biological approaches. 相似文献
324.
[reaction: see text] We report a new phosgene-free method for the synthesis of symmetrical organic carbonates via alkylation of metal carbonate with various alkyl halides and sulfonates in 1-n-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], as an ecofriendly reaction media. Alkylation of metal carbonate in various ionic liquids with 1-bromo-3-phenylpropane (1a) as a model reactant has thoroughly been investigated. Potassium and cesium carbonates appeared to be the most suitable metal carbonate due to their high solubility in ionic liquids. Besides good to excellent yields, this simple and convenient methodology is devoid of highly toxic and harmful chemicals such as phosgene and carbon monoxide, which is an additional advantage. 相似文献
325.
Seebach D Mahajan YR Senthilkumar R Rueping M Jaun B 《Chemical communications (Cambridge, England)》2002,(15):1598-1599
The importance of hydrogen bonding in beta-peptide 3(14)-helices is demonstrated by an NMR analysis of three beta-heptadepsipeptides containing a 3-hydroxybutanoic residue in position 2, 4 or 6. 相似文献
326.
Kumaraswamy G Deshmukh Y Agrawal VV Rajmohanan P 《The journal of physical chemistry. B》2005,109(33):16034-16039
The formation of talc-like compounds by the condensation of organotrialkoxy silanes with magnesium hydroxide has been recently reported. These represent layered hybrid nanomaterials that have a layer thickness of around 1 nm, have organic moieties covalently linked to the layer surfaces, and are called "organoclays." We show that such compounds are sensitive to acid treatment. When a phenylclay is treated with hydrochloric acid, magnesium leaches out, destroying the layered structure. The extent to which magnesium is leached out is a function of the time of the acid treatment and the concentration of the acid used. Magnesium leaches out rapidly when the concentration of acid used to treat the phenyl-clay is higher, and the extent of structural magnesium that is leached out is also higher for higher acid concentrations. Removal of the magnesium rearranges the structure of the phenyl-clay to form oligomeric phenylsilsesquioxanes. FTIR and NMR suggest that the silsesquioxanes formed by acid treatment of the phenyl-clay comprise a mixture of ladderlike and cagelike structures. 相似文献
327.
Experimental data from combined tension-torsion of thin walled tubes of annealed polycrystalline copper subjected to various non-proportionate loading, unloading and reverse loading paths are presented. The measurements are compared with predicted values from classical incremental theory of plasticity in terms of true stress and true strain and a recently developed incremental theory of plasticity by Bell in terms of nominal stress and nominal strain. These experimental data reveal that the plastic strain produced by the various proportionate and non-proportionate loading, unloading and reverse loading paths are in better agreement with Bell's incremental theory of plasticity as compared to classical incremental theory. 相似文献
328.
Dr. Anzhela Galstyan Dr. Yogesh Kumar Maurya Dr. Halina Zhylitskaya Youn Jue Bae Dr. Yi-Lin Wu Prof. Dr. Michael R. Wasielewski Prof. Dr. Tadeusz Lis Prof. Dr. Ulrich Dobrindt Prof. Dr. Marcin Stępień 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(37):8262-8266
Free base, zinc and palladium π-extended porphyrins containing fused naphthalenediamide units were employed as photosensitizers in antimicrobial photodynamic therapy (aPDT). Their efficacy, assessed by photophysical and in vitro photobiological studies on Gram-positive bacteria, was found to depend on metal coordination, showing a dramatic enhancement of photosensitizing activity for the palladium complex. 相似文献
329.
Photonic bandgap structures can also be utilized for the realization of transformational optical devices like metamaterials. In this Letter, the possibility of cylindrical to plane wave source transformation in an open cavity formed by one dimensional photonic crystal is demonstrated. It is observed that the gap solitary wave behavior at the near-bandgap regime is fair enough to produce highly directional plane waves out of the point source placed inside the open cavity. The limitations of such a source transformation device are governed by the strength of the bandgap that decides the amplitude of the emitted plane waves. 相似文献
330.
Bera B Patil YP Nethaji M Jagirdar BR 《Dalton transactions (Cambridge, England : 2003)》2011,40(40):10592-10597
The synthesis, characterization, and reactivity of a chromium(0) complex bearing an amine-borane moiety (η(6)-C(6)H(5)CH(2)NMe(2)·BH(3))Cr(CO)(3) (2) is reported. Photolysis of complex 2 results in the elimination of a CO ligand followed by the formation of an intramolecular σ-borane complex (η(1)-(η(6)-C(6)H(5)CH(2)NMe(2)·BH(2)-H))Cr(CO)(2) (3). This species was characterized in solution by NMR spectroscopy. Reaction of complex 2 with photochemically generated (OC)(5)Cr(THF) affords a novel homobimetallic σ-borane complex (OC)(3)Cr(η(6)-C(6)H(5)CH(2)NMe(2)·BH(2)-H-Cr(CO)(5)) (4), wherein one of the BH moieties is bound to the chromium center in an η(1)-fashion. The σ-borane complex 4 was isolated in moderate to good yield (72%). The BH(3) fragment in the complexes 3 and 4 are highly dynamic involving exchange of the BH hydrogen bound to the metal with the terminal BH hydrogen atoms. The dynamics has been studied using variable-temperature NMR spectroscopy. Complexes 2 and 4 have been characterized by X-ray crystallography. 相似文献